battery power

We recently got an electric car.  In order to be even greener, we also got some more solar PV panels, to augment the ones for the house.  These are now installed, mounted on the west facing garage roof, whilst the original ones are on the south facing house roof.  So we are also extending our generation time to later in the day.

9 new PV panels, plus a Zappi car charger (between the open garage door and the water butt)

These panels should generate approximately the amount of electricity in a year for 10,000 miles of car travel, hence making us effectively carbon-neutral on mileage (even if some of the generation will be exported, and I will need to charge the car in other places sometimes).

And to be economical with all the electricity we generate, we have also invested in 20 kWh of battery to store our PV generation for use over night:

20 kWh of storage capacity

So we have three rough use cases:

• summer, best case: we generate enough during the day to run the house (and also charge the car off the PV), and charge these batteries, which we use to run the house overnight -- so using zero mains electricity
• winter, worst case: we charge the batteries overnight on cheap rate electricity (and also charge the car overnight off the cheap rate), and use the batteries to run the house during the day -- so use only cheap rate overnight electricity 
• spring/autumn: we generate some during the day, enough to run the house during all the expensive rate electricity, but still need to charge the battery (and car) overnight -- so use only cheap rate electricity, and not that much of it

We also have an app that allows us to obsessively track generation, usage, and battery level.

Let's see what our electricity bills start to look like!  (But even so, it will take over 10 years to break even, we think: batteries are expensive!)