E&E Exchange Blog

E&E Exchange

Welcome to the Energy & Environment (E&E) Exchange, a blog dedicated to science and engineering topics that are (generally) related to energy and the environment. This blog is meant to encourage discussion about the challenges and possibilities surrounding sustainability through science and technology. The blog's owner, cheme_wordsmithy, is a former technical writer and engineering editor at IEEE GlobalSpec, the company that powers CR4.

Previous in Blog: Solar Startups Stepping Forward   Next in Blog: LEDs Made Brighter and Cheaper
Close
Close
Close
50 comments

A Look at Solar Thermal Power

Posted February 15, 2012 12:00 PM by cheme_wordsmithy

Last week, I started a discussion on some new advances in PV solar technology (found here). The feedback generated some comments regarding solar power generation using heat rather than PV cells, which I thought warranted further conversation (thanks to kramarat and others for your thoughts on the topic).

As a result, I've gathered some sources and pulled together some information to help myself (and all those interested) learn more about this growing industry.

Solar Thermal Power

When most people think solar, they think of photovoltaic (PV) solar cells which capture and convert sunlight to electricity. The main focus of solar power research has been on this technology.

Solar thermal power uses a different approach - capturing solar energy as heat in water or another medium. The heated medium can then be utilized directly for hot water heating (residential/commercial use) or used to heat steam to run a turbine and generate electricity.

In residential and commercial applications, collectors are made of metal pipes painted black and contained in a glass box or cylinder (as seen right - Credit: PocoSolar). Solar water heating is already a mature technology, but the market is still in its infancy. According to a SEPA report, though, sixteen percent of the 110 million U.S. households are suitable for solar thermal systems. So estimates say it potentially has a market of $123 billion. The limits and costs of the systems are largely dependent on the heating requirements of the household and its location (climate).

In industrial cases, solar thermal uses mirrors to reflect and concentrate sunlight, commonly known as concentrated solar power (CSP). This picture (Credit: Areva) shows a diagram of the process:

Solar thermal utilities may use molten salts as heat transfer media. They are abundant, low cost, and remain as a water-like liquid through the range of temperatures needed (~290-570°C). Molten salt CSP plants use two storage tanks to balance heat capture and storage. The cold tank (~293°C) holds salts for heating up in the receiver, and the hot tank (~565°C) holds thermal energy after it has been captured.

CSP vs. PV

The distinct advantage of CSP plants is that they can be designed to store energy. Storage capability only adds about 5% to the total project cost, and provides up to 10 hours of storage capacity. This makes them more grid-friendly and reliable than PV solar plants, which can only store energy using a much more expensive battery option.

Ausra's VP made this analogy about the comparison: "If you have a laptop computer and a thermos of coffee on your desk, the battery in your laptop and the thermos store about the same amount of energy. One of them costs about $150 and the other one costs maybe $3 to $5. On the wholesale level, storing electric power is at least 100 times more expensive than storing heat."

But why is PV surging ahead if this is the case? Some say the problem is competition. The peak usage hours for electricity are between 4-8pm. Thus, if solar PV can provide just 2-3 hours of storage, it will largely fulfill peak demand and still cost less than solar thermal. Additionally, PV technology is years ahead of CSP in terms of development and manufacturing, and both are competing for the same land, making it unlikely that CSP will be able to gain the upper hand.

Thermal + PV = PV/T

PV/Thermal (PV/T or solar co-generation) systems are a combination of solar thermal and PV systems, and they utilize the advantages of both. Conventional PV systems only convert between 10-15% of sun's energy to electricity, but adding a thermal component could boost efficiency up to 50%. Capturing this waste heat also means that PV cells will not suffer from reduced efficiency at higher temperatures (a conundrum since the hottest days are typically the most sunny and productive).

(<-- PVT panels. Credit: Ecomerchant.co.uk)

PVT collectors are constructed either like a solar thermal collector (box with a glass cover) or more like a PV panel (less insulation and no cover). Design options have tradeoffs between electrical conversion efficiency and thermal efficiency.

Adding solar thermal components to a residential solar electric system doesn't require much additional structure. This may make consumer solar systems more cost-effective and efficient as efforts to promote and develop this technology continue.

But there are always technical hurdles to overcome. Bulk and complexity can be hindrances, especially in commercial systems, due to the need for both piping and cabling in the system. In addition, there are issues with the long-term stability of co-generation units, especially considering that any failure of the heat transfer fluid to circulate could damage or destroy the PV cell due to overheating.

But I am excited about PV/T. The technical problems will likely be addressed and mitigated as the technology gains more attention. The biggest problem I see is that most companies are fully occupied developing separate PV or thermal solar systems. In order for PV/T to advance, some amount of cooperation will be needed.

