Solar Pumps

With the ever increasing cost of electricity including the  carbon tax, farmers and rural retreat owners are seeking a less expensive alternative with solar pumps. Traditionally wind mills have proved the solution but the wind does not necessarily blow when water is most needed. However solar water pumps operate best when water is most needed, that is in summer when it is hot, dry and the days are longer.

The solar pump is usually submersible and is powered by solar panels supplying power to the pump via a control box which converts the direct current in to three phase alternating current.

Solar panels can either be fixed to a static frame facing north or mounted on a solar tracker which is designed to follow the sun and increases daily output by around 30%. A solar tracker can also be fitted with a second axis mechanism to allow for winter and summer elevations to maximize performance.

For example at latitude 35degrees south the ideal angle to the horizontal is 49 deg in mid winter and 11 deg in mid summer.

Solar water pumps either have a screw or centrifugal mechanism, with the screw pump being used for higher head applications and the centrifugal where there is a lower head and more volume is required.

Heads up to 150 meters are achievable but naturally as the head increases the flow rate diminishes.

A classic application for solar pumps is in situations where a dam or bore is hundreds of meters from the house and the inconvenience of having to fuel, start and and turn off a petrol pump becomes a chore. Also the cost of installing underground power from the house to the water source is very expensive and still there is the cost of electricity.

The solar pump is also ideal to provide free water for household use from a tank.To ensure water at night the solar water pumps are connected to a battery which is charged by solar panels and id designed to provide continuous water for four hours.

There are many applications for a solar water pump including stock watering, gardens, vineyards, orchards and solving the leaking dam problem.

Solar Pumps

As wine growers have a depressed market and the price of electricity is going through the roof with the addition of a possible carbon tax, they are looking at ways to reduce production costs. One solution is to irrigate the vineyard with a solar pump which once installed costs nothing to operate.

Recently a 5 acre vineyard was converted to solar irrigation using a 1000W direct current motor coupled to a multistage centrifugal solar pump. As the vineyard is watered by drip irrigation, a constant pressure of 23 KP was required. This was achieved by connecting the motor to 4 12V deep cycle batteries, charged by 8 90W solar panels on a solar tracker.

To ensure a uniform charging rate the power from the solar panels is connected to a 48V charge controller which also has an automatic switch to switch off the motor when the voltage drops to44.6V and switch on again when the voltage reaches 49V. This function ensures the batteries will not run flat.

In converting to a solar water pump, calculations were made to ensure the vineyard received the recommended application rate. This was calculated on the formula of one mega liter per hectare per year which equates to 10,000L per day in summer in dry conditions. The solar water pump delivers 80L/M and therefore needs just over two hours to supply the 10,000L required. As the battery charging panels are attached to a solar tracker which follows the sun, charging time in summer is extended to over ten hours. Therefore a larger vineyard or orchard could be irrigated using solar pumps with this set up.

This solar pump is also connected to 22 taps in the garden, orchard and stables, providing ample water at those times the vineyard is not being watered. In wet and heavy overcast conditions the fact that the charging rate is reduced does not matter as the vineyard does not require water at that time. The beauty of solar water pumps is that they supply maximum water when it is most needed, that is in hot dry conditions in summer with long hours of sunshine.

Solar Pumps

For hundreds of years the windmill has been a major source of power for milling, water pumping and driving machinery. Up until recently the windmill was the only free to run water system. Lately due to large technological advances in solar pump and panel design, this form of free water supply has become a major competitor to the windmill. The choice of the most suitable product depends on use required and local conditions.

Naturally windmills perform best in windy areas in coastal regions or above eight hundred metes in elevation whereas solar pumps perform best in dry sunny locations.

Windmills have the following advantages

• They can operate for 24 hours a day when the wind blows.

• Can produce large volumes of water in windy areas.

• Heads up to 400M are achievable

• Easy to service mechanical operation without electronic components

• Can run dry without damage.

Windmills have the following disadvantages.

• More expensive than solar pumps

• Wind does not necessarily blow in summer when water is most needed. In southern Australia the windiest months are August and September.

• Due to Workcover requirements, maintenance staff must be certified with the necessary approved equipment to work at heights.

• In deep bores due to rigid piping the pump is difficult to remove for servicing.

• Cannot be turned off with a pressure switch.

Advantages of a solar pump.

• Operates best in summer when water is most needed.

• Very efficient with modern design of solar pumps and panels.

• Easy to install at ground level.

• The electronic controller has no moving parts and does not require servicing

• In deep bores the pump is easily removed due to the flexible poly pipe.

• Probes switch the pump off when the water level is low.

• A simple pressure switch isolates the pump when the tank is full.

Disadvantages of solar pumps.

• Do not operate at night

• Reduced pumping on overcast days

• Does not operate when it is raining.

Conclusion

Windmills are ideal in locations where the wind regularly blows in the summer months.

In most other applications particularly in dry sunny areas the solar pump is the answer and the price is now less expensive than it was.

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