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powerwall - supplied from Tesla vs third party?

Mrklaw

Active Member
Mar 5, 2020
1,901
1,252
Berkshire
looking at adding home storage. 10.5kwh is probably ideal but I’m struggling to get quotes and the only one so far has been around £6.5-7.5k depending on the battery supplied. I’ll likely need it installed outside due to lack of internal space, which probably rules out the pylontech unless I build a little shed.

Tesla are selling the powerwall for £8300 including VAT so would be installation on top of that - I’d expect that should come in around £9.5-10k? Some other third parties seem to offer lower installed prices but others are charging more than Tesla for just the battery.

Anyone looked into this and whether its more cost effective to buy direct and get someone to install, or get it supplied and fitted by the same person? Not set on powerwall but likely it’ll be that or a givenergy combo of around 10.5kwh.

I’d also want it to charge during off-peak, discharge during peak, and top up with small amount of solar during peak too - no export as the existing array is FIT registered and I don’t want to touch it. Can the powerwall do that - I’ve heard it tries to be ‘smart’ which to me can also mean ‘I have no control so have to deal with whatever it decides to do’
 

Dilly

Active Member
Feb 24, 2020
3,476
3,121
Norfolk
I have FIT registered panels.. I added one PW, then a second, then some non FIT panels that can’t export.
the PW’s will fill using both sets of panels until full. There is no effect on FIT by installing them.
PW’s will charge during off-peak using time control mode but level of charge may be altered by Artificial Intelligence.
the danger is several sunny days followed by a really dull day where off peak doesn’t give enough and solar is poor.
switching from timed to self powered and back usually wipes unwanted interference from the AI system.
in timed mode, it charges from the grid and doesn’t normally discharge. In self powered (solar) mode it doesnt use the grid Unless discharge rate it exceeded.
 
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Mrklaw

Active Member
Mar 5, 2020
1,901
1,252
Berkshire
thanks. feels like the smarts could do hindsight rather than prediction? eg always target filling the battery - then as the house uses electric it gets topped by solar, and topped up overnight. then if you get an overcast day you have capacity to use, rather than assuming it’ll be sunny. Seems an odd approach?

So for my use case - I may get 5-10kwh generation in summer so not always a ton of excess to guarantee base load + charge the battery, I’m expecting to lean on off peak fairly regularly. Sounds not really set up for that way of working?
 

WannabeOwner

Well-Known Member
Nov 2, 2015
7,231
3,994
Suffolk, UK
I’ll likely need it installed outside due to lack of internal space,

Probably not relevant for you, but my PowerWalls are in the "shed". Actually that room is part of the house, but the last in a single-room-thick ;like of three unheated rooms, and the last one gets cold in Winter Natch!. It has frost-thermostat, but since PowerWall the tiny amount of waste heat it generates means that that room has not had its heater come on. For me that's a bonus ...

Tesla are selling the powerwall for £8300 including VAT

Including Gateway?

Is that 5% VAT? If not could you get an combined-install where you were entitled to 5%? (labour has to be 40% of total, (which would need a lot of solar /etc. installed at same time!) or you have to "qualify" - basically on some sort of Benefit, or one of the primary householders over 60.

I’d also want it to charge during off-peak, discharge during peak, and top up with small amount of solar during peak too - no export as the existing array is FIT registered and I don’t want to touch it. Can the powerwall do that

I do that. I have panels on FIT. My PowerWalls are set to "Time based control", rather than "Self powered". You can set three rates, but you can't set them independently - basically you set a Off-Peak and a Peak period, and (if they don't exactly touch) anything inbetween is the "medium" rate. I hope I have explained that correctly.

It will charge during Off-Peak and discharge (only, I think) during Peak. Independently you can set "Backup reserve" for powercuts. That's a slider, so if you have a scheduled powercut you can just slide that to 100%. Tesla will set it to Storm Watch if foul weather is forecast. That will IMMEDAITELY (i.e. even if Peak) charge it to 100% and keep it there until Storm Watch is "over". I suppose manually setting it to 100% the night before is the same - you'd be running off grid during the day, so charging PowerWall when Storm Watch probably works out the same ...

You could change your Electricity Supplier to Tesla. Tesla will export from your battery at Peak (i.e. I presume they are selling at best-price), and they will choose when to charge it from Grid etc. So your PV may wind up being exported ... but the Export and Import rates are the same (11p or something like that) so apart from some efficiency losses I suspect it works out neutral. If you are a net consumer of electricity, or in Winter, then the 11p rate is probably a A Good Deal :)
 

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