On August 1, 2011, a feral heat wave grasped Texas by its drought-parched throat. Temperatures remained over 100 degrees for 40 days -- dozens of people died. Air conditioners all over the state struggled valiantly to cool buildings -- much of their effort leaked out into the hot Texas sky. Then, one by one, twenty power plants -- primarily natural gas peaker plants -- winked out because of the temperature. The cost for a KWH of electricity during the afternoon peak reached $5000. While inland wind was also low during the heat wave, coastal breezes kicked up. Wind power barely kept the grid operator from having to black out neighborhoods. Grid operators conceded that equipment failures in such heat were to be expected. The irony here is that the power plants which failed -- inefficient peakers with a high cost per KWH -- are justified on the basis that they will be required only occasionally, during extreme weather -- but apparently are not designed to be available in those very circumstances!

Remember this episode the next time you hear -- or read -- that we can't progress to 100 percent clean energy because the centralized, fossil grid is more "reliable." Our current coal and natural gas reliant grid is anything but reliable. The Galvin Electricity Intiative led by former Motorola CEO Bob Galvin and former Edison Electric CTO Kurt Yeager, describes the grid as:

"Aging, unreliable, inefficient, insecure and incompatible with the needs of a digital economy.... each day roughly 500,000 Americans spend at least two hours without electricity. Brownouts, power spikes and even minor blips can bring high-tech production lines to a halt. Such impurities and failures cost business and consumers an estimated $150 billion a year. Moreover, the system is vulnerable to terrorist attack, major storms and even moderately turbulent weather."

Heat waves are not the only source of fossil power vulnerability. Only six months before the 2011 heat wave, Texas had lost 80 power plants to an ice-storm. During last year's three-day freezing U.S. polar vortex, with temperatures 20-30 degrees lower than normal, demand soared across the Midwest and East. Simultaneously, more than 35,000 MW of electricity capacity failed; about half was due to inadequate fuel supply, either frozen coal piles or natural gas supply shortfalls; the other half was due to equipment freezing in the severe cold. (Significant brown-outs were avoided only because of demand response management -- clean power to the reliability rescue again.)

Lots of rain doesn't help either. This July Serbia lost 45 percent of its coal production due to flooded mines. From 2010-2013 floods routinely slashed coal production in Queensland, Australia, driving up global coal prices dramatically and forcing importers like India to reduce generation and cut off consumers.

Each fossil fuel power plant sits at the end of a long supply chain; these often fail. Even the utility industry is making the argument that its natural gas powered fleet does not have access to sufficiently reliable gas pipeline capacity. A quarter of U.S. coal-fired power plants this winter are operating with less than half their necessary reserve supply of coal, making the entire national grid vulnerable in the event of a severe weather event. In 2013 Pakistan experienced routine 20 to 22-hour blackouts and load shedding because its gas-fired power plants could not access enough fuel.

This August 55,000 MW of generating capacity in India were shut down due to coal supply shortage or breakdowns. Yet the U.S., Pakistan and India are among the countries with the world's largest coal reserves.

Indeed, so unreliable is the centralized, fossil dependent grid that both its operators and customers have to overbuild generating capacity to deal with these failures. Utility systems are routinely expected to have 15 percent surplus capacity above expected maximum load to deal with outages, and often maintain over 30 percent. A full 20 percent of the total electric load in the U.S. is backed up with on-site generators, mostly diesel, because facilities like hospitals, prisons, data centers, airports, and research laboratories cannot tolerate the routine power outages that they experience from grid power.

So why (Big Carbon propaganda aside) do we keep reading about unreliability as the problem with a 100-percent clean power future? The media confuses, (and is encouraged to confuse) intermittency with unreliability. A full moon is intermittent -- and so are eruptions of Old Faithful. But we would not describe either of them as "unreliable."

Wind and solar are similarly intermittent but reliable. (Geothermal, small hydro and efficiency are neither intermittent nor unreliable.) The number of hours a year they generate at peak capacity is smaller than for a typical natural gas, coal, or nuclear power plant -- if that conventional plant has fuel and doesn't break down. But that doesn't mean we don't know how many electrons renewables will yield each year, nor that those electrons necessarily cost more -- after all, the fuel is free. Increasingly renewables have raced "grid parity" and now cost less than fossils is many markets.

And clean power is less vulnerable to equipment failures, extreme weather or disruption of fuel supply chains than coal, natural gas or nuclear. Indeed, after really extreme weather events, like Hurricane Sandy or Typhoon Hudhud, the only electric power that was available, sometimes for weeks, were pockets of renewable energy.

And electric demand is intermittent as well -- with solar generating peak power at exactly the moment when air conditioning load, or irrigation pumping is the highest -- so that in California solar power has eliminated the need for summer afternoon peaker plants. In Africa and India, many earnest discussions of how "unreliable" solar power is take place in grid-powered meeting rooms where, during the meeting itself, power is shifted from a grid which has failed to local diesel generations. But outside those rooms solar panels on poor people's houses continue to operate.

Reliable, but intermittent generation, like wind and solar, requires different load-balancing strategies than coal power at risk from fuel disruptions, or nuclear which can break down for months or years at a time. Clean power needs short-term storage, to deal with variations in wind and solar generation from clouds or gusts, and a better connected set of wires so that as wind in West Texas dies down consumers simply draw on coastal winds which are kicking up.

But overall the reliability problems with a clean energy future will be smaller than if we keep trying to drag out our dependence on fossil fuels. The chart below -- which is based on experience globally -- suggests why. There are simply a lot more ways that a centralized, fossil fuel grid can let consumers down than there are with a clean energy, heavily distributed grid.

A veteran leader in the environmental movement, Carl Pope is the former executive director and chairman of the Sierra Club. He's now the principal advisor at Inside Straight Strategies, looking for the underlying economics that link sustainability and economic development. He has served on the Boards of the California League of Conservation Voters, Public Voice, National Clean Air Coalition, California Common Cause, Public Interest Economics Inc, and Zero Population Growth. Mr. Pope is also the author of three books: Sahib, An American Misadventure in India; Hazardous Waste In American and co-author along with Paul Rauber Strategic Ignorance: Why the Bush Administration Is Recklessly Destroying a Century of Environmental Progress, which the New York Review of Books called "a splendidly fierce book."