The Great 'Get Paid To Generate Energy' Hunt

Cardew

Bungle1976 wrote: »

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3. The £135 (ok, minus £2.57) a year gas saving will get bigger each year as gas prices go up.


P.S. Cardew, I know I am not going to convince you, to be honest I wouldn't even try! Just showing the other side of the coin, that's all.

!

Well you haven't even tried to convince me!! Not that it matters for me, but others might be interested.

You have claimed a saving of £135 a year off a gas bill, and with respect your justification IMO leaves something to be desired.

However even conceding those savings, the economics don't add up.

You paid £3,500. Had you invested that £3,500 in a Nationwide BS 5 year bond @ 4.75%(3.8% after tax) That yields £133 interest which is compounded each year.

So even by your figures you save £2 a year(which is wiped out by the pump running;))

You can take whatever figure for gas price inflation you want, and ignore any possible costs for repairs/maintenance and the figures just don't add up.

Doc_N

Cardew wrote: »

PV produces no output at night and relatively little during the winter when heating is needed.

The major income from PV is from the FIT and the amount you save from using the output in the property during daylight hours is a small percentage of the overall income.

You're missing the point.

Of course the FIT is the major income source, but the point of linking PV with an air source heat pump is that more of the electricity can be used to run the heat pump. The heat pump will give you more heat £ for £ than you put in.

Cardew

Doc_N wrote: »

You're missing the point.

Of course the FIT is the major income source, but the point of linking PV with an air source heat pump is that more of the electricity can be used to run the heat pump. The heat pump will give you more heat £ for £ than you put in.

No I am not missing the point at all.

As I stated, you get no output at night and relatively little in winter when you need heat.

Look at the output figures for a PV array in winter during the day and they might produce as little as 2kWh or 3kWh a day. You will use most of that for normal routine consumption, so 'linking' it to an ASHP will not utilize much extra electricity. Each extra kWh you use only gives an extra 7p or so(10p - 7p)

An ASHP stands on its own merits, as does PV.

denisiw

Cardew wrote: »

You replaced a 14 year old 'condensing' boiler??? As far as I am aware the first condensing boilers were introduced about 5 years ago.

Secondly the link you have given is simply the SEDBUK tables and the highest efficiency gas boilers listed only have an efficiency of 91.5% - so I don't know where you get 98.5% efficiency for your boiler?

It is also pertinent to point out that it is widely held view that the theoretical efficiency of condensing boilers is rarely achieved in 'real' conditions in households.

So what are the savings of modern boilers over the older non-condensing variety? The average household bill for gas is around £600. So the difference between a boiler achieving 90% and a 20+ year old boiler @ 65% might be as high as £150 in theory. In practice probably a lot less.

Yes, I did make a mistake, it wasn't 14 years old, it was 151/2 years old! It was fitted in April 1994 and cost me £700 including installation. I got a £200 rebate from the Energy Saving Trust, so it cost me £500; that's less than £33/year. The only other cost has been £50/year for servicing. It's more than paid for itself.

You really are unaware about the length of time that condensing boilers have been on the market. I believe that the Energysaver was the first generation of condensing boilers produced by Glow worm, but I think that the condensing boiler had been available in Holland for quite some years before this. I've been on the energy efficiency bandwagon since watching Granada TVs 'A House for the Future' back in 1976. I've not just jumped on-board.

The new Glow worm Ultracom 15hxi that I have now cost me £600. I had my old boiler covered by Homeserve and I got £200 back from them as it was beyond economical repair. One of the reasons that I stayed with this manufacturer (I know it's a Vaillant inside) was because fitting it involved no change to the flue and minimal change to pipe routeing.

I know the link was to SEDBUK tables. I gave the link purely to give some idea of the efficiency of an old Baxi.

Finally thank you for pointing out that the SEDBUK tables are theoretical, I was aware of that. As I said, the efficiency figure of 98.5% that I quoted is on the print out that came from the analyser reading. It's not theoretical, it's fact. At that moment in time when the boiler was running, 'real' conditions, and the reading was taken, it was operating at 98.5% efficiency.

What you can't get away from is that the heat that is being generated is heating the house, not heating outside. I'm using less gas, that's the most important thing to me.

Denis

Bungle1976

Cardew wrote: »

You can take whatever figure for gas price inflation you want, and ignore any possible costs for repairs/maintenance and the figures just don't add up.

Err, not really. If gas prices stay the same or go down my savings will reduce, if they increase (a bit of a no brainer in my view) my savings will increase!

I think I should also point out that I have now evaluated the negative figure that I had ignored (i.e. the pump running costs), but I still haven't allowed for the positive figures that I hadn't included, i.e.

1. I have modified my washing machine to use hot water ONLY for the initial fill after first discarding the "slug" of cold water in the pipe (cheap and easy mod using a scrap corridor timed light switch), so saving the electric that it would normally use to heat the water up. Anyone know how much that saves? I suppose I could run a load from cold and from hot and measure the difference.

2. Even though it does not provide ALL my hot water for the other six months, it does provide a useful pre-heat to the water in the tank, this is probably a significant gas saving but I have not evaluated it.

