Hello All! Introduction and a question

GreatBallofFire
GreatBallofFire Registered Users Posts: 16
Hello everyone! I just recently joined the wind-sun forum. There looks to be a lot of very good feedback from people on the real life experiences so I wanted to ask a question. First, moderators if this is in the wrong section then please move it to where you feel it would be best placed. Obviously almost everyone is here because of there interest in either PV or wind or sometimes both.

I have ventured more over to the solar thermal side and I'm curious about other people that have experience with not only PV and wind, but also solar thermal. When I say solar thermal, I'm not referring to pool heaters or domestic water, but solar thermal electricity generation. Now, I realize that thermal is the caveman version of generating electricity compared to the shining PV panels, but each has their own dedicated applications in my opinion. Just curious to other people's opinions.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Hello All! Introduction and a question

    Solar Thermal for electrical generation (usually some sort of molten salts energy storage, water boiler, and steam turbine) is probably one of the few "green" technologies that may actually be useful (i.e., cost supporting based on real revenue) for utility scale power (also works well to share the turbine with other energy sources such as natural gas for backup).

    Solar PV panels + Batteries (or flywheels, etc.) will (most likely) always require some sort of subsidy to keep it competitive with other forms of electrical energy production.

    There are some alternative battery technologies out there--But so far, they do not seem to be "cheap enough" for utility scale power in most applications.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GreatBallofFire
    GreatBallofFire Registered Users Posts: 16
    Re: Hello All! Introduction and a question
    BB. wrote: »
    Solar Thermal for electrical generation (usually some sort of molten salts energy storage, water boiler, and steam turbine) is probably one of the few "green" technologies that may actually be useful (i.e., cost supporting based on real revenue) for utility scale power (also works well to share the turbine with other energy sources such as natural gas for backup).

    Solar PV panels + Batteries (or flywheels, etc.) will (most likely) always require some sort of subsidy to keep it competitive with other forms of electrical energy production.

    There are some alternative battery technologies out there--But so far, they do not seem to be "cheap enough" for utility scale power in most applications.

    -Bill

    Bill, you're right that utility sized thermal designs still have some headroom left, especially if the storage can keep being extended for reasonable cost.

    I'm personally interested in trying to "shrink down" the utility designs while still trying to maintain the same economies of scale of the current commercial designs. Some of the negatives of a commercial design (taxes, high financing cost, ect.) could possibly be avoided with residential designs. I happen to agree with the rest of your comment as well, thanks for the response.

    -Mark
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Hello All! Introduction and a question

    Mark,

    The problem with thermal systems is they tend to scale down poorly... Simple issues of the surface area tends to grow by the square, while volume tends to increase by the cube... For thermal systems, this gives you much better efficiency in insulation (as an example) as the "hot volume" grows by the cube, the surface area of the "insulated box" only grows by the square (10x growth in linear dimension=> 100x surface area => 1,000x hot volume storage/ability to transfer heat energy)--increasing thermal insulation efficiency dramatically as the "box" scales up. Same issues with piping, etc. (I am certainly not a thermal/mechanical engineer--just my two cents on the problem).

    It would be interesting to see small scale "home" sized units--But I am not sure that will ever happen (at least in the next decade or so).

    Batteries (probably lead acid) appear to be the future for quite a while to come. There are other chemistries out there--But they can have higher losses, critical failures if over/undercharged, if they "freeze" (molten salt batteries), and such. Not to mention price (kWH/$$$ cost of storage).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Hello All! Introduction and a question

    thermal does work for electric generation, but the difference between this and pv is that pv does not need to track the sun. the concentrators on thermal require accurate tracking which adds a bit of extra complexity into the works.
  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    Re: Hello All! Introduction and a question

    Talking to someone the other day and they said why cant you use a heat pump to drive a steam generator? Heat pumps can have 300 to 400 percent efficiency . So 1kw in and 3 kw out, could this mean a generator that would power itself??
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Hello All! Introduction and a question
    Talking to someone the other day and they said why cant you use a heat pump to drive a steam generator? Heat pumps can have 300 to 400 percent efficiency . So 1kw in and 3 kw out, could this mean a generator that would power itself??

