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Solar Water Heating

	Today people have access to a cheaper and wider variety of goods than they ever would have had access to in the past.  It is thanks to current technology and manufacturing processes that we can buy watermelon in the winter and upgrade our cell phones every year.  While the benefits of this are obvious, much of the technology and manufacturing processes we rely upon are unsustainable and harmful to the environment.  In order to eliminate the harm done to the environment without losing our quality of life, we must work towards innovating current technology and processes to become more environmentally friendly and efficient.  While many view green technology and processes as expensive, if done right, it can be very efficient and cheaper in the long run both economically and environmentally.

	In the modern age, water heating is a necessity for showering, dish washing, and laundry.  The Encyclopedia Britannica defines water heating as a “Thermodynamic process using an energy source to heat water above its initial temperature.  In the United States, most water heaters are run by either electricity, natural gas, or propane gas (Klenck).  While currently most of our hot water relies on fossil fuels, I believe that water heating can become a green process by people switching to the efficient, and in the long run cheaper, technology of solar water heaters.

	Typically, water heating accounts for around 14%- 25 of the energy consumed in a home (energysavers.gov).  When put in the perspective of the entire population of the United States and keeping in mind that most water heaters are run off of natural gas or electricity generated by oil or coal;  it is clear that water heating is certainly a big contributor to carbon emissions in the air and global warming.  Hot water typically enters a water heater at 10 °C and is then heated up 30 °C or more for the usual hot water applications (Klenck).    There are several ways to lower the energy usage of a water heater such as insulating hot water pipes, lowering the thermostat on the water heater, and installing heat traps on the water heater tank. While these techniques may lower a home's energy costs, they will hardly turn a water heater into a green environmentally friend appliance (energysavers.gov).

	In most homes, hot water is heated by a storage water heater, also known as a tank-type water heater.  They are usually powered by either gas or electric.  A gas powered tank-type water heater works by cold water entering through the bottom of the tank, which is then heated up by a gas burner underneath the tank.  In an Electric tank-type water heater, water is passed through two electrically charged heating elements which are controlled by a thermostat which sense when cold water is added to the tank and needs to be heated up (Klenck).  With storage water heaters, “because water is constantly heated in the tank, energy can be wasted even when a hot water tap isn't running” through standby heat loss (energysavers.gov).

	The other standard water heater in people's home is the Demand (tankless or instantaneous) water heater.  Many recommend that people switch to tankless water heaters since they can be more efficient than storage water heaters.  Instantaneous water heater work by having the cold water pumped through a system of coils that are heated up by the home's boiler; since the water is heated only when needed, no energy is lost due to storing hot water as with tank-type water heaters (Klenck).  For a home that use 41 gallons or less of hot water a day, demand water heaters can be 24-34% more efficient than conventional storage tank water heaters (energysavers.gov).  While it uses less resources than the tank-type, more sustainable and more efficient water heater technologies do exist.

	Sustainability is an issue that all nations and peoples must face.  There will be no end all solution for making the world we live in sustainable for the future.  Fossil fuels will have to make way for renewable energy sources, but this alone is not enough.  We can modify our lifestyles so we use less resources per day, but we can also improve our technology so that it is more efficient and uses less resources to accomplish the same task.  While water heater efficiency is not the most pressing issue facing our globe, there is no reason the technology should not be improved upon and updated to become more sustainable.  I believe that solar water heaters are an efficient and economical way to cut down on energy usage across our country.

	A solar water heater is a renewable energy technology that harvests the energy from the sun to heat water.  Solar water heaters use collector panels, typically about 4 feet wide and around 8 to 10 feet long, place on the roof of a house, to capture solar radiation which is used to heat water (toolbase.org).  Lower end solar water heater models will usually only fulfill 50% of a household's hot water needs, while higher end models will provide most, if not all of a household's hot water (Smith, 134).  Most U.S. Households go through 50 to 100 gallons of hot water a day, and a solar water heater's storage tank is “sized to be roughly equivalent to a day's water consumption” (Smith, 134).

	Solar water heaters are designed as either a passive or active system.  A passive system is a simple, inexpensive design that relies upon gravity and convection to circulate the water (Smith, 133).  In a passive system, there is no pump and the water tank is located in or above the solar collector; as the water in the collector warms, the water moves through natural convection through the collector to the storage tank (toolbase.org).  Passive systems are cheap to install, costing around $1,000-2,000, have very little to no maintenance, but are less efficient than active systems and cannot be used in cold climates where the water is likely to freeze (Smith, 134).

