Domestic energy monitoring: Is a home battery worth it?

Cross posting a Twitter series I've started onto the blog.

@richardelliot

I love the idea of a home battery to connect to our PV system because I'm a sucker for new technology, even if I know they won't be economic until about 2030. As a way of delaying the purchase by a minimum of 12 months I've decided to collect a year of data 1/

@richardelliot

The measurements are complicated by a) getting good data, b) because we already store some electricity in the form of hot water via our power diverter and c) because I don't know what I'm doing. C is without doubt the biggest problem. 2/

@richardelliot
I'm going to ignore peak loads, that can be my reason for putting off a purchase in year two 3/

@richardelliot
June 2018: Average import of 3.5 kWh per day, stored 4.9 kWh as hot water and exported / could have stored 6 kWh in a battery. Max import on any day 5.3 kWh. Conclusion: A battery could have made us off grid. 4/

@richardelliot
July 2018: Average import of 3.6 kWh per day, stored 4.6 kWh as hot water and exported / could have stored 5.8 kWh in a battery. Max import on any day 5.6 kWh. Conclusion: A battery could have made us off grid. 5/

@richardelliot
August 2018: Average import of 4.2 kWh per day, stored 4.1 kWh as hot water and exported / could have stored 2.9 kWh in a battery. Max import on any day 6.5 kWh. Conclusion: A battery could have met 70% of our needs. Could have been off grid if we stored less as hot water. 6/

@richardelliot
September 2018: Average import of 4.2 kWh per day, stored 3.9 kWh as hot water and exported / could have stored 2.3 kWh in a battery. Max import on any day 6.5 kWh. Conclusion: A battery could have met 50% of our needs. Could have been off grid if we stored less as hot water. 7/

@richardelliot
Classic sunny, but short, autumnal day. Completely mismatched generation and demand for a working family. Exported 4.4kWh and imported 5.5kWh (so far). 8/

@richardelliot
October 2018: Average import of 6.2 kWh per day, stored 2.3 kWh as hot water and exported / could have stored 1.0 kWh in a battery. Max import on any day 10.9 kWh. Conclusion: A battery could have met 20% of our needs or 50% if we didn't store any electricity as hot water. 9/

@richardelliot
Generation continued falling in October and our electricity consumption rose significantly making it a bad month for energy independence! We have a number of electric heating sources that we use as a little top up before the central heating comes on. 10/

@richardelliot
November 2018: Average import of 7.6 kWh per day, stored 0.9 kWh as hot water and exported / could have stored 0.3 kWh in a battery. Max import on any day 9.7 kWh. Conclusion: A battery could have met 4% of our needs or 20% if we didn't store any electricity as hot water. 11/

@richardelliot

The stats this month are looking pretty bad, but if we had some form of local / district storage we could still be energy independent for about another month based on all the excess generation over the summer.

@richardelliot

December 2018: Average import of 7.5 kWh per day, stored 0.1 kWh as hot water and exported / could have stored 0.4 kWh in a battery. Max import on any day 10.6 kWh. Conclusion: A battery could have met 5.6% of our needs or 6.5% if we didn't store any electricity as hot water. 13/

@richardelliot

The December stats look pretty bad again, but if we had enough storage we could still be energy independent based on our summer generation. This is the last month I'm likely to be able to say that though. 14/

@richardelliot
In 2018 we earned £453 from our solar panels in generation and export tariffs 15/

@richardelliot
January 2018: Average import of 8.3 kWh per day, stored 0.0 kWh as hot water and exported / could have stored 1.0 kWh in a battery. Max import on any day 11.4 kWh. Conclusion: A battery could have met 12.4% of our needs 16/

@richardelliot
February 2018: Average import of 6.8 kWh per day, stored 0.0 kWh as hot water and exported / could have stored 3.3 kWh in a battery. Max import on any day 10.3 kWh. Conclusion: A battery could have met 48% of our needs 17/

@richardelliot
We generated 15% more electricity than we used in April. First month of the year back in positive territory. 18/