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SolarTown Learning

Selecting a Solar Water Pump for Any Remote Application

11-19-2009
Category: Solar Water Pumps

Solar water pumps have been proven to be cost-effective and dependable as a system for providing water in remote locations in a wide range of applications around the world. Solar power water pumps are ideal in situations where there is not any power or fuel, maintenance requirements must be low, and water resources are spread over long distances.

Comparison of Solar Water Pumps to Other Pump Technologies

There are many ways to move water around-whether it be from deep in a well to a home or from a pond for irrigation-but solar water pumps offer perhaps the most cost-effective, simple, practical tools for this purpose. Compare solar water pumps to other pumping technologies:

 

Solar Water Pump 

Gas-powered systems (diesel or other fuel)

Windmill

Gravity

Maintenance

Low

Relatively high, often inadequate resulting in shortened life

High, repairs costly

 Low

Fuel costs

None

 High with limitations on supply in many cases

 None

 None

Installation

Simple

Simple

 Complex requiring specialized tools

 Simple

Reliability

High

Regular site visits necessary

 No wind means no power, though potentially a long-lasting source of power

 High

Initial cost

Potentially higher than other options

Moderate

 High

 Low

Mobility

High

Some

 None

 None

Other considerations

Requires sun exposure during daytime hours; lower output when cloudy

Creates noise and fumes

 Parts are often difficult to source

 Practical only in certain locations

 

As you can see, solar water pumps are superior in almost every way-maintenance, fuel costs, installation, reliability, and mobility. And though it has a slightly higher up-front cost than some of the other options, the money you will save on a solar water pump system in fuel costs will more than pay for the investment in a relatively short period of time.

Potential Applications and Location Considerations

Solar water pumps are used globally and are ideal where there is no power and water sources are scattered geographically. Solar water pumps have been shown to be highly effective even in areas where solar potential is relatively low (find out your regions solar potential using the National Renewable Energy Laboratory's Solar Maps for photovoltaics).

Practical in a whole host of applications, solar water pumps are an excellent way to tap into the sun's energy. Here are some of the more popular uses for solar water pumps:

  • Off-grid homes and cabins
  • Watering for livestock, especially for rotational or prescribed grazing or remote pasturing
  • Emergency irrigation or watering in case of drought
  • Aeration, circulation, and de-icing of aquaculture ponds
  • Irrigation for small-scale agriculture applications
  • Village water systems in remote communities
  • Providing emergency water supplies for fighting fires

It is obvious that solar water pumps can be used in diverse settings, but locating your solar water pump in an efficient location is important for its overall efficient function. They work best where the solar panels can face south with no significant shading throughout the day. Room must be found for all of the system components (the pump, controllers, storage tank, if applicable, and so on) and the solar modules should be located relatively close to the pump to minimize wire size. Finally, where batteries are required, a location that is reasonably dry with controlled temperature and venting should be found to store the batteries.

Solar Water Pump Types

There are three main types of solar water pumps, including surface water pumps, submersible water pumps, and aerating water pumps. They are differentiated as follows:

  • Surface water pumps: Solar power surface pumps are used for moving water over short vertical distances but longer horizontal distances.
  • Submersible water pumps: Solar submersible pumps have the opposite strengths to surface water pumps; they move water up longer distances, but are less efficient over long horizontal distances.
  • Aerating water pumps: Similar in many ways to surface water pumps, solar aerating water pumps or solar pond aerators serve the purpose of adding oxygen to water because they are not meant for moving water over great distances, either horizontally or vertically.

At this point, you should also measure both vertical and horizontal distance from the water source to where the water is needed. These measurements will help to determine which type of pump you require. Once that is known, you will need to discern the size and specifications of your pump system, which is the subject of the next section.

Determining Solar Water Pump Size

Watering Requirements and Water Source Potential

First, you need to determine how much water you require and what kind of water resources you have available to you. To estimate your water requirements, think about how much you need over a given period of time (day, week, or month) and whether the water requirements differ through varying seasons. The following examples will give you a general idea of what you may require:

  • Young trees (dry weather) - 15 gallons/day
  • Average household (per person) - 50 gallons/day
  • Small animals (25 pound body weight) - ¼ gallon/day
  • Poultry (100 birds) - 6-12 gallons/day
  • Dairy cows (per head) - 20-30 gallons/day
  • Cattle and horses (per head) - 10-15 gallons/day

Using the figures above, you may be able to estimate a rough number for your water requirements. Next, you will need to calculate how much water can be supplied by your water source in a given time period. Whether you're working with a subsurface (well) or surface (stream or pond) water source, there are many factors to consider when determining how much water is available.

For instance, for wells, you need to know whether the water level is static, whether there are variations by season, what the water quality is, and what the recovery rate is. Likewise, with surface water sources, you'll need to determine seasonal water level variations as well as the overall water quality.

Dynamic Head Calculations

Now is the time to determine what size your solar water pump should be and the amount of power required by your solar modules. We will start by calculating several different figures-static life, static height, and losses to friction-and then combine these figures into a dynamic head calculation.

  • Static lift: Calculate this figure by measuring the distance between the solar array and the low water level in the water source.
  • Static height: This is measured from the solar array to the top of the water tank being used.
  • Friction losses: These are a result of resistance to water flow inside a pipe. The smaller the pipe, the higher the pumping rate, which means the higher the resistance. These figures can be taken from a friction loss table.

Total dynamic head (TDH) is expressed as the sum of the static lift, the static height, and the losses from friction.

Pumping Rate

Using the following calculation, you can estimate the pumping rate of your pump in gallons per minute (gpm):

GPM = gallons per day/peak sun hours per day  x   hour/60 minutes

Here's an example to illustrate how these calculations work:

Water requirements: 1200 gallons/day

Peak sun hours: 5 hours/day

Calculation:

1200/5 hours  x  1 hour/60 minutes = 4gpm

 

Conclusion: you will need a pump that operates at 4 gallons per minute to meet your water requirements.

Solar Water Pump and PV Array Size

Using the numbers you've just calculated-the TDH and the desired pumping rate in gallons per minute-you can use these numbers to determine the size of solar water pump and number of solar modules you will need. Refer to manufacturer's specified terms to use the recommendations for their products (be sure to add 25% to the specified wattage of your solar modules to compensate for losses in efficiency due to dust, shadowing, and so on).


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