MSE guide: plug-in solar panels

NedS

https://forums.moneysavingexpert.com/discussion/comment/82120312#Comment_82120312

That's a good question - I don't know.

If kits ship with smaller panels, then they are likely not going to achieve 800W. Ideally you'd want to oversize the panels slightly, so 2 x 500W panels would be ideal for an 800W plug-in inverter with two MPPTs (like the ECOFlow micro-inverter), and they are large and heavy, not something you can pick up from your local Argos and probably not something you can self install (unless ground mounting).

jimi_man

https://forums.moneysavingexpert.com/discussion/comment/82120147#Comment_82120147

Same way as they get a fridge, freezer, washing machine, large TV, furniture etc into a flat. Get a friend to help if you can't do it yourself. Octopus advertise theirs at around 22kg, so not exactly impossible to lift and there cant be many people who are incapable of lifting 22kg.

QrizB

Octopus advertise theirs at around 22kg, so not exactly impossible to lift and there cant be many people who are incapable of lifting 22kg.

My EcoFlow panels (of the same general type supplied with plug-in kits) were packed two to a cardboard carton, so about 45kg before splitting. Those were a bit of a pain to handle and were far easier with two of us.

Individual panels were also easier to handle with two people. It would have been a struggle mounting them without help.

Martyn1981

https://forums.moneysavingexpert.com/discussion/comment/82120294#Comment_82120294

Sorry, but I think you've missed the key bit completely, so just to repeat:

But it's a 6.725kWp system, and will generate far more per year than a 3.68kWp PV system would (in the same location/setup), even if all generation over 3.68kW was clipped.

The 890Wp system will generate more than a 800Wp system, even via a 800W AC inverter. In fact, I'd suggest that clipping will be so small/negligible that the ratio of generation between two such systems would be pretty much 890:800.

Please see the parts I have marked in bold.

Yes My 6.725kWp system has a battery, but please ignore that for the illustrative purposes above.

Edit - I think this line of yours is were you are going wrong:

In other words, any panel rating above what the inverter will pull to achieve 800W is an irrelevance.

Not an irrelevance, the larger system will generate more per year. Even your example (testing to the extreme) with 10 panels 4.45kWp, will generate fare more than the 800Wp or 890Wp systems over a year. But obviously suffering rapidly diminishing returns as each extra panel is added.

jimi_man

https://forums.moneysavingexpert.com/discussion/comment/82120596#Comment_82120596

Sure, two people will always be better than one. But the point being that one person (especially if they had or could borrow a trolley) could move one if necessary. Mounting them will always be better with two people I'd imagine.

I'm quite tempted by it. I have been considering solar on the house we're in but I'm still not fully convinced. One of the issues is getting the feed back to the consumer unit which is under the stairs in the middle of our house, so I'm not sure how they'd get from the battery to the consumer unit without significant disruption.

A plugin system would work for us. I'd just need to put in an outside socket but they are about a tenner in Screwfix.

I shall monitor the prices, which are likely to be quite high for early adopters but will come down. They are only a few hundred euros in Germany now. And meanwhile I can fit an outside socket while I'm waiting.

Heedtheadvice

Quite Correct Martyn.

It maybe considered a bit of a over advertising statement to specify in peak power, but it does make sense.

It is specifying the potential max power the group of pv diodes are capable of generating under specific conditions solar irradiance ( solar power and angle of incidence ), conversion efficiency at a specified temperature etc. That is not the same as the inverter power.

It does hower then give a good representation of the absolute max power and the higher that is ( all other things considered being equal ) then greater the instantaneous power capability under conditions that are less favourable. As an example halving the irradiance due to cloud then rhe power capability from 1000Wp panel ought to ( and usually does) generate approx twice that of a comparable 500Wp panel.

Thus under non ideal conditions the peak power rating is very useful and therefore relevant.

It is not as simple as the physics that. Prowla describes. In fact the load ( in this case the inverter) does not 'pull' anything. The DC is pushed by the panel diodes into the load. That load varies under the conditions that the inverter responds to including ( whatever it's output is connected to) any limits set such as max output power ( 800W for balcony systems) grid voltage ( and allowable limits), battery ( if fitted) charging or discharging. The latter is of particular relevance where the inverter is capable of hybrid operation - supplying AC power as well as DC power and can thus make use of any generation beyond the agreed AC output power spec.

Prowls you seem to have forgotten the basics of physics that it is the potential voltage ( the force ) pushed into the load resistance (DC) or impedance (AC) that determines the current I=V/R.

Let's ignore for some simplicity source resistance and MPPT that also is inverter load variations to maximise power transfer efficiency.

But the essential conclusion is that as Martyn states, effectively peak panel generation power and inverter power limit are both relevant. Higher panel Wp can make a lot more sense in terms of overall generation.

Martyn1981

https://forums.moneysavingexpert.com/discussion/comment/82120676#Comment_82120676

Thanks. Glad you mentioned the hybrid battery (powerstation) issue. This is something, as I've mentioned elsewhere, that I think is of most importance and use. Assuming of course battery costs keep falling.

Folk may well run out of room for temporary panels in that situation as 5kWh of battery with 800W max feed back into the home circuit, and an AC out of 1kW to 2kW for direct device powering, would probably be suitable for ~3kWp of panels.

But I suspect the PnP powerstation permission, if it comes, will be a good 6, 12 or more months away, sadly.

For those personally pondering potential panel power (I may have gotten a bit silly there), I'd absolutely recommend 1,000Wp (or a bit more if possible) over 800Wp for a non battery PnP set up. Clipping will still be mininimal, and if set up with a steep(ish) pitch, that boosts winter potential, at the cost of a bit of summer peak power, then clipping should be zero, or very close too.

jimi_man

https://forums.moneysavingexpert.com/discussion/comment/82120738#Comment_82120738

For those personally pondering potential panel power (I may have gotten a bit silly there), I'd absolutely recommend 1,000Wp (or a bit more if possible) over 800Wp for a non battery PnP set up. Clipping will still be mininimal, and if set up with a steep(ish) pitch, that boosts winter potential, at the cost of a bit of summer peak power, then clipping should be zero, or very close too.

That corresponds with the advice I've read elsewhere, that a larger panel setup will give a consistently higher annual average output, though obviously at a higher cost.

QrizB

I see that you can now buy UKSOL bundles via Argos (delivery times aren't great, "within 9 weeks" for my postcode):

https://www.argos.co.uk/browse/technology/plug-in-solar/c:1100009/

For dual-panel systems you have a choice of 890Wp, 1030Wp or 1260Wp for £849, £899 or £989 respectively - roughly 95p, 87p or 78p per watt of panel.

QrizB

I've just posted over on the Energy forum about DESNZ's "expression of interest" request for safety evaluation of plug-in batteries.

https://forums.moneysavingexpert.com/discussion/comment/82121274#Comment_82121274

Not immediately relevant to this thread but I'm sharing it here for the wider audience.