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Ask WorldChanging: Antarctic Solar?
Alex Steffen, 30 Apr 05

Our buddy and ally, noted polar explorer Ben Saunders, finds himself with a bit of a green design challenge on his hands, and he's hoping we can help.

Specifically: in October, Ben will be launching a four-month, 1,800-mile human-powered expedition across Antarctica -- the longest unsupported polar journey in history.

Given that polar ecosystems are taking a hell of beating because of climate change, Ben would like to make that expedition as green as possible. We're kicking around some ideas about climate-neutralizing his travel and so forth, but what he really needs is help thinking through how to make use of the South Pole's cold temperatures and abundant sunlight to harness solar energy.

Here's how he puts it:

All polar expeditions use some variation of the MSR XGK stove system, powered by white gas or petrol, to turn snow into hot water. This means that manhauling expeditions in polar regions use almost as much fuel per mile travelled as a Toyota Prius.

We want to find another way to melt snow using the 24-hour sunlight that Antarctica provides. We envision a container/bag made of flexible material (possibly Aerogel to insulate it against the outside ambient temperature) containing or surrounded by some kind of heating element/wire/skin that we could fill with snow when we get in our tent in the evening and let slowly heat up until we need it in the morning. Alternatively, could we have one large slow heater to melt snow to water over night and then one small but powerful heater that could boil small amounts when we need it.

Our biggest limitation is the low number of amps that solar power provides. We have been looking at Iowa thin film technology Powerfilm R15-1200 which at 0.88kg (1.9lb) generates 1.2 Amps. It is possible to daisychain a number of these to get up to 20 amps, but the fewer we can use the better. So in essence we are looking for a large capacity, low-amp ultra-efficient kettle!

Parameters:

* We need to create 12 litres of water per day;
* Eight litres water are used in the morning, of which four litres need to be as hot as possible;
* Volume ratio of snow to water at the South Pole is 3.71:1;
* Ambient temperature down to -40?C [brrrr... - ed]
* 24-hour sunlight;
* hours in tent when solar panels can be used: 12-14;
* Sledge dimensions 230cm x 60cm
* Tent living area = 230cm x 170cm
* Two tent vestibules = 110cm x 170cm each (most likely place(s) for snow melter(s)
* Equipment must be as light as possible;
* Must be durable enough to stand four months of heavy use and abuse in extreme cold.

A further idea we'd had was to have flexible PV panels on the sledges during the day that could a) trickle charge a battery pack and b) keep hot drinks warm, perhaps using some kind of electrically-powered vacuum flask?! This would negate the need for us to produce boiling water in the morning -- we'd need only to heat it to a 'hot' drinking temperature (a huge energy savings).

I'd love to hear all your ideas, and any specific connections to people/companies/organisations that have the knowledge and facilities to produce prototypes would be invaluable. It'd be fun to have all the ideas running through the comments on WorldChanging, so everyone can help think them through. Thanks for helping out!!

So, what do you say, Worldchangers? Can we help Ben think through the challenges of launching as brightly green a polar expedition as possible?

Let's do some brainstorming in the comments...

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Comments

PV is going to be expensive and relatively inefficient. Why not use a mirror array? Mylar foil mounted on a tough backing will be lightweight and plenty reflective, and the efficiecy of light -> heat will be better than light -> electricity (losing ~80%) -> heat.

Just a thought.


Posted by: Noah Iliinsky on 30 Apr 05

Ooo, I hadn't thought of that. What do folks think? Other ideas?


Posted by: Alex Steffen on 30 Apr 05

Actually, I was going to say the exact same thing Noah did. For melting snow, you could use simple box-cookers (like http://solarcooking.org/plans.htm#panel-style ), and for boiling water you could use parabolic cookers (like http://solarcooking.org/plans.htm#parabolic-style ).

The anarctic versions will need better insulation, but that's not difficult. The only challenge will be to have such structures survive high winds and other adverse conditions. Perhaps the box-cooker would need to be built wide and flat and staked down to the ground (like solar-hot-water-heating coils on a rooftop).


Posted by: Jeremy Faludi on 30 Apr 05

To what degree would the insulation and strength requirements make it difficult to transport, do you think? How would you get around those difficulties?

Other ideas?


Posted by: Alex Steffen on 30 Apr 05

I agree that PV and batteries are costly, bulky, and will have too much transfer and storage loss. Why not go straight to solar thermal? Evacuated tube solar collectors are tremendously effective at heating water in direct sun, and are certainly more compact than concentrated mirror solutions. Your challenges are A) protecting the tubes from damage and B) choosing a portable heat storage medium(if needed).

I am familiar with two companies--Schott and Viessmann--that make evacuated tube solutions for building use. However, you might want to call them or investigate solutions that are more durable and compact. As far as heat storage goes, a quick Google search of 'efficient thermal storage' reveals something called a "Hot Box"...this could be a gimmick or perhaps something useful. The key is to steer clear of cumbersome and energy-intensive heat storage solutions such as water tanks or concrete/stone.

