One family's solar story

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Sideways

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This is intended to be a fairly detailed run through my own domestic solar PV project in the UK.

  • I'm a retired electrical engineer in my early 60's.
  • I'm as concerned as everyone else about rising fuel costs
  • We would like to be more "green". After travelling some 1.5 million miles in the course of my working life I've certainly done enough damage to the planet and agree that we need to consume less. This project wasn't done on the basis of financial returns.
  • Our house has a relatively large SE facing roof for the size of the place. Over the years we've felt how the sun can heat up the roof and have long felt that it would be well suited to solar energy.
  • We don't intend to move house - at my age I'm looking at this as a lifetime buy.
  • We were in a position to afford solar and any delay just meant we would get less benefit from the spend so now was the time to do it.


Four years ago I visited the "Solar & Storage Live" exhibition at Birmingham NEC.
This is an annual event mostly for the trade but open to the public.
It gave me an opportunity to see most of the major brands of inverters and panels in the flesh, to ask some questions and to identify some of the wholesalers who supply the installers and in some cases also the public.
Overall impressions: Solar PV was a mature technology and improvements are mostly incremental. Batteries are the new big thing. The industry seemed to be a bit down at the time. Feed in tariff had ended and demand for new systems was down.

I parked the idea for a couple of years and went back to the show last year, with my engineering head on, and specifically looking to shortlist the panels, inverters and battery that I might buy. I had no intention of doing the job myself but I would shortlist the kit and get quotes from installers who could supply and fit it.

From the show, solar panels that interested me :
  • Hanwha Q cells - Korea - PERC technology - very nicely built with good warranty
  • Jinko Tiger N - Chinese - N type silicon - good reliability scores
  • LG Neon R - Korean - N type silicon - good reliability scores
  • REC Alpha - Norwegian owned - N type silicon -
  • JA Solar and Trina - both Chinese - also had decent panels on offer but not as refined as the others above.

Inverter manufacturers :
  • Fronius - Austrian - premium brand, very high quality design and build
  • SMA - German - makers of the reputable Sunny Boy inverters - very well built
  • GivEnergy - UK - innovative and intelligent (as in automated) set of products but very new company
  • Solar Edge - German - well established and proven - broad set of products that work together and quite intelligent - have a very good solution for roofs subject to shadows - build quality looks much lower than Fronius or SMA to me

Batteries :
  • GivEnergy
  • There were a number of battery suppliers there including the majors like the Tesla Powerwall, but I found the products hard to assess and came away unconvinced. Few impressed me.

I was looking simply for high quality product, indication that the manufacturers were large and reputable, and for some degree of integration - not just a random collection of bits.
I was also interested in the solar panel mounting hardware because one of the real risks I anticipated was poor installation leaving me with a leaking roof and unsecure panels. I came away understanding that there are high quality roof mounts available and cheaper + less well made alternatives.

Shortlisting the components

Panels

Modern solar panels pretty much evolved from the space program decades ago. These panels use so called "P type" silicon. If you ever heard of a PNP and NPN transistors in school physics, it's the same idea. If not, don't worry and just follow along.
P type silicon proved to be the most long lived, and has been developed over the years. The latest flavour being called PERC. This is used to make the vast majority of panels and an excellent guarantee is 25 years plus a performance guarantee that the panel will still be achieving 85% of it's original output after 25 years in service.

A panel is simply a metal frame, an impact resistant glass top sheet covering typically 60 individual solar cells all connected by thin metal tracks that are printed, not actual wires, and a backing sheet of some type. A panel has a DC+ and DC- connection on the back and you wire several panels up in series (just like batteries in a toy) to make a "string".
There are some functional and cosmetic differences between panels - like the all black look and different ways of arranging the (printed) electrical connections that connect all the cells together in the panel. These can make small improvements in efficiency and make the wiring unnoticeable from a distance. The majority of modern panels are very similar in size and performance. Differences are subtle. The main thing is to buy from a reputable company that achieve consistently high reliability.

In recent years, studies have been done on the other type of solar cell. "N type" silicon. N type doesn't last as well in space because it suffers more damage from cosmic rays, but on the ground that doesn't matter and it is better than P type in other ways.
The upshot is that a small number of companies make premium panels out of N type silicon, and these can be bought with longer guarantees (25 years) and higher guaranteed outputs (90% of original output after 40 years !).
I decided that I wanted this technology. In a decade it will be mainstream but for now the choice is limited : REC Alpha (Norwegian), Jinko Tiger N (Chinese), LG Neon R (Korea) or Sunpower Maxeon 3 (USA + Mexico). The long life and high performance matched my lifetime buy objective and a price premium of 15% ish felt acceptable.

In practice, global supply chain was a nightmare this Easter. No one had any of the good stuff. I first shortlisted the Tiger N panels for value and while we were looking for them, I discovered that a lot of Chinese solar manufacture is tainted by reports of forced labour. Not OK.
I chose LG Neon next as this is a reputable Korean company, but LG withdrew from solar panel manufacture this summer !
Eventually my chosen installer stumbled on a supplier with Sunpower Maxeon 3 panels in stock, took 3 days to work up the courage, then suggested them to me. Maxeon 3 are the best made panels in the world. The company is Californian and the panels made in Mexico. I omitted them from my original list simply because I knew of their reputation and assumed they would be unaffordable. They cost me about 50% more than a good PERC panel but having realised how tough the supply chain problems were, I said yes. They have turned out to be the most impressive part of the system. Simply superb.

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I'll explain the choice and layout of the panels later, but for now, I'll tell you that someone needs to consider the physical size and shape of the roof and work out the best way to arrange panels on it. I did all this for my roof and ended up with a simple, clean layout. 8 panels wide, 3 panels tall giving 24 panels in total. The maxeon 3 panels just fit my roof leaving enough space above and below. 375 W apiece x 24 = 9kW peak output.

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Inverter
Solar panels output their energy in DC (direct current). 40 or 50Volts per panel is common. My Maxeon 3 panels make over 70V DC apiece. Panels are wired in series as "strings" that can be 400V, 600V, even more.
The inverter is a box of electronics that converts DC from the panels to 240V AC mains and feeds it to your consumenr unit through a circuit breaker - typically 20 or 30 Amp rated.
The AC from the inverter is exactly synchronised with the electricity coming in from the grid so that they play nicely together. It's just at a slightly higher voltage which allows the inverter to push it's energy into your home or back into the grid if you can't use it. The AC voltage from the inverter constantly adjusts, more sun, more power generated, slightly higher voltage to push that power out.

