The Unquenchable Thirst for Electricity is One of the Driving Forces in the development and deployment of renewable energy technology. This technology also solves the quest for a clean energy source that will not be depleted. Most renewable energy comes to us directly or indirectly from the sun. Solar radiation absorbed by the Earth's atmosphere is dissipated in the form of wind, ocean currents and precipitation. It is a natural process that is constantly replenished, and the cost of the fuel is constant: zero.
Solar and wind technologies have come a long way. Bell Laboratories first developed solar cells in 1953. A watt of electricity cost on the order of US$300 from this early photovoltaic (PV) cell. Technology has improved drastically while costs have dropped significantly. We are now paying around $4 to $5 per watt from larger PV arrays. Wind has come a long way, too.
EARLY WIND MACHINES
Electricity was first generated from wind in 1888 in Cleveland, Ohio, U.S., with a 12-kW dc wind-turbine generator. Early machines were mostly simple fixed-speed squirrel-cage induction generators ranging from 20 kW to 350 kW. They covered a lot of real estate, consumed a great deal of reactive power (VARs) from the host utilities and tripped off-line very easily whenever the voltage dipped on the system. In short, these were unacceptable attributes as wind power transitioned from novelty to full-fledged power sources.
Wind technology progressed with variable-speed turbines and variable-pitch control systems for the blades. These features were combined with power electronics, which led to the double-fed asynchronous generator and the full-sized power converter.
The double-fed asynchronous generator design allowed for greater flexibility in controlling both the real and reactive power flow as a four-quadrant converter. It gave the turbine's electronics the ability to control the flow in the grid direction from the rotor, or from the grid in the direction to the rotor.
WIND INTERACTS WITH THE GRID
It wasn't long until regulatory bodies developed interconnection requirements for large wind generators. The Federal Energy Regulatory Commission issued Orders 661 and 661-A to address the issues of interconnecting wind farms. These orders define low-voltage ride-through and VAR support, issues that must be addressed if we are to see wind generation provide a more significant proportion of our energy mix.
Today, wind energy is being embraced globally and requires solutions. Wind generation accounted for 40% of all new power-generation installations in Europe for 2007 and 35% of new generation facilities in the United States for the same year. While the we spent the 1980s and 1990s installing 10 GW of wind-generation capacity globally, we have picked it up in the last decade, now surpassing 100 GW of installed capacity.
SOLAR HAS NOT BEEN LEFT IN THE DARK
Technology has not been standing still in the solar area either. Utilities around the world are putting the sun to work by adding large solar power plants to the grid. Homes and businesses have been installing PV panels on rooftops for years. PV panels are finding a place in utility-scale generating plants, too. As of November 2008, the largest PV plant was the Parque Fotovoltaico Olmedilla de Alarcon in Spain with a rating of 60 MW.
Pacific Gas & Electric (San Francisco, California, U.S.) entered into agreements to purchase solar power beginning in 2010. The first agreement is with Opti Solar, which is building the 550-MW Topaz Solar Farm in San Louis Obispo County, California, using proprietary thin-film PV panels. The second agreement is with SunPower, which is building the 250-MW High Plains Ranch II in the same area using high-efficiency solar panels that generate about 50% more power than conventional solar panels.
Southern California Edison (Rosemead, California) expects to install and commission about 50 MW of PV a year, reaching the 250 MW total in about five years at a cost of approximately $875 million, if the state regulators approve the program.
HOW MUCH IS TOO MUCH?
The penetration of wind and solar into the generation mix continues to increase. Around the world, the goal is to generate 20% or more of the total electricity from renewables. This raises concerns that systems with large percentages of wind generation will exhibit unacceptable frequency responses to grid disturbances. As an industry, we also must address ways to store our green electricity so that it will be available when needed.
Renewable sources will provide the opportunity to stretch our creative muscles. Instead of reacting tomorrow, let's take green matters into our own hands today.