3. When my girlfriend moves in we WILL use more hot water

I think this would make it much more attractive than you make out, especially point 2. But they would of course be difficult to evaluate. Having said that I may have a go at the difference between the washing machine running from hot and cold, I have a power measuring plug somewhere......

I am still happy with my decision, and at the end of the day that is what matters to me. I have also been open with the figures so anyone else who is considering it can see a real life example.

I will be waiting with interest for the report that the EST chap mentioned about ASHP kit......

Cardew

Bungle1976 wrote: »

1. I have modified my washing machine to use hot water ONLY for the initial fill after first discarding the "slug" of cold water in the pipe (cheap and easy mod using a scrap corridor timed light switch), so saving the electric that it would normally use to heat the water up. Anyone know how much that saves? I suppose I could run a load from cold and from hot and measure the difference.


...

My cold fill washing machine(about 6 years old) has 3 programs that we use; they use 0.4kWh: 0.6kWh: 0.9kWh per cycle. The majority of the time it is set at the lower two settings.

There have been a number of threads on W/machine consumption and people who have measured their machines who report similar or lower consumption.

Obviously that consumption includes the running of pumps and motors - and a cycle takes about 90 minutes.

It is surprising just how little water is needed to be heated and then only to 30C or 40C from whatever the temperature of the water in the pipes.

My gut feeling is the majority of the consumption is pumps & motors. This is borne out by the following - from the handbook.

Easy Care 40C - 2.5kG - 0.4kWh - 59 litres water.

Delicates 30C - 2kG - 0.6kWh - 80 litres

Wool 30C - 2kG - 0.6kWh - 75 litres

So the two 30C washes use 50% more electricity than the 40C wash which presumable is because the motors, pumps etc are pumping more water.

I would surmise that the heating element(pun) of the cycle is less than 0.2kWh.

So using the machine 3 times a week with hot fill(disposing of the slug of cold water), for 26 weeks would save about 15kWh - say £1.50 a year.

Dave_Fowler

Let us assume the weather is either black or white - winter or summer. and do some simple calculations on the relevance of Solar thermal heating for hot water.

In the summer months my total gas bill is less than 60p per day - and that includes the use of the gas hob. Lets assume 55p for the water. The water in the header tank in the loft is relatively high due to the heat from the sun through the roof. The loft temperature is often well above 35 deg C. The hot water tank thermostat is set at 55 deg C. So the boiler has to raise the temperature of the water by around 20 deg. In the winter, the loft tank is far colder - probably 10 deg C - and has been known to freeze. The temperature rise required for the hot water would be an extra 25 deg. This suggests that to heat the water in winter would use at least twice as much gas as in the summer.

Now we need make some assumptions. In the summer months I will not need to heat the water because of the solar panels, and in the winter, lets say the solar panels raise the temperature of the feed tank to 35 deg. So my savings would work out at about 55p per day 365 days a year. About £200 per year.

This figure is significantly lower than many calculations on the returns which are based on the total energy gathered by the panels. One reason is that during the summer when most of the energy is gained, the water in the tank will be heated to a temperature far higher than 55 degrees and effectively this excess energy is wasted. The figures quoted by the solar panel companies assume that you need and use all the water you have heated.

OK you may say, use a smaller panel and pay less for it. But the ratio of the summer to winter sun's heating effect would mean you could not raise the 35 deg temperature in the feed tank and hence the heating bills would rise and you could not save the 55p per day in winter.

aboard_epsilon

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

Cardew

Dave_Fowler wrote: »

Let us assume the weather is either black or white - winter or summer. and do some simple calculations on the relevance of Solar thermal heating for hot water.

In the summer months my total gas bill is less than 60p per day - and that includes the use of the gas hob. Lets assume 55p for the water. The water in the header tank in the loft is relatively high due to the heat from the sun through the roof. The loft temperature is often well above 35 deg C. The hot water tank thermostat is set at 55 deg C. So the boiler has to raise the temperature of the water by around 20 deg. In the winter, the loft tank is far colder - probably 10 deg C - and has been known to freeze. The temperature rise required for the hot water would be an extra 25 deg. This suggests that to heat the water in winter would use at least twice as much gas as in the summer.

Now we need make some assumptions. In the summer months I will not need to heat the water because of the solar panels, and in the winter, lets say the solar panels raise the temperature of the feed tank to 35 deg. So my savings would work out at about 55p per day 365 days a year. About £200 per year.

This figure is significantly lower than many calculations on the returns which are based on the total energy gathered by the panels. One reason is that during the summer when most of the energy is gained, the water in the tank will be heated to a temperature far higher than 55 degrees and effectively this excess energy is wasted. The figures quoted by the solar panel companies assume that you need and use all the water you have heated.

OK you may say, use a smaller panel and pay less for it. But the ratio of the summer to winter sun's heating effect would mean you could not raise the 35 deg temperature in the feed tank and hence the heating bills would rise and you could not save the 55p per day in winter.

Dave,

I really cannot understand your calculations at all.