Sources:

Ausra - An Introduction to Solar Thermal Electric Power (pdf)

PhysOrg - Thermal storage gets more solar on the grid

Renewable Energy Focus - Solar PV and thermal

Renewable Energy World - Some Skepticism on Solar Thermal Power

Triple Pundit - Solar Thermal Plant in Nevada Hits a Milestone

Reply

Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#1

Re: A Look at Solar Thermal Power

02/15/2012 1:20 PM

Thanks! I'm going to go ahead and put my link from the other thread here. Using steam to turn turbines, and mirrors to make steam is one thing, but I think the use of R-134a refrigerant in a closed system that requires much less heat to boil and turn turbines is really cool..................and it should be much less expensive. I'm probably over excited about it, I just need for someone to explain to me why it isn't feasible on a large scale.

http://www.yourownpower.com/Power/

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#2
In reply to #1

Re: A Look at Solar Thermal Power

02/15/2012 5:21 PM

This concept has been around for ever, I actually designed an r-22 system for generating residential power for individual homeowners back some 20+ years ago....They were at the time being used as waste heat reclaimers on the sugar refiners sites..The original heat exchanger fluid was benzine back in the 30's I think...I could never under stand why this wasn't used on a large scale for power generation, the fluid characteristics and efficiency were way beyond using water as an exchange fluid...What are your thoughts?

found this..

http://www.transpacenergy.com/

__________________
Break a sweat everyday doing something you enjoy
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#3
In reply to #2

Re: A Look at Solar Thermal Power

02/15/2012 5:54 PM

My thoughts are that we should be using it.

At the very least we should be utilizing the waste heat from all kinds of industrial sources. All it takes is a 100°F temperature differential between the heat source and the sink. That should be very easy. Like I mentioned in the other blog, if I had a miniature one of those units, I could power my home, (probably several homes), with some black piping, sunshine and well water...................no problem.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#4
In reply to #3

Re: A Look at Solar Thermal Power

02/15/2012 6:40 PM

Have you worked in this field at all? ...The trick is to match a refrigerant or mixture, that hits peak efficiency at your operating temperature and won't break down at max temp and seals that could hold up under such high rpm and pressure...Getting the expander or empellor, is not an easy task as I recall, we used a Joy fan turned backwards...

__________________
Break a sweat everyday doing something you enjoy
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#5
In reply to #4

Re: A Look at Solar Thermal Power

02/15/2012 7:00 PM

I haven't, but the link you provided makes it sound sound like they have come up with some custom refrigerants that can be tailored to different situations and temperatures.

From my link:

The concept of running a refrigeration cycle in reverse to generate power has been known for a long time. However, until now the refrigeration industry has never seriously pursued this idea. When Carrier Refrigeration was conducting performance tests on the 19XR centrifugal chiller, a high reverse rotational speed was noted that during simulated power outages. This is typical in a refrigeration unit, as pressures between the condenser and evaporator equalize during shutdown. However, the 19RX chiller was designed using a discrete passage diffuser, rather than the vaneless diffuser used on previous products. The vaneless diffuser was observed to allow reverse rotational speeds up to 75% of normal operating speeds, and this triggered the idea of actually using the compressor as a turbine. Carrier further developed this concept with their sister divisions, United Technologies Research Center and United Technologies Power, ultimately resulting in the 2004 release of the PureCycle™ 200. The PureCycle™ uses waste heat exhaust gases and air cooled condenser equipment. The Chena Power plant takes the PureCycle™ concept one step further, generating power economically off a 120°F temperature differential between the evaporator and condenser temperature. Interestingly enough, this approaches the temperature differential of the air-conditioning unit the power plant was derived from. For this reason, the same refrigerant typically used in Carrier Refrigeration systems can be used for the Chena power plant.

One big advantage of using refrigeration or air-conditioning equipment for power generation is that the hardware used for these applications has a cost structure substantially lower than that of traditional power generating equipment. By keeping as many components the same as possible, the UTC Power Plant can substantially reduce construction costs by taking advantage of Carrier's mass production line. In fact, if a Carrier Refrigeration mechanic were to come to Chena Hot Springs, they would not be able to tell the different between our turbine/generator assembly and a Carrier compressor/motor.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#6
In reply to #5

Re: A Look at Solar Thermal Power

02/15/2012 9:20 PM

I would like to see one of these systems paired with a fuel cell, I won't guess the efficiency, but I would bet on a record... A substantial leap forward....

Having parts available from a plentiful existing source is a big advantage over the past, add that to new refrigerant types that have been developed over the past 20 years, and a heat source like a natural gas fuel cell , and I admit I'm getting a little excited myself...

