Build a Thermosiphon Solar-Heated Shower System

Solar panel and water tank.
Photos by Kyle Chandler-Isacksen and Be the Change Project

A few years back, a friend donated a Sunvelope solar hot water panel. We were just about to expand our greenhouse, so the timing was perfect to incorporate a solar shower.

The system is pretty basic, with a panel mounted south and tilted to catch more rays just outside of our greenhouse and an old water heater tank positioned higher than the panel. Ours is a thermosiphon: Water circulates simply because of temperature differences with no need for electricity. It is also not plumbed to our house water source but instead is an isolated system, which we have to fill after about seven showers (more on that below).

How to Build a DIY Solar Hot Water Heater

Used water heaters can be found on Craigslist or Facebook Marketplace, no problem. It doesn’t matter if they work or not — just make sure they have no leaks. The heater has a cold and hot water port and a drain. For our purposes, it didn’t matter which port we used, because the water will circulate throughout the tank and to and from the panel.

I ran 1/2-inch PEX tubing from the high end of the panel (the hot-water outlet) to the tank and then from the tank back to the panel on its low end (intake). Before it cycles back to the panel, however, I put a “T” in the line and ran that into our greenhouse shower with 3/4-inch PEX. I think I just happened to have 3/4 lying around or I would've just used 1/2-inch throughout.

I both painted the PEX and covered some of it with a plastic pipe cover to prevent breakdown in the sun. I also tilted the panel forward a bit so that the outlet is lower than the inlet, which gives us a little more water to use before we have to fill it again.

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