At the end of a letter published in the Cape Times on August 18, 2005, Liz McDaid of Earthlife Africa stated the following:
Moreover the installation of 88 000 solar water heaters on residential properties at a cost of R300 million would offset the energy generated by one PBMR (approximately 132 Mw output).
I did the math and did some quick searching – she correctly calculated her numbers given that solar water heaters are commonly rated at about 1.4-1.7 kilowatts peak power.
With her statement, however, she put herself firmly into the camp of alternative energy enthusiasts that obfuscate the issue by comparing the peak power for a weather dependent solar collector with the power capacity of a nuclear power plant that can operate almost 24 x 7 x 365.
One of the real success stories about nuclear power plants during the past 20 years is a steady improvement in their capacity factors – which is defined as the percent of power that they produce for an entire year compared to the total amount that they could produce by running at their nameplate capacity for every minute of every hour of the year.
Last year, the AVERAGE capacity factor for US nuclear power plants, for example, was about 90%. Obviously, there were some that did even better and some that did not do quite as well.
The very best solar installations in the world, in the best locations with the lowest cloud cover nearest the equator achieve capacity factors of less than 33%. As anyone who has ever been outside can attest, the sun sets every day and it is not as powerful at any time of day outside of the peak hours when it is directly overhead, even if you orient yourself to directly point to it. Clouds and rain also reduce its power, or is that statement too obvious to make? Panels also get dirty; if they are not cleaned their power can be reduced by leaves, mineral residue, bird poop, and other grime. In general, solar collectors have a capacity factor that is less than 25% and their power goes down with age.
Therefore it would really take about 316,800 solar water heaters to replace the power output of a single PBMR. If Eskom plans to build 25 of them in the initial order, that would mean that they see a need for the equivalent of almost 8 Million solar water heaters. I am not sure there are that many roofs in all of South Africa. Once all of the roofs are covered, however, you still have the problem that not all power use is in the form of low grade heat. Then what?