Solar panels during a power cut - what do I need?

[Wuffles]

Suffered around 3 hours with no power the other day due to a power cut, and it was a beautiful sunny day. I've always put up with the fact that the panels on the workshop won't work without mains power for the inverter but what can I feasibly get away with as a minimum for still having the power during a power cut?

My theory is a small generator plugged into one of the sockets in the workshop which should in turn power the inverter? Once the inverter is powered, will it then "self power" once production has started and the genny can be turned off?

Does that theory hold water? Is there a better solution? How tight am I?!

 

[CHJ]

.....

My theory is a small generator plugged into one of the sockets in the workshop which should in turn power the inverter? Once the inverter is powered, will it then "self power" once production has started and the genny can be turned off?
..

Some of my immediate thoughts without researching modern distribution practice.

Never ever plug an alternate power source into a fixed mains circuit unless some serious isolation interlocks are fitted to stop your temporary feed from traveling back along the main supply system and causing serious problems if the mains supply should re-instate, also workers on the system may not have adequate clamps on your side of a mains fault to prevent them from being electrocuted, if they do your generator may well be looking at a short circuit until such times as something trips.

Is not operating a remote workshop/shed hard wired system from a generator now covered by the Part P regulations?

 

[Wuffles]

I'm not trying to power a shed from a generator, I'm trying to kickstart the inverter so the panels will kick in as they would normally during normal power. I *could* isolate the workshop (which is where the panels & inverter are located) if that makes more sense, but I wanted the panels to continue powering the house - fridge and whatnot.

If it's a totally lame idea I'll leave it, was just a shame to be able to be generating enough power to more than cover the house's requirements during the power cut but unable to because of a lack of power to the inverter.

 

[mind_the_goat]

Interesting scenario, never considered you'd need external power to make your solar installation work.
Chas raises a good point though. Without isolation of your house from the grid, you would not only be powering your own fridge but roughly 1/3 of the houses in your streets fridges too (other appliances are available) and the danger of applying power to a circuit an engineer would be expecting to be off is considerable. The inverter switching off may be a deliberate feature to prevent this occurring.
So unless you can get a safety interlock built in the idea may be a non starter.

 

[Wuffles]

That would be the case for everyone who plugs a generator into their circuit during a power cut though, which definitely happens.

I might ring western power distribution and ask their opinion as you're both right about people working on circuits that are "off" but they must surely expect it. There must be safeguards in place.

I am already feeding into the grid and powering various fridges in our village under normal circumstances remember


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[CHJ]

Interesting scenario, never considered you'd need external power to make your solar installation work.
...

Any external unit wishing to connect and contribute to main source power distribution has got to see that main source power in order to synchronise its output to the same phase and adjust it's output voltage.

You should see the hoops an aircraft system has to jump through to synchronise four or more alternators onto a common buss.

 

[RickN]

My SWMBO works for a Solar energy Distributor I'll ask her, but in the mean time rather than a generator, I have heard her mention Battery packs for storing generated power, they may be a better retrofit idea without having to mess to much with complicated black magic electrickery.

Regards Rick.

 

[Wuffles]

My SWMBO works for a Solar energy Distributor I'll ask her, but in the mean time rather than a generator, I have heard her mention Battery packs for storing generated power, they may be a better retrofit idea without having to mess to much with complicated black magic electrickery.

Regards Rick.

I know a few people who live off grid and they use battery packs, but they're in the thousands of pounds neck of the woods, plus I guess you have to get that DC current back to AC and 240v? Man, I'm typing things my brain can't comprehend.

 

[RickN]

Cough , Cough , Splutter , chokes on Brew How Much!! ? Yeah. that would work, But hells teeth A sparky and an auxilary Generator circuit will be cheaper... Just shy of 5 grand apparently....

 

[finneyb]

Is it worth the effort?
How frequently do you have power cuts? I can't remember the last time I had one
Fridge and freezer will last if you don't open them.

Brian

 

[Wuffles]

Is it worth the effort?
How frequently do you have power cuts? I can't remember the last time I had one
Fridge and freezer will last if you don't open them.

Brian

Difficult to answer that really. If for the sake of a hundred quid I could hook up a generator to allow me to continue producing up to 4Kwh for hours on end and barely notice it, that's fair enough isn't it? That was my original question.

I know what you mean, we get reasonably infrequent power cuts - blips if you like, there's not a lot of point in setting a digital clock where we are, but I'm more thinking ahead, for when the rolling blackouts start - and the outage for a couple of hours made me increase my thinking on that.

The end is nigh!

 

[Wuffles]

So I was pointed at another forum where they deal with this kind of thing and found a thread where someone asked more or less the same question as I.

That appeared to result in an all out fight between people who know more about this kind of thing than I ever will.

Bottom line, change to a hybrid inverter, I think, it was all a blur. Real bottom line, it's not as simple as my black and white brain assumed so it's off the table for now.

Just in case anyone's interested in watching a sharpening/impact driver/in or out of the EU style argument about electronics, here's the link (you will have to copy and paste it I think as the forum I am linking to doesn't appear to like people linking to it): http://www.navitron.org.uk/forum/index. ... 964.0.html

Hamster wheels and lots of hamsters it is then!

