PV and other alternative energy sources.

[jlawrence]

Ok as suggested here's another thread to continue the discussion in.

For me I'm all in favour of alternative energy sources.

PV can work in the UK - even when it's cloudy. BUT and it's a bloody BIG BUT, you would need to have a lot of them to make you independant of the grid.
I've not read up on what this 'feed in' lark is. But I'd guess it's selling back to the grid. If so then it's f'in great and about bloody time - other countries have had the ability for years.
The new 'smart' meters should allow it - without problems. Basically as I understand it they are 2 way meters - reading in and out.
If so then Cool.
One of the most expensive parts (and most dangerous) of a home energy system are the deep cycle batteries needed to store the excess energy. Get rid of them and the price of a system could well become feasible.
I need to have a chat with my friendly estate agent - after a few beers the other week he hinted that selling a house with renewable energy sources is actually a good thing. He's seeing prices higher if renewables are there - hmmm, that would offset the cost of instalation then.

 

[Ironballs]

I'd check up on Smart meters before going down that route, don't think your average domestic meter is capable of feeding/measuring power back out. Think what they're talking about when they say feed out is feed out a meter reading, probably via GSM.

Also the govt have yet to rule on when Smart meters are coming in - and what BG are offering in their current ads is not a Smart meter

 

[MikeG.]

As you know, I am interested in all things renewable, but I do have a bit of a problem with photovoltaics.

As far as I am aware there haven't been any proper studies in the UK, so I had to extrapolate from an Australian study for these figures. This involved comparing sunshine figures from here and down-under, and multiplying.........and what I came up with was that it takes over 12 years for a UK photovoltaic cell to generate the equivalent of the energy that went into its production. Their embodied energy levels are incredibly high.

Solar cells have a continually reducing output, and are often (erroneously) said to have a lifespan of 25 years. It is more like the half-life, given that they carry on producing electrickery, but less and less. Nonetheless, if there was a mass change-over to solar cells, we would see a rise in our carbon dioxide output whilst we cooked all that silicon using conventional power.

There are potential alternatives on the horizon, but whilst they tend to be cheaper, and less energy intensive, their output is correspondingly reduced. Overall, I feel that they are wonderful in the sunny countries of the world, but to be of much use to us here in the UK I reckon we await a technological breakthrough.

No, if you are going to stick a solar panel on your roof, make it a solar hot water system. You'll get your money back much quicker, they work really well and the have much lower levels of embodied energy. It is also well within the capabilities of the average DIYer to make their own.

Mike

 

[Digit]

Solar cells have a continually reducing output,

Well known to all electronic engineers Mike but not metioned AFAIK in the sales blurbs.

Roy.

 

[jlawrence]

Never thought about a solar heating system.

I tend to only look at electricity - though I've successfully dropped my home usage considerably buy turning off a 7ft rack full of old computers. I'm now using approx 25% of the electricity I used to.

I'm pretty sure that the smart meters would allow selling back to the grid - as well as the feed out meter reading. At least that's what I heard on the news - could be BS of course.
IIRC it is very difficult to get an agreement in this country to feed back to the grid.

Before they bring them in they're going to have to put in place a 100% coverage for whatever comms chanel they intend to use.

I'm not convinced that PV is the way forward - as you say Mike there is a massive inherent cost (environmentally) in creating the things in the first place.

I think if you want to offset the cost of your energy bill then it has to be a bit of everything - wind, solar etc etc.
If I was building a brand new house then I reckon I could get the figures to add up. But since swmbo wouldn't let me do that this time around I'm stuck.

 

[Digit]

Here in Wales, Llyn Stwlan, we have a pumped storage system. A reservoir and a hydro electric dam, off peak power is used to pump the water back up to the reservoir. This is a net consumer of power. But connect it to its own wind generators....!

 

[dedee]

Every time I look at doing something as regards renewable energy for the house I baulk at the cost. Then the other night it occurred to me that expecting a financial payback over x years could be deemed as a wee bit selfish. Am I trying to save the planet or save money?

Using solar heating to warm water before it is feed into the water heater is about the only "green" technology that does not involve major work inside the house and is something that I would like to know more about.
All our water comes directly from the mains at very high pressure not sure at what bar but it is sufficient to get the water from the basement to upstairs for a damn good shower.

I'd be interested in any good links for a system, home build, that can take mains water, warm it up and feed a feeder tank before going into the main water heater.

cheers

Andy

 

[MikeG.]

CAT is a good place to start......

http://www.cat.org.uk/information/info_content.tmpl?subdir=information&sku=info_is_renewables/

This little device will revolutionise DIY solar heating when it becomes well known, allowing retro-fit system to directly heat the main tank:
http://www.reuk.co.uk/Solar-Hot-Water-Heat-Exchanger.htm

There are a number of DIY systems on REUK:
http://www.reuk.co.uk/solar.htm

Join the CAT, and browse their information sheets and book shop. Everything you need is there.

Mike

 

[dedee]

thanks Mike.

Plenty to read there.


cheers

Andy

 

[Digit]

Haven't kept up with the latest Andy but some years ago I designed some pumps for solar installations and at that time the usual DIY path was a sealed system that fed a heat exchanger in the domestic hot water cylinder.

Roy.

