Solar & Powerwall 2

Embattle

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Saturday was nice, should be some further nice days coming up this week:

1000014604.png
 

old.Osy

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Just thrown together really, I'll fashion something nicer at a later date.

1726659969695.png
 

Embattle

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old.Osy

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Very interesting - I suppose research into making the panels last longer doesn't really make sense, since research into more efficient panels makes them obsolete.

So the research focus should go into manufacturing panels with less difficult to recycle materials, that also impact CO2 generation, either by producing or recycling them.
 

Embattle

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Very interesting - I suppose research into making the panels last longer doesn't really make sense, since research into more efficient panels makes them obsolete.

So the research focus should go into manufacturing panels with less difficult to recycle materials, that also impact CO2 generation, either by producing or recycling them.

I'm interested in making them easier to recycle in the first place, like so many things the core problem is plastic which besides being tough isn't really recyclable.
 

Embattle

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So on Wednesday our Tesla PW2 got its 5kW upgrade, it wasn't as simple as the guy hoped since it couldn't be done remotely because of GDPR reasons and while here he had to call Tesla multiple times because apparently since the release of PW3 it has become harder/buggy to change some of the settings of the PW2 due to integrating the PW3.
 

Embattle

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What's the 5kw upgrade @Embattle?

The Tesla PW2 has a maximum continuous charge/discharge of 5kW and a peak (10s) of 7kW charge/discharge.

Our original solar system had a inverter which had a maximum rating of 3.7kW linked to 16 panels, thus the Tesla PW2 was set to match this rate as well because it would never be charged above this rate.

So move on to 2024 with the additional 6 panels and 2kW inverter and the total possible generation is now 5.7kw, in essence 2kW over the 3.7kW the Tesla can charge at, so a couple of examples:

Old Setting

Solar 5.7kW -> PW2 3.7kW + House 0.6kW = 1.4kW to Grid

New Setting

Solar 5.7kW -> PW2 5kW + House 0.6kW = 0.1kW to Grid

So the benefits:

  1. We keep more of our generation.
  2. We'll get better charge storage on intermittent sunny/cloudy days.
  3. We are less likely to pull from the grid when a kettle is turned on if there was already something else pulling a couple of kilowatts.
  4. In theory on a very sunny summer day and with the PW2 active we have a maximum off grid capacity of 10.7kW.​
 

MYstIC G

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Dang, that's fancy...
 

Scouse

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Where you at again @old.Osy ? Would be nice to see @Embattle 's usage for the same day :)

It'll be a couple of years (at least) before we even go for another fight with the national park planning authority to try to get permission for solar here, but I'm still trying to gauge how much benefit we'd get when we really needed it - i.e. in the winter months.
 

Embattle

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Here are the charts for yesterday:

Screenshot_20250210-140439.pngScreenshot_20250210-140235.png

@Scouse stop going back to solar generation and Winter, you won't gain much unless you have a massive oversized system, over the course of the year the benefits still outweigh the cost in both savings and the environment.

In the following two screenshots, you see the energy the house required and where it came from for the worst month (Dec) and then each month for the whole year (2024) although I expect some difference this year since the upgrades done last year.

Screenshot_20250210-140744.pngScreenshot_20250210-141133.png
 

Scouse

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@Scouse stop going back to solar generation and Winter, you won't gain much unless you have a massive oversized system, over the course of the year the benefits still outweigh the cost in both savings and the environment.

View attachment 49997
We have *very* different electricity usage m8. Yours stays flat throughout the year (actually goes up in the summer??!) - and you make a load of savings through solar in the summer - but this is my electricity usage monthly graph:

1739200439718.png

There's really fuck all from March > October for me, when Solar would be producing and making savings for me. The rest of the time I'd be pulling from the grid. Battery storage is probably where I'd maybe make savings, but with up-front costs...

Most of the year I'd be fecking electricity into the ground.
 

old.Osy

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Caveats: Our panel orientation is N-NE, with a 17 degree roof slope.

