, storage battery technology is giving it a 2nd lease of life at least down here in sunny Kent.

I’d like to see a full cost analysis inc CAPEX costs for that. Given most Li-ion packs are only rated for 500 cycles, you could be replacing the batteries before you’ve paid them off….

Just ordered PV cells for the house. With the current FIT alone it will take 12 years to recoup the investment, with energy bill savings more like 6 years. It helps that we have space for a 4kW system pointing directly South for this.

We’re not really doing it for the cost, more for the fact that they’ll repay their CO2 cost in about 2.5 – 3 years.

I don’t understand why saving the planet (and reducing costs)has to have a capitol cost recovery element, you buy a car/bike, you lose money, you never think oh how many bus/train fares I’ve saved.

You buy the battery which sits in the garage alongside the expensive road/xc/dh bike and feel better about yourself, smug actually, until the error messages start and you discover the company that installed it closed the day after you signed off on your installation.

Then Tesla come along and announce their 650b version of your 26″Battery.

I don’t understand why saving the planet (and reducing costs)has to have a capitol cost recovery element, you buy a car/bike, you lose money, you never think oh how many bus/train fares I’ve saved.

The difference is that the car/bike etc allow you to do something that you can’t do without them. Most folks can still get plenty of electricity to their house without panels/batteries etc so there needs to be a different incentive.

I don’t understand why saving the planet (and reducing costs)has to have a capitol cost recovery element

Because if you don’t consider the energy cost of the CAPEX, you’re just fooling yourself. If you buy a system which took 15 tonnes of CO2 to make, but save only 1/2 tonne of CO a year, then it will take 30 years before you’re break even in CO2. If the system only last 25 years, you’ve done no good at all and just increased your carbon footprint.

But replacing like for like will have an energy capex too, so they need to consider that too.

But replacing like for like will have an energy capex too, so they need to consider that too.

of course…

But unless the existing system has died, leaving it alone is probably the best thing to do even if it’s very inefficient.

A Pv panel will generate enough energy to cover its carbon capes in about a year.

Post grad thesis on this subject about 6 years ago by a colleague of mine.

A Pv panel will generate enough energy to cover its carbon capes in about a year.

If that were true, it should also break even without the FIT tariff in the same time. The fact they don’t break even financially, for years (even with subsidies), suggests they won’t break even in CO2 very quickly either (as most of the cost of buying one is the energy cost of making it and transporting it etc).

If that were true, it should also break even without the FIT tariff in the same time. The fact they don’t break even financially, for years (even with subsidies), suggests they won’t break even in CO2 very quickly either (as most of the cost of buying one is the energy cost of making it and transporting it etc).

not really – the financial cost of production is very different to the carbon cost of production. there’s no profit element in carbon terms – there’s huge financial profits on PV panels.

there is a spread in terms of the carbon cost – a norwegian panel like the REC range will be made using lovely carbon free hydro power, a similar chinese panel will have a much greater carbon content.

having said that, a quick google failed to turn the reference i had recalled, but others suggest 2.5-5 years (see CAT, US doEnergy)

But unless the existing system has died, leaving it alone is probably the best thing to do even if it’s very inefficient.

That’s worth repeating.

Get the full life cycle from the existing installation before it’s even worth starting to think about getting a fancy efficient replacement.

A Pv panel will generate enough energy to cover its carbon capes in about a year.

At what latitude? Granted, on the equator, there’s a lot of sun.

IIRC the Chinese panels currently being installed north of the Med have a tough time breaking even over their lifetime. Produced using massively dirty electricity, shipped long distances, lower efficiency, shorter lifetime / reliability levels, vis-a-vis expensive European panels with their higher cash cost.

We have had solar panels for the last three years.

Installation cost was £7000 for a 4kw system, with a device which also heats the water during the day.

Our electricity bill has dropped by about £200 a year.

We usually get paid about £800 a year tax free from the FIT.

