"The wind doesn't always blow" and the "sun doesn't always shine" are simplistic statements often used when referring to the Wind and Solar contribution to the world's future energy needs. Although there is undeniable truth in the statements, there are a number of energy storage methods that can convert these sources into on-demand power. One example is evident at the homeowner level, where solar Photovoltaic systems can convert the sun's energy into electrical current. This current can be used directly for lighting, appliances or other uses, or it can be used to charge batteries. At night, electrical needs can be met by using the power of the batteries. This homeowner example is a small scale application of storage technology. There are a number of technologies that can be used to store the energy from large scale intermittent power such as a wind farm or a very large Photovoltaic installation.

In theory, wind energy alone, can meet and exceed the energy needs of the entire world. According to a 2001 study done at Utrecht University in the Netherlands, "The global technical potential of wind electricity is estimated to be 96 PWh/yr: about 6 times the present (2001) world electricity consumption..."(1). It should be pointed out that this is a theoretical study. Utrecht does qualify this statement with financial and other considerations. It also mentions that with the 2001 technology, this power base would require enough wind turbines to cover all of China.

According to the US Department of Energy, "of the theoretical wind resource in the United States, only 4% is recoverable, but this is still 20% more power than the entire US energy consumption, for all forms of energy(2)."

Wind farms are built in areas where the wind blows most of the time. According to the American Wind Energy Association (AWEA), Wind turbines generate electricity 65-80% of the time. They generate at full capacity 10% of the time, and on average, a typical plant will generate 30-35% of its rated capacity(3). Opponents of wind energy usually argue that the sporadic nature of wind, requires backup power. For example, Poweronline states, "Because of this limitation on wind energy, other generating units, powered by traditional resources of energy-coal, natural gas, oil, nuclear energy or hydropower-must be immediately available to back stop the wind units and generate needed electricity whenever the windmills are not producing."(4) This statement ignores the fact that wind energy can be stored through a number of technologies, including batteries, flywheels, magnetic, compressed Air, supercapacitors, and pumped hydropower.

Currently, the simplest and most promising storage technology is pumped hydropower, or water pumping and storage. Using this technology, water is pumped uphill, and stored in a reservoir, to later turn turbines, when the power is needed. This process has about an 80% efficiency rate, which is higher than other storage techniques. This is not a new technology. Today, 90 GigaWatts of electricity, or 3% of our global generation uses pumped water storage (5).

The other positive quality of this storage technique is that the end result is hydroelectric power, the most efficient power generation method on the planet. Hydroelectric power costs in the US, including pumped water storage systems, are less than half the cost of all other sources. Unlike other conventional sources, which may have fuel loading or warmup times, hydroelectric power is available immediately on demand(6).

The largest drawback to water storage technology is the large water storage requirements. Lakes or reservoirs must be positioned at least 50 meters below a damn.(7) This is not a monumental obstacle. Mountainous and hilly communities throughout the world already have massive water management systems, with series of dams and reservoirs.

In the US alone, there are 80,000 dams, but only 3% have power-generating hydro plants. According to the Latent Semantec Analysis at the University of Colorado, "The Federal Energy Regulatory Commission estimates 60 thousand megawatts of additional generating capacity could be developed in the United States."(8) This study just focused on potential sources of hydroelectric power, without the renewables and water pumping technology.

Most of the pumped water storage sites in the world use power off the grid to operate the pumps during non-peak times, to replenish the higher reservoir. Wind energy can fit into this scheme by providing power to the grid during high-demand times to help with the peak load, and to supplement the energy for pumping uphill, during non-peak times. The Alta Mesa pumped storage facility near Palm Springs, CA actually uses wind produced electricity to accomplish the pumping to the upper reservoir. "By using the abundant power produced by the wind turbines during non-peak hours to power the pumps and replenish the upper reservoirs, valuable and lucrative energy can essentially be stored until the high-demand hours." (9)

A case study of wind and water storage in Hawaii was conducted by the Electrical Power Research Institure (EPRI). The results of the study suggest that this is a feasible alternative to traditional power sources - "Based on the study's survey of the island's wind and water resources, the best sites for the use of existing water resources for pumped-storage systems occur on the north end where water resources are plentiful and where there are major wind farm developments, or proposed future developments." The study continues by evaluating some of the cost considerations. Two of the major costs were the addition of a transmission line to connect to the grid, and the possible construction or retrofitting of additional water storage. (10) This study demonstrates some of the infrastructure and cost-associated problems of pumped water storage. With today's conventionally generated energy costs, often the projects are not feasible.

As the cost of conventional sources of electrical generation continues to rise, wind power will continue to experience growth. As the costs rise even more, water storage and other storage technologies will be utilized more and more. According to the National Renewable Energy Laboratory, "They [DOE researchers] are also conducting research to develop low power hydropower resources, optimize project operations, and combine hydropower with other renewable technologies such as wind power to provide a stable supply of electricity to our nation's grid." (11)

(1) Utrecht University study

(2) Endless Energy Corporation

(3) American Wind Energy Association (AWEA), "Wind Power Myths vs Facts"

(4) Power Online, "Wisconsin's Wind Plans More of a Whimper than a Whirl",

(5) Pumped Water Storage, Wikipedia

(6) Hydroelectric Power, University of South Dakota

(7) Pumped Water Storage, Minnesotans for Sustainability

(8) Hydropower, University of Colorado, "State the Essence"

(9) Renewable Energy World, a Tenderland Power publication, May 1999 issue,

(10) Hydroelectric Assessment Study of Existing and Planned Water Systems on the Big Island, Electrical Power Research Institute, May 2005

(11) Hydropower Tomorrow, National Renewable Energy Laboratory,