The Great 'Get Paid To Generate Energy' Hunt

Dave_Fowler

aboard_epsilon wrote: »

Umm sorry, haven't read all of this or cant find the post were it was suggested to heat the feed tank .

I've thought about that before and came to theses conclusions :-

1.when the feed tank dumps its hot water into the immersion coiled tank.........cold water from the mains replaces it via the ball valve arrangement ..and cools the pre warmed supply rapidly...probably faster than it takes to leave the tank .
2.The cold water will go to the bottom of the feed tank rapidly........pushing your hot water out of the way........your pre warmed water will rise to the top of the tank.....and instead of the coiled immersion tank receiving pre-warmed water it will get mildly cold -warm-ish water.

unless you have another pre tank to fill the that pre tank ..

makes sense to me ..dont know about others reading what Ive just put.


be a good idea for someone to invent a pre tank that fills from the bottom gradually..and empties near the top perhaps
all the best.markj

The two tank system (plus header tank) is a system which I have yet to find commercially available, but it makes sense only if a) you've decided to go for solar heating and b) you realize the cost of a solar water heating system will mean that it will be years and years before there is any chance of a monetary return - if ever.

The system does get virtually every drop of heat from the panels. Both tanks in the system receive their cold feed at the bottom and the hot feed is from the top.

The feed tank similar to the hot water tank in a conventional boiler heating system. Nothing new to be invented.

As you say in point 2, as water is drawn from the system, the very cold water from the header tank enters at the bottom of the feed tank and pushes the pre-heated water out of the way. It is the hot water from the top of this tank which serves as a supply to the main tank.

In a conventional solar system, lets say it is winter and by the evening you find the water in the main tank is insufficiently warm for domestic purposes and turn on the gas boiler - heating the water to 60 deg C or whatever. You use some of the hot water which is replaced by very cold water from the header tank. By the morning the, water in the main tank will be say, 40 deg C. The solar panels, programmed to supply heat to the main tank only when their temperature is higher than the existing water in the tank, may well not provide much if any heat.

In the two tank system the programming of the flow of heated water to the main tank is the same - only supply if the temperature is greater than the tank temperature - but the program logic has the next step of supply heated water to the feed tank if not supplying it to the main tank. In so doing, the efficiency of the heat transfer from the panels to the much colder water in the feed tank is far greater.

You could argue that this two-tank system is like having one double-size tank with the solar heating coil at the bottom of the tank - to always heat the coldest water, but this would cause water turbulence and the hottest and coolest water would tend to mix. The two tank system provides the a) quickest way to heat the main tank when the panels are working with a good heat output, b) a pre-warmed water input when heating the cold water from the header tank in the winter so that the heat required from the boiler is less.

Cost? Two tanks instead of one, a diverter valve and extra temperature sensor. But who's counting cost if youv'e already decided to go for solar heating?

Cardew

Dave_Fowler wrote: »

Cardew,

My only calculations were 55p per day for one year = approx £200 per year (I based the figures on my actual spend on water heating in the summer months) and a surmise that the panels could heat all my water in the summer and heat the water to 35 deg C in the winter.


I have read the 2001 report you refer to when it was first mentioned in this thread. Whilst the tests certainly were fair in that they compared like-for-like, I was surprised that the tests were hardly practical in the way that they ran off 150 litres of water from a 140 litre tank used by one of the systems. (I think these were the figures).

I appreciate that you also are questioning the viability of solar thermal as well, it was your figure of £200 that I was questioning.

As explained above we are talking about an output in the region of 1,000kWh per year and by no stretch of the imagination can that be made to represent £200(i.e. 20p/kWh) - £40 per year savings is realistic.

Not certain where you get the 140 litre hot water tank from.

They compared running off 150 litres in one go in the evening, with running off 150 litres in 3 batches - 30l - 60l - 60l at different times during the day. The latter method gives slightly higher output - it is all in the executive summary.

clc5

Dave,

You were comparing FIT payments on an £18K PV system against the annuity which £18k could buy you. Just wondered if you had looked into the RHI Scheme planned to begin next April? Based on installing an air source heat pump in a typical 3 bed house, for an outlay of £7000-£8000 you could receive RHI payments of around £1000 per year for 18 years, tax free and index linked. You were looking at a similar annual payment under FIT scheme but for an outlay of £18000. If you are looking at the Govt payments as an alternative to a pension perhaps the RHI scheme would give you a better return on your 'investment'?

Dave_Fowler

Cardew,

Page 42 of the report (page number 36), last paragraph says that the ZEN system had only a 140 litre tank compared with larger tanks on the other competing systems and as such gave distorted results for the 150 litre run-off. Because of this it was unfair to make simple comparisons between systems. It would also be unfair if under the large run-off if some tanks were 150 litres and others, say, 200. I have not been able to find these figures in the report. The small multiple run-off figures are a better like-for-like guide as the tank size would be less important.

But in the end, all the test figures show that the expected heat generated from any of these 8 systems is far lower and of less financial value than the adverts say.

Cardew

Dave_Fowler wrote: »

But in the end, all the test figures show that the expected heat generated from any of these 8 systems is far lower and of less financial value than the adverts say.

I think that one of the most striking statistics in the report is that for all of the 8 systems that in the winter months - Nov to Feb incl that the total output for the 4 months was around 100kWh to 150kWh - say £5 worth of hot water - just over £1 amonth.

Cardew

This might convince a few more people!

The message is that solar thermal is just a waste of money - period!

http://www.dailymail.co.uk/news/article-1274784/They-tell-solar-panels-eco-friendly-save-money-The-truth-They-dont-work-time-100-YEARS-pay-.html

Doc_N

Cardew wrote: »

This might convince a few more people!

The message is that solar thermal is just a waste of money - period!

http://www.dailymail.co.uk/news/article-1274784/They-tell-solar-panels-eco-friendly-save-money-The-truth-They-dont-work-time-100-YEARS-pay-.html

But the main message, surely, is to point out the low intelligence and high gullibility of the average Daily Scare reader?

Cardew

Doc_N wrote: »

But the main message, surely, is to point out the low intelligence and high gullibility of the average Daily Scare reader?

Can't comment on the Daily M readership - but the Guardian ran similar stories some while ago - as has Watchdog and other similar programmes.

A lot of the people scammed are old and trusting!!!

With all the publicity given to Solar PV(which with the new subsidies is a totally different proposition) it is not difficult to imagine that some people will think all solar is worthwhile?

'WHICH' talks of solar thermal saving £55 a year - I assume that is an average for those with gas, oil, LPG and electric.

I also wish they would include some simple economics in their statements - like £4000 invested @4% is £160 a year in lost interest.

zarazara

wouldnt touch it with a bargepole

Scott_McLean

Miss-selling is always a danger. Make sure any installer you speak with is MCS registered and, preferably, signed up to the REAL assurance code as that will give you greater protection as a consumer. Also, do not look at the financial returns of solar thermal without taking the Renewable Heat Incentive into consideration.