Break even

ed110220

Smiley_Dan wrote: »

It becomes a question of what your goals are. PV makes a lot of financial sense. But for carbon reduction it's often your space heating you need to look at, and cavity wall insulation (unless you have enormous cavities) doesn't really cut it.

In your case, burning scrap wood, maybe less so. But the wood would go further with more insulation.

I think after the cheaper and easier DIY improvements such as loft insulation, solar PV is now pretty high on the list of big improvements for carbon saved/£.

OFGEM gives a figure of 0.527 kg carbon dioxide/kWh for mains electricity in the UK. So say you generate 3500 kWh/year from solar PV you should save about 1845 kg carbon dioxide/year.

Burning 1 kWh of gas produces 0.185 kg of CO2, so to save 1845 kg of CO2 by burning less gas you would have to save 9973 kWh of gas.

The average gas consumption is 16 500 kWh/year, so that would be a very big saving and I doubt it could be achieved by spending the typical price of PV on insulation.

Ed

Smiley_Dan

The average gas consumption is 16 500 kWh/year, so that would be a very big saving and I doubt it could be achieved by spending the typical price of PV on insulation.

Hmmm. The difference is that the lowered space heating requirement would be energy saved, whereas adding more generating power does not necessarily reduce the energy requirement if you're already using as much generated power as you can.

I guess it depends on the situation.

The 3500kWh is generated energy, not used. Average use is below 50% IIRC. There are inefficiencies in exported energy. But for us, we use more like 90% of generated (Optimmersion) so, your figures are closer to the truth.

Next, our space heating requirement is over 26MW according to the EPC (lower than that in reality because our heating is zoned). And that's oil heating. The realities are that insulation and air tightness are a far less exact science as practiced in the general case, and just slapping some CWI and a modicum of loft insulation up doesn't go the whole way. You have to pay attention to how it is installed.

kevin6666

It's appalling from a Bill Payer pov that they're footing the bill for such ridiculous roi's. Breaking even after just 4/5 years followed by another 20 years of rpi matched earnings. DECC/Ofgem should be held accountable for this and frankly heads should roll.

zeupater

ed110220 wrote: »

I think after the cheaper and easier DIY improvements such as loft insulation, solar PV is now pretty high on the list of big improvements for carbon saved/£ ....

... The average gas consumption is 16 500 kWh/year, so that would be a very big saving and I doubt it could be achieved by spending the typical price of PV on insulation ...

Hi

There are two ways of looking at this with a limited budget. Let's say that you had an improvement budget of ~£5k so .... firstly, spend the money on improving energy efficiency and not being able to outright purchase pv until the investment has repaid it's value ..or.. purchase the pv system and use the on-going savings and FiT revenue stream to finance incremental improvements.

Regarding the average gas consumption .... our property far exceeded the insulation requirements when it was built, however, that didn't prevent us using ~40MWh of gas/year until we started to take efficiency measures seriously. We dipped below the current average (16.5MWh) in 2008, below 10MWh in 2010, below 5MWh in 2011 and are currently on target for breaking the 1MWh threshold this year. From the early '90s we've had the same 'clean burn' multi-fuel stove and have burned roughly the same volume of logs each year (approx. 3cu metres/2 tonnes) ...

As can be seen, we now have very little leeway for improvements which would make any financial difference let alone show a payback .... however, that doesn't mean that we're going to stop improving - it's just that anything from now onwards needs to improve appearance or comfort, which is exactly what most people spend their money on, whilst complaining about the cost of energy and efficiency measures .... in the end, it's just a matter of recognising & setting priorities ..

HTH
Z

zeupater

kevin6666 wrote: »

It's appalling from a Bill Payer pov that they're footing the bill for such ridiculous roi's. Breaking even after just 4/5 years followed by another 20 years of rpi matched earnings. DECC/Ofgem should be held accountable for this and frankly heads should roll.

Hi

Just DECC & Ofgem ? .... when you weigh it up it's just a form of PFI funding. Typical PFI contracts (NHS/Education/Defence etc) were handed out left, right and centre by the previous government (Labour) in order to move capital expenditure 'off book' (ie - hide debt) and buy votes (mainly public sector) with a spending spree ...