Good luck!


Posted by: Andrew Lee on 30 Apr 05

You might want to check some of the products here.

http://www.cleardomesolar.com/

The SolaReflex 900 works well if the sun is not directly over head, so it should work well in Antartica. And you might want to see if you can get them to let you use the SolaReflex 900X which generates a 1300 degrees F hot spot that should melt some snow and even provide you with boiling water. Note that I have the SolaReflex 900 and, while the hotspot gets to 900 F, I can only get a pot of water up to around 180-200 F in about 35 minutes. I am not sure how it would do in strong winds and you would have to get their heat containers to keep the heat in in the cold temps. or use clear plastic oven bags. The stand that comes with it breaks down for travel and shipping. It weighs 8.5 lbs. However, at 24 inches in diameter 60.96 cm it might be slightly too big for the sledge. unless there is some wiggle room?


Posted by: Tavita on 30 Apr 05

For insulation, I wonder whether radiative insulation like mylar "Space blankets" would be useful in Antarctic conditions.

Certainly, direct solar is well worth thinking about before PV. I had a small parabolic dish out the other day at MIT and the focus redlined an oven thermometer at over 600 degrees F, 315 degrees C, in less than a minute on a 60 degree F, intermittently rainy day at MIT.


Posted by: gmoke on 30 Apr 05

Wow - an interesting (collective) train of thought - thank you all for your input!

I think we'd briefly discussd the idea of parabolic heaters, but we we saw wind stability and the need to reposition the heater to follow the sun (every 30 mins or so?) as two challenges (we were thinking of leaving it up 'overnight' - there will be 24-hour sunlight for much of our journey).

Any thoughts on ways around this?

I had no idea quite how efficient parabolic reflectors were - the Cleardome website specifically mentions melting 'five gallons of snow during the midday sun'. Hmm...

(Alex, thanks once again for throwing this open to your readership - Tony and I have talked about running this project as much as possible as an 'open source' expedition and the feedback we're getting here already (at the weekend!) is fantastic.)


Posted by: Ben Saunders on 30 Apr 05

Solar may not be feasible for the reasons above, but wind is a certain alternative. The generator could be outside, while the heating / melting unit inside the tent / shelter, which is easier to insulate for maximum effect. If you do go down and it does work, please post something on the news section of the Antarctic News service www.70south.com/news/


Posted by: Brendon Grunewald on 1 May 05

batteries don't work well when cold. i'd recommend a cross between an evacuated tube, parabolic cooker & a standard vacuum thermos.
an oversized thermos clear on one side, reflective on the inner side of the other and the center water/snow container part black. stuff it with hard packed snow & set it in the sun with the clear side facing the sun. when the sun is out heat will be added when it's not the water will be kept warm by the thermos. the top should have a mini pressure relief valve since i'd imagine that this thing would work really well.


Posted by: karl on 1 May 05

possible of some use to your project.
This article define the "BASF Develops Temperature Adjusting Material That
Boosts Energy Efficiency in Buildings".

The following is from the Business for Social Responsibility www.bsr.org
website:
http://www.bsr.org/CSRResources/News/news.cfm?DocumentID=50938


Posted by: J. Papp on 1 May 05

What about a *passive parasitic hybrid* solution. Let's divide the challenge into two. Making water and boiling water.

Since you have the advantage of time, you mentioned 12-14 hours, to make water you can do it slowly.

Collecting condensation on the inside of the tent. How about a system that promotes condensation and directs it to a collection system? Maybe a snow filled bag that hangs form the top of the tent. Heat rises, capture it before it is dissipated to the external environment.

Using thermal waste from the body during sleep. A sleeping bag that is so well insulated that it needs to be cooled? Heat and moisture exhaled while on the move might also be captured. Look at what you are already 'have' to carry. How could it be modified to help melt snow.

If possible avoid one single solution. Look for a collection of small robust 'parasitic' solutions. That way when a failure occurs you don't lose the whole system you only lose a percentage of it. Having made water is the first step. The second one is more difficult, boiling water.

I don't think you will be able to beat a fuel (petrochemical or natural) when it comes to weight. The amount of energy per cubic inch is just to high to be ignored. The trick is to be frugal and only use it when you have to. Systems like those described above will help reduce the amount of fuel you will need to carry.

Manufacturers incorporating such "passive parasitic" technology into their products would have a competitive edge. "Our jacket makes 2 liters a day", "Our new 2 man tent makes 8 liter of water in 12 hours at 50 below". I know it sounds funny but remember adds for wicking fabrics that "keep you dry all day".

