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Solar Heating and Cooling: Economics and Growth

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To address the issue of the small up-front cost, solar integrators have developed a number of financing options for their customers.

  • Power-Purchase Agreement (PPA) – Customer purchases only the thermal energy generated from the system.
  • Property-Assessed Clean Energy (PACE) – Up-front cost is paid by a local government fund and repaid by homeowner through property taxes
  • Solar Renewable Energy Certificate (SREC) – in those states in which SWH qualifies as a generating technology for SRECs, the value of the SREC sold can help to offset the cost of the system

More on Solar Water Heating

A properly designed and installed solar water heating system can be expected to provide a significant percentage (40 to 80 percent) of a building’s hot water needs. Many residential solar water heating projects can be completed in as little as one day.

Simulated U.S. Solar Water Heating Solar Fraction

Solar Water Heating Continues Steady Growth

Solar water heating grew 5% in 2010 to 2.4 million square feet of collectors sold, while solar pool heating rebounded from a five-year low in 2009 and grew 13 percent in 2010 to 10 million square feet of collectors sold. This is equivalent to a combined solar heating and cooling capacity of 814 MWthermal in 2010 alone. 

Today there are an estimated 2.3 million solar water heating and pool heating systems installed in the U.S.

What are the Major SWH Installation Markets?

California maintained its position as the leading installer of solar water heating systems in 2010 as the overall market grew 5 percent to 2.4 million square feet, or 158 MWth, compared to 2.3 million square feet, or 150 MWth, in 2009.

A Closer Look at SWH: How does it Work?

Solar water heaters have three basic components: a collector, a storage tank and insulated piping. The solar collector gathers the heat from the sun and transfers the heat to potable water. This heated water flows out of the collector to a hot water tank, and is used as necessary; this type of system is called open-loop, or a direct system. Auxiliary heating can remain connected to the hot water tank for back-up if necessary.

System Design

  • Active Systems:

-Include pumps and electronic controls

-Include a freeze protection system for colder climates.

  • Indirect systems: also called “closed loop”. In colder climates with the possibility of freezing temperatures, an antifreeze solution, such as non-toxic propylene glycol, is heated in the solar collector and circulated to the hot water storage tank via a heat exchanger. The potable water in the storage tank is warmed by the hot, antifreeze-filled heat exchanger, and the heated water can then be used as necessary, while the cooled glycol is piped back to the solar collector to be heated again.

- Drainback systems:  when no sunlight is available for heating, the solar pump turns off and the water “drains back” into the storage tank by means of gravity

  • Direct systems: also called “open loop”, potable water is pumped through the collector; only applicable in non-freezing climates.
  • Passive Systems:

-No pumps or controls

-Relies on gravity and thermodynamic principles to circulate water

Solar Water Heating: System Design

Are there different collectors?

Collectors

  • Low-temp, medium-temp, and high-temp collectors based on the glazing on the cover plate or tube
  • 4 main collector types:

-Flat plate

  • Copper pipes create a matrix of “risers” and are affixed to an absorber plate contained in an insulated box covered with a tempered glass or a polymer cover plate.

-Evacuated Tube

  • Consists of rows of parallel, transparent glass tubes that have been “evacuated” of air, creating a highly efficient heat insulator for the fluid that runs inside the length of the tube.
  • Generally used when higher water temperatures are needed

-Integral Collector Storage (ICS)

-Thermosiphon

 

 

 

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