What is Solar Water Heating and How Does it Work?

Having a Solar Water Heater Means No Cold Showers

What is Solar Water Heating and How Does it Work?

My Granny Brown didn’t have indoor plumbing until I was around 11 years old. There were no solar water heating systems then. Instead, they put a small pump on the well when I was about nine. This meant we could shower outside most of the year without having to draw water for Granny Brown baths.

They ran a water hose from the pump over the top of the well shed and voila! A shower! Brr … it was ALWAYS a cold one! I wish we had been able to have an outdoor solar shower.

Solar water heating uses the heat generating power of the sun to heat water, not to generate electricity. Solar water heating devices have been used for hundreds of years, but there have been great strides the last 20 years in absorber technology. These advances have increased the solar energy efficiency of collectors which can now convert more than 50% of the available sunlight for heating water for the home.

Using a solar water heater is one of the most effective ways to decrease your dependence on the failing electrical grid and leave a lighter footprint as you go. There’s also the financial savings to take into account when you use the free power of the sun versus electricity, gas or oil.

How Does Solar Water Heating Work?

Solar water heating systems have two components: the water storage tank and the solar collectors. There are also only two types of solar water heating systems: active and passive. The difference is an active solar water heating system has a circulating pump and controls while a passive system doesn’t.

Active Solar Water Heating Systems


These can be either a direct circulation system or an indirect circulation system.

A direct circulation system has pumps which circulate water through the collectors and back into your home. These work well in climates where freezing temperatures aren’t a problem.

An indirect circulation system has pumps which circulate heat transfer fluids, which don’t freeze, through the collectors and a heat exchanger. This process heats the water in the tank which then flows into your home. In areas where freezing temperatures are the norm, this solar water heating system works better.

Passive Solar Water Heating Systems


This type of solar water heating system is usually the least expensive way to go, but they’re definitely not as efficient. The passive solar water heating system is usually more reliable and durable than an active solar water heating system.  If you have a high demand for hot water in the daytime and evening in this type of climate, this system will work well for you.

A thermosyphon system is a passive solar water heating system. It works as the water flows through it and the warm water rises as the colder water sinks. The solar collector must be installed below the water tank so warm water will rise into the tank.

The thermosyphon systems are dependable, but you must have a contractor who knows how to install and design for the heavy water storage tank. This type of solar water heating system is more expensive and involved than the integral collector-storage system.

About Solar Collectors and Storage Tanks

I suppose it goes without saying but a well-insulated water storage tank is a must for solar water heating systems. If you want to set up this type of water heating system, you have three types of collectors to choose from.

1 – A flat plate collector

Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors – typically used for solar pool heating – have a dark absorber plate, made of metal or polymer, without a cover or enclosure.

2 – Integral collector-storage  (discussed in passive systems)

Also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.

photo credit thesunbank.com

3 – Evacuated-tube solar collectors

Evacuated-tube solar collectors feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for U.S. commercial applications.

Just as many people with solar, wind or hydro power often have backup systems such as generators, a solar water heating system should have a backup system for cloudy days. Conventional water heaters can provide a backup and many people on solar power already have one installed in line with their solar system. A tankless on demand water heater is an excellent option and one we intend to install with our solar system on our new homestead.

If you live in an area like we do, an outdoor water tank would freeze solid. We have several friends who use solar power for their homes. They all have different setups including wood stove water heaters, but the same basic principles are in play.

They have their water heater hooked to their solar power supply. When they need hot water, the system kicks in and heats the water in the tank which is hooked to their water storage tank. Another friend has a tankless on demand system and it works great with their solar power system.

Why Would You Want to Use Solar Water Heating?

  • Solar water heating provides independence from the power grid. For the same reason people choose to install solar power systems, people choose to install solar water heating systems. The obvious reason is energy freedom, but the elimination of monthly energy bills is a major factor.
  • Not only independence for our family but the more people there are who don’t draw on precious resources, the less dependence our nation will have on fossil fuels. Some people with solar water heating systems do stay tied to the grid for backup purposes only.
  • To lessen the impact we have on our environment. Some people call this lightening your footprint. We are all aware of the toxic world we’ve created with fossil fuel usage and all the waste products resulting from it. Even nuclear energy leaves waste products with hundreds of years of death attached to them.
  • Solar water heating provides financial benefits. According to the U.S. Department of Energy, having a solar power system in place increases the value of the home and land based on the amount of electricity saved over the course of one year. The ratio is, at the current moment, a $20 increase in value for every $1 saved in electric power over an entire year. This could mean a substantial increase in the value of your home.

  There are tax incentives in place for those who install green energy systems. Check the current state and federal opportunities.

photo credit rek.uk.co.uk Basic Thermosyphon System

Unless you’re a do-it-yourself kind of person or know someone who is DIY and would be willing to help you, having a professional install your solar water heating system for you is a great way to get things going.

It’s pretty easy to determine what size tank you need. The figures say to plan on 15 gallons of hot water per person in the household per day. To me, this number seems excessive, but I guess better safe than a cold shower?

The solar company you choose will have tools for you to use to figure out what size of collectors you will need to heat the amount of water you’re planning on using in your solar water heating system. They will also help you decide which kind of system and collector will work best in your climate.

Do you have a solar water heating system? We would value your experience and lessons you’ve learned. Please share with us.

Safe and Happy Journey,

Rhonda and The Pack

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