Additional info from The Climate Reality Project
When people say renewable energy isn’t reliable, they usually mean it can’t generate continuous, round-the-clock electricity, or “baseload power." And for some sources of clean energy, that's true, as far as it goes. Wind turbines only spin when the wind is blowing, and solar panels generate electricity when the sun is shining. But does that mean wind and solar aren't clean, dependable and efficient ways to supply our energy needs? Not so fast.
It’s important to remember that electricity systems operate as grids — networks of transmission lines that draw power from several sources across a region and then redistribute that power. In other words, there’s no telling whether the electricity powering your house at any given moment is coming from a coal plant in Missouri or a wind farm in Minnesota.
Electricity grids are designed to handle variability in both demand and supply (PDF) because there is no such thing as a “perfectly reliable” form of energy. Even coal plants are susceptible to interruption; so when one power plant slows production or shuts down, another power plant picks up the slack. This means the lights don’t go out if a wind turbine stops spinning or a solar panel goes dark. And around the world, clean sources of energy like solar and wind are already being integrated into existing power grids. Take the American Midwest, for example, where 12 states rely on a system that has seen a 10-fold increase in wind energy between 2007 and 2011.
The idea of relying on large, centralized grids is also considered a little outdated. In parts of the world where grids have yet to be built or where they would be too expensive to construct, the concept of decentralized power systems is becoming increasingly popular. This means that if a certain region has lots of sunlight, it can generate solar energy to meet its local energy demand through a mini-grid. Similarly, areas with high wind power potential can harness the wind for their own local or regional requirements and not depend on expensive energy sent from far away. In some places, programs that support decentralized energy generation also help local producers make money by selling surplus power back to local or regional grids (PDF).
In addition to these trends, innovation in smart grids and storage technology is helping make renewable energy more reliable all the time. Smart grids can forecast the availability of renewable energy and adapt to changing power production levels, as demonstrated successfully (PDF) by the Electric Reliability Council of Texas, the biggest grid operator in the state. And energy storage projects — which can be used to store electricity for use when a power plant is offline — are starting to change the way we think of the availability of wind and solar power. Examples include the Advanced Research Projects Agency – Energy (ARPA-E) Grid-scale Rampable Intermittent Dispatchable Storage (GRIDS) project and projects capable of storing enough power to light 120,000 homes in China.
In summary, adding more diversity to the electric grid by adding more renewable sources actually helps strengthen the ability of the grid to supply power at all times. As more renewable energy is added to the energy mix, it gives us more flexibility and helps bring power to areas that traditional grids may not reach.