The inverter can be running 16 hours straight over a long day, handling several kWatts, and doing it 365 days a year for a decade or more. It's a pretty demanding job and the electrical eng in me thinks that a good quality, well designed and built piece of electronics matters if you want a long life and reliability. I was absolutely looking for something built to a "commercial" or "industrial" standard, not something that felt like a domestic appliance that you would expect to last 3 to 5 years.


Batteries
You have to consider batteries and inverter together.
When adding a battery to a solar PV system, there are two ways to do it.

First is to use an AC coupled battery which simply wires in to any new or existing system using 240V AC. The battery includes a charger. This approach is simple but has the advantage that an AC battery can be added to any solar setup, including ones already in service. Also, any battery can be matched with any inverter so you have freedom to mix and match. Tesla Power Wall is an AC coupled battery.

Second is to use a DC coupled battery matched with a specific inverter.
Batteries store power as DC. Solar panels make DC.
For maximum efficiency and maximum intelligence, the inverter can double up as a battery charger. It takes DC power from the panels and feeds it still as DC to charge the battery. There is no need to convert to AC in between and this improves efficiency. The battery pack doesn't have a charger built in because the inverter does this task.
The inverter draws DC power either from the solar panels and / or from the battery and converts this to AC to supply the needs of the house. This type of inverter is smart and has full visibility of the power in and out of the battery which a simple inverter with an AC battery does not. It is the better system if you are putting in a new, solar + battery system. The downside is that you need the battery and inverter to be designed to work together like this. That limits the available choices.

Battery size
How deep are your pockets ?
Our average daily electricity consumption is very typical for our size of home and family of 3-4.
Measured over the last couple of years it's 13kWh a day. We have gas hot water and central heating
The amount we use while the sun is down is maybe half that. We often use the oven for an evening meal.
We could choose a battery that held enough power to take us through the average "night" so just 6kWh say.
We could choose a battery big enough to carry us through an entire average day, so 13kWh
In the event, I decided that I wanted a battery that could feed a 6kW load - this is our oven plus a kettle in the evening or oven plus microwave. whatever.
It's a bit arbitrary, but small batteries can't supply that much power. and that 6kW load figure meant that I needed a battery with 16kWh of capacity. A bit more than one entire, average, day.
That's a lot of storage. About £10k and almost half the cost of the entire installation.
It means that we will be self sufficient - able to move the power generated by the solar to when we want it - almost 100% - for about 10 months of the year. Only in the two coldest months of the year is our solar generation predicted to fall to 8kWh a day. For the rest of the year, the solar will supply our average daily needs or much more and the battery will hold more than the average day's demand and deliver it when we need it. Overnight or during the next cloudy day.
If we have a run of bad weather we need the grid so never 100% but well up there.
Without the battery our self consumption will be hard pushed to reach 50%, 25-50% is more likely.
But ignoring inflation and Net Present Value calculations, I think the battery will take over 10 years to pay back and I genuinely don't know how long it will last for us. Potentially long enough and maybe much more, but this comes down to what we're willing to pay to be more green. We're willing to take the risk that this system will be more expensive than the grid in the end, in order to do our bit and not be so much at the mercy of governments and energy companies in future.

Battery Chemistry and Life
I didn't know as much about batteries when I chose mine as I do now, but reading around trends in EV battery tech is helpful.
For cars, people tend to want range and the greatest amount of energy storage for the least amount of weight. The batteries that fit that bill in 2021 and 2022 are Lithium Nickel, Manganese (?) Cobalt. So called NMC technology. This tech is expensive, uses Cobalt which is in short supply and a humanitarian car crash, more prone to fires, and lastly has a poor cycle life - around 1,000 charge discharge cycles before capacity drops to 80% of new. That could be just 3 years. Maybe 6yrs if you take it down to 60% of new capacity.
It's light weight but sitting in your house, who cares ?
For houses, Lithium, Iron (aka Fe), Phosphate (aka PO4) is a better tech. LFP batteries are more stable, less fire risk, much longer lasting (4,000 maybe 6,000 and max perhaps 8,000 charge discharge cycles) and cheaper. It's far heavier but improving. LFP batteries are used in buses and will be going into the base model Tesla3 made in China and many more new EVs. LFP batteries going in cars hold about 2x as much energy per Kg as the ones I'm still waiting for to put in the house. My battery stack weighs 1/4 ton, 250 odd Kg.

A huge factor in this is trying to guess what lifespan my storage battery will have. Cost divided by lifetime energy throughput will give a very real "pence per kWh" figure that has to be costed into all the energy that is temporarily stored in the battery.
LiFePO4 battery warranty is typically 10 years.
At one full cycle per day that's 3,650 cycles. A LFP battery should do that. An NMC battery is unlikely to be doing well after that many cycles.
LFP in fact may well be usable even at 6,000 cycles. At once per day, that's nearing 20 years as long as your battery was a bit oversized to start with.
20 years is somewhere near the calendar age limit of lithium batteries. They die of old age even if never cycled at all.
Putting all this into a hat and shaking it up, I figured my own eventual selection of batteries have a chance of lasting closer to 20 yrs than 10, and will cost me somewhere near 12p / kWh stored over that lifetime. A long way from free, but a lot less than the power company charge if I can't store my daytime generation and have to buy electricity in the evenings.

Inverter and Battery Selection
In the end, I had only two serious candidates because I wanted a "hybrid DC" inverter and battery solution described above.
One was "GivEnergy" - a very new company based in Stoke on Trent, UK but with overseas investors and partners. They are growing very fast because they offer inverters, batteries and an intelligent control that works with some of the most innovative energy company agile tariffs. The snag is that their inverter is 5kW and battery 8kWh. I would need two inverters and two batteries in my system and even then it was only rated for 5kW maximum discharge from the pair of batteries. It's a new company, unproven.

The second, and the option that I chose, was to pair inverters made by Fronius in Austria with batteries made by BYD in China.
These are separate companies, but they are cooperating to make their products work together to deliver a solution. BYD batteries are tested to work with Fronius inverters.
Fronius are a family owned firm that specialise in power electronics. They make just 3 groups of product: welders, forklift truck battery chargers and solar inverters. The core competence in power electronics is the same for all three.
They have an excellent reputation and I own one of their Magicwave AC DC Tig welders. It's design and build is very, very good. Up there with Kempii and Miller, arguably better than both. I've also dealt with their technical support and found them good. All this gave me confidence that the inverters should be good.
BYD was a real unknown, but if a respected supplier chose to partner with them they might be OK. It turns out BYD are the largest manufacturer of batteries for industry / traction application in China and I think the world. They make more batteries than Tesla and their batteries are the ones that power the new electric bus fleet in Sydney, Aus. Their batteries are LiFePO4 type prismatic cells that are better suited to long life needs of domestic energy storage than the car battery technology used in the Tesla Power Wall. Only time will tell if this is right, but an Australian facility that has been testing solar storage batteries and making the results public has tested the BYD battery and it lost very little capacity. The results give me some hope that battery could manage a 20 year useful life, maybe more,
 
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Panel layout, strings and generation forecast

Here are some things that I discovered about panels.

