Bad month for solar generation

[JohnV6]

On grid with batteries and export tarriff.

 

[Everest]

I'm losing track of people here. Are you guys off-grid, without an export tariff?

We're grid-tied, but don't use any grid power for 9 months of the year. Not yet paid for export (work in progress), but we generate much more than we are permitted to export, so can still charge the EV from solar for free.

 

[Rolfe]

Everybody's system seems to work differently!

 

[T1 Terry]

You people are just rubbing in .... we are getting close to the very poor solar mths, May, June, July and sometimes August, the punishment for living so far south I guess, it must get close in winter in sth Tassie, but the BIL seems to get by just fine ..... although, his stove, heating and hot water are through a wood stove, so he only has lights, fridge, water pump and tv to power from the solar .... and he has pelton wheel generator as well when needed.

T1 Terry

 

[decrep]

Yes tapering off here as well. Car's on charge but half the power is from the grid, (it's a little overcast)
I'm not sure of the details, but households here are limited to 6kW systems, ours is only 3kW, I think we need more panels for Winter.

 

[T1 Terry]

Yes tapering off here as well. Car's on charge but half the power is from the grid, (it's a little overcast)
I'm not sure of the details, but households here are limited to 6kW systems, ours is only 3kW, I think we need more panels for Winter.

Put the extra panels on an off grid battery charging system, they can't restrict the capacity for off grid, make up a battery from tired EV cells/modules and use a 2500w inverter and the granny charger ..... or wait until I sort out how to do direct DC charging from the solar and install the number of panels required for an open circuit voltage a bit higher than the pack max voltage .....

T1 Terry

 

[decrep]

our problem here is room, there's a bit of space on the east roof. But not enough to even get to 6kW. Not much point on the South roof.

 

[Rolfe]

You people are just rubbing in .... we are getting close to the very poor solar mths, May, June, July and sometimes August, the punishment for living so far south I guess, it must get close in winter in sth Tassie, but the BIL seems to get by just fine ..... although, his stove, heating and hot water are through a wood stove, so he only has lights, fridge, water pump and tv to power from the solar .... and he has pelton wheel generator as well when needed.

T1 Terry

Stop complaining. You guys have it jammy most of the time. You know how much solar generation I got on New Year's Day? 340 watt-hours.

 

[T1 Terry]

our problem here is room, there's a bit of space on the east roof. But not enough to even get to 6kW. Not much point on the South roof.

Make a gate with rollers that you can move to the desired nth facing direction, then a pivot point to tilt the panels to the best angle .... it's not a fixed solar array .... it's a gate that you are utilising as a spot to mount solar panels ........ I can't claim originality on that one, read it somewhere years ago when a council wouldn't allow him to build a ground mounted solar array

T1 Terry

 

[mg4nick]

Bumper April for me this year with 796kWh Yield (6.5kW solar and 9.6kWh battery system).
April 2024 - 600kWh, April 2023 - 635kWh

I've been discharging the battery to 30% around dawn so that it has room to collect the solar generation that would otherwise be clipped by my 5 kw export limit.

When they designed my system they've planned for a 5kW export limit but I "begged" them to install the "strongest" inverter in the series (Solis RHI-6K-48ES-5G which happened to have a 6kW max grid output power).
The initial DNO letter had the 5kW limit set but after pointing out that the inverter can do more they've gone back to the DNO and I now have an updated letter with a 6kW limit (it took about 8 months to get the updated version).
I suspect the inverter had to dissipate the extra energy as heat (obviously very wasteful and turning the garage into an oven in the middle of summer).

Maybe you can talk to your installer to get you an updated DNO letter...

 

[Everest]

The initial DNO letter had the 5kW limit set but after pointing out that the inverter can do more they've gone back to the DNO and I now have an updated letter with a 6kW limit (it took about 8 months to get the updated version).

Normally, the installer would apply to the DNO for the maximum output of the inverter on a G99 application and the DNO will either permit it, or restrict the limit via G100 compliant export power limitation. The reason for limiting export power is down to the topology of the existing grid connection and number of other houses exporting on your phase - so unless that has changes, I'd be surprised if a DNO would increase a limit already applied.

