This article is a continuation of our series about various topics in renewable energy. Pumped hydro storage entails pumping water to an elevated reservoir when excess or less expensive electricity is available (i.e., low demand times such as late night or early morning). Water is released to flow back down through a turbine generator when the electric power is needed. Electrical energy is both difficult and expensive to store, yet energy storage is extremely important, particularly for intermittent renewable energy. Pumped hydro is a mature technology and may well be, depending on topography, the least cost alternative for large scale energy storage.While hydro power is both stable and constant, the chief problem with the other renewable energy sources is that they are only available intermittently because the sun can supply energy for a limited number of hours per day (solar energy) and the wind doesn’t always blow (wind energy).The storage challenge of renewable energy therefore becomes of paramount importance. This is exactly why pumped hydro electric power has the edge, as storage systems have been in place and in use for many years. Water can simply be pumped into reservoirs during off peak hours and can be released to produce power used when demand for electricity is needed.Hydro power is the electricity generated from the gravitational force of water. It has its long history of usage. The first plants were built in 1890 in Italy and Switzerland. For the first half of the 20^th century, many large hydro power plants were built, mostly in the USA, paving the way for big developments of this the largest form of renewable energy in the world.

• It produces 21% of the renewable energy and supplies over 1/7 of the earth’s population with power.
• It is a very positive energy source as it produces few fossil fuels or what is called green house gases.
• It is very cost effective. No need for fuel and no need for fossil fuel fluctuations. No need for fossil fuels means they don’t create CO2 directly. Note: traditional fuel is often used to provide the power for pumper storage solutions
• Hydro electricity produces the least of carbon dioxide when production, construction and running come into consideration
• The hydro power plants can last long periods and are normally automated.
• The dams for hydro power cost little to build. Return on investment (ROI) can be realized in a few years.
• Reservoirs can also be used for fishing, sports and irrigation. They can be constructed in areas where flooding is prone.

A hydro electric power system has its disadvantages

• It requires large areas of land and submerges a once dry area in water. This affects the natural surroundings and the local environment.
• It can dissolve the oxygen content of water creating damage to the fishes. People living nearby would have to relocate because of this.
• Reservoirs often become full of sediments because the water carries silt and deposits from the area, causing more problems to the dam.

Hydro electric power has its advantages and disadvantages. However, it is still one of the most important sources of power in our world today.