It’s coming up to 12 months since we switched the system on; here are the vital statistics* and my own conclusions about its performance.
My 5kW solar system has generated 5800kWh over 51 weeks. Bang on what you’d expect for solar in Melbourne with a 13 per cent capacity factor against nameplate. No surprises there. Panels are so cheap these days, we installed as many as we could fit on the roof. While others wash their cars in the driveway on weekends, I get up on the roof with a squeegee.
Of the total amount of solar power generated, I have exported 3000kWh of electricity to the grid, getting paid 8c/kWh, while I have imported 1800kWh from the grid at 17c. Bummer. Time we had a one-for-one feed-in tariff, to eliminate distorting investments and behaviours.
The Powerwall stored and discharged 1600kWh of electricity, or about 33kWh per week. The aim, of course, is to fill and discharge the battery every day, while never importing any electricity. But we are not there yet, given our pattern of electricity use which is mostly at night time. There have been just a few days when we used more than 100 per cent of the capacity of the 6.4kWh Powerwall battery. That is to say, we filled it, discharged some, then filled it again.
Our electricity use is about 14kWh per day. We were always pretty frugal, but we do have our splurges on the hottest and coldest days, with electric heating and cooling.
Just over 50 per cent of my production was exported to the grid – it ‘overflowed’ the battery and it wasn’t used in the house. So I’ve either got an oversized panel system or an undersized battery. Or something. Gee I wish there was an app that would take all my data and tell me my ‘right sized’ storage, and give me an internal rate of return. That’s the big number everyone is speculating about.
One use for my excess electricity (on average 8.5 kWh/day) could be to store it as hot water. At the moment, we have instantaneous gas hot water. Maybe I could switch that to electric heat pump or resistance storage and disconnect the gas entirely? Big savings by eliminating that daily gas connection charge, and the gas itself isn’t getting any cheaper.
And now for something really exciting. I’m signed up with Reposit and Diamond Energy to export electricity to the grid at times of high prices, via software and a meter that they control. On Friday, my iPad flashed me a notification:
“GridCredits Event. Your battery has been requested to discharge for 44 minutes starting at 05:15 PM. You will receive $2.47.”
That’s $1/kWh at a time when the Victorian wholesale market was bidding about $1500 per megawatt hour. I’m competing with the big boys! That’s only happened three times this year, but looking forward, who knows? Fifty thousand more homes and businesses like me and we are on our way to a completely new form of energy market. Exciting times! * I’m no tech head, so I hope I’ve got this right. I’ll give access to my monitoring portal to any energy boffin who wants to have a crack, as long as they’re prepared to write it up for OneStepOffTheGrid
Greg Barber is leader of the Greens in the Victorian parliament