Solar Panel Guide Discussion

Martyn1981

Sirlaughalot wrote: »

Hi Martyn,

All three companies have surveyed the roof and supplied quotes accordingly. On a postive note they all agree on orientation around 230 degrees(S/W) on a roof pitch of 35 degrees and there are no shading issues:rotfl:.
But that`s where the consensus ends, to get 4k two of the sales man said i would need to spread the solar panels over 2 roofs but doing this would produce a drag effect which would be counter productive. The third sales man said that this is not the case.

Who`s right?

SL

Hiya SL. No.3 is right, if done properly. Or more correctly, if the installer wants to do it properly. (Back to this in a bit).

SW orientation is great news at around 860kWh's per kWp installed (again just a random pin in Birmingham). So will depend on how much can go up on that roof. If the SW can take 3 or 3.5 then might not be worth installing a small amount on another roof. Alternatively, if the roof can only take 2.5 then might be worth trying to max out install with another roof. You could even go over 4kWp total, especially if split system as you might not need to go any bigger with the inverter - I'll explain more if this is an option, but the FIT rate for 4-10kWp is 10% lower.

So obvious questions are, how much can go on the SW roof?
What orientation is the 'other' roof, is it opposite, so 50d (NE)? If so then that's only 600kWh's per kWp. Not very good, but definitely worth considering if in addition to a SW roof. What do I mean .... well if the installers are already there, and all the fixed costs are already in the mix, so adding some extra panels means they are cheaper ... but less efficient. Think £4k for 2kWp, or £6k for 4kWp - the extra panels 'only' add 50% to the cost, so generation of 50%+ is possibly acceptable.

Back to drag. All panels on a single string must, must, must be at the same orientation, pitch, shade, type etc as each other, otherwise the lower performing panels will seriously drag down the others. This is very important, but easily solved. A dual MPPT inverter would treat the two roofs almost as separate systems eg 2.5kWp SW + 1.5kWp NE (a SMA SB3600 TL-21 for instance).

Another option, if there was varying shade (which you say isn't a problem) would be micro-inverters or power optimisers on each panel. So there are solutions.

Not wanting to criticise your installers, especially the third, but since you don't have a due south 4kWp sized roof, you need a company that considers all your options, not one that just wants to throw a system up on the easiest roof, if that means ignoring an alternative/additional option. Did no.3 fill you with confidence, if so, then discuss the options, and slap the info on here for comments. Any prices?

Mart.

Sirlaughalot

Thanks Martyn,

Will be back with indiviual prices later but none would quote below £6K are you familiar with REIGA and is the accreditation worth the paper it is written on?

SL

Martyn1981

Sirlaughalot wrote: »

Thanks Martyn,

Will be back with indiviual prices later but none would quote below £6K are you familiar with REIGA and is the accreditation worth the paper it is written on?

SL

Sorry, don't know much about them. Having clicked on the link supplied by the Green Hornet, and read their 'front page' it certainly sounds good, but I don't know how those guarantees work. Could be from membership fees, or possibly more likely individual warranty insurance policies purchased against each install.

You could e-mail them and ask, and also ask the EST, and see if you get matching stories.

[Edit: Prices - could be that the tariff war with China is starting to take effect. There's a company further north of you that I started to keep an eye on as they once posted on here (about 6 months ago) with some very good info on large systems and PV economics. So I've been following their blog and prices.

I notice that they've recently increased their example price for a 4kWp Hyundai (all black) system to £6.6k. So not great news. M.]

Mart.

John_Pierpoint

I noticed that the insurance operation had signed up several branches of "The Mark Group" - they were the firm where the "surveyor" turned up and generated several quotations, depending on how many resellers you had asked for a quote (eg Tesco) Not exactly a fly by night firm, though the fiasco created by The Green Deal must be damaging everyone in the "eco" industry.

Sirlaughalot

Martyn1981 wrote: »

Sorry, don't know much about them. Having clicked on the link supplied by the Green Hornet, and read their 'front page' it certainly sounds good, but I don't know how those guarantees work. Could be from membership fees, or possibly more likely individual warranty insurance policies purchased against each install.

You could e-mail them and ask, and also ask the EST, and see if you get matching stories.

[Edit: Prices - could be that the tariff war with China is starting to take effect. There's a company further north of you that I started to keep an eye on as they once posted on here (about 6 months ago) with some very good info on large systems and PV economics. So I've been following their blog and prices.

I notice that they've recently increased their example price for a 4kWp Hyundai (all black) system to £6.6k. So not great news. M.]

Mart.

Thanks mate.

The organisation is based on membership fee`s before i give details of the first quote from company A all three that quoted gave quotes based on a SAP standard which they say significantly underestimated the potential yield but when their figures were put into the EST calculator there figures were somewhat over estimated compared to the EST model!

But to be fare to all three companies proposed to make up any shortfall in their quotes for YR1.

Can you explain the big difference in yield values BST vs companiey quotes?

