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  • FIRST POST
    • Zarch
    • By Zarch 13th Jun 18, 10:05 PM
    • 51Posts
    • 37Thanks
    Zarch
    Quotes and install questions
    • #1
    • 13th Jun 18, 10:05 PM
    Quotes and install questions 13th Jun 18 at 10:05 PM
    Hi all,

    Three potential locations on the property in Sheffield.
    • Main Roof (maybe 9 panels, 2.7kWp) SW Facing - PVGIS approx 2500kWh
    • Dormer Flat Roof (4 panels, 1.2kWp) - SW Facing (flat) - PVGIS approx 940kWh
    • Rear Extension (3 panels, 900kWp) - E Facing - PVGIS approx 770kWh (gets sun from sunrise, but has shade issues from noon onwards)

    Wife isn't happy about using the dormer as the builders (4 years ago) said the vinyl roof will eventually need replacing.

    After weeks of reading forums etc i'm pretty happy with all the FIT and savings figures i've pulled together. I think I understand them all.

    I've been monitoring my own usage for the last month via an old Current Cost usage meter into a Raspberry PI running measure it and then uploading to PVOutput.

    ** I can post my PVOutput url, not enough posts **

    Electricity bills also confirm approx 3700kWh per year usage.

    Quotes so far
    1. Ikea via Solarcentury - 13 panels 5,600
    2. 'South' installer - 11 x 300w = 3.3kWp (5,200), 11 x 320w = 3.5kWp (5300) Solaredge inverter
    3. 'North' installer (Bisol panels)
    Main roof and Rear Extension (12 panels x 300w = 3.6kWp) - 5470 (plus power optimisers for shade)
    Main roof and Dormer (13 panels x 300w = 3.9kWp) - 5300
    All three locations (16 x 300w = 4.8kWp) - 6350 - quote says permission required

    4. 'Local' installer - hopefully coming next week.

    1. Don't think I will be going any further with Ikea from comments i've read.
    2. This quote is via emails, photos and google maps. No site survey yet, so discussions are on-going.
    3. Again, this from photos and emails etc. They've also gone to the trouble of checking the building plans for the dormer for the flat roof weight bearing.

    Would I be right in thinking both these quotes on the high side? I've seen 4k upwards on here for up to 4kWp systems.

    Both quotes have come back with around 10-11 year break even calculations.
    Which sort of ties in with the spreadsheets i've pulled together using PVGIS/FIT/energy saving etc.

    I think whether the system costs 4k or 5k/6k, it just seems to add a few years to breaking even. Obviously, the cheaper the better.

    Are these private installers open to negotiation? Are these first quotes ripe for discussion?

    Any thoughts on any of the above?

    Cheers.
    Last edited by Zarch; 13-06-2018 at 10:07 PM.
Page 2
    • gefnew
    • By gefnew 3rd Aug 18, 7:25 PM
    • 106 Posts
    • 111 Thanks
    gefnew
    Hi all
    But this could be future proofing for batt install, ev, v2h etc.
    where is the limit.
    regards
    • Zarch
    • By Zarch 3rd Aug 18, 7:58 PM
    • 51 Posts
    • 37 Thanks
    Zarch
    Okay, had a think and yes Pinnks, I agree. 700 is not worth it for just 286kWph extra, even with widely optimistic FIT/usage figures. Obviously unless I can negotiate a price on those 320 panels.

    So the south-west ish (35 orientation) facing panels (Porch (26 degrees tilt), Main Roof (35 degrees) and Dormer (15 degrees)) come in around 3719kWh on PVGIS

    and the east-ish (-29 orientation) facing Extension (29 degrees) around 764kWh PVGIS for the year.

    So could a 5000 inverter be a waste of money too and the DNO to go with it?

    The Extension has big shading issues from noon/1pm onwards. That install is really to get dawn to lunchtime generation only, then its in full shade.

    So come the afternoon the only panels really working will be the SW facing stuff.

    There will probably be a very short timeframe where both sets of panels are getting any/decent sun. Maybe a few hours tops in the summer.

    So will there be enough power to properly drive a 5kWh inverter? Would a 3.68 be more efficient? I'm a bit lost on the technical reasons why here?

