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Everything You Wanted to Know About Solar Water Heating Systems

October 7, 2014 - 2:39pm

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Solar panels heat water that is delivered to a storage tank. | Photo courtesy of David Springer, National Renewable Energy Laboratory

Solar panels heat water that is delivered to a storage tank. | Photo courtesy of David Springer, National Renewable Energy Laboratory

October is #EnergySaverSolar month and we've received some great responses. Among them were several questions about solar water heaters. Solar water heating systems are different than solar electric systems. Where solar electric systems use the sun's energy to generate power for your home (like your refrigerator or lights), solar water heating systems pump hot water, heated by the sun, into your home.

Choosing a Solar Water Heating System

There are two types of solar water heating systems: active and passive.

Active
Passive
Direct circulation systems: Pumps circulate household water through the collectors and into the home.

Pros: Automatic controllers installed on the system sense when sunlight is being collected.
Cons: Best for areas where temperatures rarely fall below freezing. Only works for single application domestic use.

Integral collector-storage passive systems: Made of a storage tank, solar collection tank, and the pipes that run between them, these systems require cold water to be pumped into the solar collector in batches.

Pros: They work well in households with significant daytime and evening hot-water needs.
Cons: Best in areas where temperatures rarely fall below freezing but overall can be less effective.

Indirect circulation systems: Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home.

Pros: Still functions in freezing temperatures. Suitable for multiple solar heating applications like a solar swimming pool as well as domestic use.
Cons: Can be more expensive than direct circulation systems.

Thermosyphon systems: Water flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank.

Pros: Reliable system.
Cons: Contractors must pay careful attention to the roof design because of the heavy storage tank. Can be more expensive than integral collector-storage systems.

 

Sizing a Solar Water Heater System

Sizing your solar water heating system involves determining the total collector area as well as the storage volume you'll need to meet 90%–100% of your household's hot water needs during the summer.

COLLECTOR AREA

Contractors usually follow a guideline of around 20 square feet of collector area for each of the first two family members. For each additional person, add 8 square feet if you live in the U.S. Sun Belt area or 12–14 square feet if you live in the northern U.S.

STORAGE VOLUME

A small (50- to 60-gallon) storage tank is usually sufficient for 1-3 people. A medium (80-gallon) storage tank works well for 3-4 people. A large tank is appropriate for 4-6 people.
To prevent overheating in active systems, the size of the solar storage tank increases with the size of the collector -- typically 1.5 gallons per square foot of collector. 

Maintaining a Solar Water Heating System

SCALING

Domestic water that is high in mineral content (or "hard water") may cause the buildup or scaling of mineral (calcium) deposits in solar heating systems. You can avoid scaling by using water softeners or by circulating a mild acidic solution (such as vinegar) through the collector or domestic hot water loop every 3–5 years, or as necessary depending on water conditions.

CORROSION

Oxygen entering into an open loop hydronic solar system will cause rust in any iron or steel component. Such systems should have copper, bronze, brass, stainless steel, plastic, rubber components in the plumbing loop, and plastic or glass lined storage tanks.

Financing a Solar Water Heating System

Solar water heating systems usually cost more to purchase and install than conventional water heating systems. However, a solar water heater can usually save you money in the long run. On average, if you install a solar water heater, your water heating bills should drop 50%–80%. Also, because the sun is free, you're protected from future fuel shortages and price hikes. Later this week, the Energy Saver blog will delve deeper into the financial incentives that can help make solar more affordable.

For more on solar energy at home, check back into Energy Saver and the Energy Saver Facebook during the month of October. We will have several blogs and posts dedicated to solar energy at home. These topics include solar energy basics, installing solar energy at home, and the financial benefits of solar energy, just to name a few!

If there are any topics you'd like to hear about, click on the "tell us" box on the top of the page or use #EnergySaverSolar on social media, and we will try to incorporate your questions in future blogs!

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