Home Battery Use - 1 year (and a bit) in

January 16th, 2018

Full year home battery summary for you…

Have a look.  You know you want to!

From the numbers on the first chart, below we’ve exported to the grid more solar over the year, than we’ve imported back from it (more than double).

Annual comparison of solar generation (in green), battery storage and use(in blue) versus our imports from the grid (little red bits)

So overall we’re net exporters of green power.  We have checked our earlier numbers (published on our blog here) and they continue to stack up reasonably well, with those original caveats still in play.

We believe we are on track to repay the cost of the supply and install of the battery and PV system within 5-6 years.  The warranty on the battery is 10 years.  So this leaves us, roughly, half the length of the warrantied life of the battery in which to start to get financially ahead and over time reducing our petrol consumption, too.

(Of course we already are ahead in terms of warm fuzzy green glows)

However, there is a mismatch in our PV generation and battery capacity, with the TIMING of our usage.

In a typical summer month we export more than we import by a margin.

Typical summer month: solar generation outstrips our usage on most typical days (red is down below green/blue).
On cloudy days you can see impact on generation, dropping that down.

However, generation drops in winter but our consumption peaks then if we use space heating etc. So we still pay retail prices, and have the pleasure of burning some coal…

Typical winter month where usage outstrips generation. Where red line hovers up above corresponding blue/green line with are both importing from the grid AND importing MORE than we are exporting.

We could either

  1. not care about this (it’s a pretty small amount and overall performing really well… and we’ve enjoyed missing some of the blackouts and power outages and aren’t planning on disconnecting the grid anytime soon), OR
  2. Do something about it if we want to.

Ways we could act to close the gap between energy we have available and WHEN we use it, include:

  • Use power at different times… this doesn’t hurt us – just means we have to plan a little. This would match the red (grid import) and green (our export) bits up a bit better:.
  • For example: Put the dishwasher or washing machine on timer setting for those times in the afternoon when the battery is typically full and we’re exporting power to the grid… rather than running them first thing in the morning when the battery is typically drained and the sun isn’t intense enough yet
  • Use less power… we could easily do this if we wanted to.
    We could wash out our breakfast bowls and do only 1 load in the dishwasher instead of 2. Or rug up a bit more in winter and run heaters less. Watch a bit less #Netflix (Wait. That’s crazy talk)
    Will see how far we get using other means though
  • An easy way would be to charge the car less, or only through the middle of the day.
    A lot of our energy use is the car charging. This is a good thing (helps pay for the battery by avoiding buying petrol, and help reduce the amount of pollution we pump out of the ground, and into the kids.)  But it also means we can flatten the house battery quickly those days where we charge it a couple of times a day, or overnight
  • And finally: with more storage (another battery) we’d export less to the grid, and use more of our own power… our aim is to push the little red line down below the little blue line…
  • It’s pretty easy to do that for 8 out of the 12 months
  • But those 4 winters months will be trickier… (where the little red line stretches up above the green one) where we are using, in total, more than we are generating… In those cases we need to either use less power, OR add more PV’s.

Of course… no system is perfect and it helps make sense of the existence of the grid by reducing the overall stress on the system.

Where if we all disconnected from the grid – most of us would then chase oversized power systems for our own homes… Which isn’t an efficient solution, either.