 

[wobblycogs]

Over the last 18 months or so I've helped a friend install a small PV system to power lights and the odd tool in a barn in the middle of a field. He decided to go the PV route after he got a quote to connect to mains in road. In the end the price to connect up to the mains came in only slightly over the price of the PV system but when you consider that the mains connection would been done by the electriciy company and the PV system was done by us the figures don't really add up.

As for how well the system performs I'd say it's not bad. On a bright but cloudy day it generates a little power, probably enough to have the lights on. If it's raining then you get no power at all.

From this little experiment and what I've read about PV generation I'd say that it's marginal at best in the UK and a lot of hassle. I follow PV development with interest and read a little while back about someone making a wider bandgap system (in the lab) that was much more efficient, about 15 to 20% I think. IIRC the maximum theoretical efficiency for a PV system is in the range of 30 to 40% and we are no where near that yet with mass produced panels so there is some hope.

 

[dedee]

Roy,
the problem here is that there is no domestic hot water cylinder just an electric hot water cylinder that heats the water on a economy 7 type tariff overnight. Hence by theory is to use solar heated water to heat an auxiliary feeder tank which then feeds warmed water to the water heater.

Whether this can be done at mains pressure and with my limited abilities remains to be seen but Mike links have given me something to go on for now.

Andy

 

[Digit]

The idea with the immersion heated cylinder is that even on a dull day the solar panels would pre-heat the water in the cylinder so that less electricity is needed to 'top up'.
Certainly the system could be used with mains water, but the amount of heat you would get would be negligable as the water would not stay in the panels long enough to receive any energy. Solar systems work on a storage system in the UK.

Roy.

 

[dedee]

Roy,
Surely there is a way of slowing down the feed rate into the solar heater such that a tank can be heated. The existing electric water heater would then draw its water from the heated tank rather than cold from the mains?

Andy

 

[cambournepete]

A colleague has recently installed this system from Solartwinand is very happy.
As it just connects into an existing water heating system it's a relatively straightforward installation.
He wouldn't have bothered if he wasn't convinced it was worth it in terms of overall "green" costs...

 

[Digit]

Yes Andy, into a tank, I thought you meant straight to a tap! Sorry!
With any system, either direct or indirect, you need controls so that the warm water doesn't feed through the collectors when the temp drops. But unless you have an enormous area of collector you are not going to get hot water, hence the usual use is for pre-heating.

Roy.

 

[MikeG.]

The Solartwin system is exactly the thing I would make if I were doing a DIY solar hotwater system, because the photovotaic cell which runs the circulation pump takes the place of all the electronics, such as thermostats and relays etc. When the sun shines (and thus there is heat to be extracted from the solar panel), the pump moves the water around. When the sun doesn't shine, the pump stops. To an extent, the more sunlight, the faster the pump moves water through the system.

Roy, I'm not sure exactly what you were meaning, but I think you were talking about Direct Vs Indirect systems. In a direct system, the water which goes through the panel comes out of the tap. In an indirect system, the water in the panel goes through a coil in a cylinder and heats a tank of water.

The latter is obvious imperative in the UK, because otherwise you would have frozen water on your roof in the winter, and no water coming out of your tap. It isn't quite so obvious at first glance as to why it is also the best way in a hot country, until you hear this. My dad, in Perth, West Australia, had a direct solar system. If you turned the taps on in the afternoon, you got high pressure super-heated steam blasting out, and many a person has ended up in the burns unit as a result.

So always, always have an indirect system. The other question is "one tank or two?". In other words, do you have a pre-heat tank taking only solar input, which then feed into your main tank in place of the mains feed? This can work well if you have the space, but you do, of course, greatly increase your volume of stored hot water, and your surface area of tank, so your heat losses will be corrrespondingly higher.

The secondary coil which fits in place of an immersion element in a normal tank clinches it for me. The would appear to solve all of the difficulties, and should, as far as I can see, even work with a sealed system (mains pressure hoter system). It brings solar hot water right into the realms of a DIYer, especially as the collecting panels are pretty straightforward. I reckon that with a few plumbing skills, you could install a decent solar system for around a couple of hundred pounds, and with a typical UK system producing 40 to 50% of the annual household needs, that could pay for itself in very short order.

Mike

edit.....crossed with Roy's post, and I see what you mean now.

 

[CNC Paul]

I reckon that with a few plumbing skills, you could install a decent solar system for around a couple of hundred pounds, and with a typical UK system producing 40 to 50% of the annual household needs, that could pay for itself in very short order.

Mike,

Thank you for some interesting information.

For a decent solar system what wouild you use for collectors ?

Many thanks

 

[Digit]

For a decent solar system what wouild you use for collectors ?

Paul, before you get too keen a few questions. Would you use your roof? Which direction does the roof line run, if N/S for example, forget it!
I made up a collector some years ago using the heat exchangers from the back of fridges. I reasoned that if they give up heat efficiently so they will absorb it efficiently.
Worked rather well!

Roy.

 

[dedee]

Mike,
I hope I can make sense of this:-

If I place one of those solar hot water heat exchangers in a hot water tank with water input from the mains and water output to my existing electric water heater and then made a collector from copper pipes, wooden box, glass panels etc and filled the pipes and heat exchanger with antifreeze and used a solar powered pump to pump the antifreeze around the collector and exchanger this would preheat the water in the tank and hence my electric water heater would not have to works so hard?

Is it really that simple? or as I expect am I missing something?

Andy