Solar Hot Water Simplified

Solar hot water systems convert sunlight into heat through solar collectors mounted on the roof.

Heating water is a very cost-effective use of solar energy, providing hot water for showers, dishwashers and clothes washers. Every year, thousands of solar water heaters are installed worldwide and manufacturers have developed some of the most cost-effective systems in the world to meet the needs of a wide variety of climates. For example, freeze-protected solar water heaters are designed to operate reliably through the entire year. They are especially suited for many Canadian climates where temperatures can be well below freezing or extremely hot.

Solar hot water systems convert sunlight into heat through solar collectors mounted on the roof. Water, or a water/antifreeze solution, carries heat from the collectors and pumps it through a heat exchanger to a tank for storage and subsequent use. A typical system requires up to 6 square meters of roof space for collectors, and a sloped, south-facing collector orientation is ideal for installation with minimal shading from nearby trees and buildings.

1. Energy Collection: Sunlight is collected and converted to heat energy.

The solar collector is mounted on or near your home facing south. As the sunlight passes through the collector’s glazing, it strikes an absorbing material. This material converts the sunlight into heat while the glazing prevents the heat from escaping. Think of a car parked in the sun with its windows rolled up. The temperature inside a glazed solar collector on your roof can easily reach 150°C when there is no heat transfer fluid flowing through it. The two most common types of solar collectors used in solar water heaters are glazed flat plate and evacuated tube collectors. A glazed flat plate collector consists of a shallow rectangular box with a transparent glass pane covering a flat black plate. The black plate is attached to a series of parallel tubes or one serpentine tube through which air, water, or other heat transfer fluids pass. An evacuated tube collector consists of several individual glass tubes, each containing a black metal pipe through which the heat transfer fluid passes. The space between the pipe and the glass tube is evacuated, so the air is removed.

2. Energy Transfer: Circulating fluids transfer the collected energy in the form of heat to a storage tank.

Heat energy is transferred from the collector to the water storage tank. In some water heaters, hot fluid is pumped from the collector to the storage tank. The pump is powered by electricity that either comes from an electrical wall outlet or a small photovoltaic module located beside the collector. In other types of solar water heaters, the sun heats the storage tank directly, so the fluid in the collector is heated and rises naturally to a storage tank above the collector. This type of solar water heater is often referred to as a thermosiphon system. It does not require an electric pump. Passive solar and solar photovoltaic-powered systems will continue to operate even if there is a power outage. The products that require electricity from a wall outlet will not operate during a power outage.

3. Energy Storage

Solar-heated water is stored in an insulated tank until you need it. Hot water is drawn off the tank when tap water is used, and cold make-up water enters at the bottom of the tank. Solar water heaters tend to have a slightly larger hot water storage capacity than conventional water heaters. This is because solar heat is available only during the day and sufficient hot water must be collected to meet evening and morning requirements.