# PV and other alternative energy sources.



## jlawrence (14 Dec 2009)

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.


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## Ironballs (14 Dec 2009)

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


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## MikeG. (14 Dec 2009)

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


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## Digit (14 Dec 2009)

> Solar cells have a continually reducing output,



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

Roy.


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## jlawrence (14 Dec 2009)

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.


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## Digit (14 Dec 2009)

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....!


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## dedee (15 Dec 2009)

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


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## MikeG. (15 Dec 2009)

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


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## dedee (15 Dec 2009)

thanks Mike.

Plenty to read there.


cheers

Andy


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## Digit (15 Dec 2009)

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.


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## wobblycogs (15 Dec 2009)

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.


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## dedee (15 Dec 2009)

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


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## Digit (15 Dec 2009)

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.


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## dedee (15 Dec 2009)

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


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## cambournepete (15 Dec 2009)

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...


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## Digit (15 Dec 2009)

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.


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## MikeG. (15 Dec 2009)

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.


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## CNC Paul (15 Dec 2009)

Mike Garnham":3vt5wx6c said:


> 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


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## Digit (15 Dec 2009)

> 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.


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## dedee (15 Dec 2009)

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


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## Digit (15 Dec 2009)

Andy! Basically yes, it is that simple, in theory. A little more complicated in practise but well within most sensible DIYers capabilities. 

Roy.


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## MikeG. (15 Dec 2009)

Spot on Andy............

You didn't have any plans for the weekend did you! Show us the pictures next week.  

Oh, and depending on where you are in France, with a decent south facing roof you should be able to comfortably exceed the figures I gave.

Mike


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## dedee (15 Dec 2009)

Roy,

It's the "A little more complicated in practice" bit that bothers me. 
Could you explain further?


Andy


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## Dibs-h (15 Dec 2009)

Came across this the other day - looking for some other info on heat exchangers,

http://www.bigginhill.co.uk/solar.htm


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## MikeG. (15 Dec 2009)

No, Andy, there is nothing to worry about. Just make sure that everything is done well, and don't use plastic pipes. The only complication I can think of is that you will need to be able to bleed and drain the system.......and I know nothing at all about how expansion is dealt with (if there is any, with antifreeze).

BTW, I have heard of engine oil being used in place of the anti-freeze solution.

Mike


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## dedee (15 Dec 2009)

I't will take me a while to get all this together and I am a bit bothered by Roy's remarks - see my earlier post. But I do feel like giving this a try.

Of course sourcing the bits over here is bound to be more complicated than in blighty, but if I can get the planning right (the 6 Ps) I could have this done after Easter when my next supply drop arrives


Andy


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## Digit (15 Dec 2009)

Any system of hot water heating needs to have the smallest water content possible, you want to warm the domestic hot water, not spend half the day heating the water in the collectors and pipework. 
On a poor day let us assume that the water in the collector system is 15 Degrees C, if the water in the tank is at higher temp the collectors will extract heat from the tank, not heat it! 
Therefore controls to arrange that the collectors deliver water to the tank's heat exchanger at the right temps is necessary. 
Using a small water content usually means small bore pipework in the collectors, therefore a pump is necessary, again with appropriate controls.

Roy.


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## MikeG. (15 Dec 2009)

Roy,

the solar driven pump overcomes the need for all that complication. 

Admittedly, it will have imperfections on intermittently cloudy/sunny days, but it has the huge advantage of being simple. When the sun shines, the pump circulates the fluid through the system. When it doesn't shine, the fluid sits still. You could build delays or thermostats into the system to improve it, but I would go for simple and just have the 12V panel & pump.

Good point about the water content, BTW. Some of the basic DIY collectors are just domestic radiators painted black and put in a box, but they do suffer from having too great a volume of water and are correspondingly inefficient. 

Mike


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## Digit (15 Dec 2009)

> the solar driven pump overcomes the need for all that complication.



Absolutely Mike, I was simply trying to explain the principles involved. 
The answer to Andy's basic question is yes, it is simple. Just don't fall off the roof!
My place faces south with a roof area of 30 sq mtrs, and once I get rid of the Asbestos cement covering solar panels are going on!

