Solar Powered, Off-grid EV Charging

This post was written by Christopher Borton, Co-founder and Director of the Sage Mountain Center and MREA Board Member. Chris recently made an exciting upgrade to the Center that promises to be part of the quickly evolving market of electric vehicles. 

The electric heater in my office is humming while outside it is 20 degrees F and our 2017 Chevy Volt is charging up from the solar electric panels on our site. In the 30 years we have operated Sage Mountain Center – our off-grid home and retreat center – we have always known there was a missing link in our sustainable lifestyle: clean transportation. We have organic and permaculture gardens, straw bale and cordwood buildings, solar heated hot water, recycled and re-purposed everything, and have even nurtured two Toyota Priuses (Prii) to more than 300,000 miles each. However, we have been unable to move our transportation to be fully powered by renewables. Like everyone, we’ve always had to go to the gas station because there was no other practical alternative to our remote transportation needs. Until recently, solar was too expensive, electric car technology was primitive and the mileage range of plug-in hybrids was too short for the big state of Montana. Things have changed.

There is a global electric vehicle (EV) revolution taking place and in preparation for that Sage Mountain Center has recently upgraded it’s off-grid facility to accommodate a charging station for EVs. We can now use the charger for daily business operations, as well as offer free solar-powered charging to visitors. Surprisingly, this solar upgrade was technically easier than we thought it would be given how difficult it was finding anyone who had done it before.

For a typical on-grid building, charging your electric car at home is a piece of cake. In fact, it’s exactly like charging your phone. You use it until the battery is drawn down and then you plug it into the wall to charge it. In the morning it’s full. You rarely drain your phone down until it dies and the same goes for the car. On-grid, the power company supplies hundreds of kilowatt-hours to you and you pay them once a month. With an off-grid home, you don’t have the luxury of “unlimited” power whenever you want because you are limited to the battery bank capacity of your self-sufficient home system. You can only withdraw energy that you have deposited earlier using your solar or wind systems. However, if you balance your usage throughout the day and night, off-grid car charging from the sun is very possible.

For the techies out there, here’s what we modified within our existing system while keeping the battery bank the same (19 kWh @ 24 Volt DC): 1) increased the size of the solar array from 4 kW to 11 kW; 2) added two 100A MPPT charge controllers; and 3) upgraded our 120 Volt AC system to 120/240 Volt AC. With the Level 2 charging system that we installed, the Chevy charges in about 4-5 hours at 16A @240 Volt AC but the system is designed with a 32A station (which is the norm for Level 2 car charging). Most houses have 120 Volt outlets, which is what the slower, Level 1 charging systems use. Because we are off-grid, we ONLY charge the vehicle when the sun is out, otherwise we are pulling from the house batteries which we want to avoid.

With the upgrades we made, we now have unlimited solar electricity for all kinds of niceties because the car doesn’t need charging every day. We can take advantage of selective electric heating, electric cooking, air conditioning for guests and electric water heating. Moreover, installing a larger solar system for the vehicle has now brought us to the point of never using a back-up gas generator again. Not a bad value-add! Solar electricity is silent, pollution-free, and finally, very affordable. Nature runs on sunlight. Shouldn’t we?