One of the annoying arguments against solar and wind power is "intermittency" -- the fact that the sun doesn't always shine, and the wind doesn't always blow. This allegedly proves that solar and wind can't be anything more than add-ons to a more reliable coal-based grid.
I say "annoying" because I don't have a solid, easy comeback. But it something about it sticks in my craw.
The obvious way to address the problem would be storage -- store the energy and use it when the sun/wind isn't "on." But store it how? If we ever produced electric cars, or even plug-in hybrids, the batteries therein could be used as a kind of distributed storage, feeding into the grid when circumstances require it. Or we could develop industrial-scale batteries. I've heard some interesting stuff about using methanol to store the energy. And of course there's always hydrogen fuel cells.
Robert Rapier discusses storing wind energy as compressed air, based on this MSNBC story. Sounds promising to me.
Anybody out there know more about this stuff? What's the best way to overcome intermittency?
Comments
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david anderson Posted 8:43 am
15 May 2006
In fact, there is significant value in having a solar boost on the grid. Solar produces power during the times when the power demands are the highest, hot weather when people are at work and cranking up their AC.
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David Roberts Posted 8:53 am
15 May 2006
Of course, as you wisely point out, that time is a long way off.
www.grist.org
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greenstork Posted 9:07 am
15 May 2006
Solar and wind also tend to compliment each other. It's typically windier when the sun isn't shining due to storms and such but there is no perfect inverse correlation unfortunately.
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Kif Scheuer Posted 11:36 am
15 May 2006
What I'm thinking is that wind is intermittant but not consistantly intermittant. If wind is down somewhere it is likely be up somewhere else. You don't have the constant supply in individual locations, but spread out enough windmills and can't you make your overall supply consistent? Not sure if this would apply to solar.
Of course this is in way off time when wind power is cheap enough (and politically digestable enough) to be all over.
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sunflower Posted 2:08 pm
15 May 2006
The first rule is look at end-energy use before looking at sources. The second rule is to follow the path of least cost energy sources. Conservation (efficiency) is an energy source. The third rule is do not make solar in the image of nuclear. Then, in 1986, OPEC (Saudi Arabia) ended the oil embargo and the party was over, everybody went home.
The near-future major end-energy use is heat. The expectation is that coal will make power for heat and hot water when natural gas and oil become too expensive and too valuable for making fertilizer and for fueling transportation therefore gas and oil should not be used for heat and for power plants. In the 1970s a law was passed that made natural gas power plants illegal. People were retrofitting their trucks with natural gas tanks. Solar energy was used for heat and hot water, not electricity. Today solar energy roof top pv making electricity is the most expensive and least efficient method of collecting solar energy, and makes little sense when that power is to be used for heat and hot water. Solar displacement of electricity is 2000% more cost effective than solar production of electricity. Energy metrics is months instead of years.
Home storage of solar heat was good for only up to 40% of home heat requirements. Then a breakthrough was invented in Sweden, "seasonal heat storage". They were able to store heat for one year at 90% efficiency at very low cost. They punched holes in the ground with a well drilling truck 30 meters deep every 2 meters over one to a few acres, dropped 2 cm pvc loops into the ground, then pulled up the well casings allowing the dirt or clay to collapse around the pipe. Ground mounted flat plate solar thermal collectors transferred the solar heat into the ground during the summer and this heat was recovered during the winter to heat whole communities, making those communities 100% solar heat self sufficient. Large volume to storage boundary area ratios made this system very efficient for thousands of homes and apartments. This does not work well for small groups and not at all for individual homes. District heating also has the advantage of collecting industrial waste heat and can use central heating plants that burn anything including crop and wood waste. Solar collector fields and central heating plants were located tens of kilometers outside of town. The Swedish objective was to shut coal power plants down. International conferences were held on just seasonal heat storage in Europe, Toronto, and Seattle. Those were exciting times. Now, back to the future...
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amazingdrx Posted 3:29 pm
15 May 2006
How? Well by charging the batteries in off peak situations, at lower off peak rates, then selling the power back onto the grid at peak rates, or using that power at peak rate times, signifigant reduction in power bills could be realized.
Enough to pay for these storage systems in a few years. Then adding solar and wind to these homes and businesses would increase the cost advantage from there.