Paolo


Posted by: Paolo on 1 May 05

This is off the cuff, but I imagine a solar cooking box like those mentioned above with black tubes filled with melting snow inside a clear-topped box lined with aerogel. Would the aerogel let in enough light to heat the tubes while not letting the heat back out? The pictures I've seen show aerogel as fairly translucent, but would some necessary part of the spectrum be stopped by the aerogel itself? Hmm. Dunno.

If it worked you could have several tubes going at once, and cycle them, the hottest having been in the longest, the next almost ready to go, etc.


Posted by: Jeff Rusch on 1 May 05

One possible way to deal with the sun tracking problem is to use the vacuum solar tubes; since they are round the sun is always striking some part of them directly. An example of such tubes can be found at

http://www.metaefficient.com/metaefficient/archives/hot-water-systems/solar-tubes-very-efficient-heating.html

I do not know if there are versions small enough or sturdy enough to handle the trip.

Also, even though PV solar has problems there might be a way to use it. There are solar bags on the market, see,

http://www.csmonitor.com/2005/0421/p14s01-sten.html

http://www.treehugger.com/files/2005/04/reware_solar_ju.php

So what if one created a solar tent? Where the entire tent is a flexible PV panel. That solves the sun tracking problem. And if the panel power can go directly to a heating element to melt snow there would be no need for heavy batteries (remember 24 hour sun). The question would be (other than cost); would the sun exposed side of the PV tent generate enough power to get a heating element hot enoiugh to melt enough snow while our explorers sleep?. I do not know enough to answer that question, but perhaps someone out there can?


Posted by: Tavita on 2 May 05

There's a real mass and energy problem here. Data from 4 Antarctic stations show an average daily solar potential of about 2.4 kWh per M2 on a horizontal surface; make that perhaps 3.0 kWh for a fixed surface at a 60° angle, faced solar North, under the best conditions. Collection time is about half a day - a generous estimate of energy available is then about 1.5 kWh/M2. If you use PV's to make electricity, then back to heat, you'll only capture about 10% of that. Much better to use solar thermal. Heat loss is a real problem, but let's set that aside for now. The 1.5 kWh/M2 potential is about 860 kcal, or enough to raise 12 liters of liquid water about 72°C. Trouble is, you'll start with snow, and it takes a LOT of energy to change solid water to liquid - 80 kcal per liter to melt ice to liquid water. So to thaw 12 liters of ice (or water equivalent frozen in snow?) takes 960 kcal. That's before you begin to raise the temperature. And this is not factoring in any heat loss during solar collection.

I think you may need to consider using some fossil fuel. But, if you can use solar collection to melt snow into cold water, the amount of fuel you'll need then to warm the water will be far less.


Posted by: David Foley on 2 May 05

Great comments, everyone!

Keep 'em coming...


Posted by: Alex Steffen on 3 May 05

OK. You need a watertight container with surface area, conductive, able to be painted black to absorb sunlight, with an accessible opening so you can stuff snow into it. I'm thinking of an "ammo box," such as:

http://www.galleria-e.com/cgi-bin/Colemans.storefront/en/product/220501

Still thinking about how to deploy these inside a light, strong, efficient solar collector.


Posted by: David Foley on 3 May 05

Have you heard of Thermo-Acoustics ? There's some research about turning sound into heat or cold using a speaker producing sound waves within pressurized pipes. So somehow contain the pipes within a cooler or thermos and have the sun power the speakers.

Jack


Posted by: Jack Sam on 4 May 05

As Alex said, this is all fantastic stuff. My apologies for not being more involved in the conversation - we've been taking all of this fantastic information and trying to come up with a system to test in Greenland (in ten days' time!)

The people at ClearDome Solar (http://www.cleardomesolar.com/) have been immensely helpful and the potential of direct solar energy. I'll keep you posted!!


Posted by: Ben Saunders on 4 May 05

Sounds like a combination of the dual-mirror 900X box heater from Clear Dome Solar with some thin-film PV's for battery-operated heat may be the way to go, given the needs you have, which are durability, simplicity, reliability.

1. You have to set the whole system up quickly in windy conditions wearing gloves.

2. You don't have the ability to be perfect.

3. You don't have a chance to be delicate.

Thin-film PV's are the way to go for portable field-based electrical charging. They're used in Afganistan and Iraq by US special forces.


Posted by: Michael Slavitch on 4 May 05

Oh, and as aside, using propelyne glycol in a pipe as a heating medium towards an insulated container may be a constructive way of moving heat efficiently.

An insulated tub with a tube going to a central small node (heating object) that contains prop glycol would carry heat well, however it would need a pump, which may not help. This wouldn't be truly reliable unless you could somehow use convection to move the fluid.


Posted by: Michael Slavitch on 4 May 05

This'll be heavy...

What about a stirling engine? The big problem with stirling engines is the cold cycle, but you'll be in a permanent cold cycle, you could use a solar cell to power a heater for the warm cycle, and then hook up the spinning arm to a standard car alternator and go electric, electric stove, lights etc...


