Solar Power Minus the Light

An anonymous reader writes "Popular Science is running a story about a small company trying to take advantage of all the global warming hype. Matteran Energy uses 'thermal-collection technology to heat a synthetic fluid with a very low boiling point (around 58F), creating enough steam to drive a specially designed turbine. And although a fluid-circuit system converting heat into electricity is nothing new, Matterans innovative solution increases the systems efficiency to a point where small-scale applications make economic sense.' Notably, this comes during a record breaking heat wave here in the US. So has the day finally arrived where I can run my AC off of all that heat outdoors?"

Only solves 50% of the problem

[chriss]

Hm, looks simply like a small sterling engine or mini gas turbine used to drive an AC. They managed to make it cheap so it will be applicable in small installations, but both the sterling engine and the gas turbine (using a fluid in a closed circuit) require a temperature difference, so the machine would not be driven by heat alone. You'd have to cool down the steam after it had passed the generator to make it condensate to a fluid again and pump it back into the thermal collectors. The article does not mention how this should be done or where the energy for this should come from.

Power stations using closed fluid circuits (e.g. nuclear plants) use a secondary circuit to cool the first one after the steam passed the turbine. They are usually located near rivers for this. Larger installations for sterling engines can store heat during the day in a water tank and use the difference in temperature between the water and the surrounding cooler air during the night to drive a sterling engine. This obviously works best in areas where the difference in temperature between day and night is significant, i.e. deserts. I don't think it to be realistic to turn 1/4 of your apartment into a heat/cold storage just to drive the AC.

So in the end they made it cheaper, but inefficient (5%) even compared to solar panels (20%) without offering something that could replace a conventional AC. To achieve this you'd still have to build houses in a smarter way, e.g. isolate the walls from the inside and outside and use them as thermal storage. More energy efficient construction has been done for cold regions (where houses require almost no heating during winter when isolated well, the inhabitants' body heat is sufficient) and warmer regions (traditional buildings build with clay and wind-traps and smaller windows to the sunny side). So it is possible, but do not expect too much from our current architecture.

Thermo

[LesPaul75]

So has the day finally arrived where I can run my AC off of all that heat outdoors?

Ok... I'll be the first to admit I wasn't paying close attention when this was discussed in my college physics class, but something having to do with the laws of thermodynamics feels wrong here. :)

Re:Only solves 50% of the problem

[NightRain]

Presumably however, you'd at least be able to use the existing temperature difference to at least offset the cost of running the airconditioner? Obviously it's not a perpetual energy machine, so you'd lose out in the end, but it seems to me that at least it could use some of the cooled air that is otherwise just going to be wasted.

Re:Thermo

[Umbral Blot]

What's specifically wrong is this: to condense the steam back into a liquid you need something colder than its boiling point. Thus on a hot day you couldn't get it to condense, and thus it wouldn't work. What you really need is a a large heat sink, like the ocean or a big peice of ice, and then you could turn the tempertature differential into energy using this device (at the cost of heating up whatever cold thing you were dumping heat into).

Re:Only solves 50% of the problem

[lordcat]

You want cool? bury it! The temperature underground tends to stay nice and cool, even during the heat of the summer... If you've ever lived in a house with a full basement... you'll know that during the summer, that basement is the coolest part of the house... Similarly, in the winter time, that basement doesn't get as cold as the rest of the house can... (obviously heat rises so if you heat the house the upper levels will get warmer quicker, but if you didn't heat the house the basement would be the warmest part from the radiant heat in the walls vs the radiant cold upstairs)... Either you should get a nice difference in temperatures between the surface and 10-20 feet underground (maybe less... and you should get a nice difference both durring summer and winter)... or you don't need the ac!

it aint that great

[hamburger lady]

~5% efficiency.

what's wrong with a reflective dish and a stirling engine [stirlingenergy.com], anyways? much higher efficiency, materials aren't as expensive as solar panels and not nearly as bad for the environment.

Very inefficient

[Cyberax]

This turbine can't be very efficient. Efficiency of any heat engine is limited by the Carnot cycle (http://en.wikipedia.org/wiki/Carnot_cycle).

Basically, you can estimate it with this formula: e=(T2-T1)/T1 where T2 is the highest temperature of the working body and T1 is the lowest temperature. For such a small temperature drop as in this engine we'll get a very minuscule efficiency.