    Perpetual motion revisited, only this idea takes it a step further, not just keeping itself powered forever, but outputting vast amounts of power as well.
    Alas, regardless of the hype of scammers, there has never been built, in the history of mankind, an operating perpetual motion device.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Hello All! Introduction and a question

    Some 40 years ago I designed a solar powered steam engine. It used solar to boil Freon (12 - now banned) to run the engine. Not sure you could get a product with good enough expansion to heat ratio for such a thing to work today, although the solar concentrators would be better and use of a rotary vane "motor" (reversed compressor) would help.

    Before anyone asks: did it work? Yes. Was it any good? No. :p That's why you can't buy one today.

    But perhaps the younger, brighter minds of this brave new century can overcome the shortfalls.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Hello All! Introduction and a question

    The efficiency of thermal engines (steam, even gasoline/diesel/etc.) is defined by the differences in working temperatures. A heat pump will only (roughly) give you a difference of ~32F to 120F or so (just made up numbers for example).

    The most efficient natural gas combustion turbines are on the order of 50% efficiency or diesel combined cycle engines of ~60% maximum (based on ambient vs burning fuel).

    It has been too many years for me to remember any thermal classes I have had, but from Wiki, the maximum engine thermal efficiency can be defined as (Carnot cycle):

    Efficiency = 1 - (absolute low temperature / absolute high temperature) (in degree K)

    So, if we had a Carnot cycle engine operating with a temperature differential of 32F to 120F, its efficiency would be:

    Eff = 1 -(273K/322K) = 15% maximum theoretical efficiency

    Of course, in real life, there are other losses... Friction, mechanical to electrical back to mechanical conversion losses (Carnot cycle engine generating electricity to drive heat pump to generate thermal difference, etc.), energy loss to moving air/working fluids, etc....

    It was an interesting idea.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Hello All! Introduction and a question

    Sounds like Marc (Cariboocoot) was way ahead of his time--And probably spent a whole lot less money than these guys did:

    Stirling
    Energy Systems Files for Chapter 7 Bankruptcy

    September 28, 2011

    New Hampshire, U.S.A. -- The falling cost of PV continues to wreak havoc on manufacturers of other solar power technologies. The latest casualty is Stirling Energy Systems (SES), maker of the SunCatcher, a 25-kW solar-powered stirling engine designed specifically for the utility market.

    RenewableEnergyWorld.com learned late Tuesday evening that SES had filed for Chapter 7 bankruptcy and was going into liquidation.

    SES had deployed a pilot project using its stirling engines in early 2010 with the 1.5-MW Maricopa Solar Plant [note, this link is now dead] in Arizona. But the company was ultimately unable to compete with the cost of PV and filed bankruptcy documents with the U.S. Bankruptcy Court in Delaware last week.

    In 2008, SES was slated to supply its dish-engine technology to a huge 850-MW power plant in San Bernadino County, California. The project developer Tessara Solar, however, sold the project — known as Calico Solar — to K Road Power Holdings in late December 2010 right after it had received all necessary approvals from the California Energy Commission. K Road then announced that 750 MW of the 850-MW project would be developed using PV instead of CSP. K Road said that it would still use next-generation SES dish-engine technology for phase two of the project, which included the last 100 MW.

    Also at the time of that announcement, in December 2010, Southern California Edison terminated the PPA it had signed for Calico Solar.
    ....

    At this point, it appears doing the standard Heat to storage to hot water/steam to turbine is the hardware of choice for Thermal Solar utility scale systems.

    Note that in the above article, the comments are very educational too... Apparently, the thermal efficiency of the Stirling engine at their thermal differentials was around 30% (another data point in thermal efficiency game).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Hello All! Introduction and a question

    Well at least I didn't go broke trying to make it work!