SL

Martyn1981

Sirlaughalot wrote: »

Can you explain the big difference in yield values BST vs companiey quotes?

SL

In a word .... no!

But I can take a few guesses. The problem is, you said that they were quoting against SAP, so their quotes should be very similar to each other (are they?) and also to the EST, as I believe they are using SAP too.

I just did a quick test for my house and a 4kWp system at 110d or -70 azimuth and got:
PVGIS climate - 3,370
EST - 3,081

Then tried due south and got:
PVGIS climate - 3,820
EST - 3,535

Next I stuck a pin in Sheffield, where the solar research centre is and SAP figs are based, and got 3,550 - remarkably similar, so looks like EST are just using SAP figures, so will understate for locations south of Sheffield and over-state for north of Sheffield.

BTW Birmingham, almost exactly half way between Cardiff and Sheffield showed 3,710.

I hope I'm not speaking out of turn for others, but the PVGIS figures, especially the climate model, that has now replaced the older one, appears to be very accurate. Obviously solar levels and generation will vary, so this is only an anecdote, but last year I got 99.4% of target, and as at end of June (with the rest of the year just estimated as average) my generation was predicting 4,231.5 v's target of 4,248 - 99.6%.

So, are the installers using SAP or a newer/different version of it. I gave up on SAP about a year or so back as it's so imprecise. But I'm sure I read something about the single SAP calc being replaced by a set of regional ones, possibly 20+. I might be making this up, but could the installers be using a more local/accurate SAP calculation than the EST is using????

Sorry for all the guesses.

The best thing you can do is have a play with PVGIS and see how your results compare to the installers. Send me a PM if you have any problems and I'll work it out for you / walk you through it.

Mart.

Sirlaughalot

Martyn1981 wrote: »

In a word .... no!

But I can take a few guesses. The problem is, you said that they were quoting against SAP, so their quotes should be very similar to each other (are they?) and also to the EST, as I believe they are using SAP too.

I just did a quick test for my house and a 4kWp system at 110d or -70 azimuth and got:
PVGIS climate - 3,370
EST - 3,081

Then tried due south and got:
PVGIS climate - 3,820
EST - 3,535

Next I stuck a pin in Sheffield, where the solar research centre is and SAP figs are based, and got 3,550 - remarkably similar, so looks like EST are just using SAP figures, so will understate for locations south of Sheffield and over-state for north of Sheffield.

BTW Birmingham, almost exactly half way between Cardiff and Sheffield showed 3,710.

I hope I'm not speaking out of turn for others, but the PVGIS figures, especially the climate model, that has now replaced the older one, appears to be very accurate. Obviously solar levels and generation will vary, so this is only an anecdote, but last year I got 99.4% of target, and as at end of June (with the rest of the year just estimated as average) my generation was predicting 4,231.5 v's target of 4,248 - 99.6%.

So, are the installers using SAP or a newer/different version of it. I gave up on SAP about a year or so back as it's so imprecise. But I'm sure I read something about the single SAP calc being replaced by a set of regional ones, possibly 20+. I might be making this up, but could the installers be using a more local/accurate SAP calculation than the EST is using????

Sorry for all the guesses.

The best thing you can do is have a play with PVGIS and see how your results compare to the installers. Send me a PM if you have any problems and I'll work it out for you / walk you through it.

Mart.

No the figures are all different, partly my fault as i asked for systems upto £6000. Quote 2 seems to have mentioned every system known to man but to get 4K needed to stagger 16 panels across both roofs costing £7400. As Quote 3 would supply 4k from 12 panels on one roof for a similar price i will ignore quote2.

A generall question to all MSE users who have had solar panels installed did any of the energy/fit savings over yr1/yr2 meet the installation companies estimate?

EST figures are freely available but where can you get the fore mentioned PVGIS figures from?

SL

orrery

Sirlaughalot wrote: »

A generall question to all MSE who have had solar panels installed did any of the energy/fit savings over yr1/yr2 meet the installation companies estimate?

ISTR the estimates being based on some 'standard' formula. I'm very comfortably exceeding these.

tunnel

Sirlaughalot wrote: »

No the figures are all different, partly my fault as i asked for systems upto £6000. Quote 2 seems to have mentioned every system known to man but to get 4K need to stagger 16 panels across both roofs costing £7400. As Quote 3 would supply 4k from 12 panels on one roof for a similar price i will ignore quote2.

A generall question to all MSE who have had solar panels installed did any of the energy/fit savings over yr1/yr2 meet the installation companies estimate?

EST figures are freely available but where can you get the fore mentioned PVGIS figures from?

SL

Try Here

http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php#

Pin your location on the map and add a few extra bits of info, ie system size and direction and click climate(drop down box at top) and away you go. You'll soon get the idea.

John_Pierpoint

I exceeded - I am off due south by 42 degrees in a SE direction

https://forums.moneysavingexpert.com/discussion/comment/59448301#Comment_59448301