Published on December 5th, 2014 | by Peter Young


A Quick Guide To How A Solar Hot Water Heater Works


Solar hot water heaters (here’s one solar water heater option) are a great way to make your home more energy efficient, but if your system isn’t set up properly it might not actually save you any money. Thankfully, there are a few quick and easy ways you can check yourself to see if your system was installed and set up the right way. Just follow this guide to ensure that your solar hot water heater is installed and working properly.

First, however, a few basics. There are active and passive solar water heaters. Active ones have circulating pumps and controls. Passive ones do not. Among Active solar water heating systems, there are two types. One is direct, where water is simply circulated up to the roof and heated by sunlight directly in a solar collector. These work well in tropical climates.

For places where temperatures get down to freezing, however, an indirect (or “closed loop”) circulation system is the active solar hot water heater you’ll most commonly find.

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From Energy.Gov



These are closed-loop systems in which an antifreeze fluid is circulated up to the roof, heated, and then circulated down to a heat exchanger, where its heat is transferred to the water tank, thus heating the water indirectly. The cooler antifreeze is then recirculated back up to the roof and heated again. For the purposes of this article, we address direct circulation pumps, but the mechanics are not that different from that to indirect ones.

A quick guide to how a solar hot water heater works

The Basics: Let’s begin be taking a look at a short video to get an idea of how these systems work:

While your system may not be identical to the one featured in the video above, the basics principals are still at play when it comes to heating your water. Now let’s take a look at the various settings and controls that are in place that tell your system when and how to work.

System Settings: Your solar hot water heater will work in conjunction with either your gas or electric water heater, and because of this, certain settings will need to be in place to ensure that they’re doing so seamlessly. Let’s take a closer look at what those are:

“The Little Grey Box” – This box should look something like this:

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This little grey box is actually a timer that tells your electric water heater when to turn on and off each day. As you may have guessed, your solar hot water heater will only heat water during the day (when the sun is in the sky), and your electric water heater will supply the rest. Let’s take a closer look at the inside of the box and what that should look like if it’s set up properly:

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Inside the “little grey box” you’ll find a yellow time dial and a series of pins attached to it. The time dial rotates on a 24hr cycle and pins are set at the intervals for when you would like your electric water heater to turn on and off. Most of these timers will come with one set of pins, but we recommend that you use two sets in order to save as much energy as you can. Ideally you want your electric water heater to turn on for two separate two hour intervals each day (4am-6am and 6pm-8pm). This way your home will be supplied with hot water for both your mornings and evenings, but you won’t be spending extra money or using extra energy to do so. During the day, the tank will be kept hot by the solar heating, and setting the electric/gas backup to kick on from 6-8 PM will assure that there is hot water in the tank all night. If it gets used, the system will kick on from 4 AM to 6 AM and fill the tank with hot water again.

Setting these pins is easy to do and doesn’t require any special training to do so, just follow these easy steps:

1. Check that the timer is showing the appropriate time. If it’s not set correctly, setting the pins to the right times won’t matter. If it’s off, simply pull the timer toward you gently, rotate, and set to the proper time before setting back in place. Typically, this will need to be reset after power outages.

2. Loosen the screws on your first set of pins. Simply take your fingers and loosen the screws, they shouldn’t be any more than finger tight. Once the pins are loose they should freely move around the face of the timer.

3. Place your first set of pins at your desired on and off times. Simply align the pin labeled “on” with the time you’d like your electric water heater to first turn on (4am) and your “off” pin two hours later (6am). Once they’re aligned over your preferred times, simply tighten the screws till they are finger tight.

4. Repeat steps 2 and 3 for your second set of pins. Remember, you want your backup system to kick “on” at 6pm and turn off at 8pm.

That’s all there is to it. Now lets take a look at your Delta T (the device that controls your solar hot water heater)

The Delta T: This is the device that controls your solar hot water heater and it tells your system when to pump water up to the solar panels for heating. Let’s take a closer look:

controllers group shot copy

When it comes down to it, installing and programing your system should be left up to a professional installer. However, there is a switch on the device itself that you’re more than qualified to look at and change if needed. On the side of the Delta T box (which will be located near your hot water tank) there should be a switch with either an “On” or “Auto” option. If you’re going to be home throughout the week that switch should be in the “Auto” position, and conversely, if you’re going to be away on vacation the switch should be in the “On” position. If you’re experiencing problems with your Delta T system, we recommend that you contact your installer for assistance.

Photos courtesy of Flickr Creative Commons (Solar Hot Water Heater), Forest City Military Communities, Energy Evolution, Delta Controls

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About the Author

graduated from Pacific Lutheran University (PLU) with a degree in journalism and has made sustainability and eco-conscious living mainstays of both his professional and personal life. It was during his time at PLU that he began his journey with sustainability and it's what has led him to writing for Green Living Ideas. He currently resides in Honolulu and works for Pono Home, an energy efficiency company focused on reducing carbon emissions and promoting a healthier, greener lifestyle.

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