Works in theory! Practice? That's something else
- Sep 20, 2019
- Key Largo
The grid's gone down, but the sun is out! Your panel's are generating 10 kW, your batteries are full, and the 10 critical circuits you've hooked up the backup system are drawing 2 kW.
You're throwing away 8 kW!!!
I have not built this and you're probably crazy if you do.
That said, I'm throwing this idea out there to see how you'd improve it. If you build these, get them UL approved, and make a ton of money; please send a fruitcake to me for Christmas!
A Smart Panel allows you to utilize power you'd otherwise throw away. Rather than throw that power away you could be heating up your hot water tank, charge your EV car, connecting to the internet to read Will's forums, etc.
How it works
Simple! Put a CT on the battery or monitor battery voltage if that's more reliable. Then use a microcontroller to open/close relays to circuits one at a time until the battery starts expending energy and then close the last relay. One relay per circuit, dynamically configure things via your cell phones wifi/bluetooth connection. It might look something like the diagram below.
The green box is a 3 position switch. In Grid mode it connects to the grid. But in Solar mode it pulls from the grid unless the grid is down in which case the microcontroller decides if there's enough power to close the relay. Each output has a CT so any load change (e.g., the water heater shutting off) triggers a recalculation as to what circuits are open. By default circuits would operate sequentially, but since it's just software wifi/bluetooth access could allow you to alter that or allow some current out of the battery (e.g., you have a job interview coming up and really need hot water for a shower). Finally, the output CTs watts could be calculated and summed to validate the Inverter had enough wattage (and if not, relays would open). Could also add some intelligence such that the microcontroller learns what each loads pulls so it can estimate if a circuit can be safely activated.
This isn't really a new or particularly novel idea; when I heard how the Sol-Ark's "smart" relay worked I thought it was cool, but too limited.