thermoelectric solar power

yes, but they are highly inefficient

Could you explain what do you mean by "highly inefficient" concerning to any other solar power technology? May you consider power device module/area, power generation over 24 hours /day, a 2 KW local plant and sure U$/watt market cost? Can a photocell panel works more than 7 hours/day?

Hi, HUX!

Didn't I read this week or last in one of the GlobalSpec newsletters about direct solar-to-thermocouple technology that short circuits the old problems and brings the solar energy into a feasible efficiency rating in this field?

Mark

Happy Thanksgiving, Vasco.

Actually, it is seebeck effect when going from thermal energy to electricity, Peltier when going from electric to thermal;

second, thermocouple junctions of this form are typically no better than 10% effeicient, so to get 400 watts, of electric output, you would need 4000 watts input.

SO your application would have to have boodles of extra capital equipment to collect it...

milo

It´s a honour for me to learn from a person who has so much comments and so high score of "good answers" in CR4 Forum. OK, i am looking for "Seebeck generators". Thanks very much. However, about efficiency, capital and costs i realized that a 2KW small solar plant for produce 48 Kwh /day will be very expensive with PVs choice. Please see our post #2 in this Forum. Certainly, specific numbers are much better than generic words! Addictional information: From 23°S to 05°N we have over all year high level of thermal solar energy radiation ( 600 to 1000 W/m²), at least seven hour/day, very easy and cheap to store it in a underground rock. So, with 10% efficiency Seeback Generator the system can works fine without costs over more than 24 hours/day.

Why introduce two types of enrgy conversions and hence two inefficiencies--one from solar to heat mineral oil and two from heated mineral oil to electricity through thermo-electrics ( yes, Seebeck effect and not Peltier) . This is bound to make the system more inefficient.

Instead , why not use solar PV to convert incident solar heat directly into electricity?

Thermoelectrics will be useful if you have low-grade heat in the form of heated

mineral oil and you wish to convert that heat into electricity.

For me it´s not technical and economical suitable to install "N1" PVs solar panels, 120W: 12V-10A each one, "N2" batteries, "N3" inverters, plus a PV sytem controler to run only 2KW - 48Kwh/day. I invite you to consider 2KW PV panels / area and U$ / watt to realize the inreasonable practice of such system. In future time may be?

I am learning about Seeback effect. So, i am active in this thread. Till this post, i am very surprised to find a large gap in the world market. Perhaps, in future time also we shall have 0,5 KW - 2KW "solid states" family devices to produce minimum clean, local and sustainable electric solar power energy to supply a small home, 3 persons at least.

Fernando, I agree with your assessment about expense of need for inverters & system controllers.

AC 120 V is artifact of Grid Electrical generating means.

Why not develop a 12V DC protocol for home? We have many 12 V appliances for our RV (Recreational Vehicle-Campers) Trucking, and automotive markets.

Thermopiles would still need inverters and batteries (even though you envision storing much hot mineral oil.) to get to the voltage and ac wave form .

As lighting moves to LED's this may be the time to "change paradigms."

I have a friend in Michigan who has used PV with deep cycle batteries for over 20 years in his earth sheltered house, but he's not running 120V AC...

milo

Milo you ask: Why not develop a 12V DC protocol for home? We have many 12 V appliances for our RV (Recreational Vehicle-Campers) Trucking, and automotive markets.

The reason is technical. Losses in the power cables are greater by percentage at lower voltage than at higher voltage. I squared R is the formula. For the same wattage level you end up with greater current at low voltage such as 12V DC than you do at 24V or 48V. In other words the cost of copper wire needed is greater for the lower voltage DC system. When Tesla and Edison first promoted their power distribution systems it quickly became clear that Tesla's DC system was not capable of delivering power for as great a distance as the AC system. To dismiss AC as an "artifact of Grid Electrical generation" is to ignore some very real technical issues.

With today's reliable inverters it makes more sense to use the common higher AC system voltages because there are many more appliances available on the market. None of the DC appliances such as coffee makers last any amount of time compared to AC domestic appliances doing the same function.

I agree. however the critique of "capable of delivering power for as great a distance as the AC system" is irrelevant as the application was for a single off grid dwelling. or two. So transmission losses and cost of heavier gage wire for a single dwelling don't lookto be real showstoppers, just reasonable tradeoffs.

