A Solar Journey

Last weekend we had 26 solar panels, some battery storage and a couple of inverters installed at the new house. All was installed fine and seems to be working OK so far. We went through a local county-based scheme with Solar Together. They awarded the Suffolk scheme to Greenscape Energy and turned around the install really quickly.

The installer walked me through the online app that monitors generation, consumption, storage and returned it to the grid.

The generated energy is used as follows :

• Service the house energy load.
• Charge the storage batteries.
• Export to the grid.

When the load from the house is greater than the generated energy then the house gets energy from :

• Discharging the storage batteries.
• Import from the grid.

The credit for exporting energy to the grid is low compared with importing. Once the battery is fully charged, then any excess energy created goes to the grid. I think this means the perfect scenario is to use the energy throughout the day and have a 100% charged battery at the point the sun goes in. As such moving certain tasks like washing machine/dishwashers operation to the generation time can be beneficial.

Things are a little more complicated than this though. The battery system has a maximum charge and discharge rate. So for example even though it’s February, on a particularly sunny morning this week the solar generation exceeded the charge rate and exported energy to the grid.

I’m an electric vehicle owner, so thought I’d simply turn on the car charger and suck up some free energy from the sun and drain the solar storage battery for a while and then let it charge back up later. Well, it turns out that the default charge rate for the car significantly exceeded both the generation and the maximum discharge rate from the storage battery. So that meant that I was pulling energy from the grid. It turns out that I am able to reduce the charge load from the car, so I was able to balance this out (slower charge, but nothing from the grid).

This got me thinking it would be really nice to create some simple rules like :

“On a sunny day, charge the solar storage battery to 90% and then divert any excess to the car ensuring you don’t draw any electricity from the grid.”

It can’t be that hard to do, right?

All the data I would need to write something to do this is sat in the solar management application, I just need a way to get hold of it. So I searched for a public api, and nothing is available. A couple of folks have written screen scrapers for the web application, but this sort of tech isn’t that reliable. At this point, I was resigned to sniffing the calls from the web/mobile apps to the server and trying to reverse engineer an api. Again something that’s brittle, but it didn’t feel like I had much of an option.

Then I found two of the pictured boxes in some of the rubbish the installers had asked me to recycle. Each one is plugged into an inverter to send the data to the cloud. I’ll write up more on these next.