Roy.


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## CNC Paul (15 Dec 2009)

CNC Paul":2snz1q37 said:


> Mike Garnham":2snz1q37 said:
> 
> 
> > 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.
> ...


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## MikeG. (15 Dec 2009)

Sorry Paul!!!

I wasn't ignoring you, I just didn't see your post. 

I would use small bore copper tubing, available from any plumbers merchants, and roll it into a pattern on a piece of copper sheet scrounged from an old hot water cylinder. I would mount this on a sheet of ply, and "twitch" everything together with some thin wire, laced through holes in the sheet copper & ply. This is no more than fiddly DIY work, no soldering at all in the collector. The important thing is to achieve as much contact as possible between the copper sheet and the copper tube.

Back the whole lot up with some decent insulation, put it in a box with a 4mm glass lid, seal it all up and away you go!

I guess the major complication is getting the whole thing up on the roof, and keeping it there. You'll need some sturdy mounting brackets, and some fiddly lead-work where they protrude through the tiles.

Mike


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## Steve Maskery (15 Dec 2009)

Mike
Wouldn't his work better with the unit on the ground? I would have thought that the tank needs to be above the sloar panel for it to work without a pump, given that hot water rises. If the panel is on the roof, then won' the hot water of the tank drive the flow, sending all that nice heat out onto the cold nght roof? What am I missing?

S


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## dedee (15 Dec 2009)

Mike/Roy,

I see no reason why it has to go on the roof. In my head I plan to place the collector on an angled stand in the garden as close as possible to the exiting water heater. Running the necessary water pipes to and from the roof is adding complications especially as I wold need to drill through 2 concrete floors!

As for the likelihood of running heated water back through a cooler collector I'll take that risk just to keep things simple. KISS and the 6 Ps always help me!

Andy


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## Digit (15 Dec 2009)

You can mount them anywhere. The roof is usual to keep pipe work to a min and avoid shade from trees etc. If your roof faces N/S alternative positions would need to be considered anyway. Solar pumps are after my development work so I only know of them from what I've red, but I _believe_ they would prevent any back flow. Mind, with small bore pipework gravity circulation is most unlikely. 

Roy.


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## CNC Paul (15 Dec 2009)

Thanks Mike, Nice and simple


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## MikeG. (15 Dec 2009)

Steve,

yep, the collectors can be placed anywhere......so long as they are in the sun! The problem with being low down is that they are more likely to be over-shadowed at some point, but if you have a big clear garden, or say, a first floor flat roof, then it is perfectly feasible to stand them there. Bear in mind the losses from long pipe runs. 

As we are suggesting micro-bore pipes and a pump, the vertical relation of the collector to the cylinder is irrelevant. 

I can't exactly remember the formula for the angle at which they should be placed, but it is something like "latitude minus 10 degrees", so in the UK that is between 40 and 45 degrees, roughly. It just so happens that this fits in well with the angles of most rooves.

Mike


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## Steve Maskery (15 Dec 2009)

Mike Garnham":1zr1kgmh said:


> that is between 40 and 40 degrees, roughly.
> 
> 
> Mike



That's _rough?_


S


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## MikeG. (15 Dec 2009)

Steve Maskery":21jlbq1h said:


> Mike Garnham":21jlbq1h said:
> 
> 
> > that is between 40 and 40 degrees, roughly.
> ...



Ooops!  .....now edited!!


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## wobblycogs (16 Dec 2009)

I always thought you had to have an expension vessel in an indirect solar water heating system? I would have thought the system would just self destruct in the heat otherwise.


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## Digit (16 Dec 2009)

I'd have thought so too.

Roy.


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## Dibs-h (16 Dec 2009)

Mike Garnham":1ncukbso said:


> I can't exactly remember the formula for the angle at which they should be placed, but it is something like "latitude minus 10 degrees", so in the UK that is between 40 and 45 degrees, roughly. It just so happens that this fits in well with the angles of most rooves.
> 
> Mike



I recall something similar - the -10 is to cater for the winter sun (IIRC).


