Solar pond pumps are becoming increasingly popular in the United States after having enjoyed startling success across Africa and Southeast Asia. Of course, in those places, solar powered pumps are almost a necessity — in the United States, as the drive for greater eco-consciousness meets the need to pay less on monthly energy bills, they’re rapidly replacing their more electricity-hogging counterparts.
When searching for the right solar pond pump, there are several important factors that need to be considered in order to match the appropriate pump for its application:
Maximum Output (Flow Rate)
Gallons per hour (or litres per hour, if metric) is the number in question here. How many gallons of water (GPH) can the solar pump move under ideal conditions in one hour? This assumes that the pump isn’t actually lifting water above its own surface level and it assumes perfect water conditions (no algae or debris restricting the pond pump’s performance). In reality, the solar pump will generally move fewer gallons per hour than what is stated as the maximum output (or maximum flow rate).
The term “head” technically means “pressure”. But, it is actually easier to talk about height rather than “pressure” when referring to pumping water, so, for practical purposes “head” is the height to which you want to pump the water.
For a given solar pond pump, the maximum head is the height at which the pump delivers zero water – meaning the centrifugal pressure produced by the pump is one hundred percent consumed in trying to force the water to the desired height. Maximum head is really only useful when comparing two similar solar pumps. For example, a pump with a maximum head of 6 feet is more powerful than one with a maximum head of 4 feet.
Head rating is one of the most useful statistics to check when considering a solar pond pump it as it uses both flow rate (gallons per hour or litres per hour) and head statistics. Head rating is easiest to understand as a graph and most solar pond pumps provide head rating charts in their technical specifications:
This head rating chart compares two solar pond pumps, one represented by the blue line, the other by the green line. Both pumps have a maximum output or flow rate of 115 gallons per hour (the point at the bottom where both lines meet). But the green solar pond pump has a much greater head rating — meaning that as the pump head (the height of the water above the pond’s surface level) increases, the green pump’s flow rate decreases much more slowly. The blue solar pond pump can only get water 3.5 feet above surface level before the flow rate hits zero — the green pump can get water 11.5 feet above surface level before that happens.
Head Rating is a good way to measure the size of the solar pond pump you need. Most experts agree that to maintain a healthy pond, the water needs to circulate at least twice per hour. With this goal in mind, look up the pump head (the height of your desired water output) on a given pump’s head rating chart, then follow it down to determine the flow rate at that height. If the flow rate is not at least half the total volume of your pond, you need a bigger solar pond pump. Keep in mind, however, that bends or turns in the tubing as well as narrow outputs can also slow down the overall flow, so it’s best to get a pump that’s a bit bigger than the minimum requirements.
Type of Pump: Submersible Versus External
There are two basic types of solar pond pumps: the submersible kind and the external kind. In general, submersible solar pond pumps are cheaper, quieter, and more innocuous. However, they are also harder to clean and don’t move as much water, so they are most useful in smaller ponds that don’t collect a lot of debris from the surrounding environment. External solar pond pumps are usually more powerful, more expensive, and harder to hide. But, they are much easier to maintain, repair, and keep clean because the pump does not live in the water.
Flow Pumps or Pressure Pumps?
Flow pumps are pumps with a huge maximum output (flow rate) but a minimal maximum head; pressure pumps are just the opposite. Flow pumps are notoriously poor at pushing water through a water filter, but if what you’re looking for is an unfiltered waterfall or stream, they can be useful. Pressure pumps are better for pond fountains, which require less in terms of gallons per hour but need to get the water quite a distance vertically; and also for pushing water through a series of dense biological filters.
If you are going to put up a waterfall or another feature that requires a high gallons per hour (flow rate), here’s a back-of-the-envelope way to figure out what size pump you need. Take the business end of a standard green water hose over to where your waterfall is going to start, and adjust the water flow until it looks about right. Then, grab a standard 5-gallon bucket, and count the number of seconds it takes to fill the bucket at that rate of flow. Divide 18,000 by the number of seconds, and you’ll get roughly the number of gallons per hour that the hose was spouting. For example, if it took 60 seconds to fill the 5 gallon bucket, then 18,000 divided by 60 equals 300 gallons per hour.
Next, measure the “head” or the height of the water source from the surface of the pond. Then, use the head rating chart on the pumps you are considering to choose a pump that pushes at least the gallons per hour you calculated at the head height you measured. Most experts suggest oversizing your pump by 25% to 50%, especially if there is a long run of tubing or twists and turns in the tubing.
Drive Style: Direct Dive vs. Magnetic Drive vs. Hy-Drive
Years ago, all pond pumps had motors that were “direct drive” — the motor turned a propeller which moved water. This was problematic because the motor had to be filled with oil to work properly, and the propeller had to be in water in order to move it. This necessitated a seal between the two, which frequently broke down and resulted in both a ruined motor (full of water) and a ruined pond (full of oil).
The next evolution of pond pumps were “magnetic drive” — the motor turned a magnet, which pushed a magnet on the other side of a solid wall, which in turn pushed the water. That solid wall made it much easier to keep the oil out of the pond water and vice versa, but the fact that both magnets had to constantly turn led the pump to wear out. And, occasionally tiny punctures would still cause the water and oil to mix.
The latest evolution in solar pond pumps is the ‘hy-drive’ – a variation of the magnetic drive except that the motor powers an electromagnet which doesn’t move. Because the electromagnet is stationary, it’s can be housed in a partition that’s filled with epoxy, making it almost completely waterproof and virtually eliminating the potential problem of leakage.
Solar Panels: Size, Power & Composition
Most solar pond pumps are sold as kits, meaning that the pump comes packaged with an appropriately sized solar panel which should supply enough energy to power the pump. However, sometimes the solar panel is where some manufacturers will skimp and you need a basic understanding of solar panels to help you make an informed decision between various brands.
A solar panel is made up of a collection of individual silicon cells that generate electricity when light particles (photons) strike the surface of the cells. A single solar cell produces only about 1/2 (.5) of a volt. However, a typical 12 volt panel contains about 36 cells connected together in a series to produce about 17 volts at peak output. Note that the panel has to deliver more than 12 volts to compensate for voltage drops. What does all this technical mumbo-jumbo mean to you? Essentially it means that you need to make sure that the stated solar panel output (in volts) is greater than the voltage of the pump. For example, if your pump is rated at 6 volts, a 12 volt solar panel should be more than adequate.
Another factor to consider when assessing the solar panel is the material of the panel frame. For example, some solar panels have flimsy cardboard backing or cheap plastic frames and you can well imagine their condition after a season or two of inclement weather.
Lastly, think about where you are going to place your solar panel to determine your mounting needs. Some solar pond pump kits come with stakes or small mounts which make it easier to install the solar panel in an optimal position tot he sun. Other solar pond pumps do not supply these conveniences so you must fabricate your own mount, unless you prop the panel against a rock or log.
Unless specified, most solar pond pumps do not come with battery back-ups. This means that the pond pump will only work during the day when sunlight is present – and even then, the performance of the pump will fluctuate based on the available sunlight. Some people enjoy the variations in the sound and flow of the water as weather conditions change; others do not. If you want your solar pond pump to perform at a consistent level, you should invest in a model with a battery back-up (sometimes marketed as “night” pumps). During the day, while the sun is shining and the pump is working, part of the energy from the solar panel is used to charge the back-up battery so that at night or during cloudy conditions, the battery supplies the missing power. Depending on the size of the battery, a full battery can supply anywhere from 3 to 8 hours of additional power.
The downside to purchasing a solar pond pump with a battery back-up is the increased cost; in some cases adding the battery back-up can double the price of the solar pond pump.