Additional issues at Ivanpah: melting the salt and high winds

In my learning about energy, I’ve picked up on a few more problems with concentrated solar power, which is the design of the wing-toasting facility at Ivanpah.

Keeping the molten salt melted

All those mirrors focus the sun on the top of the tower in order to superheat a liquid, which is then circulated to turbines, which spin, thus generating electricity. The liquid returns to the top of the tower for another superheating.

The liquid?

Molten salt.

The melting temperature of molten salt is in the range of 225° C or perhaps 260° C. Of course my accounting brain doesn’t think Celsius, so I translated those numbers, coming up with something in the range of 437° F or 500° F. Let’s just call that 400°.

My accounting brain can tell that is really hot.

Another thing I have learned is that once the sun goes down the molten salt is allowed to freeze. It would take a lot of energy to keep that much salt over 400 so that it stayed liquid. That means in the morning it is either sludge or solid and needs to be heated above the melting point so it will work.

That would explain to me how it was that the mirrors started a fire on the tower: the heat from the mirrors was being used to melt the salt in the pipes.

That also explains why the Ivanpah facility uses so much natural gas. It is needed to melt the salts every morning. See previous article on the natural gas consumption here.

How much natural gas? Enough to generate 46,000 metric tons of CO2 annually, or the equivalent of the Frito Lay plant in Bakersfield. (Yum, pass the chips!)

Back in February 2016, 18% of the output from Ivanpah was offset by the natural gas consumed in order for the plant to get ready in the mornings.

Danger from wind

Wind in the desert blows dust and dirt around. Some of the dirt settles on each of those hundreds of thousands of mirrors. Keep in mind how dirty your car gets if you leave it sitting outside. Same thing happens with the mirrors, only your car is not sitting out in the middle of the desert. Imagine how dirty our car would get sitting in the desert 24/7.

So, to offset the degradation in performance from having the mirrors coated with dirt, they have to be washed. They are turned horizontally facing down and a crew goes by and washes each of the garage-door-sized mirrors. Washing 347,000 mirrors. With water. In the desert.

(Wonder what efficiency degradation there is after several years of those mirrors getting hit by wind-born dirt? Hmm. Topic for another day.)

Oh, about that wind that results in the mirrors being covered by dirt… Ever hold your hand outside the window while riding in a car, changing the angle of your hand, feeling the wind resistance on your palm? Ever fly a kite? The resistance on your hand and the ability to keep the kite in the air is due to wind generating lift against a surface.

Same thing happens with those mirrors. When the wind kicks into high gear it creates a danger of tearing a mirror off the mounting and launching it airborne doing a rather unpleasant kite imitation.

I have learned that when the wind is too high the mirrors have to be turned to the horizontal position (remember the wash setting just discussed?) to prevent damage. Oh, I think that also means that when there is high winds and lots of mirrors are turned horizontal, the diesel generators will have to kick in again, burning lots of earth-killing fossil fuels, just to keep the molten salt molten.

So, Ivanpah generates electricity during the day.

Only after the sun gets high enough in the sky.

Except for rainy days.

Except when there are passing clouds.

And except when the wind is blowing too strong.

Yeah, I know these issues were baked into the design and everyone else has probably know about those features for a long time. Yeah, I’m slow on the uptake and have know that a long time. But I am slowly catching on. That’s why I blog.