Solar PV Quote seems excessive

groovyf

Ray, I had 16 panels fitted, your 28 panels would of course take longer - hard to calculate extra "man hours".

As for panels on a non-South roof, I don't think I'd've given it serious consideration if not for the PVGIS site. In fact, one installer I had visit for a quote didn't think it worth it on the NE roof, whereas another installer had the opposite opinion and said maximise your roof space... so I did.

Ageing_Stick_Insect

Hi Martin,

I take your point about the fixed costs of scaffolding etc. but using this calculator it doesn't go further north than west which suggests the savings to be made are minimal. http://www.energysavingtrust.org.uk/Generating-energy/Getting-money-back/Solar-Energy-Calculator

I think with your install as you have a gable end the WNW roof was the only option after you had used all the ESE one. My situation is different in that I have two roofs to use and although I cannot reach 4kWh it's pretty close at 3.8.

I will be getting other quotes so once those come in the future should be pretty clear. The Trienergia panels are obviously costly with so many optimisers required but they do maximise roof space.

More in the days to come when I have some quotes.

Thanks tunnel. Clearly the combo of air cond and WNW panels works for you.

Groovy, once I have more quotes (and opinions) it should help with my decision. I just wish I had a different shaped roof!

Martyn1981

Ageing_Stick_Insect wrote: »

Hi Martin,

I take your point about the fixed costs of scaffolding etc. but using this calculator it doesn't go further north than west which suggests the savings to be made are minimal. http://www.energysavingtrust.org.uk/Generating-energy/Getting-money-back/Solar-Energy-Calculator

Hiya.

**Beware the EST**

Their info is always a little iffy. Nothing unusual about only suggesting PV be installed between East and West, some sites say SE to SW. That's why you have to do your own research (ideally with PVGIS) to see that off south is lower, but definitely not minimal.

I had a play with that calculator and a couple of issues jumped out at me.

Firstly the price. they suggest that a 4kWp system will cost about £7,080. That's not too bad, as their examples always used to be about £2k+ over. So if £6k is a good target, £7k isn't a bad site suggestion. Unfortunately, they then go on to suggest:
3kWp £6,430 - bit steep
2kWp £5,770 - getting silly now
1kWp £5,110 - they're aving a laff

Secondly, the leccy savings bit is misleading. For 4kWp it suggests leccy savings of £79. Now, I'll put my hands up as I suggest £80 to £160, so similar to me. But mine are low and high figures (and both are a little pessimistic). The EST haven't said that their figure is low. I'd suggest minimum savings of baseload for an average of 10 hours per day, with say a 20% chance of terrible weather (not bad, but terrible) that drops generation below 150W.

So 150W*10*365*0.8 = 438kWh. At 15p that equals £65.70 as a figure pretty much impossible to not save. The figure then goes up for higher baseload, and up again for daytime, evening and weekend consumption above baseload.

It then gets worse, for smaller systems, they suggest smaller savings:
3kWp £70
2kWp £52
1kWp £26

But applying a bit of logic, even a 1kWp system should meet that minimum baseload most of the time. It's the savings above and beyond as higher consumption items get switched on, that it may not be able to meet.

So, nice tool, but even by my standards, is rather pessimistic.

Mart.

Martyn1981

Hiya Ray. Sorry, just to say, not trying to push you towards 'off-south'. I think those triangles will look pretty good (yes Tunnel, I really do need to get out more) just explaining for others benefit, that PV has a hell of a lot more options than might at first appear.

Have fun. Best of luck with the quotes.

Mart.

Ageing_Stick_Insect

Hi Martin,

Thank you for all those calculations. It's nice to know they err on the pessmistic side.

I've written back to my quoter asking if he considered rectangular panels especially higher output ones recommended by ed yesterday. T'will be interesting to hear what he says.

I've found a MCS certified installer in Cheadle Hulme and have sent a request for a survey. Hope to hear from them soon.

Ageing_Stick_Insect

I entered my details on the PVGIS site assuming a 4kWh system on each of the 3 roofs in turn. I then entered info for a south calculation.

