Solar pumps offer a CLEAN and SIMPLE alternative to fuel-burning engines and generators for domestic water, livestock and irrigation. They require no fuel deliveries, and very little maintenance. Solar pumps are powered by photovoltaic (solar-electric) panels and the flow rate is determined by the intensity of the sunlight and the water depth.

 

Solar panels have no moving parts, and most have a warranty of at least 25 years. Most solar pumps operate without the use of storage batteries. A water tank provides a simple, economical means of storage. Solar pumps must be optimally selected for the task at hand, in order to minimize the power required, and thus the cost of the system.

 

This introduction aims at providing the basic information to decide whether a solar pump is suitable for your farm and whether it can economically replace a pump powered by a diesel engine or a wind mill.

 

Diesel - Can You Build A Business on It?

 

To decide whether solar or diesel pumping is more economical for your farm, everything comes down to the question: How much do you have to pay per liter of water pumped up?

 

Very often investment decisions are based only on the cost for purchasing a technology, neglecting the operational, maintenance and replacement costs. For example: leaving aside the fuel costs when comparing solar to diesel water pumps. This skewed economic perspective sometimes results in the general perception that “solar is expensive”.When comparing solar and diesel water pumps in terms of total costs over the minimum 20-year lifespan of the solar panels, one must add the cost of fuel that has to be delivered to the borehole for the next 20 years, to the cost of the diesel pump itself. This compares “apples with apples”.

(1)   The initial costs for the diesel pump are lower. Not much, but every penny counts, doesn’t it?

(2)    Next add replacement costs. This includes replacing the diesel pump every 5 years and the submersed solar pump unit every 7 years. When these costs are added to the initial costs, the cost for diesel already surpasses the solar pump.

(3)    Now add maintenance costs. For diesel pumps, as every farmer knows, these costs are significant. Already at this point the diesel pump is twice as expensive as the solar pump.

 

(4)   Adding operational costs reflects the true costs when choosing a diesel pump as a water supply technology on a farm. The actual all inclusive costs over 20 years is 20% for a solar pump relative to a diesel pump (at today’s diesel price).

 

PUMP TYPE

There is a large variety of solar water pump types in the market. The most common types of mechanisms are

• Helical rotor (mono).

• Centrifugal.

• Piston or diaphragm.

 

The most simple and robust pump ends are themono or helical rotor type pumps with only one turning part: a rotor turning in a rubber stator. They are a good choice for daily flows of 6 to 20m³ for medium to high lifts (50 to 150m).

Centrifugal pumps are very economical for shallow to medium lifts (up to 80m) with large flow rates.

Piston or diaphragm pumps are much more complex with a lot of moving parts. Usually they require oil lubrication inside the pump which might be a potential risk in water well. Typically they are used in low voltage (24-48V) applications with small daily flows (up to 5m³/day) for lifts up to 150m (max. 2m³/day).

 

SUBMERSIBLE motors for solar pumps

 

Solar Power is direct current power, also called DC. Hence DC motors are used most commonly. DC motors can be up to 100% more efficient than AC motors of the same size. Unlike AC motors, DC motors use permanent magnets which are responsible for the large efficiency advantage. Due to this advantage, solar pump systems below 4-5kW typically use DC motors.

 

Double efficiency means: you need only half the power for the same performance, accordingly you can work with a much smaller solar generator than you need for an AC system. The solar generator is the most expensive part of the system and usually accounts for 70-80% of the total system cost. There are two different types of DC motors that differ a lot: Brushed and brushless DC motors.

 

• Brushed DC motors have small carbon blocks that are called brushes. They are needed to create the turning field to make the motor rotor spin. They wear out and must be replaced after some time. Brushed motors must be air-filled in order to make the carbon brushes work; otherwise a short circuit will occur. If the motor shaft seal or any other motor seal fails the motor will be damaged and cannot be repaired.

 

• Brushless DC motors do not use these brushes. The brushless motor concept is the answer to these problems and was developed about ten years ago. They do not need reliable seals – in most cases they are water filled anyway! They where designed to be maintenance-free for many years and as reliable as AC motors are.

 

For more data about the solar pumps we use, please visit the next LORENTZ web site  http://www.lorentz.de