HVAC | Plumbing | Electrical | Ductwork | Solar Hot Water Heating Systems | Grid-tied Renewable Energy Electric Systems
Solar water collectors can provide up to 80 percent of a house’s hot water (and even more depending on the climate and location of the home), and save the United States millions of barrels of oil every year by reducing the need for conventional heating.
The basic technology of solar water heating is very simple. Sunlight strikes the roof system and heats an “absorber” surface within a “solar collector” or an actual storage tank. Either a heat-transfer fluid or the potable water (to be used) flows through tubes attached to the absorber and picks up its heat. Systems with a heat-transfer-fluid loop include a heat exchanger that then heats the potable water. The heated water is stored in a conventional water heater tank until needed or in a separate preheat tank. If additional heat is needed, it is provided by the conventional water heating system.
As for size and installation, there is no “one size fits all” solar water-heating system. The size of the collector will depend on where the house is built and how much hot water is required. It is possible to build a solar water heating system using an experienced installer or system supplier. Installing the system on a roof will require an analysis of the design load of the roof and the weight of the equipment. It is best to go with a solar heating system that carries an OG300 rating by the Solar Rating and Certification Corporation in order to qualify for available tax credits.
FAST FACT: Read “A Consumer’s Guide: Heat Your Water With the Sun” from the U.S. Department of Energy.
What is Solar Power?
Solar radiation is a general term for the electromagnetic radiation emitted by the sun. We can capture and convert solar radiation into useful forms of energy, such as heat and electricity, using a variety of technologies. The technical feasibility and economical operation of these technologies at a specific location depends on the available solar radiation or solar resource.
Watch a video about the Center for Photovoltaics and the research they are doing
Types of Solar Heating Systems
Direct System. This system uses a pump to circulate potable water from the water storage tank through one or more collectors and back into the tank. The pump is regulated by an electronic controller or an appliance timer.
Indirect System. In this system, a heat exchanger heats a fluid that circulates in tubes through the water storage tank, transferring the heat from the fluid to the potable water.
Thermosiphon. A thermosiphon solar water-heating system has a tank mounted above the collector. As the collector heats the water, it rises to the storage tank, while heavier cold water sinks down to the collector.
Draindown System. In cold climates, this system prevents water from freezing in the collector by using electric valves that automatically drain the water from the collector when the temperature drops to freezing.
The Economics of Installing 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.
- How much money you save depends on the following:
- The amount of hot water you use
- Your system's performance
- Your geographic location and solar resource
- Available financing and incentives
- The cost of conventional fuels (natural gas, oil, and electricity)
- The cost of the fuel you use for your backup water heating system, if you have one.
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.
Solar Energy Collectors
There are three types of collectors useful for residential homes:
- Flat Plate Collector. This popular collector uses a rectangular box with a transparent cover attached to the roof. There are small tubes in the box that have fluid (either water or an antifreeze solution) running through. The tubes are attached to a storage plate and as heat builds up in the collector, it goes through the tubes and as the fluid goes through tubes it is heated. The fluid is then stored in a storage tank.
- Integral Collector-Storage System. Also known as ICS or batch system, this features one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.
- Evacuated-tube Solar Collector. This features parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for U.S. commercial applications.
How to Evaluate Your Site for Solar Water Heating
Before you buy and install a solar water heating system, you need to first consider your site's solar resource. Your local solar system supplier or installer can perform a solar site analysis. You will also need to purchase some additional equipment (called “balance-of-system” to safely transmit electricity to your loads and comply with your power-provider’s requirements.
> LEARN MORE ABOUT SOLAR SITE ANALYSIS
Implementation of Solar Hot-Water Heating Systems
- Review applicable building codes. Chapter 23 of the International Residential Code briefly covers solar systems. It states that solar systems and storage units must be listed with an approved testing agency, and heat transfer fluids cannot be flammable.
- Eliminate unnecessary water heating loads. Maximize the home’s energy efficiency and reduce water heating demand before implementing solar strategies by installing efficient shower heads, setting the water temperature lower, and other measures.
- Take advantage of solar energy during the design process. Maximize a home’s use of solar energy with good siting and architectural features, which add little or nothing to the cost of the house.
Contact an appropriate subcontractor to decide the appropriate solar water heating system for the site.
Benefits of Solar Hot Water Heating Systems
- For the amount of money and energy saved, solar water heating doesn’t involve a large investment for each household—from $3000 to $6000 is typical.
- The technology can cut the average family’s energy costs to heat water by 20 to 40 percent (as much as 90 percent in some southwestern regions).
- Check for current available tax rebates for installing solar heating systems
Challenges of Solar Hot Water Heating Systems
- They can add additional construction cost and time.
- A third-party inspection may be required.
- They will require some attention and maintenance by the homeowner, and therefore require a degree of homeowner education.
Installing and Maintaining the System
The proper installation of solar water heaters depends on many factors. These factors include solar resource, climate, local building code requirements, and safety issues; therefore, it's best to have a qualified, solar thermal systems contractor install your system.
After installation, properly maintaining your system will keep it running smoothly. Passive systems don't require much maintenance. For active systems, discuss the maintenance requirements with your system provider, and consult the system's owner's manual. Plumbing and other conventional water heating components require the same maintenance as conventional systems. Glazing may need to be cleaned in dry climates where rainwater doesn't provide a natural rinse.
Regular maintenance on simple systems can be as infrequent as every 3–5 years, preferably by a solar contractor. Systems with electrical components usually require a replacement part after or two after 10 years.
> LEARN MORE ABOUT SOLAR HEATING SYSTEM MAINTENANCE AND REPAIR