The attached pie chart shows the efficiency of each roof compared to one facing due south. The WNW one is not as bad as I feared. Thoughts?

tunnel

Now you know why myself and Mart both have them. If you check out my signature you'll see I have a system pointing in each of your pie chart segments. Nothing to be scared of, specially as you'd be putting up scaffold for the other rooves anyway.

Ageing_Stick_Insect

Tunnel,

I'm not convinced to be honest. This new chart will explain why.



I think we both agree that few people would mount panels facing due north. But if you did then according to that calculator it would still be nearly 56% efficient compared to them pointing south. And my WNW panels would only be 10.5% more efficient than those pointing north.

That can't be right, surely? Convince me those numbers make sense. Regarding scaffolding, wouldn't I just need more at greater expense rather than them moving one of the other assemblies around to the back of the house?

I'm not trying to be argumentative - honest. Just trying to make sense of these calculators.

EricMears

Ageing_Stick_Insect wrote: »

Regarding scaffolding, wouldn't I just need more at greater expense rather than them moving one of the other assemblies around to the back of the house?

I'm not trying to be argumentative - honest. Just trying to make sense of these calculators.

The big expense with scaffolding is the lorry trip there & back plus wages for the erectors. Having twice as many bits of pipe & planks doesn't double the overall cost - indeed it may make very little difference. But don't take my word for that, get a scaffolder round to quote (though bear in mind that a SP installer would be a regular customer and get better discounts than you would; and they'd only pass on vat at 5% rather than 20%).

Martyn1981

Ageing_Stick_Insect wrote: »

I'm not trying to be argumentative - honest. Just trying to make sense of these calculators.

Don't worry, I know exactly where you are coming from - 'it doesn't look as good as a percentage, so why do it?'.

But the issue is far more complex. For instance, whilst the WNW may not be as good as the SSW, in reality, your SSW is limited by size and shape, giving the WNW a kWp advantage.

Next we have cost. Again, having maximised the 'S' roof(s), and paid for the most expensive kWp's to be installed, it may be worth looking at the 'N' roof(s) if still well shy of 4kWp:

best example is 2kWp on 30d south roof for £4k, giving 100% generation, and
an additional 2kWp on 30d north roof for £2k (additional) giving 60% generation, giving us,

100%/£4k = 25%/£1k
160%/£6k = 26.67%/£1k

whilst the performance drops off, so does the additional cost.

Another way of looking at it, is simply to maximise what you have. Again sticking with a 30d roof example, and choosing my location, for a split roof 180d apart I get:
E/W
E 1,560
W 1,550
T 3,100

SE/NW
SE 1,810
NW 1,240
T 3,050

S/N
S 1,910
N 1,120
T 3,030

Now, based on, use what you've got, an east/west install seems reasonable, and most people (resigned to not having a south roof) would accept it. But the proportionally very low north to south figure, makes a north choice look 'daft' perhaps?

However, look at the totals, and for the same system, location, cost etc, they all generate about the same.

Checking the fall back position on cost, going south only v's S/N works out:

£4k/1,910kWh = £2.09/kWh
£6k/3,030kWh = £1.98/kWh

These numbers improve as you get further from south, such as SE v's SE/NW:

£4k/1,810kWh = £2.21/kWh
£6k/3,050kWh = £1.97/kWh

In your case it gets distorted further as the rooves have different sizes and shapes too. Not relevant to you, but another factor could be unavoidable shade, making the more ideal orientation, less attractive.

Lastly, as Eric said, extra scaffolding shouldn't be proportional. Their main cost is the 4 trips (back and for), and labour from depot to depot. Labour on site, shouldn't be too much more. For my extension the installer was travelling from Rochdale, so he asked me if I could arrange scaffolding, giving me a £500 budget. I got it done for £200 (actually £180 plus 2 cases of lager/beer as a thank you to the guys for a rush job). The scaffolders new the installer (how????) so I got a trade price, and split the saving 50/50, rather than pocket it all.

[Edit: **extra income** PV is use it or lose it. Maximising south generation sounds great, and gets maximum FiT income, but may mean exporting more excess leccy. Having a wider, flatter generation curve, can allow for more consumption and leccy savings, especially later in the day (from a W system) when returning home, or preparing tea/dinner, a consumption that is harder to shift to mid day.]

Time for a new post!

Mart.