Just thought I'd share my new solar pool heater project.
The marketplace is full of solar gadgets. They all work, but how well? With solar, performance efficiency varies wildly, and ROI due to system cost varies just as much. And that doesn't take into account the latitude and weather.
First, a word about Solar Covers: It is my opinion that this name is nothing short of misleading. Unfortunately, it has been widely adopted to describe a cover that has very little to do with collecting solar energy. It is just a pool cover that floats on the water. It is blue (usually), not black. It does collect some solar energy, but its primary ROI comes from a substantial reduction of air/water contact. Most pool heat is lost through evaporative cooling (think 'swamp cooler'), so covering your heated pool with anything at all that reduces the exposed surface area when not in use is by far the best way to reduce your heating bill. A truckload of ping pong balls will work almost as well as a so-called 'solar' cover, although the cost of ping pong balls will probably be somewhat higher, and a bit more of a PITA to manage (but the kids would love swimming with them- not possible with a cover).
Collecting solar energy has 2 key elements: The collector and the plumbing. The efficiency of the collector is dependent on 3 things: the color affects how much energy can be collected per square foot. Black is best. Anything claiming to be solar should be black, not blue or clear. The square footage determines the overall capacity of a solar system It is the single most important factor in a solar heating system. I see a lot of 'solar domes' (a coil of black pipe inside of a clear plastic dome a few feet in diameter) for sale in the marketplace, but they have a very poor ROI because they simply don't have enough square footage to be meaningful. The third factor is something where a solar dome does have one advantage over other designs: the collector pipes are encased in the dome, meaning that they are effectively insulated from re-radiating the heat they collect to some degree.
The plumbing element includes the pipe, and a means of moving the water (a pump). Efficiency in this area is determined by friction, pump efficiency and insulation. Friction is directly related to the length of ALL of the pipe in the system, the diameter, and the number of corners that the water must take on its journey through the system and the speed at which the water travels through the pipes. Without a thorough analysis to back this up, it is my opinion that the insulation part is where most of the heat energy is lost, because most of the connecting pipes are exposed in a way to promote heat loss, rather than additional collection area.
My experiment: A black billboard tarp on top of my regular auto-cover.
Positive factors:
Black is a better collector than gray
Second Layer reduces re-radiation at night
Zero efficiency losses through plumbing
Huge collecting area
Super cheap: $45 for a 14 x 48 tarp (cut down to 36' long)
Negative factors:
Water is not in direct contact with black collector (slight insulation effect)
Wind could be a problem
Must be manually removed (and stored somewhere) before rolling up the autocover
Starting conditions this morning: 56 degree water, pool pump is running. Weather is expected to be sunny and 70s for the next several days. Location: greater Minneapolis.
History: I opened the pool 5 days ago. Water temperature rose from 41 to 56 in that time with sunny, slightly cooler weather, but just the gray auto cover. I have not turned on the pool heater yet.
I'll repost in a few days with the results.
The marketplace is full of solar gadgets. They all work, but how well? With solar, performance efficiency varies wildly, and ROI due to system cost varies just as much. And that doesn't take into account the latitude and weather.
First, a word about Solar Covers: It is my opinion that this name is nothing short of misleading. Unfortunately, it has been widely adopted to describe a cover that has very little to do with collecting solar energy. It is just a pool cover that floats on the water. It is blue (usually), not black. It does collect some solar energy, but its primary ROI comes from a substantial reduction of air/water contact. Most pool heat is lost through evaporative cooling (think 'swamp cooler'), so covering your heated pool with anything at all that reduces the exposed surface area when not in use is by far the best way to reduce your heating bill. A truckload of ping pong balls will work almost as well as a so-called 'solar' cover, although the cost of ping pong balls will probably be somewhat higher, and a bit more of a PITA to manage (but the kids would love swimming with them- not possible with a cover).
Collecting solar energy has 2 key elements: The collector and the plumbing. The efficiency of the collector is dependent on 3 things: the color affects how much energy can be collected per square foot. Black is best. Anything claiming to be solar should be black, not blue or clear. The square footage determines the overall capacity of a solar system It is the single most important factor in a solar heating system. I see a lot of 'solar domes' (a coil of black pipe inside of a clear plastic dome a few feet in diameter) for sale in the marketplace, but they have a very poor ROI because they simply don't have enough square footage to be meaningful. The third factor is something where a solar dome does have one advantage over other designs: the collector pipes are encased in the dome, meaning that they are effectively insulated from re-radiating the heat they collect to some degree.
The plumbing element includes the pipe, and a means of moving the water (a pump). Efficiency in this area is determined by friction, pump efficiency and insulation. Friction is directly related to the length of ALL of the pipe in the system, the diameter, and the number of corners that the water must take on its journey through the system and the speed at which the water travels through the pipes. Without a thorough analysis to back this up, it is my opinion that the insulation part is where most of the heat energy is lost, because most of the connecting pipes are exposed in a way to promote heat loss, rather than additional collection area.
My experiment: A black billboard tarp on top of my regular auto-cover.
Positive factors:
Black is a better collector than gray
Second Layer reduces re-radiation at night
Zero efficiency losses through plumbing
Huge collecting area
Super cheap: $45 for a 14 x 48 tarp (cut down to 36' long)
Negative factors:
Water is not in direct contact with black collector (slight insulation effect)
Wind could be a problem
Must be manually removed (and stored somewhere) before rolling up the autocover
Starting conditions this morning: 56 degree water, pool pump is running. Weather is expected to be sunny and 70s for the next several days. Location: greater Minneapolis.
History: I opened the pool 5 days ago. Water temperature rose from 41 to 56 in that time with sunny, slightly cooler weather, but just the gray auto cover. I have not turned on the pool heater yet.
I'll repost in a few days with the results.