And if crappy 12 V appliances are the rule, well, there's an opportunity too.

Finally if the dwelling isn't as humble as I am thinking, then locating the batteries at multiple points in the dwelling, say at the two points one third way of its length will minimize the distance that the actual power travles, as opposed to from asingle source at one end of the dwelling to the other.

Thanks for reminding me of the relevance of Ohm's law. appreciate you pointing that out.

The Artifact of Grid electrical generation remains relevant in the same sense, as does the old yarn about the width of roman chariots responsible for the size of modern roadways. While that remains an old saw, having been in some charmingly small towns in Europe, There's a kernel of truth nonetheless. You'd not get a cabover peterbuilt and 53' trailer though the center of "old towne" annecy or heidleberg.

So to my mind, The choice of voltage is a similar Legacy. Its optimized for transmission via grid via various stepdowns from the real high transmission voltages. Does this scheme merit reconsideration when considerring a singular dwelling? What was the choice for the Int'l space station? I'm not thinking its 110 60 hz.

Thanks for the engaging discussion.

milo "I was thinking austere, not auspicious"

Hi Milo, lets re-examine this AC versus DC for a minute. Comparing a typical 12V DC system and a common AC system using 120V (Involving 10X voltage but 1/10 current for same power)

Distance from battery to end of line appliance is 50 feet. Round trip is therefore 100 feet. This is not an unreasonable size. My house of 1200 sq. feet is 47 feet long. From under floor ( basement ceiling, to just above room ceiling (typical light fixture) is 8 foot 2". The solar panel feeds a battery bank which is placed against the outer wall in order to facilitate ventilation, entry of wires from solar panel, and also to be close to a basement wall on which all the electrical stuff is mounted.

It may or may not be practical to install the battery bank in the middle of a house..

Assume we have to deliver a maximum of 1000 watts from the battery to the load ( appliance).

My calculations show that using #14 AWG ( common house wire size) we will incur a loss of 1.816% or an actual V drop of 2.1788V for that distance.

To deliver the same 1000 watts by a 12V system requires using #6 Ga wire. And will incur a whopping 28.449% or 3.4139V loss. Clearly we have an issue of cost and efficiency.

You can play with the numbers all you like. But it becomes obvious very quickly that to live with a 12V system imposes either severe restrictions, or extraordinary costs for copper wire.

Lets talk appliances and examine something like a coffee maker. An AC model is often using a 600W heating element. At 120V this involves using about 5 amps. A cordset of 18Ga is more than ample and meets UL criteria. Finding a coffee maker of 600W heating capacity means it draws 50A at 12V. Not very likely to find such. The compromise is a much lower wattage which equals a much longer time to heat the same quantity of water be it one cup or more. Water takes so many BTU to reach boiling point. So right of the bat you are looking at a lot longer wait to heat the same cup of water to make coffee.

But 400 watts is still using 33.3 Amps at 12V. Now that coffee maker needs a #10 Ga wire as a minimum. And because the losses are greater in the house branch circuits you lose a greater pecentage of your energy in the wiring compared to using 120V.

The amount of energy you harvest from sun or wind remains the same. Do you want to use that energy to do useful work or do you want to dissipate some of that in the distribution system inside the house?

Lets go back to the original example of delivering 1000 watts. A good sinewave inverter will lose 10% in the conversion. We calculated a 1.816% loss in the wires. Now add the 10% in inverter for a total loss of 12% and compare that to the 28.449% loss in a DC system that has to use #6 Ga wire.

Se we have much more loss and still have to use much large wires (greater cost).

Most modern off-grid houses uses 48V inverter systems because the losses, even in the very short cables used from battery to inverter is much less. This is a significant gain. After the inverter you use conventional house wiring. Cost of common house hold wire is also going to be less per foot than having to buy #5 Ga wire.

Volume of sales also means that you have a much greater choice of appliances and light fixtures when you use conventional AC fixtures and appliances. I realize it's also true that great strides have been made in energy conservation such as LED lights. But the range of fixtures are still limited compared to the conventional. While guys may not mind living in a hovel that makes you feel like you are camping out; using RV appliances that last a few months or a year at the most in daily use, momma may not be quite as enthusiastic. Remember; "if momma ain't happy; nobody is happy". So keep in mind what the wife might like in the way of conveniences and appearances. Just because you live off grid does not means you have to go primitive or become a minimalist in everything.

