Considering getting a Powerwall

[MrBadger]

Subject to still having funding available at the end of this crisis we have plans to build a passive house next year with a pretty large PV array - probably about 12-14kw coupled with a powerwall. One thing that I cant really find info on and that is how we coordinate this with our DNO? We are in southeast Scotland so it is SP Energy Networks. I have made initial contact with them but the feedback is really too technical for me. I just wondered what the potential issues were/costs involved in getting consent to connect an array of this size to the grid? Thanks.

May be worth getting in touch with Russ at http://www.stationbrae.uk/

Also his journey The new adventure continues ! along with other answers to your questions

An array that size will almost certainly need three phase or be output limited such as via a device such as an EMMA. 3 phase is usually palatable cost wise if installing from scratch, not so for most retrospectives.

 

[MrBadger]

This afternoon I decided to put my money where my mouth is and order a battery storage system, but not a Powerwall.

I had done the calculations on a few occasions in the past on Powerwall with my usage and solar generation pattern and came up with a 10 year breakeven figure of approx £2.5-3k based upon the assumptions of the day. There was no way that a Powerwall was ever going to pay for itself even if I could get 20+ years out of it, or me.

But I had revisited things recently and found a solution that would, well very nearly hit the £3k mark, give or take a few optional extras and fitting, the latter I am hoping to combine with installation of an additional consumer unit to support car charging. At end of the day, its a regular 16A circuit connection, I just do not have any spare 16A connections.

The solution that I have gone for is a modular solution based upon PylonTech 2000 battery modules and a Sofar ME3000 inverter, both well regarded by those in the know. These give 2.4kWh of storage which, limiting DOD to 20%, 3 modules will give me a total of 5.76kWh usable storage at 3kW charge/discharge. This aligns fairly closely with our typical summer consumption values. I'm not bothered with free electricity or full power EV charging capability that a larger battery may occasionally give, but I believe that this solution will significantly reduce our summer energy import at a very economic price - I want some value out of my 25p/day standing charge!

Since my initial calculations, a number of factors have changed making the initial £3k breakeven figure so I think with winter time shifting, 10 year breakeven may even be a little bit quicker than I had calculated. And being a modular system, just adding a battery module is simple and relatively cost effective.

The hardest part will be finding a sparky to get the AC wiring to it. The DC side I can do myself.

So for anyone considering a Powerwall, but who is put off by the price, there are modular solutions out there that start off from very reasonable amounts of money - albeit smaller than the 5.76kWh entry point that I chose. For instance, a single module system that would cover 80% of a 100W baseload can be had for well under £2k.

 

[NorfolkMustard]

That's awfully cheap for 2.4kWh of LiFePO4 , just for the batteries on their own I've been looking at roughly £1k / kWh

you went for something like this? SoFar ME3000 & PylonTech US2000 2.4kWh Solar Battery Storage complete kit

 

[MrBadger]

Yes, but I went for 3 modules of 2.4kWh nominal each (just under 2kWh each if I configure to 80% max discharge) so 7.2kWh nominal / 5.76kWh@80%. The 2.4kWh modules work out at around £800 each including mounting brackets and its expandable to 8 modules / 19.2kWh but power is limited by the inverter. A few extras were added such as mounting supports, bi-directional meter, isolation switch and warning stickers. There are places cheaper than the link listed, but cannot vouch for them, yet.

 

[NorfolkMustard]

'the hell is this - 8.2kWh LiFePO4 for £2k ?

GivEnergy 8.2kWh LiFePO4 Battery

add a solar charge controller and 5kW inverter for £1k ?

GivEnergy 5.0kW Hybrid Bundle with 8.2kWh batteries

 

[MrBadger]

Yes, battery tech is becoming more affordable.

If thats an ex vat price, then its pretty much the same kWh/£ as I paid for my well regarded PylonTech batteries, ex optional stacking brackets. The GivEnergy looks to be a more aesthetically pleasing which is nice, but may not be so compatible with some inverters so might need a bit more 'advanced setup'.

 

[arg]

came up with a 10 year breakeven figure of approx £2.5-3k based upon the assumptions of the day.

How do you arrive at a fixed £ amount independent of the device spec? Or are you assuming "approximately the same capacity as a powerwall"?

 

[kevuwk]

This afternoon I decided to put my money where my mouth is and order a battery storage system, but not a Powerwall.

I had done the calculations on a few occasions in the past on Powerwall with my usage and solar generation pattern and came up with a 10 year breakeven figure of approx £2.5-3k based upon the assumptions of the day. There was no way that a Powerwall was ever going to pay for itself even if I could get 20+ years out of it, or me.

