Solar panels and combi boiler - feasible?

Skiduck

paul_h wrote:

...but that still doesn't take into account leaving the cost of installation on high interest deposit for that 20 year period, or any maintenance, repairs or running costs.

Current fuel price trends are abnormal - most industry analysts are predicting energy prices to fall in the short to medium term, even BG are offering a guaranteed cut in prices after next year. I would agree with you, however, that long term energy prices are likely to rise, but to what degree is uncertain. When trying to guess what trends will be for the next 20 years, you cannot look at the last two years in isolation and ignore the previous twenty - fuel prices have been at an historical low for many years and are still haven't reached the highs of 25 years ago if inflation is taken into account.

Incidentally, our fuel costs have increased by about 20% over the last 6 years, not 10% per annum - we are on solid fuel, which I do admit is cheaper than most forms of domestic heating.



We are a family with 2 small children, so we often run at least one bath a night - we use quite a lot of hot water and I would say our usage is higher than average.

Solid fuel is cheaper than most forms of heating, but even so the average family home uses around 5000 KWh of DHW heating per annum - BG Click energy economy 7 tariff is around 2.2p per KWh on cheap rate in our area (East Midlands), so even with electric heating 5000KWh could cost as little as £110 per annum. A 50% saving from solar in these circumstances would only amount to £55 per annum.

However, if you were to use oil to heat your water, the saving would be far more substantial - but then again, you may as well use economy 7...

In the last 20 years nobody was bothered about the use of fossil fuels, over the last 20 years we have increased our useage through industry, transport and heating. Unfortunately there is no going back, fossil fuel is at a premium, you will never revert back to cheap prices, unless everyone is happy with a nuclear reactor near them.

jonnyw_2

Paul_h

5000 KWh of DHW heating per annum is about 7000 litres of oil in a decent oil central heating boiler by my calculations.

Is this right?

If it is then your figures for annual consumption is 1/3 that of skiduck who had 20000 litres a year which would be about 14000 KWH.

Anyone know of any published sources?

Continuing on, if off peak is 2.2 p a KWH and that can provide all the DHW you would need then if skiducks people are using that much oil they would save £250 a year changing to off peak without investing anything in a solar system! There is even a fair margin if they had to use a few hours of on peak!

jonnyw_2

Skiduck wrote:

jonnyw wrote:

here ya go, done a few years ago, so costs for fuel and installationn have changed but obviously consumption hasn't.


http://www.energie-cites.org/db/belfast_140_en.pdf

Well that looks convincing.

Can you look at how i tried to convert literes of oil to KWH.

paul_h

jonnyw wrote:

Paul_h

5000 KWh of DHW heating per annum is about 7000 litres of oil in a decent oil central heating boiler by my calculations.

Is this right?

If it is then your figures for annual consumption is 1/3 that of skiduck who had 20000 litres a year which would be about 14000 KWH.

Anyone know of any published sources?

Continuing on, if off peak is 2.2 p a KWH and that can provide all the DHW you would need then if skiducks people are using that much oil they would save £250 a year changing to off peak without investing anything in a solar system! There is even a fair margin if they had to use a few hours of on peak!

My point exactly.

The figures I have seen universally quoted in many publications are all around 5000KWh per annum for DHW and 15,000KWh per annum for central heating.

The nearest one I have to hand is Mark Brinkley's excellent "The Housebuilder's Bible" (highly recommended reading might I add) which quotes 5000KWh for DHW and 14,800KWh for heating, for a four-bedroomed detached family home.

British Gas themselves quote total average usage as 20,500KWh.

Even this pro-solar site quotes only 3000KWh per annum for DHW

http://www.smartenergyuk.com/thermalsolar.asp

paul_h

jonnyw wrote:

Well that looks convincing.

Can you look at how i tried to convert literes of oil to KWH.

Convincing, but hardly impartial...

To convert litres of oil to KWh -

First multiply litres by 10.2 (the calorific value of 28-second grade oil equates to 10.2KWh per litre). Then multiply by boiler efficiency, i.e. 0.75 if your boiler is 75% efficient.

To convert KWh to litres -

Divide by 10.2, then divide by boiler efficiency.

Example...

5000KWh divided by 10.2 = 490. Divide by 0.75 = 653 litres, or therabouts.

paul_h

Skiduck wrote:

here ya go, done a few years ago, so costs for fuel and installationn have changed but obviously consumption hasn't.


http://www.energie-cites.org/db/belfast_140_en.pdf

Hardly impartial, as I say. Please refer to my previous posts. I still can't see how an average user can save 1000 litres when the average requirement for DHW is 650 litres or thereabouts. On your figure of 2000 litres, oil heating would cost £700 per annum just for the hot water.

Skiduck wrote:

In the last 20 years nobody was bothered about the use of fossil fuels, over the last 20 years we have increased our useage through industry, transport and heating. Unfortunately there is no going back, fossil fuel is at a premium, you will never revert back to cheap prices, unless everyone is happy with a nuclear reactor near them.

Unfortunately, I suspect that that a nuclear future is inevitable now, so perhaps this will help stabilise prices.

Skiduck

paul_h wrote:

Unfortunately, I suspect that that a nuclear future is inevitable now, so perhaps this will help stabilise prices.

The UK currently generates about 40% of its electricity from gas, 19% nuclear, 33% coal, 4% renewables and 4% from other sources including oil.
We would need quite a few nuclear stations, especially by 2050.

I have no problem with nuclear, but there are a lot of people that do. Also increased nuclear production equals increase nuclear waste - disposing of this safely is a priority before even thinking of building more plants. (we don't want a new "climate change" before we start, if you get my meaning.)

paul_h

Skiduck wrote:

The UK currently generates about 40% of its electricity from gas, 19% nuclear, 33% coal, 4% renewables and 4% from other sources including oil.
We would need quite a few nuclear stations, especially by 2050.

I have no problem with nuclear, but there are a lot of people that do. Also increased nuclear production equals increase nuclear waste - disposing of this safely is a priority before even thinking of building more plants. (we don't want a new "climate change" before we start, if you get my meaning.)

Because of the wholesale cost of gas, electricity production from coal is actually currently running at over 50% of the total.

I am not pro-nuclear, but people also need to be aware that coal fired power stations emit more radioactivity into the environment than nuclear stations - 'clean coal' technology means that enormous quantities of pulverised fuel ash is having to be disposed of. This PFA is known to contain 2ppm of Uranium, plus other radioactive minerals that are contained in coal, as well as the many heavy metals.

I live near a 2000MW coal fired station which has successfully applied to dump 4 million tonnes of the stuff on our doorsteps - at 2ppm thats 8 tonnes of Uranium in that mountain.

Another power station, but much the same problem...

http://www.radleyvillage.org.uk/ourvillage/Didcot_PFA/hazards.htm

All these issues do make the argument for green energy sources stronger, but the financial considerations remain unless support for these schemes improves.

jonnyw_2

So if the national average figure is 5000kwh, then converting to oil at 700 odd litres gives a hot water cost of £250 a year?

At half solar are we agreed the saving is going to be around £125 a year on a capital cost of £3500?

But if you are a very heavy user at about 3 times the national average (like in Belfast!) then for oil it does start to stack up? But at this level of use you'd save nearly as much switching from oil to off peak electricity and wouldnt have to make the capital expenditure?

paul_h

Here's another source...

http://www.sun-harvester.co.uk/case.htm

...which quotes:

A typical four person household in the UK uses approximately 3,000 Kwh to 4,000Kwh per year for domestic water heating alone.