March 2020 Performance Update

The big news in March 2020 was, of course ‘Black Death 2.0’ (aka COVID-19), bringing death, fear and economic implosion on a worldwide scale.

On the upside, it was an exceptional sunny month! Only March 1929, 1995 and 2003 have produced more hours of sunshine in the North East of England since MetOffice records began (in 1929). So a juicy 521 kWh of free electricity fell out of the sky and into our house, domestic storage battery and two EVs.

And lockdown meant that, in the latter part of the month, we hardly did any mileage in the cars, so we used less off-peak electricity on the exceptionally good value Octopus Go tariff.

Headline summary data (rounded to nearest whole number) is listed below. Click the image at the end of this post for the usual detailed PDF of the month’s performance. And click the banner here for a referral link that will save you (and us) an additional £50 on their dirt-cheap overnight energy.

  • Solar generation: 522 kWh, of which 177 kWh was stored in the Tesla Powerwall domestic battery and discharged during peak hours.
  • Tesla Powerwall discharge of stored electricity: 546 kWh, of which 177 kWh came from solar and 369 kWh from off-peak electricity.
  • Octopus Go off-peak grid supply: 802 kWh, of which 369 kWh went to Powerwall and 433 kWh went to charging the two cars.
  • Peak grid energy consumed: 180 kWh.
  • Total financial benefits in month: £421 including motor fuel saving.
  • Total CO2 emissions savings in month: 570 kg.

This rather helpful month has helped keep the whole system on track for a rapid payback. Running totals are here. However, if the COVID-19 lockdown persists for a prolonged period over the summer months, a rather counter-intuitive effect will become apparent. If we drive very few miles in our EVs, then it is likely that they can be entirely ‘refuelled’ from completely free solar energy. The payback equation subtly alters:

  • Payback to date has been on the basis of reasonably high mileage, which is refuelled using a blend of solar and (quite a lot of) off-peak electricity. There is massive delta between the cost of that electricity blend and the cost of petrol to propel a conventional car over the same mileage.
  • In lockdown, far less miles will be driven, which will mean that this delta does not come into play, as the vast majority of charging is likely to be solar, at £0 cost.
  • Our savings, versus petrol for a given distance, are likely to be less overall. In short driving “a few miles at absolute zero energy cost” is likely to deliver less of an overall benefit than “many miles at a very low blended energy cost.” The effects will play out over the next few months.

During this month, Alan also published an article analysing the major upgrade to the package of tax breaks and other incentives the UK Government is introducing on 6th April 2020 to encourage the uptake of electric vehicles.