Solar + Battery quote with EV

hong318500

TLDR

Hi there, I am new to the country and moved in to our new house last year. Still learning the new culture and etiquette on posting/discussing on forum so apologise if I am doing something unusual.

We have a 3 storey house, south facing 35-45 degree slope tile roof. We have been exploring the possibility on having solar panel with battery as a cost saving investment in a long run since we expect to live here for long. We are now a couple but expecting to expand with kids soon. Current usage would be around 3500kWh a year but since we just bought a EV, usage is expected to double up and even more when kids come in the future. We are currently with Octopus intelligent Go tariff which gives some us off peak session in day time as well.

We got a quote with the council solar together programme with 12 Aiko 445W gen2 panels, Fox ESS EP5 14kWh battery and Fox hybrid inverter for around 9k. we thought it was a competitive quote until we see this MSE board. We ran through some posts here and understand there might be better options with local installer for similar cost. Powerwall 3 is also on our list for its ability with Intelligent Flux tariff. We don't mind putting bit more upfront cost as long as the system is reliable and reputable. I see some long term contributing users here are helping other users and suggesting solutions, I appreciate if you could help me with regard to the below things.

1. what would be the best tariff combination/strategy given I have an EV. IOG import with fix export? or straight to Intelligent Flux? or any other suggestion?
2. I don't know what size of battery is best for my situation. Users say it is not the bigger the better, i just don't get it.
3. any system is better for future expansion? i am working on my garden and planning to get pergola, i see discussion on DIY extra solar panel on pergola and i am thinking on the shad as well. I guess Powerwall 3? since it has multiple MPPTs?

appreciate if you have read the whole post and shad some light.

QrizB

Welcome to the forum!

£9k isn't a terrible price but you're right that there are other options.

I did some calculations on costs and returns for solar (no battery) and EV in a different thread recently; you'll see them here:

https://forums.moneysavingexpert.com/discussion/comment/81473442/#Comment_81473442

Adding a battery brings another factor into the calculations and I don't find it especially easy to model but (so long as Octopus continue to offer their Intelligent Flux tariff) a battery that's compatible with that tariff can be hard to beat.

Reed_Richards

hong318500 said:

  
2. I don't know what size of battery is best for my situation. Users say it is not the bigger the better, i just don't get it.

That's an easy one.  Suppose you get that 14 kWh battery.  If you get an EV tariff then you can charge your battery cheaply from the mains at the same time that you charge your EV, particularly in the depths of winter when there isn't much sunshine for your solar panels.  So if your house uses around 12 kWh during the daytime hours of your peak electricity tariff, that can be met by discharging your battery from 100% to 10 % (10% is the usual allowed minimum).  But if your house only uses 6 kWh of daytime electricity then you only need a 7 kWh battery and you have paid more to get a bigger battery than you need.     

Screwdriva

hong318500 said:

1. what would be the best tariff combination/strategy given I have an EV. IOG import with fix export? or straight to Intelligent Flux? or any other suggestion?
2. I don't know what size of battery is best for my situation. Users say it is not the bigger the better, i just don't get it.
3. any system is better for future expansion? i am working on my garden and planning to get pergola, i see discussion on DIY extra solar panel on pergola and i am thinking on the shad as well. I guess Powerwall 3? since it has multiple MPPTs?

appreciate if you have read the whole post and shad some light.

1. I've found IOF to be the most lucrative from April to October and IOG from November to March. I've checked with some of the installations I've helped with, and several are earning £25 a day on IOF! 

2. I would highly recommend focussing on quality of brand instead. A Fox system cannot compare to a Tesla PW3, which is the battery inverter to go for! 

3. PW3 has 3 MPPTs and a software programmable inverter (no need to purchase a larger inverter down the road) should your system size increase.  

12 X Eurnener 500W bifacial panels (>12.5% more generation) paired to a Tesla PW3 should cost ~£11K. If you can fit more panels on there (often the case), it's another £250 odd per panel. 

hong318500

QrizB said:

Welcome to the forum!

£9k isn't a terrible price but you're right that there are other options.

I did some calculations on costs and returns for solar (no battery) and EV in a different thread recently; you'll see them here:

https://forums.moneysavingexpert.com/discussion/comment/81473442/#Comment_81473442

Adding a battery brings another factor into the calculations and I don't find it especially easy to model but (so long as Octopus continue to offer their Intelligent Flux tariff) a battery that's compatible with that tariff can be hard to beat.

thank you, that's a really comprehensive calculation. I am pretty sure I could optimize bit more with day time off peak rate if I choose to charge the EV day time.

hong318500

Reed_Richards said:

hong318500 said:

  
2. I don't know what size of battery is best for my situation. Users say it is not the bigger the better, i just don't get it.

That's an easy one.  Suppose you get that 14 kWh battery.  If you get an EV tariff then you can charge your battery cheaply from the mains at the same time that you charge your EV, particularly in the depths of winter when there isn't much sunshine for your solar panels.  So if your house uses around 12 kWh during the daytime hours of your peak electricity tariff, that can be met by discharging your battery from 100% to 10 % (10% is the usual allowed minimum).  But if your house only uses 6 kWh of daytime electricity then you only need a 7 kWh battery and you have paid more to get a bigger battery than you need.     

That's an easier answer than I expected. thank you.

hong318500

Screwdriva said:

hong318500 said:

1. what would be the best tariff combination/strategy given I have an EV. IOG import with fix export? or straight to Intelligent Flux? or any other suggestion?
2. I don't know what size of battery is best for my situation. Users say it is not the bigger the better, i just don't get it.
3. any system is better for future expansion? i am working on my garden and planning to get pergola, i see discussion on DIY extra solar panel on pergola and i am thinking on the shad as well. I guess Powerwall 3? since it has multiple MPPTs?

appreciate if you have read the whole post and shad some light.

1. I've found IOF to be the most lucrative from April to October and IOG from November to March. I've checked with some of the installations I've helped with, and several are earning £25 a day on IOF! 

2. I would highly recommend focussing on quality of brand instead. A Fox system cannot compare to a Tesla PW3, which is the battery inverter to go for! 

3. PW3 has 3 MPPTs and a software programmable inverter (no need to purchase a larger inverter down the road) should your system size increase.  

12 X Eurnener 500W bifacial panels (>12.5% more generation) paired to a Tesla PW3 should cost ~£11K. If you can fit more panels on there (often the case), it's another £250 odd per panel. 

Thank you Screwdriva, do you mind if you send you DM?

Screwdriva

hong318500 said:

Thank you Screwdriva, do you mind if you send you DM?

Happy to help everyone I can!