Re:it aint that great

[chriss]

The main problem with stirling engines and reflective dishes is that they consume a lot of space, most of which is the empty area between dish and engine. While they may be more efficient and their production be less hazardous to the environment, they cannot compete with solar panels which can be put on roof tops or basically any flat surface. Newer PV technology even promises "paint on" solar cells. They are simply less invasive and therefore can be put into more places, leveling their lower efficiency. For rural areas this may be different, but for cities PV wins.

Re:Only solves 50% of the problem

[Jedi Alec]

this very principle is currently being put to use in a part of the Netherlands that used to be mined for coal. The water in the now abandonded mine-shafts will be used to provide heating in the winter and cooling in the summer.

More flies in the ointment ...

[JumpingBull]

First, the refrigerant used in their independent calculation is R-22, a cloroflorocarbon that kills the ozone layer, implicated in crop failure due to high uv exposure.

Second, the cooling cycle uses water. Considering that potable water is in short supply, this is a problem...

Third, the thermodynamic Carnot cycle is a cap on the efficiency. Higher working temperatures do give a better efficiency, but you still have to cool them!

A different working fluid can be used. unfortunately, organic fluids tend to be flammable. Methanol might be a candidate. It is less toxic then ammonia.

Before the advent of mechanical refrigeration, some AC was done with evaporative air coolers. (for cinemas at the start of the 20th century). This might mitigate the second point.

Perhaps we are missing an important use. The humidity usually makes an environment uncomfortable. This system might find even more effectiveness driving a dehumidifier.

Finally, it might be equally effective to use a two stage boiler. A flat plate to get the fluid up to working temperature, and a solar concentrator to superheat the fluid to drive the system to a higher efficency

Not a chance it will work, or ever break-even.

[Ancient_Hacker]

Ahem, this thing won't work.

The diagram shows 10 PSI gas being condensed. Then somehow, without a pump, the 10PSI liquid "flows" into a 65 PSI boiler. No way, Jose. And no, you can't use the height of the condenser to supply "gravity" pressure. There is no free lunch.

Then there's this dang thing called the Carnot Cycle, which is impossible to violate, and dooms all these low-temp difference heat engines to extremely low efficiencies. So low, in most cases, you can't even keep up with paying the interest on the investment.

I didnt see a single numeric calculation for the loop efficiency, a really bad sign. These calculations have been basic, simple, and mandatory for upwards of a century and a third.

Re:Only solves 50% of the problem

[Smidge204]

Photovoltaic panels get hot because they absorb all that sunlight with only ~20% efficiency. Install the heat exchanger in close proximity to the back of the solar cells to make use of this high temperature and take advantage of the shade it provides (prevent the heat sink from being heated by the sun as well. Now your microturbine may be only 5%, but that's effectively ~25% overall for the PV-turbine system combined.

Make that a concentrating PV and your efficiency increases for both systems.

Every little bit helps.
=Smidge=

Re:Very inefficient

[IcePop456]

I thought we only worry about efficiency when the energy supply is low? Granted I wouldn't want a huge piece of equipment, but considering how much thermal energy is in the air during the summer, cost is what I'm worried about more than efficiency.

Re:Only solves 50% of the problem

[Aceticon]

Actually as you go deeper underground the temperature of the soil gets closer and closer to the average yearly temperature in that area as shown here [nrc-cnrc.gc.ca]

How fast the temperature approaches the yearly average as depth increases depends on the type (and moisture content) of the soil, but as a rough guide, at 8m depth the temperature is very close to the yearly average.

Note that this is not valid for extreme depth (or vulcanic areas) for the obvious reason ;)

BTW, the graphic was taken from here [nrc-cnrc.gc.ca] - if you want to know the depth at which the yearly variation of temperature has 1% of the amplitude of the variation outside, look for "Table I. Depth of Penetration of Diurnal and Annual Temperature Cycles" (sorry, no anchor in doc) and check the column "Depth Year (m)"

You already have thermal energy

[dbIII]

I think aircons should run primarily on photovoltaics

Run them on heat instead - instead of having water in a rooftop solar hot water system you could have your airconditioning working fluid (eg. ammonia) getting hot then expand it through a nozzle to give you cooling. This gives you cooling with no moving parts and would use a lot less roof space than the photovolatics required to run an electric airconditioner. Electricity is not the answer to everything - it's a way to get energy from one place to another.

