Skills Used: Mechanical Design, Problem Solving, Welding, Electrical Design, Assembly/Construction
Project Dates: 2019
Additional Documentation Available: Yes, pictures, documents, and video
Project Description:
Back in 2019, I began an endeavor to build a large off-grid solar setup to supply 100% of the power demands of a house and shop. Due to time and budget constraints, I never did build the house or shop, but the solar was more-or-less completed.
My setup featured 6KW of solar panels mounted to a shipping container using only off-the-shelf parts available at any hardware store. I used standard strut channel and black iron pipe to create a mounting structure on the shipping container. The panels were affixed directly to the strut channel. The entire setup could be folded against the side of the container and moved if need be. Load calculations were applied to the mounting scheme to make sure the setup could withstand wind and snow loads in the area.
For a batteries, I went with more affordable Lead-Acid batteries from Crown. Specifically, I used 16 of the CR-430 L16 batteries, totally 860Ah of capacity in a 48V bank. They were configured as two parallel strings of 8 batteries in series (each battery is 6V and 430Ah). This gave me ~40KWh of total storage capacity, though only ~20KWh was realistically usable for longevity and temperature-adjusted capacities. The batteries were housed in an insulated room within the container. The room featured a temperature controlled exhaust fan to vent the space during charging or hot days, and a heat exchanger on the intake that cold water could be run through to help keep temperatures down on really hot days.
My inverter and electrical setup allowed for up to 12KW continuous and ~30KW peak power at 240V Split phase – just the same as any on-grid house. I used an inverter with a 60A automatic transfer switch and generator input. This allowed me to automatically switch to gen power when necessary. The inverter also featured a 100A battery charging feature which would run whenever gen power was available. I primarily used this to de-sulfate the batteries every so often. I also wired in a separate manual transfer switch of sorts just in case the inverter were to fail, I could bypass it and run on gen power. All the solar panels also came through special DC breakers for safety.
Charging was accomplished with a single 100A charge controller. While this did mean I could not realize the full 6KW capacity of the panels, I found that the smaller secondary charge controller I had did not play nice with the larger one, and would shut off early. The charge settings did not match and could not be changed.
Finally, the backup option: a massively overkill 100KW diesel genset. Honestly, I only used this because a) the price was right b) the smaller genset I had output such a terrible sinewave that the inverter would trip back to battery constantly. Once I re-wired the generator from 3 phase to split phase it was basically good to go. The large continuous-rated diesel set was rock-solid stable and output power just as clean as grid power. The only real drawback was the noise, being an old 6-71 2 stroke Detroit diesel (6 cylinder, ~7L), and the fact that at such low load for that size genset, longevity would be much shorter (fuel could wash down cylinder walls). Somehow, the fuel efficiency (in gal. burned/KWh) was near identical to the small one cylinder 5500W gas genset I had.
The setup was very good, but it was not completely without issues, and lessons learned will be applied to any future solar projects. Ultimately, the setup proved to be quite reliable and the envy of the neighborhood, providing constant 24/7 power with only one single interruption in 6 months of operation.
Towards the end of the project, I started keeping very accurate track of the battery charge state, power usage, and solar generation. Below are my log and solar capacity calculator. This data will help me in any future solar endeavors to develop a better performing system.
