Guidance for solar system please

ddi

The difference between a power expansion pack and a 2nd powerwall 3 is £1,200 installed. I don’t fully understand the difference. 

Screwdriva

ddi said:

The difference between a power expansion pack and a 2nd powerwall 3 is £1,200 installed. I don’t fully understand the difference. 

Think of an expansion pack as a "dumb" Powerwall 3 i.e. without a built in inverter. 

Pros:

1) Cheaper

2) Bolts onto the existing PW3 (can fit upto 3)

Cons:

1) Doubles storage but not continous output

Based on what you have shared, your continous output requirement is < 3 kWh during the winter. Even with a another heat pump running, it will likely never approach 11kW, which is why I would save the £ and get the expansion pack (vs. another PW3).

Remember to insist that the installer agrees to fit a 3rd expansion pack for a mutually agreed price as part of your contract, should you decide to exercise that option within the next year - this will save you having to pay for additional costs (labour etc.) down the road should you decide to add more storage later. If you believe you don't need it, simply decide not to exercise that option.

ddi

Sorry to be so difficult but how have you worked out our continuous output please? Is it basically daily usage divided by 24hrs? 

If so, then yes, our daily usage of 45-60 divided by the 10 hours of day time we are home with everything running doesn’t come to 11. 

Ooh crikey, can I really insist that the installer adds an expansion labour cost free? 

ddi

Solar PV & Battery Storage

Size of system 12.5kW & 27kW Battery Storage

Equipment;

25 x 500w Eurener Nexa TOPCon N-type Bi-Facial panel 30-year warranty

  2 x Tesla Powerwall 3 integrated inverter & 13.5kW battery storage 10-year warranty

  1 x Tesla Gateway 2 10-year warranty

  1 x Zappi EV Charger

  1 x Bird Protection

  1 x All cable run’s isolators and fitting’s

  1 x Micro generation meter

  1 x System Wi Fi monitor

  1 x System registration

  1 x Access Equipment

  1 x MCS and G99 Certificates

Does circa £23k seem a lot for this? 

Another option for £15k is…

20 Dmeg 500w all black panels,

Fox 10kw single phase Hybrid inverter,

20.72kW of battery storage made up of two Fox 10.36kW batteries. Bird protection, certification etc. 

Screwdriva

ddi said:

Does circa £23k seem a lot for this? 

I would ask for the expansion pack (vs. a 2nd PW3) and would expect to pay a firm £21K for it all. I have never seen a comparable system quoted for less and would feel confident that this was near impossible to best (like for like).

Putting aside the fact that alternative is a 25% smaller monofacial system with 35% less storage capacity and nowhere near comparable capability, I do not recommend installing Fox/ DMEG equipment in anyone's home unless it's free via the government backed ECO4 scheme - which it often is.

ddi said:

Sorry to be so difficult but how have you worked out our continuous output please? Is it basically daily usage divided by 24hrs? 

Ooh crikey, can I really insist that the installer adds an expansion labour cost free? 

Yes and yes (a price of ~£6K for a 2nd expansion pack at your option).

ddi

You’ve been amazingly helpful thank you! 

Qyburn

ddi said:

Sorry to be so difficult but how have you worked out our continuous output please? Is it basically daily usage divided by 24hrs? 

If so, then yes, our daily usage of 45-60 divided by the 10 hours of day time we are home with everything running doesn’t come to 11. 

There's some different usages of the same term. In the context of the PW3 battery and its inverter, "continuous" output means the output that can be sustained while there's sufficient solar energy and/or battery charge. If that's 11kW then if the house loads come to more than 11kW then the balance needs to come from the grid. It doesn't mean it can supply 11kW 24/7, that would run it flat in around 75 minutes if there's no solar.

So really what you should be doing is comparing peak house loads with that figure. How often and for how long will any combination of devices push the total over 11kW. For example are you likely to be cooking, or having an electric shower at the same time as the heat pump(s) are running.