The simplest of all the solar hot water systems on the market is the solar batch hot water system.

Solar batch water heaters are popular in many tropical countries such as Mexico. In such instances, solar batch water heaters consist of a single water tank mounted on the roofs of homes and other buildings. The tanks are often painted black to increase the absorption of solar energy.

Solar batch water tanks absorb sunlight all day long, heating the water inside. When hot water is required, it flows directly out of the top of the tank into the hot water supply line that feeds various hot water faucets inside the home. Cold water enters the bottom of the tank to replenish hot water drawn out of the tank with each use. Because the water used in the house is heated in the tank, the solar batch hot water system is considered a direct or open-loop solar hot water system.

Solar batch water heaters such as this are simple, economical, and reliable. However, they do have some shortcomings. One of those shortcomings is that the tanks are not insulated. As a result, they tend to lose much of their heat at night.

Hot water is, therefore, typically available only in the afternoons and the early evenings.

But don’t close the book on solar batch water heaters just yet. More efficient — and more attractive — models are available. One type, shown in Figure 3-4, consists of a large black water tank inside a glass-covered, insulated collector. Sometimes referred to as integrated collector and storage (ICS) water heaters because the collector and storage tank are one unit, these models are mounted on roofs, so long as they can support the additional weight, or alongside buildings.

The solar batch water heater is one of the simplest and most cost effective solar hot water systems available on the market today.

Unfortunately, it can only be used in warmer climates, where freezing rarely, if ever, occurs.

For best results, batch heaters must face true south, not magnetic south. (True south corresponds to the lines of longitude and is not often the same as magnetic south, which is determined by magnetic fields. Magnetic fields don’t always run true north and south.) Like all other solar collection devices you’ll encounter in this and other chapters, solar batch water heaters need to be in a sunny location free from shade day in and day out, 12 months a year for optimal performance.

As noted above, solar batch water heaters heat water during the day. In the United States and other more developed countries, however, solar batch water heaters are typically plumbed into a home’s water heater. That is, they provide preheated water to a conventional water heater.
To understand how a solar batch water heater operates, let’s trace the flow of water, beginning in the bathroom shower, say on a hot summer day

In a solar batch hot water system, hot water for use inside the house is typically drawn from the storage water heater tank. The tank is replenished by water from the solar batch collector. Its tank is replenished by line water.

When a hot water faucet is turned on in the bathroom sink or shower, water is drawn from the conventional water heater.  ....read more