Ever since I was a kid, water heaters either ran on Shore Power or with a heat exchanger from the motors hot water. When I took out my diesel motor to put in an electric motor, I gave up half my heating options. When I went cruising, I disconnected from shore power and gave up hot water all together!
After 5 years of cold showers, we finally have hot water again! A company called Missouri Wind and Solar makes a 48VDC, 700W water heater element that simply threads into your existing water heater. It has all the necessary components built into it so all you need to do is give it electricity!
Water heats at a known rate, 2.4705 Watt hours to raise 1 gallon 1°F. This means that if you have a 6 gallon water heater, you will need 14.8W per °F that you want to increase in the tank. If your sailing in cold water where the temperature is 50°F and you want a nice hot shower at 130°F, you need to increase the temperature by 80°F and that will use 1.18kWh of power!
1184W (needed to warm your shower water) / 700W (the power of the heating element) = 1.7 hours or 1 hour 41 minutes to heat the water for your shower.
1kW is a lot of electricity to use on a hot shower, but when you are cruising, you don’t shower everyday. On shower days, simply turn the water heater on about 2 hours before you want your hot shower and then turn it off when you are done!
To make showering even more efficient, we are able to still be charging from our solar panels with the heater on, letting us heat the water for an afternoon shower without draining our batteries.
You might be wondering why even bother with a DC water heater. Why not just get and inverter or run a generator? Those things are expensive! If you have an electric motor, it probably runs on 48VDC or higher, and you are familiar with set up and step down DC-DC converters from Victron and how affordable they are! The water heater element costs about $80 from Missouri Wind and Solar, while an inverter to power an AC water heater will cost you close to $1000! A generator is another option, as it will crank out the power to run the water heater, but they also cost about $1000 to buy and more in gasoline to operate.
All of these alternatives are going to cost you while having a DC water heater element lets you run it off your batteries for under $100.
