How do Pool Solar Covers Work?

As the story goes, and engineer at the Sealed Air corporation covered his pool with the company's bubble wrap product in the early 60s, to prevent so much heat loss at night. He quickly found that not only was the pool warmer in the morning, but it was also warmer in the evening when he returned home from work. Solar blankets work very simply by absorbing heat from the sun and transferring it to the pool water. The air filled bubbles of a solar pool cover catch and refract the sun's rays, focusing them deeper into the water. But that's only half the story! Solar blankets can also reduce evaporative heat loss from the surface by over 95%, retaining the heat in the pool at night, and during cloudy days.

How are Pool Solar Covers Made?

Solar pool covers are made by an extrusion process that is used for a wide variety of plastic films, like trash bags and plastic drop cloths. Solar blankets are made with UV stabilized, low-density polypropylene (PP) or polyethylene (PE) in two layers, the flat layer and the bubble layer, which are heat fused together. Solar blankets are made in large rolls, and then cut to specific sizes of rectangle, oval and round shapes. Freeform shape pools use the largest rectangle shape that will fit over the pool, then trim away the excess with scissors or razor, to fit the curves of the pool, bubble-side facing down.

How Well do Solar Covers Work?

A recent study conducted on solar blanket effectiveness at the Cal Poly pool research facility found a 95% reduction in evaporative heat loss (and evaporation) in pools fully covered by a solar blanket. They did not study or measure temperature rise, but the average pool will gain 10 degrees F by using a solar blanket during sunny weather. Very sunny pools can gain more heat, up to 15 degrees, while shady pools with just a few hours of daily direct sunlight may only gain 5 degrees from using a solar blanket. Solar blankets are very effective, both at reducing evaporation and stopping heat loss, while also adding 5-15 degrees to the water temperature.

Types of Solar Pool Blankets - Thickness and Color

In comparing solar covers, we can contrast them in regards to blanket thickness (8, 12 or 16 mil) and blanket color (Clear, Black or Blue). Thicker covers tend to withstand chemical and UV damage better than thinner blankets, and also have an improved R-value. However, thicker covers also are heavier and bulkier, which can cause some solar reels to bend, and roll-up thicker on a solar reel, which may cause low-profile reels to rub on the deck or diving board. The 8 mil blankets on the other hand, are so thin that high winds may shift them around. Less weight makes thinner covers easier to manage, but also more susceptible to chemical damage, and more easily torn or punctured. A 12 mil solar cover is a happy medium for most pool owners.

The second point of contrast between solar blanket types is the color. There is the traditional blue solar cover, which seems to work fine for most people. SPP also offers a 16 mil Ultra Clear blanket (actually an opaque silver color), that allows the sun's rays to penetrate into the water more deeply than darker colors. Our 12 mil Blue Black solar blanket works differently, to absorb more heat on the surface, and transfer it directly to the water. Blue solar blankets, in 8 mil and 12 mil, do a little bit of both, warming the water surface with direct transfer, and absorbing UV rays into the pool water.

Installing a Solar Pool Cover

Open the box (carefully, no razor knife) and shake out the solar cover. Machine packing squishes them so tightly to remove the air, that it takes two people to unfold a new solar blanket. Spread it over the pool (bubble side down), and work around the edges to pull out packing wrinkles. Allow it to sit for a few hours in the sun to soften and begin to lay flat, before you do any trimming.

Cutting to Fit: Round, Rectangle and Oval pools should have very little trimming to do, as long as you purchased a solar cover using your inside pool dimensions. For freeform pools, bowed ends or anything with a curve to it, stretch the rectangular solar cover over the pool tightly, and allow it to fully relax, which can take 24 hrs or longer in colder weather.

If you are using a reel with your solar blanket you will want to connect the reel tube to the solar cover with the straps and clips - before cutting the cover. Especially true for aboveground pools, the cover straps connect to a folded-over solar cover, which shortens the pool cover by 2-3".

Spend the time to center the solar cover properly, or position it to reduce the amount of cutting needed where pool edges run straight. Allow the cover to rise up over the edge of the coping stone and cover deck areas around the pool shape. Use the inside edge of the coping stone as a guide, and cut the solar blanket material with a sharp razor knife. You can also use scissors, but a sharp box cutter or razor knife, dragged along the inside edge of the coping, is a bit faster and cleaner.

Ideally and in a perfect world, your solar blanket will be an exact side-to-side fit, meeting the tile line on each side of the pool, with a slight 1" up-curl toward the tile. However, in the real world it can be hard to cut a solar blanket perfectly, so don't worry if you are an inch too large here, and an inch too short there. Of course you can always trim again if too large, but if cut too short, you can't add material back.

As you move around the pool, trimming the excess away, be sure the solar cover does not shift from the wind or from your movements around the pool. You can place planters or water bags around the edges as a way to keep the solar cover in place while you are cutting to fit your pool shape.

Using a Solar Cover Reel

We always recommend using a solar cover reel with your solar blanket, not just for the convenience it offers, but because it helps protect your solar blanket when it is removed from the pool. For inground pools, solar reels make it easy to roll-up the blanket and roll the reel out of the way, and for aboveground pools with no deck, solar reels save the grass and makes a difficult task a one person job.

For inground pools, the solar reel is placed on the end of the pool with the most access to operate and store the cover reel. After assembly of reel and tube, straps are screwed onto the tube every 2 ft. The straps are connected to plastic clips that pinch the end of the pool cover. As the reel is rolled-up, the straps first roll around the tube, followed by the pool cover.

For aboveground pools, or inground pools with no room at the end of the pool to set up a cover reel, the solar reel is mounted across the center of the pool, or at the end of the last straight wall panel, for oval pools. Once the reel is in place across the widest part of the pool, the cover straps are screwed to the reel and attached to the plastic clips. For aboveground pool solar reels, attaching the straps to the tube and cover may be more easily accomplished in the lawn or driveway. Or, you can fold the cover on itself, rolling it up in front of you, until the strap clips can be reached, while standing in the pool.

For free form shaped pools with outside radius curves, you can fold in the curved edges on the sides to roll up a smaller width rectangle shape onto a solar reel. Alternatively, some prefer to cut the cover into a large rectangle to use with the reel, plus 2 or 3 smaller curved sections that are pulled out of the pool by hand.

Solar Reels also make a great winter storage solution for your solar blanket, but to protect it from weather and sun, cover your cover with a solar reel winter cover, ordered by width to fit your solar blanket and reel exactly.

Are Solar Pool Blankets Safe?

Solar pool covers are not safe, in that they will not support the weight of a person or pet who attempts to walk across the cover, or falls onto a solar cover. For the inexperienced swimmer or a disoriented person, the solar cover could create a difficult challenge as it wraps tightly around the legs and body of a person, softly trapping them as pool water rushes to fill the depression.

Are Solar Pool Covers recyclable?

Yes, ITS solar blankets are made from LDPE #4, which can be recycled by most city or county recycling facility. In areas not so equipped or for other materials, solar covers can be repurposed into weed blocking material for gardens and walkways, or can be used to cover a wood pile, mulch pile or compost pile. You can also use old solar blankets, or trimming scraps as bubble wrap for shipping fragile items, or when packing for a household move.