    So what is the suggestion? Ask for a quote on the cheaper 300w panels again, but with a 3.68 inverter instead? A quick google suggests about 100 saving retail price 5.0 versus 3.68?

    Suppose it depends if there are any other costs associated with the DNO application and connection to consider?

    Thanks all. Loving the input.
    Last edited by Zarch; 03-08-2018 at 8:56 PM.
    • pinnks
    • By pinnks 3rd Aug 18, 8:48 PM
    • 618 Posts
    • 1,369 Thanks
    pinnks
    Good questions. Take a look at this https://www.dropbox.com/s/6igylwtwqv3gijk/Comparison.pdf?dl=0. It's a couple days during the recent super blue sky days to show my total production and that of each of my two systems.

    Top row is total for each of two days; middle row is my larger WSW-facing system; bottom row is the SSE-facing smaller system.

    So, bottom row - 45 degree roof with real shading issues from the chimney from about 13:30 and then from the ridge itself. In the morning you can see how generation ramps up as the sun comes up and the panels are in full sunlight. As I say, come 13:30 catastrophic. Should have gone SE but that boat has sailed!

    Now middle row. 40 degrees with no shading to speak of. Gets borrowed light until the sun starts edge round to the west of south. Until then the graph is flat at a couple of hundred watts. Then the panels get sun and POW! Lovely bell curve until the sun goes down and no shading issues once the sun comes round.

    So, take that as a guide for your roof areas and you might get some indication of what your production curves might look like.

    If you add those theoretical curves together in your head (yeah, I know) then you will probably find your max production is not much more that 3.68kW even on the best days when you are maxing out on each panel.

    One of the reasons I bit the bullet and had the second, small, system installed was that I was annoyed that I had no generation to speak of in the mornings. I had considered going large and all the things you are thinking of and because of the looming FiT reduction rushed my decision and gave upon the DNO. I was thinking 23 x 330W panels or 7.6kWp. Ended up with 21 x 250W panels at 5.125kWp. The irony is, doing it as two installs was probably slightly more expensive than taking the most expensive panels of the time and going large from the outset, but I'm no longer bitter and twisted as a result of learning with hindsight

    Haha, here's the shading issue with my small system - forgot I posted this a couple of years ago abd just stumbled cross it https://www.dropbox.com/s/2k06xp8bjehyx32/More%20on%20the%20impact%20of%20shading.pdf?dl=0
    Last edited by pinnks; 03-08-2018 at 8:55 PM. Reason: added more links
    Wiltshire - 5.25kWp
    3.5kWp: 14 x Phono Solar 250 Onyx, Sunny Boy 4000TL, WSW 40 degrees, June 2013
    1.75kWp: 7 x Phono Solar 250 Onyx, Sunny Boy 1600TL, SSE 45 degrees, March 2014
    • gefnew
    • By gefnew 3rd Aug 18, 8:50 PM
    • 106 Posts
    • 111 Thanks
    gefnew
    Hi all
    Forget the idea of fits and look to the future of every thing electric.
    • Martyn1981
    • By Martyn1981 4th Aug 18, 7:26 AM
    • 7,223 Posts
    • 11,686 Thanks
    Martyn1981
    One of the reasons I bit the bullet and had the second, small, system installed was that I was annoyed that I had no generation to speak of in the mornings. I had considered going large and all the things you are thinking of and because of the looming FiT reduction rushed my decision and gave upon the DNO. I was thinking 23 x 330W panels or 7.6kWp. Ended up with 21 x 250W panels at 5.125kWp. The irony is, doing it as two installs was probably slightly more expensive than taking the most expensive panels of the time and going large from the outset, but I'm no longer bitter and twisted as a result of learning with hindsight
    Originally posted by pinnks
    That might be where my heart over head nagging voice is coming from, as I did exactly the same as you adding a proportionally very expensive small second system in order to get afternoon/evening generation.

    The good news here, however, is that both options are good sizes, so whatever the decision regrets should be small to none.