__________________
Break a sweat everyday doing something you enjoy
Reply
Commentator

Join Date: Jun 2011
Location: New Zealand
Posts: 75
Good Answers: 5
#7
In reply to #6

Re: A Look at Solar Thermal Power

02/15/2012 10:58 PM
Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#9
In reply to #7

Re: A Look at Solar Thermal Power

02/15/2012 11:17 PM

Have they built a prototype? These stirling engines are showing some small promise of useable power, but haven't seen any actually producing electricity yet...

__________________
Break a sweat everyday doing something you enjoy
Reply
Commentator

Join Date: Jun 2011
Location: New Zealand
Posts: 75
Good Answers: 5
#11
In reply to #9

Re: A Look at Solar Thermal Power

02/15/2012 11:35 PM

They are selling them

Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#19
In reply to #11

Re: A Look at Solar Thermal Power

02/16/2012 11:40 AM

Link please?

__________________
Break a sweat everyday doing something you enjoy
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#14
In reply to #6

Re: A Look at Solar Thermal Power

02/16/2012 6:36 AM

It's being done. These guys are part of the team that worked on the Alaska plant.

http://www.utcpower.com/knowledge-library

From here:

http://www.utcfuelcells.com/fs/com/bin/fs_com_Page/0,9235,03400,00.html

I've never heard of phosphoric acid fuel cells.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#21
In reply to #14

Re: A Look at Solar Thermal Power

02/16/2012 11:50 AM

These acid fuel cells have been around since 1838, they were they first large scale commercial application deployed, and UTC the largest dist to my knowledge, if memory serves....but they do not offer a fuel cell paired with an ORC setup, that I have seen....Natural gas fuel cells are everywhere, Bloom Box, even automotive applications are growing in popularity...

__________________
Break a sweat everyday doing something you enjoy
Reply
Commentator

Join Date: Oct 2011
Posts: 88
Good Answers: 9
#23
In reply to #6

Re: A Look at Solar Thermal Power

02/16/2012 12:01 PM

May I ask what you mean?

a fuel cell produces electricity and admittedly some waste heat. The system proposed above is a simple thermal machine producing electricity from temperature differences.

The way I see it, you could only add the proposed system to improve the fuel cell efficiency very slightly by converting a small part of the waste heat from the fuel cell to electricity. By carnot's law the efficiency of that would probably hover at below 20% of waste heat conversion. In other words, let's suppose your fuel cell has 75% conversion efficiency (not an actual number but I hope I am not too far off) then you could convert about 20% of the 25% of waste heat which this fuel cell generates. That is, the overall efficiency would go from 75% to 80% (75%+25%*20%). If the economics of it work out it should be done, but it looks like it could just be too expensive.

Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#27
In reply to #23

Re: A Look at Solar Thermal Power

02/16/2012 12:46 PM

A fuel cell produces a great deal of heat, this is one of the problems that has held them back....The efficiency is much lower than you cite at 75%, now the overall efficiency if they are using the waste heat may approach that, and even exceed that, I've seen claims of 90%, but typical efficiencies range from say 35% to 55% for the fuel cell alone...This is from memory, I could be off a little....The 20% efficiency you are citing for ORC systems, are typical for waste heat streams not approaching the waste heat of fuel cells, which range from around 600F to 1200F and offer a much higher differential with which to work...

__________________
Break a sweat everyday doing something you enjoy
Reply
Commentator

Join Date: Oct 2011
Posts: 88
Good Answers: 9
#29
In reply to #27

Re: A Look at Solar Thermal Power

02/16/2012 1:28 PM

Then I am with you: in that case it is an idea that is worth more than a shy thought. Especially when you consider it for a larger commercial installation, where the additional complexity can surely be offset by the fuel saving.

Reply
Member

Join Date: Feb 2012
Posts: 6
#10
In reply to #1

Re: A Look at Solar Thermal Power

02/15/2012 11:24 PM

This is called an Organic Rankine Cycle (OCR). They normally run about 20% effeciency off waste heat.

Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#22
In reply to #10

Re: A Look at Solar Thermal Power

02/16/2012 12:01 PM

That's at low temperatures, as you raise the temperature the efficiency goes up...Fuel cells can produce temperatures over 1000°F...

__________________
Break a sweat everyday doing something you enjoy
Reply
Power-User

Join Date: Dec 2008
Location: Australia
Posts: 143
Good Answers: 24
#8

Re: A Look at Solar Thermal Power

02/15/2012 11:16 PM

Nice thread guys. Very good information.

I think the end goal everyone is working towards is increased energy efficiency, and better utilisation of waste energy.

It seems to me there are many ways of improving the overall efficiency of the process. In my part of the world a very large % of household energy use is for heating and cooling. And seems illogical to me to invest in equipment to convert sunlight --> electricity --> heat (with the inherent conversion losses between light to electricity & from electricity to heat). Instead it makes so much sence to go directly from sun light to heat, using a thermal battery for managing the peak loads.