Lastly. Some common RV type DC appliances simply refuse to work properly unless fed a steady diet of 13.6V. Unfortunately, even a fully charged 12V battey is not going to deliver more than 12.6V

Most Ac appliances will deliver aceptable performance over a range of 105V up to 125V. It can be argued those limits can be extended to 95V – 130V AC.

Thanks. I wasn;t thinking heat powered by photovoltaics, I figured an PV adapted lifestyle. PV to drive resistance heating makes NO SENSE to me.

Your math is compelling. The losses are significant. added to that conversion efficiency of the thermopile and my original point remains. sounds like a great way tomake a small fortune out of a large one.

I was thinking LED lights, small electrionics, maybe 300 watts for a computer. An adapted lifestyle, not SUV equivalent appliances. ipods. best of the best , not biggest energy hogs. minimum footprint.

Not disputing your math. the assumptions of using high wattage appliances in a post grid world- yes, i dispute that.

Thanks for the great explanation!

milo

Milo, ah yes, I had forgotten the subject line of the original post. I

agree that thermo couple cells is NOT the best way.

I was under the impression the hot liquid was a necessary process and the intent was to derive some electrical power from this existing heat source instead of letting the heat go to waste. Or incuring expense with a moe expensive power generating process.

The truck builders who are using a thermopile around the exhaust stack is recapturing waste heat. My guess is once Sterling cycle engines become more common, these will be found to be more efficient than thermopiles.

My comments were addressed to the issue of how to use the electrical energy once it is generated.

I am curious as to what you consider high wattage appliances. In my example I was mentioning a coffee maker. In my work I routinely recommend many other AC appliances that are actually LOW wattage compared to products of just a decade ago. I was also posting on another forum at the same time. In those posts I was pointing out that you can now cook with electric appliances using a few hundred of watts instead of the thousands of watts used previously.

LED lights yes, but sometimes even these are insufficient. For more lights we have CCF. Unfortunately CCF wil not fire at -20C temperature so what do we do when filament bulbs are banned as of 2010. Now you must have a heater element inside the fixture to warm it up to a temperature at which it will turn on. The energy saving is not as great as you might assume.

In areas with ample hydro-electric power it doesn't make a lot of sense to chose more expensive power sources, especially if those power sources leave a bigger carbon foot print than hydro-electric. I do not think it fair to use the phrase "SUV equivalent appliances". You are using a denigrading term which is not universally applicable. All the major appliance manufacturers have improved their product lines to make them more energy efficient. Are you perhaps suggesting we switch to washing machines that are half the size? Sorry but people are not growing smaller and clothes are still the same size and they stlil get as dirty as before. Or perhaps you are suggesting we revert to a less sanitary lifestyle and only wash clothes when they can stand up by themselves or we only take a bath if we can't stand our own smell. Wash dishes! Naw just let the dog lick them clean. Its good enough!

Hot water is one application which can be improved on. Several options are available. Insta-hot which only heat water as it is actually used. Those make sense for my area. We are already down to 8 daylight hours per day and it will get shorter. On days lke today you wouldn't collect enough heat for a pot of tea let alone a good wash up. We had 10/10 could cover all day. Has been for three days. Some physical laws cannot be ignored.

Electrical appliances are still among the safest. Propane and natural gas have combustion by-products that can cause problems unless adequate venting is available. Leaking gas is more of an issue in terms of frequent occurence than leaking electricity. Compare the statistics for deaths caused by leaking electricity versus leaking gas. Wood burning stoves may or may not be a good choice. In areas of greater housing density the wood smoke will become objectionable.

Insurance companies can tell you in great detail just how much of a risk wood stoves are. So what do you propose. Ban all population above the frost line whe homes require heat during winter?

So my original point in rebuttal to your's n regarding use of just 12V appliances because these are available for RV use stands.

I recently quoted a customer on a Wind generator. Because his tower will be located 300 feet away from where his existing solar panels and battery bank is located the only option that makes financial sense is a 220V AC wingen model. Calculated losses and the cost of the connecting wires are much lower for this "high voltage AC" system compared to any of the low voltage DC systems. We are evidently comparing appples and oranges at this stage. .

Thanks again. I will be sure to consult you if I ever get the opportunity to actually install something.

milo

I believe that there is greater loss in AC transmission than in DC. The losses are capacitance, induction, and corona discharge.

