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A major application for small off-grid PV systems is supplying power for outdoor equipment, also in urban areas, such as:

• Sign lighting
• Parking meters
• Bus shelter lights
• Outside area lighting
• Environmental monitoring equipment (air quality, traffic flows, etc.)
• Other relatively low-energy-consuming equipment away from the electric grid

Installing these low-power systems can cost less than connecting them to the grid, which might involve digging up roads and laying underground cables. These systems are usually sold in kits and are relatively easy to install. Most off-grid systems of this type consist of a PV module(s), charge controller and battery.

Solar powered parking meter.

 

In systems providing outdoor lighting, the lamps are usually LEDs, which consume little energy and have very long working lives. Ideally the battery should be in an enclosure under the ground so it does not overheat. If batteries get hot, their working lives are considerably shortened. However, as the danger of theft and flooding may prevent this, most systems have a battery enclosure at the top under the PV module. The battery should also be appropriate to the temperatures it will be subjected to.

Solar powered road sign.

Outside area lighting.

Most off-grid systems of this type consist of a PV module(s), charge controller, battery and the load.

 

All these systems require a maintenance plan to ensure long working lives. The main maintenance task is regular battery replacement. Dust on PV modules might also be an issue in some regions.

Off-grid solar electric systems can also be used to provide drinking water by:

• Water purification
• Water desalination

A very wide range of products of different sizes is available. Many companies supply bespoke solutions for water purification and desalination, especially for smaller applications.

PV-powered UV water purification system. Water is passed through a pipe where it is exposed to ultraviolet radiation. Power for the pump and the UV generator is provided by the PV modules. This can be either stand-alone or integrated into a larger PV system.

PV-powered desalination plant using reverse osmosis (RO) semi-permeable membranes to purify salt water. Power for the pumps is provided by the PV modules. Another similar method is membrane distillation (MD).

Water quality can also be assured by PV-powered monitoring systems. These generally require very little power and are ideal for locations away from the electric grid.

Solar thermal alternatives are also available for water purification and desalination. These use the heat from the sun as a power source.

Solar pumping systems which pump water from rivers, lakes and reservoirs (but also some wells) use surface pumps which float on the surface of the water or just under it. The water is stored in a tank or can be used directly.

These types of system are usually used to provide water supplies for livestock or irrigation. They are efficient, robust and durable, with very low and easy maintenance. Systems are available in a range of sizes. However, pumps may be subjected to environmental damage (floods, freezing, etc.), theft and vandalism.

Irrigation systems for solar pumps need to be efficient and not waste water. Drip irrigation, which feeds water directly and efficiently to crops, is often used. This is an issue which needs to be considered when a diesel pumping system is being replaced with a solar water pumping system.

Solar water pumping system with a pump that floats on the surface of the water or just below the surface.

Solar pumping systems which pump water from deep wells or boreholes use submersible pumps which are installed in the well or borehole. They are efficient, robust and durable, and require very low maintenance.

These types of system are usually used to provide water for human consumption or water supplies for livestock. Pumped water can also be used for irrigation, depending on water requirements and the value of the crops.

Solar water pumping system with submerged pump under the water in borehole or well.

Most of the work and cost will be drilling and preparing the well or borehole (if it does not already exist). Knowledge of hydrology is required when designing and sizing solar pumping systems for large borehole pumps, so it is recommended to purchase systems from companies which specialise in this field.

Selecting and sizing a solar pump depends on the daily water requirement, the height the water needs to be pumped (the ‘head’) and the level of solar irradiation at the location.

Some typical daily water requirements include:

• People:………………………..280 litres per person
• Milk cow: ……………………133 litres per milk cow
• Cow & calf: ……………….. 38-144 litres
• Horse, head of cattle: … 38-76 litres per animal
• Sheep: ………………………. 8 litres per sheep
• Chicken: ……………………. 15 litres per chicken
• Irrigation: …………………. highly variable depending on crop, irrigation system and

weather conditions.

Basic steps required when selecting / sizing a solar pumping system. Needless to say, the details are more complex and most companies use sizing software, which is often supplied by system manufacturers.

Water is a universal need and pumping is a major energy issue, especially in regions where there is no grid or where electricity is expensive or unreliable. Solar pumping provides access to water in a clean and quiet way, in remote and hard to reach places, and can be a replacement for diesel pumps. Demand for water is often greatest when solar irradiation levels are high, which makes PV an ideal power source.

Water is pumped by the solar system when the sun shines, and is usually stored in a tank and used when required. Pumping systems do not have batteries.

The main components are:

• PV modules
• Pump controller (for either a DC pump or an AC pump)
• Tank to store water

The main applications are:

• Drinking water for homes and communities
• Water for livestock
• Water for crop irrigation

Complete systems (PV modules, controller, pump) are usually purchased from a single supplier.

Typical solar pumping system.

The PV modules produce electricity to drive the pump. The controller ensures that this is done efficiently. The water is pumped to a tank for later use, but can also be used directly, for example in irrigation systems.

 

Diesel and grid-connected electric pumping systems are usually designed to pump a large quantity of water over a short time period. Solar pumps pump the water more slowly but over a longer time period. This needs to be taken into account when selecting/designing a water supply system using solar pumping.

Solar water pumping can also be used in water treatment plants, for swimming pools, and in many other situations.