Solar Roof Powers the H2o Pump, Steam Engine

[digitaldc]

How about recycling the gathered water back to the steam engine with energy collected by solar roof shingles [oksolar.com], then you have both heat and light-powered A/C.

This house [oksolar.com] would be the best of both worlds.

Re:Just use solar already...

[Alioth]

I'm afraid it's a bit naive to think you can pay a lot for solar and forget about it.

The panels eventually do fail/wear out. They do last a long time - most are guaranteed to still produce 80% of their rated output when 25 years old. Cells will fail and will need replacing from time to time, and will be expensive to do. So you have to *keep* paying a lot time and time again. Also, you need somewhere to store the energy for later - home energy usage is pretty much the exact inverse of when the most solar radiation is available - where I live, you need the most electricity in the winter when it doesn't get light till 9am and is dark by 4pm - so you need to store the power during the day for your peak night time usage. The most cost effective way of doing this currently is deep cycle lead acid batteries (since you don't care about weight as it's in a building). Try pricing up enough lead acid batteries to be able to get you through a week of shitty, dark, rainy winter weather just when you need the power the most. Then realise you'll probably have to replace the whole set of batteries every 8 years (and that's optimistic). And factor in the energy cost to make and (preferably recycle) those batteries.

Solar is fine for running small things; I am considering it for running outside lighting and things like the pond pump - the whole thing only needs one 120W panel and a leisure battery, inverter and controller - and in the winter time when the solar energy isn't very abundant, I'm hardly going to need the power anyway. However, for serious microgeneration, at the current time the only halfway practical and affordable renewable energy source is wind, which is vastly cheaper - and when you need the power most, it also tends to be windy, so the energy availability actually matches domestic energy usage much better. Wind also has a much better energy payoff. The energy to make a typical wind turbine is generated by the turbine over a period of six months - it's more like 6 years for solar. Unless photo voltaic solar becomes vastly cheaper, it's simply a non-contender except for novelty value, even if you live in the desert.

Re:Only solves 50% of the problem

[Fordiman]

I don't get how this works without bleeding the efficiency of the systems it draws from.

I don't see what's wrong with having a parabolic mirror concentrate sunlight on the hot side, and running the cool side through a finned radiator, and blowing ambient air through it (mounted under the mirror to take advantage of its shade would be most efficient, I think). You could go stirling (more efficient, lower speed) or turbine (less efficient, higher speed) that way.

I wouldn't be worried about night-time or cloudy-day stuff. Electrical use is highest when the sun is beatin'est.

Re:You're not using your head

[Don853]

I don't know where in Pennsylvania you live. I grew up in the middle of the state (out in a podunk town past Gettysburg, if it makes any difference), and for the 21 years I was there, 100 degrees happened an average of maybe twice a year, and 0 degrees less often than that. Granted, 0 is a lot more common in say, the Allegheny forest, but 100 isn't. In terms of temperature change, the Mid-Atlantic is far less extreme than the plains states.

And this is totally trivial, but it's a peeve of mine: 90 degrees and 80% relative humidity is an 83 degree dewpoint, which never happens in this area of the country. Maybe the Amazon basin. The hyperbole scales badly from there.

Re:Only solves 50% of the problem

[AnotherBlackHat]

There just isn't enough energy hitting the roof of even a moderate office block to power the aircon irrespective of the price of solar cells. Energy from the sun totals about 1kW per sq m. Look at amount of unused space on the roof most office blocks. The amount of power you can generate simply isn't enough to power the aircon even if solar cells were 100% efficient. Even the best solar cell is 20% efficient and that drops with time (not counting the fact that huge amounts of power go into making a solar cell int he first place).

Solar cells have a loooooong way to go before they are worth it. Wind turbines on the other hand are nearly there.

The colo facility my servers are in has about 5,000 square meters of roof space, of which more than 50% is unused.
2,500 square meters = 2.5 megawatts at 100% efficiency, or more than twice the power used.

