Saturday, 1 September 2018

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/

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