Posted by: christian on 5 May 05

I have two quick ideas. One is some variation on the 'Kelly Kettle' which essentially is a water jacketed stovepipe. Increase the surface area to suck every last bit of heat from the collector/generator into the snow/water.

The second is a little dreamy. If parabolic mirrors are too unstable in the wind (and a tent-pole and mylar array was my first idea, too) then how about a refractive tent fabric. Use the strong dome of the expedition tent as a lens, and bend the light inside to focus on a pot of snow ( or better, a column of snow that feeds the pot as it melts).


Posted by: Ruben Anderson on 5 May 05

Open the door to the boxed minds and return from hi-tech to a direct approach utilizing the calories in food.
A large flattened pouch is filled with snow when strenous activity is begun. This is hung from neck in area of waist so that when garments are opened to prevent sweating, a no-no in cold climates, this absorbs excess body heat being vented.

No, not directly next to skin. Even us Norski's wouldn't be happy with that! A bit of thought will produce the needed container.


Posted by: James Marple on 6 May 05

Two part solution:

1. Preheat the water using solar - this just melts the snow. Really CHEAP. Basically a solar shower bag (black plastic) filled with snow is placed onto a closed cell foam pad that has a clear sheet of plastic duct taped to the top (leave some slack). Insert some coat hanger wire to keep the clear plastic suspended above the black plastic bag. You can adjust the amount of snow you shove into the black plastic bag so almost all of it melts. This gets you the most water possible and makes the heating job easy. For the real deal you can make the top clear sheet out of two layers heat sealed to one-another. If you put in an inflation valve and make the top sheet slightly larger you can inflate the space between the two sheets and skip the coat hangers. Then this whole assembly can roll up compactly during the day. Just unroll, inflate and stuff with snow, stake it down and go to bed.

2. Use that MSR XGK stove with biodiesel. It is already CO2 neutral. Because of the cold you will need to add a GOOD antigel additive but there are many on the market - some of the ones advertised for biodiesel claim environmentally friendly manufacturing. Optionally you can run the stove on pure grain alcohol. It will light easier and has additional uses over biodiesel but contains less energy per unit of fuel. You can test the biodiesel and antigel additive if you have access to a good freezer and some dry ice - just adjust to the expected temperatures.

Good luck on your trip.

Jason


Posted by: Jason Quinn on 6 May 05

You could consder using portable fuel cells.

You could even prepare the hydrogen ahead of time using renewable energy - even though the conversion efficiencies are poor - at least you wouldn't be lugging and burning fossil fuels on the trip.

It seems to me that rigging up a solar still, or a solar oven should be doable, even in the wind and cold.

I spent some time in the arctic and recall that the sun never does come up very high (15 or 20 degrees). It circles around 360 degrees (in my case with a slight dip in the south). You should keep this in mind when considering solar oven geometries.

One good thing is that if you are past the tundra and out on the snow and ice, you'll have a lot of reflected solar light because everything will be fairly white.

I never tried using solar thermal when I was up north, but it seems to me in hindsight that it would be worth trying.

(Note that I was not on an expidition, but rather stationed that far north in the military for a short time.)

Even small wind turbines made with composite carbon blades (which are very light) and a composite carbon tower, would still require a very heavy generator/alternator (with current technology) to produce any measurable power. I think you'd have to rule that out unless you were planning on staying in one spot for a long time.

I think exploring fuel cell technology would be worth while. I'm sorry I don't have any good links off of the top of my head here...

Good luck!


Posted by: Rick on 6 May 05

I think Jason Quinn is on the right track. I question filling solar showers directly with snow, using gloved hands. But why not make a "solar shower" like container? I'd still vote for the black-painted ammo boxes. Simple, waterproof, dirt cheap, meets the need. Once filled, place inside a "pillow" with clear vinyl on top, black vinyl in the back. The fastening system could be zippers or velcro. The insulation behind the black vinyl could be a modified down sleeping bag. It would be possible to use cords to fasten this to the sides of your tent or tent vestibules. It's low-tech, but I think it would work. This would be just to melt snow - which is the heavy lifting part of the mass and energy problem. After that, a biodiesel stove may work, if you can keep the biodiesel from gelling. I also don't know if you can use diesel in your circumstances without risk to your lungs from particulates.

If you can make a rectangular "chimney," into which you can place the ammo box, so heat convected from the stove below passes over the entire surface of the ammo box, you'll have very efficient heat transfer. The "chimney" could be dual-wall sheet metal, with a high-temperature insulation called "Fiberfrax" in between. You can get "Fiberfrax" from ceramics supply stores.

It would be great if there were a way to post drawings here. Trying to tell, rather than show, is difficult.


Posted by: David Foley on 6 May 05



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