While escaping to the coast to a friends house in a secluded area near the Pacific, I was amazed to see how low her gas bill was. Why? She has a hot tub as well as a small lap pool that my friend keep very warm. On the hot tub, pool and her home she had installed solar thermal collectors.
When I saw how much hot water my friend was producing with such a low gas bill, I became a believer. Even in the cloudiest climates, the sun, heating solar thermal panels, can provide 50 to 60 percent of a household’s annual water heating, and in sunnier places, 80 percent or more. How does it work?
System Types; Five main types of solar thermal water heating systems are sold today. These five are a distillation of dozens of types sold over the past 25 years. They are:
• Open-loop direct
• Pressurized glycol
• Closed-loop drainback
The proven winners are simple, reliable, and long lasting. Some systems are “open loop” (the domestic water itself is directly heated) and some are “closed loop” (a heat transfer fluid is heated by the collector and the heat is passed on to the domestic hot water by means of a heat exchanger). Some systems are “active,” using moving parts such as pumps and valves, and others are “passive,” using no mechanical or moving parts.
Solar collectors are also commonly called solar thermal panels. A solar collector consists of a network of pipes through which water (or in colder climates, antifreeze) is heated. Collectors come in various sizes, with 4 by 8 feet the most common.
On a typical summer day (sunny and warm), the fluid in the collectors reaches 140 to 180°F (60–80°C). On a clear winter day (sunny and cold), it can reach 120 to 150°F (50– On a typical summer day (sunny and warm), the fluid in the collectors reaches 140 to 180°F (60–80°C). On a clear winter day (sunny and cold), it can reach 120 to 150°F. When it’s cloudy and warm, it can reach 70 to 90°F.
Mounting the solar thermal panels.
The three most common mounting systems for solar collectors are the roof mount, ground mount, and awning mount. roof mounted collectors are safely held by brackets, usually parallel to and a few inches above the roof. Ground mount solar systems can be as simple as four or more posts in the ground, lengths adjusted to affect optimal tilt. An awning mount attaches the collectors to a vertical wall. Horizontal supports push the bottoms of the collectors out to achieve the desired tilt.
A solar water tank is an insulated water storage tank. Cold water that used to go directly to your conventional water heater enters the solar tank and solar heated water exits. In closed-loop systems, the water is heated by contact with a coil of pipe containing the water or antifreeze that circulates through the collectors. In open-loop solar systems, the potable water is directly circulated up through the collectors and back.
The preheated solar water is then plumbed back to the cold side of your existing heater, which now functions as a backup. Whenever hot water is turned on in the house, preheated solar hot water is moved from the solar tank to the backup heater.
Pumps are used in active systems, but are not required in batch or thermosyphon systems. They the solar collector and the storage tank. The right pump for the job depends on the size of the system and the distance and height between the collector(s) and the storage tank. AC pumps plug into a wall outlet while DC pumps are powered from a DC source, such as a photovoltaic panel. Good pumps can last as long as 20 years with heavy use.
Heat exchangers are used in closed loop solar hot water systems. They enable the transfer of heat from one fluid to another without the two the insulation and cover. As the heated fluid from the solar collector travels through the coil, the heat is passed from the hotter fluid to the cooler potable water. An external heat exchanger is usually a pipe within a pipe. The solar fluid and potable water flow counter to one another, and heat is transferred within the heat exchanger pipe.
Solar thermal installations usually pay off quicker than solar electric making solar hot water an excellent investment. At least it was for my friend. Source; Used with permission. © Home Power, Inc.