Facts About Solar Water Heaters
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Facts About Solar Water Heaters

Due to soaring energy costs there has been a push for solar hot water heating systems which many consumers think are completely new ideas. On the contrary, solar water heaters have been commercially available since the 1800s. This difference between the first solar water heaters and modern solar water heaters is basically how they look. Most modern solar water heaters are installed in line with a home's roof and resemble skylights. The modern solar water heater is more efficient and can be used to preheat or augment your existing water heater to reduce energy bills. Most solar hot water heaters are roof-mounted and used for domestic hot water, pool heating and space heating needs.

Due to soaring energy costs there has been a push for solar hot water heating systems which many consumers think are completely new ideas. On the contrary, solar water heaters have been commercially available since the 1800s. This difference between the first solar water heaters and modern solar water heaters is basically how they look. Most modern solar water heaters are installed in line with a home's roof and resemble skylights. The modern solar water heater is more efficient and can be used to preheat or augment your existing water heater to reduce energy bills. Most solar hot water heaters are roof-mounted and used for domestic hot water, pool heating and space heating needs.

Depending on what area of the country you live solar collectors can meet part or all of a home's domestic hot water needs. Site conditions, system design, collector orientation and size will determine how much energy can be provided for domestic hot water heating.

Solar water heaters come in a various configurations and designs which affect the initial cost, performance, and complexity of the system. Most solar water heaters have back-up water heating such as electricity or gas. A solar water heating system usually consists of a hot water storage tank, a solar collector that absorbs solar energy, a back-up energy source, and typically a pump and controls.

System Types

There are two main types of systems: passive and forced circulation. Within each type, there are several configurations. A passive water heater consists of a water tank integrated into or located above a solar collector. In an integrated collector storage (ICS) system, also called a thermosiphon water heater, the water is heated and stored inside the collector. These systems are primarily suitable for warm climates where there is no risk of freezing and there is ample sunlight to provide water heating. In a passive system where the storage tank is separate from the collector, water flows by natural convection through the collector to the storage tank as the water is heated. A forced circulation system requires a pump to move water from the storage tank to the collector. Most solar water heaters in the United States are the forced circulation type.

Some solar water heating systems utilize a heat exchanger installed in a separate tank to keep the working fluid in the solar collector separate from the domestic water supply. This system is referred to as a closed-loop active system.

Indirect Closed-Loop Solar Hot Water System

Passive Solar with Integral Tank

Thermosiphon Schematic

Solar Collectors

There are several types of solar collectors with the most common consisting of a flat copper plate which is painted black with piping attached to the absorber plate. As sunlight hits the copper plate and is absorbed, the energy is transferred to water flowing in the tubes. The absorber plate is mounted in a panel that has a clear covering and insulation to protect the absorber plate from heat loss. Other solar collectors include an integrated collector and storage system and an evacuated tube collector.

Integral collector and storage systems combine the function of hot water storage and solar collector into one unit. Evacuated tube collectors produce higher temperature water and are more complex than flat plate collectors. Evacuated tube collectors consist of a series of tubes that contain a heat pipe to absorb solar energy and transfer it to a liquid medium. The tubes are evacuated, placed under a vacuum, so that there is very little heat loss from the tube. These collects do not require a clear cover or insulation to reduce heat loss so they can be mounted above windows to act as a solar shade or installed on exterior walls.

EvacuatedTube Solar Collector

Evacuated tube collectors mounted exterior wall

Installation and Maintenance

An experienced contractor should install solar water heating systems as the system must be connected to the home’s plumbing system and is most cases a roof penetration is required. Warranties range from 3 to 10 years, depending on the manufacturer.

There are a number of manufacturers of solar water heating systems that can provide information on local dealers and installers. The Solar Rating and Certification Corporation (http://www.solar-rating.org/ ) provides evaluations of solar collectors and solar hot water systems. The evaluation also calculates the performance of different systems based on the location where the system will be used.

Solar water heating systems may require periodic maintenance and have a relatively high initial cost. The payback period however is different depending on the cost of energy for heating water. In areas where electricity is used for water heating, the payback periods are shorter than for areas that use natural gas for water heating. Care must be taken to guard against freezing of the collector and piping. Solar collectors may have installation limits some communities.

Costs

An active, flat plate solar collector system can cost between $2,500 and $3,500 installed and produce about 80 to 100 gallons of hot water per day. A passive system will cost between $1,000 and $2,000 installed but will have a lower capacity. Savings are dependent on the amount of sunlight your collector receives.

Many states have incentive programs to support the cost of installing solar hot water heating systems. Check at Database of State Incentives for Renewable Energy (DSIRE) for a listing of these incentives. (http://www.dsireusa.org/ )

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