Concentrated Solar Power Plant Design

[marciokoko]

Hello,

We are a solar energy solutions provider and we are looking to explore CSP plants at smaller scales. I would like to understand the design better. Basically a CSP consists of:

1) steam turbine
2) solar energy collectors (mirrors)
3) water container (boiler)

I would like to know about 2 of these items in particular:

1) steam turbine: What kind of steam turbine would I be looking at? Any particular kind? I am thinking of a 100kW to 500KW plant. Maybe as far up as a 1MW plant to start off with. I understand there are many kinds of steam turbines.

2) water container design: How would the container have to be designed, basically, not in detail. CSP towers make it seem like the water container is at the top of the tower. I am guessing the turbine actually sits above the water container? Or is the steam simply piped down to the ground level where the turbine sits?

 

[Bobbywhy]

When one has a challenging equipment specification for a desired functional system, one can benefit from a search for how others have already accomplished that same function. Here on Physics Forums we have a saying: “Google is your friend”. You can probably find information using this searching technique that will guide you towards the successful completion of your project. I used the following search terms on Google:

solar power steam turbine
solar energy steam turbine
solar power steam engine
solar power steam generator
solar power electric generator
disadvantages solar power steam turbine
steam turbine power plant
advantages steam turbine plant

Here are just a few sites of interest:

http://en.wikipedia.org/wiki/Solar_power_tower
http://www.scienceagogo.com/news/20121019185106data_trunc_sys.shtml
http://www.ge-energy.com/products_and_services/products/steam_turbines/concentrated_solar_power_steam_turbines.jsp

 

[marciokoko]

Yes thanks, I did do a lot of google searches and have a lengthy read ahead of me. But i understand the general concept and I believe what I would have the most trouble with is the steam turbine. I am thinking of buying one to just do some tests. My idea is to make a small unit for a group of houses for example. Perhaps a 1MW unit which would supply about 6MWhrs daily which could feed about 30 small homes.

Hmm, perhaps even smaller. But basically, i want to get started on this at a small scale to learn and then grow. I guess my first question would be, what is the smallest practical size, even if for one home? IOW, what if I wanted to make a 5kW system? What kind of mirrors and turbine would I be able to use given the fact that its such a small system? I am sure the mirrors are not a problem because I could get them fairly easy, but I am guessing there is a steam turbine lower threshold - which is why I asked my question about turbines.

 

[256bits]

Where are you going to put all the mirrors?

 

[marciokoko]

I have an available piece of land (39 acres).

 

[HobartTas]

Greetings

For that small power size I think you should give up on your idea to use steam turbines and use steam piston engines instead, have a read of this page here as to why this is so, where they state you need something bigger than 250 horsepower (185 KW) before turbines become more efficient and you must also deliver DRY STEAM ONLY which means heating it to 800F to superheated status.

A much better way to go is a http://www.spilling.de/english/produkte.php and you can buy any size from 100KW to 1500KW and they would not be unduly affected by wet steam.

I think you should start off small and I suggest you have a look at the technology used in an http://www.stginternational.org/how-it-works.html first with a technical evaluation here and then you can probably consider moving to a larger hot oil system like a http://www.nexteraenergyresources.com/content/where/portfolio/pdf/segs.pdf plant, once you convert water to steam then storing large quantaties of it and moving it around becomes a bit of a problem due to the high pressures involved, you are much better off circulating hot oil under minimal pressure and generating the steam on demand via a heat exchanger.

Sopogy are already doing something like this in the power sizes you are interested in.

If you manage to get something up and running then please keep us updated with future posts, anyway, that's all I can help you with my limited knowledge in this field, I hope it helps.

Cheers

 

[marciokoko]

Ok so you're saying that anything under 185kW should use steam piston engines? I saw the Sopogy link, 500kW for 250 homes, that's 2kW per home which could produce for 6 hours which comes to 12kWh per home per day.

And that cost them 20million US$! Yikes! And that uses oil instead of steam. So what's the smallest dry steam turbine setup feasible?

I just wanted to set up a steam turbine, even if for 1MW or 2MW. What would a steam turbine cost for that kind of CSP? I want to get an idea of what to tell my possible investors would be the cost of a small pilot program.