Firstly, they can be installed either way, "portrait" orientation or "landscape".
Initially, as our roof is rather wide compared to it's height, I made all my layouts with the panels in "landscape". Later after chatting with my installer, I accepted their preference to install "portrait" style and reworked the layouts.
The difference isn't anything dramatic. They simply find that it is easier to install the supporting roof brackets and the extruded aluminium rails that the panels clamp to when the panels are "portrait". If you need a landscape layout, they will need more brackets and rail and the installation will be more expensive.

DC wiring for solar panels isn't done using mains cable - or at least it shouldn't be. Beware of the cowboys. A special cable is needed
1. because it will be installed outdoors behind the panels and needs to be durable to cope with exposure, wet, heat and abrasion for decades.
2. because dc voltages are likely to be several hundred volts. Much more than the AC mains. So it is made with two layers of high performance insulation.
3. because the layouts often daisy chain a single conductor from panel to panel, not two cores and an earth
4. lastly, cable and special waterproof, locking, plugs and sockets are made to work together for a safe installation in the exposed conditions of the roof.
The wire looks like radio or TV coaxial cable but isn't. It has a very robust stranded wire in the centre to carry the power. The best quality plugs and sockets are by Staubli / Multicontact of Austria and these are crimped onto the DC cable using a special crimp tool (£100+ if you want to DIY the panel installation). My installer let me joint some at one point. It's not hard if you have someone there to demonstrate.

How many panels ...
There are some simple tools that allow you to predict how much power you will get from a roof. I'll link to them. They are available to all.
First you identify where in the country you are. UK has been split into numerous areas for this solar forecaster because hours of daylight, angle of sun etc are different around the country.
Second, you need to know the angle your roof slopes at from flat to vertical.
Third the direction it faces, like 6 o'clock / due south, or whatever.
Lastly, you enter the peak power of your array. X many panels x however many Watts per panel.
With these simple facts, you can look up standardised forecasts for how many kiloWatthours your installation will make in a year. Also, you can compile a bar chart graph showing how many kWh for each month Jan to December
This information is super useful, and all MCS (Microgeneration Certification Scheme) installers must use the same data and same methodology to make their forecasts. This lets you compare their forecasts with confidence.

My approach was very simple. If we were going to the bother of installing solar, make it as big as possible. The the cost of a 9kW array isn't 2.25x the cost of a 4kW one. It's less. The bigger we went the more chance of it making useful power in winter when it's at it's weakest.

Panels stacked in the garage waiting to be fitted.
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Angles and slopes
Our roof stands at 50 up from horizontal. A little more than ideal for max power over the year because the sun will rise higher in the sky in summer when it generates most, and will hit the roof at a slant, not square on. It's actually better for the low sun in winter but that doesn't add as much to the annual total. Regardless, being a few degrees to steep or too flat doesn't make much difference, don't sweat the angles.
Our roof faces south east. Not perfect like due South but pretty good. Again, don't sweat it.
We can see the effect of south east. Our panels start to work at 6.30 am and do their best work in the morning. By 4.30 to 5pm the sun has gone around the end of the roof and generation plummets quickly from say 3kW to 1kW for a final 1-2 hours of our solar day.

A friend with East and West facing roofs put panels on both. He gets a long day of generation with each roof working well for half of the day and overlap in the middle. Don't let the angles put you off. Put your own numbers into the model and see what you can expect.

My own forecasts.
We use 3700 to 4500kWh a year according to our last 2 years bills.
The solar forecast said 9kW peak of panels on our roof should make nearly 7000kWh over the year.
The profile said 8kWh a day average in the two coldest months (we use 13kWh a day on average). Not self sufficient but not bad.
For 9 or 10 months, we should get at least our average daily requirement, and 30 odd kWh a day in the summer months. More than 2x what we need. Enough to make surplus for heating hot water and eventually, charging a car.

Since the system went live at start of April, we see daily outputs of 20 to 30kW a day, 700, 800kWh a month. A quarter of our annual demand in a single month if only we could move it to when we need it.

Shadows and strings.
You need to be aware of trees and buildings that can cast a shadow on your panels.
If even one panel is in shade, the power generated by the whole string of panels in series that it belongs to is reduced a lot. It is just llike having one weak battery among several good ones in your cordless drill. That one weak cell ruins the whole pack. In solar PV terms, just for as long as the shadow is there. It doesn't do any damage, it just means you don't get anywhere near full power.
So when your installer decides how to connect up the panels, he needs to look for shadows and may wire the panels to minimise the effect.
Just like battery packs can be wired in combinations of series and parallel, so can solar panels.
We have a neighbouring house parallel to ours that throws a shadow on our roof in the early morning. The shadow moves down the roof over 1/2 to 1 hour (suummer and winter) so the top row of panels sees the sun first, then the middle and finally the bottom row.
Because of the the way the shadow affects the whole width of the roof the same way, our panels were wired in 3 strings of 8. Top row, middle row, bottom row.

((Edit at Early November: the shadow moving down the roof is very real. At this end of the year the roof wakes up much later in the morning - 9.00 odd, and the lowest row of panels isn't in full sun until after 10.30. Our solar day has become much shorter. It can still generate very useful power but the real hit is more days of poor weather and consequently fewer hours of clear sunshine. I really need those batteries to capture the energy when we see it.))

Here are the two DC+ and DC- inputs of one of the inverters. The black outer / whire inner cables are the high voltage DC single core cables down from the panels.
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The installer has to ( and in my case I did) check that the typical and the peak voltage of each string of panels, and the power that they make, match what the inverter is designed to accept. This is all about the electrical design. Interesting to nerds. No one else need worry about it because it's the installers responsibility to do all that. But it may mean an inverter isn't suitable for a certain combination of panels.

By this time, the inverters were wired in and a row of new AC and DC isolating switches installed so that everyrhing can be turned off for maintenance

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Lastly. If shadows are a real issue for you, there are two brands of inverters that have a technological fix to overcome it.
Enphase brand micro inverters are small weatherproof mini inverters that fit on each solar panel. One inverter per panel means every panel can adapt to make it's own maximum output without affecting any other panel. This is a costly but high quality solution if you have difficult shadows on your roof from trees power lines and objects.
Solar Edge do something similar. They have a central inverter like normal plus a small box of electronics on each panel called an optimiser. It's a half and half between the standard design of one shared inverter and the Enphase solution using micro inverters on all the panels instead.
These two are both good, but more expensive and unnecessary for many people. My shadow problem was simple and short enough not to need this.
 
