electric car

We changed car in January, and now have an electric one.  The idea is to use our solar power during the day to charge it, and cheap rate electricity at night as needed.  We don't have our 7kW Zappi charger installed yet (watch this space!), so are charging off the mains more slowly, at just over 2kW.  Even so, we get about 20% added to the battery overnight (exact amount seems to depend a bit on temperature and starting charge in an as yet ill-understood way; I am gathering data), and about 10% on a sunny February day (we anticipate more during longer summer days).

Here's our electricity usage for the beginning of February (more details on my solar stats page).   The vertical axis runs from -8kW to 8kW. The region above the axis represents our usage: orange is generated usage, red is imported from the grid. The green region below the line is surplus generation exported to the grid.  The numbers are total kWh for each day.

On 1st Feb, a nice sunny day, we charged the car on solar power (the orange block around midday), adding a reported 9% to the battery, with an estimated range increase of 25mi, for "free" (as we broke even on the cost of the PV installation several years ago).

Then on 4th Feb we charged overnight (the red block, midnight to 7am), adding 18% charge, with an estimated range increase of 37mi, for  £1.42 on our low cost overnight tariff.  That's 3.8p/mi.

The fuel consumption stats are a bit more fiddly to calculate than with petrol, going from filled tank to filled tank, as not every charging session "fills" the battery.  And the cost of charging varies wildly, from free off PV, to low off overnight tariff (9p/kWh), to eye-watering in service stations (79p/kWh).  So, no "filling up" at service stations; rather, adding just enough to get home.

I do like the fact that during charging, you can measure how fast the estimated range is increasing, in units of miles per hour.