You would be better replacing the existing system with one which included hot water provision off the boiler. Almost anything you do to improve the efficiency or running cost of existing systems will be more worthwhile than solar panels.
Mostly :-). The best you will get from a south facing correctly angled collector is about 350kWh/year per m2 of installed collector. In the winter months this drops to well under 500Wh a day. Most practical installations are about 4m2. In the winter they can't provide enough energy, in the summer you usually end up unable to use all the energy collected as you simply don't use enough hot water. Solar water heaters are most economically in places with large hot water demands, such as schools and hospitals.
Typically you might save about GBP100 a year. However solar systems are not as maintenance free as some suppliers and ecowarriors would have you think and failures in the panels, which are obviously subject to a lot of temperature cycling, is not uncommon. Certainly the figure of 25 years useful life quoted by protagonists are not supported by past experience anywhere in the world (unless you invoke Triggers Broom).
I said thermal stopre and heat abnk. I can't get any clearer. If don't understand the principle then....
You keep saying that without knowing what a thermal store is. Again, is is not less efficient is it more efficient and controls that prioritise the use of solar gained heat are in place.
Understand what I am describing. Draw it out and think it through.
I did, re-read. Read again, draw it out and come back to clarify.
Whats your hw costing you now? Last time I looked at commercial system savings they were in the region of =A315-20 a year. Lets very roughly double that for E7, so =A330-40. Do you think spending 1k will pay back over 10 years?
I'm puzzled by that, as the idea is to insulate all sides, not merely the loft.
On Sun, 05 Mar 2006 13:26:11 +0000 someone who may be Peter Parry wrote this:-
It would certainly be worthwhile replacing the existing hot water cylinder with a solar one, able to take heat from the boiler and solar panels as necessary. With electric heating as a backup this would give the best range of options. A heat bank is another option, especially useful if there is a suitable source of fuel around, like wood.
Probably not, though it depends on the water usage and size of the storage vessel, as well as the amount of light. However, that is not really the point. What energy they do provide is energy that is not provided in other ways.
That rather depends on the water usage and size of the storage vessel.
Assuming you are talking about flat plate panels, in a year they cycle less than radiators. With evacuated tubes a tube may fail, but this does not affect the other tubes.
It will, given enough time. For instance when the Iranians/Chinese/Indians start exporting their miniature nuclear reactor technology giving an all in one solution that never needs refueling for 100 years, yet provides 40 litres a minute of hot water at delta T 55 deg C and 500kW output for the radiators, you'll be able to strip out all that expensive insulation and leave the windows open all year round.
Hacksaws will have to be banned though - just in case anyone decides to replumb the cooling circuit.
Alt energies keep getting cheaper and cheaper per watt as the technology improves. At some point they will become cheaper than oil and gas... and keep getting cheaper. Our future is one of plantiful energy at low cost. How long it wll take to get there no-one knows, and we probably will have to go through a period of steep costs first. I suggest this is a more realistic long term forecast than the popular never-have-it-so-good-again predictions.
How Mr Parry can say that solar DHW heater don't pay for themselves over 20 years is mystifying. He must have had a very inefficient system. DIYing it, they can pay for themselves in about 3 to 5 years. The more energy costs rise along the way, the quicker the payback.
You are the "only" one who comes out with such allegations. Everyone else seem to make them work properly and make back the cost in fraction of that time.
Putting the question the other way around, could you say what the total installed price for a marginally justified system would be - with a 20 year payback say.
If you'd payed a lot (£2,000 say) for the system then I have no doubt you'd not recover the cost. What might be the threshhold?
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Peter Parry saying something like:
I don't see how. Sure, if you buy factory-made panels and all the necessary pro stuff and pay for the installation.
This is a DIY group. Building panels from base materials and feeding a pre-heat cylinder works out at less than a couple of hundred quid if you DIY the whole thing from salvaged materials.
In my own situation, I have several suitable sized radiators and double-glazing units which will be pressed into a different role from their intended one. I have a few used-but-good hot cylinders and the perfect position upstairs for a gravity solar system fed by 3 or 4 panels at ground level.
I don't expect it to work miracles, but I do expect it to work a bit - enough to cut the cost of electrically heating water by at least a third and probably half.
This thread is from uk.diy, and is kinda relevant for a.e.h too.
Ed Sirett wrote:
Good question. I'll have a go.
Lets say it saves =A320 a year heating dhw only. Lets say we want it to break even after 10 years, interest is 5% and we optimistically ignore the risk of system failure, underperformance or repair for the moment.
