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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?"
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.
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58f = 14.4C or 287.6K
Now lets be generous and let our panel "superheat" the stuff up to 80C or so, and put the cold reservoir in a bucket of ice.
That gives us a heat source at 353.15K and a sink at 273.15.
Efficiency = 1.0 - cold/hot = 1.0 - (273.15/353.15) = 0.226, or about 23% efficient.
Not great.
~5% efficiency.
what's wrong with a reflective dish and a stirling engine, anyways? much higher efficiency, materials aren't as expensive as solar panels and not nearly as bad for the environment.
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Is this the MPAA? Is this the RIAA? Is this the DMCA? I thought it was the USA!
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
I guess you're making a perpetual motion joke, but the strange thing is it's not a daft as it sounds.
You could have an electrically powered heat pump to pump heat into the ground in summer, and back out again in winter.
http://www.igshpa.okstate.edu/geothermal/geotherm
Very popular here in Sweden.
If you insulate your house enough, the energy required to heat or cool it is pretty minimal, so you could generate it from solar panels, at least in the summer. And heat pumps are 3 to 4 times more than resistive electric heaters.
As wikipedia puts it
http://en.wikipedia.org/wiki/Heat_pump
When used for heating on a mild day, a typical heat pump has a COP of three to four, whereas a typical resistive electric heater has a COP of one. That is, one joule of electrical energy will cause a conventional heater to give off one joule of warmth, while under ideal conditions, one joule of electrical energy can cause a heat pump to move more than one joule of heat from a cooler place to a warmer place. Sometimes this is expressed as an efficiency value greater than 100%, as in the statement, "XYZ brand heat pumps operate at up to 400% efficiency!" This is not quite accurate, since the work does not make heat, but moves existing heat "upstream". This does not violate the second law of thermodynamics, because it takes less work to move the heat than to make the heat.
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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.
Energy is being extracted from the fluid circuit system and being converted into electricity. Steam re-condenses into fluid because it has lost it's energy to the turbine.
No perpetual motion or violation of the laws of thermodynamics involved, just energy transfer.
Then again, I could be wrong.
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
This is progress?
it very clearly states in the animation at the company's website that ambient air temp is sufficient to cool it back down. You seem to be forgetting that those big black panels on rooftops that heat water using the sun's solar energy heat the water up to a much higher temperature than the ambient air is. What exactly would be the point of a solar water heater if it only gave you water that was the temperature of the ambient air? Anyway, so, you use that heat source to boil the liquid in the closed circuit. Don't forget, it ain't water. It's some liquid that boils at a pretty low temp. And then you use the ambient air for the heat exchanger to cool the 'steam' in the closed circuit back down, condense, and start all over again. So, from what I gather the only requirement for this to work is that the boiling point of the liquid in the closed circuit needs to be higher than the ambient air temp, and lower than the temp you can achieve from a device similar to / same as those rooftop solar water heaters. Then you should have no problem boiling or condensing that liquid, since you have the capability of getting the substance up to the boiling temp, and back down below that temp so it condenses again.
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.
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You're talking about getting off the grid entirely, it seems. Where I live, the power company is required by law to purchase any excess electricity you put back on the grid. So, no need to store your home generated electricity with batteries.
Depending on how expensive electricity gets in the near future, solar panels to supplement what one takes off the grid might make the whole thing economically viable. Combine this with tax credits and suddenly it doesn't seem so expensive.
Not all places are equally windy. Where I live, we get a good deal more sunshine than we do wind. Wind power wouldn't work for me.
It's not offtopic, dumbass. It's orthogonal.
... by planting Trees nearby. Their shade keeps your house cool, all trees produce fuel for the winter, and if you choose the right varieties they deliver free organic fruit. You'll save power by not having to run your air conditioner so much. Why must some engineers make things difficult for themselves?
Reduce, reuse, cycle
I bet you wouldn't mind looking at the windmills if I put some porn on them. Eh. You like that. I bet you do. You so dirty.
Can I bum a sig?
Anyone else confirm this (or, prove yet again, that I'm talking out of my arse?)
I don't know about that, but I've just thought of a great place to put a wind turbine.