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Active Solar Heating
Advanced and Dependable Solar Water Heating Systems
Active solar heating mean that the solar water heating system uses pumps to circulate water or a non-freezing heat transfer solution between the solar heating panels and the storage tank.
An active solar heating system uses pumps, sensors or other mechanical parts to control the system. A PV solar panel can power the pump eliminating the need to use utility power.
Characteristics of an active solar energy:
Recommended in hot or freezing climates
More efficient
More expensive than passive systems.
First some definitions:
Active systems use pumps to circulate water or heat transfer fluids through the system.
Passive systems
rely on gravity or natural convection to circulate fluids through the system.
Direct (open loop) systems circulate household or potable water through the solar panels. The heated water from the solar panel feeds directly into the storage tank.
Indirect (closed loop) systems use a heat transfer fluid; water or diluted antifreeze, to collect heat and a heat exchanger to transfer the heat to household or potable water.
Active Indirect (Closed Loop) Solar Heating System
Common in cool climates, an indirect or closed loop system; also called indirect water heaters, always uses a heat exchanger to transfer heat from the non-freezing heat transfer solution circulating fluid to the water in the storage tank.
The circulating fluid uses an antifreeze solution (propylene glycol) with a low freezing point in the collector loop. The propylene glycol is a not-toxic heat transfer fluid. Do not confuse propylene glycol with ethylene glycol used in automobile radiators, which is toxic.
The graphic below shows an Active Indirect or closed loop Solar Heating System always uses a heat exchanger to transfer heat from glycol to your domestic hot water system. Courtesy DOE
Pros & Cons
The indirect or closed loop indirect water heaters are recommended in climates where freezing temperatures are expected. This is by far the most popular solar water heating system on the market today.
You need freeze protection even if you get any freezing temperatures.
This system can be used in warm climates, but you must prevent a stagnant condition that makes the glycol overheat.
The glycol needs to be changed every 10 to 15 years. Your solar professional can provide further recommendations based on your site conditions.
Active Direct Open Loop Solar Heating System
Common in mild climates, the direct or open loop systems, always uses water in the solar panel loop as the heat transfer fluid. The water is heated in the solar panel and circulates through the water heater using pumps, sensors and controls.
Pros & Cons
Water drains automatically when the Sun isn’t shining preventing damage of the system from freezing. These systems are suited where it rarely freezes like Hawaii and Florida. This system is not suited where freezing conditions are persistent.
Direct open loop systems cost less.
The engineering technology has advanced so active solar heating systems are more efficient and maintenance free.
Active solar heating systems offer the advantage of freeze protection but cost more because of the pumps and controller systems. Common in mild climates, the direct or open loop systems, always uses water in the solar panel loop as the heat transfer fluid. The water is heated in the solar panel and circulates through the water heater using pumps, sensors and controls.
The graphic below shows an active direct or open loop system always uses water as the heat transfer fluid to heat your domestic hot water system. Courtesy DOE
Take the next step and go to
Passive Solar Heating
... using gravity and natural convection.
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