Solar updraft tower
 

I'm intrigued by this idea...

http://en.wikipedia.org/wiki/Solar_updraft_tower

A German company actually built one in the 80's in Spain thats 200m tall...

http://www.sbp.de/en/html/solar/aufwindkraftwerk.html


Anyway, I'm designing a desert home and I'm trying to incorporate one that is made out of 55 gallon oil drums that would be about 45 to 50 feet tall w/ a 40' x 10' collector.

Anyone with the brains to figger out the practical possibilities of such a system mathematically is invited to comment.. please show your work ;)

the diameter of a 55 gallon drum is 23"

I'm still working on the specifics of the collector, but it would receive both direct sunlight and reflected light from the bldg in an attempt to increase the heat.

I've had the same idea,

I would use brick painted black / dark to create the chimmney, holds heat better.


Also considered mirrors around it to reflect more heat

Might be a good idea to think about the weight of each barrel. And the --- what, Young's Modulus? I forget. Anyway, under what weight will the bottom barrel deform.

Then think about wind.

Walgamuth is an architect. Bet he can steer you right.

B

Thanks Bot, I have considered the wind, but hadn't considered the weight..

a drum weighs about 40 lbs and I'd need 17 of them. The stack will not be free standing, and I believe that sufficient reinforcement could be added to the bottom barrel(s).

http://rbk3.com/sketchup/desertdwelling.jpg

Check this out.

http://www.youtube.com/watch?v=1dTt2s6YwJ8

Back in ancient times I took a calculus course in which we had to demonstrate that weight-for-weight, a cylinder is stronger than a solid column. I (mercifully) have forgotten the intricacies but I'll bet an engineer somewhere has provided, on the Internet, a method for determining the deformation of a barrel under stress in 1 direction.

The reason I mention wind is that I can imagine that a combination of lateral thrust and gravity is pretty serious. I'm guessing a function to the 3rd or 4th power. Is there an M.E. in the house?

Definitely BLACK!

I also considered a secondary stack behind the main stack made of barrels split lengthwise with the inside painted silver and making a vertical reflective 'cradle' (for lack of a better term) so that the main stack gets max heat.


Anyway, I hope TW chimes in.

680lbs is very little weight. I've seen 3000lb pallets stacked on top of an empty drum. Pretty sure they stack full drums at least 6 high.

A T collar or other way to support the welded connections and keep them perfectly plumb would be very important; as would cables or attaching to your structure. Might want some sort of barrier around the base so someone couldn't accidently dent the bottom couple of barrels.

So the Jones are going to 4 stories now?

Would it help any to have the bottom of the barrel flared (like an upside down velocity stack) ? Wouldn't you want the entire stack to be smooth inside?

Bet that depends on the velocity of the draft. If lits low velocity then turbulence is less important. If it's high velocity then you have all of those issues with laminar flow and viscosity.

Makes sense.

Well....I'd be curious to hear what the average velocity is, and if there might be any benefit from having a 90 degree elbow at the top, to take advantage of any wind, and the suction it could create.

The point of those is to drive turbines to generate electricity. Is that what you are going to do? I think you would need more height. Sorry no math for you. The idea is the same as a dam except upside down. So bigger drop/rise = more energy. And in this case the hotter the air at the bottom the better (obviously). I think that is why in the drawing they show large heat collectors at the base. The tower itself is not the collector.

Makes sense.

I am a welder, I have built some large steel structures, Plumb is my middle name. I can build anything and make it strong enough to withstand 80mph winds, (Palm Springs CA area bldg code) Anyway, the Joneses are going as high as they can.



My issue is the height and diameter of the stack versus the velocity of the airflow in relation to the collector and turbine... Perhaps I should be using 35 gallon drums with a diameter of 14" to decrease air mass and increase velocity... but I'm not smart enough to apply whatever field of mathematics this entails to the problem at hand. :(

Thats it precisely


Sadly I think 50ft might be the upper legal limit, so perhaps I need to massage the other pertinent factors/numbers to observe this limit.

Thats correct, but we certainly don't want any cooling to take place in the stack itself, indeed more heat in the stack should equal some added acceleration of the airstream... at least this is the logic formulated by my admittedly limited brainpan.

I think the problem is your extremely small scale compared to the other examples given. Just off the top of my head I would think maybe you could make 100 or 200 watts on a sunny day. That might actually be optimistic. This is the same as a single PV panel. But the PV would be much cheaper to implement (and easier). I think PV would be the way to go for electricity. But for heat storage, barrels have been used. Solar is very successful in deserts usually. If you have some water you can do some evaporative cooling also. Just saw a house like this on TV recently.