	The more common type of solar water heaters are the active or forced circulation type.  Active systems are more expensive and complex than passive ones, but they are much more efficient and reliable.  Active systems use pumps and controls to circulate water or heating fluid throughout the system and maintain a constant flow of water.  Unlike in a passive system, the storage tank in a forced circulation system can be placed lower than the sunlight collector (toolbase.org).  Another advantage of active systems is the extra control the user is given over the water heater, such as remote access, temperature readings, information displays, and interaction with a backup electric or gas driven water heater (toolbase.org).  The pump in an active system is controlled by a differential controller which senses temperature differences between water in the solar collector and water in the storage tank and then turns the pump on and off to adjust accordingly (Smith, 134).

	Most active systems rely upon flat plate collectors to absorb heat and then transfer it to the water.  Flat plate solar thermal collectors are insulated weather proofed boxes that contain a dark absorption plate, under one or more glass or plastic (polymer) covers (energysavers.gov).  The solar collector is “typically installed on a south-facing roof to maximize heat absorption from the sun  (Smith, 134).  Most collector plates are made of copper painted black and have water tubes attached to the absorber plate; as the energy from the sun is absorbed by the copper plate, the energy is transferred to the water flowing in the tubes (toolbase.org).  “A narrow pipe, coated with anti-reflective black paint, runs back and forth through the collector, connecting to an external storage tank” (Smith, 134).  Other types of solar panel collectors are Integral Collector-storage systems, which are meant for mild climates, and evacuated-tube solar collectors which are used more frequently for U.S. Commercial applications (energsavers.gov).

	Solar water heaters may operate in a direct or indirect loop system.    In a direct or open loop system, cold water enters through the bottom of the solar collector and absorbs solar radiation as it circulates through the pipes in the collector till it flows out of the top of the collector into a hot water tank (Smith, 134).  In an indirect or closed loop system, a liquid, usually antifreeze, is pumped through the collector in an isolated loop, gathering solar radiation (energysavers.gov).  After the antifreeze has been heated by the solar collector, it is sent to a heat exchanger coil which transfers the heat to the water which is then ready to be sent to the tap (Smith, 135).    Direct systems are cheaper than indirect ones but are also subject to overheating unless there is a heat export pump, or freezing unless the collector is freeze tolerant (toolbase.org).  Because of this, indirect systems should be used in climates that receive subfreezing temperatures.

	Solar water heaters are not a perfect technology and do have some downsides.  In most instances, solar water heaters need to be supplemented with an electric or gas fuel backup, which is integrated into most commercial solar water heaters (Smith, 135).  This is to ensure a reliable supply of hot water even on cloudy days with little sunlight, or during the winter when there may not be sufficient solar heat.  The initial cost of solar water heaters, even though they can save money in the long run, can also be a deterrent to people especially if they are perfectly content with whatever hot water system they currently have.

	While not very common in the United States, Solar water heaters have become huge in China.  Almost 30 million Chinese households use solar water heaters, and China accounts for 80% of the global solar water heater market (Harrison).  “One reason for the explosive growth of solar water and space heaters in Europe and China is the economic appeal.  On average, in industrial countries these systems pay for themselves from electricity savings in fewer than 10 years” (Brown, 248).  In China basic models cost around 1,500 yuan (US$190) and go up to 18,000 yuan (US$2,250), making them economical for the average middle class Chinese citizen.  The solar collectors are also much easier to produce than the electricity producing photovoltaic panels, and in China “The relatively low-tech factory floor helps keep costs down to around US$120 to US$150 per square meter, well below the US$700 to US$800 charged for similar heaters in Europe” (Harrison).



Works Cited

Brown, Lester Russell. Plan B 3.0: Mobilizing to save Civilization. New York: W.W. Norton, 2008. Print. 

Harrison, Emma G. "Energy-Hungry China Warms to Solar Water Heaters." Planet Ark. Colonial First State, 05 June 2006. Web. 04 Aug. 2012. <http://www.planetark.org/dailynewsstory.cfm?newsid=36636>. 

Klenck, Thomas. "How It Works: Water Heater." Popular Mechanics 01 Sept. 1997: n. pag. Web. 04 Aug. 2012. 

Perlin, John. "California Solar Center - Solar Thermal History." California Solar Center - Solar Thermal History. Rahus Institute, n.d. Web. 05 Aug. 2012. <http://www.californiasolarcenter.org/history_solarthermal.html>. 

Smith, Kimberly K. Powering Our Future: An Energy Sourcebook for Sustainable Living. New York: IUniverse, 2005. Print. 

"Solar Water Heaters." ToolBase.org. NAHB Research Center, n.d. Web. 04 Aug. 2012. <http://www.toolbase.org/technology-inventory/plumbing/solar-water-heaters>. 

"Water Heating." EnergySavers.gov. U.S. Department of Energy, 02 Sept. 2011. Web. 04 	
	Aug. 2012. 
<http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12760>.