    The more I think about it now, perhaps the gain is too small. If the panel jump was say 280Wp to 330Wp (for more money again of course) then that might justify the future proofing, but the 700 here might be better put aside as part of a battery install for the future, where that consumed leccy will make a bigger difference.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • pinnks
    • By pinnks 4th Aug 18, 9:10 AM
    • 618 Posts
    • 1,369 Thanks
    pinnks
    Good point about putting money aside for batteries. I assume the inverters are all "battery ready" these days but if not it might be worth ensuring that whichever size and version is bought has that capability. Might there be other preparatory work that could be done now to make a battery essentially "plug and play" whenever that day comes? I am thinking here wiring, space preparation, isolators and the like....
    Wiltshire - 5.25kWp
    3.5kWp: 14 x Phono Solar 250 Onyx, Sunny Boy 4000TL, WSW 40 degrees, June 2013
    1.75kWp: 7 x Phono Solar 250 Onyx, Sunny Boy 1600TL, SSE 45 degrees, March 2014
    • gefnew
    • By gefnew 4th Aug 18, 10:42 AM
    • 106 Posts
    • 111 Thanks
    gefnew
    Hi all
    Some general info with regards batts and solar.
    maybe of interest on the way you can add at a later date.
    https://www.solarguide.co.uk/solar-batteries#/
    regards
    • EricMears
    • By EricMears 4th Aug 18, 11:33 AM
    • 2,340 Posts
    • 4,098 Thanks
    EricMears
    So, 286kWh expected increase in generation each year, so still about 15 extra FiT and 15 extra own consumption savings equals 30 more return each year, for a spend of 700. I think I know what I would do - haggle or ditch the more expensive one
    Originally posted by pinnks

    A 30 return on 700 is still over 4% in the first year (and no doubt increasing in subsequent years). Whilst that's nowhere near the 13% I'm getting on our system, it's still a lot more than you'd get by leaving it in a savings account.

    So if you have a spare 700, I'd vote for the bigger system
    N Derbyshire.
    4kwp S Facing 17.5deg slope (dormer roof).
    • Zarch
    • By Zarch 4th Aug 18, 11:35 AM
    • 51 Posts
    • 37 Thanks
    Zarch
    Okay, so I had a poke around PV Output for East facing and SW facing systems around my area. I took a look at their best production days and scaled my potential 0.9kWh East panels and 4.2kWh SW panels onto their figures with a bit of maths.

    I came up with the following graph.......

    https://www.dropbox.com/s/mn2jww9uwrztfb2/Solar%20Guestimate.png?dl=0

    So It looks like i'd never really bust the limit of a 3.68kWh inverter as the East and SW panels won't produce at the same time.

    Is this a fair assumption and what you were getting at Pinnks?

    So the question is, DNO aside. Is it better to drive a 3.68 inverter closer to max for more of the time, than have a 5.00 sat there hardly working for large parts of the day?

    What's the best solution there?
    Last edited by Zarch; 04-08-2018 at 11:43 AM.
    • pinnks
    • By pinnks 4th Aug 18, 11:49 AM
    • 618 Posts
    • 1,369 Thanks
    pinnks
    That is exactly what I was thinking and would suggest the smaller inverter running near max will do the job. General consensus seems to be to run inverters hard rather than coasting but I don't know whether that is fact or legend-based.


    Eric makes a good point re investment return of 4%. The only difference of course between PV and bank savings is you can still spent the money in the bank. Pretty much comes down to personal choice I think - have you done your graph with the larger system to see how soon you get to about 2.5kW production in the mornings as that will be when you can run those leccy guzzlers like washing machine or dishwasher. Maybe that will help you decide?
    Wiltshire - 5.25kWp
    3.5kWp: 14 x Phono Solar 250 Onyx, Sunny Boy 4000TL, WSW 40 degrees, June 2013
    1.75kWp: 7 x Phono Solar 250 Onyx, Sunny Boy 1600TL, SSE 45 degrees, March 2014
    • Zarch
    • By Zarch 4th Aug 18, 12:01 PM
    • 51 Posts
    • 37 Thanks
    Zarch
    That is exactly what I was thinking and would suggest the smaller inverter running near max will do the job. General consensus seems to be to run inverters hard rather than coasting but I don't know whether that is fact or legend-based.


    Eric makes a good point re investment return of 4%. The only difference of course between PV and bank savings is you can still spent the money in the bank. Pretty much comes down to personal choice I think - have you done your graph with the larger system to see how soon you get to about 2.5kW production in the mornings as that will be when you can run those leccy guzzlers like washing machine or dishwasher. Maybe that will help you decide?
    Originally posted by pinnks
    I'm not sure 17 x 320w versus 17 x300w is going to make much of a dint in getting me to 2.5kWh quicker. Its approx 7% uplift 300 to 320.

