Hi all,
I've got an ESS system up and running recently and started thinking about how I might be able to calculate the energy cost savings it generates over time.
I'm billed by a dynamic hourly rate from Tibber so one way I use my system is to charge the battery during cheap hours at night (simple scheduled charge for now) to then use during more expensive morning hours. On a sunny day I'll draw almost nothing from the grid between 06:00 and midnight, to then draw a lot between midnight and 06:00. To get an accurate estimate of what I save by doing this, I'm pretty sure I'd have to calculate what i would have paid without the ESS system on an hourly basis - hourly usage * hourly price and then subtract the actual grid usage cost. So something like:
Savings = (AC Consumption - AC Grid usage * hourly price)
So this has to be calculated hourly but then only makes sense over a 24h period. Most 24h periods should return a positive value. I need to have my price from Tibber here and not just common spot market rates since I need to have taxes, producer rates etc. included. Location is Sweden BTW.
I've briefly explored some alternatives - any pointers or input would be much appreciated:
- Spreadsheets? Ugh, somehow pull a week or a months worth of past hourly prices from Tibber and then somehow merge with the minute-by-minute data from VRM, and then repeat for each week or month. That's going to get old and boring real fast.
- Home Assistant? Ok, so there's some good Tibber integration here to get the hourly pricing and it can be set up to read Victron data over ModBus or MQTT but it's not obvious to me how one would combine that data, in what format to store it and whether I'd be able to export it later. Any comments/issues?
- Node RED? I've seen the webinar basically. An advantage is that it's closer to the ESS data. Has anyone set up an integration with Tibber here? Would it store any data on the physical Cerbo or up in VRM, or is it just not suited to generate and store data, just to act on it?
Hardware:
3x 3kVA Multiplus-II in 3-phase, running ESS assisstant.
1 MPPT RS 450/100, currently only with about 2.4 kWp of panels. To be expanded.
10 kWh stack of Nissan Leaf battery modules. To be expanded, probably.
Cerbo S GX + Touch 70.
Raspberry Pi running Home Assistant since yesterday =)
Misc thoughts:
So just to have it said - I don't really expect to have the time shifting of grid power-use pay off the system, I have the battery for other reasons, but now that it's there I might as well let it do some work, and it would be great over time to have the data on cost savings generated by shifting grid usage to cheap hours. I plan to get more panels and expect that the actual power generation is what will pay off the system in the end. I'm not sure yet if it's important to calculate savings from battery usage separately from solar production - in my view probably not since it's all part of the same system.
Any input is much appreciated!