So, the heat rising in the column spins a turbine? Is that how this works? That's pretty cool. I've never heard of doing this before. If you build this, please put some progress pictures on the forum. That's very interesting.

I take and appreciate your meaning. PV as well as wind are also on the drawing board, but PV has some drawbacks especially in a desert/summer environment. As you are no doubt aware PV suffers from an inverse relationship between temperature and efficiency... ie. the hotter the PV panel gets the less efficient it becomes. This fact is what led me to the SUT, heat is a friend insted of an enemy.

Another benefit to the SUT is that it continues to produce power after the sun goes down, the heated medium (in my case black rocks) in the collector continues to 'do its thang' for some time.


Big thanks to all who responded, please keep it coming!!!

Will your house be on or off the electric grid?

Here is a product that works with hot air as well

http://www.cansolair.com/

It is for space heating in the winter, but maybe you can get some ideas from it. They use aluminum cans with holes drilled in the bottom and top. They use Aluminum because it absorbs the heat rapidly. You could use two materials for the collector, aluminum or similar, that heats up rapidly, then a more dense material like the rocks you mention, as a heat store.?

Just looking as some of the claims in the Wikipedia article, and thinking about this from the standpoint of how much power one might get from a given collection area:

OK, about 1.1 W per square meter of collection area.

OK, about 5 W per square meter of collection area.

You're proposing a collection area of 37 square meters. Even if it were the case that, building on a vastly smaller scale, you could match the efficiency of what they suggest might be possible - and I wouldn't bet on that without a lot more information - what would you have? 185 W?

in a perfect world... off... I am fully conversant in battery banks, LEDs, and DC appliances. But realistically speaking, I enjoy my creature comforts as much as the next man, plus my various welders pull mega amps, and I'd hate to fire up the genny every time I want to weld.

Seems to me you would want to be on the grid if at all possible to avoid the initial investment and replacement cost of batteries. All you have to do is find out the cheapest /watt way to generate more than you use. and chances are great that the electric company will be required to at least trade the energy you provide in the month for what you need on a watt to watt basis. When it comes to heat, it seems like it would be hard to beat passive solar and geothermal... if you're starting from scratch that is.

Thanks Eskimo for dumbing it down for me... Thats some good info there, (mpolli was darn close in his watt estimation BTW) its gonna be awfully hard to justify such an investment for a meagre return. I'm looking for at least 4 kW daily, and it doesn't look like that can happen with the current design.

Back to the drawing board.

Did you check out the other designs utilizing solar heat?

I'll see if I can find them again through the various links that I followed

Yes, I've checked out the parabolic mirror/stirling engine setup($$$$)

And theres a new system in the works that uses superheated molten salt that is almost too scary to contemplate.

And I'm looking into a wind driven 'accessory' to the SUT, but that idea is still incubating in the ol' cerebellum.

I greatly appreciate any and all suggestions and information, but I'm most interested in things that I can build out of reasonably cheap and readily accessible materials (especially steel)

here she is from the front... I compare this structure to Sara Jessica Parker...

Ugly?... Possibly.
weird looking?.. Certainly.
Strangely intriguing?.. Yup.

http://rbk3.com/sketchup/desertdwelling2.jpg

It's an intriguing idea and I don't want to rain on your inclination, cuz I like it, but . . .

The big ones get part of their updraft power on the difference 'tween air pressure at the entry and exit points, a large distance for the one proposed in Australia. I just don't know if you'll get enough wattage that you can effectively harness with a smaller one.

One thing that probably could work in a smaller application, is to just have the column of barrels on the south side of the house. As they get hot, air is going to want to rise up and you can use that updraft to exhauxt hot air at the top of ceiling in the house by using ducts connected to the bottom of the column of barrels.

4 kw a day is not very much, if you can do grid-tie, net metering and you are in Arizona or somewhere similar, that would be easy to do with PV. You can estimate an average of 6 hours of sunlight per day. You could do that with 4 x 200 watt panels. Not sure if that is enough voltage for a grid-tie inverter. $800 x 4 for the panels, plus $1500 for an inverter is $4700. Build your own pole mount rack that is seasonally adjustable.

I have always thought that wind and PV are a good combination. When it's not sunny, it's usually windy, and the wind can blow all day and all night. Lots of plans online for home built wind turbines. I have read good things about this guy.

http://www.scoraigwind.com/

You mentioned you work with steel, It that house made out of shipping crates? Cool idea.

