One Year With A Solar Battery

To recap, we have 5,040W of solar panels, with a 3.6kW inverter, and a 4.8kWh battery.

That's a lot of (expensive) gear! What does it mean in terms of energy savings?

Over the last 12 months we have:

• 4,000 kWh generated by the solar panels.
• 1,200 kWh purchased from the grid.
• 1,200 kWh sold to the grid.
• 1,300 kWh discharged from the battery.

(Data taken from various APIs and rounded to make life easier).

It's important to note that the battery doesn't only charge from the panels. Because we have a a smart electricity tariff, it will fill up from the grid when electricity prices are negative and empty when they are expensive.

Calculations

Generation - Export = Solar Use

4,000 - 1,200 = 2,800kWh

So we directly use about 70% of what we generate. Some of that is used immediately, and the rest goes into the battery for later use.

Using the battery's API, I was able to call up the statistics for each month. For example, in June, we only paid for 10% of our electricity!

I got the data for each month, these aren't quite as precise as I'd like, but they're good enough for modelling.

Domestic Electricity use kWh by Source per Month:

Wow! Averaged across the entire year, we've cut our electricity bill by about ⅔rds!

Across the year, we sell back as much electricity as we buy. We are net zero!

For reference, the average UK home uses about 3,500kWh. We're a little above average - probably due to working from home.

Cost

Electricity prices have been wild in the last 12 months. The dynamic tariff means we can buy cheap energy but use it when it is expensive. So it is hard to say with any accuracy how much money we've saved. I'm going to say very roughly that electricity costs 24p/kWh and we sell it for 12p/kWh.

( (Solar Used + Battery Used) x 0.24 ) + (Electricity Sold x 0.12) = Total Savings

( (1,280 + 1,243) x 0.24 ) + ( 1,200 x 0.12 ) = £750

The cost of installing solar and a battery will vary depending on where you are, what local incentives there are, how complicated your roof and existing electrics are, and a whole host of other factors. Payback depends on your usage patterns and energy prices.

We estimate our payback period to be between 6-8 years.

Obligatory Referral Links!

If you'd like a dynamic electricity tariff, or want an API to monitor your own use, or need to sell electricity back to the grid - join Octopus Energy today and we both get £50.