Unfortunately, it couldn't be helped. 24x425W panels = 10.2 KW, with a 2.76KW x 4 HVM battery module installed, for 11.04 KW total capacity.

So yes, voluntarily oversized due to the orientation. I have a mate with 6KW panel power installed (proper orientation), in nice sunny days he totally dwarfs my production, putting me to shame. Such is life.
 

Embattle

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We have *very* different electricity usage m8. Yours stays flat throughout the year (actually goes up in the summer??!) - and you make a load of savings through solar in the summer - but this is my electricity usage monthly graph:

View attachment 50000

There's really fuck all from March > October for me, when Solar would be producing and making savings for me. The rest of the time I'd be pulling from the grid. Battery storage is probably where I'd maybe make savings, but with up-front costs...

Most of the year I'd be fecking electricity into the ground.

Then scale your system plan down not up, match your power needs over the summer months and get a smaller battery.

Below is last year's solar generation broken down in to where it went:

1000016624.png

As you can see 858.8 kWh went out to the grid, this year's (2025) figures will be more representative when compared to 2023 since the upgrade happened during last year (2024) and now all the adjustments are complete.
 

Scouse

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Then scale your system plan down not up, match your power needs over the summer months and get a smaller battery.
Doesn't make sense.

A) Panels are cheap (and getting cheaper still). Most of the cost for me would be in installation. Doubling the number of panels would not cost a hell of a lot more.
B) A smaller battery would mean I wouldn't be able to take advantage of the overnight electricity rates for when I do use a lot of electricity. It would compound the "not producing" problem in winter with a "not even saving" issue.

Solar would be great for me if my electricity bill was flat all year round. But for some summer month savings on the scale it's on about the ROI would be low. I'd have to see what else I could do to use the available electricity in the summer months.

I'm still looking at it though. But loads of shit to do first :)
 

Scouse

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So, not wanting to be a negative ninny, but the guy makes all my points for me unfortunately:

For a start:

View: https://youtu.be/YW-SRNUgGtk?t=237


So - it's all about summer output and usage and "if you want to heat your house through solar - think again".

I can't artificially make us use solar in the summer - we simply don't need the heating and, unlike Harry, I don't have a swimming pool to fuck a load of waste heat into. But I do need it in the winter - when solar is clearly useless.

He's interesting on the ground source heat pump. He's massively overspecced his pipes so it's efficient. I could potentially do that - but then have you seen the size of the kit he's using? I'd need a plant room and my home simply don't have the space.

So I'd be on to air-source, which he says is absolute pap in the winter - which is when I'd need it. He says it's much less efficient when air temperature goes below ten degrees. Air temps here haven't been above ten degrees since I think October - and generally I have a ground frost about 25% of the days from December > April (although this year is weird (and hopefully not permanent)).

But even if the newer air source pumps are more efficient, he's put triple the amount of insulation into his massive new-build house. I've absolutely gone big on the insulation (dug up the floor slab, insulated plasterboard on the new bits of the house, hemp-lime plaster on the old bits, double glazing all round), but compared to the thermal efficiency of his place, mine will still be as leaky as a sieve. Air source is highly unlikely to cut it during the months that I desparately need it to cut it - winter time. (And that's borne out by other people with similar properties in my area who've done the same as me, and are ripping their air-source pumps out and changing to LPG).


I'd love the facts on the ground to be different, but as I haven't got a massive new-build house and a swimming pool to piss summer-time energy into then, whilst I still would love to put solar in (bascially to reduce summertime dependency on the grid) it makes very little economic sense. And to be honest, not an amazing amount of environmental sense either because whole-lifecycle impacts matter, so is it better to consume electricity from the grid, or conume electricity from a local solar installation that might actually be less efficient than the sprawling windfarms?

Last point - batteries - he's correct, they're useless in the winter and for him he's using everything in the summer. The only benefit for me would be economic - I could fill up on a cheap tarrif and discharge when it's expensive. I don't think he cares though at £500/month electricity spend.
 

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