FWIW, I did this thread on the topic a while back:

http://www.peachparts.com/shopforum/off-topic-discussion/215171-solar-chimney-thermal-energy-plants.html

What about using a parabolic through to provide heat for an absorption refridgeration unit? Let the sun give you A/C... Well...at least when the sun is out, anyway.

That's been a fantasy of mine for some time. Maximum cooling could be produced at times of maximum heat.

I'm thinking neighborhood sized set-ups. There could be a community center freezer, with lockers, and perhaps some sort of cold liquid piped underground in insulated pipes, to various houses in the co-op. Water at 40 degrees would do fine in AC "radiators" with air and water circulation performed via PV cells.

A new setup of the parabolic trough method seems appealing. The mirrors are smaller and less prone to wind problems and I would think, cheaper. As long as you're still focusing the same amount of surface area of sunlight onto the collector, should be about the same.

http://i14.photobucket.com/albums/a3...tors_ausra.jpgWind load is avoided by the low position of the mirrors. Light construction of tracking system due to separation from the receiver.

I found this bit about them on Wikipedia:

Fresnel reflectors

A linear Fresnel reflector power plant uses a series of long, narrow, shallow-curvature (or even flat) mirrors to focus light onto one or more linear receivers positioned above the mirrors. On top of the receiver a small parabolic mirror can be attached for further focusing the light. These systems aim to offer lower overall costs by sharing a receiver between several mirrors (as compared with trough and dish concepts), while still using the simple line-focus geometry with one axis for tracking. This is similar to the trough design (and different from central towers and dishes with dual-axis). The receiver is stationary and so fluid couplings are not required (as in troughs and dishes). The mirrors also do not need to support the receiver, so they are structurally simpler. When suitable aiming strategies are used (mirrors aimed at different receivers at different times of day), this can allow a denser packing of mirrors on available land area.

Recent prototypes of these types of systems have been built in Australia (CLFR[41]) and by Solarmundo in Belgium.

The Solarmundo research and development project, with its pilot plant at Liège, was closed down after successful proof of concept of the Linear Fresnel technology. Subsequently, Solar Power Group GmbH (SPG), based in Munich, Germany, was founded by some Solarmundo team members. A Fresnel-based prototype with direct steam generation was built by SPG in conjunction with the German Aerospace Center (DLR[42]).

Based on the Australian prototype, a 177MW plant is proposed near San Luis Obispo in California and will be built by Ausra[43]. Plants with smaller capacities being an enormous economical challenge for plants with conventional parabolic trough and drive design, only few companies intend to build such small projects. Plans were revealed for former Ausra subsidiary SHP Europe building a 6.5 MW project in Portugal as a combined cycle plant. The German company SK Energy[44]]) has published its intention to build various small 1-3 MW plants in Southern Europe, esp. in Spain on the basis of their own Fresnel mirror and steam drive technology (Press Release[45]).

In May 2008, the German Solar Power Group GmbH and the Spanish Laer S.L. agreed the joint execution of a solar thermal power plant in central Spain. This will be the first commercial solar thermal power plant in Spain based on the Fresnel collector technology of the Solar Power Group. The planned size of the power plant will be 10 MW a solar thermal collector field with a fossil co-firing unit as backup system. The start of constructions is planned for 2009. The project is located in Gotarrendura, a small renewable energy pioneering village, about 100 km northwest of Madrid, Spain.

Deep Lake Water Cooling

http://www.enwave.com/home.php

Deep ocean salinity gradient for electrical potential.

I wanted 4KW out of SUT to 'justify its existence'.

Solar panels will be mounted on the south side of the structure and will be seasonally adjustable.

Very cool Idea, not mine of course, not even a new idea, but to my mind they are the perfect building 'block'... windproof, waterproof, Earthquakeproof (mostly), With the use of one modest crane the entire structure can be assembled in one day, the best part is that every modification can be performed with 2 tools... plasma cutter and MIG welder.

There are downsides of course, a steel building in a desert requires significant insulation, and there is the 'love it or hate it' design, plus they weigh approx 6K lbs each... so the foundation, or pilings (in my case) had better be damn sturdy.

Our shop here is about half made of them. We have 6. The pros: cost. The cons: everything else! I would not recommend it unless you just want to see how cheap you can build any structure out of waste materials. I wouldn't do it since I experience it every day. No thanks. Even if I got them free I wouldn't do it for a house. Unless I was broke.