Mikes Solar Hot Water Heater

The other day I showed you Mike’s Micro House which he has been building for under $3,000.

Mike is also quite an inventor and is interested in solar and wind energy. He has created a simple hot water heater that I think would be useful for a tiny house or a large home. I asked Mike to share the details on how he creates his solar hot water heater.

Solar water heater. Sun during the day preheats the water in a 30 gallon water tank, prior to it being sent into the on demand water heater inside the house. This solar heater has preheated the water up to over 100F more than once when the outdoor temp was in the 30F range.

water heater

This simple setup works great, and is pretty much maintenance free. Just keep the glass clean, and you are good to go. If it starts to warm the water to hot during the summer months, just cover a portion of the solar window, to lower the sunlight bombardment into the solar chamber.

The solar water heater is simply a standard water heater (preferably one that was electric not gas powered).

Here’s what you do:

  1. Peel off the outer sheetmetal skin of the water heater, and cut off the foam insulation in order to get to the internal steel tank.
  2. Remove the electric heating element if needed and replace with a simple pipe plug fitting if the original element was bad, causing a leak.. Otherwise do nothing but remove all the electrical wiring to the element and the thermostat controls.
  3. Verify that the overtemp/pressure valve operates and looks to be in good condition, otherwise replace it, so you have a safety feature if the pressure were to build up to high from the heated water.
  4. Paint the water tank, “Flat Black” in order to help it absorb more of the sun’s energy.
  5. Build an insulated enclosure that the water tank can fit into, with a window on top at roughly a 45degree angle.
  6. Place the tank in the enclosure so that the southern sun exposure will shine directly onto the water tank inside.
  7. Plumb the cold water going to your existing home’s water heater to the input of the solar water heater, and the output of the solar water heater to the original cold water input of the original home water heater.

Now when the sun preheats the water in the solar water heater, it will be feed into your home’s existing water heater as hot water, therefore your now backup water heater should not work nearly as hard to provide hot water for your home.

To view more of Mikes inventions check out his flickr site here.

water heater2

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Ryan M - July 12, 2009 Reply

I have thought about doing this when I build my tiny home.

What is that white box with a speaker looking thing?

Some ideas for improvements.

When running the pipe from the tank to the house, what about having a copper tube painted black bent in a “S” shape several times to.

Second thing is take the tank, coat it with glue and roll it in sand. When it is dry, then paint it with flat black paint, this will create more surface area.

Finally, make sure you glass that you use doesn’t block any UV rays, solar radiation and the like.

Rob`C - July 12, 2009 Reply

I have been looking at on demand tankless water heaters. I have a small house without gas/propane. The electric on demand heaters look like they cannot heat enough water even for a low-flow shower. I’m sure there are some who would say they can live with luke warm water, but with a growing family, I would like to have a reasonable amount of hot water when I need it.

Has anyone found electric on demand heaters that can do 6-7/gal per minute?

Do people who have an electric on demand water heater have an seperate heater for the tub/sink etc? Sort of a daisy-chain?

Kent Griswold - July 12, 2009 Reply

Hi Ryan – here is what Mike says about the white box on his photo. I will see if I can get more specific information from him as to what it actually is:

“Merely a backup heat source to keep the tank from freezing if ever there were enough days in the winter that the sun wasn’t able to shine, to heat the water”.

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Benjamin - July 13, 2009 Reply

Ryan’s idea to glue sand on the tank doesn’t sound right to me. I suspect that the advantage of the added surface area would be more than lost by the insulation caused by the sand and the glue. I think the simple flat black paint is the best idea and one should take care to paint as thin a coat as possible to keep the paint from acting as an insulator.

Also, the glass cover worries me. Maybe a plastic cover would be better to avoid the chances of it getting broken. Especially if you have any trees around that might drop branches in the wind.

P B - July 26, 2009 Reply

Note that tankless water heaters may be a good alternative for businesses as well as homes. Pubs, Restaurants, Hotels, Motels, and more, all use TWH’s for the very large cost savings, being able to expense or depreciate the up-front costs. So if you have an in-home business, or you just want to make points with your boss by cutting expenses, keep that in mind.

Cobberman - October 22, 2009 Reply

A very interesting approach to a solar hot water heater. I’m wondering if there is an insulating cover that he places over the unit at night to reduce the loss of heat directly to the sky. He’s removed any of the insulation from the salvaged water heater so that it can absorb the sun’s energy but then he loses the heaters ability to retain that heat. I’m imagining that the greatest demand for hot water is in the morning for a shower. Unless you shower at night wouldn’t the water be only lukewarm by then?

Mandy - October 23, 2009 Reply

That is a great article. Very informative. Thank you for sharing it.

Solar hot water heaters - August 5, 2010 Reply

Its good to know “how to make Mikes Solar Hot water heaters”. I want to add here something more. Solar hot water systems are environmentally friendly and can now be installed on your roof to blend with the architecture of your house. More than 1.5 million homes and businesses in the United States have invested in solar heating systems, and surveys indicate that over 94% of these customers consider the systems a good investment.It also saves our pocket from 15-20% of our monthly electricity bill.

sc solar hot water - September 19, 2010 Reply


Solar hot water systems are Eco-friendly. Solar water heaters make use of radiation of sun in order to heat the domestic water. Solar water heaters Reduces carbon footprint and it saves fossil fuels. Solar energy is a strong source of green energy which can be regenerated from sun and it doesn’t provide any damage to our environment.

solar hot water rebates - February 14, 2011 Reply

Good article.Mike suggest a good way to exploit sun energy without concerning of expensive equipments. Thanks for sharing.

Jackson - June 27, 2011 Reply

Why the Southern Sun? I have a home office that faces west and here in North Texas it always seems like the sun is shining in my window, from the West.

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Hortensia Schwimmer - November 27, 2012 Reply

Water heaters can sometimes increase your electric bills. ‘

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john - August 18, 2017 Reply

Hello Mike, I am glad to read your blog. It is very useful, affordable and energy efficient solar hot water heater. I would definitely try this at my home by following your guidelines. I have a small doubt that in the days of winter when the sun was unable to shine then this water heater works?

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