Pumps are critical to irrigation and communal water supply systems in rural economies. However, in many parts of the world, plugging into a reliable local power grid is not always an option. Nearly one-fifth of the world's population—1.6 billion people—lives without access to electricity. According to the U.N., agriculture accounts for 70 percent of global freshwater withdrawals—a harsh reality when considering the amount and consistency of power needed to obtain this water.
In rural areas of countries such as India, Pakistan, South Africa, Bangladesh and Yemen, continuous access to the electric grid is restricted. Most of the electricity is produced with diesel fuel. These diesel generators cause noise, environmental pollution and are costly to operate—especially as water demand rises during the growing season and fuel prices spike.
Solar Versus Diesel
Solar pumping systems are a practical solution to water scarcity in these communities. In addition to irrigation, solar pumping systems are used in community water supply, fish farming and agriculture, forestry, and wastewater treatment engineering. The systems are also becoming more popular for use in municipal engineering, city parks, tourist sites, resorts, and even landscapes and fountains in residential areas.
Solar pumping delivers several benefits over diesel:
- Better return on investment
- Low maintenance
- No periodic tariff increases
- No dependency on often unreliable grid power
- No environmental pollution
- Carbon credits savings
One solar pumping solution combines drive technology with solar panels and a maximum power point tracking system (MPPT). The MPPT controls the pump as a function of solar radiation. Rural pump operators, such as farmers, can benefit from the maximum amount of pump output during the day. The solar pump drive is independent from the grid and produces no pollution or noise.
The complete system consists of four components: photovoltaic (PV) cell, drive, motor and pump. The PV cell links to direct current (DC) connectors on the solar pump drive. The drive is connected to the motor that runs the pump.
The wide power and voltage range enables operators to use solar pump drives for a longer time. Larger applications, such as high-power pumps in agriculture, water supply and desalination, can depend on the drives' consistent performance.
Challenges & Benefits
Efficiency is the greatest challenge when designing a solar pumping system. The drive has to be so efficient that it yields enough energy to start the pump's motor and keep it running. This includes starting at sunrise or during cloudy days.
MPPT provides uninterrupted flow, even during drastic changes in radiation. When equipment is installed at remote sites—where maintenance is infrequent—the tracking system provides remote monitoring that eliminate the need for site visits.
The drive's fault resets and other features are all automatic. The drive automatically shuts down to prevent equipment damage if the pump runs dry. Sensorless flow measurement gives a direct indication of performance, allowing the end user to measure system performance on flow rather than electrical parameters.
The automatic start-and-stop functionality ensures optimal use of the equipment, providing long life for the pump and motor. When equipped with a changeover switch, the drive could operate off the grid—for example, at night or when not enough solar power is available to reach maximum flow.
Thousands of solar pump drives have been installed in India, where farmers in remote areas have increased their yields. Some Indian states fund as much as 86 percent of the cost of solar pumps as a long-term investment in the country's agricultural output. Markets in Asia, South America, Africa and the Middle East are experiencing growing demand for solar drive technology.
About 6 percent of cultivated land in sub-Saharan African is equipped for irrigation. Many of these countries have already started to use solar pumps to secure a dependable water supply for clean drinking water. Even in countries that do not subsidize renewables, several finance alternatives—including rental programs, cooperatives with shared ownership and micro-loans—are making solar water pumps economical for smaller off-grid farms and communities.
With the world's thirst for water and energy continuing to rise dramatically, solar pumping systems are both a short-term and long-term solution. Innovations in drive reliability and compatibility with renewable energy sources will advance access to drinking and irrigation water around the world.