Clean Diesel

Solar water heating systems for homes have become quite common. These systems preheat the incoming cold water to be used in baths, kitchen and to do laundry. A correctly sized solar water heating system will supply about 40-70% of your hot water needs. In order to qualify for the currently available federal tax credits however, your system must provide at least 50% of your water needs. Combine these tax credits with the higher efficiency of today’s systems, and it has become affordable for many homeowners to install a solar water heating systems.

Two types of solar domestic hot water heating systems are used in residential applications: the closed loop system and the open loop system. A closed loop system separates the collector loop from the domestic water side with a heat exchanger: the domestic water system is closed to the solar collectors. A freeze-proof liquid, usually a glycol solution, is circulated through the solar collectors and the heat exchanger, which is located in the solar storage tank. These systems are also recommended for areas with hard water. Closed loop systems unfortunately cost more than an open system. People living in areas where temperatures always remain above freezing can install open loop systems. The domestic water loop is open to the solar collectors and the incoming cold water is circulated directly through the solar collectors and then to the solar storage tank.

Number and size of solar collectors will be determined based on the type of collectors, where you live and on your hot water requirement. Solar collectors for water heating most commonly installed are flat plate or evacuated tube collectors. Evacuated tube collectors are more efficient than the flat plate collectors and are recommended for colder or cloudy climates and areas with hard water. You will pay a premium however, for the higher efficiency evacuated tube collectors.

It is important to know that a solar water heating system must have a regular water heater as a backup to make sure that you have sufficient hot water during, and after, a number of days of cloudy weather. I like to look at a residential solar water heating system as a system that PRE-heats the incoming cold water on most days and on some days it heats all your hot water up to the required 130degF. The water heated in the solar collectors is stored in the solar storage tank from where it flows into your regular water heater to be fully heated as needed. With a well designed system, enough hot water will be produced in the solar collectors on clear days so that you don’t need the regular water heater.

I guess you will put the solar collectors somewhere on the roof of your home. The location of the collectors is probably the most important decision you will make. Not enough direct sunlight will make the best system perform poorly. Choose well! If you need help, call a local solar system installer (they just might do a free analysis for you), or buy/rent a solar radiation tool and do it yourself. Make sure you include any trees that shade your roof.

Once you know where on the roof you want to put the solar collectors, check with a contractor about the requirements for re-inforcements necessary to mount the collectors and frames. Also ask the contractor about the roofing. Several roof penetrations will need to be made. These have to be sealed at the end to keep your roof absolutely waterproof.

The next item on the list is the solar storage tank. It should be located right next to your existing water heater. The solar tank will be about as big as a 40-gallon water heater. If you plan for a closed loop system, you will also need some space for a pump and a small expansion tank. Access for easy maintenance is highly recommended as well.

The last big item to research is where and how to run the pipes between the solar collectors and the solar storage tank. That is easy if your tank is on the first floor and you have a single story home. It gets more challenging, the more stories you have to go through. Look for a space large enough for two 1″ pipes, each with 1″ insulation and about 2 inches in between. The pipes do not need to be next to each other. Hopefully your bathrooms on the first and second floors are one above the other. If so, you might be able to fit the solar piping in the same wall as the water and sewer pipes.

You are on the way. Once you have the answers to all the issues mentioned above, you can move to the next level: serious, detailed planning and design. Either make it a do-it-yourself solar project, or use your knowledge to negotiate and work with a contractor to have them install the solar hot water heating system for your home.

Don’t make the mistakes others have made before you when they were designing and installing a solar hot water system. Educate yourself and learn how to plan and prepare for a successful system.