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## dedee (16 Dec 2009)

Is the expansion tank deemed necessary because the solar water heated water would just get hotter and hotter and needs somewhere to "expand" to?

If one had a valve that prevented the warmed fluid in the collector and exchanger from circulating over a certain temperature would the expansion tank still be required?

Cheers


Andy


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## MikeG. (16 Dec 2009)

Yes Andy, because hot water takes more room than cold water, and if there is a closed loop there is no allowance for expansion. However, it is really easy........like a header tank on a hot water system.

Here http://www.solarfriend.co.uk/ is a simple diagram. The first system is the type of thing I have described.

Mike


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## Digit (16 Dec 2009)

Header tank or pressure vessel on a sealed system Andy. 
But to go into a little theory Andy. 
Firstly, the water in the domestic hot water tank can never be hotter than the temp of the water delivered to the tank's heat exchanger. 
If you were to purchase a heat exchanger from a supplier it would have stated with it that it was capable of raising a given quantity of water through a given temp range in a given time. 
It is the heat exchanger therefore that determines how long it takes to heat the tank full. 

Roy.


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## dedee (16 Dec 2009)

Mike thanks for the link.
I knew there would be complications.

The 1st plan on the page you liked to is doing what I will call the usual solar water heating system

Using the heat the exchanger filled with antifreeze to preheat mains water before entering a water heater is a wee bit different. Bit I get the flow of the diagram.

As regards the expansion tank where does it go on my rather embarrassing diagram but I think it captures what I know so far.








cheers

Andy


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## RogerS (17 Dec 2009)

Mike

I have asked this question (and which you answered) in another thread but I can't find it.

If you replace the immersion heater with that clever 'doofa' then how do you heat up the water in winter or in summer when the sun isn't shining?


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## mickthetree (17 Dec 2009)

what about a solar air heater? / pop / beer can heater? to reduce the requirement for central heating.

I found thistoday. Not seen one before, but it looks great as there is no water involved. Just air!

I have a flat roof at the back of my house which faces south/south/east which would would be a potential location.

aaaaaaaaaaaaaaaaand you have to drink 105 cans of beer to make it a valid project.


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## MikeG. (17 Dec 2009)

Mick,

great little demonstration.....but not much use to us over here. We have low, weak sun and lots of cloud at the time of year when we need central heating. This simply won't work in cloudy Britain. You'll have noticed how clear the sky was in the demonstration........and people who travel from Britain are usually amazed at how bright and sunny it can be in other people's winters. 

Were there an element of thermal mass about this.............say, it heated up a big rock store, for instance, then it could make a difference. 

Roger,

the "doofa" would only replace the electric element if it was the secondary (back-up) form of water-heating. Most people heat water with gas or oil boilers, and have an immersion simply as a back up. If you consider the solar as a sort of back-up for your gas boiler then you can see how it could work.

If you rely on electricity as your primary source of water heating, then you will need to fit a second tank to take the hot water from the solar panel, but it will still work fine.

Mike


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## mickthetree (17 Dec 2009)

well I'm going to drink the beer, regardless. 8) 

Cheers for the explanation though Mike.


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## RogerM (17 Dec 2009)

Another excellent site for all things solar is Navitron. This is the outfit that Dick Strawbridge used for the solar installation in his house in Cornwall, and televised a couple of years back as It's Not Easy being Green. There is also a solar forum, which whilst a bit "wacky" at times also contains some pearls ( a bit like W/S UK really!)  The Navitron site in particular is aimed at provision of materials and advice for the diy installer - I am very tempted.

One of our neighbours has just had a combined solar h/w and p/v system fitted by these people. According to him (and he's a pretty clued up guy) every watt produced is fed into the grid, and you're paid 36p per unit for everything you produce - *including what you draw off yourself*, so there is no storage problem. The system generates about 2kw on a sunny day, and in the event that you generate more than you use, you get an additional 10p per unit for the surplus. Could be useful if you spend a long time away from home - it'd be generating an income for you in your absence. This compares with a cost of about 12p per unit from your domestic supplier. 

