The reliability of an energy source is an important economic factor. Since large sums of electricity cannot be stored at a time, energy supply must meet energy demand in real time. This means that when the most electricity is being used, the most electricity must be simultaneously created, and vice-versa.
This creates an interesting and constantly changing problem facing energy companies. They not only need to predict electrical output throughout the year, but also throughout the day. After predicting the energy needed, they will need to actually produce it. If their prediction is wrong or they are unable to create the energy needed, ratepayers could experience a shortage or the energy company could waste a lot of money via wasted electricity.
Since this is the case, extensive research has gone into electricity usage over time. Looking at a figure provided by the U.S. Energy Information Administration, we can see that electricity usage on October 22, 2010 in New England peaked at 8 in the morning, called the morning ramp, and 6 to 7 PM, which is the peak demand time. This data follows a regular pattern of electrical use. High use when people get up in the morning, and high use right when they get home from work. These are times when the most electrical supply is needed.
This kind of data is also collected on a month to month basis. As seen in the figure below provided by the U.S. Energy Information Administration, electrical use goes in cycles with low use in the springs and falls and high use in the winters and summers. This is generally due to the use of heaters and air conditioners during these months.
With this, the reliability of energy sources must be considered. Nuclear, natural gas, and coal are all time independent. You can always burn coal or natural gas, and you can always run nuclear reactors no matter the time of day or time of year. For renewables like wind and solar, this is not the case. The wind doesn’t always blow and the sun doesn’t always shine.
For solar, there are many parts in the country, including Colorado, in which the sun doesn’t shine during peak energy usage. At 7 and 8 AM in Colorado in the winter time, the sun has hardly risen. By 5 PM, the sun has completely set in the winter thus completely missing the peak hour of usage. Furthermore, what if we experience large cloud cover or storms during times of high energy demands? Surely, there will be a shortage.
For wind, the story is similar. Luckily, the wind isn’t as variable upon seasons as the sun is, thus giving wind more chances of possible electrical generation time, but definitely not guaranteed time. There is no way to guarantee a satisfactory amount of wind will be blowing to ensure it will meet energy demands, thus making it unreliable.
Due to how unreliable renewable energy is, many countries, like Germany, are paying to keep coal generators in reserve in case the wind isn’t blowing or the sun isn’t shining. In the case of Germany, the government is paying billions of dollars to keep inactive coal generators in reserve. However, not only is it expensive to keep up the maintenance of these inactive coal generators, it is also expensive to flip these generators on and off (Porter).
A similar story occurred in South Australia. South Australia became heavily dependent on wind energy, though due to its unreliability, prices were unstable and surged frequently. The surges placed prices as high as $14,000 per megawatt-hour, frequently surged above $1,000 per megawatt-hour, and averaged at about $360 per megawatt-hour. The electrical prices seen in Victoria, Queensland, and New South Whales are around $50-$60 per megawatt-hour. Due to the surging prices, the South Australian government is begging and incentivizing gas-powered stations to begin operation again as reserve.