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Inverter Details

Once I had worked out how many panels I could fit on our roof and got a peak kWh number based on the N type panels I wanted ( they are very similar from brand to brand at any given physical size) I started looking at inverters.
I did get quotations for a GivEnergy system, but after the second go around when I realised I'd need two interters, two batteries and it was all going to cost over £20k, I focussed on the Fronius products. I may as well have top brand gear at that price point.
I found Fronius have recently introduced a new range of inverters called GEN24.
Their previous generation have been selling well for a decade or more. The new ones are hybrid DC inverters designed to work intelligently with batteries. Their industrial design is very nice from an engineers point of view.

The largest GEN24 inverter in the single phase range is 6kW.
I'd chosen a 9kW array. Hmmm.
But there is a principle in solar PV that connecting more panels than the inverter is rated for is actually a good thing. It's called oversizing. Everyone knows about it and the manufacturers test and certify their product as safe upto quite a high overload because of this.
The reason is that a) maximum power peaks don't happen often, and b) inverters need a certain minimum voltage from their panels to start working.
Oversizing the array means the panels reach the inverters minimum voltage quicker and drive the inverter better when the light is weak. It also means the inverter is occasionally overdriven in peak conditions. The inverter just "clips" - it adjusts so that the excess power isn't taken from the panels. Effectively it is wasted as heat. No harm done. The gains that oversizing the array gives in low light outweigh the loss of peak power. Oversizing by 20% to 50% is common. The Fronius inverter is safe upto about 70% oversize.

So I was set, and we ordered a 6kW GEN24 inverter to match the 9kW of panels. Both the installer and myself used Fronius' sizing software to check compatibility with the planned 24 N type panels and this recommended some wiring configurations for good efficiency.
One string of 8 panels would connect to the #2 input of the inverter.
Two strings of 8 panels would connect in parallel to the #1 input.

Not all inverters have two inputs but it is useful for a larger array. It allows panels to be grouped, for example an east facing and a west facing string can be connected to the same inverter. In mine, each of 3 rows of panels made a string, top two rows in parallel because they get the light first, bottom row that is the last to wake up would go into input 2.

When the inverter was delivered and installed I was impressed. Excellent quality.
It has built in wifi. You connect direct to the inverter to configure it from a phone app or a web browser - things like telling it what country it's in sets things like maximum voltages, what to do if the voltage goes too high, how quickly to shut down if anything misbehaves, etc.
The installation included it's own smart meter. Not a normal utility type, this is a Fronius part and part of the intelligent controls. With this, the inverter can be programmed to limit export to the grid to any value. So if the electricity company infrastructure can't accept your power, your inverter will deliberately reduce it's efficiency to limit export to whatever you agree with them.

Day to day, the inverter is linked to our home wifi and uploads data continually to the Fronius server which you can access via an account on their website to see all the graphs, manage users, do software updates, etc.
You can do the same with Fronius welders and the GEN24 is likewise straightforward and easy to control. Just complicated if you really want to get into it rather than leaving it to the installer.

I hit one snag shortly after committing this project. When we decided to buy the maxeon 3 panels rather than Jinko tigers, my installer ran the fronius sizing software with details of 24 maxeon panels. It turned out to be too much for the inverter. Just by one panel.
Rather than change the array design, we decided to fit 2 inverters. The 6kW one as planned plus a second 3kW unit from the older Primo range. This gave an exact match with no oversizing and we installed otherwise as planned. The 3kW inverter is fed from my #3 string. Strings 1 and 2 drive the 6kW GEN24. This is why you see two solar sources (2 inverters) on the myenergi app.
The batteries will be charged only by the 6kW inverter, but of course it can draw on the solar energy produced by the 3kW inverter as well as the power of the panels connected directly to it.
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Here are the two inverters (newer design above) newly fitted before wiring in. With the cover removed, the innovative air cooling design and die cast aluminium case + heatsink of the GEN24 inverters is unmistakeable.

With 20:20 hindsight, I would choose both inverters to be new GEN24 models next time. The older design Primo is very reliable but not as smart. But that would be a few £hundred more expensive.

I also need to add as a postscript (Nov 2022) that just like Microsoft, Google and Apple, Fronius software updates are a long way from perfect. I am a reluctant updater when new softare releases come along and my scepticism has been proved right. 3 releases back Fronius screwed something up in their firmware that messed up my inverters and they haven't fixed it in the two updates since. The system still works but with multiple resets and error reports daily. This is an outstanding issue waiting to be fixed. If they don't, I'll be sending mine back and adding a strong DO NOT BUY to Fronius inverters of any model.

In the event, they did fix the mistake and the daily "overnight insulation resistance test" errors ceased when I installed the latest firmware update in early December.
 
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MyEnergi smart controls

There is little argument that the way to get maximum value from solar PV is to maximise self consumption.
Key to this are
1. A solar diverter that measures surplus energy that you are trying to send back to the grid and instead sends exactly the surplus amount of power into an immersion heater or some other electric heater like electric radiators.
2. A smart electric vehicle charger that does the same for charging an electric car. It has the option to send only the surplus generation to charge the car battery.

There are plenty of EV chargers but few that are smart enough to only use surplus energy whenthat is what you want to do.
There are a few options for solar diverters.

The best system on the market at present is offered by a UK company called myenergi.
They have a long technical history in the game and offer both of the above, plus an app to visualise and control both.

We aspire to an EV so the solar was designed with a car in mind. Within days of installing the panels, we realised how much surplus we had and I went online and bought a Myenergi Eddi solar diverter immediately.

Eddi works great. It cost £300+ but it is well built and pumps several kWh a day into our immersion heater. Once the tank is hot and the immersion thermostat opens the circuit, Eddi realises this and sends any more surplus to a second circuit, which could be an electric rad or a second immersion heater.
This is actually smart. A big tank with immersions top and bottom can be set to heat water at the top of the tank first for a shower then preheat the bulk of the tank through the day.
While heating the second load, Eddi switches back to the primary load every 15 minutes in case it will take more.

Here is Eddi heating our immersion on priority 1. Note the periodic spikes happen when it checks back and manages to push a little more heat into the tank.
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Also notice the dotted temperature line.
Eddi has an optional sensor circuit board. An end user installable thing. This allows you to control some extra circuits and to connect one or two standard temperature sensors. The dotted line shows the actual temp of our water measured by the sensor. You can allow that to control the heating.

