Solar Water Heaters

Solar water heaters systems include solar collectors, a well insulated storage tank and piping.    Solar water heating systems fall into two main categories: active systems and passive systems.  Active systems are generally more expensive than passive systems, and they’re generally more efficient.  But passive systems can be more reliable and longer lasting.

There are two basic types of active solar water heater systems:

Direct circulation systems
Household water is circulated by pumps directly through the collectors and into the storage tank.  They work well in mild climate areas where it rarely freezes.

Indirect circulation systems
A non-freezing, heat transfer liquid is circulated through the collectors and a heat exchanger.  Household water is also pumped through the heat exchanger where it is heated then pumped into a storage tank.  These systems are popular in climates where it frequently freezes.   

There are also two basic types of passive systems:

Integral collector-storage passive systems
These work well in houses with heavy day and evening hot water use, and in areas with mild climate where it rarely freezes.

Thermosyphon systems
These systems are reliable, but are usually more expensive than integral collector-storage passive systems.  The solar heater installation contractor should pay close attention to the roof design because of the heavy system storage tank.

How to determine if you should buy a solar water heater.
There are several considerations to determine if a solar water heater is right for you:
1. Investigate local municipal codes and any HOA covenants and restrictions to ensure it’s allowed.
2. The amount of available solar energy at your property.
3. The appropriate size and type system for your house.
4. The efficiency of the system(s) you’re looking at.
5. The costs of the systems, including installation and maintenance.
6. The economics of the solar water heating systems.

Solar water heater economics
The economics of a solar water heating system, and the amount of money the system might save you each month, is dependent on several variables. 
1. Your hot water usage.
2. The available solar energy at your property.
3. The efficiency and performance of your system.
4. Available incentives and/or financing.
5. Fuel costs of your conventional water heater system.

Considering that fuel costs for your conventional system (natural gas or electricity) are very likely to increase in the future, a solar water heater may turn out to be a better deal than you currently think.

A purchase of a solar water heater looks even more attractive if the cost of the system can be financed as part of a 30-year mortgage.  It is very possible that the monthly savings from the solar water heater would exceed the monthly payment of the financed cost of the system.

How to determine the size solar water heater you need
An experienced solar water heater contractor has fairly precise and detailed methods to determine system requirements and sizing.  But there are some general guidelines you can use to get an idea of the size system you should look for. 

You want a system that has the collector area and storage tank capacity to meet 90% to 100% of your home’s hot water requirements in the summer

A good rule of thumb for the collector area is about 20 square feet for each of the first two family members.  For each additional family member, add 8 square feet of collector area if you live in the southern U.S. and 13 square feet if you live in the northern U.S.

As an example, it would require a collector area of about 56 square feet (roughly a square are about 7.5′ per side) for a family of four in the southern U.S., and a collector area of about 66 square feet (roughly a square area about 8′ per side) for a family of four in the northern U.S.

A small storage tank of 50 to 60 gallons should suffice for one or two people.  A medium storage tank of 80 gallons should handle three or four people.  Four to six people would need one of the large storage tanks.

In an active system, the storage tank should increase with the size of the collector.  The guideline is generally 1.5 gallons for each square foot of collector area, and two gallons per square foot of collector area in hot, sunny areas.

You’ll want to hire a contractor that is experienced (and perhaps certified) in installing and/or maintaining solar water heaters.  Ask any potential contractor:
1. How many years experience does your company have installing and maintaining solar water heaters?
2. How many solar water heaters have you installed?
3. Is your company licensed or certified to install solar water heaters?

Also call your local BBB office and ask about the contractors you’re considering.

About the Author

Mark H. Witte is a strong proponent for energy efficiency and renewable energy, and believes individuals should have more control over how the energy for their homes is produced.