Solar Panels UK - is it worth it?

[RedMod3]

If you switch from time control to self power and then back, that should wipe the AI memory.
also setting reserve so that it is breached at 00:30 will kick it into life.

Mine has been running for less than a day, so I don't have Time Control Yet.

As my cheap rate is from 00:30 to 04:30, I'm thinking of setting the alarm for 01:00 to set reserve power to 95%, and then, reset it to 8% at 04:30. The thought of paying full price 15.59p/kWh instead of 5p/kWh is upsetting.

 

[Fred2]

Passive House heating requirement goal is 15 kWh per m² per yr. (Rome closer to 10 kWh, Stockholm closer to 20 kWh)

Maybe Google can find an average-central-heating cost per sq.m. for averagely-insulated UK housing stock?

Well ofgem says the average house uses 12000 kWh a year of gas. Some of that is hot water , so maybe roughly 10000 kWh of gas used on heating. I don't know what the average house size is, but that's probably at least 3-4x as much as that passive house requirement.

 

[Mrklaw]

you can’t just tell the powerwall to charge up during ‘go’ hours and then top up with solar during the day and discharge to avoid grid import during the day?

 

[Dilly]

you can’t just tell the powerwall to charge up during ‘go’ hours and then top up with solar during the day and discharge to avoid grid import during the day?

Well, yes. there are two settings; time control and self powered.
Time control will use it’s AI to determine whether it needs grid import during the period you set. This is OK but only has hindsight. The net result is several sunny days followed by 1 or two dull days May prevent it from charging fully. It will only import from grid during the day if it runs out and solar is poor. Self powered will only charge from solar and again uses the grid if the battery runs out and it’s dull.

 

[RedMod3]

Well, yes. there are two settings; time control and self powered.
Time control will use it’s AI to determine whether it needs grid import during the period you set. This is OK but only has hindsight. The net result is several sunny days followed by 1 or two dull days May prevent it from charging fully. It will only import from grid during the day if it runs out and solar is poor. Self powered will only charge from solar and again uses the grid if the battery runs out and it’s dull.

In self powered, can't you set reserve % to say 95% at the start of the cheap period, and then reset it to say 10% just before the end of the cheap period?

 

[Dilly]

In self powered, can't you set reserve % to say 95% at the start of the cheap period, and then reset it to say 10% just before the end of the cheap period?

Yes you can if you’re up at 00:30. My reserve is normally 30%. If I have say 50% and there’s a dull day ahead (in winter) I’ll set reserve at say 45% when I go to bed and I know it will start to top up shortly after 00:30. If I get up the night I check it and alter it if necessary.

 

[scdoubleu]

If you switch from time control to self power and then back, that should wipe the AI memory.
also setting reserve so that it is breached at 00:30 will kick it into life.

I've tried various combinations of settings and import/export tariffs over the last few weeks without much success. Bumping the reserve up to 100% at 00:30 would work best, but isn't conducive to a good nights sleep and only gets the PW to around 50% over the 4 hours. Better than nothing I suppose, so I may look into automating the reserve setting.

 

[Avendit]

so I may look into automating the reserve setting.

I was about to ask, can you use ifttt or tasker or anything to automate any of it?

 

[barry.perfect]

Yes indeed, but on the other hand with the Powerwall, you've got a bigger battery (13.5kW), and get access to the Tesla Octopus Energy Plan which is the most effective one. I have compared the Octopus Go and the Tesla Energy and I have reduce my return on investment by 1 year . I have aready found 3 accredited supplier in the Northwest with quote and I am now just waiting for confirmation of the leadtime and the physical house check .
The most interesting quote for me is the one for £15,750 (for 15 panel - 1 powerwall2 - the gateway - and a 6kW inverter in/out) I have two other one between £15k to £15.5k but with 12 panels.
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@RichardTheKing
I am looking at whether getting solar and a powerwall makes sense (versus other batteries). Would be interested to see how you generated the ROI graph in this post. Is it one you created or does it exist somewhere else?

As a high electricity user 11300KWh/yr the potential savings of the Tesla Energy Plan will probably justify the extra cost, but having trouble finding a way to quantify it as all the online calculators can't cope with the Tesla Energy Plan.

 

[scdoubleu]

I was about to ask, can you use ifttt or tasker or anything to automate any of it?

I don't think the standby reserve can be adjusted via the local Gateway API, so this would require using Tesla's cloud API + my credentials. Pretty sure there are open-source solutions for it, I've just yet to investigate properly.

 

[Mrklaw]

ironically the tesla plan needs a powerwall, but the plan itself makes a battery for personal use almost irrelevant as the in/out price is the same so the grid is your battery effectively. You're paying a lot to unlock that but have certainty of pricing.

With solar and self consumption you'd bring that average unit price down but there can be considerable peace of mind knowing even without fussing on controlling your backup/export etc you have a capped rate

 

[RichardTheKing]

@RichardTheKing
I am looking at whether getting solar and a powerwall makes sense (versus other batteries). Would be interested to see how you generated the ROI graph in this post. Is it one you created or does it exist somewhere else?

As a high electricity user 11300KWh/yr the potential savings of the Tesla Energy Plan will probably justify the extra cost, but having trouble finding a way to quantify it as all the online calculators can't cope with the Tesla Energy Plan.