This is not a cheap system - about £12K I believe, but he reckons that at current fuel prices it gives a return on capital of about 8% - equivalent to 10% gross - so much better than cash in the bank so far as investment return is concerned, and implies a payback period of about 12 years at current electricity prices. And of course we all know what fuel costs are likely to do over a 12 year period - if they only double we'll have got away lightly. 

The main drawback I can see is that the economics rely heavily on continuing to get the inflated subsidy from the govt for the power you produce because it involves trusting politicians not to withdraw the scheme once you've invested in the system, and anything that involves trusting politicians to keep their word, or to do the right thing, is fraught with problems. Just IMHO of course.

The solar H/W system he's installed seems to feed into a heat exchanger in a very small tank that sits beside the main h/w tank and which in turn feeds its h/w into the top of the domestic h/w tank - just where it is needed, and where it doesn't get diluted by feeding it in to the bottom of the tank. Cunning. The secondary h/w comes from glass tube collectors on the roof, and apparantly with these a pv powered circulation pump is not sufficient to circulate the water fast enough to stop the water boiling in the tubes on a sunny day, so must use a mains powered c/h style pump. However, the power drawn by the pump is more than compensated for by the extra efficiency of the glass tube collectors.

I think you also need to think a little about how you use your hot water. For instance most washing machines and dishwashers are cold fill and then use electricity to heat their water. Modern machines often allow hot fill, but then you'd need some system to revert to cold fill when there is no solar h/w or else you'd be using expensively heated h/w for the rinse cycle which is usually done in cold water. So in practice, you'll only be using solar heated h/w at the sink or for bathing/showering.

As always, the devil is in the detail, which Mike alluded to in an earlier post. Interesting thread!


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## mickthetree (17 Dec 2009)

he gets paid for using electricity? Really?

I think the efficiency of solar panels degrades over time too, so after 5 years he may not be getting as much output as when first installed.


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## dedee (17 Dec 2009)

I still don't see where to place the expansion tank on my proposed system.

The existing electric water heater vents out a litre or so of water most nights.

Does my proposed preheated water tank require an expansion tank, if so as this tank is filled with water at mains pressure what is the device caused that prevents this tank from emptying into the expansion tank?

Does the solar heat collector/heat exchanger loop require some sort of expansion tank/vent as well?

cheers

Andy


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## RogerM (17 Dec 2009)

mickthetree":25gd9jsc said:


> he gets paid for using electricity? Really?



Thats what they claim here.



> I think the efficiency of solar panels degrades over time too, so after 5 years he may not be getting as much output as when first installed.



Agreed - but maybe offset by the rise in fuel costs?

FWIW, I think in most cases, an economy Solar HW system makes good economic sense, particularly if you can DIY for around £800 - £1200, when you can also service it yourself because you know how it works. Not sure that a commercial £6k installation will ever pay for itself though.

So far as PVs are concerned, I think the money will be better spent on low energy lighting and improved insulation first.


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## Digit (17 Dec 2009)

I don't understand the question Andy. Why a separate solar heated tank?

Roy.


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## dedee (18 Dec 2009)

Roy,
The reasons for the separate tank are as follows.

I have not seen that type of immersion heat exchanger in France. If I buy one in the UK it will not be easy to fit any tank bought over here either. If I put a system together as per my sketch with UK sourced parts these will not meet with french standards and could cause me a problem with insurance and when we come to sell the house.
By adding a separate preheat tank I can isolate the whole system and make it easy to remove if necessary and even by pass it if it does not work.

If I buy a DIY type kit over here using conventional solar heating panel, new tank, etc etc the cost would be be close to euro 1600-2000.

I think I could put together my proposed system for about £800-900 gbp

However I am stretching both my knowledge and abilities so the concerns raised about expansion tanks concern me somewhat.

Andy


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## wobblycogs (18 Dec 2009)

dedee, I'm not a plumber but I am friends with one and he has taught me a thing or two about sealed systems which is what you diagram seems to propose. An incorrectly built sealed system can be very dangerous, think explosion and boiling water flying all over the place http://www.youtube.com/watch?v=JmJoyuUJj2Q. 

