An Off-Grid Electric Hot Tub

John Root is a longtime solar pioneer and this is his journey to powering an off-grid hot tub at 6,000 feet in the Sierra Nevada mountains:

“I’ve been living on- and off-grid for 40 years. I started out building hot-air solar collectors and designing root cellars with sunspaces on top. For those designs, I fed air to the root cellar via a 50-foot ground tube. I then vented the root cellar into the sunspace or greenhouse. It worked great, preserving food for winter, helping heating the house, and cooling the sunspace in the summer. I was hooked.”

“Next came a Jacob’s 10-kilowatt wind turbine. You have got to love 40-percent tax credits, which allowed for my business, The Rootcellar, to be born. For the next 40 years, I dedicated my efforts to promoting renewable energy and sustainable living. However, years of climbing towers, installing solar, and general hard work left me with one knee replacement with the other due to be replaced in the fall, and my hands full of arthritis. I’m not complaining here, just stating the facts. I’d do it all again in a heartbeat. I’ve been fortunate to live in a wonderful time and am watching my vision turn into reality.”

“Today, I am a campground host living in my solar-powered travel trailer and residing in off-grid campgrounds. I love this life and the people I meet! In order to continue this lifestyle, I needed to find a way to relieve my arthritic pain pills that made me sick. Supplements help but soaking in a 104-degree Fahrenheit hot tub really did the trick.”

“But how to run a hot tub in an off-grid campground with a 7-year-old, 150-amp-hour battery bank? Installing a 1,200-watt solar array was the trick. Also, it gets down to the 40 degrees at night in the mountains, so we are seeing a 20-degree temperature drop at night. This was really going to be quite a challenge.”

“I started out testing an Intex inflatable hot tub and found out it draws around 1,200 watts when the pump and heater are running. That’s a 27-amp draw on my 48-volt battery bank, which is producing 24 amps peak power. Clearly, I needed more PV and battery power.”

“Upon retiring, I outfitted my work truck with a 1,200-watt solar array and a 200-amp-hour, 8-year-old battery bank. I then wired the RV battery bank in parallel with the truck battery bank. That solved my daytime capacity issue, but the old batteries were not up to running the hot tub after 5pm. Also, the hot tub heater wasn’t suitable for raising the hot tub temperature up to 104 degrees, which is the temp that makes the pain go away.”

“I knew from my early days in wind that it was possible to heat water with a direct-current (DC) element. We would use water heating as a diversion load for excess wind power. However, I hadn’t heard it done with solar. I thought, what the heck, I’ll give it a try.”

So, I went to my good friend Rob Hach at Trusted Energy in Alta, Iowa, and he helped me out fit my 12-foot cargo trailer with three 385 Sunpower 67-volt modules. Next, I contacted my friends on the solar pioneer website asking if anyone knew how a water heater element would work best with a PV array with an open-circuit voltage of 180 volts and an amp rating of 6 amps. After some discussion, the answer came back to try a 240-volt, 3,500-watt element. I had a place to start, so to Amazon I did go. I found the element for $8 and when it arrived, I installed it in my floating DIY element holder. I was ready to test.”

“To my surprise, both the voltage and amperage varied dramatically. I achieved a maximum voltage of 107 volts and a maximum amperage of 6.2 amps — which is about 700 watts from a 1,100-watt array mounted flat. I’m sure as the summer progresses, those numbers will improve.”

“The beauty of this system is that it turns itself on and off, and eliminates the need for a charge controller, battery bank and inverter. I’m sure that if I added more modules, the wattage could be increased.”

“A final note: Amazon carries 48-volt, 10,000-watt elements. However, I think it would be less expensive to add modules than to purchase a charge controller and batteries.”

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