Storing water in a cistern or tank has many advantages. It's less expensive and more efficient than storing power in batteries. Since water is always a critical issue, we recommend the tank should be able to store a minimum 3 to 6 days worth of water or whatever you think your needs may be during cloudy weather or in case of a system failure. Generally speaking, animals, plants and humans use less water on cloudy days. Conversely, the sunniest days are when we consume the most water and when the solar modules are providing the pump with the most power.
The photovoltaic effect produces a flow of electrons. Electrons are excited by particles of light and find the attached electrical circuit the easiest path to travel from one side of the solar cell to the other. This excitation of electrons causes an electron flow. The solar cell takes these electrons and directs them to flow in a path or an electrical circuit. Photovoltaics is the process of solar electric cells converting sunlight directly into DC power. This DC power is then used to run a pump.
While batteries may seem like a good idea, they have a number of disadvantages in pumping systems. First, they reduce the efficiency of the overall system. Second, they are another source of problems and maintenance. Third, they add cost to the system.
Solar water pumping is the process of pumping water with the use of power generated by sunlight. The advantages of solar water pumping are many. Solar pumping systems are reliable stand-alone systems that require no fuel and very little attention. Generally, when water is needed most, is when the sun shines the brightest. Solar panels generate maximum power in full sun conditions when larger quantities of water are typically needed. Because of this natural matching effect, solar water pumping is an obvious and economical choice over windmills and engine-driven generators for most locations away from utility power.
There are two main categories of water pumps, submersible and surface mounted. Submersible pumps are installed under the water while surface pumps are mounted out of the water. Submersibles are usually installed below the water level in a well but can be installed in a lake, cistern or river. Surface pumps are usually mounted above the water level which requires a suction lift, the distance between the water level and the inlet of the pump. However if a water storage tank is used the water level could be above the pump creating a positive suction head.
Almost always you should store water and not power when possible and you will have much better performance and reliability with your solar pumping system. However there are cases where we recommend batteries in solar pumping systems, as in home pressure systems when you need a booster pump to maintain system pressures at night and in cases were it is more cost effective. For example, if a home power system using batteries already exists and you need to pump water out of a well and into a pressure system, then connecting to your existing battery bank could be more cost effective.
