[Kamilah Hauptmann]

Originally Posted by Kamilah Hauptmann

Solar Market Insight Report 2016 Year In Review | SEIA

Solar had a great year, coal looks dead as the Pharaohs as the costs of solar installation keeps dropping and output keeps improving.

So I asked back to the engineer who posted me that in the first place with this:

Originally Posted by Kamilah Hauptmann

SMBC is pretty good at laying out random difficulties in science reporting and though I don't doubt the rapid increase in capacity and drop in price of installation I was wondering if we could get some comment on this:



Saturday Morning Breakfast Cereal - Capacity

And he wrote back:

The number being referred to in the cartoon is "Capacity Factor", the ratio of average output to rated capacity in percent. It's not correct to think of this as "percent of the time the plant is running", because power plants are not light switches - either fully on or off. Customer demand varies by time of day and season, and therefore plants operate somewhere between fully on and shut down to meet that demand.

Rated capacity is universally used in electrical design, from things you plug in at home up to power plants, because invariably they are connected to wires which must have matching capacity, else you cause overloads. So a wind or solar farm is rated in terms of the best output it can supply to the grid, even though conditions often produce less than that.

Recent utility capacity factors are reported for utility-scale Fossil Fuel and Non-fossil energy sources. They are all over the place. They also vary by season, and operating cost. Fossil fuels have a fuel cost when operating, other sources have minimal or no fuel cost. Total annual & monthly output by type for all major sources, and details for renewables are also reported. These reports are part of the EIA Electric Power Monthly, which supplies more than you could possibly want to know on the subject.

The problem which every utility has to solve is meeting all customer demands minute to minute, at the lowest total cost, without overloading transmission lines, and with enough reserve capacity to meet unexpected problems. That's not as simple as "higher capacity factor is better".

For those interested.