Simmons has build several large, high voltage, and long distance DC transmission lines.

The main advantage of AC is the ability to easily change voltage up or down using a simple transformer.

HVDC

Main article: High-voltage direct current

High voltage direct current (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. When electrical energy is required to be transmitted over very long distances, it is more economical to transmit using direct current instead of alternating current. For a long transmission line, the value of the smaller losses, and reduced construction cost of a DC line, can offset the additional cost of converter stations at each end of the line. Also, at high AC voltages significant (although economically acceptable) amounts of energy are lost due to corona discharge, the capacitance between phases or, in the case of buried cables, between phases and the soil or water in which the cable is buried.

HVDC links are sometimes used to stabilize against control problems with the AC electricity flow. In other words, to transmit AC power as AC when needed in either direction between Seattle and Boston would require the (highly challenging) continuous real-time adjustment of the relative phase of the two electrical grids. With HVDC instead the interconnection would: (1) Convert AC in Seattle into HVDC. (2) Use HVDC for the three thousand miles of cross country transmission. Then (3) convert the HVDC to locally synchronized AC in Boston, and optionally in other cooperating cities along the transmission route. One prominent example of such a transmission line is the Pacific DC Intertie located in the Western United States.

"When Tesla and Edison first promoted their power distribution systems it quickly became clear that Tesla's DC system was not capable of delivering power for as great a distance as the AC system."

Not to be a wise@$$ but you have that backwards. Tesla(along with Westinghouse) was the proponent of AC and Edison was the one touting DC.

It was known as the "War of The Currents" and Edison did some pretty nasty things to demonize AC as unsafe. Including many cases of animal cruelty and the invention of the electric chair.

Hi Milo. Let me give you my congratulations again. My original post ask CR4 members for autonomous solar generation. Later, we said that our electric application would be a a single home, 03 persons (plus 1 dog). Your idea about 12V protocol is much greater than electrical world people can accept as a technical as a political point of view. Any way i am engaged with 48VDC home appliances powered by autonomous solar energy generation. Sure, we will do that. I am a dancer over the abyss too. But i am feeling that world manufactures can not supply suitable equipments for this kind of "change of paradigmas". Thermocouples, PVs, gensets and so an are not suitables. May be a "Stirling Motor" can run with reasonable efficience with 250°C hot source powered by solar energy and 30°C environmental could source. If so, may would be our next step.

In a philosophical poit of view i would like very much to join Nikola Tesla (my great electrical Master) with Thomas Edson inventions and ideas. If you like, you can e-mail me directly about philosophical and history matter. You have my adress e-mail in www.acquaway.com.br

Why introduce two types of enrgy conversions and hence two inefficiencies--one from solar to heat mineral oil and two from heated mineral oil to electricity through thermo-electrics ( yes, Seebeck effect and not Peltier) . This is bound to make the system more inefficient.

Instead , why not use solar PV to convert incident solar heat directly into electricity?

Thermoelectrics will be useful if you have low-grade heat in the form of heated

mineral oil and you wish to convert that heat into electricity.

"Why introduce tow types of energy conversions and hence two different inefficiencies..." There may actually be some advantage in that, under certain circumstances, thermal energy may be easier to store than electrical energy, and thus improve the shift of peak availability to peak demand times. One of the most significant cost factors for solar systems generally ignored by promoters is that most storage batteries have a significant life limitation, and must be replaced on two to four year cycles- and ALL the batteries should be replaced at the same time (mixing batteries of different ages can significantly reduce the life expectancy of the newer batteries). Heating mineral oil may actually be more cost-effective when one does a long-term cost analysis (say, 20 year life expectancy). Last time I did a cost analysis for a solar system (maybe 3 years ago), payback was still 50 years...

So can anyone describe how to assemble the said device ?

I had to disassemble a commercial product one time because the feed wire broke off. The complete assembly consist of many tiny cells all connected in parallel. In effect a sandwich of pellets in between two ceramic boards. A conductive circuit pattern was deposited onto the ceramic board to link the pellet ends. The connection was made by soldering the pellets to the ceramic circuit board substrate. The soldering technique is similar, if not identical to how surface mounted components are soldered to a circuit board such as you have in your cell phone or other computer devices.