At it's most basic level there is only one thing to think about when building a sealed system: where is the water going to expand to when it gets hot? Your solar heating loop - the green arrows and coil - are completely sealed in your diagram so you need an expansion vessel somewhere in that loop. 

Sealed systems should also be fitted with an emergency pressure relief valve in case something goes wrong - this valve will blow and should vent all the hot water to a safe location. In the UK there are strict rules about what is considered a safe location but typically near the ground away from where people generally go (a drain is not necessarily a good choice it could crack or melt) - remember if the valve blows it will be venting boiling hot water under pressure. 

A kit like this http://www.plumbworld.co.uk/8-litre-sealed-system-kit-584-704?CAWELAID=205025542 would probably be what you are looking to fit. 

The alternative option is open vented which is the most common system installed in the UK http://www.hashheating.co.uk/Central-heating-Systems.html. This system has a header tank open to the air so the heating loops are always maintained at atmospheric pressure. There are two downsides with open vented systems: it lets air into the heating circuit which corrodes radiators over time (small amounts of atmospheric oxygen dissolve in the heating water) and it requires a tank in the loft. This second downside could be a problem if you want to use this design for solar heating, the expansion tank needs to be the highest point in the solar loop which could be hard to achieve if you have the panels installed on the roof. 

Don't forget - I'm not a plumber. Plumbers have a special set of exams they have to pass before they are allowed to commission sealed systems


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## Digit (18 Dec 2009)

Right Andy, point taken. Expansion tanks are also the supply tank. Water entry is via a 'ball valve' and the expansion pipe returns any excess water to the top of the tank. The water level when cold must leave sufficient volume to accommodate the 'expanded' water without causing any overflow. 
HTH. 

Roy.


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## dedee (18 Dec 2009)

Wobblycogs/Roy
thanks for you thoughts. Open vented systems (ie with an open header tank) I am sure are not allowed here in France. So the sealed expansion vessel with relief valve would seem to be the answer? 

All of my planned system would be located in the basement/garage (except the solar panels of course).

I have re drawn my plan:-

[





Does the preheated water tank also need an expansion vessel?

Cheers

Andy


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## wobblycogs (18 Dec 2009)

I don't think open vented is allowed for hot water tanks in France but it might be allowed for the solar heating loop. One of the benefits of a sealed hot water system is that the hot water should always be potable whereas in an open vented system it might not be.

As for whether you would need an expansion vessel for the pre-heat tank that's hard to say. If it is going to be a proper sealed system hot water tank maybe not, if it's just a bog standard copper tank then probably and a fairly large one at that. As the water in that tank heats up it will obviously expand, that expansion would probably be dealt with by whatever expansion relief system your existing hot water tank is using but personally I wouldn't count on that.

Interestingly though I think you said that your hot water tank vents about a litre of water each night which would concern me a little. Modern sealed system hot water tanks have a bladder in the top or sometimes just an air gap which takes up the expansion of the water so that you don't need a external expansion vessel for the tank. If your tank is of this design and it is venting water it might be that the air gap needs re-establishing. There is normally a valve on the side to do this but it varies from model to model and you would have to look it up. It could be that the system is designed to vent through a relief valve and is therefore working perfectly but it's worth checking.

I think you also will probably want to consider what will happen if you manage to boil the water in your solar heating loop. An expansion vessel will deal with the fairly modest expansion as the water heats up it can't deal with water turning into steam. Your safety valve would deal with this situation but it would leave you with a system that had insufficient water in it which could damage the pump (and it's a bit last resort for my liking). This is the benefit of an open vented system it will / can automatically top it self up if necessary.


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## Digit (18 Dec 2009)

To be honest Andy I cannot see how that can work at all. Your current hot water cylinder is heated electrically? Does it have more that one heater boss or any plugged connections? Is it copper or SS, and is it lagged with sprayed on foam?

Roy.


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## dedee (18 Dec 2009)

Roy,
Oh dear. Why will it not work? 

