I read a letter a gentleman wrote to “The Australian” where he calculated how many solar panels would be required to replace a 2,000 MW coal fired power station. He used 500W solar panels and concluded that the replacement number was 4 million. I thought I would see what the answer really is.

Rated capacity does not give any indication of the total energy produced over time. The critical parameter is the capacity factor, (CF) which indicates the percentage of time that the generator produces energy. A typical coal power plant has a CF of around 0.9 which means it will generate energy for 90% of the time. Solar has a CF of between 0.17 and 0.2 depending on whether the panels are fixed or have a tracking system that allows them to change angle as the sun angle changes over the seasons.

I am going to use 435W solar panels in this analysis as they are the highest rated panels I have found to be available. They have a service life of 25 years. Each panel will produce 0.76 MWh per year at a CF of 0.2.

The table below shows the comparisons. A 2,000 MW coal station with a CF of 0.9 will produce 15,768,000 MWh annually so the number of panels required to “replace” it is 20,689,655. If CF was ignored and there was just a “straight MW” replacement the number of panels would be 4,597,701 so it is always important to know whether someone is talking about power in MW or energy in MWh when they make statements about renewable energy projects.

It is not as straightforward as it seems, there are some factors here that make it look better than it really is.

First; the output is averaged over a year. Solar systems degrade to around 40% of maximum output in the depths of winter so relying on an average is dangerous. There will be over production in the summer months and under production in winter. The chart below comes from one of my posts that did not make the cut, titled “Why solar power is not worth a cracker”, and shows the month by month comparison between a conventional 1 MW generator that can run all the time and a 1 MW solar system. It shows that the rated MW is not a basis for comparing generating options.

Second, and probably most obvious, is that we have day and night every 24 hours so the solar system will provide energy for about half of the year and some other system needs to cope with the nights.

Third, when the daily variations are considered things get even worse. The chart below shows a “typical” January for a 1 MW system, with the x axis showing the day of the month and the y axis showing MWh produced each day.

Output varies from a high of 6.44 to a low of 2.23 and these changes can be sudden. There is a view that solar “works” when the sun shines however the output can fluctuate widely with cloud cover and this is one of the reasons why domestic “rooftop” solar causes so much grief when it is connected to the grid. Things might be going OK then some clouds cause the output to plummet.

The next chart shows the output for a bad July day, again for a 1 MW system.

The output varies from a high of 4.39 to a low of 0.45.

For some strange reason those who have control over the decisions made about “energy policy” seem to have absolutely no idea what they are talking about, extremely piss poor decisions are made and the consequences are dire.

In simpler times large coal fired power stations churned out reliable electricity year round and were built to last a long time. Renewables last about half the life of a coal fired station, are unreliable and cost us the earth. All this because some charlatans would have us believe that carbon dioxide has a “special property” that no other gas has, namely the ability to “trap heat” and then radiate it back towards us in defiance of the laws of thermodynamics.