Apart from the production methods to fabricate the ceramic board your biggest challenge will be the methods you use to fasten the heat sink blocks to the ceramic board sandwich for best heat transfer.

Incidentally at least one truck company is already making a 1 kilowatt power generator from peltier cells mounted around the exhaust pipe. Maybe you can adapt something like that. But be warned the capital cost to acquire or fabricate such a device is totally out of proportion to the return in energy that you can achieve. There are many other methods of getting power that will not cost as much per watt.

they are actually connected in series...

Thanks! The assembly I dismantled was only 2cm X 2cm so it was hard to follow individual traces. So what factor determines current if the series connection determines voltage. Is it volume of each block, or surface area of the contact between block and circuit trace?

Back to you elnav. What a great question:

"So what factor determines current if the series connection determines voltage. Is it volume of each block, or surface area of the contact between block and circuit trace?"

"The voltage produced by thermocouple junctions is strictly dependent upon temperature. Any current in a thermocouple circuit is a function of circuit resistance in opposition to this voltage (I=E/R). In other words, the relationship between temperature and Seebeck voltage is fixed, while the relationship between temperature and current is variable, depending on the total resistance of the circuit. With heavy enough thermocouple conductors, currents upwards of hundreds of amps can be generated from a single pair of thermocouple junctions! (I've actually seen this in a laboratory experiment, using heavy bars of copper and copper/nickel alloy to form the junctions and the circuit conductors.)'

"Thermocouples, however, can be built from heavy-gauge wire for low resistance, and connected in such a way so as to generate very high currents for purposes other than temperature measurement. One such purpose is electric power generation. By connecting many thermocouples in series, alternating hot/cold temperatures with each junction, a device called a thermopile can be constructed to produce substantial amounts of voltage and current:

With the left and right sets of junctions at the same temperature, the voltage at each junction will be equal and the opposing polarities would cancel to a final voltage of zero. However, if the left set of junctions were heated and the right set cooled, the voltage at each left junction would be greater than each right junction, resulting in a total output voltage equal to the sum of all junction pair differentials. In a thermopile, this is exactly how things are set up. A source of heat (combustion, strong radioactive substance, solar heat, etc.) is applied to one set of junctions, while the other set is bonded to a heat sink of some sort (air- or water-cooled). Interestingly enough, as electrons flow through an external load circuit connected to the thermopile, heat energy is transferred from the hot junctions to the cold junctions, demonstrating another thermo-electric phenomenon: the so-called Peltier Effect (electric current transferring heat energy). "

Here's the link: http://www.allaboutcircuits.com/vol_1/chpt_9/5.html

Looks like it s deltaT more than T itself; and current is negotiable...

SO now the heat sink engineering looks to be every bit as important as storing all that hot oil.

The idea of junction size and size of conductors makes sense, when I think back to my early projects with voltaic cell, voltage is fixed based on choice of metals for plates, but amperage was determined by size of the plates..

milo

This thread is running very nice for me. Now, l have some few basic lines for a 2KW - 48Kwh Project over 24h/day. Sure, there are hard work to specify and to know the live time and efficience of each part of the"solid-state" thermoeletric power plant, powered by sun. I don´t have english capacity enough to explain it in a correct few lines. So, i would like to say, at least: 1- Plus sun thermal "adiabathic storage" energy in cheap rocks designs and minus electrical bateries parts. 2- I want a "Electric Protocol" for future time way of live (may be 48Vdc !!!). I don´t believe in hydroeletrics power plants because its "very low" power / flooded area and its total amount U$ / watt. Certainly, i mean finance + social + environmental system costs. About usual thermoeletrics running from petrol, coal, wood, etc i think the planet live can´t accept no more time this kind of "human insanity battle". 3- I am working over other project lines and of course. "Stirling Motors" would be a good alternative way for 10KW up 30 KW only if they can run in a efficient performance close 250°C and 30°C differential sources temperatures. I need to study more the "fluid work" of this kind of engine and his "thermodinamic cycle" to talk about. 4- I am sure, that we have time still to "change paradigms". "Green House Effect" will bring for all people of the world thousand times more social and economics problems than actual international finance crisis.

Thank you very much and for all CR4 members that engaged this thread. I feel, like Nikola Tesla & Thomas Edison: It´s only a "begin to begin" for future electrical world clean ans sustainable protocol.