To answer your questions.
The current water heater is made by Thermor and is heated electrically. It is made from steel. The heating element is a "stealite resistor housed in an enameled sheath". The tank has an enameled lining and the heat insulation is polyurethane foam. The insulation is very good. Even when at max temperature the outside of the tank does not even feel warm.
It is a 250l tank. and looks like this







I have written to Thermor about feeding heated water rather than cold into their appliance and am awaiting a reply.

The overnight venting (when it is heating the water) is perfectly normal. This type of water heater is very common here.

Thanks for your help, sorry if I am being a bit dim.

Cheers

Andy


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## Digit (18 Dec 2009)

From your drawings Andy you're not heating your DHW from solar panels, you are mixing the water. That precludes any idea of anti freeze and means water from the solar panels will only enter the DHW cylinder when water is drawn off and the approriate vales are opened/closed. 
You need a heat exchanger inside the DHW cylinder. 
I can't find any info on that make of cylinder, but in the UK bosses for fitting heat exchangers into cylinders after installation are available. They are available both as solder fittings and mechanical fix. 

Roy.


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## wobblycogs (18 Dec 2009)

I read the plan as having a completly sealed solar heating loop heating a second hot water tank in line with the main hot water tank. Therefore the solar heating loop could contain anti-freeze as it never comes into contact with the water. I must admit I was confused about the use of a fancy coil in place of an immersion heater because it would be simpler to just buy a tank with a coil fitted.

The problem with this design is that hot water from the solar tank won't be drawn into the main tank until water is drawn from the main tank. This isn't as efficient as heating the main tank directly but it looks like it will work. An alternative solution would be to have a three port valve connecting the two outputs from the two tanks into the single hot feed for the house. When the sun is shining the valve would be set to draw water from the solar tank and in winter from the normal tank. You could even have a switch in the house to change the valve position.


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## Digit (18 Dec 2009)

> You could even have a switch in the house to change the valve position.


 
:lol: :lol: 

I did that with our CH. Due to surgery for prostate cancer the boiler commissioning was left to a local heating engineer. 
I was in PJs, on a reclining chair with a catheter stuck in me me explaining for over an hour to this guy that the circuit was designed to allow DHW from the cylinder to be used at the taps if/when the boiler went US. 
He went off muttering 'never seen anything like that before!' 

Roy.


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## dedee (18 Dec 2009)

Wobblycogs ( can I call you graham? )

I think you have explained it better than me.

I understand what you are saying about the flow of solar heated water to the main water heater but being as most of our hot water is used after dark it means that the water heater will be filling up with solar heated water and hence will not have to work so hard to bring it up to temperature. The water heater BTW is only heating water from 10pm to 6am and although I've never measured it the water at the taps feels as hot at 9.30pm as it is at 6.30am.

You mentioned a tank with a coil already fitted. is this a heat exchanger type coil that I could connect to the solar panels? Could you give me an example?

I've have seen a couple of cylinders here that have an exchanger type coil in the bottom of the tank with a conventional heating element at the top - but they are VERY expensive.

Cheers

Andy


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## wobblycogs (18 Dec 2009)

Graham or Wobblycogs either is fine by me.

I wasn't actually aware that you could get hot water cylinders that didn't have a heat exchanger coil built in. Anyway, I was thinking of something like this http://www.heatandplumb.com/acatalog/Heatrae_Sadia_Hot_Water_Cylinders_Megaflo_HE.html. Megaflo is one of the best makes and is priced as such, you can get cylinders much cheaper than this.

The things to note though are the heat exchanging coil at the bottom of the tank, this is what you connect to your solar heating system. Cold water goes in at the bottom, and hot out the top of the tank as usual. Notice that the tank also has a built in expansion gap at the top. You can also get twin coil tanks which allow you to, for example, heat the top half of the tank with gas and the full tank with solar or the other way round (we have one of these but currently only use gas).


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## dedee (19 Dec 2009)

wobblycogs":2ik1ig4d said:


> I wasn't actually aware that you could get hot water cylinders that didn't have a heat exchanger coil built in.



