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General: Solar - too many panels?

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    • CommentAuthorminisaurus
    • CommentTimeFeb 17th 2025
     
    I post this in the hope of helping others.

    Here in Sweden, I think we can say we were perhaps misadvised (ripped off?) when we installed our solar panels.
    The recommendation was - fill the entire roof! - so 11 kW effect it became.
    And in a way the advice was correct - last year we bought 8.5 MWh and produced 9.2 MWh (sold approx 7 MWh). Great! Yet we paid circa £1500 for incoming electricity, saved £350 on not buying, and received maybe £30 for selling ...

    We have no battery, and only electric energy (no gas, no stove, no pellets, no district heating), so when we really need electricity (nov, dec, jan, feb), we're not producing much.

    In summer, when we have no need for space heating, we use around 15 kWh/day. Yet we'll produce up to 70 kWh and give almost all of it away on the Nordpool market, at prices of maybe 10-20p/kWh

    Obviously a battery would help a little with this situation, but from April to Sept we're nearly always producing at least double our need, and at a time of the day when loads of other people are producing electricity. If we had a Nordpool hour-price tariff, and it was windy, we'd often have to pay to export our electricity on a sunny May day!

    In winter we can use up to 50 kWh a day, but produce almost nothing, and it doesn't feel like e.g. a 10 kWh battery would make a massive difference to things.

    So, my tip would be, if purchasing panels, just buy enought to cover your requirements on a sunny April day :)
    •  
      CommentAuthordjh
    • CommentTimeFeb 17th 2025
     
    Interesting - thanks for posting. :) Our situation here in the UK is similar in some respects but different in others ...

    We're all-electric and also have no battery. We have 4 kWp as I suspect many other people do, because that's the maximum you can fit (well 3.68 kW actually) without applying for a licence from your local electricity distributor (DNO). Our electricity demand is a bit less than yours - last month we used 363 kWh during the days (12 kWh/day) and 904 kWh at night (29 kWh/day). Almost all heating, both space and water, and car charging is done at night because of our E7 tariff. Estimated total import over the year is 52 MWh. For the six warmest months we import an average of 7.5 kWh/day.

    We get paid under the old FIT scheme here at 19.7p/kWh generated plus 7.14p/kWh for 50% 'deemed' export. That is nobody actually measures how much we export, it's just assumed that it is 50% of what we generate. For imports we pay 28.23p/kWh during the day and 12.15p/kWh at night. Plus a standing charge of 46.09p/day.

    As regards batteries, the argument seems to be either buy a battery to cover usage during the 'dirtiest' hours from 1630-1930, or buy one to charge cheaply during the night and export during the day at a better rate. Or both of course. That involves getting a battery and getting a (working!) smart meter and changing to a suitable tariff. Maybe I'll do it one day. Maybe I'll buy a heat pump one day as well :bigsmile:
  3.  
    We have a more advantageous system here. If you install PV without grant aid (as we did) you are on an annual reconciliation, annual import set against annual export and the excess in which ever direction is paid or charged. This is guaranteed for 10 years when the system changes to monthly reconciliation. For us that is another 8 years but the rules might change by then anyway. So we have a roof full of PV, no battery, an EV, do the summer DHW on the PV (winter DHW on the wood burner) and supply the home and farm electric power. Last year they paid us a bit over 10 quid on the year.

    (for grant aided PV you are on monthly reconciliation straight away and you are required to have a battery under the terms of the grant)
    • CommentAuthorphiledge
    • CommentTimeFeb 18th 2025
     
    I think the benefits of PV vary wildly from person to person and their circumstances and aims.

    Panels are cheap but labour isn't so if you've got an installer coming to install PV it's probably cost effective to fit as much as you can whilst they are there and the scaffolds up. DNO restrictions are on export controlled by the inverter not the generating capacity of the panels. Many inverters will allow DC input power well in excess of their rated power which can give increased usable power away from peak summer months.

    For us, our annual export cost will likely offset the bulk if not all of our import cost even at different import export rates so well worth the investment for us but that's in the UK with a certain supplier, with a specific array size, specific useage and specific investment all of which will likely vary alot for others.
    • CommentAuthorminisaurus
    • CommentTimeFeb 18th 2025
     
    Hm, yes the Swedish situation doesn’t really help low level consumers such as us. Such a shame, we thought we were doing the right thing, but will have 32 years pay-off at current prices.

