WHy go solar?

A solar blanket—also called a pool blanket or a solar cover—is the least expensive type of swimming pool cover. Solar blankets are a necessity for any home pool owner. The cost advantage is distinct: Using a solar cover instead of an expensive pool heater to keep water warm and inviting may well cut pool heating costs by as much as 70 percent.
Remember: A pool heater will drive up the home utility bill, even when a pool is enjoyed for only a brief season. Solar blankets are made from a durable polymer material with thousands of tiny sealed air bubbles. These covers float "bubble side down" on the surface of the pool water when the pool is not in use, and allow solar energy to pass through. That energy is then trapped as retained heat in the pool. Solar covers might actually be thought of as passive solar heating for a pool. Solar covers work equally as well on above-ground and in-ground pools.

Be a sun-savvy pool owner: Learn what solar energy is, and slash pool heating costs this season

The sun is the strongest natural heat source for a pool. That's exactly why today's educated pool owners will attest to the advantages of using a transparent plastic solar cover. A transparent solar pool cover lets the sun's rays pass through the cover and raise the water temperature. And at a cost of $0.40 - $0.80 per square foot, a transparent pool cover can pay for itself in a year. Take a look at the bottom-line benefits of using a solar pool cover:

1. Greater heat retention

2. Less water evaporation and better water conservation by reducing the amount of make-up water needed by 30%-50%

3. Reduced chemical consumption by 35%-60%

4. Decreased cleaning time

5. Keeps dirt and debris out of the pool

Indeed, pools lose energy in a variety of ways, but evaporation is by far the largest source of energy loss. As much as 70% of heat loss from a swimming pool is evaporative. When compared to evaporation, all other losses are small. Since evaporation is the major source of heat loss for all swimming pools, the best way to minimize evaporation is to cover the pool. A transparent pool cover acts as a vapor barrier for both indoor and outdoor pools, dramatically preventing radiant heat loss and resulting in significant energy savings. Covering the water when the pool is not in use is the single most effective way to reduce heating costs. Savings of 50% to 70% are possible.

Water and heat loss

Almost all of a pool's heat loss—about 95 percent—occurs at the surface, mostly through evaporation to the air and radiation to the sky. Pool evaporation involves a huge amount of energy. While it only takes 1 BTU (British thermal unit) to raise 1 pound of water 1 degree, each pound of 80ºF water that evaporates sucks 1,048 BTUs of heat out of the pool.

The evaporation rate is dependent on the pool’s initial temperature, the surrounding air temperature and humidity, and the wind speed at the pool surface. The higher the pool temperature and wind speed and the lower the humidity, the greater the evaporation rate.

A windbreak—such as a fence or vegetation surrounding the pool—will reduce evaporation and make pool "lounging" more comfortable and private. For example, a 7-mph wind at the pool surface can increase heat loss by 300 percent. A windbreak needs to be high and close enough to the pool so that it effectively blocks wind from moving across the pool surface, but doesn't shade the area and therefore block beneficial solar energy.

Solar energy is defined as the energy received by the earth from the sun in the form of solar radiation, which makes the production of solar electricity possible. An outdoor pool may gain a significant amount of heat from the sun, absorbing 75 to 85 percent of solar energy striking the pool surface. A transparent bubble cover made specifically for swimming pools may reduce solar energy absorption by 5% to 15%, while an opaque cover may reduce it by 20% to 40%. And even though indoor pools aren't subjected to weather elements, they still lose the same percentage of energy from evaporation as an outdoor pool.

To be sure, the humidity that exists in an indoor pool area confirms the high levels of evaporation. An indoor pool also requires ventilation and air conditioning systems to cut through the humidity, which increases energy costs.

Solar pool covers help pool owners save on energy costs. Certain types of solar covers are made from UV-stabilized polyethylene, polypropylene, or vinyl to resist deterioration. Some of these covers are reminiscent of bubble packing material, but comprise a thicker grade of plastic with UV inhibitors. The vinyl solar covers are made from heavier material and usually have a longer life expectancy than bubble covers. Finally, insulated vinyl covers also are available with a thin layer of flexible insulation sandwiched between two layers of vinyl.

To determine the effectiveness of a pool cover, consider whether the evaporation and other losses prevented by the cover exceed the solar gain reduction caused by the cover. As previously indicated, dry or windy conditions increase the evaporation rate off of the pool’s surface. A pool in this environment benefits from a transparent or bubble cover to maximize light absorption. As warmth and humidity increase, the evaporation rate decreases.

More on methods

When a pool is expected to be in use all day, the solar cover should be taken off just before the pool is opened, and placed back over the water as soon as the pool is no longer in use. There are several methods for covering a pool. The simplest and lowest-cost method is to manually pull the cover on and off, fold it, and place it out of the way. When paying someone to handle this chore, consider that cost in the economic evaluation of any pool cover.

Another option is to purchase a pool cover reel that can be used to manually roll up the pool cover. The reel, usually on wheels, can then be rolled out of the way. Semi-automatic covers use a motor-driven reel system run by electrical power to roll and unroll the cover. These types of systems usually require someone to pull on the cover when unrolling, or guide the cover onto the reel when rolling the cover up. Automatic covers feature permanently mounted reels that cover and uncover the pool at the push of a button. One must weigh the cost of labor for the manual and semi-automatic covers to determine which route is best for their particular situation. Some pool covers are fitted into tracks along the sides of the pool, preventing anything or anyone from getting into the water. They even support the weight of several people. If liability is a concern, these type covers are worth exploration as they can be run manually, semi-automatically, or automatically.

Editor's sources:
Materials found at http://www.swimmingpool.info/pool-covers.html, was edited by Chris Whitten based on source material from the U.S. Department of Energy RSPEC (Reduce Swimming Pool Energy Costs) Program, and
http://www.solarhome.org/solarpoolcovers.html
http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13140
http://bathrooms.bobvila.com/Article/771.html

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