 

[sunnybob]

Across the street from me was a restaurant that had no mains power. He used a truck engine powered 220 volt generator while he was open to power everything in the 60 seater place (mainly charcoal cooking though) but also while it was running, it used three inverters to turn it back to 24 volts to charge battery packs that kept all his fridges and freezers running when he went home.

When he moved out i helped him disconnect everything. Those batteries were the size of large petrol cans, and he had two pallets filled with them. A huge ongoing expense that is not viable for a private home.

 

[Eric The Viking]

I feel your pain Wuffles!

I still have the inverter my dad designed and built from many years ago when we lived in Surrey during the "winter of discontent" in the 1970s. It moved house with us, and became really important when we moved to Brent Knoll (down the road from you). Power cuts there were part of normal life and it got several rebuilds. Its main job was to power the central heating (oil boiler and pump).

You probably know this, but in case:

1. Find out what power your solar inverter requires. If it needs to be "clean" (sinusoidal rather than square waves), that's more expensive to do. You might need to get the info from the solar inverter's supplier or manufacturer. If it's not fussy about the shape of the mains wave supplying it (the waveform), there are many cheaply-designed inverters (rough mains from 12V or 24V) that will do the job. But...

... Your solar inverter needs to be phase-locked to the incoming mains frequency in normal use, probably to within one degree. I'd expect it to be designed to get this sync from whatever source normally powers it. So it will almost certainly lock to the separate genny/inverter you'll be "black starting" it with. This is bad news: (a) the little inverter will have to stay on all the time you're using the solar system and you can't use it like a starter motor on a car engine, (b) the stability of your solar-powered mains will depend on the frequency stability of the little inverter, (c) you could have problems switching back to normal mains afterwards, as your ad hoc system probably can't phase lock to the incoming mains if the solar has been operating whilst the mains is unavailable.

2. It has to be safe, for you and others upstream of you working on the mains distribution system. Make sure you can isolate (disconnect) the load you want to power from your solar system (a) from the incoming normal mains supply, and (b) from other things on the property that might be too big or too awkward a load for your solar inverter to handle. "Awkward" means things like big motors, or lots of fluorescents, which introduce a significant phase shift and/or have high inductance. In other words check that you _can_ run the things you want on your maintained supply.

If you imagine the normal mains as a big flywheel, in normal use your solar system is just giving it a little push when you supply power to the grid. Because the 'flywheel' is so huge compared to your property, odd loads such as motors don't have any significant effect - it just keeps 'turning' at the same speed.

Running off-grid, your solar system will behave like a car engine without a flywheel: it will bump around in voltage and frequency as the load changes - this may not matter, but it might. Switching big loads off, especially large induction motors may cause large voltage spikes too, that could damage the inverter and/or other loads. This may just be me fussing, but I'd want to know how it behaved before committing to use it for real.

3. Make sure the solar inverter isn't damaged by no-load conditions. It shouldn't be, but you will probably need to kill the power to everything on the maintained circuit before reinstating it to the normal configuration when the mains returns. You have to be very careful with generator sets - traditional mechanical generators ("reversed motors") can act as loads instead of generators (i.e. runaway with themselves), if they are presented with a low enough load impedance (actually another, much more powerful generator) and a big enough overvoltage and the wrong phase relationship to the power they are producing. It's too easy to try to re-connect with the two generating systems out-of phase.

There should (must) be some protection against this on your solar system, but solid state kit is rarely comfortable with sudden changes in voltage/current and large voltage spikes etc. You need to know how your solar inverter copes with sudden phase changes in the incoming supply, as might occur at the start or end of a power cut. It should behave gracefully, but as I indicated, it will almost certanly have to interrupt its output to avoid damage (whilst it re-syncs).

It's all conceptually simple, but as you can see plagued with devilish detail. You can do it, but you'd have to be certain all the individual elements will behave properly, and I'd work out a procedure for the start of a power cut, and another for setting it back to normal afterwards, write them down and follow them religiously. Also, without spending a lot of money, you probably can't easily automate any of this, so it will remain a solution for someone who knows what they are doing, and not, for example, for a non-technical spouse.

E.

PS: is there a phase meter of any sort on the solar inverter or even some sort of phase locked indicator?

 

[Wuffles]

Yes, nothing's much changed in terms of reliable power round here Eric, part of daily life. We're closer to Rooks Bridge than Axbridge too, so we're very close to Brent Knoll.

It's just not anything like as simple as I invented it could be in my head, so I'm walking away.

Unfortunately I couldn't ever go fully off-grid like my friends and their banks of batteries, I'm a higher power user than any battery could hope to provide power for. When our two heat pumps kick in they eat up around 7kWh, perhaps when the feed in tariff for them ends in a few years time I'll investigate another form of heating/hot water then we could.

You still get the feed in tariff for the solar panels whether you sell it back to the grid or not, you just have to generate it. It always amuses me when my friends on the 44p per kWh tariff receive their cheque - there is no connection back to the grid. All the money goes back towards the £7k+ they spent on batteries in the first place, which will need replacing in a couple of years I think.