Below is happens when we use hot water in the morning and and Eddi has time and surplus available to reheat the tank. On occasions we have heated and used three tank fulls of water in a day. It takes about 12kWh. In our old hot tank we are limited because the immersion only reaches halfway down into the tank, but at 70C this is enough for a good tub.

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The system has upto three current sensors that can be hooked up to the meter tails to see what is coming in and out of the grid, and in my case to measure the generation from each of two inverters. The myenergi app shows all the energy flows in one place and is our goto in deciding whether we can run our kettle, oven, microwave, tumbler, etc for "free"

Here's the app showing the multiple devices. When we add a Zappi 2 car charger, there will be one more petal.
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And some screens showing history and consumption in different ways
First shows 15kWh of generation. We used only 1.2kW of that and exported the rest.
We had to buy 5kWh from the grid because we don't have our batteries yet.
But the app doesn't count the energy diverted to hot water so we need to add about 8kWh to the 15 in the first screen, we actually generated about 24kWh and used nearly 10kWh of it.

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This screen shows generation by the smaller our two inverters.
Notice how it starts at 7am. The small inverter is fed from the lowest our panels, the bottom our roof gets sun about 30 minutes after the top first gets it. So Eddi starts heating the water at 6.30 thanks to the larger inverter and the little 'un kicks in a bit later.

For both inverters the best power is made in the morning and early afternoon thanks to the SE facing direction of the roof. When the time comes, we'll be able to charge the car in the morning and go out in the afternoon :)

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@Sideways , you say "First is to use an AC coupled battery which simply wires in to any new or existing system using 240V AC."
I don't understand that idea, explain please?

Excellent and thorough view, much appreciated.
 
Love this. Very timely for us too as we are thinking about solar!
Subscribed to this thread for future update. Thank you for taking the time to detail this out.
 
This is intended to be a fairly detailed run through my own domestic solar PV project in the UK.

  • I'm a retired electrical engineer in my early 60's.
  • I'm as concerned as everyone else about rising fuel costs
  • We would like to be more "green". After travelling some 1.5 million miles in the course of my working life I've certainly done enough damage to the planet and agree that we need to consume less. This project wasn't done on the basis of financial returns.
  • Our house has a relatively large SE facing roof for the size of the place. Over the years we've felt how the sun can heat up the roof and have long felt that it would be well suited to solar energy.
  • We don't intend to move house - at my age I'm looking at this as a lifetime buy.
  • We were in a position to afford solar and any delay just meant we would get less benefit from the spend so now was the time to do it.


Four years ago I visited the "Solar & Storage Live" exhibition at Birmingham NEC.
This is an annual event mostly for the trade but open to the public.
It gave me an opportunity to see most of the major brands of inverters and panels in the flesh, to ask some questions and to identify some of the wholesalers who supply the installers and in some cases also the public.
Overall impressions: Solar PV was a mature technology and improvements are mostly incremental. Batteries are the new big thing. The industry seemed to be a bit down at the time. Feed in tariff had ended and demand for new systems was down.

I parked the idea for a couple of years and went back to the show last year, with my engineering head on, and specifically looking to shortlist the panels, inverters and battery that I might buy. I had no intention of doing the job myself but I would shortlist the kit and get quotes from installers who could supply and fit it.

From the show, solar panels that interested me :
  • Hanwha Q cells - Korea - PERC technology - very nicely built with good warranty
  • Jinko Tiger N - Chinese - N type silicon - good reliability scores
  • LG Neon R - Korean - N type silicon - good reliability scores
  • REC Alpha - Norwegian owned - N type silicon -
  • JA Solar and Trina - both Chinese - also had decent panels on offer but not as refined as the others above.

Inverter manufacturers :
  • Fronius - Austrian - premium brand, very high quality design and build
  • SMA - German - makers of the reputable Sunny Boy inverters - very well built
  • GivEnergy - UK - innovative and intelligent (as in automated) set of products but very new company
  • Solar Edge - German - well established and proven - broad set of products that work together and quite intelligent - have a very good solution for roofs subject to shadows - build quality looks much lower than Fronius or SMA to me

Batteries :
  • GivEnergy
  • There were a number of battery suppliers there including the majors like the Tesla Powerwall, but I found the products hard to assess and came away unconvinced. Few impressed me.

I was looking simply for high quality product, indication that the manufacturers were large and reputable, and for some degree of integration - not just a random collection of bits.
I was also interested in the solar panel mounting hardware because one of the real risks I anticipated was poor installation leaving me with a leaking roof and unsecure panels. I came away understanding that there are high quality roof mounts available and cheaper + less well made alternatives.

Shortlisting the components

Panels

Modern solar panels pretty much evolved from the space program decades ago. These panels use so called "P type" silicon. If you ever heard of a PNP and NPN transistors in school physics, it's the same idea. If not, don't worry and just follow along.
P type silicon proved to be the most long lived, and has been developed over the years. The latest flavour being called PERC. This is used to make the vast majority of panels and an excellent guarantee is 25 years plus a performance guarantee that the panel will still be achieving 85% of it's original output after 25 years in service.

A panel is simply a metal frame, an impact resistant glass top sheet covering typically 60 individual solar cells all connected by thin metal tracks that are printed, not actual wires, and a backing sheet of some type. A panel has a DC+ and DC- connection on the back and you wire several panels up in series (just like batteries in a toy) to make a "string".
There are some functional and cosmetic differences between panels - like the all black look and different ways of arranging the (printed) electrical connections that connect all the cells together in the panel. These can make small improvements in efficiency and make the wiring unnoticeable from a distance. The majority of modern panels are very similar in size and performance. Differences are subtle. The main thing is to buy from a reputable company that achieve consistently high reliability.

In recent years, studies have been done on the other type of solar cell. "N type" silicon. N type doesn't last as well in space because it suffers more damage from cosmic rays, but on the ground that doesn't matter and it is better than P type in other ways.
The upshot is that a small number of companies make premium panels out of N type silicon, and these can be bought with longer guarantees (25 years) and higher guaranteed outputs (90% of original output after 40 years !).
I decided that I wanted this technology. In a decade it will be mainstream but for now the choice is limited : REC Alpha (Norwegian), Jinko Tiger N (Chinese), LG Neon R (Korea) or Sunpower Maxeon 3 (USA + Mexico). The long life and high performance matched my lifetime buy objective and a price premium of 15% ish felt acceptable.