Data centers aren't typical though, a more typical business uses less than 100 watts per square meter of office space.
Without bothering to post the details, the breakdown point is about two stories, buildings taller than that don't get enough sunlight to completely power themselves, though if all you wanted to run was the air conditioning you could probably go taller.

All of which is irrelevant.
Solar cells on the roof are worth it when they generate more electricity than it costs to put them there.
Whether that's 100%, 50%, or 2% of the total amount of electricity consumed by the building doesn't matter.
You don't have to run all the air conditioning off solar, you can have a mix of conventional and nonconventional technology.
The "magic" price point is a dollar a watt, which we aren't at yet, but we are close. ($3 a watt is the cheapest I've seen)
And more importantly, it's likely that we will have some fundamental improvements in solar cell technology, like cheap Gratzel cells.
Wind turbans on the other hand are are very old technology.
There have been some improvements, but they nearly as cheap today as they will ever be.
The only real "improvement" is that the price of alternatives is going up.

-- Should you believe authority without question?

Re:Only solves 50% of the problem

[bhiestand]

It would be nice, except for the cost. I bet a 120 watt solar panel costs around AU$1000 in volume. Even in a sunny place you're going to want at the bare minimum 10 of those panels per kilowatt you need, so by the time you're done you're going to be spending $200,000 on solar panels to run your house.

Nice to know you pulled a nice round number out of your ass. I know a small CNC machine shop (think several large computerized cutting machines constantly running), complete with air con at 74 degrees and several computer workstations on 12+ hours per day that runs entirely off of solar. The whole system cost around $40,000 before tax rebates, if I remember right. During the summer months the meter actually rolls back (it's on the grid), so that the net electricity bill is essentially nill.

Re:Just use solar already...

[Bryansix]

Solar obviously does not make sense for everyone. However it makes complete sense for people in the Los Angeles area of California. The reasons are various. First of all most energy usage is in the Summer when solar energy is abundant. Secondly there is plenty of time when the sun shines here and we have many more sunny days then overcast or stormy days. Thirdly, Southern California Edison has a program to interconnect solar panels to their energy grid. In essence wehn you generate electricity you spin your meter backwards. This means they have to buy less power from outside sources and this saves them money too and no batteries are involved. If you need power at night, you are still connected to the grid. Most estimates say that it will take about 19 years to pay off a solar panel installation. However power prices have risen since those estimates where made and they will most likely rise again. The point is that solar not only pays for itself but it adds clean energy to the grid and bypasses most of the distribution associated with large power plants thereby cutting those costs as well. All of society as a result benefits. Solar is not just a novelty.

Radioisotope thermoelectric generators (RTGs)

[ElliotLee]

Can we harness a technology similar to RTGs for the consumer market? RTGs last for a long, long time: 10 to 20 years or more. They're currently used in spaceflight, and have been used by the Apollo lunar landings, the Viking Landers, the Voyager explorations, and, of course, Cassini. RTGs are not nuclear reactors, have no moving parts, and use neither fission nor fusion. The heat generated by the natural radioactive decay of plutonium, mostly Pu-238 (a non-weaponsgrade isotope), is changed into electricity by solid-state thermoelectric converters. Would it be possible to generate electricity from other sources of heat, too (such as the sun, described in this article)? On Cassini, Power and Pyrotechnic Subsystem (PPS) provided a regulated 30V DC electrical power to the spacecraft, derived from the three RTGs onboard. It is then conditioned and distributed to the powered spacecraft components. RTGs don't provide a lot of power at once, but they provide it for a long time. But they're designed to last for many, many years. If the timespan were shortened, could they generate more power?

Re:Just use solar already...

[WeAreAllDoomed]

buckminster fuller suggested putting a windmill on basically every existing high tension line tower.

they're an eyesore already, and the generated electricity can be transferred directly to to grid. (supplementally, of course).

Re:our galactic stone-age

[thealsir]

I have an idea: Peer to peer power. The power company subsidizes some of the cost of installing a solar panel on people's homes, and in turn, power can be shared home-to-home. The power company wins, because they do not have as much load on their plants and can power more area with fewer plants. The people win because they have a more stable energy supply (not reliant on one/few sources). Financially, I'm sure it could be made so that people pay less for power bills and get more reliable power. The company will still have more money than they did before to invest in new plants and power more area with the same number of plants.