Solar hot water (SHW) systems use basic heating principles to capture incoming solar radiation in order to heat water for domestic and other uses. Over the years, a variety of system designs have been developed and tested to meet specific consumer needs in various environmental conditions. The most common solar hot water system designs are labeled according to their specific freeze protection method. At times, particularly for a new solar customer, the vocabulary and options can seem a bit overwhelming. This section provides background information concerning the most common uses for solar hot water systems, system types, sizing and system components. APG SOLAR can help you further determine the system that is best for your particular application.

Solar hot water systems are most commonly used to heat water for basic household needs such as laundry, bathing, and dishwashing. To give you an idea of how big this industry is, 190,000,000 sq. ft. of hot water panels were installed worldwide in 2007.  Hawaii, for example, leads all states within the US with 22,500 residences enjoying the advantages of SHW systems. As a cumulative result of SHW in Hawaii the benefits are as follows; avoidance of 63 million kwh, 105,000 barrels of oil, 55,000 tons of CO2 emissions & customer savings of $8.8 million.    These systems are commonly referred to as "domestic hot water systems" or DHW. DHW systems typically use solar energy to pre-heat the water that is incoming to a conventionally fueled hot water heater. The warmer the water from the solar heater, the less conventional fuel will be needed to provide the household's hot water needs. During the summer months in most of the nation, a properly sized solar hot water system will provide 100% of a household's needs. In the winter, or during extended cloudy periods, the amount of hot water provided by the sun may be 50% or less. APG SOLAR desires to install systems that meet between 50% and 100% of the annual load.

The size of the solar collectors suitable for your site will depend upon the geographic location and your hot water demand requirements, but typically they will require between 40 and 80 square feet of mounting area for a standard residential application. The most common mounting technique used today is installation of the collectors flush with the roof on a south facing exposure. Alternatives, such as ground mounting, or rack mounting on undesireable roof pitches or orientations are also possible.

APG SOLAR recommends installing a tankless heater in parallel with the storage tank in order to avoid conventional tank water heater standby losses. These losses occur when the entire tank contents are heated to the set temperature, however only a portion of the contents are used. The remainder of the heated water temperature is cooled and lost, for example, overnight. This is one of the advantages of a tankless water heater, they do not incur standby losses. The other being a modulated flame, meaning the intensity of the flame, or amount of fuel being consumed (BTU Rate) is directly related to the volume and temperature of hot water called upon.

APG SOLAR also recommends the use of evacuated tube collectors due to several advantages. The first being higher efficiencies over conventional flat plate and another being less roof loading due to their lighter weight.

For more information regarding tankless water heaters and evacuated tube collectors, call us today!

Solar heaters are often the most economical way to heat a swimming pool. Compared to conventional pool heaters using propane or natural gas, solar pool heating systems can pay for themselves in six years or less. Installed system prices are approximately $15.00 per sq. ft. of collector area. If you currently do not heat your pool, a solar heating system can provide an economical way to extend your pool season, starting earlier in the spring and extending later into the fall.

Solar pool heaters work by rerouting pool water directly through polypropylene collectors and then returning the warmed water to the pool. The collectors used for pool heating systems are often less expensive than those used for domestic hot water systems. Please note that systems installed in the Central Valley are typically sized requiring the solar array square footage to be approximately 70% of the pool surface area.    

APG SOLAR prefers AquaSol and SunSwim panels which are competitively priced and offer a 12 year warranty. Click here for more information on AquaSol pool heating panels.

Solar water heaters can also be used to provide space heating mainly in the form of radiant floor heating & are commonly combined with DHW. The same set of solar collectors can be used to provide hot water for both space heating and domestic hot water needs. Space heating will generally require a much greater collector area and storage capacity. Additional controls and heat exchangers are also needed.

An APG SOLAR professional can recommend a system sized to provide the amount of space heat for your specific needs, and help you consider the pros and cons of various options. You should also be sure to carefully consider passive solar and other building efficiency measures that will reduce your heating & cooling loads in order to help you take full advantage of the available solar resource.

Active Systems: Open Loop Recirculation, Closed Loop Drain back & Glycol, Closed Loop Combination

• Open Loop Recirculation
  Open Loop Recirculation systems are most common in the North Central Valley. Their principal of operation works as follows; In the event a higher temperature exists on the roof in relation to the tank, a differential controller turns on a pump that circulates well or city water through flat plate collectors and back to a conventional water heater or the supply side of a tankless. This differential temperature comparison takes place between 2 temperature sensors, one mounted on the roof & one in the tank. When the differential is minimal the controller signals the pump to cease. In the event another roof mounted sensor (snap switch) determines a freezing condition, the controller signals the pump to operate thereby sending warm water from the tank to the roof in order to prevent panel damage, thereby recirculating.
  
• Closed Loop - Drain back System
  Drain back systems use water as the heat-transfer fluid within the collector loop. The water is forced through the collectors by a pump and then is drained by gravity to the storage tank and heat exchanger. These systems have no valves to fail and when the pumps are off, the collectors are empty, thereby assuring freeze-protection and auto shut-off if the water in the storage tank becomes too hot.
  
• Closed Loop - Glycol System
  Closed loop systems use a heat-transfer fluid to collect heat and a heat exchanger to transfer the heat to domestic water. Active closed loop systems use electric pumps, valves, and controllers to circulate the heat-transfer fluid, usually a glycol-water antifreeze mixture, through the flat plate collectors. This glycol-water antifreeze mixture makes closed-loop glycol systems effective in areas subject to freezing weather down to below zero F temperatures. For this reason, closed loop systems are preferred for year round use in areas that experience common freeze.
  
• Closed Loop Combination
  This system could be a variation of the above designs however must contain multiple heat exchangers.

Passive Systems: Open Loop Thermo Siphon & ICS (Integrated Collector Storage) also called Batch.

• Open loop, batch or ICS
  Open loop systems heat and circulate household (potable) water directly in collectors prior to distribution in the household. One type of open loop system is a batch heater that is simply a tank inside an insulated housing or a series of smaller tanks surrounded by an insulated box with a glass lens filled with water and positioned preferably on a south-facing roof system where it absorbs solar energy. The housings may incorporate a selective surface that absorbs the sun but inhibits radiant loss.
  
  In climates where freezing occurs, batch heaters must either be protected from freezing, drained for the winter, or contain a thermostatically controlled heating element. Batch heaters are considered passive, and perform using the principle of thermo siphon.  They are less expensive as a result of fewer components, and they require less maintenance and experience fewer failures. These systems are good economical choices for seasonal applications such as summer camps. Installed system costs are approximately $5000.00.