This year has been the worst of the three years in terms of energy generated, the sun seems to have gone away.

I look at it this way.

I’ve spent the £7000, and if I had bought a more expensive car, then that money would have depreciated and the car would be losing value and costing me money.

At least this way , my £7000 is providing me with approx £1000 of income each year.
I’m happy with it.

not really – the financial cost of production is very different to the carbon cost of production. there’s no profit element in carbon terms – there’s huge financial profits on PV panels.

Is that the case?

PV panels is a pretty competitive market, so I would expect the net margin to be 5-10% at best.

The gross cost of making one, shipping & installing will be pretty close to the energy cost which is directly proportional to the CO2 cost.

The energy produced by the panel and it’s saving is a saving from not buying energy off the grip which is directly proportional to the CO2 saving.

So if they were break even in CO2 in under a year, I’d expect break even in £ around a similar period (within a factor of 2 ish).

A domestic installation with a FIT rate of the real energy cost exported (ie no subsidy) would take 20ish years to break even. So I can’t see how the CO2 can break even in under a year…

NB I’m not for or against PV, just interested in the Maths…

There’s a lot of mixing units here.
£ are not directly linked to tonnes of CO2

Panels are quite cheap. Cells even cheaper (repeating what I said about weatherproofing).
Installation and certification are the big expenses.

FIT don’t pay as much as you buy a kWh, so you can’t say that the £ are linked to the CO2 for lots of reasons.

£ are not directly linked to tonnes of CO2

It should be roughly proportional overall as most of the cost of doing something is the energy cost involved (in our petro economy)…

I realise it’s a back of the fag packet analysis, hence I’d love to see the real numbers end to end inc all manufacture, installation and transport costs etc for a domestic installation.

FIT don’t pay as much as you buy a kWh, so you can’t say that the £ are linked to the CO2 for lots of reasons.

I thought the FIT rate was more than you buy (or used to be) – or was it set at 50% assuming you used half and exported half?

Some maths:
https://info.cat.org.uk/questions/pv/what-energy-and-carbon-payback-time-pv-panels-uk/

The gross cost of making one, shipping & installing will be pretty close to the energy cost which is directly proportional to the CO2 cost.

The guy we spoke to said that about half the £££ cost of the install is manpower, scaffolding and fixtures/fittings – pretty hard to account for in terms of carbon cost.

Some maths:

No maths, just a few single summary numbers.

The thing which will make a big difference is do they just consider the CO2 cost of a panel or the gross cost of shipping it from China to the UK, storing it, having a local company drive and buy it from a warehouse, store it again, then transport it again to site and install. All of which bump up the cost form a few £ in china to costing £100s installed on a roof (and also bump up the CO2 cost).

Hence, why large scale solar farms make much more sense.

No maths, just a few single summary numbers.

In the pdf reports linked

(in our petro economy)

The problem with that, is that it doesn’t account for people’s living.
i.e. £1000 paid to me for an app design, is seen as the same as burning £1000 worth of fuel in your example. Whereas one sustains a person and one does not. Yes, I consume CO2 as part of my life, but you can’t take them as being one and the same.

Denis99, sure it’s great if you can get a 14% return annually. But the current FIT doesn’t do that, it’s not close. I could have put £7000 on the roof and got about 4% per year and in 20 years the system is (probably) knackered before I even get my money back. Or else I could have bought ARM shares and doubled my money in 6 months, which is what I actually did 🙂

i’m going to backtrack a bit and admit a mistake – i said the pv panel recouped its carbon capex in a year – sorry, i should have said its energy cost. The carbon cost varies by so many factors as pointed out by smart cookies above that i doubt you could ever have a ‘one size fits all’ carbon payback figure.

The wind turbines were done by witch mag a while ago and wernt worth the outlay.

Probably a biased report as they interfered with their broomsticks.
I’m here all week.

captain – you are right about current fits…..