D'oh, can I have a senior moment at 47? Yes of course it's how the hot water from the boiler heats the water in the cylinder. All I'd be doing is swapping the boiler for the solar panels.

I'll spend time time over christmas doing some proper costings on this.

cheers

Andy


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## Jake (19 Dec 2009)

I haven't read the whole thread, so forgive me if I am way off base or repeating something already said, but heatbanks are ideal for this, rather than conventional cylinders.


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## MikeG. (19 Dec 2009)

Jake,

if I understand these things correctly, a thermal store is essentially a cylinder kept permanently full of hot water, with a second heat exchanger. This second heat exchanger (coil) takes the cold water feed (mains) and heats it for use at the hot taps. The contents of the cylinder therefore never come out of the taps, and are effectively part of a closed loop. Is that a fair summary?

The problem is that you are maintaining a large body of water at high temperature for 24 hours a day. The inherent losses are necessarily high, simply because of the differences between the water temperature and the ambient air, and in most circumstances I would therefore need some persuasion that there was any benefit to be gained from the system.

Mike


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## RogerM (19 Dec 2009)

As Mike Garnham has pointed out, you can remove the need for a new HW cylinder by installing a heat exchanger in place of the immersion coil. However this has the disadvantage that it will only heat water to the depth of the coil - typically 80 cms, and does of course mean that you have no immersion backup for quick hw on a dull day.

This looks like a cunning plan that removes the need to install a new solar hw cylinder, lets you keep your immersion heater, and will heat the whole existing cylinder, feeding the hot water in to the top of the cylinder, exactly where it is needed, and where it will stratify until the cylinder is full. It's called a Willis Solasyphon and it sits alongside the existing h/w cylinder. Here's how it works.


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## wobblycogs (19 Dec 2009)

That's a really clever idea. I would be interested to see how well it works in practice though. AIUI Andy has a DHW system though so I'm not sure this is suitable. I'd be wary about drilling a hole in a DHW tank as they are designed to resist pressure and I wouldn't want to weaken it. I wonder though if attaching this gizmo to the cold feed pipe rather than direct to the tank would work? I don't think it would be as efficient.


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## RogerM (19 Dec 2009)

wobblycogs":1ovxumfl said:


> I wonder though if attaching this gizmo to the cold feed pipe rather than direct to the tank would work? I don't think it would be as efficient.



Funnily enough I had exactly the same thought. Maybe just take a T off the infeed from the cold water tank?


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## RogerS (19 Dec 2009)

wobblycogs":3dfxns81 said:


> ..... I'd be wary about drilling a hole in a DHW tank as they are designed to resist pressure and I wouldn't want to weaken it...



No need to worry. It's fairly standard practice ....look up Essex flange.


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## big soft moose (19 Dec 2009)

RogerS":2kqb59jh said:


> .look up Essex flange.



but make sure safe search is on, and swimbo isnt in the room first


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## OPJ (20 Dec 2009)

Apologies for interrupting this thread but, I came across this link the other day which may be of interest to some. It's designed to store a small amount of pre-heated water entering a combi boiler or storage cylinder and reduces gas. It looks like one of the cheaper options available today although, saying that, it probably doesn't provide as much energy as some of the others


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## RogerM (20 Dec 2009)

OPJ":9hrb6892 said:


> Apologies for interrupting this thread but, I came across this link the other day which may be of interest to some. It's designed to store a small amount of pre-heated water entering a combi boiler or storage cylinder and reduces gas. It looks like one of the cheaper options available today although, saying that, it probably doesn't provide as much energy as some of the others



At around £1500 inc VAT that looks a bit pricey for what it is. I appreciate that is the price fully fitted, but for someone with good DIY skills they could have a full solar system for under £1,000 using a 20 tube panel, or around £1300 if fitting a new twin coil domestic hw cylinder using one of these kits. I have no connection with this company, but I've read many good things about them.

Whilst on the subject of recommendations, I mentioned a neighbour had fitted an installation from NaturalWatt based in Exeter. Whilst his initial experience was very good, the relationship has soured and he has told me that he cannot recommend them.


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