    Mind you I've gone broke trying to make a lot of other things work since. Over and over. A kind of "less-than-sterling cycle". :p
  • GreatBallofFire
    GreatBallofFire Registered Users Posts: 16
    Re: Hello All! Introduction and a question
    BB. wrote: »
    Mark,

    The problem with thermal systems is they tend to scale down poorly... Simple issues of the surface area tends to grow by the square, while volume tends to increase by the cube... For thermal systems, this gives you much better efficiency in insulation (as an example) as the "hot volume" grows by the cube, the surface area of the "insulated box" only grows by the square (10x growth in linear dimension=> 100x surface area => 1,000x hot volume storage/ability to transfer heat energy)--increasing thermal insulation efficiency dramatically as the "box" scales up. Same issues with piping, etc. (I am certainly not a thermal/mechanical engineer--just my two cents on the problem).

    It would be interesting to see small scale "home" sized units--But I am not sure that will ever happen (at least in the next decade or so).

    Batteries (probably lead acid) appear to be the future for quite a while to come. There are other chemistries out there--But they can have higher losses, critical failures if over/undercharged, if they "freeze" (molten salt batteries), and such. Not to mention price (kWH/$$$ cost of storage).

    -Bill

    Bill, you covered all the problems with downsizing solar thermal fairly well. There is definitely diminishing returns on increasing surface area if the thermal losses are greater. However, I'm slightly more optimistic than you on the decade time frame.
    Some 40 years ago I designed a solar powered steam engine. It used solar to boil Freon (12 - now banned) to run the engine. Not sure you could get a product with good enough expansion to heat ratio for such a thing to work today, although the solar concentrators would be better and use of a rotary vane "motor" (reversed compressor) would help.

    Before anyone asks: did it work? Yes. Was it any good? No. :p That's why you can't buy one today.

    But perhaps the younger, brighter minds of this brave new century can overcome the shortfalls.

    Cariboocoot, the rotary vane motor is right up my alley only I prefer a more readily available power medium than freon. Compressed air can provide the necessary expansion while still operating at relatively low temperatures (250-300F). Unfortunately, if the air is not compressed somewhat close to isothermal, than you end up backwards. It is possible to design around the inefficiencies of compressing air and that can open the door for lower operating temperatures that might be a little more realistic for the residential sector.

    I'm quietly tip toeing past the question of the heat pump and steam engine since I don't feel like being stuck on a hamster's wheel

    -Mark
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Hello All! Introduction and a question

    I used Freon 12 because its boiling point was 117F as I recall: good change in volume for the change in temperature.

    What you'd use these days ... I'm too far out of the loop to hazard a guess.
  • GreatBallofFire
    GreatBallofFire Registered Users Posts: 16
    Re: Hello All! Introduction and a question
    I used Freon 12 because its boiling point was 117F as I recall: good change in volume for the change in temperature.

    What you'd use these days ... I'm too far out of the loop to hazard a guess.

    There are quite a few different materials that have a low enough boiling point while still providing decent pressure. Unfortunately, I just don't like the idea of using chemicals for a residential design unless its for air conditioning or something similar. I always end up right back at compressed air again. It's just hard to beat an endless local supply plus the ability to store high pressure at ambient temperature. The downside is if you don't compress the air properly (isothermal), then you would be better off watching paint dry on your neighbor's house.

    Even though it was 40 years ago, you were still way ahead of your time.

    -Mark
  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    Re: Hello All! Introduction and a question

    So is there any point at which a very efficient heat pump could make this work?
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
  • GreatBallofFire
    GreatBallofFire Registered Users Posts: 16
    Re: Hello All! Introduction and a question
    Talking to someone the other day and they said why cant you use a heat pump to drive a steam generator? Heat pumps can have 300 to 400 percent efficiency . So 1kw in and 3 kw out, could this mean a generator that would power itself??
    So is there any point at which a very efficient heat pump could make this work?


    I assume you are talking about the heat pump and steam engine, correct? Well, the short answer is no. Even if the heap pump has COP of 3-4:1, the steam engine still has an extremely low thermal efficiency and you will always end up with less energy than you started. That's nature's law and there is no way around it.

    It's kinda like walking backwards in hurricane winds, you might think you're going forward but you're actually going the wrong way.

    -Mark