So, the story started with the wildfires here in California in 2018, one of which cleaned the town of Paradise off the map. I wasn’t directly affected by that fire, but the next year the power company instituted a policy of preemptively cutting power in the face of high winds to prevent future occurrences. That led to a series of outages lasting hours, potentially to days. After the first of these nearly resulted in the loss of the food in the kitchen fridge, I invested in a “big” battery (92AH AGM) and a used 2kw inverter to at least keep the fridge running. But that battery capacity lasts maybe a day, so the problem shifted to recharging the battery. The original plan was to use the gas car and jumper cables, but that was a bit dangerous. Sparks and flaky jumper cables… Eeech.
Then I got a deal on a solar panel, creating Plan B. Much safer, but I had to move the panel around all afternoon because of moving shade. Annoying, but infrequent. Also annoying was seeing the solar panel just sitting there in the garage when not in active use, a sunk cost. Why not put it to work?
New goal: Yes, be able to recharge the battery, but in the mean time use the solar energy to offset the base electrical load.
The system has evolved (expanded) over the years. One solar panel turned into two, mounted on the roof. The initial battery was a small AGM, just there to keep things stable since daily cycling a lead-acid battery won’t last. Swapped that out for a 50AH LiFePO4 and adjusted things to enable time-shifting the energy, then upgraded it to a DIY 315AH from cells to time-shift even more energy. Upgraded the 20 amp solar charger to 30 amps, too, as the 20 often got maxed out during part of the day. So, here’s where it ended up. At least, so far :).
Victron SmartSolar 100/30 charger, Phoenix 500VA inverter, and a Samlex 12v DC power supply are the core components. The power supply is set to a slightly lower voltage than the solar charger, so during the day the solar has implicit priority, replacing the power coming in through the DC supply, with the excess going into the battery. The accumulated battery capacity is then used in the evening as the sun goes down, increasing its value as the power company charges a premium for those “peak use” hours. The battery and DC power reach equilibrium voltage at night (or on cloudy days), letting the system run uninterrupted on mains power for as long as necessary. Because the battery never gets below about 50%, I always have a reserve for unexpected outages. A pair of existing UPS units bookend the system, allowing for more resiliency and short maintenance outages without having to shut down the computers.
The latest improvement to the system was to replace a home-brewed Arduino-based display for the Solar charger’s output with a Raspberry Pi running the Victron Venus OS, including the Phoenix Inverter and a connection to the battery’s BMS via a 3rd party driver. (Thank you Victron for providing the Raspberry Pi image. It adds a lot of value to the rest of your ecosystem!) The final piece was to add a SmartShunt to measure and track the DC power supply’s contribution. One bug was found, where the SmartShunt needed to be classified as a “Fuel Cell” or “Alternator” in order for its contribution to count. Calling it a “DC Source” or “AC Charger” did not work. So, the power company is officially a “Fuel Cell”; I guess that fits.
The system has generated just over 1,000 KWH of power since first turning on the Solar, which at the ridiculous rates we pay here is something like $400 US. That has not (yet) paid for the system, but it’s well on the way. And I still have the ability to keep the kitchen fridge cold by recharging that original “big battery” from the Solar / LiFePO4 system.
System Diagram:
Solar panels on the roof:
Battery (315AH LiFePO4, OverkillSolar BMS)
The overall electronics package:
And the resulting system under operation:
