FAQs

Generators are commonly used to provide power beyond the power line. We have several economic studies of solar versus generators as a power choice. These studies consider all costs involved: modules, mounting structure, pumps, miscellaneous components, installation, operation, maintenance, yearly inspection, component replacement & resale value. With this we can determine a life cycle cost & a present value. One such comparison was done by the Bureau of Land Management at Battle Mountain, Nevada specifically comparing solar water pumping systems. For one 1036 L/Hr system with an 84 meters design head, the PV system costs only 64% as much over 20 years as the generator system did over only 10 years. This remote solar site also used only 14% as many labour hours.

 

In 1989, Sandia National Laboratories noted that photovoltaic pumping systems in remote locations would often be cost effective compared to generators, even with 5 times the initial capital cost. Low end generators, which are initially inexpensive, require consistent maintenance & have a design life of approximately 1,500 hours. Small to medium sized solar pumping systems often initially cost less than a durable slow speed engine driven generator. Most larger pump systems initially cost more than generator systems, but tend to be far more economical in the end.

While batteries may seem like a good idea, they have a number of disadvantages in pumping systems. They reduce the efficiency of the overall system. The solar modules operating voltage is dictated by the battery bank & is reduced substantially from levels which are achieved by operating the pump directly. Batteries also require additional maintenance & under & over-charge protection circuitry which adds to the cost & complexity of a given system. For these reasons, only about five percent of solar pumping systems employ a battery bank & are generally used in household situations that require water pressure at night for showering, bathrooms etc.

Fixed Mount structures are less expensive & tolerate higher wind loading. By fixing the modules due north, less water is pumped than a tracking system which orients the modules towards the sun as it arcs across the northern sky. However, with solar panels becoming so cheap it is considered better value to add a panel to a fixed frame instead of investing in a tracker.

 

Tracking mount structures keep the modules at a 90 degree angle to the sun all day long. This provides more power to the pump over a longer period of the day, which produces 20 to 30 percent more water daily in the summertime.

 

Trackers offer a great advantage when pumping water. Positive single axis trackers are not known for their reliability & service life. They take very little power from the system as they operate (4 watts). Positive trackers are highly recommended in all locations. The heavy duty actuator is operated by some very simple electronics that measure the length of the previous day by measuring the time that the panels are producing any voltage. This time span is then split into 6 equal periods & the array is moved from east to west in 15 degree intervals. Gas/Fluid trackers have no electronics & are even more reliable but come at a higher cost. At night the array is moved to the horizontal position to minimize wind loading.

There are still thousands of windmill water pumping units standing in rural Australia. Regrettably, many are inoperable. These mills were very valuable for remote (off grid) sites, with the minimum wind conditions & when manpower was plentiful & cheap. Windmills, though potentially long lasting, need dedicated maintenance. The down hole leather pump buckets require regular inspection & high winds can cause mechanical damage to the blades. Parts for these mills are expensive & sometimes hard to find. There is another side to windmills which can have devastating effects on water supply, these are wind droughts (no wind, no water) which can last for quite long periods of time, solar pumps do not suffer this problem.

 

Solar water pumping systems have many advantages over windmills. Though the initial cost of solar powered systems can be similar to that of a windmill (however, in many cases far less) the life time costs are much lower. Windmills must be used where there is a steady, constant wind for maximum results while solar pumps operate anywhere the sun shines. Solar pumping systems can be installed in less than a day by an individual or small crew & can be portable, while windmills (because of the need to erect a tower) can take a larger crew a much longer time to install. Windmills are secured to the ground & are stationary. There is also the added safety benefit of ground level operation, meaning no climbing dangerous windmill towers. Solar powered water pumping systems are the modern day upgraded version of the windmill which uses natural resources to deliver water in off grid locations.

 

Solar power & water pumping are a natural combination. Generally, water is needed most when the sun shines its brightest & longest. Solar modules generate maximum power in full sun conditions when we typically need larger quantities of water. Because of this “sun synchronous” matching, solar is an economical choice over windmills & engine driven pumps for most locations where utility power is non-existent. Owners of solar water pumping systems enjoy a reliable power system that requires no fuel & very little attention.

Solar modules should be located in a sunny spot where no shading occurs. Even shadows from a tree branch, tall grass, or fence posts can substantially reduce power output.

 

For these reasons we typically mount the solar modules on a ground mount, windmill tower, tank top or building roof above any obstacles. Remember the solar array can be placed some distance from the water source if shading is a problem. Cable size can be increased to compensate for longer cable runs & the associated voltage drop. The solar panels should always be mounted facing north with an average angle of 20 degrees.

The economic value & reliability of solar electric power make it an excellent choice for remote water pumping. Livestock producers in Australia, USA, Africa & Mexico are enthusiastic solar pump users. Their water sources are spread over vast areas, where power lines are few & refueling & maintenance costs are substantial for generator & engine use.

 

If your water source is 1 km or more from the power line, solar is a favorable economic choice. This fact is reinforced by the staggering costs of extending power lines in rural Australia & the escalating price of diesel fuel. A solar pump minimizes future costs & uncertainties. The fuel is free. Moving parts are reduced to as few as one. A few spare parts can assure you many years of reliable water supply at near-zero operating costs.

Solar pumping systems work anywhere the sun shines. The majority of Australia enjoys plenty of sun to operate a pumping system economically.

 

The intensity of light varies greatly throughout the day. Morning and afternoon sunlight is less intense because it is entering the earth’s atmosphere at a high angle & passing through a greater cross section of atmosphere, which reflects & absorbs a portion of the light.

 

We measure sun intensity in peak full sun hours. One hour of peak sun is roughly equivalent to the sunlight on a clear summer day at noon. The sunlight or isolation levels also vary seasonally. Fortunately, most needs for water correspond with the sunniest seasons of the year – spring, summer & autumn.

 

Small to medium solar electric pumping systems are easily portable. By mounting the solar system on an axle or trailer, a system can be moved from bore to bore, dam to dam, etc… This increases the economic return of a system by increasing the seasons of use. It may also correspond with the rotation of grazing areas.

The process begins with the photo voltaic effect producing a flow of electrons. These electrons are excited by particles of light & find the attached electrical circuit the easiest path to travel from one side of the solar cell to the other. Envision a piece of metal such as the side panel of a car. As it sits in the sun, the metal warms. This warming is caused by the exciting electrons, bouncing back and forth, creating friction & therefore, heat. The solar cell merely takes a percentage of these electrons & directs them to flow in a path. This flow of electrons is, by definition, electricity.

 

Photo voltaic or solar electric cells convert sunlight directly into electricity. This electricity is collected by the wiring in the module & then supplied to the DC pump controller & motor, which, in turn, pumps water whenever the sun shines. At night or in heavy cloud conditions, electrical production & pumping ceases.