Hmm. Good point. I was thinking of some black plastic buckets full of water I left standing in the sun, which got quite warm. I expect it was the outside of the bucket absorbing the IR? Perhaps paint the outside of the pool black? Dunno.
I have solar heating. In winterm,, the windows in the drawing room face south. We open the curtains and gain about 2-3 degrees temp rise during the day.
Thats probably at least a kilowatt of input.
Insolation in middle England is about 0.1kW/m2 on average. A DIY solar install is going to cost around 500 quid/m2, it's going to be at best
50% efficient. If you think 5p/kWh is a fair price, that means over 20 years to pay for itself. There's no way the system will last that long, particularly if you use Navitron roof mounts. T
Dave is a Believer. Facts will not alter his opinion.
The reality is that given a clean sheet of paper it would be possible to design a house that maximizes every possible energy factor. Such a house would be very efficient, but would be utterly unlike a conventional house.
Essentially I have in mind a 'hobbit hole', with about 6-10 ft of earth over it, south facing double glazing ONLY, light pipes for internal illumination, and a full heat recovery ventilation system.
Insulated to the hilt, and built of massive amounts of masonry.
This would be its own heat store (or cool store)
I'd use a heat pump connected to pipes buried in the earth roof.
Possibly photovoltaics to charge batteries to drive the pump.
The key though for house heating is to have huge heat exchangers on the ventilation. Ventilation is the dominant heat loss in a super insulated house. If teh heat pump heated incoming air (or cooled it in summer) that would be the final tuning of the internal temperatures.
In summer, reverse the heat pump and drive heating coil in an outside swimming pool etc. And refrigerate the house..
Needless to say this would be a very ecpensive house, and would take a lot of energy to make...
In the end you have to do the cost benefit analysis on whatever you make and amortize it over the expected lifetime of the house.
For urban situations, the answer is to essentially roof over a city block. And use photochromic glass..
Yes, you asked "It would be really useful to find out how he achieved the fivefold increase in performance"
and I answered, or at least pointed you to the answer.
cheers, Pete.
The front bedrooms of my house are currently 4degC hotter than the rear ones due to being SE facing. With clear skys the sun's input is about 1kw per square meter at right angles to its rays, reduced slightly by air absorption when at low angles. Vertical windows can absorb quite a lot of that on a December day.
I suspect solar panels could be more effective in winter if mounted on vertical surfaces rather than roofs, but would be less effective in summer.
That because it's measuring the IR given off by the hotwater...
A Navitron 20 tube panel is about 2.5m2. The average insolation on
2.5m2 in the UK is about 0.25kW. Over the year that gives about 2.2MWh. The very best possible yeild from such a panel, attached to a system designed to absolutely minimise losses will be half that. Thus 1.0MWh is a believable figure, giving a reduction of 40 pounds on your annual gas bill, so long as you can store the energy with zero losses, and don't have to dump any heat.It is beyond the laws of physics to claim 5MWh from a 2.5m2 panel in the UK. At 40 quid a year, it will only take 30 years for the 1.2k system to pay for itself, by which time it will be scrap.
T
It is not physically possible for a 2.5m2 panel to save you more than
40pounds compared to gas. Solartwin only claim 1MWh, and if you read the technical Q+A on their website they suggest only 25pounds per annum payback.So, I think you are fooling yourself if you believe yours "has saved far more than [40 quid per year]"
T
Is it really just a question of payback? I thought the whole idea was to save dwindling resources of gas and oil.
Oh, dear. The price of a commodity is information about the availability of that commodity, as well as the means of exchange. If oil/gas/WHY is so cheap that it isn't worth seeking alternatives, then it simply isn't worth doing.
Obviously, in the long term, the price of fossil fuel will rise and seeking alternatives will become economic, at which point it will be done.
This is (one of the reasons) why markets are superior to command economies; the flow of information conveyed by the prices of things.
The problem is the inconsistency of that answer. It simply isn't possible for the solar panel to contribute the amount of heat saved. However, nor is it likely that the control changes could amount for the unexplained 80% of the saving which cannot be attributed to the solar panel.
If the control changes alone _did_ make this difference then that makes them a much more worthwhile investment than would normally be thought to be the case. The alternative is there is ome of factor or factors which have led to the saving or its calculation and we don't know what they are.
For most households the budget is limited. If you spend it on totally useless things like wind turbines or marginally effective things like solar water heating it usually leaves less to spend elsewhere. Spending the money elsewhere will invariably produce greater savings of energy than overhyped "alternatives" manage.
If the cost isn't known (both financial and energy) then you cannot make rational decisions. There are some who believe that is a good thing and that irrationality is the way forward.
On Tue, 11 Dec 2007 02:04:30 -0800 (PST) someone who may be snipped-for-privacy@gmail.com wrote this:-
I'm not particularly bothered with such crude figures. If we used simple payback periods very few new things would be built.
However, I have been just bothered enough to calculate such things, in order to rebut the assertions of the antis. I don't think I am being generous.
On Tue, 11 Dec 2007 00:21:37 -0800 (PST) someone who may be snipped-for-privacy@gmail.com wrote this:-
Heat losses are minimised by having a smaller pipe. The reduction in heat losses can be dramatic for relatively small reductions in pipe diameter. Elementary heat transfer theory.
Navitron sell insulation rated for continuous operation at ISTR
170C. One can see it in the photographs I referred to earlier, it is the black insulation.
have to assume you are making it up. I'm not an anti - in fact I'm going to install solar thermal. I won't however buy the system from anyone who claims I can get more than a MWh from a 2.5m2 panel, for they would be a bullsh*ter. I also won't be buying from Navitron as their roof mounts are rubbish. I'll be getting a professional install with top quality kit - it money was an issue I wouldn't be doing it anyway would I?
T T
I've been interested in the Navitron stuff and was thinking of a 10 ton heat store underground.
My experience of fitting heating systems and controls would suggest that improving the controls a good standard would save around £50-100 a year on most systems depending on the boiler and how crude the system was before hand. On a large house the control improvments could save £120 /year.
On Tue, 11 Dec 2007 09:35:19 -0800 (PST) someone who may be snipped-for-privacy@gmail.com wrote this:-
Nice try, but incorrect.
You seem to have forgotten to post the figures that would justify that denial...
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