    So added that on to the graph.

    https://www.dropbox.com/s/skslk7y5x3t89vk/Solar%20plus%207%25.png?dl=0
    • pinnks
    • By pinnks 4th Aug 18, 12:09 PM
    • 618 Posts
    • 1,369 Thanks
    pinnks
    yep - does this get you closer to knowing where next? I would wait for comments to come in on the 3.68 v larger inverter
    Wiltshire - 5.25kWp
    3.5kWp: 14 x Phono Solar 250 Onyx, Sunny Boy 4000TL, WSW 40 degrees, June 2013
    1.75kWp: 7 x Phono Solar 250 Onyx, Sunny Boy 1600TL, SSE 45 degrees, March 2014
    • Zarch
    • By Zarch 5th Aug 18, 6:51 PM
    • 51 Posts
    • 37 Thanks
    Zarch
    Have been watching plenty of E and SW facing arrays today on PV Output (SAD!) Plus i've been watching my E facing roof and when the sun hits and shade comes in (sort of noon, 1pm onwards).

    Which has helped me get a better view of how my array could look when installed and the subtleties of my potential 'best' generation graph.

    Here's what i've come up with.

    https://www.dropbox.com/s/y6a86dudiw7w7u2/Guestimate%20v3.png?dl=0

    So I still can't justify the 320w panels over the 300w ones for 700 extra. All this graph shows that really all I will get from 320w panels is more when I'm unlikely to use it, ie when i'm already generation lots! So I think i'm still leaning towards 17 x 300w.

    But what this has showed me is that even on the very best days, like today and other top days that i've found on PV Output for arrays pointing the same directions is that I could probably get away with a SolarEdge 3.68 inverter.

    This could be 100 cheaper, I need to ask the installer. Yes, there would be short periods of the very best days (like today) where i'd be a few hundred Watts down on generation, but I don't think i'd ever get that 100 back.

    Say worst case i'd miss out on 330w for 3 hours each day through the summer. That's 1kW a day for each day missed. So 7.5p (for each kW - edit, its 6.55p!!) i'd miss out on generation and export FIT per day. So i'd need 1,333 days or 44 months to recoup that 100. If my maths is right? Does that make sense? Its only the very tip of that graph above the flat line i'd be missing out on.

    Plus, and this is question I don't know the answer to yet.

    Is driving a 3.68kWh inverter close to or at maximum demand (ie 3.68) more efficient that driving a 5.00kWh inverter at much lower demands (ie 3.68)?

    I've read this was the case with older inverters, but not sure with these new ones.

    The question is the same through the winter when i'm maybe topping out at say 1000w generation. Will the 3.68kWh inverter handle that 27% usage better than the 5.00kWh one at 20%. Or does it matter? The SolarEdge blurb says >99% efficiency and makes no mention of any recommended minimums etc. Anyone know if this is an issue?

    Final question regarding using a 3.68kWh inverter instead of a 5.00kWh one. Am I right in thinking that even though i'd be installing a 5.2kWh panel system, I could swerve the DNO application and any associated costs that come with hooking a larger inverter up because the 3.68kWh inverter limits the amount that goes back to the grid.

    I think I was told or read these charges can now be 300? Did I hear that right? This charge could be what makes a 3.68kWh inverter a no brainer in my config.

    Thanks as always.
    Last edited by Zarch; 06-08-2018 at 11:46 AM.
    • pinnks
    • By pinnks 5th Aug 18, 8:45 PM
    • 618 Posts
    • 1,369 Thanks
    pinnks
    I think the maths is on the right lines but is 7.5p right (I thought it was about 3.9p for generation and 50% of 5p for export - but have not checked). That would be about 6.5p?

    Anyway whatever the pence, the 44 months would be spread over the best days of the best months, so perhaps 3/4 of those days or 75% of 180 days a year. That is 135 days. So your 1333 days would take about 10 years to recoup the cost. If my maths is right.