And similarly for energy used for cooling - inherent losses both in creating electricity and consumption through the refrigeration cycle. Instead go direct (from heat to cold) with the adsorption refrgeration (http://engineering.ucsb.edu/~yuen/references/rer-8.pdf).

Not saying either of these solutions are viable (they may not be for many reasons) - just that a single process may be more energy efficient as the efficiencies of the multiple process are multiplied & compounded vastly reducing the overall efficiency.

Cheers,

Anthony

Reply
Member

Join Date: Feb 2012
Posts: 6
#12
In reply to #8

Re: A Look at Solar Thermal Power

02/15/2012 11:44 PM

There are a number of ways to increase efficiency. In the US the focus has been on increasing the solar cell efficieny while off-shoring the technology once is has been developed. This has left huge gaps in how efficiency can be pursued. Also, you have PV systems, PV/T systems, Thermal Wall systems (hot air) etc. So, while it seems the technology base is well covered, really it is not. In my opinion the next wave will be PV/T at least for homes. Looking at PV panel systems one of the major drawbacks is overheating of the solar cells. PV/T systems can not only provide thermal energy they can also increase effeciency of the solar cells by keeping them cooler. Every 10% increase in temperature is about 1% decrease in efficiency, so cooling the solar cells can give a 10-15% boost to the solar cells. At current projections for of about 1.5% increase in cell efficiency, it would take 7-10 years before PV systems can match the electrical output of PV/T (not even counting the value of the hot water). OCR systems using themal energy in a combined PV/OCR system would also be possible. You might even do a PV/OCR/Thermal system using the waste heat for hot water. There are lots of possibilities waiting for someone to pick them up and run with them.

Reply
Commentator

Join Date: Oct 2011
Posts: 88
Good Answers: 9
#24
In reply to #8

Re: A Look at Solar Thermal Power

02/16/2012 12:09 PM

Indeed very satisfying discussion!

let me propose a counter argument to your direct conversion for cooling as well (actually for the heating part I have already posted it a bit further below). Currently I have not seen a solar absorption chiller with a work factor of 2 under optimal conditions yet. Compressor based chillers have typically work factors somewhere between 3-5 under real conditions.

In other words there might be more complexity but the compressor chillers give a great head start to the overall system efficiency. as long as electric generation efficiency keeps up, it might remain the better solution. (see also my post below for example)

Reply
Power-User

Join Date: Dec 2008
Location: Australia
Posts: 143
Good Answers: 24
#36
In reply to #24

Re: A Look at Solar Thermal Power

02/16/2012 7:03 PM

Yep, logically agree - the effectiveness and development of the absorption chillers is still far off that of the carnot cycle based refrigeration.

Point was - with the poor energy conversion of PV to electricity, then another inherent loss in the carnot cycle, the net energy conversion from sunlight to reduction of heat is pretty low.

And going direct from sunlight to heat reduction via the adsorption process, eliminates both efficiency losses. The adsorption process will certainly have efficiency losses of it's own, and other disadvantages. I'm not going to pretend I'm experienced enough to compare them objectively.

Just wanted to throw in an alternative route to the same result.

Cheers,

Anthony

Reply
Power-User

Join Date: Aug 2007
Posts: 458
Good Answers: 6
#13

Re: A Look at Solar Thermal Power

02/16/2012 12:25 AM

In junior high school I checked out his book titled "Modern Inventions" that was published around 1901 and in it was this parabolic dish lined with mirrors focussed on a steam boiler. It was located in Arizona and had an output of five horsepower.

Reply
Guru
Hobbies - DIY Welding - New Member Hobbies - Target Shooting - New Member Engineering Fields - Civil Engineering - New Member United States - Member - New Member

Join Date: May 2009
Location: Red Hook, New York (Mid-Hudson River Valley)
Posts: 4364
Good Answers: 177
#15

Re: A Look at Solar Thermal Power

02/16/2012 9:11 AM

Not a mention about solar thermal encapsulated tubes here. They are highly efficient, depending on who manufactured them.

Just curious why everyone is centered on refrigerants for use in solar thermal applications. For residential use, wouldn't their utilization be cost prohibited? A great many homes here in the USA use Hydronic heating systems, whether they're fired by #2 fuel oil, propane, or NG. I'm not an ME, but it seems to me to be much easier to modify the existing Hydronic system to accept solar-generated heat via heat exchangers whilst using a water-RV antifreeze solution in the solar circulating loop rather than using a refrigerant. Also, if the loop springs a leak that can be an expensive proposition to fix and replace the refrigerant, and also a rather difficult time actually locating the leak source.

