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Hannah

Solar hot water heating

My husband has just read that according to the Energy Saving Trust, 4m2 of solar panels will provide 50-70% of a typical home's annual hot water needs" (source IMechE magazine)

Can anyone corroborate this (or not, as the case may be)?

We were looking at getting this for hot water, but then he read somewhere else that the percentage was really low (but I can't remember where it was).

Many thanks for any help.

Hannah
Chez

We've had two twenty-tube panels fitted since October and they're pretty much providing all our hot water now (although their are only two of us). In November, Dec and Jan/beginning of Feb less so - only kicking in on sunny days; but now, even when it's not sunny, they are working. Yesterday the bottom of the tank was up to 51 degrees.
dpack

if the outlay is quickly returned chances are it is a good idea
low tech good
a pump is the most comlicated part
excellent Cool
Hannah

Hi Chez - thanks for that.

Who did you get yours through?
Do you have a boiler/woodburner/other heating as well?
Chez

We got them through Green Energy Solutions, who we found via the It's Not Easy Being Green forums. Can't recommend them highly enough.

We've got the system so that it's topped up by our oil central heating and also by an immersion if necessary - but we are looking at completely replacing the oil with a multi-fuel set-up.
judith

Hi Hannah,

Our system probably supplies around 70% of our hot water. Our's is a 2-person household as well, but I suspect that the figure could actually be higher if it weren't for the fact the panel is linked to a thermal store. This won't allow the water temperature to drop below 40C, and causes the boiler to cut in at this threshold even though there is a prospect of a sunny day in store.
Chez

Re what Judith's just said re thermal stores - ours is, too. You can turn the thermostat up and down, but the min ours will go to is 50. It rarely comes on though. And if we do make the swap to a multifuel system, that bit will come out and it will just heat up when the fire is on.
dougal

Re: Solar hot water heating

Hannah wrote:
My husband has just read that according to the Energy Saving Trust, 4m2 of solar panels will provide 50-70% of a typical home's annual hot water needs" (source IMechE magazine)...


Its fairly easy to meet 100% of your 'needs' in high summer.
Its much harder to get anything much in mid-winter, when there is less than 1/10th of the energy available.

In between it gets interesting!

There are two basic types of collector.
"Flat plates" are cheap to make, normally quoted by simple area, and not a lot of use outside high summer.
"Evacuated tubes" are relatively expensive to make, people often talk about them by the number of tubes (as though all tubes were equivalent - not quite so) and because they are *much* more efficient (they lose very little of the heat they catch) they can do very useful service for at least nine months of the year.
Systems using evacuated tubes have a *much* longer useful season.

The type of tank can make a difference to "efficiency" - as measured by the reduction in boiler fuel used. Even a larger tank can allow surplus heat from one day to be 'banked' to be used the following day should the weather be less helpful - reducing boiler usage and so increasing 'efficiency'. And even the way the system is used can also impact the performance - it doesn't make sense to 'preempt' the solar availability by using the boiler to heat a tankful of water in the early morning... however having the boiler on a timeclock to ensure that there is a heated tank in the evening would be more sensible for most people.

See http://www.navitron.org.uk/solar_collector_panel.htm for evacuated tube collectors, tanks, and controllers at rather good prices. And they do the misc gubbins for the pressurised system too.
Hannah

Hi everyone, thanks for all your help so far.

Judith how many tubes do you have?
judith

Hannah wrote:
Judith how many tubes do you have?


We have a Thermomax 20-tube collector (2 m2).
lazzasurf

the new company i work for "Harland Rise" do them on the warm front grant system.. i dont know jack about them yet as they bring in fitters from our other depot...
Lorrainelovesplants

This is really interesting. We have LPG as were miles from the gas pipe, but its costing us a fortune. We have woodburners in the kitchen and living room which are great and Id like to do more solid fuel...
The LPG is a pain though. Even if I just want to wash my hand the bloody boiler fires up, and all I can think about is the amount of gas getting used. There must be a cheap way to get small amounts of hot water for doing the dishes.
What about solar or heat sink things for this - any ideas anyone?
Lorraine
wellington womble

Get a kettle that sits on the woodburner all the time. I used to do this when ours was alight to fill hot water bottles, tea, do washing up etc etc. And them make everyone wash at the same time!
Chez

Could you do some kind of diy solar panel with an old radiator painted black (perhaps behind a bit of glass), that connected to a little tank that would then stay warm enough for hand-washing etc.?
Lorrainelovesplants

Very Happy
This is what we want - ingenuity - being a Scot I would call it common sense and being careful, but The Big Dick on INEBG would call this 'going green'.
More good ideas please!
(wait till he comes home from work to find this list of things for him to do!)
Lorraine Twisted Evil
AnneandMike

Chez wrote:
Could you do some kind of diy solar panel with an old radiator painted black (perhaps behind a bit of glass), that connected to a little tank that would then stay warm enough for hand-washing etc.?


Easy to do - they have some demonstration ones set up at CAT (Centre for Alternative Technology). The critical factors are glass in front and insulation behind. Also you need a pump if the panel is above where you want the water (the usual case) because hot water is less dense. You need to buy 'Solar water heating a DIY guide' from CAT, price 5.99.
AnneandMike

Just to add to the last post. The guide includes a 'controller' to control the pump. The design is somewhat primitive. When I move house in the next year I intend to build a DIY solar system quickly, but I would use a PIC microcontroller to control the pump - much simpler and flexible. I'll post details of the circuit when I do it.