But I had revisited things recently and found a solution that would, well very nearly hit the £3k mark, give or take a few optional extras and fitting, the latter I am hoping to combine with installation of an additional consumer unit to support car charging. At end of the day, its a regular 16A circuit connection, I just do not have any spare 16A connections.

The solution that I have gone for is a modular solution based upon PylonTech 2000 battery modules and a Sofar ME3000 inverter, both well regarded by those in the know. These give 2.4kWh of storage which, limiting DOD to 20%, 3 modules will give me a total of 5.76kWh usable storage at 3kW charge/discharge. This aligns fairly closely with our typical summer consumption values. I'm not bothered with free electricity or full power EV charging capability that a larger battery may occasionally give, but I believe that this solution will significantly reduce our summer energy import at a very economic price - I want some value out of my 25p/day standing charge!

Since my initial calculations, a number of factors have changed making the initial £3k breakeven figure so I think with winter time shifting, 10 year breakeven may even be a little bit quicker than I had calculated. And being a modular system, just adding a battery module is simple and relatively cost effective.

The hardest part will be finding a sparky to get the AC wiring to it. The DC side I can do myself.

So for anyone considering a Powerwall, but who is put off by the price, there are modular solutions out there that start off from very reasonable amounts of money - albeit smaller than the 5.76kWh entry point that I chose. For instance, a single module system that would cover 80% of a 100W baseload can be had for well under £2k.

Any reason you went with the PylonTech 2000 over the 3000? The price is close but kWh is close but I thought the 3000 worked out slightly cheaper when I last looked at battery tech.

 

[jimbo_hippo]

This afternoon I decided to put my money where my mouth is and order a battery storage system, but not a Powerwall.

I had done the calculations on a few occasions in the past on Powerwall with my usage and solar generation pattern and came up with a 10 year breakeven figure of approx £2.5-3k based upon the assumptions of the day. There was no way that a Powerwall was ever going to pay for itself even if I could get 20+ years out of it, or me.

But I had revisited things recently and found a solution that would, well very nearly hit the £3k mark, give or take a few optional extras and fitting, the latter I am hoping to combine with installation of an additional consumer unit to support car charging. At end of the day, its a regular 16A circuit connection, I just do not have any spare 16A connections.

The solution that I have gone for is a modular solution based upon PylonTech 2000 battery modules and a Sofar ME3000 inverter, both well regarded by those in the know. These give 2.4kWh of storage which, limiting DOD to 20%, 3 modules will give me a total of 5.76kWh usable storage at 3kW charge/discharge. This aligns fairly closely with our typical summer consumption values. I'm not bothered with free electricity or full power EV charging capability that a larger battery may occasionally give, but I believe that this solution will significantly reduce our summer energy import at a very economic price - I want some value out of my 25p/day standing charge!

Since my initial calculations, a number of factors have changed making the initial £3k breakeven figure so I think with winter time shifting, 10 year breakeven may even be a little bit quicker than I had calculated. And being a modular system, just adding a battery module is simple and relatively cost effective.

The hardest part will be finding a sparky to get the AC wiring to it. The DC side I can do myself.

So for anyone considering a Powerwall, but who is put off by the price, there are modular solutions out there that start off from very reasonable amounts of money - albeit smaller than the 5.76kWh entry point that I chose. For instance, a single module system that would cover 80% of a 100W baseload can be had for well under £2k.

Looks like a feasible solution at a good price.

one of the key specs that I liked about the PowerWall was it’s ability to deliver back 7kW peak and 5kW continuously. So if the oven is on and someone boils the kettle, it’ll probably still be within the capability of the system. At the price you have and with your techie nature you’ll probs work around the 3kW limitation but without sitting down 3 teenagers and doing some home schooling on how it all works, it wasn’t going to happen. When a 16yr old wants toast, they ain’t checking no app, I’m sure!

I’m also pretty sure your sums are better than mine and it’s probably cheaper to let it draw grid on those rare occasions.

 

[MrBadger]

tl;dr - for us, battery capacity made very little difference in cost savings.

How do you arrive at a fixed £ amount independent of the device spec? Or are you assuming "approximately the same capacity as a powerwall"?

It was based upon the capacity that we knew about the original Powerwall spec at the time and a few simplifications such as not taking into account power limits so was simplified but the answer that I was after was ballpark not exact - even if 100% out, it would be a useful number and it would have been far better than that - fact checked again my actual annual bill - its impossible to save more than my actual bill for the period. I was on a fixed tarrif so a simplified approach would have given an almost best case scenario.

