Renewable Power – Clean And Green – Well, Not Really

PA Pundits International ^ | 29 Dec 2009 | TonyfromOz

[TonyfromOz]

In fact, neither clean nor green at all. We are told that Concentrating Solar Power (Solar Thermal) can actually provide power to replace power generated from coal fired sources. While the solar element can provide power for some of the time, the only way they can supply power for the requisite 24 hour period is to have a backup source using a Natural Gas turbine, emitting CO2, and you would be shocked to know just how much CO2 it does emit.

[chrisser]

Nicely written article.

I think an interesting bit of info would be this scenario.

Let’s say the example solar plant is built. Because it takes so long to build the next one, it is unlikely the local government will settle for it running at 150MW on sunlight. More likely is it will run at 200MW whenever possible and the rest of the time, it will run maxed out on NG.

What does that do to the carbon emissions compared to the coal-fired plant merrily putting out 200MW constantly?

[OCCASparky]

200MW? Try on the order of 800-1200MW. PER UNIT.

[chrisser]

Thanks, I got my units messed up.

In the example, there are 14 200MW (max) solar plants actually putting out 150MW (constant) on solar/NG to replace one 2000MW coal plant.

[OCCASparky]

It gets worse. Currently FPL has the largest solar photovoltaic plant in the nation, at $200 million for 25MW. Now, considering modern PWR nukes can generate nearly 1300MW, to get that out of solar would cost on the order of $11 BILLION—more than DOUBLE the cost of a nuke and nearly 5 times the cost of a comparable coal plant. Yeah, it’s gonna work.../sarc

[antiRepublicrat]

Actually, no. Check out the technology behind Solar One, producing power 24/7 through liquid sodium storage tanks.

[businessprofessor]

The analysis omits the variability of sunshine, seasonal differences in daylight, and the daunting maintenance costs. I am not sure if the analysis includes the transmission capacity, a huge additional expense for wind and solar plants. In addition, the water requirements for the plants makes them unsuitable for arid locations.

[wolf78]

While the solar element can provide power for some of the time, the only way they can supply power for the requisite 24 hour period is to have a backup source using a Natural Gas turbine, emitting CO2, and you would be shocked to know just how much CO2 it does emit.

You're confusing Solar Thermal with Solar PV. Solar Thermal can run for 24h, it's all just a question of how big you design the storage tank (oil, molten salt or you can even use concrete blocks for heat storage) in relation to the turbine size. Most designs use a somewhat smaller tank because there's more energy demand during the day than during the night, so it's not truly 24h rated power like a nuclear power plant.

In addition, the water requirements for the plants makes them unsuitable for arid locations.

That goes for most conventional or nuclear designs as well, i.e. operation is less efficient in arid locations or during drought season.

[RedhairRedhair]

Most large US coal fired power plants are already capable of running on natrual gas.

The power companies already figured out the cost of running on natural gas is very expensive.

So coal is our friend.

Pretty sure that will still be true after this greencrap has gone full circle.

[The Great RJ]

It is the same problem with windmills. While the wind blows someplace all of the time the number of windmills needed to capture these fleeting winds would be enormous. Add to this the problem that it takes a minimum wind speed to move these giant blades and when the wind reaches above certain speeds they must be shut down least they be torn apart. (there is a very interesting video on the Internet showing exactly what happens when this shut down mechanism fails). For these reasons windmills are equally unreliable for sustained power needs and also need gas fired turbines as a constant supplement.

[businessprofessor]

I disagree with your comments. The article indicated that solar thermal cannot run 24 hours. On average, solar thermal probably runs 12 hours (considering season variations and sunshine interruptions). Natural gas provides backup when the heated liquid cools.

You are correct about water requirements for nuclear plants. However, nuclear plants do not need to be located in arid, sunny areas. Nuclear power plants can be located near water sources.

[Erasmus]

The biggest nuke to my knowledge, Palo Verde, is in the desert west of Phoenix. I don’t know what they do for water.

[OCCASparky]

They use reclaimed waste water from the city of Phoenix.

[thackney]

Palo Verde is the largest US nuclear power plant. They get water from the waste water system of Phoenix.

http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1350/appa.xls

http://www.pinnaclewest.com/main/pnw/AboutUs/commitments/ehs/2004/environmental/water/default.html

[wolf78]

I disagree with your comments. The article indicated that solar thermal cannot run 24 hours.

In short: The article is wrong. From an engineering standpoint you can of course build a solar thermal plant to run 24 hours. The problem - as almost always - is not technical feasibility but economics. So I'm disagreeing with the "cannot" as it denotes an imposibility, where there's just a mere impracticality. A 24/7 solar PV plant would need quite a lot of expensive thermal storage in relation to its rated power to produce power at a time of day (or more precisely: night) when electricity prices are lowest (lots of base load available already). Under the current conditions nobody would do that (in the US - maybe in Africa where even coal fired plants work only 4 hours a day and the grid is horrific).

Don't get me wrong: I'm well aware of all the problems of solar - be it PV or solar thermal. I just don't like the generalizations. People who use "cannot" "never" etc. are just like the anti-nuke crowd: They are talking from an ideological standpoint, not a logical / economical one. Almost anything is doable: You can also use renewable cow feces instead of natural gas, it's all just a question of economics (economics will tell you if it makes sense in the end).

I personally don't like "cheap" coal that much because of its external costs (soot and radiation in the air, health insurance costs for miners etc.). I prefer nuclear, but yes, if Google - always looking for world domination - makes good on the promise to half solar thermal costs or that MIT guy can deliver affordable home fuel cell units, that would be great, too. So would nuclear fusion.