I’ve always been uncomfortable when I read or hear media reports of the proud completion of yet another windmill far where they seem to always say something like “Will meet the energy needs of more than 60,000 homes” or something like that. How they come up with that number is never explained and I suspect what they do is take the sum of the name-plate power rating capacity for each machine, multiply by some “attractive” load factor (say 30 or 40% where in fact the number is often closer to 20% or below) and call it a day.
I have a proposal for a different and probably more informative way.
Developers of windmill fields surely do short-interval (continuous?) long-duration (a year or two?) time-series site survey measurements of the patterns of winds (speed, direction, vertical profile) in the locations where they plan to plant a machine. It is from this wind from which energy is transferred into useful power to be dispatched to the customer. Using that data with some science and engineering, and the Betz Limit one can surely compute a probability distribution profile of the expected power output of that wind stream passing the windmill. Regardless of the name plate capacity of the machine (and how many near-by homes there are), this probability distribution shows how much power can be expected to come out. Certainly the size of the machine and other machine parameters are part of the output energy computation, but the basic input is how much wind does and will pass through the machine. And remember, no wind–no power. Too much wind–no power.
Then, agree (government can do this sort of thing easily) the probability percentile to pick off the cumulative distribution curve as the “standard” rating for that machine at that location and the time over which power/energy is harvested. I propose we use 95%, which means the windmill operator can say “We have 95% probability that over the course of a year this machine will create produce XX mega-watt-hours of electricity over the course of a year for our customers.” They can compute the confidence factor on that number, but there probably is no need to quote in media, but the investors surely should be informed.
With other methods of power generation, e.g. burning fuel (coal, gas, oil, nuclear, etc.) to produce power based on the thermodynamics capability of the machine it makes sense to quote the power capacity of the machine as the economic basis of how much sellable power will be produced. This is because the machine operators will, for sure, keep feeding the machine with a constant supply of fuel to ensure the machine produces what the customers demand and the investors expect. Whatever it takes, they will do it.
However, this approach to look at the machine to quote power production capability is misleading for renewable energy machines. Yes, serves the interests of those who want more of these machines, but what about the customers and the rest of society?
With renewable energy machines using solar, wind, tides, and waves … the operators are no longer in charge or nor have any responsibility to fuel the plant. We are at the mercy of Mother Nature.
Hence measure and predict Mother Nature.
Will it happen? Probably not. Or maybe they do it now. I don’t know. But if I had anything to do with it we would.