The simplified approach:
Maximum stored PV excess for the day = deemed days solar export capped at capacity of the battery so 100% usage of excess solar - assumed 100% round trip efficiency and no charge limit (latter likely to have no effect as days when peak power limits breached would likely to exceed battery capacity limit)
Maximum stored energy reuse = measured days energy usage less maximum stored PV excess for the day - assumed no limit on import.

The above had very small difference in saving between a 4kWh battery and a 6.1kWh battery. Above the daily energy usage, size of battery had no effect. This however assumed that residual charge in the battery was lost at end of the day but this would be offset by the assumption that energy could be used before it was generated - averaging these out, there would not be much in it, but the larger the battery capacity, the larger the difference, but pretty minor.

I've just gone back and revisited the spreadsheet and done some what-if's on battery capacity. These values are based upon our energy usage - others will have different usage patterns. But i've put in our energy usage for that year, 2015. Figures were based upon 15p/kWh electricity price (we are less than that so current savings would be even less). Values also based upon CT clamp meaturing, so not that accurate at low power levels.

4kWp PV System, ~3360kWh generation, ~2060kWh calculated export (no export meter), 1830kWh imported (current ~2100 metered), at 2015 price/usage 0.15p/kWh = £308 (current price and usage 0.138p/kWh = £290). IF WE IMPORTED ZERO ELECTRICITY THESE VALUES REPRESENT THE MAXIMUM ANNUAL SAVING POSSIBLE THAT WE CAN MAKE. The figures predate EV charging so savings now potentially better.

What ifs...
Usable battery capacity (kWh) / £ per year export stored / £ per year saving at 15p/kWh
1 / £42 / £42
2.4 / £87 / £79
4.8 / £155 / £115 - probably best bang for the buck - a system may cost around £2300
5.8 (7.2kWh @80%)/ £178 / £120 - just added so not reflected in text below. System price around £3050.
7.2 / £210 / £121
10 / £257 / £121
14 / £292 / £121 - approx Powerwall spec at I believe around 9k installed.
20 / £308 / £121

System prices do not include installation

So based upon the above and our 2015 usage patterns, somewhere between 4.8 and 7.2kWh storage, delta savings converges to 0. So no cost saving to be had exceeding 7.2kWh storage - within caveats mentioned above. Sweet spot seems to be somewhere between 4.8kWh and 7.2kWh. We have gone 7.2kWh, 5.

Assuming cost saving of £121/year, 10 year payback of £1210 - the battery system that I have ordered is £3k give or take a few ££. So that on paper is not going to pay back even in 20 years which is not good as a 10 year life span is probably to be expected.

As a sanity check, this gives self consumption at around 80%, which is inline with many published values. So I am fairly confident that the simplified approach is within reasonable bounds.

However, at time of calculating, I took other factors into account, such as energy inflation (its actually deflated) and assumption that my figures were 100% out being generous to wanting to justify a battery system, the real saving for us is somewhere between these approx figures and £308 (currently £290). Now with EV charging, and ability to time shift in winter and possibly move to something like Agile (this will flatten the evening peak) these figures above will be lower than current usage patterns, but I suspect cost saving wise, our system will come in close to 10 year or less break even.

All above assumes 100% round trip efficiency.

 

[MrBadger]

Any reason you went with the PylonTech 2000 over the 3000? The price is close but kWh is close but I thought the 3000 worked out slightly cheaper when I last looked at battery tech.

Yes, the deal that I got on the 2000 modules was better than I could get on 3000 units - the 2000 units are more readily available so seem to attract better discounts. Plus, if a unit failed, £770 (inc) is more palatable than £1200 or whatever they were.

 

[MrBadger]

Looks like a feasible solution at a good price.

one of the key specs that I liked about the PowerWall was it’s ability to deliver back 7kW peak and 5kW continuously. So if the oven is on and someone boils the kettle, it’ll probably still be within the capability of the system. At the price you have and with your techie nature you’ll probs work around the 3kW limitation but without sitting down 3 teenagers and doing some home schooling on how it all works, it wasn’t going to happen. When a 16yr old wants toast, they ain’t checking no app, I’m sure!

I’m also pretty sure your sums are better than mine and it’s probably cheaper to let it draw grid on those rare occasions.

The number of times that I would require a battery to support > 3kW (larger inverters are available) is few and far betwen - I have 6+ years of data so have done that check. The view that I take is that I am paying 25p/day for grid connection so I'm happy to get some value from it. Different if I was off grid, but I'm not, but if I was, a completely different solution would be required - traction batteries and two forms of renewables would be the direction that I would go, but I don't have option of 2 forms of renewable, so no off grid for me.

