How Active and Passive Solar Water Heaters Work
Green, Renewable Systems reduce utility bills and save money
© 2010 Kelly Smith; all rights reserved; content may not be copied, rewritten, or republished without authors written permission. Authors Google profile
This article was updated on 09/01/18.
There are two basic types of solar water heater systems: active systems which are equipped with controls and circulating pumps, and passive systems that are not so equipped. One of the best times to think about installing this energy-efficient alternative is when doing a kitchen remodeling project or a general remodel project.
Are they eligible for a federal energy tax credit? Unfortunately, not at this time; only oil, gas, electric, and propane get the government nod.
Heating Water with Solar Energy Isnt Overly Complex
What places these systems in the green building arena? Similar to residential solar panels, they use radiant energy from the sun, which is free and renewable!
The fundamental system is composed of 1 or 2 insulated storage tanks plus a solar collector. The collectors job is to receive the energy. There are different types; here are some or the popular ones:
- Flat-Plate Collectors. This type employs a dark colored absorber plate, glazed or non-glazed, which resides under a polymer or glass protective cover.
- Integral Collector-Storage. This type is a collection of either black tubes or tanks sheathed in a glazed, insulated box. You may hear them called batch or ICS systems. The function of the integral collector-storage is to preheat cooler water.
This flows on to a conventional-type tank heater or to a more efficient natural gas or electric on-demand water heater.
- Evacuated-Tube Solar Collectors. This collector takes advantage of parallel rows of clear glass tubes. More commonly encountered in larger commercial systems, they are also used in private homes as well.
On the interior of each glass tube is a metal absorber tube equipped with a fin.
Passive Solar Water Heating Systems
Passive systems have some trade offs that active systems dont. First, theyre less complex (they do not use electricity), they are more reliable because of that, and they have a longer life span. On the flip side, theyre not quite as efficient. Lets look at the 2 models:
- Integral Collector-Storage Passive models. Thats a mouthful but this type is most often encountered in a system using a tankless or instantaneous water heater, also called on-demand water heater.
- Thermosyphon models. These are put together with a storage tank that has a collector placed at the bottom. The collector heats the water located at the base of the storage tank which then rises while the colder water sinks.
Active Solar Water Heating Systems
Active units are more costly and complex. As with their passive cousins, there are 2 basic models:
- Direct Circulation Systems. This type is rather simpler because a heat-transfer fluid is not utilized. Instead, the water circulates through both the heat exchanger and the collector.
- Indirect Circulation Systems. This type usually installed in areas that tend to undergo a hard freeze in the winter. They use a heat-transfer fluid analogous to car antifreeze.
Circulation pumps are used to flow the fluid through the heat exchanger and collector. Next, the heated fluid flows through coils in the storage tank which in turn heats the water.
What About on Cloudy Days?
Solar water heating systems are nice but are hardly ever a 100% answer for delivering hot water. Instead, theyre a factor in the total equation. A backup utility like a tankless water heater is perfect for filling in and ensuring the simple pleasure of a hot shower or tub soaking.