I have given the link(post#54) where the government(the DTI) commissioned a test of 8 solar thermal systems. See:

Have you seen this exaustive trial of 8 systems carried out for the Dti at Cranfield? *

http://www.dti.gov.uk/files/file16826.pdf

That seems a pretty robust set of results to me? Admittedly carried out in 2001(before your time?)

*
For those not conversant with the units used!
For the 8 systems tested(evacuated Tube and Flat plate) the annual output ranged from 3440 MJ(megajoules) equal to 955kWh to 4,820MJ(1,339kWh)
However from that total had to be deducted the ‘parasitic’ energy to run the pump and electronics. This ranged between zero and 390MJ(108kWh) pa. This of course is daytime rate electricity.
The average for the 8 systems was just over 1,000kWh per year.

The total annual output, in perfect conditions averaged 1,000kWh!

If you pin down the firms installing systems you will get them to 'admit' that a ballpark figure for a solar thermal system is around 1,000kWh pa for an installation cost of around £4,000.

This firm came out quite well in the report - so much so that they even quote it on their website.

http://www.solartwin.com/

The best solar panels for sustainability. In a 2001 DTI report, called Side by Side Testing of Eight Solar Water Heating Systems, not all solar panels were found to be equal, even though most delivered similar amounts of net carbon savings. The issue was “net”. In terms of total sustainability, as judged by carbon clawback, which is a touchstone of sustainability in solar water heating systems, Solartwin was by far the best performing solar water heating system – by a very big margin – and evacuated tubes were the worst performing solar heating systems on this key parameter.

A verbal quote they give for their system is 'around £4,000'.


Now, depending on the efficiency of your gas boiler, to produce 1,000kWh you might use between 1,100kWh for a modern A rated boiler to 1,500kWh for an old G rated boiler.

So at 3p/kWh for gas(BG Websaver 7 is 2.63p/kWh) you will save £33 to £45 a year from your panel.

The output in the winter months is tiny compared to the summer(it is all in the report)

If you doubled the size of the solar panels, you would most probably not be able to use all the water in the summer months. However for the sake of argument let us assume your, now, huge system produced 2,000kWh of hot water that you could use, you would now save £66 to £90 a year. and how much would such a system cost? £6000???

We really must adopt a sensible approach if we are to estimate cost effectiveness of solar thermal.

In the real world you 'invest' around £4,000 and lose around £150 pa in interest, to save around £40 pa on hot water costs if you have gas, perhaps £60 pa if you have oil CH and £100 pa if you heat your water with an immersion heater on daytime rates(or £50 pa on economy 7)

Anyone care to dispute the figures?

Dave_Fowler

Cardew wrote: »

Dave,

I really cannot understand your calculations at all.

I have given the link(post#54) where the government(the DTI) commissioned a test of 8 solar thermal systems. See:



The total annual output, in perfect conditions averaged 1,000kWh!

If you pin down the firms installing systems you will get them to 'admit' that a ballpark figure for a solar thermal system is around 1,000kWh pa for an installation cost of around £4,000.

This firm came out quite well in the report - so much so that they even quote it on their website.

http://www.solartwin.com/




A verbal quote they give for their system is 'around £4,000'.


Now, depending on the efficiency of your gas boiler, to produce 1,000kWh you might use between 1,100kWh for a modern A rated boiler to 1,500kWh for an old G rated boiler.

So at 3p/kWh for gas(BG Websaver 7 is 2.63p/kWh) you will save £33 to £45 a year from your panel.

The output in the winter months is tiny compared to the summer(it is all in the report)

If you doubled the size of the solar panels, you would most probably not be able to use all the water in the summer months. However for the sake of argument let us assume your, now, huge system produced 2,000kWh of hot water that you could use, you would now save £66 to £90 a year. and how much would such a system cost? £6000???

We really must adopt a sensible approach if we are to estimate cost effectiveness of solar thermal.

In the real world you 'invest' around £4,000 and lose around £150 pa in interest, to save around £40 pa on hot water costs if you have gas, perhaps £60 pa if you have oil CH and £100 pa if you heat your water with an immersion heater on daytime rates(or £50 pa on economy 7)

Anyone care to dispute the figures?

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 did not try at any point to justify the cost of the panels against the savings in gas bills. I did not say what size of panel or cost could achieve the heating requirements for the water. In fact, I thought I had shown that they were impractical. Perhaps we are agreeing here, but coming to the same conclusion from two different angles.

I give figures for my actual spend on heating water (plus gas hob) during the summer when there was no central heating. I also said that the figures given by the solar panel manufacturers are often way above what you get in actual practice. I think on this latter point we do agree.

Perhaps I should have made more of the point that my surmise was that the panels would raise the temperature of the water in the winter by the same amount as they did in the summer, and this is clearly not the case. I said if the panels supplied all the heating required in the winter to heat water to a temperature of 35 deg C, there would be a lot of wastage in the summer as the water temperature would be excessive and the heat output from the panels could not be fully utilized. I went on to say that if the panels were matched for the summer output (a smaller area of panel at a lower cost) they would not reach the 35 deg C temperature in the winter.

Whatever the size of the panel there would be no match between summer and winter and the theoretical returns reported by the manufacturers are highly unlikely to be achieved.

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).