Solar thermal systems – Heating your water with the sun

Heating the water for your home or commercial property can add significantly to your overall energy bills. But solar thermal heating systems offer the most cost effective renewable energy money can buy. They can cut water heating bills by up to 90 percent, reduce your carbon footprint substantially, and typically pay for themselves in less than five years.

In general, there are two types of solar thermal or solar hot water systems: active and passive.

Active solar thermal water heaters

Active solar thermals systems have circulating pumps and temperature controls that move water or an antifreeze fluid through tubes that run from the outdoor solar panels to inside the home.

There are two types of active solar thermal systems: direct and indirect. Direct systems heat water by using pumps to move pressurized water through the collectors. As the temperature of the fluid increases, the pump turns on and circulates into the home where it is stored in an insulated tank until needed. They work best where the water is soft and non-acidic, and when installed on buildings and homes in climates that do not freeze for long periods of time.

Unlike direct systems, indirect thermal systems heat antifreeze fluid (usually a food-grade propylene glycol) instead of water. The fluid is heated by the collectors and as it circulates through the exchanger, it transfers the heat energy to a coil. The coil in turn transfers the heat to the water, which is then stored in an insulated water tank until required. Some indirect thermal systems include a drainback system which will ensure that the liquid in the collector loops is drained into a reservoir tank when the pumps stop to avoid freezing, making these systems especially suitable for colder climates.

Passive solar thermal water heaters

Passive solar thermal water heaters, on the other hand, do not make use of pumps and circulation tubes. There are no moving parts whatsoever. Instead, they rely on gravity and water’s tendency to naturally circulate when heated.

Here again, there are two types of systems: integral-collector storage systems and thermosyphon systems. In integral-collector storage systems, storage tanks are installed into insulated boxes that have glazed sides facing the sun. Because the storage tanks are often placed outdoors, these systems are best for locations that don’t go below freezing.

Thermosyphon systems use a system of pipes much like active solar thermal heaters, but instead of installing the collectors on the roof and the tank somewhere below it within the house, thermosyphon systems involve putting the tank above the collectors. Then, as the water warms, it rises naturally up to the tank (often located in the attic). These systems can be installed with either direct or indirect heating mechanisms much like active solar thermal systems.

Applications for solar thermal water heaters

Solar thermal systems can be installed in any climate, work even on cloudy days by using the full spectrum of the sun, and are able to provide a variety of water heating services:

• Domestic water heating: Water is heated for domestic purposes such as showering, laundry, and hand washing. Solar thermal water heaters can even help during colder times of the year, acting as a preheating system to reduce your overall water heating energy load.
• Pool and hot tub heating: Using direct, active solar technology (with some modifications to avoid scalding water in warm weather), solar pool heaters can provide a consistent 80°-85°F temperature, are very low maintenance, and work well in any area where the daytime air temperature is above 60°F. In order to provide heating through spring and fall, most solar collectors need to be 50-100 percent of the square footage of your pool. Even more panels can provide a warm swimming experience into the winter season. Costs for these systems can be between $2,000 and $10,000, and although they are often exempt from state and federal financial incentives, you may see returns on your investment in as few as 1.5 years.
• Space heating: Using either a passive or active system, instead of transferring the heat from your thermal collectors to your domestic water supply, your solar thermal heater can transfer energy to water used for radiant space heating in your home or commercial building. The heated water is stored in a large thermal collection tank connected to pipes installed under floors to provide radiant heat, which is both cozy and evenly distributed. Most systems are sized so that you have between 1 ½ to 2 gallons of water for every square foot of heated space and typically run 40 percent more efficiently than forced air heating systems. Best of all, they can be zoned to provide individual heat controls for each room, which can save even more energy.

Solar electric photovoltaic (PV) systems – Generating electricity with the sun

If clean, renewable electricity is what you’re after, than a solar photovoltaic system is what you need. PV or solar cells form the building blocks of these solar electric generators. They’re made from various types of semiconductor materials, such as silicon (the most common today), polycrystalline thin film (using copper indium diselenide (CIS) cadmium telluride (CdTe), or single-crystalline thin film (often made with gallium arsenide).

Each PV cell collects solar energy and turns it into approximately 1 to 2 watts of electrical power. That’s not much, but when many PV cells are connected together into long modules, and then those modules are interconnected into arrays, you’ve got the potential to produce a great deal of electrical energy.

But the arrays need some supporting components to turn the sun’s energy into power we can use. For that, we depend on items such as inverters to convert direct current (DV) electricity into alternating current (AC) and batteries to store the energy (optional). These components are typically wired directly into a building and sent to a dedicated breaker in the main electric panel to provide seamless, no-fuss electricity. Additional options include a charge controller (to maintain the batteries at the proper charge level and protect from overcharging), and balance of system components (such as an array combiner box, fuses, switches, cabling, circuit breakers, and meters).

Together, these components make up a whole solar PV system, which generates electricity that can be used for lighting a building, running appliances and electronics, providing electric heat, and much more. Most solar panels are mounted on south-facing structures to take full advantage of the sun’s rays.