The Great 'Get Paid To Generate Energy' Hunt

Doc_N

Streethawk wrote: »

this is in my library, so I'll go get it out at the weekend. Many thanks
(no one else go get it from my library! not telling you where, just in case!!!)

I wouldn't worry too much about the rest of us getting the book from your library - it's free online.

Dave_Fowler

Cardew wrote: »

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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?

There is a lot of confusion about these efficiency ratings - even with qualified gas engineers. I had an installation engineer quoting figures of 98%-99% for the boilers he was installing. It appears to be the burning efficiency which is being quoted, not the energy-to-heat efficiency. Hence the measurement of the flue gasses, not the heat output.

Cardew

Dave_Fowler wrote: »

There is a lot of confusion about these efficiency ratings - even with qualified gas engineers. I had an installation engineer quoting figures of 98%-99% for the boilers he was installing. It appears to be the burning efficiency which is being quoted, not the energy-to-heat efficiency. Hence the measurement of the flue gasses, not the heat output.

Agreed! However Dennis quoted 98.5% for his boiler and gave a reference for the SEDBUK tables.

The only meaningful efficiency is energy-to-heat. i.e. that quoted in the SEDBUK tables.

Even then, it is only possible to measure that efficiency under laboratory conditions. I have read technical reports that indicate in 'real world' operating conditions in domestic installations it is difficult to get within 5% of the theoretical efficiency.

However boiler efficiency is but one factor in the decision to replace an old but working boiler.

I am a heavy user of gas and have a 22 year old boiler with a SEDBUK rating of 65%. In that 22 years it has had one thermocouple replaced(a five minute job).
Like most(all?) boilers of that vintage, there are no adjustments at all required in the servicing - it consists of cleaning and visual inspections.

Now I might save, what?, £200 a year on my gas bill if I spend, what?, £3,000 on a new boiler. That boiler than might last 10 or 15 years and need far more maintenance/repairs than my current beast.

Dave_Fowler

Cardew wrote: »

Agreed! However Dennis quoted 98.5% for his boiler and gave a reference for the SEDBUK tables.

The only meaningful efficiency is energy-to-heat. i.e. that quoted in the SEDBUK tables.

Even then, it is only possible to measure that efficiency under laboratory conditions. I have read technical reports that indicate in 'real world' operating conditions in domestic installations it is difficult to get within 5% of the theoretical efficiency.

However boiler efficiency is but one factor in the decision to replace an old but working boiler.

I am a heaver user of gas and have a 22 year old boiler with a SEDBUK rating of 65%. In that 22 years it has had one thermocouple replaced(a five minute job).
Like most(all?) boilers of that vintage, there are no adjustments at all required in the servicing - it consists of cleaning and visual inspections.

Now I might save, what?, £200 a year on my gas bill if I spend, what?, £3,000 on a new boiler. That boiler than might last 10 or 15 years and need far more maintenance/repairs than my current beast.

I absolutely agree with you. My old boiler, fitted in the early 1980's needed only one thermocouple replaced in the 25 plus years too. However, after a house extension, it was no longer capable of heating the house during cold weather. Having fitted a modern condensing boiler (I understand all new domestic boilers have to be the condensing type), gas consumption has gone up slightly (a much more powerful boiler but better efficiency). I would never have replaced the old boiler but for the extension to the house.

Streethawk_2

Doc_N wrote: »

I wouldn't worry too much about the rest of us getting the book from your library - it's free online.

Now, how stupid do I feel?!

Dave_Fowler

Ref my post #64.
In this morning's news it is predicted that the basic rate income tax will have to rise by at least 6p in the £ if the public spending and borrowing deficits are to be reversed. It is now becoming even more like good sense to take a tax-free lump sum of £18,000 from my pension pot and 'invest' this in a PV system with a probable annual FITs income of £1,200 / year index linked rather than the quoted pension income of £600 / year not index link and taxed at a predicted 26+%.