Now if you said that you suffered regular power cuts and wanted a whole house backup solution, then Powerwall and Gateway 2 would be a consideration (my chosen inverter has a UPS/backup circuit but its a dedicated circulate of limited power), but having a 16A solution greatly reduces installation complexity and for me, a compromise that I am willing to take especially when my chosen solution is a little over 1/3 the price of a Powerwall system that financially offers little difference in saving.

Obviously, a few fortunate people have large PV installations, but these are exception to the rule so of limited relevance to the average man on the street.

 

[MrBadger]

As a sanity check, this gives self consumption at around 80%, which is inline with many published values. So I am fairly confident that the simplified approach is within reasonable bounds.

Ignore this schoolboy calculation. But still confident that things are within reasonable bounds.

A Pimms based calculation puts self consumption at around 74%.

 

[gangzoom]

What ever setup you get you wouldnt be disappointed. Given our unusual amount of sun recently, even with rain earlier this week, and doing some longer commutes in the car, thanks to battery storage May could see us using even less grid electricity than April.

If it keeps up like this around 10kWh, I can see why whole sale prices are turning negative!!

 

[ACarneiro]

Well, I have two EVs in the household. When we both do our daily commute we “burn” about 70kW of power on the EVs alone so my solar installation even with two PWs will never be enough to cover that.
I guess I’ll be happy enough to shift all my usage to E7 rates...

 

[nightowl]

Thanks for the info on alternatives to the Powerwall. Certainly some very interesting batteries out there and they may possibly be more appropriate for my setup. If I got a battery, I could probably make do with something that has less capacity than a Powerwall.

Looking at recent generation and usage, it seems my peak generation is 2.5kW. With the recent clear skies I've mostly not been drawing from the grid for a majority of the day. I'm drawing from the grid for brief periods when one or more appliances need more than this, and a much smaller amount overnight for stuff that's always on.

So if I were to try and avoid the grid as much as possible, I'd probably need something that can cover the brief periods where power usage goes above what I'm generating (e.g. kettle drawing 3kW when I'm generating 2.5kW.)

I guess powering evening/overnight loads is more reasonable/worthwhile than trying to balance the above. I'd estimate 4-5kWh would cover most of the evening/overnight use. At least anything after this would be cheap rate.

 

[Battpower]

I'm not bothered with free electricity or full power EV charging capability that a larger battery may occasionally give, but I believe that this solution will significantly reduce our summer energy import at a very economic price

I think this is important to remember. You don't have to go to the capacity and expense of PW to get a large proportion of the benefits. Biggest benefits on mixed sun / cloud days where the battery buffer can often see you through the day without grid consumption even though your battery may not charge up very far.

 

[ACarneiro]

Yes, but the coolness factor goes up in proportion to the available storage

 

[Battpower]

Yes, but the coolness factor goes up in proportion to the available storage

Of course.

But when my batteries stop doing their job eventually, I'm sure I will look back at their financial benefit as well as coolness in deciding how much to spend replacing them.

And at least on my energy tariff, the least cool thing is throwing energy back at the grid, so finding ways (like water heating and EV charging with Zappi) probably offer most cool for your £'s.

Using a heat pump with battery storage for time shifting can be very worthwhile, but not if you just throw the energy away with poor insulation. The battery can easily cut electricity cost by 1/3rd and the heat pump multiply up its efficacy by a factor of 3 to 4 times, so compared with straight daytime resistive electric heating you could be cutting costs by a factor of 10 (rather unrealistically ignoring battery & equipment cost).

 

[Battpower]

Well, I have two EVs in the household. When we both do our daily commute we “burn” about 70kW of power on the EVs alone so my solar installation even with two PWs will never be enough to cover that.
I guess I’ll be happy enough to shift all my usage to E7 rates...

Sounds like you have a lot of low lying fruit. Certainly sounds like charging on decent E7 rate saves most with no additional outlay.

Taking the view posted elsewhere in this thread iirc, my first EV was based on an overall budget and I split it between a small EV and solar PV + battery system rather than all on a more extravagant car. Compared with buying petrol for 12k miles pa over 6 years I have already paid back 85% of the PV system and it is still producing at same rate as new.

When I look at (especially) my winter electricity use, it does make me wonder if it made any worthwhile difference switching to LED lights, but I guess that's the old question of would you care about saving 50p on a £5 purchase any more or less than saving £5 on a £50 purchase.