Many parts of the Texas experienced rolling blackouts today, coinciding with unusually cold temperatures across many parts of the state.

Millions of customers statewide appear to have been affected. Here are the facts as they are currently understood:

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• Wind energy played a major role in keeping the blackouts from becoming more severe. Between 5 and 7 A.M. this morning (the peak of the electricity shortage) wind was providing between 3,500 and 4,000 MW, roughly the amount it had been forecast and scheduled to provide. That is about 7% of the state’s total electricity demand at that time, or enough for about 3 million average homes.

• Cold and icy conditions caused unexpected equipment failures at power plants, taking up to 50 fossil-fired power plants totaling 7,000 MW of capacity offline.

• The cold temperatures caused electric heating demand to exceed the demand expected for this time of year. Many fossil and nuclear power plants take planned outages during non-summer months for maintenance, since electric demand is usually lower during these periods than in the summer.

• The cold temperatures led to very high demand for natural gas for heating purposes, which may have strained the ability of the natural gas pipeline and distribution system to meet both these heating needs and the need to supply natural gas power plants (Texas obtains about half of its electricity by burning natural gas, and gas power plants account for about 70% of the state’s generating capacity).

“While we are still learning about what happened today, this weather event clearly demonstrates the importance of developing and maintaining a diverse energy portfolio that is not overly dependent on any one energy source,” said Michael Goggin, Manager of Transmission Policy, American Wind Energy Association. “This experience shows just how valuable a clean, affordable and homegrown energy source like wind can be in contributing to a reliable electric system.”