Hello, yes this why I build that spreadsheet, I have been able by changing the data to compare shell, oct.go, oct.tesla, edf ... Plan. This had help me with my kWh load configuration to decide which one will be the best for me, in my case the No1 is Octopus Tesla and 1 year Roi after octopus Go etc...
Now I am testing the quotes I have received on that model with that Octopus Tesla plan data.
If you sent me in private message your email address I can sent you a copy of the last updated Excel spreadsheet.
The spreadsheet is not macro or Vba and you still need to enter your data manually in some specifics part of it. I prefer it, because I can really modifing/improving it when and if necessary. On the costs increase forecast, I have decided to go for a 54% energy increase in year one and a 5% energy increase the other year. But I can change it at any time.

 

[RedMod3]

Yes you can if you’re up at 00:30. My reserve is normally 30%. If I have say 50% and there’s a dull day ahead (in winter) I’ll set reserve at say 45% when I go to bed and I know it will start to top up shortly after 00:30. If I get up the night I check it and alter it if necessary.

Actually, it did not work as the Powerwall only charged at 1.7kW; I was hoping for a 5kW charge rate. I only topped the battery up from 6% to 42%. I'm now hoping the Time Based charging is activated soon.

 

[RedMod3]

@RichardTheKing
I am looking at whether getting solar and a powerwall makes sense (versus other batteries). Would be interested to see how you generated the ROI graph in this post. Is it one you created or does it exist somewhere else?

As a high electricity user 11300KWh/yr the potential savings of the Tesla Energy Plan will probably justify the extra cost, but having trouble finding a way to quantify it as all the online calculators can't cope with the Tesla Energy Plan.

I use slightly more than you and have gone for the Octopus GO solution as my intension is to not export anything and only buy at the cheaper GO rate except for a few months over winter when I'll need some peak electricity.

 

[Avendit]

@RichardTheKing
I am looking at whether getting solar and a powerwall makes sense (versus other batteries). Would be interested to see how you generated the ROI graph in this post. Is it one you created or does it exist somewhere else?

As a high electricity user 11300KWh/yr the potential savings of the Tesla Energy Plan will probably justify the extra cost, but having trouble finding a way to quantify it as all the online calculators can't cope with the Tesla Energy Plan.

I also built my own spreadsheet, built it up of a fair bit of time starting off workinging out where they hell our 17000kwh/year consumption goes (turns out the always on network and server equipment adds up a fair bit, on top of the car and a HP). Mine is really messy tho as it continuously compares 4 different panel & battery combos.

Use PVwatts to get your monthly and daily generation vs usage I then matched what I can move to either high gen or cheap rate electricity and from there worked out savings per day/month/year. Then take that rate and project into the future. I've not accounted for energy price increased other than the obvious near horizon because the more it goes up, the quicker the system pays for its self.

This is my graph at 28p/7.5p, assuming putting what solar you can into the battery, then filling the battery over night if needed (over 25 years):

Lines are P (panel count) and b (battery count in KW).
If the day rate goes up to 50p/unit and night to 12p, payback is between 3-4 years:

The big array with the 10k battery in this condition puts you £80k up in 25 years .

 

[scdoubleu]

Actually, it did not work as the Powerwall only charged at 1.7kW; I was hoping for a 5kW charge rate. I only topped the battery up from 6% to 42%. I'm now hoping the Time Based charging is activated soon.

1.7 kW is normal for charging to the standby reserve (and for Stormwatch). It'll charge from the grid at the full rate if the AI deems it necessary.

 

[barry.perfect]

I use slightly more than you and have gone for the Octopus GO solution as my intension is to not export anything and only buy at the cheaper GO rate except for a few months over winter when I'll need some peak electricity.

Staying with Octopus Go would be easier as it is my current tariff.

Did you compare the payback between a powerwall v other batteries (e.g. GivEnergy) when making your choice. If the Tesla Energy Plan isn't viable then the attraction of a powerwall goes down due to it's high cost?

 

[Mrklaw]

had a crack at my own spreadsheet looking at cost and savings based on different battery sizes (my current pain point trying to 'right size' the storage)
8.2kwh should be fine, with some additinoal savings moving to 10.5kwh and very little if any saving beyond that (for my current use).

 

[Avendit]

had a crack at my own spreadsheet looking at cost and savings based on different battery sizes (my current pain point trying to 'right size' the storage)
8.2kwh should be fine, with some additinoal savings moving to 10.5kwh and very little if any saving beyond that (for my current use).

View attachment 781559

Looks like the same fundamentals as mine - its all about modelling your usage, hence there isn't really one true spreadsheet out there to bring them and in the sun model them.

 

[Mrklaw]

Looks like the same fundamentals as mine - its all about modelling your usage, hence there isn't really one true spreadsheet out there to bring them and in the sun model them.

Yep although some of the fundamentals are solid enough to reuse - mine let’s me tweak
- unit pricing and peak/off peak windows,
- solar generation (using an external tool like pvwatts or pvgis or your own measurements)
- home usage with splits during solar and off solar times
- battery sizes

My simple version only lets me pick one average value for solar generation so I’d need to run twice for summer vs spring - I’m using spring figures to try look at ‘worstish’ cade, accepting winter probably has edge cases that are impractical to cover.
(Thinking about it I might run with zero pv to see whether that changes things and skews better for the 10.5 battery over bad/winter days), and might also try some experiments with a north facing array

So this output is specific to me but it would be great if installers could provide something like this too.