These fixed batteries would not need to be the expensive hitech batteries for vehicle use either. And this gives individual homes, neighborhoods, and whole regions autonomy from the grid in storm emergencies, which would pay off big time in staving off the economic damage from lost business during the ever more frequent and severe storm outages.
Distributed storage pays for itself in so many ways and makes renewable power easier to use in a cost effective manner for homeowners and small businesses, as well as buffering intermittency from large scale installations.
http://amazngdrx.blogharbor.com/blog
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caniscandida Posted 7:51 pm
15 May 2006
What is the story with developing geo-thermal energy sources? You would think there is no problem with intermittency there either. My understanding is that that will turn out to be the most reliable renewable source of energy -- or better, self-replenishing source -- of all the current options. But what is holding up the development of it?
Kif, you are quite right that no wind here usually means yes wind there. Still, as satisfactory and promising as wind farms have been thus far, given modest expectations, I cannot help but feel they are not the way to go. There is the fact that they require a lot of dedicated acreage; bird mortality may not usually be a considerable problem, but in some places it might be; the matter of aesthetics is relative, but will always be an issue if the wind turbines are in view, as they would be in the Cape Wind project. None of these quibbles is a mortal blow, and even taken together they do not amount to one; and so I remain a supporter of wind energy development. Nevertheless, I cannot help feeling that wind will never be the ideal replacement, which David is searching for, for the non-self-replenishing fossil fuels that we are "addicted" to.
Another self-replenishing source that should not be troubled by intermittency is ocean tides. Presumably the principle by which energy is collected is the same as in medieval river mills and wind mills, and modern hydro-electric dams; but hopefully the physical mechanism, the "footprint," would be much smaller and less intrusive. But in fact I suspect a good amount of ocean volume, including a certain surface area plus a certain volume beneath, might be required. Anyway, this sounds promising.
Sunflower, what you are describing of the Swedish project sounds terrific. Is something that like being tried out in the US? Is it a problem that Sweden lies at latitudes rather higher than the continental US?
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Icelander Posted 11:48 pm
15 May 2006
But I do have enough room in my basement for a battery or fuel cell system that can store energy, but I'm pretty sure the folks who rent won't be able to put a system like that in their houses.
Perhaps a better system for city dwellers like me, aside from taking up more space to keep cars, is to make PHEVs part of a car sharing program within the city. Unfortunately, a small city like mine probably doesn't have the market for a car sharing program to be successful.
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sunflower Posted 12:41 am
16 May 2006
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amazingdrx Posted 4:08 am
16 May 2006
I have checked into thermocouples and sealed systems that recycle a refrigerant type fluid through a turbine. These are just not cost effective compared to wind due to low efficiency, deep drilling, and complexity.
A 50% efficient thermocouple would really make geothermal fly though. I have seen rumors of inventions like this using altrernating current somehow in the thermocouple.
But the real practical, immediate use of geothermal is very promising. Ground heat/cold is used for leating and cooling buildings with either direct heat transfer through simple circulation or using heat pumps where the heat difference is too great. Bush has a geothermal heat pump on his ranch, along with solar PV.
Geothermal heat pump heating/cooling and direct circulation cooling has the potential of eliminating all combustion to heat homes and buildings and reduce the energy used for air conditioning to maybe 20% of what it is now.
In areas where temps reach 95-100 degrees in cooling season, direct transfer of 55 degree ground coolness can do the job og an enerfy wasting air conditioner with a very low power circulating pump.
Think of all the fuel oil, natural gas, and electricity saved. Air conditioning is what causes grid failures, it's a HUGE load. Geothermal has truly awesome potential in this role of heating/cooling, as well as industrial processing normally done with combustion.
http://amazngdrx.blogharbor.com/blog
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caniscandida Posted 6:37 am
16 May 2006
One wonders what goes through the head of the owner of that ranch in Crawford, when he shows off his geothermal heat pump. Is it unfair to suspect it probably never occurred to him on his own to install it?
Anyway, I quite appreciate that sending a stable energy-collection facility down into Mount Saint Helen's would be a rather daunting engineering task. Science-fiction authors at least might have some success there. But I hope you see what I have in mind.
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