Why should I consider solar?

Photovoltaic (PV) water pumping systems can be a very cost-effective solution for locations where there is no existing power line. A well-designed PV system will operate unattended and requires minimum periodic maintenance. PV panels are so reliable that most manufacturers give a 10-year warranty, and a life expectancy beyond 20 years. The savings in labor costs and travel expense can be significant.

PV systems create no pollution, generate no waste products, work well in cold or hot weather, and can be designed for easy expansion. If you think your power demands may grow in future years, the ease and cost of expansion should be considered when designing your system. Although today's prices for PV panels make most irrigation systems too expensive, they can be cost-effective for pond aeration and irrigation systems.

How do solar pumps work?

Solar water pumps are specially designed to utilize DC electric power from panels. They work during low light conditions at reduced power, without stalling or overheating. Low volume pumps use positive displacement (volumetric) mechanisms which seal water in cavities and force it upward. Lift capacity is maintained even while pumping slowly. These mechanisms include diaphragm, vane and piston pumps. These differ from a conventional centrifugal pump that needs to spin fast to work efficiently.

How about exposure, will I need a tracking device?

Whether a submersible pump or a surface pump is best depends upon the nature of the water source. Submersible pumps are suited both to deep well and to surface water sources. Surface pumps can only draw water from about 20 feet below ground level, but they can push it far uphill. Where a surface pump is feasible, it is less expensive than a submersible, and a greater variety is available.

For maximum output, PV modules should be exposed to the sun as much as possible, especially during peak sun hours of 10 a.m. to 3 p.m. The southern exposure in particular should be free of obstructions such as trees, mountains and buildings that might shade the modules. Consider both summer and winter paths of the sun, as well as the growth of trees and future construction that may cause shading problems. You’ll also need appropriate terrain and sufficient space to install the system.

A solar tracker may be used to tilt the PV array as the sun moves across the sky. This increases daily energy gain by as much as 55%. With more hours of peak sun, a smaller pump and power system may be used, thus reducing overall cost. Tracking works best in clear sunny weather. It is less effective in cloudy climates and on short winter days.

How do they compare to windmills?

Compared with windmills, solar pumps are less expensive, and much easier to install and maintain. They provide a more consistent supply of water. They can be installed in valleys and wooded areas where wind exposure is poor. A PV array may be placed some distance away from the pump itself, even several hundred feet away.

How large of a system do I need?

The size and cost of a PV water pumping system depends on the local solar resource, the pumping depth, water demand, and system purchase and installation costs. You may be surprised at how efficient a small solar pump can be. The smallest ones require less than 150 watts, and can lift water from depths exceeding 200 feet at 1.5 gpm. In a 10-hour sunny day it can lift 900 gallons, enough to supply several families, or 30 head of cattle, or 40 fruit trees!

Slow solar pumping also allows you to use low-yield water sources and reduces the cost of long pipelines. Small solar pumps can be installed without heavy equipment or special skills. Storage is important, though. Three to ten days’ storage may be required, depending on climate and water usage. Most systems use water storage rather than batteries, for simplicity and economy. A float switch can turn the pump off when the water tank fills to prevent overflow.

To determine the hourly flow rate required for your system, divide volume per day by the number of hours of available peak sunlight. Peak Sun Hours refers to the average equivalent hours of full-sun energy received per day. Check the solar maps noted in the Resources section to get an idea of solar availability for your location.