Green Building Forum - Solar - too many panels? Sun, 08 Mar 2026 18:24:16 +0000 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307761#Comment_307761 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307761#Comment_307761 Mon, 17 Feb 2025 19:29:48 +0000 minisaurus
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 :)]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307762#Comment_307762 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307762#Comment_307762 Mon, 17 Feb 2025 20:40:41 +0000 djh
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:]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307763#Comment_307763 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307763#Comment_307763 Mon, 17 Feb 2025 21:07:45 +0000 Peter_in_Hungary
(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)]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307764#Comment_307764 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307764#Comment_307764 Tue, 18 Feb 2025 06:22:17 +0000 philedge
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.]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307765#Comment_307765 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307765#Comment_307765 Tue, 18 Feb 2025 06:43:07 +0000 minisaurus
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?]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307766#Comment_307766 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307766#Comment_307766 Tue, 18 Feb 2025 08:24:57 +0000 fostertom Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307767#Comment_307767 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307767#Comment_307767 Tue, 18 Feb 2025 10:20:54 +0000 Peter_in_Hungary Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307768#Comment_307768 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307768#Comment_307768 Tue, 18 Feb 2025 12:40:28 +0000 djh
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.]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307769#Comment_307769 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307769#Comment_307769 Tue, 18 Feb 2025 13:12:23 +0000 fostertom
Any better reasons against?]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307770#Comment_307770 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307770#Comment_307770 Tue, 18 Feb 2025 13:29:34 +0000 philedge Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307771#Comment_307771 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307771#Comment_307771 Tue, 18 Feb 2025 15:21:14 +0000 Peter_in_Hungary 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.]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307772#Comment_307772 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307772#Comment_307772 Tue, 18 Feb 2025 15:50:25 +0000 revor 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.]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307773#Comment_307773 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307773#Comment_307773 Tue, 18 Feb 2025 16:45:34 +0000 minisaurus Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307774#Comment_307774 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307774#Comment_307774 Tue, 18 Feb 2025 17:24:09 +0000 fostertom Posted By: philedgeReasons not to optimise for winter is to maximise generation when the wind isn't blowingBut 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.]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307775#Comment_307775 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307775#Comment_307775 Tue, 18 Feb 2025 18:10:30 +0000 philedge
Do we load shed solar in the uk??]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307776#Comment_307776 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307776#Comment_307776 Tue, 18 Feb 2025 20:37:10 +0000 fostertom Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307777#Comment_307777 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307777#Comment_307777 Wed, 19 Feb 2025 13:49:57 +0000 andrew_rigamonti Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307778#Comment_307778 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307778#Comment_307778 Wed, 19 Feb 2025 14:03:01 +0000 philedge Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307779#Comment_307779 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307779#Comment_307779 Wed, 19 Feb 2025 15:47:51 +0000 djh 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.]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307780#Comment_307780 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307780#Comment_307780 Wed, 19 Feb 2025 15:58:07 +0000 fostertom
Agree, we're talking about curtailment, not load shedding.

andrew_r makes sense, above.]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307781#Comment_307781 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307781#Comment_307781 Wed, 19 Feb 2025 16:31:22 +0000 sgt_woulds
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!]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307782#Comment_307782 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307782#Comment_307782 Wed, 19 Feb 2025 18:30:13 +0000 fostertom 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 .... ?]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307783#Comment_307783 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307783#Comment_307783 Wed, 19 Feb 2025 19:40:52 +0000 djh Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307784#Comment_307784 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307784#Comment_307784 Wed, 19 Feb 2025 23:08:22 +0000 fostertom Posted By: djhthe economic models for all these possible ways to use excess electricity usually depend on a constant supply of electricityexcept making hydrogen out of any excess?]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307785#Comment_307785 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307785#Comment_307785 Thu, 20 Feb 2025 06:24:30 +0000 Gareth J Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307786#Comment_307786 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307786#Comment_307786 Thu, 20 Feb 2025 11:00:51 +0000 minisaurus Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307787#Comment_307787 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307787#Comment_307787 Thu, 20 Feb 2025 11:02:56 +0000 minisaurus Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307788#Comment_307788 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307788#Comment_307788 Thu, 20 Feb 2025 12:45:51 +0000 djh 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.]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307789#Comment_307789 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307789#Comment_307789 Thu, 20 Feb 2025 12:47:27 +0000 djh 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.]]> Solar - too many panels? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307790#Comment_307790 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18263&Focus=307790#Comment_307790 Thu, 20 Feb 2025 12:47:59 +0000 owlman
As djh pointed out above the correct term is curtailment; the deliberate reduction of output in order to balance supply.

edit; cross posted.]]>