I must try and fit one of those solar diverters this year too.

 

[DiscoStu]

What are you looking to power? Without some form of battery in the system you'll struggle as you want smooth power. If you think that some tools are 2000w then you'll need about 3000w of panel to generate that. I think for the odd occasion you'd be best off just using a generator on a specific tool?


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[Wuffles]

What are you looking to power? Without some form of battery in the system you'll struggle as you want smooth power. If you think that some tools are 2000w then you'll need about 3000w of panel to generate that. I think for the odd occasion you'd be best off just using a generator on a specific tool?


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It's all in the thread. It wasn't about powering a workshop, just the house and "stuff".

 

[n0legs]

Ideally you would need some positive isolation of your supply. A double pole isolator, suitably rated, fitted into your meter tails would be fine. There is equipment available that senses mains failure and automatically switches to another source of supply, and some can auto start a generator if needed. These cost £££££.
Reverse generation or "Back feeds" is no laughing matter for the mains boys. We don't consider anything at LV or MV to be "Dead", it is all treated as "Live". It was a common question on a test.

Q,, When is a cable dead
A,, When it's still on the drum.

We wear rubber gloves and use rubber mats once bare conductors are exposed. All our tools are insulated. We use temporary insulation to cover all conductive materials. We eat, sleep and s*** with our test lamps and proving units.

On the HV circuits (11Kv upwards) we earth down the conductors to protect against the supply being restored (polite way of saying in case someone f**** up) and back feeds.
In the HV switches this is a built in feature. On the overhead lines we use earth clamps an bonds, the clamps are attached and then connected to an earth spike or the pole stay wires. It has been known for pole mounted transformers to receive a LV back feed then generate HV, the earth bonds take care of this. None of this work is taken lightly, we use a "Permit To Work" system with "Limitations Of Access" . All switching operations are given and received by central control, notes are taken and reporting back when the operation has been carried out is done. No one is left in the dark, work does not start, or stops, when communication is lost or not attained.

I've used the temporary earth bonds on underground HV cables in certain circumstances and we've used them sometimes when we've experienced customer back feeds on the LV network. By dragging the current down to earth we stall, trip out and even damage a customers generation plant. Don't do it :evil: N0legs gets very upset when people try to play silly beggars.

In 1997 following some bad weather, we had a pasting, an Abergavenny farmer decided he'd wind up his old generator. What the farmer didn't know was the LV overhead lines he was feeding into were down. My boys would have been okay, using the equipment mentioned earlier, the general public were not protected in the same way.
I consulted my network diagrams to find the source of the back feed and paid the farmer a visit. We demanded he shut the generator down, he didn't comply. My insulated core cutters were employed to ensure my request was met and he could no longer feed back into the LV network :lol: . Then the good old farmer made another mistake.
Well I don't mind telling you I ended up in the cells, again. Fortunately not for long and a happy ending was ensured when the company solicitors paid Mr Farmer a visit. Charges dropped, a quick telling off (with added wink) from the boss and we all lived happily ever after.

If you do it right, and considering the money these solar panels cost, I would say go for it. Especially if you live in an area which is prone to power cuts. It's an ability that is very very useful, but like I said if you do it right.

 

[Eric The Viking]

My boys would have been okay, using the equipment mentioned earlier, the general public were not protected in the same way.
I consulted my network diagrams to find the source of the back feed and paid the farmer a visit. We demanded he shut the generator down, he didn't comply.

So he was putting any number of lives at risk by ignorance and stupidity, and he'd had all this explained to him... you must need the patience of Job sometimes.

I continue to be really impressed by the tenacity of your lot in the depths of winter. The media are quick to report power cuts (a pointless exercise in the main as those affected already know and can do nothing about them), but rarely if ever mention the sheer heroism that happens routinely to restore supplies.

Way back in the early 1980s I was on a job near Lowestoft in the middle of winter (and the middle of nowhere). It was very cold. We got to the hotel in the late afternoon. Everyone assembled in the bar in the evening because there was nowhere else to go and, IIRC, no food on! Shortly after we'd gathered the lights started dimming rhythmically with about 2sec period. Then total loss of power. which continued. I went to bed by torchlight.

In the morning everything was back on, I think.

It turned out that there was a huge demand for power that night across the country, so everything serviceable was being brought on-line. Somebody connected a generating station incorrectly, with a significant phase angle to the grid, and it became a load instead. The current surge welded the breakers (or something), and it couldn't be disconnected until there was catastrophic failure.

I don't know the details, but an old friend, now no longer with us, who worked at the grid control centre in Keynsham, confirmed to me that something like that did happen, although he was coy about the details - apparently someone had been seriously embarrassed and quite a bit of damage was done.

 

[dickm]

As a matter of interest, who is buyng the OP's generation? I sell to SSE (or "the Hydro" as we all call it) and also get my supply from them. Pretty sure that somewhere in the conditions for purchasing my generation, there is something that says inverter must switch off/be switched off in event of failure of mains supply. For all the reasons given above.