Even if I were to take the £18,000 and invest it in a selection of bonds, the income from any non-ISA bond would be taxed at the increased rate - ( I couldn't put £18,000 into an ISA in one year).

With the warranty of 10 years for the complete PV system and a quoted annual panel degradation rate of fractions of 1%, even the cost of the replacement of an inverter after 10 years seems not to outweigh the advantages.

clc5

Dave_Fowler wrote: »

Ref my post #64.
In this morning's news it is predicted that the basic rate income tax will have to rise by at least 6p in the £ if the public spending and borrowing deficits are to be reversed. It is now becoming even more like good sense to take a tax-free lump sum of £18,000 from my pension pot and 'invest' this in a PV system with a probable annual FITs income of £1,200 / year index linked rather than the quoted pension income of £600 / year not index link and taxed at a predicted 26+%.

Even if I were to take the £18,000 and invest it in a selection of bonds, the income from any non-ISA bond would be taxed at the increased rate - ( I couldn't put £18,000 into an ISA in one year).

With the warranty of 10 years for the complete PV system and a quoted annual panel degradation rate of fractions of 1%, even the cost of the replacement of an inverter after 10 years seems not to outweigh the advantages.

Hi Dave, what figures did you base your calculations on? I calculate that it will be about 20 years before the PV system gives you a better return than investing the 18K. This assumes the 18K provides an after-tax annual return of 3%, compounded; versus £1236 PV money invested each year at the same annual rate of return and that the figure of £1236 increases each year by 3% (estimated inflation rate).

Sylvan

Dave_Fowler wrote: »

If I 'invested' the £18,000 in a 3.5kW PV system, the returns on the first year are likely to be £1,236 - this is FITs income plus savings from electricity for my own use - and this sum would be index linked to the RPI.

What exactly does "a 3.5kW PV system" mean? Is 3.5kW the amount it's capable of producing under optimum conditions (a cloudless midsummer day on the south coast) or the average amount over a typical year?

Ben84

Dave_Fowler wrote: »

I absolutely agree with you. My old boiler, fitted in the early 1980's needed only one thermocouple replaced in the 25 plus years too. However, after a house extension, it was no longer capable of heating the house during cold weather. Having fitted a modern condensing boiler (I understand all new domestic boilers have to be the condensing type), gas consumption has gone up slightly (a much more powerful boiler but better efficiency). I would never have replaced the old boiler but for the extension to the house.

Not everyone who installs a condensing boiler gets significantly greater efficiency as these boilers only condense from the gas vapour when the water being returned to the boiler is below a certain temperature.

Good installations now use large radiators or underfloor systems as they require lower output temperatures to heat the house, and they return cooler water to the boiler which boosts efficiency. Old systems like mine have comparatively small radiators, requiring hotter water to heat the house well, and a new condensing boiler isn't going to do much condensing when attached to them. I unfortunately have to keep the boiler thermostat up high and heat the radiators to pretty scorching temperatures to heat the house well in the coldest weather.

My back boiler is about 65% efficient, so a new boiler would improve this, and by burning outside air (rather than sucking it in from my sitting room) reduce loss of heat from the house, but I don't believe I could get anywhere near the 80-90% figures often quoted without changing my radiators for bigger ones.

Cardew

Sylvan wrote: »

What exactly does "a 3.5kW PV system" mean? Is 3.5kW the amount it's capable of producing under optimum conditions (a cloudless midsummer day on the south coast) or the average amount over a typical year?

It is actually 3.5kWp(kilowatt peak) which is an output under defined laboratory conditions.

All modules are rated by manufacturers in terms of their peak power (Wp) under standard test conditions: ie. 1000W/m² of sunlight (‘peak sun’); 25 ºC; and air mass of 1.5.

- it is simply a 'standard' against which all panels are measured.

All that matters in the annual output in kWh for the area of the world where the panels are installed.

A 3.5kWp solar array situated on the equator with a motor to position the array to track the sun will produce a vastly higher output than the same array situated in UK.

A figure of around 800kWh a year per kWp is typical for UK.