In practice, global supply chain was a nightmare this Easter. No one had any of the good stuff. I first shortlisted the Tiger N panels for value and while we were looking for them, I discovered that a lot of Chinese solar manufacture is tainted by reports of forced labour. Not OK.
I chose LG Neon next as this is a reputable Korean company, but LG withdrew from solar panel manufacture this summer !
Eventually my chosen installer stumbled on a supplier with the Maxeon 3 panels in stock, took 3 days to work up the courage, then suggested them to me. Maxeon 3 are the best made panels in the world. They cost me about 50% more than a good PERC panel but having realised how tough the supply chain problems were, I said yes. They have turned out to be the most impressive part of the system. Simply superb.

I'll explain the choice and layout of the panels later, but for now, I'll tell you that someone needs to consider the physical size and shape of the roof and work out the best way to arrange panels on it. I did all this for my roof and ended up with a simple, clean layout. 8 panels wide, 3 panels tall giving 24 panels in total. The maxeon 3 panels just fit my roof leaving enough space above and below. 375 W apiece x 24 = 9kW peak output.

Inverter
Solar panels output their energy in DC (direct current). 40 or 50Volts per panel is common. My Maxeon 3 panels make over 70V DC apiece. Panels are wired in series as "strings" that can be 400V, 600V, even more.
The inverter is a box of electronics that converts DC from the panels to 240V AC mains and feeds it to your consumenr unit through a circuit breaker - typically 20 or 30 Amp rated.
The AC from the inverter is exactly synchronised with the electricity coming in from the grid so that they play nicely together. It's just at a slightly higher voltage which allows the inverter to push it's energy into your home or back into the grid if you can't use it. The AC voltage from the inverter constantly adjusts, more sun, more power generated, slightly higher voltage to push that power out.

The inverter can be running 16 hours straight over a long day, handling several kWatts, and doing it 365 days a year for a decade or more. It's a pretty demanding job and the electrical eng in me thinks that a good quality, well designed and built piece of electronics matters if you want a long life and reliability. I was absolutely looking for something built to a "commercial" or "industrial" standard, not something that felt like a domestic appliance that you would expect to last 3 to 5 years.


Batteries
You have to consider batteries and inverter together.
When adding a battery to a solar PV system, there are two ways to do it.

First is to use an AC coupled battery which simply wires in to any new or existing system using 240V AC. The battery includes a charger. This approach is simple but has the advantage that an AC battery can be added to any solar setup, including ones already in service. Also, any battery can be matched with any inverter so you have freedom to mix and match. Tesla Power Wall is an AC coupled battery.

Second is to use a DC coupled battery matched with a specific inverter.
Batteries store power as DC. Solar panels make DC.
For maximum efficiency and maximum intelligence, the inverter can double up as a battery charger. It takes DC power from the panels and feeds it still as DC to charge the battery. There is no need to convert to AC in between and this improves efficiency. The battery pack doesn't have a charger built in because the inverter does this task.
The inverter draws DC power either from the solar panels and / or from the battery and converts this to AC to supply the needs of the house. This type of inverter is smart and has full visibility of the power in and out of the battery which a simple inverter with an AC battery does not. It is the better system if you are putting in a new, solar + battery system. The downside is that you need the battery and inverter to be designed to work together like this. That limits the available choices.

Battery size
How deep are your pockets ?
Our average daily electricity consumption is very typical for our size of home and family of 3-4.
Measured over the last couple of years it's 13kWh a day. We have gas hot water and central heating
The amount we use while the sun is down is maybe half that. We often use the oven for an evening meal.
We could choose a battery that held enough power to take us through the average "night" so just 6kWh say.
We could choose a battery big enough to carry us through an entire average day, so 13kWh
In the event, I decided that I wanted a battery that could feed a 6kW load - this is our oven plus a kettle in the evening or oven plus microwave. whatever.
It's a bit arbitrary, but small batteries can't supply that much power. and that 6kW load figure meant that I needed a battery with 16kWh of capacity. A bit more than one entire, average, day.
That's a lot of storage. About £10k and almost half the cost of the entire installation.
It means that we will be self sufficient - able to move the power generated by the solar to when we want it - almost 100% - for about 10 months of the year. Only in the two coldest months of the year is our solar generation predicted to fall to 8kWh a day. For the rest of the year, the solar will supply our average daily needs or much more and the battery will hold more than the average day's demand and deliver it when we need it. Overnight or during the next cloudy day.
If we have a run of bad weather we need the grid so never 100% but well up there.
Without the battery our self consumption will be hard pushed to reach 50%, 25-50% is more likely.
But ignoring inflation and Net Present Value calculations, I think the battery will take over 10 years to pay back and I genuinely don't know how long it will last for us. Potentially long enough and maybe much more, but this comes down to what we're willing to pay to be more green. We're willing to take the risk that this system will be more expensive than the grid in the end, in order to do our bit and not be so much at the mercy of governments and energy companies in future.

Inverter and Battery Selection
In the end, I had only two serious candidates because I wanted a "hybrid DC" inverter and battery solution described above.
One was "GivEnergy" - a very new company based in Stoke on Trent, UK but with overseas investors and partners. They are growing very fast because they offer inverters, batteries and an intelligent control that works with some of the most innovative energy company agile tariffs. The snag is that their inverter is 5kW and battery 8kWh. I would need two inverters and two batteries in my system and even then it was only rated for 5kW maximum discharge from the pair of batteries. It's a new company, unproven.

The second, and the option that I chose, was to pair inverters made by Fronius in Austria with batteries made by BYD in China.
These are separate companies, but they are cooperating to make their products work together to deliver a solution. BYD batteries are tested to work with Fronius inverters.
Fronius are a family owned firm that specialise in power electronics. They make just 3 groups of product: welders, forklift truck battery chargers and solar inverters. The core competence in power electronics is the same for all three.
They have an excellent reputation and I own one of their Magicwave AC DC Tig welders. It's design and build is very, very good. Up there with Kempii and Miller, arguably better than both. I've also dealt with their technical support and found them good. All this gave me confidence that the inverters should be good.
BYD was a real unknown, but if a respected supplier chose to partner with them they might be OK. It turns out BYD are the largest manufacturer of batteries for industry / traction application in China and I think the world. They make more batteries than Tesla and their batteries are the ones that power the new electric bus fleet in Sydney, Aus. Their batteries are LiFePo type prismatic cells that I believe are better suited to long life needs of domestic energy storage than the car battery technology used in the Tesla Power Wall. Only time will tell if this is right, but an Australian facility that has been testing solar storage batteries and making the results public has tested the BYD battery and it lost very little capacity. The results give me some hope that battery could manage a 20 year useful life, maybe more,
Thank you for sharing your knowledge and experience in this thread.👍
A few questions if I may:
1. Whereabouts do you live (ish)?
2. Who did you use for sourcing and installation?
3. Did you consider ‘in roof’ as opposed to ‘on roof’ panels?
4. Did you consider Victron inverters/control gear?
 
