Anatomy of a Solar Water Heater: Drops of Golden Sun

If you've never seen a solar water heating or thermal system, you might expect it to look different from your current system. Even though these products have been around for quite some time, the term "solar water heating" still has a futuristic sound to it.

The fact is, aside from the solar collectors themselves (which are usually placed on the roof anyway), the other major components of a solar water heating system don't look a whole lot different from a conventional water heater or boiler. They basically consist of the water storage tank for the solar-heated water, the insulated pipes that connect it to the solar collectors and the ones that feed into the conventional water heater.

Types of solar water heating systems
Looks aside, solar water heaters are not all created equal. There are two major types of solar water heating systems: active or closed loop systems, which have forced circulating pumps and controls, and passive or open loop systems, which do not.¹

Active systems could be likened to a person's circulatory system and are often used in colder climates where freezing temperatures are likely to occur. In these systems, a heat transfer liquid, usually an antifreeze solution, is heated in the solar collector and circulated to the hot water storage tank via a heat exchanger. Passive systems have no pumps and rely on gravity or thermosyphon technology to move the heated water through the system.

In either case, the solar-heated water in the storage tank pre-feeds the conventional water heating system. When pre-fed with the solar-heated water, the boiler or water heater is either not activated or activated for less time than if there were no solar hot water system.

In a passive (open loop) system, the potable water runs directly through the solar collector, where the sun's energy heats it. The hot water then flows into a solar water storage tank, where it remains until demand for hot water draws it into the conventional water heater tank. Then it either goes directly into the pipes that feed the areas requiring hot water or the conventional water heater boosts the temperature, if necessary.

In an active (closed loop) system, cold water flows into the solar water storage tank. The heat of the sun raises the temperature in the solar collectors and activates the heat transfer liquid pump. This causes the heat transfer liquid to flow into the solar collectors. From there the heated liquid flows into the heat exchanger inside the solar water storage tank.

In much the same way the lungs infuse the bloodstream with oxygen, the heat exchanger transfers all the sun-generated warmth collected in the heat transfer liquid to the cold water in the solar water storage tank. Preheated water from the solar water storage tank is drawn into the conventional water heater tank and is further heated as necessary to supply hot water used throughout the day.

What else can solar water heating systems do?
Hot water from solar water heating systems can also be used for space heating and cooling. Active solar space heating systems collect and absorb solar energy and use electric fans or pumps to transfer and distribute heat. This can dramatically reduce costs. Solar absorption cooling uses solar-heated water to drive an air conditioner. Solar desiccant cooling removes moisture from the air to decrease the relative humidity. Using the sun this way reduces the amount of conventional energy that is needed to heat the water and increases the business's energy and cost efficiency.

Working with a contractor
If you do plan to install a solar water heating system for your business, a licensed contractor can help determine which kind of system is right for your business. Choosing the right contractor is one of the most important decisions for any project. The California Solar Initiative (CSI) Thermal Program has a Contractor Database that allows businesses to search CSI-certified contractors by ZIP code. The database also allows them to filter results by the number of projects completed by the contractor or by distance to the location entered.

• To find eligible contractors in your area, visit the CSI Contractor Database
• Verify the contractor has an active A, B, C-10 or C-46 license by checking the Contractors State License Board (CSLB) website
• Interview a minimum of three eligible contractors
• Request references from previous customers
• Obtain written bids from each contractor for comparison
• Make sure all bids are based on the same type of system and include a system warranty

To learn more about solar water heating and working with a contractor, download PG&E's free eBook, "How to Make Solar Water Heating Affordable for Your Business."

1. U.S. Department of Energy
2. Pacific Gas and Electric Company