The Differences between Active and Passive Solar Water Heaters

September 2, 2019

Free hot water, freshly warmed by the sun, that’s what solar technology has provided to homeowners. The energy-efficient panels grab the heat right out of the sky. However, from here, things flow in two possible directions. That’s because there are two separate solar water heating architectures. In one system, warm water is convection circulated. In the second, powered apparatus impels the water through and around the hot water pipes.

For Warmer Climates: Passive Solar Water Heating

Let’s draw up a conventional solar water heating circuit. At the top of the circuit drawing, a couple of collector panels are sketched. They’re the heat sinks, the dark glass frames that absorb thermal energy from the sun. Inside those panels, copper or glass tubes and plates transport the energy into a fluid. Typically, we’re referring to a direct circulation set up, one that sends water through the collectors. From here, the hot water pipe uses a thermosyphon configuration, so the hot water tank is located up high. Added to the technical drawing, the insulated water heater is drawn close to the collectors. It’s probably going to end up in an attic, where it’ll recirculate the warmer water as it rises. As the water cools, it then returns to the collector panels. That’s a straightforward layout, and it works well in warmer regions.

Best for Cooler Locales: Active Solar Water Heating

Natural convection systems are popular, but they’re hamstrung by several operational constraints. They can freeze if the temperature falls below freezing point at night. Another regional issue, hard water conditions, can also impede passive system flow rates. Active solar water heating circuits dramatically reorganize the above circuit drawing. Natural convection is out, so the storage tank can install in a better-insulated location within a home. Clogs and hard water problems are also reduced, with an electrically powered pump now providing fluid circulating impetus. Also, and this feature comes in handy when cold climates dominate, indirect heating layouts work better when active apparatus is installed. A pump meshes with a heat exchanger, which receives heat from an antifreeze-like fluid. That fluid won’t solidify when it flows out and onto a white-frosted building roof.

Sure, passive solar water heating layouts are simple and inexpensive, but they’re rarely used in cool weather conditions. Active solar water heating systems are a little more expensive, what with their pumps and heat exchangers adding installation costs to the apparatus layout, but their pump-impelled flow rates assure clog-free operational performance. Just as a quick by-the-way, passive equipment configurations require little maintenance. Active solar water heating circuits incorporate more pipes and valves, plus a heat exchanger, so they naturally need more care and attention.

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