Long story short, I have a secondary, very weedy, solar PV system with a max output of 0.7 kWh installed on a barn that has its own mains meter. Background usage is only ~ 30w continual, so when the sun shines most of the generation goes out to the grid for no recompense.
I have very little that I can use this “wasted” power for. An obvious start would be to power two small fans that keep a classic car storage “bubble” inflated 24/7. AIUI they use 2 x 220 mA = 440 mA = 0.4A @ 12 vDC.
This is all very small amounts so I don’t want to spend £££ saving a few pennies, but it might be a fun project to divert the excess generation in to a 12v battery, and then run the fans from that.
What would be a good way to a) monitor when excess generation is happening and b) then turn on the battery charger?
I have an emonTx & an emonPi capturing generation and usage. They currently report to a local emonCMS.
Would this be a use for MQTT (something that I have yet to investigate) coupled to NodeRed or IFTTT and then a smart 13A plug socket for the battery charger? Or would there be something better? Ideally I’d like to include some form of buffer so that the charger doesn’t activate until there is specified threshold of excess production (perhaps 50-100W???).