Thank you for sharing your knowledge and experience in this thread.👍
A few questions if I may:
1. Whereabouts do you live (ish)?
2. Who did you use for sourcing and installation?
3. Did you consider ‘in roof’ as opposed to ‘on roof’ panels?
4. Did you consider Victron inverters/control gear?
We live in Cheshire, UK
I was initially very happy with my installer but as time passed came close to starting legal action against them. The problem has been the BYD HVM high capacity batteries. These were promised for August against the initial installation completed eary April. Unfortunately supplier Midsummer Wholesale reneged on the battery order some weeks in and my supplier had to reorder from a different wholesaler. They didn't tell me this and ignored my email requests for update for a solid 6 weeks. Comms are now a little better but the HVM battery is still pending, latest forecast (as at mid Oct) is 2nd half of November.
I'm not quite ready to name and shame because the supply problems are not their fault but customer management has been incompetent verging on intolerable and I'm not entirely sure I won't have to drag them into court before I'm done.

I think "in roof" is great. It looks smart and would be the way to go with a new build or a reroof. Two caveats though. First is that mounting solar panels flush with the roof means little or no ventilation behind them. Solar panels get hot and generation is reduced when they are hot. So in roof is electrically less efficient because the panels run hotter. I haven't quantified this. Second is that some in roof systems use or require specific panels. The in roof systems on show at the trade show I mentioned all used panels that were just a mid range PERC technology. My preference for the high spec N type panels wasn't negotiable.
Victron equipment looks excellent to me. They have a very good reputation for off grid solutions and the equipment appears well made. I'd recommend anyone interested to consider them.
 
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This is very good information. Maybe I missed it but are you using lifepo4 batteries or lithium ion ?

Ollie
 
LiFePO4 :)
They haven't landed yet but it will be a BYD HVM battery stack.
7 modules of 2.x kWh apiece making 16kWh
It looks like a stack of shoeboxes and stands about 1.6M tall x a couple of feet wide.
 
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Everyone loves graphs. Here are our generation figures for the first few months in operation:

You're interested in the top line. These are the sum of the 6kW inverter (purple) plus the 3kW inverter (green).
Apart from a few dull days where generation drops into single figures, we've mostly been above 15kWh and at peak, all the way up to 45kWh a day.

April
We switched on on 1st April, but had some teething problems that took a month to sort out.
It wasn't a big deal but for most of the month we were generating only about 2/3 of the system's capacity and for a few days I turned it off altogether.

20220906_132857.jpg

May
20220906_132921.jpg

June
20220906_132945.jpg

July
20220906_132816.jpg

August
20220906_132754.jpg


And September. The generation is falling off. We had our worst day to date of just a couple of kWh in late Sept, followed by 20kWh the next day. That big battery would have helped even those out !

20220929_172259.jpg


April through August monthly totals. About 3800kWh over 5 months.
That's our entire annual consumption if only we could move it to when we actually need it !
Then I've tacked on September's plot.

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20221002_220613.jpg
 
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2022 year end update

It got lost in the ether for a long time (i.e. installer didn't do it or follow up properly first time around so had to make a new application) but I'm pleased that our DNO agreed to the G99 application and we have permission to export upto the max 9kW our system is able to generate.

The battery saga has been an utter nightmare.

Midsummer Wholesale dropped my installer in the poo some unknown number of weeks after they placed the order for the HVM battery and announced they would be unable to fulfill the order. Along the way July had become June or September. The battery was reordered via another wholesaler but I wasn't notified of this. Deadlines came and went. Slipping a month each month through Sept, Oct, Nov and now the latest forecast is for the battery to reach the wholesaler on Dec 26th (yeah, right !).

I can't be bothered stressing about it so the installer has been warned that they need to manage the wholesaler (the way I'm now managing them - behave like schoolchildren, get treated that way) and that everything will change if I'm still waiting in January.

I've followed the progress of the shipment into Rotterdam and as I write this it should be on the way back out for the 36 hr hop to the UK. Come January, I'll either be happy or I'll be filing papers to take them to court. All good fun :)

On the positive side, my DNO (electricity network operator), has approved the G99 application and in in principle I am now allowed to export a full 9kW of surplus power to the grid. In practice, I think that the state of the grid locally means that I may not achieve that in practice without raising the AC voltage higher than allowed in order to "push" that much power back into it. But it's nice to have the approval and as years go by and more people draw on the grid for EV charging, there may be more demand for our exports.

Experience of the system in Nov and December :
The low sun seriously impacts the output of the array as expected, and shading on the lowest row of our array doesn't clear until almost 11am. Because each row of the array is a separate string, we see the output increase each time a row comes into full sun as the shading moves down the roof. There is nothing much we could do about this. I knew it would happen and the panels have been wired in a way that best copes with it.

In the last few weeks, we have had endless days of cloud where generation was very small. Our peak output today in low bright sunlight was a little over 3kW vs the peak capacity of 9kW. We had 2-3 good hours enough to put 4kWh into the hot water tank, feed the house and tumble dry a load of laundry. It would have been v useful to have been able to store todays power for essential use instead of "using it up" as heat.

I'll add the monthly generation graphs to the previous post until you have a picture of a full year in the UK.

Solar panels make an awesome ski slope for launching snow off your roof :)

20221215_163746.jpg


Last observation: sadly, my experience of software updateable products has been proven right. I never like to be an early adopter and my experience of microsoft and other companies over a working lifetime are that all suppliers routinely break things because their software updates are inadequately tested. Fronius have proved to be no exception and they introduced two significant errors into my system when I allowed one of their routine updates a few months ago.
The lesson is that once you have a properly working config, "just say no" to subsequent updates.

2023 January update
THE BATTERY FINALLY ARRIVED !
And I'm pleased to say that I'm very happy with it.

My installer were good to their word with the start of the new year and having taken delivery of 7 pallets full of product were with me in the first full week of the new year.

The BYD HVM stack was very straightforward to install.
Clear the space, position and level the baseplate (in my case with a sheet of 25mm celotex PIR insulation pre placed behind it along with the required 12-20mm air gap)
Then stack the battery modules taking care with the connectors,
A connection, control and breaker unit sits on the top and the modules screw together for stability.
The battery wires directly into the GEN24 inverter. The connection is DC so it wires in right alongside the DC cables from the solar panels.
An earth is essential and an ethernet type cable for the "modbus" communication link between inverter and battery complete the process.