IMO, keep it KISS.....and why, why, why go off on tangents after tangents on this subject?

Sorry to be a kill-joy here, but I've spent literally several hundred man-hours researching this topic in textbooks, solar thermal books of all types (including USDOE books etc.), and online solar websites in order to construct (which I'm slowly fabricating presently in my spare time) the best cost-effective DIY'er solar thermal project for my needs and that doesn't include refrigerants of any kind.

Let the Sun shine baby!

__________________
"Veni, Vidi, Vici"; hendiatris attributed to Gaius Julius Caesar, 47 B.C.
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#16
In reply to #15

Re: A Look at Solar Thermal Power

02/16/2012 9:39 AM

The use of refrigerants to run a turbine isn't any more complicated or expensive than the central AC systems that many of us have....................how often do those spring leaks?

The beauty of refrigerants, is that they boil and vaporize at much lower temperatures than water, and require a temperature differential in the heat exchange that runs a minimum of 100° F. Far more efficient than boiling water into steam.

When you take into account, that not only solar can be used to provide the heat needed, but virtually any source of waste heat that we currently are blowing up stacks and into the atmosphere, it becomes pretty clear why using refrigerant to run turbines should be getting more attention.

Of course, no thread like this would be complete without a little conspiracy theory, so I'm gonna go out on a limb here and say, that I don't imagine that the large utility companies would look too kindly on this type of independent power generation..........................particularly given, that in many states, (if not all), the utilities are required to purchase any excess electricity that is generated and fed back into the grid. But I digress.................this is a subject for another thread. One in which we discuss who owns the grid, who is responsible for upkeep and upgrades, and why isn't it being done.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru
Hobbies - DIY Welding - New Member Hobbies - Target Shooting - New Member Engineering Fields - Civil Engineering - New Member United States - Member - New Member

Join Date: May 2009
Location: Red Hook, New York (Mid-Hudson River Valley)
Posts: 4364
Good Answers: 177
#17
In reply to #16

Re: A Look at Solar Thermal Power

02/16/2012 10:08 AM

I understand where you're coming from Kram in regard to refrigerants, but the average Joe does not know squat about design and constructing such a system. That was my primary focus in my post.

I ask how many times in the past have you sweated copper water pipe fittings and found afterward that the joints leaked? I'm pretty damn good at sweating copper pipe, but always there will be a pinhole leak somewhere in the work.....truthfully, I really hate this new silver-tin solder and the crappy white flux paste they pass off as acceptable goods these days. I always end up going back to my old lead solder and resin flux to get the job done.

Well, in this state there are laws on the books that dictate that the power companies must by back (or credit you) excess power production from your grid-tied solar PV system....of course you must have a system installed by a state-approved solar PV Contractor, be inspected by the local power company having jurisdiction, and have an approved "reverse meter" installed by that same company. Hell yes it's expensive to have an approved contractor install it, but in this state there is no way around going this route here if you want to receive the state rebates, and the Federal/state/local tax incentives/credits. Other states may do things differently and the state laws may be like a limp noodle and unenforceable.....it's a crying shame when they are and the state legislators ought to be ashamed of themselves for enacting ineffective statutes.

__________________
"Veni, Vidi, Vici"; hendiatris attributed to Gaius Julius Caesar, 47 B.C.
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#18
In reply to #17

Re: A Look at Solar Thermal Power

02/16/2012 10:18 AM

No. These systems wouldn't be installed by the homeowner or business. It would take professionals..............of course, most homeowners can't install PV systems either.

As for the rules and regulations....................this is yet another case in which, rather than trying to help, the government simply needs to step out of the way. If they play a role at all, it would be to perform a safety inspection and go home.

When people, particularly engineers, are left to their own devices..................they will always come up with better ideas than the government.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#25
In reply to #15

Re: A Look at Solar Thermal Power

02/16/2012 12:32 PM

The use of refrigerants to drive a turbine has several advantages, the most important being molecular density, more bang for the buck...also the fact that you can design the mix to work at the temp available, for maximum efficiency...there is also a problem with steam driven turbines called pinging, which is the water droplets hitting the turbine blades and causing wear, this is much less of a problem with refrigerants...and they are not expensive, if you buy wholesale, as opposed to your local auto parts dealer....Refrigerants are also much more efficient at transfer of heat than water....

__________________
Break a sweat everyday doing something you enjoy
Reply
Commentator

Join Date: Oct 2011
Posts: 88
Good Answers: 9
#20

Re: A Look at Solar Thermal Power

02/16/2012 11:49 AM

Lots of interesting entries here.  I hope I add another grain of thought.

the reversed AC to produce energy from waste heat sure is a good idea for geothermal or waste heat conversion.  For solar I am not so sure: in the end the conversion efficiency is limited it the reversible (Carnot) cycle efficiency so 1-T_low/T_high.  So if we do this with something that has a low boiling point, and the low temperatures difference of let's say 55K (about 100Fahrenheitt), then the efficiency is quite limited for a residential solar system.  Plugged in the Formula with 300K for the ambient temperature it gives a theoretical maximum efficiency of about   18%.  This is already available today as real efficiency in PV modules.

