It's about wind power. Here is the context : "Few topics generate more controversy than capacity credits for wind plant. The capacity credit of any power plant may be defined as a measure of the ability of the plant to contribute to the peak demands of a power system. Capacity credit is often defined as the ratio (firm power capability)/(rated output). As thermal plant is not 100 per cent reliable, values for all plant are less than unity. To a first order, 1,000 MW of nuclear plant corresponds to about 850 MW of firm power and hence has a capacity credit of 0.85; coal plant has a capacity credit of about 0.75. These figures are, roughly, the statistical probability of the plant being available at times of peak demand."
What is meant by this sentence : "values for all plant are less than unity"? What are these "values"? I guess the "values" are the results of this "ratio (firm power capability)/(rated output)", aren't they?
Many thanks for your help.
INCIDENTALLY, what is meant by "To a first order"?