    On the DNO issue, I think you dodge the bullet as it were if the inverter is 3.6 as that is the max that could be exported notwithstanding the size of the panels. But others will confirm.

    Personally, I think I would opt for the 3.6 inverter - save the 100, save the DNO costs which can be a couple of hundred or more and either save that money or put it towards a diverter or whatever. That is, unless someone could advise me why that would not be the better route...
    Wiltshire - 5.25kWp
    3.5kWp: 14 x Phono Solar 250 Onyx, Sunny Boy 4000TL, WSW 40 degrees, June 2013
    1.75kWp: 7 x Phono Solar 250 Onyx, Sunny Boy 1600TL, SSE 45 degrees, March 2014
    • Martyn1981
    • By Martyn1981 6th Aug 18, 6:44 AM
    • 7,223 Posts
    • 11,686 Thanks
    Martyn1981
    I think I was told or read these charges can now be 300? Did I hear that right? This charge could be what makes a 3.68kWh inverter a no brainer in my config.
    Originally posted by Zarch
    I don't know the exact cost, but that's correct, and your questions about efficiency are certainly true in the past, that a smaller inverter worked harder is more efficient than a large inverter run gently.

    It's not a policy suitable for high sun areas, like Spain, but in the UK, sizing an inverter for 'messy' generation and poor weather is more sensible, especially when every Wh is important first thing in the morning, last thing in the evening, and all through the winter.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • hawkwinddotcom
    • By hawkwinddotcom 6th Aug 18, 11:26 AM
    • 422 Posts
    • 496 Thanks
    hawkwinddotcom
    ofgem figures
    FIT 3.93kWh
    EXPORT 5.24 kWh

    https://www.ofgem.gov.uk/environmental-programmes/fit/fit-tariff-rates
    3.78 kWp PV SolarEdge with iBoost South facing.
    30 pitch roof 4% shading. Installed 6th June 18.
    Gloucester
    • Zarch
    • By Zarch 6th Aug 18, 11:45 AM
    • 51 Posts
    • 37 Thanks
    Zarch
    Originally posted by hawkwinddotcom
    Yep, my mistake not 7.5p, but 6.555p combined per kWh generated and exported.

    1 x 0.0393 + 0.5 x 0.0524 = 0.06555 = 6.5p (or 6.6p if we are rounding up)

    Last edited by Zarch; 06-08-2018 at 7:52 PM.
    • pinnks
    • By pinnks 6th Aug 18, 7:49 PM
    • 618 Posts
    • 1,369 Thanks
    pinnks
    And we all wondered at school what we would do with all those maths lessons
    Wiltshire - 5.25kWp
    3.5kWp: 14 x Phono Solar 250 Onyx, Sunny Boy 4000TL, WSW 40 degrees, June 2013
    1.75kWp: 7 x Phono Solar 250 Onyx, Sunny Boy 1600TL, SSE 45 degrees, March 2014
    • Zarch
    • By Zarch 8th Aug 18, 10:03 AM
    • 51 Posts
    • 37 Thanks
    Zarch
    Can't believe i've not asked this before, but what generation can you expect from panels in full shade?

    These East-ish facing 300w panels i'm hoping to put in will be in full shade from 2pm onwards. So it could still be a bright summers day everywhere else.

    What performance do you get in full shade during the day? Good, bad of indifferent?
    • Dave Fowler
    • By Dave Fowler 8th Aug 18, 11:11 AM
    • 480 Posts
    • 845 Thanks
    Dave Fowler
    Can't believe i've not asked this before, but what generation can you expect from panels in full shade?

    These East-ish facing 300w panels i'm hoping to put in will be in full shade from 2pm onwards. So it could still be a bright summers day everywhere else.

    What performance do you get in full shade during the day? Good, bad of indifferent?
    Originally posted by Zarch
    It depends on the amount of cloud in the sky. If the sky is clear blue and the panels are shaded, there will be very low power production. However on a half and half cloudy day there will be a significant amount of light reflected from the clouds and that will produce a surprising amount of power.

    Dave F
    Solar PV System 1: 2.96kWp South+8 degrees. Roof 38 degrees. 'Normal' system
    Solar PV System 2: 3.00kWp South-4 degrees. Roof 28 degrees. SolarEdge system
    EV car
    Location: Bedfordshire
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