| Solar Water Heating |
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| Written by Phillip Hamilton, PhD |
| Sunday, 04 May 2008 14:19 |
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The oldest and most basic use of solar energy is to heat things up. And this is exactly what solar hot water systems do. Solar hot water systems are in general composed of three sections a collector, a heat transfer fluid, and a storage tank for later use. The collector is the main visible part that sits in the sun absorbing its radiant energy. The collectors then transfer this energy to the heat transfer fluid which carries it to the point of use, in most cases a heat exchanger used to increase the temperature of the water supplied to your house to the desired temperature of use. The tank then stores the hot water until you are ready to take a nice warm shower or wash dishes whatever the hot water need. The systems can be used to heat water for bathing, clothes washing, dish washing, swimming pools, hot tubs, under floor heating or as an energy input for space heating.  In general there are three types of solar collectors used for residential applications:
Flat-plate Collectors:Â Insulated, weatherproofed boxes with dark absorber plate under glass or plastic covers. Â
Integral Collector-Storage (ICS) or Batch Systems: Feature black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water continues to the conventional hot water heater. These systems should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.
Figure 2:Â Â Integrated Collector and Storage SystemÂ
Evacuated-tube Solar Collectors: Feature parallel rows of transparent glass tubes, each with a glass outer tube and metal absorber tube attached to a fin. The fin's coating absorbs solar energy but inhibits radiative heat loss.
There are also 4 categories of solar hot water heating systems that utilize collectors.
Forced Circulation or Active systems:Â Use a pump to circulate water or other fluid from the collector where it is heated by the sun to the storage tank.
Figure 4: Active Forced Circulation Solar water heating system Integral Collector Storage (ICS) or Batch systems: Combine the collector and the storage tank in one. The sun shines into the collector and strikes the storage tank directly, heating the water. See Figure 2 in combination with the collector. Thermosyphon systems: Have a separate storage tank, located above the collector. Liquid (water or refrigerant) warmed in the collector rises naturally to the storage tank.
Self-Pumping systems:Â Use a phase change (liquid-vapor) or other passive means to cause the fluid in the collector to circulate and transport heat from the collector to the storage.
Items 1 and 3 (ICS and Thermosyphon systems) are generally called passive systems. Figures 2 and 4 respectively, show a general diagram of how a passive and an active system are connected and heat your household water. Passive systems are usually somewhat cheaper and more energy efficient than active systems. Active systems however have a better tolerance of cold weather and are usually required for colder climates. Average prices and temperature tolerance information can be found in the Table below:
Solar water heating systems are usually designed to produce between 40 and 80% of typical hot water needs in conjunction with conventional water heating systems. In this way an auxiliary energy source such as electricity or natural gas can be activated if the water in the tank drops below a set temperature, ensuring that the system can still provide hot water in times of low solar energy input. The installation costs for a solar water heating system can range from $1200 to $1600. Based the costs in the table and the installation costs a typical solar water heating system will pay for itself in about 3 to 5 years from energy savings (depending on location and energy prices) when used to supply hot water for a family of 4. Most solar water heating systems have a life expectancy of 25 to 30 years making this technology one of the most economically advantageous renewable energy investments available to homeowners. Based on averaged usage a solar water heating system can prevent about 4.5 metric tons per year of greenhouse gas emissions production when compared to conventional water heating systems. To understand how solar hot water heating will work financially in your specific location and usage conditions please visit our RENEWABLE ENERGY CALCULATOR . The impact a solar hot water heater can have on your emissions can also be estimated using the calculator. |