4kw system will generate ~3200kwh/annum. fits is 4.25p, export is 4.91 deemed on 50% of generation. you’ll get

£136 Fits (3200 x 4.25p)
£78 export (3200 x 50% x 4.91p)
£208 saved off energy bill (assuming you use 50% at 13.5p)
£56 if you push excess to hot water tank and offset gas usage (1600 x 3.5p)
£480/annum.

dennis got in at the 21p fit rate IIRC. i did it at the start so get 49p right now. 🙂

theres a pretty good calulator here.

EST PV Fit calculator

500? This is where smart charging and optimised conditioning cycles comes in.

If you just bang in current to 100% and empty it down to cut out (about 3.0v per cell from what i can remember) you might only get 500 cycles, and a hot battery. Thinking a bit more technically, running it from 3.6v to 95% full and keeping the temperature controlled (fans, refrigeration, whatever) might loose a chunk on capacity and efficiency (or you’ll need a bigger battery to get the same capacity) but you can (easily) get to a couple of thousand cycles before capacity (that 95% threshold) is limited by any drop offs in battery performance. And at least another 1000 before it needs replacing.

Having a bigger battery might cost more, but the long term gain is well worth it, especially as you’re effectively unlimited on space and weight, same goes for posh charging equipment and cooling gear. You can steal the excess heat too.

I got mine and the one before that and the one before that without any consideration for CAPEX I did it because I can and if feels the ‘right’ thing to do. I’m not going to lecture y’all about the carbon footprints of your bikes, cars, white goods, kitchens, log burners, wifes shoes, handbags, jewellery, your plasma telly’s the ridiculous wages you encourage by watching soccer, which is just as nonesensical as concerning yourselves with the potential or lack of investment these systems afford, they exist and every kw I generate means I don’t pay the robbing bastard French and I can feel in some small way I’m doing my bit to counter the excesses of others, that is all really. One day I shall get a wind machine if I could find someone knowledgable enough to link it into my battery system and if I could come right off the grid entirely, wouldn’t I be a happy bunny?

This blogpost quotes a study which claims that for temperate latitudes more energy is produced making solar panels than they produce over their lifetime. Then of course the CO2 of production is in the atmosphere now while the CO2 savings will only accrue over the next 20 years or so.

The Energy Return of Solar PV

You need a big, tall turbine, big to get enough wind, tall to get away from roof lines, trees, turbulent flow, noise.

I grew up on a cattle ranch in Nebraska and we didn’t have electric power lines onto the ranch until I was about 5 or so. We had a wind-charger mounted on about a 50 foot tower that fed a big bank of batteries. Wasn’t great, but did provide enough power to run lights, etc. for a few hours each evening. God, am I getting old or what? 🙄

Bizarrely I’m off to Nebraska after Christmas as the power company I work for is based there.

But the install costs, and reading about the FIT dropping and dropping, make me think ‘is it worth it’?

No, if you’re thinking in purely financial terms. But that not necessarily the point, is it?

Thinking a bit more technically, running it from 3.6v to 95% full and keeping the temperature controlled (fans, refrigeration, whatever) might loose a chunk on capacity and efficiency (or you’ll need a bigger battery to get the same capacity) but you can (easily) get to a couple of thousand cycles before capacity

100% DoD 300–500
50% DoD 1,200–1,500
25% DoD 2,000–2,500
10% DoD 3,750–4,700

(table from battery university site)

I think that figures out to get around 50% better total capacity over usable battery life, by using 50% discharge cycles.

95% full is way too much, BTW – charge cutoff at about 80% [4.05V ish] for maximum life, drain down to 30%. Rinse, repeat.

Temperature control isn’t that big a deal for continuous use. Its a problem for long term storage, if that’s part of your use pattern, but for daily cycling like this? Might as well forget about it. The battery will become warm internally from charging & discharging anyway. Incidentally, running a refrigerator to maintain battery temperature to improve battery life by a % or two? You just shot your carbon footprint in the foot…