Under what circumstances are concentrated solar power plants more feasible than conventional solar panels?

Question

Tell me about concentrated solar power plants. Under what circumstances are they more feasible than conventional solar panels? It seems to me, a layman, that there are way too many energy transfers for it to be a better solution (PV devices appear to capture that solar energy more "directly" or something). On the other hand, concentrated solar appears to be superior to other types of solar in terms of power density

Answer 1

Concentrating solar-thermal power is an entirely different way of producting solar power. There are two types of concentrating solar-thermal plants. One type has parabolic mirrors in a line. Then a pipeline with some oil for example runs at the focal line. The heat from sunshine warms up the oil. With thousands of parabolic mirrors, the oil is warmed up very hot. Then the heat of the sun can be used in a thermal engine that uses steam as the working fluid. You need some way of disposing of the waste heat at lower temperature. One possibility is running water, but in hot deserts water may not be available. Another possibility is a cooling tower but it consumes water too. There are also air cooled condensers that cool the steam without consuming any water.

Another possibility is flat mirrors that are all oriended so that they direct the sunshine to a single tower. Then the oil is heated in the tower.

So it's a traditional steam engine that works entirely like coal plants do. It shares the poor thermal efficiency of coal plants. However, solar panels too have a poor efficiency and if you take into account that, it doesn't look so bad anymore.

A benefit of concentrating solar thermal power is that heat is much easier and cheaper to store than electricity, in molten salt for example. If you build a concentrating solar thermal power plant in a hot desert that has about equal sunshine every day of the year, it's possible to store the heat for use during nighttime. Then you get 24/7 electricity without needing to invest in any batteries.

A drawback of concentrating solar thermal power is that it's already today more expensive than photovoltaic cells and lithium ion batteries. Then when you take into account that photovoltaic cell prices are exponentially decreasing, lithium ion battery prices are exponentially decreasing, and that new battery chemistries like iron-air are appearing, promising cheaper energy storage than lithium ion, you'll see why practically nobody builds concentrating solar thermal power plants anymore.

Another drawback, especially of the tower type installations, is that the sunlight intensity near the tower is very high so if a bird flies there, it'll be killed. Yet wind power kills birds too and it's still installed en masse.

Concentrating solar thermal power works only for large installations. You can't install a concentrating solar thermal power to produce electricity for a single house, unlike what you can do with photovoltaics. Perhaps some of the techniques could work to provide solar heat for a single house at a far lower temperature, though.

Edit: there's another form of concentrating solar power too -- concentrating photovoltaics. In this case, mirrors are used to make the sunlight more intense at the solar cells. It still uses solar cells like ordinary solar power, so it has the benefits of photovoltaics (very cheap), but also the drawbacks of solar power (no way to produce power at night without batteries).

Benefits of concentrating photovoltaics is that:

1. Most solar cells have better efficiency under concentrated sunlight -- so yes, power density is slightly better but only so slightly this shouldn't matter in most cases. Here's the chart of efficiency: https://www.nrel.gov/pv/cell-efficiency.html -- you can see that non-concentrating single-crystalline silicon has a record of 26.1% and concentrating 27.6% so it's not a big benefit.
2. You need less solar cells -- but you need more mirrors
3. The solar cells, since you need less of them, can be more expensive so you can use higher-efficiency cells, the best money can buy. However, the best efficiency cells (multi-junction III-V cells) are still too expensive to be used in any other application than in space applications

My opinion is that given that today solar cells are very cheap, building a concentrating system for them probably doesn't make sense. Those mirrors need to be moved, so it's no longer a static structure. Another idea that has been proved bad is installing solar panels on movable mounts so they track the sun. The reason this is so bad is that solar panels are today very cheap, but installing them is expensive. Tracking devices make the installation even more expensive, like any sunlight concentrating plus tracking system would.

Maybe for a DIY project where labor is cheap, but cells are expensive, it could make sense to build a concentrating and tracking system. But any installation paid at market labor rates, not so.