I suspect the inverter had to dissipate the extra energy as heat (obviously very wasteful and turning the garage into an oven in the middle of summer).

Not quite.... when an inverter limits its output power it simply generates less. The Solis does this by reducing the current drawn from the highest current delivering string on one or more of its MPPT inputs. It doesn't generate unwanted power to then dissipate.

 

[mg4nick]

Not quite.... when an inverter limits its output power it simply generates less. The Solis does this by reducing the current drawn from the highest current delivering string on one or more of its MPPT inputs. It doesn't generate unwanted power to then dissipate.

Well - that is good to know. I really hope the Solis inverter is smart enough to do that. I think I noticed at the time a drop in the inverter operating temperature (once the export limit was removed) - but it may just be that I looked at/touched it on a colder day.
On a sunny day (with the limit on) I would get the LmtByEPM warning and it would be impossible to keep my hand on the heatsink at the rear of the inverter (thus my assumption that it is dissipating the difference).

 

[Rolfe]

I did read something on Twitter by an installer explaining about the clipping. He was saying that the idea of installing enough generation so that it would clip was about getting wide shoulders so good generation morning and evening. Also that so often the weather is such that it doesn't clip anyway. He said my system was well set up in that respect. But since it's possible to harvest the rest with a bit of ingenuity, why not?

It took me nearly three months to get the 5 kw out of them. My neighbour has a 5 kw G99 too, and another neighbour across the road has 16 panels on a feed-in tariff. The roofs of the houses are so good for solar I wouldn't be surprised if some other neighbours go for it.

For April, my total this year was 933.19 kwh, of which 744.34 kwh was exported, 123.75 kwh powered the house and 65.1 kwh went to the battery. I think that last figure represents what I harvested that would otherwise have been clipped. It could have been more - the first five days of the month were very sunny and I hadn't yet worked out what to do about it. Even after that, I missed some due to failed experiments. I reckon I could have got 80-90 kwh if I'd been doing it right from the start. (Though having said that, I don't necessarily trust the GivEnergy web site, some of the numbers look a bit off.)

Mayday itself is a bit disappointing. In the morning there was a heavy rain shower during which the solar barely powered the house base load, which was low at the time. After that there was a bright spell and the battery picked up 7%, but since then there has been a lot of cloud and essentially no direct sun on the panels. I don't think I'll get any more today.

 

[Everest]

Well - that is good to know. I really hope the Solis inverter is smart enough to do that.

I will pm you some more info about the Solis, as it's a bit specific for this forum.

 

[Everest]

I did read something on Twitter by an installer explaining about the clipping. He was saying that the idea of installing enough generation so that it would clip was about getting wide shoulders so good generation morning and evening. Also that so often the weather is such that it doesn't clip anyway. He said my system was well set up in that respect. But since it's possible to harvest the rest with a bit of ingenuity, why not?

Absolutely. The general concept of having more kWp of PV panels than your inverter is capable of inverting is known as overpanelling; it's a good thing and systems (especially at the UK's latitude) should be designed for. Though to get all technical about it there are two (if not three) reasons for the clipping - in your case (and ours) it is mostly due to your export power limit and the configuration of the inverter to not export more than your DNO has permitted. The other reason is that your panels could generate (say) 8kW but your inverter is only a 6kW inverter. Yes, you will have clipping in high summer on good days, but on other days you will have more useable production than if you had less panels.

Fortunately modern hybrid inverters can typically harvest more power from the panels than they can invert to deliver as AC on the grid. But because the battery charging comes from the inverter's internal DC circuitry, that extra power can be sent to the battery via DC alone, without 'using-up' any of the inverter's AC power capacity.

 

[Rolfe]

It's just difficult to know on which days it's worth the (small) extra hassle of setting the system up to harvest that extra solar, and when not to bother, because the weather forecast isn't particularly reliable. Of course if the day turns out to be poor then I could just quit early and let the battery have the solar that's there rather than exporting it directly. It will get exported in the evening from the battery anyway. It just adds an extra step with transmission losses.