Solar for Beginners [ask your questions here]

Unabashed solar dummy here. Very happy with my new solar PV system, but rather confused by the following:-

Last Monday, warm and humid, wall to wall sunshine without a cloud in the sky. Lovely curve on my PV output graph, but as you can see below, the max kW reached was about 3.7

Last Thursday, cool, cloudy, showers with decent periods of sunshine in the afternoon.

This output graph is a lot less curvy, but a peak of 4.4 kW was reached on a couple of separate occasions. (That's my theoretical max.)

So how come the peak output achieved was significantly lower (by about 17%) on what seemed to be a perfect PV day? 🤔

Thanks.

That's very interesting thanks. I wasn't aware of that.

Presumably it also means that a cool summer could be up to 17% better (from a PV generation perspective) than a warm summer!

Yeah, in the heatwaves in May+June last year I was getting perfect curves but a lower overall peak on the curve than on cooler sunnier days. Down to panel temp.

Can also be the inverter temp. If it gets too hot, some inverters throttle the output. If it's in the attic which is already baking and the inverter is going full tilt on a bluesky day…keep an eye on inverter temps getting 50C+. Some here put fans under them in the summer. The manual will list an optimal operating temp.

This one? http://davidhunt.ie/solar/

Ignore me! Figured out I had a home assistant automation turning eddi off at sunrise.

SOC = state of charge. It's basically the same as the battery level on your phone. Phone battery = 54% is the same as battery SOC = 54%. A fancy way of saying the same thing on how full your battery is.

Related to that is "Depth of discharge" and for house batteries typically they go from 100% → 10%. Depends a little on the manufacturer. What this means is say you buy a battery that is 10Kwhr in capacity. Well, your "usable" amount is only 9kwhr as the battery likes to go from 100%→10%. Without getting into the tech, just take it that the batteries don't like to be depleted down to 0% regularly. You can do it, but repeating 100%→0% will shorten the useful life of the battery, so the recommended is 100%→20%, although most can do down to 10% with no ill effects.

On the charging side, you can set the times and levels that you want to go to. I've automation with sets my charge level - but for most people, they set the times (say 2am → 5am) and set it to 100%, and then whatever level the battery is at…..let's say it was at 23% full, it will charge from the grid until it gets to 100%, or whatever limit you have set, and once it's charged it will stop importing power from the grid. Then outside the "charge time" you have set…..it will satisfy the house by slowly depleating the stored energy it's got to meet house demands.

So in you example,

So if the grid charge window is 2-6am and SOC was 10% does this mean that the battery will only charge from the grid during those hours and outside of this window once depleted to 10% 

It means that at 2am your battery was 10% full, and it will charge it from 10% up to 100% from the grid, that probably won't take 4 hrs to 6am, so at some stage during the 4 hrs, it will stop charging.
Once 6am comes along, then your battery will start discharging and meeing house demands.

As for amps etc - I wouldn't bother too much about that. for 95% of people baring techs like myself and a few others here, let the defaults on the inverter work for you, no need to change anything and you'll get years out of a battery.

Perfect, thanks makes sense. Thanks

Yes, a significant impact. The production from a shaded panel can drop to ~20% of the max if the shade covers one or more of the individual cells. 'Half-cut' panels won't help significantly and neither will optimisers unless the shading is isolated to a minimal number of panels.

At 6-7 away and 4-5 meters above roof level, that would block all direct sun in winter I would have thought

Yes, you can, but you'd need specialist software to model the seasonal sun paths and obstructions. Somebody posted such in one of the threads on here last week,

Let us know how it goes!

Have you have any issues with vibrations or wobbles in high wind? Looking at how far apart the horizontal supports are on the panel and how exposed you are.

I've got 550w panels (7.5ft high!) and will put a run in the middle. I'm in an exposed area and am even considering a 4th to help sleep better.

No

Where about is the slot? I don't see it

Result.👍