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Solar updraft chimneys convert warm air to electricity. Solar-heated warm air can be incredibly inexpensive with zero environmental issues.



A warm air chimney was built in Manzanares, Spain and generated 50 kilowatts every sunny day for seven years.  We know that the concept works and has few environmental issues.  Warm air isn't considered a pollutant.  Wildlife and hikers will both steer away from overly warm air and from warm objects, just as barefoot people will avoid tarred parking lot surfaces in July.

A 5,000 foot tall vertical solar chimney is incredibly expensive.  The same chimney snaking up a mountainside could be built in an appropriate technology manner.  We want an arch that lasts forever and is easily repaired after a meteor strike.

One argument against a much longer mountainside chimney is air friction.  It turns out that air friction is related to the fourth power of air velocity.  So, building an air tube 10% larger lowers air velocity, which lowers air friction dramatically.  The main remaining air friction is at the turbine.

These devices quickly scale up to the megawatt and hundred megawatt range.  A one gigawatt chimney is possible.

Wikipedia lists solar heat collection as the major cost of running a chimney.  I've discovered that the Manzanares chimney suffered from a horrible balance of system problem.  Their air friction loss at the outer edge of their solar collector field was a huge number of factors of ten lower than it needed to be. 

So, I've redesigned the heat collection field.  I use glass objects recovered from the waste stream to capture sunlight.  I don't care that much about the holes between these glass objects because I have a soft downward laminar flow of air drifting down through these holes, to the collector area, to the air tunnel system.  I don't pay that much per square foot of collector.  To be more particular, I don't pay that much per acre of collector.  At these prices, the cost per therm of raw energy drops into the pennies range.  Natural gas heat costs dollars and raw solar heat costs pennies.  Guess which energy source is about to win this race outright?

Category of the action

Reducing emissions from electric power sector.

What actions do you propose?

I need to pull together a team of engineers to handle an ARPA-Energy proof of concept grant, followed by a prototype running up Mt Wachusett, up Mt. Bromley, 8,000 feet up Charleston Peak near Las Vegas, up a mountain TBA.

I need an outdoor solar heat collection lab in a field, possibly in a parking lot or on a sturdy rooftop.  We need to optimize heat collection with the usual constraints:  maximize collection at low angles, minimize losses, store heat for evening generation, minimize losses of heat during rainstorms, channel away as much water as possible (there will be unmanageable downpours in time), store heat centrally for evening generation, keep costs low.

The second level air tunnels also gather solar heat.  We have to look at upcycled glass and aluminum roofs and at linear troughs superheating the air as it travels inward.  Most such tunnels will run east-west for best sun exposure.  Air friction losses are always in the picture.  Heat storage, either from in situ earth or from 2 inch rocks at the bottom of the air tunnels, gives the system the capacity for evening and cloudy day power generation.  It also lowers power intermittency, a classic plague of all solar and wind projects.

The main air tunnel is insulated to retain heat.  It must be built up 45 degree slopes at times, so a robotic piece-moving cable system lifting modular tunnel pieces into place will be useful during chimney assembly.  The tunnel needs to be tested outside against rot, frost and rust.  Guy wires inside and out can help hold the tunnel together.  Note the pressure gradient between outside the tunnel and inside.  We may want to paint the air tunnel to match the background as seen from the nearest populated area, a few miles away.

The top of the mountain (or a subpeak if the mountaintop is iconic) may well have a 100 foot chimney extension on top.  A canvas extension that hoists up on slow wind days and down during tornadoes is one substitute for a solidly built extension.

We need a mechanical engineer to design a turbine for 3000 cubic feet per second, about 1 psi of pressure gradient, with power dropping down by a factor of ten by midnight.  One option is several turbines for different power needs.

We need an environmental impact study.  Pulling masses of hot air out of an inland valley causes a notable loss of smog in the valley, as well as a drop in the valley's aggregate air conditioning load.  Pulling the cold air out of the bottom of a Vermont valley in January raises the temperature just a bit, reducing the valley's total heating load.  Pulling the mild air out of a valley next to a ski area on a March afternoon lowers the temperature a bit, causing a reduction in snow melt.  What if nobody ever complains?

I have my own proprietary balance of system software, yet another of my inventions.  We need to minimize our cost per kilowatt-hour.

Who will take these actions?

If Congress isn't afraid of offending the fossil fuel industry that got them all their jobs, ARPA-Energy will see the wisdom of funding this grant proposal.  Otherwise, we try major foundations for funding.

I'm fine with rocket propulsion, and warm air solar isn't rocket science.  I prefer to nudge each little known edge of solar technology forward just a bit at a time.  Most of these experiments can be performed by undergraduates under some educational supervision. 


Where will these actions be taken?

Building subsystems for proof of concept can be done in Cambridge.  A first prototype could go up Mount Wachusett or up one of many hills.  The early commercial money will construct chimneys up 5,000 foot or better mountains out west in desert climates.  Massachusetts electric generation will probably be on the Taconic Range or elsewhere in far Western Massachusetts.  East coast prime sites range from Northern New England down through Appalachia. 

How much will emissions be reduced or sequestered vs. business as usual levels?

As a ballpark figure, I see 100 gallons equivalent of electricity coming out of one gallon of oil invested.  We can replace perhaps 2/3 of all electric generation in the United States quickly and eventually as much as 90% if we work on better heat storage.   Most transit will soon become electric-powered.  We still have to solve building heat and industrial heat. 

What are other key benefits?

Runs well at night due to outside temperature drops, massive instant smog reduction because of the vacuuming effect, leading to fewer asthma deaths, lowers aggregate air conditioning costs, near-zero deleterious environmental impact, easily repaired, nothing to leak out except air, can be built with appropriate technology, build all you want, no bird kills or bat kills, kids can pretty much climb all over it (except for climbing on the electric wires), will use the waste heat from other solar plants or from other industrial facilities, attractive nuisance for hang gliding enthusiasts at the top end.  It may dump snow all over a nearby ski area in winter, depending on moisture inputs.  As such it might distill brackish water.  The chimney may act as a natural firebreak.

What are the proposal’s costs?

My overly-optimistic internal numbers say 1 cent per kilowatt-hour in 15 years.  I'll back off to 3 cents per kilowatt-hour within 10 years.

We might expect local weather disturbances.  We can build air tunnels that leap ravines for local wildlife migration.  The solar collector fields won't be producing food.

Updraft chimneys are better neighbors than, say, wind turbines, but some people still won't like them in their backyards.

Time line

If we get the next grant, we start next January.  We need to raise $200,000 of private capital by January of 2017.  We start building a prototype in 2019. 

Growth will be slow at first, then moderate, then explosive.  Climate change building on itself will only fuel the explosiveness of the changeover.  After 50 years there will be slow growth because our energy demands will have been met for the most part.

Roman arches are stable enough to have lasted 2000 years.  Our arched tunnels and our solar fields might last many decades.  The generators should wear out about every 20 years or better.

Related proposals

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U.S. Patent #8823197