Solar Water Heat
Solar Water Heat (SWH) is one of the least understood yet most efficient of solar technologies. At its simplest, a SWH system turns solar radiation into heated potable water for everyday home or business use. The system uses special Solar Thermal collectors to absorb heat, and often includes a backup system for when Solar heat is not available. Solar Thermal Collectors are generally much larger and fewer in number than their Solar Electric counterparts, and work at a higher power efficiency. SWH systems transfer heat from collectors to water, and store heated water in collectors or a separate tank for later use. A variety of system types provide tailored solutions to each property, roof, and plumbing situation.
Solar Alternatives only uses higher grade SRCC OG-300 approved systems which have been tested to meet the efficiency and quality levels claimed by the manufacturer. Rooftop systems are installed with short standoffs and flashings to provide complete waterproofing, and can optionally be tilted to face the sun’s average position. Most systems are installed with a water conditioning unit to reduce the effects of hard water on heat transfer units as well as the entire hot water system.
Active Indirect Solar Water Heat
This is the most popular class of SWH, and includes Closed Loop Glycol and Drainback designs. In an Active SWH system, pumps are used to move heat from the collector location to a storage tank, often using a heat transfer fluid (HTF) and heat exchanger (HX). This arrangement avoids any possibility of freeze damage to the system as well as the worst effects of hard water calcification. Active systems tend to be more efficient but require slightly more maintenance.
In a Closed Loop Glycol SWH (or just “Glycol”) system such as Heliodyne or SolarHot, the collector circulation loop is filled with Propylene Glycol (non-toxic antifreeze) and pressurized to about 30 pounds. This keeps freeze-resistant fluid in the collectors at all times and simply requires circulation to start to begin heat transfer to the tank. A Glycol system involves one or more Solar Collectors, a Heat Exchanger with pumps, an insulated Storage Tank, and a digital controller. Controllers automate the water heating process and can optionally be monitored with data card or wireless interconnections. A Glycol system is very flexible and can be augmented to provide heat for space heating, pool heating, and other applications with the same collector loop.
A good Drainback System provides very high return on investment with relatively low maintenance, as long as quality components and installation methods are used. These systems use many of the same components as a Glycol system, except distilled water as the heat transfer fluid, and a Drainback Tank holds the HTF when not in use. Distilled water requires less testing and maintenance and is slightly more efficient at moving heat than Glycol. Instead of fluid remaining in the collectors, the HTF returns through gravity drain to the Drainback Tank after the system shuts down. Drainback systems must be installed with precision to work properly, and should never use plastic, PVC or PEX piping for collectors. Because of the need for gravity drain, these systems are only appropriate in situations where the tank is lower in height on the property than collectors.
Passive Solar Water Heat
When a very simple near-zero-maintenance system is desired, or when storage tank space is an issue, Passive SWH systems can provide an elegant and convenient solution. Passive systems do not use pumps or separate collector/tank configurations to move heat into storage, but rely on direct heating and water mains pressure to collect and move heated water. The most common types of Passive SWH system are Thermosiphon and Integrated Collector Storage, although several options are commercially available.
A Thermosiphon SWH system uses the natural tendency for hot water to rise to move heat from collectors into a connected tank (see diagram). Collectors in a Thermosiphon system are either Flat-Plate or Vacuum Tube type, and are directly connected to the bottom of a special high-insulation storage tank. Heat circulates from collectors to tank, and water is withdrawn to the property via mains pressure similar to a normal water heater. A backup element in the tank provides heat in inclement weather.
Integrated Collector Storage units are essentially oversized collectors which have enough volume in their piping to hold up to 100 gallons of water. Water remains in the collector to be heated directly by sunlight, and is fed into and drawn out of the unit by mains water pressure. A special freeze drip valve and a bypass manifold are used to control flow and minimize the chance of freeze damage. These systems are by far the simplest, but are less efficient and will have standby losses on cold nights. They are an excellent fit as pre-heater for tankless water heating units however, and will provide many years of maintenance-free service.
