• Understanding renewables
    October 01,2013
     

    @Body Ragged Right:The issue of renewable energy in Vermont is a really hot topic that elicits a lot of emotion and advocacy on both sides. These exchanges frequently include a lot of bias, incomplete or very selective facts, and often a great deal of difficulty in having a meaningful and factual discussion that might result in a compromise in investment, trade-offs and implementation.

    @Body Ragged Right:This is not because the people involved are as dysfunctional or unwilling to compromise as our Congress — that would be an insult I would never say about a fellow Vermonter. Rather, it is most often simply that the discussion is between people with a lot of technical knowledge about electrical energy production and distribution and your average citizen who is more concerned about safety, aesthetics, cost and the environment. Without a common language or understanding, there can be no meaningful discussion that might lead to a solution or compromise.

    Two aspects of electricity that are most often misunderstood are the concept of the electrical grid and the amount of energy involved. First, let’s understand what we mean when we talk about “the grid.”

    Imagine that the electrical grid is like a very large shallow pan. On the supply side there is a large pump (generators) with tubes feeding water into the pan. This shallow pan fills up very quickly, and the water flows out through many smaller tubes on the demand side — the water (electricity) used by the consumer and businesses.

    The pan is much too shallow to use it for any storage, so at any given instant the supply pump in-flow has to exactly equal demand or use outflow. If the supply side pumps more than the demand side is using, then the grid simply overflows and some electricity is shunted to ground and is wasted. If the user or demand side needs more than the supply input, then someone doesn’t get any electricity (blackout) or a lot of people get less than they need (brownout).

    This is the way the electrical grid works. The large shallow pan represents the network of wires running from the power generation plant to the back of your radio or refrigerator. With no storage, the grid supply side must always equal the demand side. The problem is that the use is constantly changing — often in predictable cycles but frequently it can spike or drop unexpectedly.

    Now imagine that there are dozens of these large shallow pans on a very large table and the sides of the pans are touching each other. Each pan represents a local grid with local suppliers and users. When one pan has a greater demand than supply, it can temporarily tap into a pan next to it that may have a temporary excess. The generators that provide the supply are slow to respond to changes in demand, but by sharing their output across several grids or by shunting some excess to ground, the grid is kept in balance in real time by a very sophisticated network of control centers.

    In this example, you can easily see that if either side (supply or demand) varies in its input or withdrawal from the grid, it presents a problem. Either excess electricity is wasted or the user gets cut off. For example, in 2012, the Sheffield wind farm wasted about 20 percent of its annual power production because it was producing more than was needed at the time and the base load generators could not be adjusted rapidly enough to accommodate the intermittent surges. This is very common with wind power because it can vary from hour to hour.

    Without energy storage on the grid, photovoltaic solar power presents similar problems.

    For example, PV provides the most electricity from 10 a.m. to 2 p.m. on sunny days, little on cloudy days, little at dawn and dusk, and none at night. Photovoltaic output can increase and fall rapidly during cloudy weather, making it difficult to maintain balance on a grid. Additional generating capacity, usually gas-fired turbines, are kept in “spinning mode” or at partial load, which is inefficient and produces more carbon dioxide per kilowatt-hour. This is partly why photovoltaic solar is among the highest in capital cost per installed kilowatt and the lowest in power production and carbon dioxide reduction per dollar invested.

    Photovoltaic solar systems produce a very small quantity of variable, intermittent and expensive power and avoid the emission of a minuscule quantity of carbon dioxide per installed megawatt.

    One kilowatt is 1,000 watts, or about 1.34 horsepower. A 1,000-watt heater, running for one hour, consumes one kilowatt-hour. The kilowatt-hour unit is what we are billed for and represents an average over each hour of use. For instance, an oven using 3,000 watts for 30 minutes uses 1.5 kilowatt-hour of electricity.

    The total electrical energy used in the U.S. is sometimes hard to grasp. In 2008, the U.S. consumed about 4.14 trillion kilowatt-hours. Who can relate to that? This was produced by more than 18,500 generators in 6,600 U.S. power plants.

    Using renewables, it would take about 1,259 wind generators or about 240 square miles of solar panels to produce this much energy. This assumes wind or solar 100 percent of the time. Of course, on average, these renewables create zero power 60 percent of the time, so they are not really viable replacements.

    In part two, I’ll show you some surprising aspects of the costs of renewables and will closely examine the German model.



    Tom Watkins lives in Montpelier. He can be reached at TomW@21VT.US.

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