Mike
hardworkinghippy

This is a 30 year old solar panel I repaired last year. I had two at the front and two at the back of a west/east roof in Essex and they reduced our wood consumption by half over the year. I had a complicated system with solar pump controllers, two water tanks, and two back boilers and the system never broke down in 14 years.



I took them to France with me and two of them still supply hot water when the fire isn't lit but without all the technology because our panels are low so the hot water rises without a pump.

If you can afford it, have them installed, but the basic idea is simple, and honestly they're quite easy to make and, if you ever forget the anti-freeze, Embarassed repair yourself.
MrWomble

there are so many different systems that it is almost impossible to give an answer that will cover everyone.

essentially dougal is right - if you have solar panels you need a timeclock on the boiler so that it only heats your water when you need it to - most central heating systems will have this. If however you have a thermal store you probably wont have a timeclock fitted. This can be fitted inexpensively but you will need to "trial and error" when you want the boiler to fire. This will be dependant on your own hot water usage patterns and the time of year.

rule of thumb for a retro fit solar hot water system is that it will provide 70% of you hot water demand but it really does depend on your type of system and how you use it.

an inexpensive system will provide most of your hot water from march though october from the south - north of england which will mean very little or no gas usage for this period.

home made panels will not provide the qaulity of heat that you will need - so unless you really like doing things with your hands i wouldnt bother. Thre are some quite cheap evacuated tubes now available which provide much better heat output.

If you are looking to combine technologies i.e solar and gas and wood burner you will need to speak to a plumber who REALLY knows what he is talking about - this is very difficult to make work efficiently but is possible.

i'm not on the forum much but if you want let mrs womble know i can always give you a bell .

Regards,

alex

p.s. there are national companies advertising heavily who will charge 10 grand for a solar installation - you can get a good plumber to do this for half the price.
dougal

Lorrainelovesplants wrote:
The LPG is a pain though. Even if I just want to wash my hand the bloody boiler fires up, and all I can think about is the amount of gas getting used. There must be a cheap way to get small amounts of hot water for doing the dishes.

Lorraine, the chances are that you have a 'combi' boiler (and no hot tank). Either that or you need a timeswitch... Very Happy
A combi *only* heats water when you run the (or a) hot tap. So it barely wastes any gas on heating water you don't use --- as long as it's quite close to the tap! The longer the pipe run between combi and tap, the more water is going to be heated and then left to go cold in the pipe (ie the more gas gets wasted).
One simple and important thing to do is to insulate that pipe between combi boiler and the hot taps. That way, there's a greater chance that the next time you want hot water, the water that is in the pipe will still be usefully warm...

The more expensive the fuel that is replaced, the more cost effective solar becomes.
But solar doesn't integrate easily with a combi... (most combi's anyway)
Lorrainelovesplants

Hi Dougal
Yes, its a combi-boiler, and yes there is a fair run from the boiler to the bath (about 30ft) and to the kitchen(about 15 ft). I have to run the taps in the bathroom for ages to get hot water, (which annoys me because the water is just wasted.)
The system was just installed a year ago - so we have to keep it and it is economical during the winter.
What I want is some method to get cheap hot water the rest of the year.
I like the solar panels low down to heat water - we could do this here. The whole back wall of our bungalow faces south.
I will alert the man of the house who is the handyman to look at the ideas here, but all ideas so far are great. We dont use the tumble drier at all now (dried inside polytunnel).
Lorraine Very Happy
dougal

Lorrainelovesplants wrote:
Hi Dougal
Yes, its a combi-boiler, and yes there is a fair run from the boiler to the bath (about 30ft) and to the kitchen(about 15 ft). I have to run the taps in the bathroom for ages to get hot water, (which annoys me because the water is just wasted.)

Hmm. That's not exactly ideal for a combi (which is after all just an Ascot Geyser type instant water heater 'combined' with a ch boiler.)

The waste of water isn't as significant as the fact that, once your sink or bath is filled, the pipe-ful of water at 60C or thereabouts just goes cold.
The energy wastage is more significant than the water waste.

Unless your combi was labeled explicitly as being 'solar-compatible', it probably isn't.
Which means that installing solar hot water means either changing the existing boiler and plumbing, or having a third tap from a separate solar system. And if the boiler had to be that far away, where is the solar hot water tank to go that is much closer? I have to say that I doubt the real world practicality of batch heaters in the UK climate. Would they produce hot water when you wanted it? (Personally, I doubt it would be there, hot enough, very often.)

Insulating the hot pipe has to be worthwhile. OK, when the heating's on, the lost heat reduces the amount of heating. But at all other times, it's just wasted.
Hence insulating those pipes better.
There is a 'better' insulation that actually has an electric heating element in it. Its called Hotwat. Its rather similar to the freezing prevention (and heating oil waxing prevention) that is sometimes used for outdoor pipes.
Its bloody cleverly self-regulating. When the pipe is hot, the heater almost draws no power at all. However, as it cools, so the resistance of the element falls, current flows and keeps the pipe warm.
Here's a link that refers to the stuff http://www.warmfloor-solutions.com/hotwat.asp
Coobeastie

We have solartwin panels:
http://www.solartwin.com/

Which are great, because as the pump is solar powered as well the water only goes through the system when there's enough sun to make it worthwhile. I'm not sure how this combines with different types of boiler. Ours produces a decent amount of hot water (and since you can hear the pump kick in you know when it's going) - south facing roof in the Highlands for those interested.
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