Investigate active solar energy and discover the why, what and how…

Active Solar Energy systems use a variety of collectors, reflectors and concentrators to capture solar thermal energy. They transfer the energy via air, water, or glycol for use. Then electoral/mechanical devices store it for distribution later. Regardless whether the medium is liquid or air, drawing heat from storage will provide warmth on cloudy days, during the night no matter the season.

Understanding the difference between active solar energy and Passive Solar Energy is a step in the right direction if you intend to use the sun. Using passive solar because of its simplicity is always a good way to go for heating air.

A general rule of thumb is that south facing main windows should receive for at least 25% of the total sunlight hours including 5% during the winter months; i.e., between September and March. Receiving less than these is simply inefficient. The only possible exception is incorporating window boxes, air panels for walls and other non-storage collectors for the hours sunlight is available.

When passive solar is a dead end because an optimum supply of sunlight is unavailable: an active solar energy system will usually fill the bill. Actually, a good active system will produce enough hot water and heating, to satisfy a household’s requirements.

Nevertheless, beginning preparation of an active solar energy system should always include solid information to assist in its development. For example, it’s always a good idea to do a solar radiation survey to provide data for your project. Determining a buildings position relative to available sun light will provide the bases for choosing the right system and optimizing the design.

Survey results will generally indicate the best system to use; i.e. ground or roof mount, though wall mounted, storage placement, etc. Deeming a roof top collector’s aesthetics unappealing will certainly eliminate both Batch and Thermosyphon types. On the other hand, roof placement of these types may be of little concern and therefore included in the list.

As with passive solar, designing an active solar energy system for the location, for the best price and the best fit for your aesthetic values is paramount. Thus optimized, you can begin taking advantage of the sun’s energy - year around. Hey, even the winter sun.

Two active solar energy groups, heated air collection and hot liquid collection systems. Let’s take up the matter of the heated air first. Ironically, sometimes heated air uses hot liquid to get that way. Then there's heating some kind of a solid mass, but it still starts with the two active solar energy groups.

As for an optimized system: the most economical design will provide from 40 to 80% of a home’s (air) heating requirements. Going for 100% is not cost effective and is impractical. A properly sized system, will always comprise a dependable backup system, i.e., wood, gas or electric.

As we’ve seen, the two ways to produce heating is to use air or liquid as the energy transfer medium. A storage system collects heat from a variety of collectors. It is then distributed to the spaces where needed.

Those seriously interested in active solar energy will likely use one of the systems below. Adding solar panels to generate control power will further enhance the design,

1. Active Air Based Systems
2. Closed-Loop Drainback Systems
3. Closed-Loop Glycol Systems
4. Open-Loop Direct Systems
5. Links

Air Based Solar Systems
We know that the mechanism used to transfer the sun’s energy from one medium to another is the Collector. Air based collectors use the sun’s energy to heat air. These do the same job as the liquid based systems, only without piping, fluid, pumps and what not. They do however use normal ventilation system fans, sensors, controllers and so forth to transfer the heat absorbed.

There are three types of air ventilation systems. The first is an Air Ventilation And Heating system. The second is Space Heating system and the third is a Crop Drying system. These in turn use one of four types of Air Based Solar Collectors.

All three systems use either, the Unglazed Perforated Plate, the Glazed Flat Plate or the simple Back Pass or Trombe heat collector. Each range in performance from poor to excellent.

Each of these systems can readily integrate into a buildings design in order to form an integral part of the structure’s envelope. Solar thermal energy used to dry agricultural products is inexpensive and efficient method. In fact, it is one of the oldest solar energy applications around. Farmers rank it first among alternate energy sources for agricultural applications. Down through the ages, it has been known that air is a fast reactor for drying annual crops.
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Closed-Loop Drainback Systems
This system is suitable for moderate to cold northern climates where freezing weather is common. The closed-loop drain back system is basically a composite of open and closed-loop designs. Since its development in the 1980’s, this design has proven efficient and reliable. The heat transfer medium is non-pressurized water. The collector-loop incorporates a small reservoir located below the collector.

In operation, water fills the closed-loop to just to the top of the reservoir. When the solar collector sensor detects a rise in its temperature, the controller turns on the pump. The pump circulates cooler water into the collector inlet pipe located at its bottom. Heated water flows through the collector outlet pipe located at it top, down into heat exchanger, returning back up into the collector inlet.

When the solar collectors temperature falls below an adjustable reference point, the pump turns off and the water falls back into the reservoir, because it is located below the collector. When the collector sensor detects the set point temperature, it reactivates the pump and the cycle is repeated.

Water drains away from the collector providing good freeze protection when the pump is off. Sizing may include multiple collectors to meet hot water requirements. All in all, this active solar energy system design is very simple. Best of all, it has a limited number of component’s to worry over. The effect is system efficiency, reliability and cost effectiveness.
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Closed-Loop Glycol Systems
This system is suitable for cold northern climates where the winter sun and freezing weather are common, as the glycol that circulates in this system is freeze proof. Individual sizing requirements may include multiple collectors to meet hot water demands.

In operation, a sensor detects the temperature of the glycol. When it reaches a certain (adjustable) level, the controller starts the pump. The glycol circulates through the closed-loop absorbing heat from the collector. The heated fluid then circulates through the heat exchanger in a potable hot water tank.

The pump returns the cooled glycol, back through the collector for solar reheating. Glycol never comes in contact with the water.

You should take precautions during the summer time, to keep extremely hot solar thermal energy from boiling the systems fluid. This may require draining the system, or using an air-cooled fan heat exchanger to reduce the fluids temperature. Neither may be necessary depending on hot water demands and system design.
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Open-Loop Direct Systems
This system is suitable for mild to moderate climates where the risk of freezing is rare. Of all active solar energy systems using solar power, this is the simplest. For example, using a standard 52-gallon hot water tank along with normal 40 square foot solar collectors is standing operating procedure.

In operation, the pump picks up water from a common water delivery system under standard line pressure and circulates it through the collector. Potable water circulates through the solar collector and directly into the hot water tank. Notice that a heat exchanger is not used; heat transfer is direct. If demand increases over that which the present system can handle, simply add another water tank.

While simplicity of the system is its chief attribute, the down side is during cold weather, some of the heat may be lost when the pump re-circulates the system. This happens because cool water comes from near the bottom of the tank or supply line. However, the losses are minimal. Installing snap-switches to maintain tank temperatures will keep temperatures constant.

Freeze protection will need electrical power to operate the re-circulation system. Warm water simply re-circulates through the collector to keep from freezing. A 10 to 15 watt photovoltaic will provide enough power for a small pump.

Any active solar energy system, cost, demand requirements, how extensive integration with existing systems is important factors to consider in the design.

Do it yourselfers will enjoy the satisfaction of building a renewable energy system, while those with installed systems will benefit not only from system payback, but the knowledge that they’re using sunlight – the free energy available to one and all.
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Links
Remember, it is important to know the type and amount of usable energy you require before proceeding with an active solar energy system. Calculate the potential savings using solar, verses the amount of water heated by the grid, currently used.

Using Active Solar Energy is sort-a like... Hummmm