This special interest group is for professionals to connect and discuss all types of carbon-free power alternatives, including nuclear, renewable, tidal and more.


Why do PWR have a tendency to produce less power as the as temperatures increase?

Ander Eguiluz Belar's picture
Marine Engineer, EHU

FInal year student. Woking on a ship nuclear propulsion document. 

  • Member since 2021
  • 5 items added with 1,139 views
  • Nov 11, 2021

There´s a white elephant in the room and no one is talking about it (its a spanish saying and I don´t know if fits in english), plenty of studios about nuclear reactors have this sentence: "PWR have a tendency to produce less power as the as temperatures increase". It appears in at least in ten "academic" studios (you can look for it in academic google and have a nice time), but I think that they add it cause it looks great. However, i haven´t found anyone that explains that fenomeno to me and I would like to add it to my studio, cause I don´t want to add some incomplete information.

So if anyone knows anything about it, I would appreciate it and i´ll change the info in wikipedia so more people could know it.


Your access to Member Features is limited.

It makes sense. Chemical energy, like electrical energy, produces (transforms) a percentage of heat (steam BTU per time or watts) known as heat loss. As temperature increases to reactor limits (or electrical facility limits) power efficiency decreases (electrically watts equal  I2R) due to heating restraints (electrical line & load facilities). Water for reactors (forced air, forced oil and heat sinks for electric and electronic equipment) are used for cooling to increase power efficiency -- heat loss is considered waste heat but can be used effectively in co-generation systems..

Ander, the output of PWRs is intentionally lowered in extremely hot weather. As water from external sources gets warmer, its ability to condense steam used to drive turbines is reduced, and there is a danger of the reactor overheating.
With older French reactors, which operated in "on" or "off" mode, it wasn't uncommon to have to shut them down completely. There was at least one occasion where a plant on the Rhone River had to have water trucked in, when water from the river was too warm to serve as coolant.

Jim Stack's picture
Jim Stack on Nov 13, 2021

In France they actually had to truck in cold water to keep their reduced power reactors from over heating. Most Nuclear are located next to water to use it for cooling. This water is many times on a fault line. Oh Oh. 


While in the summer when days are longer and hotter solar produces the most. Solar PV uses no water and produces no waste or pollution.

Bob Meinetz's picture
Bob Meinetz on Nov 15, 2021

"While in the summer when days are longer and hotter solar produces the most."


"It may seem counter-intuitive, but solar panel efficiency is affected negatively by temperature increases.  Photovoltaic modules are tested at a temperature of 25 degrees C (STC) – about 77 degrees F., and depending on their installed location, heat can reduce output efficiency by 10-25%.  As the temperature of the solar panel increases, its output current increases exponentially, while the voltage output is reduced linearly. In fact, the voltage reduction is so predictable, that it can be used to accurately measure temperature. "

"Solar PV uses no water and produces no waste or pollution."

Wrong again:

"Because of the particular nature of clean energy sources like solar and wind, you can’t simply add them to the grid in large volumes and think that’s the end of the story. Rather, because these sources of electricity generation are “intermittent” — solar fluctuates with weather and the daily cycle, wind fluctuates with the wind — there has to be some means of continuing to provide electricity even when they go dark. And the more renewables you have, the bigger this problem can be.

Now, a new study suggests that at least so far, solving that problem has ironically involved more fossil fuels — and more particularly, installing a large number of fast-ramping natural gas plants, which can fill in quickly whenever renewable generation slips.

'All other things equal, a 1% percent increase in the share of fast reacting fossil technologies is associated with a 0.88% percent increase in renewable generation capacity in the long term,' the study reports."

Turns out wind and solar have a secret friend: Natural gas

In other words: say we have a grid completely powered by natural gas plants, and it produces 100 GWh/day. Adding enough solar panels to generate .88% of its power mix (880 MWh) would require adding an additional 1,000 MWh of gas generation. Adding solar creates even more carbon emissions (1%) than adding none.


Tap Into The Experience of the Network

One of the great things about our industry is our willingness to share knowledge and experience.

The Energy Central Q&A platform allows you to easily tap into the experience of thousands of your colleagues in utilities.

When you need advice, have a tough problem or just need other viewpoints, post a question. Your question will go out to our network of industry professionals and experts. If it is sensitive, you can post anonymously.