Solar Pool Covers or Solar Blankets do have some benefits, but they also have some drawbacks that you need to be aware of. Solar Blankets do reduce evaporation by 30-50% and can also help your pool retain the heat from the Sun. Chemical usage is also reduced in most cases. But the benefits have been overblown in some cases, especially in areas suffering from drought.
Even with a Solar Blanket on top water will evaporate, but just at a lower rate. To get the full benefits of evaporation reduction the cover needs to be left on 24/7. If you take the cover off a few days during the week to use it, the benefit becomes less noticable.
Having the pool covered can reduce your chemical usage by up to 30%. Since the cover blocks some of the Sun's UV rays the chlorine will last longer in the pool. You will still need to check the pool chemistry at least once a week and adjust the pH and Alkalinity but you will notice a reduction in the chlorine usage. This would not be a reason to purchase a Solar Blanket, but it is a good side benefit.
As far as heat retention or heating up your pool, they can raise the pool water temperature in some cases up by as much as 10 degrees. Most people will experience a 3-4 degree increase as there are a lot of factors that determine how much heat is retained in the pool. When installing for maximum effectiveness for heat retention, the bubble side goes down and the flat side goes up.
The number one factor is how much sunlight actually hits the pool all day. If your pool is shaded most of the day, don't expect much of a bump in the water temperature. The size of the pool is also a factor. If you have a very large pool, the heat will not be retained as well as in a very small pool. The temperature at night is also a factor as most of the pools heat is lost at night. If the nights are very cold don't expect the pool to hold the heat.
So if your buying a Solar Blanket to keep the pool water warmer during the season, note the above factors.
The actual color of the cover may also effect heat retention. Lighter colored covers seem to warm the pools up more than the darker blue colored or silver colored covers. But the lighter color covers are also usually thinner.
Which brings me to the issue of cover longevity. The thinner the cover the more heat benefits you will experience, but the thinner the cover the quicker it will wear out. The Sun's UV rays are very powerful and if you leave your cover on all Summer long, expect a short lifespan for your cover. 1 to 3 years would be a reasonable expectation.
The darker covers and thicker covers will last longer but won't allow as much heat to be retained in the pool. The bubbles will eventually pop due to Sun exposure and chemical exposure which in turn will lessen the covers effectiveness and make is heavier. You will notice platic particles in the pool when the cover starts to wear out.
There are of course drawbacks to a Solar Blanket. It takes away from the overall look of a backyard pool. If you like the look of the water reflecting on a Sunny day, a solar blanket is not for you. Dirt, calcium and algae will start to settle on the cover, as well as leaves and debris making it look even less attractive.
Algae can bloom very quickly under the cover if you let the chlorine drop down to zero. This can be very bad as algae grows in the shade and it will cover the entire pool in some cases under a covered pool. Keeping your pool balanced is critical if you decide to cover it.
Taking the cover off and putting it on can be a real chore. A lot of the dirt and debris will fall into the pool when you remove it and wear to put it in the off season becomes an issue. I suggest purchasing a reel to store it on and the reel also makes getting it off and on the pool easier.
Most of my customers who do purchase a cover only use it for one season. They find it is a real hassle to get it on and off the pool and that it takes too much away from the look of the pool. As a pool service guy I personally don't care for them as they make maintaining the pools on my route a real hassle.
But they do have some good benefits such as reducing evaporation and possibly warming up the pool water so a solar Cover may be worth the hassle.
Poolman Tips and Tricks: For Pool Service Professionals and DIY Homeowners: https://youtu.be/sUcjLt9Sk8s
How to Maintain and Service A Swimming Pool: A Step By Step Guide: https://youtu.be/UmHqL2EvG10