    A thought occurred - maybe my 32 panels & 11 kW give me the same effect on a cloudy April day, as e.g. 4 panels in June?
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      CommentAuthorfostertom
    • CommentTimeFeb 18th 2025
     
    I can't understand why installations are always angled and oriented to produce max output over the whole year, even tho that means producing much more than can be used, at pathetic financial return, during summer months. Why not instead orientate for max mid winter production, or if that's even then too small to be useful, optimise for some well-considered spring/autumn date?
  7.  
    The majority of domestic PV is on roofs which constrains the orientation to roof direction and angle sometimes forcing split arrays for N/S ridge lines or hipped roofs. The few domestic ground based arrays have a better chance of selective orientation but even there small plot sizes, trees and adjacent buildings can have an impact.
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      CommentAuthordjh
    • CommentTimeFeb 18th 2025
     
    As Peter says, the angles and orientation are determined by the roof geometry, not by any output planning. Ours faces due south because the house does, and there's three rows all at different angles because the roof is curved.

    Yes, the DNO limits are for export, but at the time we installed there was no sensible means of measuring that other than a separate meter, with the expense and financial inducements in FIT not to bother. Things are probably different now.
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      CommentAuthorfostertom
    • CommentTimeFeb 18th 2025
     
    Yeah about the roof(s) you're given, but if the optimisation was re-thought, for example panels could be propped to nearer vertical, possibly bracketed off walls instead of roofs. South, and high up, would become much more essential. Overall, the look would be distinctively different.

    Any better reasons against?
    • CommentAuthorphiledge
    • CommentTimeFeb 18th 2025
     
    Reasons not to optimise for winter is to maximise generation when the wind isn't blowing. Might not be optimal for personal gain but may be better for overall societal emissions??
  11.  
    Posted By: fostertomYeah about the roof(s) you're given, but if the optimisation was re-thought, for example panels could be propped to nearer vertical, possibly bracketed off walls instead of roofs. South, and high up, would become much more essential. Overall, the look would be distinctively different.

    Any better reasons against?

    Any better reasons against? Hmm - demands of planning permission and the foibles of permitted development.
    • CommentAuthorrevor
    • CommentTimeFeb 18th 2025
     
    @ minisaurus.
    Have a look at the detail of the controls of your inverter. Mine (a Delios) you can set export to min 0, to max 6kWh. You may need a password to get at the menu it resides, usually the installer will set this value to the maximum your distributor will allow. At least if you can then set it too zero if you are in a pay to export time slot. I guess most inverters will have this control as the installer has to set the system up to conform.


    Posted By: Peter_in_HungaryThe majority of domestic PV is on roofs which constrains the orientation to roof direction and angle sometimes forcing split arrays for N/S ridge lines or hipped roofs. The few domestic ground based arrays have a better chance of selective orientation but even there small plot sizes, trees and adjacent buildings can have an impact.


    A friend has 17kw of panels but maximum at anyone time is about 7kWh generation. He made use of practically every part of the roof so he his generating most of the day. They are inset panels so some of the cost was saved by having less slates.
    • CommentAuthorminisaurus
    • CommentTimeFeb 18th 2025
     
    @revor - thanks for the tip, I'll have a look if we go down that road - it's solar edge, there's a local webapp, I have the password somewhere ... For now, we're avoiding hourly prices, we pay and receive a "monthly average" of nordpool's prices, so can avoid negative prices so far ...
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 18th 2025 edited
     
    Posted By: philedgeReasons not to optimise for winter is to maximise generation when the wind isn't blowing
    But if that means optimising for summer, that's too frequently into load-shedding conditions, so then def not
    Posted By: philedgebetter for overall societal emissions
    Society needs all the renewable generation it can get in winter, even if it's windy at same time as winter-sunny.
    • CommentAuthorphiledge
    • CommentTimeFeb 18th 2025
     
    If you've got a resource such as a solar panel then I'd have thought it would be better to use it in conditions where you get the most benefit from the resource so set up for sunnier times?? All the solar farms I've seen are set up as such.

    Do we load shed solar in the uk??
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 18th 2025
     
    No, because UK solar is too fragmented to be feasible, so wind has to carry all the shedding of renewables - a lot.
  17.  
    The important point is that cost is in steps, the inverter is often key. I use a Growatt inverter, it wasn't much more cost to get one that that can handle 6KW of panels, even though I can only supply 4kw to the grid. So with the extra panels it was only a few hundred pounds to get 50% more generation outside summer (when it doesnt generate over 4kw). I got a battery as it was only a few hundred more for the hybrid inverter. That works well in the UK as I can charge it at cheap rate over night to use the cheap elec in the morning. In the UK, if you have the space then add it. I do agree, we should all get paid more for generation, if you have neighbours, what you generate deosn't even hit the grid, its used by them.
    • CommentAuthorphiledge
    • CommentTimeFeb 19th 2025
     
