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An Introduction to Solar Water Heating – the Other Solar Technology!

By now, we hope you’ve already heard this under-reported fact: solar water heating is a renewable energy technology with a BIG bang for your buck! Why do people overlook this affordable and proven option?

How They Work

An example of solar water heating at its most basic level is a garden hose left out in the sun. When you turn on the spigot, the first water to come out of the hose is warm since it’s been baking in the sunlight. A solar water collector works in a similar fashion. Water flows through tubes housed in a solar collector. Throughout the day, a sensor monitors the difference in water temperature between the water in the storage tank (inside the home) and the water in the collector (typically mounted on the roof).

At a preset temperature difference, the sensor triggers a pump to circulate the water through the collectors where it absorbs solar heat. In summer months, a solar hot water system can meet all your household hot water needs! Over the course of the year, the system can cover up to 85% of your hot water needs. The typical investment is about $3,000 to $6,000, not including installation. Be sure to investigate tax credits and rebates in your area which can help reduce that initial investment.

There are a variety of systems with well made flat plate collectors. The systems can be used to preheat water before going to your existing storage tank, or you can choose to use just one solar storage tank.

Flat Plate Collectors are the most commonly used collectors in domestic hot water applications. The collectors should last well over 20 years and can handle an operating temperature up to 180 degrees F. Surprisingly, a typical flat plate collector holds less than 2 gallons of water! You might think the more fluid-filled tubing the better; but the trick is getting the heat into the water, so the ratio of surface area to water volume is limited by the collector technology.

Water storage tanks in solar water heating systems are typically larger and better insulated than your average home hot water tank, and generally they have four ports (instead of two) on the tank. You'll want to have at least 80 gallons of storage for a 1-3 person home or 120 gallon tank for a 4-6 person home. Sizing collectors is easy as well: allow about 20 square feet of collector area for each of the first two family members and 8 square feet for each additional family member if you live in the Sun Belt.

If you live in the northern US, allow 12 to 14 additional square feet per person. Flat plate collectors are about 3'x 7' up to 4' x 10' and can weigh between 100 and 150 pounds each.

In addition to selecting an appropriate sized system, you'll also have several options to choose from. Here's where the vocabulary comes in: active/ passive; open/ closed; PV powered or AC powered; drainback, etc.

These systems use pumps to move the liquid between the collector and the storage tank. Passive systems, or thermosiphon systems, rely on gravity: the hot water will naturally rise to the top of the collector as it heats. Another main category of distinction is an open versus closed system.

An open system, also referred to as "direct" circulates the potable water through the collector. A closed system (a.k.a. "indirect") circulates a mixture of water and glycol through the collector and then transfers the heat to the potable water through a heat exchanger. A drain-back system allows water from the collector to drain back into a small tank to prevent water from freezing in the collector.

Solar Hot Water System Manufacturers: Your system selection depends primarily on your location. For example, an open (direct) system is a simple system that works well only in areas that will NEVER see freezing temperatures.

Most often, people choose a closed (direct) system. The propylene glycol mixture prevents fluid from freezing in the collectors and is suitable for all locations.

A system with a drain back tank offers similar freeze protection. Alternatively, a drain back tank can protect the water from being overheated during periods of reduced usage.

No matter what manufacturer you prefer, you'll be taking a great step forward by installing a solar water heating system in your home or business. Solar water heating is also a great option for Solar Pool Heaters and Pumps. Although the concept of heating water with the sun is simple, the installation of a complete solar water heating system can be a fairly complex. Consult a local professional if you need installation advice.