I wouldn't discard it, just saying I am skeptical.  With renewables we are in a weird situation: there is so much potential that conversion efficiency is really not important.  The only thing that matters is what can be done economically.  Experience has shown that in anything using solar panels efficiency is very Important as low efficiency means the use of more costly surface.

With the same kind of approach I have to say that pV/T systems sound better than they are.  Consider the following: solar thermal system (domestic hot water) have efficiencies in their 80% range.  In essence they are tuned performance machines for heating water.  The PV panels are tuned for converting light into electricity.  That doesn't usually go well with tweaking the total absorption and low emissivity to maintain thermal efficiency.  

Also, while the argument about PV cells performing better when cool.  I argue that in PV/T modules the cells are on average not cooler than in a pV module.  In a typical PV module the temperature of the cell is typically 25K above ambient in normal operating conditions.  How hot do you want your hot water?  Consider your 30C (somewhere in the nineties for the  Americans) summer day.  Your cells in a PV module might be at 55-60C.  This is probably just about what you need for your hot water demand.  That also means in fall, when it is maybe 15C outside the PV module will be at  maybe 40C but you will still want your hot water panel to be at around 55C.  In other words, you design a system that most of the time of the year keeps your PV cell hotter than it needs to be and therefore more likely reduces overall efficiency than improve it.  Theoretically you can find intelligent combinations like using a PV/T panel but they are not the general case.

In essence, my stance is still that - until someone comes up with a solution where the two applications don't hinder each other - it is probably more efficient to mount independent systems for PV and hot water.  For me the best home system is the one that has as much thermal panels that al the collected thermal energy is used in the house directly or stored in a tank for later use and uses the remainder of the surface for PV.  While heat is easy to store, electricity is easy to use!  What I try to say is that if you have excess heat it is wasted, if you have excess electricity and your PV installation is on the grid there are so many consumers with running so many different appliances that the generated electricity won't go to waste.

A final thought to that point, won't PV modules reaching 20% and potential for more and heat pumps with work factors of 3-5 this means by going sunlight-->PV-->heat pump already we can achieve technical efficiencies of 60-100% for hot water preparation.  That means PV is on the way of outpacing the thermal panels completely and this while having the benefit that you can always use the electricity for other things.  Try powering your laptop with the thermos (no offense, just completing the analogy someone used earlier)

Concentrated PV is a very interesting method with its thermal storage.  It is something that I think we will see more of in the future in desert zones.  Due to the need for concentration, it is not practical for residential use.  concentration also means that these plants have to deal with the laws of optics to concentrate the light.  That works fine in locations with a lot of direct light (deserts typically).  In locations with lots of diffuse light these plants don't perform.  PV will.  Therefore they are complementary.  

It is true, grid stability and storage will become a major challenge for PV in the future.  I am confident that universities and industry have understood this and will be ready with new solutions as PV takes considerable shares of electric consumption worldwide.

If all of us keep working on solutions I am sure we will make progress at good pace. Sent from my iPad... so excuse the weird typos 

Reply
Commentator

Join Date: Jun 2011
Location: New Zealand
Posts: 75
Good Answers: 5
#33
In reply to #20

Re: A Look at Solar Thermal Power

02/16/2012 3:43 PM

I think the concern that you have about the PV/T keeping the PV at an artifically high level (ie greter than 25K above ambient temperature) for much of the year could be addressed by treating the water heating side of the system as a pre-heat and then using another heat source to bring the the water temperature up to its final heat. For example a califont could be used or an electric element in the storage cylinder to get that boost.

This approach would then keep the temperature of the PV at a good level and scavange heat.

Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#26

Re: A Look at Solar Thermal Power

02/16/2012 12:44 PM

I also think that we are paralyzing ourselves with safety concerns..............particularly in small applications. I think I read that a Bloombox about the size of a breadbox could power an average home, but I don't have a way of getting natural gas.

At the risk of being beaten, lynched, beheaded and thrown under a train, I don't see why, (for small scale applications), solar can't be used to create HHO from water, and the resulting gas used to power a fuel cell like the Bloombox. The gas could even be stored................. in limited quantities of course.