 

[HobartTas]

Greetings

The smallest I have found starts at 75 KW from Siemens

No! I didn't state that under 185KW you should use steam turbines, the first article I linked to did and one of the two reasons they quote is the requirement for DRY STEAM "Finally, there is the expense. A steam turbine with the boiler and accessories to provide superheated steam of 800° F. or up is going to run 7 figures (or better). If you're a power company, you can probably afford it. For the rest of us, piston steam engines are a whole lot more practical and less expensive."

That is the only reason why I suggested a piston engine over a turbine as you will destroy a turbine with WET STEAM as water droplets will pit and corrode the turbine blades but will not affect a steam piston engine, as far as costs go you will have to contact Spilling for the piston engine and Siemens for that turbine (or one of the larger models) and figure out which is a better way to go.

I'm a bit confused about what exactly your intentions are? is it

(a) A "solar power system" which is the latest funky trend like a brand new smartphone so let's go ahead and raise some capital, borrow some money, build the plant and hope to make a positive rate of return after all expenses?

or

(b) We are 5000 miles from civilisation and we are building a mine with no mains power available so we need to do our own (with storage) even though we know it will be more expensive?

If its (a) then have a look at this NREL cost and performance data for power generation technolgies report specifically pages 38-43

roughly summarising

1. Solar PV is about $3K per installed KW

2. Solar CSP without storage is about $5K per installed KW

2. Solar CSP with storage is about $7K per installed KW

Do you see the problem with CSP, yes its more expensive than PV, given that electricity in Hawaii is at 37 cents per kWh due to them generating it solely by burning oil, so the Sopogy plant which runs at lower temperatures (hence lower Carnot efficiency) at $10K per installed KW doesn't look that unreasonable when you look at their electricity prices.

Grid connected PV is the cheapest way to go but it

(a) doesn't generate any power when the sun is down and

(b) some utilities might not accept the power generated as they then have to find something else to supply power at night or even during the day if the weather is overcast or raining.

Solar CSP is more expensive but with storage can supply something approaching peaking and intermediate power and with a large enough storage tank even some baseload power.

Solar PV with storage is possible, here is a 100GW power plant idea floating around that the authors reckon will produce power at a LCOE of 8 cents a kWh.

As far as a micro CSP (without storage) or PV amounting to 1 or 2 KW for a residential house goes a PV plant would be cheaper but a CSP plant would have the ability to also supply hot water and thus reduce somewhat the cost for this technology for that reason.

Unfortunately, I'm a bit confused as to what your exact intentions are, I could probably advise you further but I think pretty much what you need to know so you can make further independent enquiries I have stated thus far. I am only reasonably familiar with all the different solar power technologies from a theoretical perspective and have never worked in the power generation industry.

Cheers

 

[HobartTas]

P.S. Sorry, forgot to answer this question for you

2) water container design: How would the container have to be designed, basically, not in detail. CSP towers make it seem like the water container is at the top of the tower. I am guessing the turbine actually sits above the water container? Or is the steam simply piped down to the ground level where the turbine sits?

In the tower they usually have just the boiler there and they pump the water up to it as it has to be under high pressure anyway, the steam usually comes down via return pipe and everything else other than the boiler is usually down at ground level where its cheaper to maintain and service, also makes the tower lighter and cheaper to build.

I also forgot to add a solar power tower with heliostats is apparently cheaper than parabolic troughs, however, given that the parabolic SEGS plants have been operating for several decades then bankers and investors are more comfortable with parabolic technology as opposed to power tower technology which is somewhat regarded as "new and unproven".

Cheers

 

[marciokoko]

Well I have the opportunity to purchase a used 1 MW turbine from an old cogeneration sugar mill project that was dismantled. I was thinking of using it to provide energy for a house development of about 30 units.

At the same time I was wondering if there was a way to do the solar thermal project at a smaller scale.

So I am caught in between both projects. For the first project, I would have the backing of the company that owned the sugar mill that is interested in the project to upscale it for their own industrial use or possibly to sell to the power utility. For the second project, I was curious to know how small I could go in order to make it feasible for a house or a small group of houses.

 

[gmax137]

... DRY STEAM ONLY ...

Well there are very rugged turbines that will handle wet steam. The Terry turbine was well known but I don't know who owns those designs now or if they're marketed anymore. The ones I had experience with were 800 hp / 600 kw, if I remember correctly.

 

[marciokoko]

Ok so for small systems, my more practical options are steam piston engine, rankine engine and hot oil engines, correct? Which would you suggest for a 500kW system?