How to Build a Passive Solar Water Heater

Cut the cost of utilities and reduce your reliance on fossil fuel emissions by building a simple passive solar water heater.

  • Building a solar hot water heater is simple and can produce significant savings on utility bills with minimal investment.
    Illustration by Dave Channon
  • A “breadbox” heater (containing a single, horizontal storage tank) may supply all of your hot water needs for a season or simply “boost” or preheat water.
    Illustration by John Canivan
  • The U.S. lags behind in domestic solar water systems.
    Chart courtesy National Renewable Energy Lab
  • A collector with multiple tanks, like this vertical batch heater, can produce much of the hot water a small family needs. Adding an insulated cover to the collector conserves heat and can also function as a reflector.
    Illustration by Dave Channon
  • A building-integrated hot water system offers protection against freezing temperatures. This system is less obvious than ground- or platform-mounted heaters.
    Photo courtesy National Renewable Energy Lab
  • A single-tank batch “breadbox” heater.
    Photo by Solar Components Corporation

Follow these guidelines to build an easy and affordable solar hot water heater. Explore the various types of solar water heaters. Learn how a passive solar water heater can be simple to construct and reduce your utility bills.

How to Build a Passive Solar Water Heater

For the do-it-yourselfer seeking an inexpensive, easy-to-build solar water-heating system, the integral passive solar water heater (IPSWH, pronounced ips-wah) is a dream come true. All you need to build this down-to-earth water warmer is a discarded electric water heater tank, a homemade insulated plywood box to house the tank, a sheet or two of used window glass or clear plastic, a few common plumbing fittings, some pipe and a bit of insulation. Add a few satisfying hours of measuring, thinking, sawing, hammering, painting and wrench-turning, and you’ll have a continuous supply of hot water, provided virtually free of cost by that friendly furnace in the sky (the only safe nuclear reactor, 93 million miles away).

First, let’s review the basics of solar heating for new recruits to the wonderful world of renewable energy. There are two basic types of solar water heaters, active and passive. Active systems depend on external power to run pumps to circulate the heat they gather; passive setups don’t. Passive systems may be less efficient at any given moment, but they are much more dependable and cost less per unit of heat captured. Integral passive solar water heaters, also called batch heaters, are the simplest of the passive systems, and their reliability and independence from external power lead to long-term production at a very low cost. I know of a system in Davis, Calif., that has operated for 30 years at a cost per kilowatt-hour equivalent of about a penny.

Batch heaters have long been known as the best choice in warm climates or for seasonal use in colder areas, and recent work with improved materials and designs suggests they may also be the best choice even in colder areas. For owner-built applications, they outshine their flat-plate and evacuated-tube competition in almost every way, including reliability and ease of installation. They have excellent potential for retrofits and are ideal for a range of farming and commercial applications, providing low-cost hot or warm water for washing or preheating for higher temperature uses.

Solar Water Heaters: Five Hot Ones

Now that you know the basics, let’s take a look at five of the many types of batch heaters in use today.

The Solar Shower is really a small-scale batch heater, a classic design using clear and black plastic to make a portable and surprisingly effective solar water heater. Water is placed in the bag and then set out with the clear side facing the sun. Within an hour, the water starts to heat up, providing a delightful shower on even a cool day if the sun is bright. I have used these for years while camping and am always impressed with how well they work.

10/25/2019 2:33:45 PM

I find it disheartening that the article claims the sun is “the only safe nuclear reactor”. Nuclear reactors have their issues, but they’re zero-carbon (aside from the mining, which is the same for most other plants) and aren’t intermittent. We need to switch to nuclear until we figure out energy storage, because we need to tackle climate change with every option we have. Eventually we won’t need nuclear anymore, but we’re not there yet.

7/4/2017 9:12:32 PM

the article says how to build. there is nothing in the article that describes how to build a solar water heater. It talks about various parts etc. but no concrete plans. Why not describe with pictures how this writer did this. It would be so much more helpful

3/18/2016 2:47:31 AM

Thanks for sharing this blog,its really informative one,now a days solar has been used by every houses,due to power consumption.​



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