I don't know, but it seems to me that this notion of, 'If there is the slightest risk of one person dying by utilizing a particular technology, then it isn't worth trying', doesn't seem sustainable.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Commentator

Join Date: Oct 2011
Posts: 88
Good Answers: 9
#28
In reply to #26

Re: A Look at Solar Thermal Power

02/16/2012 1:25 PM

Electrolysis (splitting water fonts oxygen and hydrogen) is indeed often discussed. So far it seems like none can propose an economical system but it might become more interesting as storage becomes a growing urgency.

the biggest issue apart from overall system efficiency is probably the storage of hydrogen, there are few things it doesn't leak through...

as for safety. Hydrogen is a flammable explosive gas. So care has to be taken. Not saying don't do it but you know how quickly bad press of a couple of accidents discredits a good idea. I prefere the system to be built well.

Reply
Power-User
Technical Fields - Technical Writing - Technical Writer Engineering Fields - Environmental Engineering - New Member

Join Date: Jul 2011
Location: Albany, NY
Posts: 247
#30
In reply to #26

Re: A Look at Solar Thermal Power

02/16/2012 2:07 PM

I think that's what the Artificial Leaf research has been all about. The major hurdle, as you might expect, is finding an effective and safe way to capture and use the gases once they are produced.

In this case the technology is pocket sized and doesn't accomplish all that much. But the principle behind it has potential if it could be implemented in a different way.

__________________
“A man wrapped up in himself makes a very small bundle.” — Benjamin Franklin
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#31
In reply to #30

Re: A Look at Solar Thermal Power

02/16/2012 2:36 PM

I think so too. I'm thinking that the answer to the storage problem, (of the volatile gas), would be to use some type of expandable bladder, (like a balloon), as opposed to a metal tank. Granted, they would have to be stored in a safe place, but accidental ignition would result in a fireball instead of a bomb.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#32
In reply to #31

Re: A Look at Solar Thermal Power

02/16/2012 3:26 PM

Hydrogen is no more flammable than other fuels, LP is stored everywhere, people have them next to the house....Gasoline and ethanol are even more dangerous if you ask me, at least the hydrogen is lighter than air and dissipates rapidly, LP being heavier than air can pool, and natural gas in an enclosed space is just as bad, if not worse....I don't see that this safety concern is reality based at all...

__________________
Break a sweat everyday doing something you enjoy
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#34
In reply to #32

Re: A Look at Solar Thermal Power

02/16/2012 5:48 PM

If we're talking HHO, it's the oxygen component that makes it much more explosive. If it was enclosed in a metal tank, any ignition would flash back to the tank itself. Big bang................that wouldn't happen with LPG.

But you're right. Different fuels require different storage methods. Anything that burns can be dangerous. As far as I know, there aren't any laws preventing me from setting up a solar powered HHO generator in my back yard.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 31551
Good Answers: 1744
#35
In reply to #34

Re: A Look at Solar Thermal Power

02/16/2012 6:39 PM

This guy has it ...

http://www.youtube.com/watch?v=xEdQRVQtffw

Hydrogen production as an energy storage medium vs batteries does seem to be the wave of the future...this from 08..

http://web.mit.edu/newsoffice/2008/oxygen-0731.html

__________________
Break a sweat everyday doing something you enjoy
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#37
In reply to #35

Re: A Look at Solar Thermal Power

02/17/2012 7:31 AM

I think hydrogen will have a place too.

Man.................I think the guy in the video might be a little obsessive.

I wasn't aware that the oxygen could be separated off. That makes it a lot safer. I was also a little surprised by the relatively small amount of energy that was stored in those tanks. There are definitely storage issues that will have to be dealt with.

Cool system, but I could never afford, or justify it. I got my electric bill yesterday, $64 for 603 Kwh's. That's for 3 of us in an 1800 sq ft house.

I could get by with something very small. At least at first. Enough run my well pump, a few lights, refrigerator and chest freezer would be sufficient.

Too bad Moore's law doesn't apply to off grid technology. We'd all be able to pick up an affordable system at Walmart.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#38
In reply to #37

Re: A Look at Solar Thermal Power

02/17/2012 11:45 AM

Oxygen appears over one electrode, hydrogen over the other, therefore they are really easy to separate and keep separate.

Look here:-

http://en.wikipedia.org/wiki/Electrolysis

...and you will see this:-

__________________
"What others say about you reveals more about them, than it does you." Anon.
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#39
In reply to #38

Re: A Look at Solar Thermal Power

02/17/2012 12:09 PM

Yep. It just didn't occur to me.

Like a lot of people, I've played around with HHO at home.........................it burns a lot better with the oxygen in it.

Seems like it would make more sense to separate the hydrogen and oxygen, store them, and remix them at the burn point for more heat/better combustion.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#40
In reply to #39

Re: A Look at Solar Thermal Power

02/17/2012 12:21 PM

You are right.