Typical PFI contracts repay somewhere in the range of 3x to 7x the capital cost back to the investor .... the NHS alone currently has a PFI debt of around £80bn, multiply that up and the scale of economic incompetence starts to materialise .... Close to where a relative lives there's a school for ~1000 pupils which cost a staggering £30million to build, but will cost ~£450million over the term of the contract - of course, it didn't cost anybody anything up front, so it was 'free' money which could be used to invest in the future of following generations .... if it lasts 50years (which is high for schools these days) and has an intake of 200/year ... the cost of buildings alone is costing £45000 (450000000/(200*50)) per head, that's more than the full cost of a degree course .... perhaps, if the 'vanity' project had been recognised as being so expensive and adequately good school buildings had not been demolished then all of the children could have had a 'free' degree-level education ... alas, no .... but, of course, it's Nick & Dave taking the flack for education, not Tony, Gordon, Ed & Ed, similarly, for the comparatively insignificant FiTs it's Ofgem & DECC not Tony, Gordon, Ed & Ed ...

... Perspective .....
HTH
Z

zeupater

Hi All

Reading the last post back I missed something which could invoke a chuckle, but more likely a groan ...

I suppose the difference in perspective is between believing that "DECC/Ofgem should be held accountable for this and frankly heads should roll." ... & ... the politicians responsible for pushing PFIs should be held accountable for this and frankly two Eds should roll ....

... sorry, must be time to pour a stove-brewed cuppa
Z

ed110220

kevin6666 wrote: »

It's appalling from a Bill Payer pov that they're footing the bill for such ridiculous roi's. Breaking even after just 4/5 years followed by another 20 years of rpi matched earnings. DECC/Ofgem should be held accountable for this and frankly heads should roll.

Where do you get the figure of 4 or 5 years from? Seems you're using outdated information, especially your "another 20 years". The FIT is now for 20 years (it was once 25 years).

And is this before or after their heads roll for agreeing to pay almost twice the usual wholesale price of electricity for 35 years (not 20 or 25) to companies owned by the French and Chinese governments for them to build Hinkley Point C? ;-)

Ed

ed110220

Smiley_Dan wrote: »

Hmmm. The difference is that the lowered space heating requirement would be energy saved, whereas adding more generating power does not necessarily reduce the energy requirement if you're already using as much generated power as you can.

I guess it depends on the situation.

The 3500kWh is generated energy, not used. Average use is below 50% IIRC. There are inefficiencies in exported energy. But for us, we use more like 90% of generated (Optimmersion) so, your figures are closer to the truth.

Next, our space heating requirement is over 26MW according to the EPC (lower than that in reality because our heating is zoned). And that's oil heating. The realities are that insulation and air tightness are a far less exact science as practiced in the general case, and just slapping some CWI and a modicum of loft insulation up doesn't go the whole way. You have to pay attention to how it is installed.

I was looking at total carbon savings regardless of where the electricity from the solar PV is used. If you generated 3500 kWh of PV electricity and only managed to use 500 kWh, you'd still export 3000 kWh to the grid and displace the same amount of fossil fuel generation there.

We used 8400 kWh of gas for heating, hot water and cooking in the last 12 months. I have done a lot of insulation upgrades (loft and wall insulation) but there is still a lot to do. About a third of the external wall area has had its insulation upgraded, so there are more cuts to be made.

Ed

Smiley_Dan

If you generated 3500 kWh of PV electricity and only managed to use 500 kWh, you'd still export 3000 kWh to the grid and displace the same amount of fossil fuel generation there.

I'm not sure that's entirely true. The grid has losses. Not sure how much though.

Nice work on your insulation.

zeupater

Smiley_Dan wrote: »

I'm not sure that's entirely true. The grid has losses. Not sure how much though.

Nice work on your insulation.

Hi

Losses should be very small ... the (slightly) higher inverter voltage effectively creates a backflow until someone opens a demand tap, then rushes towards it .... effectively a pv array on one house will feed the nearest demand on the same phase first, then the next nearest, then .... until it's all consumed.

With the current level of pv penetration I'd be surprised if much generation even makes it past the first transformer (caveat - remote properties & areas with high density of installations)

HTH
Z