A system that does this in 10 years is worth paying =A3157 for now.
saving or a lot less cost than commercial solar dhw systems deliver.
If one got a bit desperate and justified a 20 year payback, system value would rise to =A3251. But I dont think thats justifiable in truth, nor is the extra spend allowance very significant. Either will make a cheap system and nothing more.
Now, since almost all solar dhw setups fail miserably to pay their way, lets see how low cost we can get. Start with a dirt cheap direct drain-down system for summer use only. This preheats the header tank, which of course must be hot water safe in this design. That rules out use of plastic header tanks where already fitted. Metal headers are ok, a plastic one would need replacement.
Collector and loft piping:
100' garden hosepipe: =A320 sheet of green house polythene: =A3? Lets say we use a =A31 poundland plastic patio table cover set
4x8 sheet 7mm WBP ply =A3? rough guess =A35 stainless roof fixings =A3? guess =A35 black paint =A31
CH pump =A330
loft piping insulation: cardboard and/or rags =A30, sellotape to hold in place temporarily =A30.50, string to fix it permanently =A30.50. header tank insulation: as above, no more spend needed connecting 2 pipe ends to header tank: =A32
1mm cable from lighting jbox to pump =A31-2 FCU & pattress =A32 panel thermostat, bimetal, =A35
HW header tank if metal one not already present: =A3 not sure, and will vary according to source
Now, if you had to buy all the above new, total cost is: =A373 + maybe a new header tank
The numbers look quite a bit better if you've got various bits lying around already, or can use chuckouts to build it from. Then it might actually be worth the 2 days work.
But given the low value overall of such systems, I dont think this is the way to go. More sensible to go for a system that delivers much more, such as flat panel solar space heating, which is cheaper, easier, requires no roof access, and delivers more payback.
Solar flat panel space heating is little more than a frame, polythene, black mesh cloth and holes in the wall. I'll let someone to play with the numbers if they wish.
The market will decide that. Energy prices will increase. Volumes of solar heating products may well increase and more manufacturers will enter the market, increasing competition and reducing purchase price. There will be more people out there fitting them.
I'll give you an example. It's very common in Israel to see solar water heating systems on the roofs of houses and apartment buildings consisting of a solar panel propped up on a typically flat roof and a header tank on a stand. Frankly they look extremely ugly, but Israel is not a country where these kind of aesthetics are high on the agenda.
These systems cost a few hundred US dollars and are not very sophisticated because they don't need to be - there is plenty of energy to heat much of the hot water used for most of the year.
People buy them because they are cheap, they make a substantial saving in that climate and because they don't care about the appearance.
another good question, and another bastion of solar DHW support. So, lets find out:
At todays prices a =A32000 commercial system saves in the region of =A320 per annum on hot water bills. This is in the region of a tenth the amount that woud be needed for the unit to eventually pay its install cost.
To pay back =A32000 @ 5% over x years would require a yearly payback of
- calculator time -
over 10 years: =A3254.52 per annum over 15 years: =A3189.84 per annum over 20 years: =A3158.40 per annum over 25 years: =A3140.28 per annum over 50 years: =A3117.6 per annum over 100 years: =A3100.68 per annum infinity years: =A3100 per annum.
So, even if all such systems lasted the entire life of the universe with never a need for repair, the =A32000 spend would be almost entirely lost. In no sense are these systems an investment, whether short term, medium term, long term, or even infinite term.
Lastly, how much do energy prices need to rise to make these pay their way? Well, if an infinite amount of time to pay off their cost is acceptable, and there is zero risk of ever needing repair or decommissioning, then current energy prices would need to rise to roughly around 5x the present price. Since there are already various renewable energy technologies up and running, with huge implementation capacity available, at a fraction of 5x current oil based costs, this paying-their-way scenario will never happen. They can never pay off their cost, not even applying the most extreme and unrealistic optimism.
another good question, and another bastion of solar DHW support. So, lets find out:
At todays prices a £2000 commercial system saves in the region of £20 per annum on hot water bills. This is in the region of a tenth the amount that woud be needed for the unit to eventually pay its install cost.
To pay back £2000 @ 5% over x years would require a yearly payback of
- calculator time -
over 10 years: £254.52 per annum over 15 years: £189.84 per annum over 20 years: £158.40 per annum over 25 years: £140.28 per annum over 50 years: £117.6 per annum over 100 years: £100.68 per annum infinity years: £100 per annum.
Since you can get about 20 quid interest a year on about 800 quid, if you have the 800 quid, and it will save 20 quid a year, its worthwhile spending that on solar heating.
Which is different from £157.
The difference being the bid/offer spread on renting money ;-)
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