One of the main reasons that it is not done this way is simply that Oxygen (unbelievably so), is one of the most dangerous gases to store. Few people believe it.....

Even a spot of grease or oil will spontaneously burn/explode if Oxygen leaks.

__________________
"What others say about you reveals more about them, than it does you." Anon.
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#41
In reply to #40

Re: A Look at Solar Thermal Power

02/17/2012 1:12 PM

True, but everyone has seen the old people hauling around an oxygen tank. I would think that a safe way to introduce it into the combustion process would be attainable. Probably microsecond long pulses with enough line between the metering device and the flame to prevent flashback to the tank.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#42
In reply to #41

Re: A Look at Solar Thermal Power

02/17/2012 1:58 PM

Giving old people oxygen cylinders and no proper training is tantamount to murder, but we somehow get away with it, probably because the actual dosage is relatively small.

My mother used to flood her bedroom with oxygen so that she could sleep without the mask, she got away with it somehow.......I was expecting to hear that she had landed in the next county, but there again, she had her broomstick as backup!!!

I remember years ago seeing a guy with an oxygen cylinder on a little trolley to pull around behind him in the town, sitting down and enjoying a cigarette in the park.......OMG!!!

Nothing happened.

__________________
"What others say about you reveals more about them, than it does you." Anon.
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#43
In reply to #42

Re: A Look at Solar Thermal Power

02/17/2012 2:50 PM

I've seen the smoking, oxygen tank, people too. I've never heard of one of them blowing up.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#44
In reply to #43

Re: A Look at Solar Thermal Power

02/18/2012 10:47 AM

OUCH!!

Hopefully only they were involved and nobody else......

__________________
"What others say about you reveals more about them, than it does you." Anon.
Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#45
In reply to #44

Re: A Look at Solar Thermal Power

02/18/2012 10:56 AM

No. I've seen people with oxygen tanks, smoking cigarettes. I've never heard of them blowing up from doing it.

I like the visual though.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#46
In reply to #45

Re: A Look at Solar Thermal Power

02/18/2012 11:46 AM

Sorry, I misread your earlier comment, my bad!

__________________
"What others say about you reveals more about them, than it does you." Anon.
Reply
Commentator

Join Date: Oct 2011
Posts: 88
Good Answers: 9
#47
In reply to #39

Re: A Look at Solar Thermal Power

02/19/2012 11:34 AM

If you actually had H2 and O2 anywhere near a 2:1 mix in a gas bottle and you would open the tap ever so slightly and light the outdoing gas you would just have triggered a full blown bomb! The fire would backfire into the bottle at least at the speed of sound and the two gases in the bottle would immediately ignite all the content in the tank.

Reply
Guru
Hobbies - Fishing - New Member

Join Date: Jun 2008
Location: Raleigh, NC USA
Posts: 13529
Good Answers: 467
#48
In reply to #47

Re: A Look at Solar Thermal Power

02/19/2012 12:23 PM

Yep. Actually it would be H2 and O1 if we're talking HHO. I think there could be ways to utilize the oxygen component...........like separating and remixing, or possibly a metering device at the burn end. After all, if I placed a teaspoon full of gasoline in the same bottle, I would have a pretty impressive bomb too.

__________________
Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
Reply
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 17996
Good Answers: 200
#49
In reply to #47

Re: A Look at Solar Thermal Power

02/19/2012 3:40 PM

Dead right.

It would just leave drops of water around!!

The Germans call the mixture "Knallgas" or "Bang-gas", for very good reasons.

Plenty of people have caused 12 volt car batteries to explode and got pieces of lead and plastic, covered in sulphuric acid in the face and eyes.....

__________________
"What others say about you reveals more about them, than it does you." Anon.
Reply
Commentator

Join Date: Jun 2011
Location: New Zealand
Posts: 75
Good Answers: 5
#50
In reply to #49

Re: A Look at Solar Thermal Power

02/19/2012 4:14 PM

What about moving away from hydrogen to ammonia as the combustion material. Check out http://newenergyandfuel.com/http:/newenergyandfuel/com/2011/02/02/nh3-for-fuel-eyes-look-to-texas-tech-and-new-zealand/

They claim "...huge cost savings in the production of hydrogen using electricity. The processor is suggested to cost $200US and is predicted to produce fuel for about 27¢ a liter, about $1.00 a gallon."

Reply
Reply to Blog Entry 50 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Copy to Clipboard

Users who posted comments:

ajwinemaker (2); Andy Germany (6); CaptMoosie (2); Charlie Greenwood (1); cheme_wordsmithy (1); cristle (4); kramarat (15); Marsium (2); SolarEagle (11); Tompa (6)

Previous in Blog: Solar Startups Stepping Forward   Next in Blog: LEDs Made Brighter and Cheaper

Advertisement