The battery has a wifi interface so after stacking and wiring up, there are firmware updates to be installed and some configuration to be done via a mobile phone app.

Lastly, it is back to the config menus of the inverter to tell it that it has a battery attached. Model, capacity, etc have to be entered and I selected the max and minimum charge levels that I wanted to work between. I have chosen the default 90% max and a higher than normal minimum of 15% which costs me some usable capacity but I hope will increase the lifespan of the battery.

It's enormous !
20230112_151216.jpg


The sun came out and gave us a rainbow to celebrate !
20230112_151419.jpg


Batteries are charged to 30% state of charge (SOC) at the factory and ours showed 28% as installed.
Charge and discharge of the battery and SOC data are immediately added to the Fronius android app. There is no need to run another app to view and manage the battery storage.

Instantaneous power flows
20230115_165439.jpg


Historical graphs
20230115_165232.jpg


And visible in the web based version too.

Notice the thin green line that now shows STATE OF CHARGE and how this rose to 30 or 40% during the day and discharged back down to 15% as the lights, freezer, tv etc drew on it overnight.
20230115_165355.jpg


Some quick maths tells me boiling a kettle will take 2% of the battery capacity. 20 minutes Microwaving is 4% and freezer + lights etc consume about 2% per hour through the night.

Our self consumption theough the year has been around 50%. Very much in line with "typical" solar users. With the battery, this instantly doubled to 100% at least at this time of year.
 
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BYD batteries are as I understand it all LiFePo4 they ceased production of Li-ion units in the 1st 1/4 of this year. BYD is the biggest name in the battery industry that nobodies heard of in the real world. They recently become the sole supplier for Toyota's future EV battery needs, from next year they will supply over half the batteries used in Chinese manufactured Tesla model 3s, are the preferred supplier for the Aussie national grid battery storage infrastructure make the only approved city EV taxi and bus fleets for use by Chinese municipalities, 3 cities currently have EV only fleets for all public transport. BYD are launching their cars in Europe this year with the Atto3, personally I cant wait for the Han sportswagen to launch (a 300+ mile 5 series size estate car) which should be here next year with their "Blade" type batteries. They make more EVs than Tesla and out strip Tesla by around 300times in terms of building power storage units for buildings use. They are also the largest supplier to industry of battert power storage in the world. And yet nearly no one has heard of them.
 
A good write up, when you talk of battery strings it reminds me of working with UPS's and the large rooms full of battery racks which were also wired in long strings but in them days we used sealed Hawker Oddesey lead batteries. These systems are in some ways similar to your solar panel setup with the need for conversion to 230 Vac. I would say that using the least amount of conversion has be more efficient, if your panels generate Dc then why convert to Ac to only have to convert back to Dc to charge the batteries?

In houses of the future you could run extra low voltage Dc circuits to deliver power to all the appliances that are currently powered by Ac to Dc wall chargers and such which again saves in conversion.

We did have the advantage that these UPS systems were often three phase so by using transformers with both a Delta and Star wound secondary you got a 12 pulse output which allowed for very smooth Dc and less capacitance needed for smoothing and maybe the future will be more electic heating using three phase domestic supplies.
 
Something that contradicts what a lot of people say about Chinese manufacturing is evident in @Sideways post, we all complain about the cheap rebranded Chinese machinery on offer and the problems it can give but as I have said it is just you get what you pay for. The Chinese certainly seem to be in the running with Solar panels and are probably the ones pushing technology forward.

I was also interested in the solar panel mounting hardware because one of the real risks I anticipated was poor installation leaving me with a leaking roof and unsecure panels.
When you think of the modern truss roof then you have to question it's ability to also carry the weight of an array of solar panels, a lot of people don't even think about this aspect and end up with issues.

Another area is that of potential lightning strikes, how many people fit surge arrestors in there instalations.
 
What's the incentive in the UK for batteries instead of direct grid tie in. Do you have variable ("smart") rates that differ based on the time of day?

In the US where I am, we have the option to use tiered rates, but the incentive is poor- little potential savings and a lot of extra planning. Further from where I live, especially in more progressive areas, rate fluctuations during the day and tiering for total use make solar a lot better on a net cost basis.

For now, we have net metering where I am - you get a huge benefit to reduce your bill to zero but any surplus generation yields little, so the burden of distribution is on the grid instead of a battery. Solar factor in my region is poor (<65% of the very sunny regions in the US, and 20% worse than areas only a couple of hours east), but panels have become cheap enough that even when they're installed by cost-overladen leasing groups, they're still at least break even with net metering, but wouldn't be with batteries/onsite storage.

Other interesting side point here is that installed levelized cost for panels is about double rooftop of the cost of installation in commercial arrays. But nobody here likes the looks of commercial arrays, so there's less opposition to rooftops. Across from where my parents live and scattered around in different clusters are 2 1000 acre solar "farms" in an area that 15 years ago, nobody ever thought they'd see.

I sense in time we'll see incentives for more EVs and incentive to leave the EVs tied into the grid as part of the storage and distribution.
 
I suppose if you just sell the surplus back into the grid then you do not have the expense of batteries and there maintenance but if the grid goes down due to the current crisis with enough batteries you can keep the essentials going. I would suspect a generator would be cheaper than a battery bank large enough to support a house for any duration though.
 
I suppose if you just sell the surplus back into the grid then you do not have the expense of batteries and there maintenance but if the grid goes down due to the current crisis with enough batteries you can keep the essentials going. I would suspect a generator would be cheaper than a battery bank large enough to support a house for any duration though.

Generators are common here in rural areas. I live in the burbs and have one, but it's only big enough to run either the furnace (gas - just need enough power to run the fan) or the freezer and fridge, and not all three at the same time.

I believe our rate at this point in dollars is about 0.16 per kwhr. I don't have panels (some inlaws do), so I'm not sure about surplus other than to hear that their sentiment was that even the generation rate isn't returned. Of the 0.16 here, I think the generation rate is a little less than half, so if you're generating surplus by accident and the figure is something like 4 cents, it doesn't make sense compared to the installed cost.

It can't be too long before in the US, there are reductions to the net metering as solar has taken off. Both commercial solar and wind are viable without subsidy at this point.
 
What's the incentive in the UK for batteries instead of direct grid tie in.

For me it seems the point of going solar with a battery is to not have to buy electricity from the grid at all if possible.
It seems silly to generate electricity, sell it to the grid at a poor rate, only to have to buy it back again at a much higher rate.
The government's incentives for buy back rates have stopped now, my brother still gets a good rate as he signed up before it changed.
Of course in winter you will have to buy some with short days etc.

Ollie
 
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