Solar Panels UK - is it worth it?

[Pink Duck]

It was happily charging up overnight for Flux with 8 p/kWh export and 18 p/kWh supply, but there was the opportunity to sell at 32 p/kWh later, a 13 p/kWh gain. Perhaps 8 p/kWh gain is below its threshold to overcome 10% AC-DC-AC conversion loss.

 

[phil4]

I'm not sure either. I had mine set as you'd expect 30p import, 15p export, and then super off peak, same 15p export, 7.5 import... but no, wouldn't charge. Changed that super off peak export to 0, and it happily filled itself. I've seen others have had the same issue and made the same change, so it's not just me.

Good luck.

 

[Pink Duck]

It might be that they test if the gain from import then export in super off-peak equals that from exporting in the other period. If so, I could try setting sell price overnight to 14 p/kWh for a 1 p/kWh arbitrage gain to discharge in peak. Though with 6 hours there’s time to fully discharge than charge up again for a daily profit, but perhaps they disapprove of that sort of handling as en masse it is inefficient use of energy.

If calculation is simply export minus import then 7-15 = -8 p, and 7-0 = 7 p, being positively less than 15-7 = 8 p, is why zero works to trigger arbitrage.

Might even be a Tesla app bug if they haven’t considered this unusual case where export pays more than import in a period and use unsigned value.

 

[phil4]

Might even be a Tesla app bug if they haven’t considered this unusual case where export pays more than import in a period and use unsigned value.

That's my theory also.

 

[Pink Duck]

Another theory: Since PW2 went to 100% under Flux overnight rate of 18.46 p/kWh, perhaps they consider the energy within as bundles tagged with cost. So it only makes sense for now to discharge instead of day time peak rate (31 p/kWh), as that represents a saving. Once 0% it might reinitialise and start charging from cheapest source (overnight). Hopefully not draining then using grid without PV excess. If so I'll call their UK support line (+44 1628 450630).

 

[ringi]

Octopus should have made export be the same as import for fixed overnight cheap rate time. They should also have had export a little higher between 3pm-7pm so people who are export limited at peak solar times try to empty batteries at peak grid demand times.

 

[phil4]

Octopus should have made export be the same as import for fixed overnight cheap rate time. They should also have had export a little higher between 3pm-7pm so people who are export limited at peak solar times try to empty batteries at peak grid demand times.

You're assuming people can export from battery. You might be able to. I can't.

 

[Pink Duck]

Probably toying about with a new time of use period with very high export reward could force it to discharge, but I’d prefer to stay out of falsehood territory on training its behaviour. Could do with a 'Bump Discharge' button for certain niche situations.

If Octopus want to get more export at peak then they need to do something about their Flux tariff pricing.

 

[yessuz]

Also remember, that power from batteries is seen as "brown" as in many cases you can top up these during off peak while there is no sun and very little wind and it is produced by coal/gas mostly.

 

[Pink Duck]

UK coal is thankfully usually 1–3% (plus that hidden in imports), so it’s often 45% gas overnight and those transformer/transmission losses.

 

[yessuz]

UK coal is thankfully usually 1–3% (plus that hidden in imports), so it’s often 45% gas overnight and those transformer/transmission losses.

well, uk coal is just Ratcliffe most imports are from France (nuclear) anyway.

 

[Pete UK]

Also remember, that power from batteries is seen as "brown" as in many cases you can top up these during off peak while there is no sun and very little wind and it is produced by coal/gas mostly.

 

[Pete UK]

Only some electricity suppliers say its “brown” electricity” - to avoid paying decent export rates.

For Octopus customers it should be seen as “super, extra green+” as it’s from them - sold as green energy, plus a bit of solar added and then it’s concentrated into “super, extra green+” electricity because of the efficiency losses

 

[Pink Duck]

My PW2 started charging from 0% at 23:31 and stopped charging at 43% as it turned out, enough to match daily forecast need. I found that setting a sale price of 6 p overnight triggered arbitrage, and 0 p doing same by rejecting it as an available export window. The basic maths they do appears to be import + export cost < target period export price. Could argue that if configured with 8 p in and 15 p out that there’s also a 7 p payment to make that 8 + 15 - 7 < 15, but that’s 16 < 15 = false. With fractional, 7.5 p in and 15 p out, then it’s 22.5 - 7.5 = 15 < 15 = false too. Given that 23:30 to 05:30 is peak demand it makes sense to just go the zero route to intentionally avoid discharge plus enable arbitrage.

Ideally just need to make sure export doesn’t clash with pre-conditioning or high consuming home devices.
Have configured an extra mid-peak period of 21:00–23:30 with fictitious 16 p/kWh export rate.

 

[thewishy]

If anybody fancies a laugh, just had a colleague quoted under the Surrey Solar Together scheme. 14 x 425w panels = 5.95kWp.
And they quoted.... a 3kw hybrid inverter. Not even a 3.6kw. Admittedly they can side-bar some of the extra to the battery (3kw charge/discharge), but.. wow... (Single Aspect)

Installer is doubling down, saying that the is designed to match the system and "typical UK weather", but can do a 3.6kw for an extra 50 quid if the buyer insists.

Sanity checking, this is total bullshit right, the "some clipping is fine" argument is between 5 kw and 6kw?

 

[phil4]

Installer is doubling down, saying that the is designed to match the system and "typical UK weather", but can do a 3.6kw for an extra 50 quid if the buyer insists.

Sanity checking, this is total bullshit right, the "some clipping is fine" argument is between 5 kw and 6kw?

Nah, it's rubbish. If they've got shading issues that would reduce the output, then deal with it via optimisers or the like, not by putting a tiny inverter in.

There's no excuse for clipping unless the slightly (and I mean slightly, eg. going from a 5kw- 6kw), smaller inverter has a lower start-up voltage, and hence in winter generates more as it started earlier (and you never reach the peak), there's just no excuse.

The way I see it, get a new installer. The installer should be fitting what you want. If that's not right, for a good reason fair enough (eg. electrical, weight, fitting, size)... but this is just bobbins, like they have a stock of cheap 3kW they need rid of.

 

[thewishy]

Nah, it's rubbish. If they've got shading issues that would reduce the output, then deal with it via optimisers or the like, not by putting a tiny inverter in.

There's no excuse for clipping unless the slightly (and I mean slightly, eg. going from a 5kw- 6kw), smaller inverter has a lower start-up voltage, and hence in winter generates more as it started earlier (and you never reach the peak), there's just no excuse.

The way I see it, get a new installer. The installer should be fitting what you want. If that's not right, for a good reason fair enough (eg. electrical, weight, fitting, size)... but this is just bobbins, like they have a stock of cheap 3kW they need rid of.

Only shading is potentially the depths of winter. There are trees at some (20m?) distance, if the sun is very low.. But you're going to be producing naff all with 45 degree panels at that point anyway...

I've said walk away and report them to the group buy scheme.

 

[Momonga]

Maybe the installer doesn't want the hassle of doing the G99 approval prior to install, which would be required for a 5kw inverter. Doesn't sound good.

 

[yessuz]

Maybe the installer doesn't want the hassle of doing the G99 approval prior to install, which would be required for a 5kw inverter. Doesn't sound good.

so installer could go with G98 and 3.6 kw.

 

[thewishy]

They talked up the delays involved with a G99 during the installation - "3 month of delays minimum" which seems excessive for a 5kw inverter. (G99 Fast Track SGI-3?)

Almost certainly they don't want the do the G99 and are compromising the system as a result