    PVGIS tells me that a 4kwp system at our location will produce 3865kwh a year at 35 degrees or 2828kwh at 90 degrees(vertical) so there seems to be quite an annual loss if panels are set up for winter production. If we're not load shedding solar and Gridwatch suggests we're not load shedding wind in the summer either, then it seems to me that we'd get best bang for buck out of solar by setting up for best year round production.
    •  
      CommentAuthordjh
    • CommentTimeFeb 19th 2025
     
    Posted By: philedgeGridwatch suggests we're not load shedding wind in the summer either,
    Could you provide a link to the figures please? I'm having trouble finding them.

    When you say 'load shedding wind' I presume you mean curtailing wind generation? Load shedding seems to mean disconnecting customers?

    According to https://www.telegraph.co.uk/business/2024/12/02/britain-paying-wind-farms-record-1bn-to-switch-off/ "The amount of wind power “curtailed” in the first 11 months of 2024 stood at about 6.6 terawatt hours (TWh), according to official figures, up from 3.8 TWh in the whole of last year."

    Curtailment seems to be mainly enforced on Scottish onshore wind farms, because of the transmission system limitations, going up to 30% in some cases.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 19th 2025
     
    In Devon/Cornwall in summer, turbines, whole windfarms, are v frequently stationary.

    Agree, we're talking about curtailment, not load shedding.

    andrew_r makes sense, above.
    • CommentAuthorsgt_woulds
    • CommentTimeFeb 19th 2025
     
    Ideally we should have as much overgeneration as possible to force more storage onto the grid.

    Use excess for steel smelting and aluminium recycling.

    Cheap green electricity would allow for more cost-competitive manufacturing in the UK - viva la green revolution!
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 19th 2025 edited
     
    Posted By: sgt_wouldsUse excess for steel smelting and aluminium recycling.
    Unfortunately, suddenly finance for unlimited growth of data centres for AI is going to talk louder than hydrogen storage, green steel and aluminium, for any surplus. Still, perhaps AI is going to make everything more efficient .... ?
    •  
      CommentAuthordjh
    • CommentTimeFeb 19th 2025
     
    Sadly, the economic models for all these possible ways to use excess electricity usually depend on a constant supply of electricity rather than an intermittent supply only available when there's excess generation. That includes most storage facilities. And sometimes on a supply of labour that's available elsewhere than near the generation. So improving the transmission network is really the only way to deal with the problem.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 19th 2025
     
    Posted By: djhthe economic models for all these possible ways to use excess electricity usually depend on a constant supply of electricity
    except making hydrogen out of any excess?
    • CommentAuthorGareth J
    • CommentTimeFeb 20th 2025
     
    I don't get why you're only getting £30 for selling if your selling at 10-20p/kWh. If selling 7000kwh @ 10p, you should be getting £700, not £30...?
    • CommentAuthorminisaurus
    • CommentTimeFeb 20th 2025
     
    @Gareth J - good question, I get Swedish kronor, so it could be my conversion was erroneous. We get very little money, that I know - one portion from the “market”, another from the local provider. I’ll get the real figure and convert to sterling :)
    • CommentAuthorminisaurus
    • CommentTimeFeb 20th 2025
     
    What is load shedding?
    •  
      CommentAuthordjh
    • CommentTimeFeb 20th 2025
     
    Posted By: minisaurusWhat is load shedding?
    Cutting off some customers when there isn't enough generation to supply everyone, in order to avoid crashing the whole grid. In this country it'susually done with specific large consumers of electricity - they're basically paid to take an extra holiday. There have also been recent cases where domestic customers are paid to reduce electricity use at particular times. In some countries, whole areas are cut off.
    •  
      CommentAuthordjh
    • CommentTimeFeb 20th 2025 edited
     
    Posted By: fostertom
    Posted By: djhthe economic models for all these possible ways to use excess electricity usually depend on a constant supply of electricity
    except making hydrogen out of any excess?
    What makes hydrogen-making special? Why does the cost of that equipment not need amortising like every other application? Plus the best schemes I've seen suggested also depend on a specific location, where there's sufficient underground storage, so you still need to beef up the transmission network to that location.
    • CommentAuthorowlman
    • CommentTimeFeb 20th 2025 edited
     
    It's a process when demand exceeds supply and and load is "managed" by e.g. switching off certain loads etc. thereby limiting demand.

    As djh pointed out above the correct term is curtailment; the deliberate reduction of output in order to balance supply.

    edit; cross posted.

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