Trailer Mounted Solar Concentrator / Tracker Array

[Phil Timmons]

Trailer Mounted Solar Concentrator / Tracker Array

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BACKGROUND

I have finally collected and accumulated the parts to build some serious solar concentrators.  

Up front -- yes, yes, and yes, I am fully familiar with trough collectors, multi-junction PV concentrators, and how conventional pole and rack mounted single dimension (or two dimension) trackers work   Instead my goal was to "low tech" the basic design to the point that anyone with an 8th grade or so education could copy this with parts easily available in most any rural area from materials that are mostly salvage, quick and cheap to repair or replace, and not worth stealing -  as contrasted with Aluminum frames, PV arrays, or exposed copper.

After poking at this for a year or so, I now have TONS flat mirror (yeah, really, literally  tons of scrap mirror laying about) that I have gotten for little to no cost and is otherwise trash, along with steel frames and other equipment needed to build a set of fully function sets of test equipment.

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THE WHY:


The highly portable aspect (trailer mounted) of this design is to give it the potential to be a profitable business adventure for me.  As any successful "bidness" folks know, you can run a charity as a business, but you cannot run a business as a charity.  While just one of these fully built will give our household all the power and heat we need for our house and shop, I am thinking there should be a market in putting these out at customer sites.  


Presently our major electric utility supplier is gouging the snot the out the consumers in the major electric markets here (Texas).    However, if a would-be renewable energy (RE) producer wishes to operate from a fixed site, and place power upstream onto the grid, you get very little for the power you send up, but whoever buys it back off the grid from the utility gets hammered.  


To get around that utility corporate model, I had looked at doing local distributed generation from local sites where power could be shared with multiple commercial neighbors, however, as that involves fixed capital costs for the underground ducts, wire, transformers, and comes under the domain of building codes it is much more expensive and slower to implement than mobile equipment.


By going fully portable to a customer site all the cost and loss of power transmission (the high voltage power towers and transformers) the cost and loss of distribution (the poles, wire and meter part) and administrative costs and CEO stock options are all avoided.  


My present thinking is to place the RE generator on the customer site, and do not make them buy hardware (like PV arrays, inverters, batteries and all the rest of the mess), as these are business people - not techies or nerds like us -- and just let them buy electric power being generated at their site for half the price of the big utility.  After visiting with a few potential customers it looks like a serious "GO."


Additionally, there are aspects of property taxes - vehicles and trailers are not fixed property -- that this may avoid, as well as service to the units can be done in shop conditions rather than the field by towing a new mobile RE generator to the customer site, swapping the plug connection, and driving home with the one to be serviced behind the truck.  


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THE HOW:


I have details of the intended trailer mounted array and tracking below.  I have left the heat collector portion off the diagrams for simplicity, but will cover it in a separate diary entry, as well as the control system, turbine, and motor/generator.


The first round of this should be very simple, it is basically spec'ed in Step 1, below, and shown in the first picture, and it is only 50 mirror tiles totaling 50 square feet - about the same as an 8 foot dish.  These all focus onto a one foot square target.  While I know this will work, it is not getting the most use of the equipment.  


The second step (Step 2, below) gets a little more complex mechanically.  It has wings that fold in to stay within the trailer boundaries, and within the legal width limits for highway travel.  As there are now 150 mirrors focused on the same 1 foot square target, the heat will be much more intense.


On the back of these wings will be a hardcover to make the whole device hail and severe weather resistant when folded down - typical night time or severe weather (no sunshine, anyway) storage.


On the third step, (Step 3, below) I add another 5 feet to the top of the array bring the total area to 225 square feet and giving a multiplier effect of around "200 Suns."  The trade-offs is in how quickly the heat can be drawn away and put to work.  If I cannot pull this much concentrated heat away quickly enough, larger individual mirrors are in order for larger arrays.  (see mirror options on step 4)


By the time I get to the fourth step, I will be using a larger trailer, with 8 feet width for highway travel, and 8 feet wide wings.  The lifting frame will be salvaged commercial steel roof trusses, and the underlying trailer will be 20 long ones we use for carrying bulk steel and pipe.


I suppose it should be noted that this rack and tracking mechanism is also suitable for PV and is probably rather cost effective when compared to the large bore hole, pipe and concrete foundation systems I have seen installed.   It also appears to have a longer daytime tracking travel, and would not have to be adjusted seasonally, as do the one dimension tracking arrays.


Other potential improvements include making it drop-on/drop off from the trailer with a pivot bearing on the ground at a customer site.  


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DETAILS NEEDING RESOLUTION AND SUGGESTIONS

Here are some of the details that I am still pondering through:

"Best" lifting mechanism - a couple come to mind that I have lying about the shop:  

1.  A garage door opener style gear and chain drive, or
   
2.  A cable and motorized hoist, or
   
3.  A long screw jack
   
   

Does anyone have any other good ideas in this domain, or anyone see anything bad in any of those?  I also think I should add some sort of speed brake to slow the descent if the lift mechanism were to somehow fail.  

Wind load management - while it will clearly be live tested to withstand a 70 mph headwind (going down the highway as a trailer), that will be only while it is fully folded down.  As far wind loads directly on the open array -- as the array is always in line with the length of the trailer making it unlikely that a straight wind could topple it, but it would place quite a wind load on the lift mechanism.  

To guard against side gusts toppling the equipment it may be advisable to hard anchor the pivot mount under the axle and tie the whole system down through that pivot joint.  I am thinking that a wind speed anemometer may be also be advisable, and to have the whole device lay down and fold up if the local winds get too high.

Weatherproofing the mirrors - This is a vital area, and where prior art similar devices tend to eventually fail.  What does anyone think about painting the backs with epoxy based paint? And sealing the edges with silicone?

Anything else that is obvious that I have missed come to mind?

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Step 1:  (See figure 1, below)

Array Size  50 square feet, 5 X 10 feet

Mirrors:  (50) 12 inch X 12 inch

Array and Equipment Weight:  150 to 200 pounds

Trailer Size:  single axle, 14 feet long, 6 feet wide

:Step 2:  (See figure 3, below)

Array Size  150 square feet, 15 X 10 feet

Mirrors:  (150) 12 inch X 12 inch

Array and Equipment Weight:  450 to 600 pounds

Trailer Size:  single axle, 14 feet long, 6 feet wide

Step 3:  (no picture)

Array Size  225 square feet, 15 X 15 feet

Mirrors:  (225) 12 inch X 12 inch

Array and Equipment Weight:  700 to 900 pounds

Trailer Size:  single axle, 14 feet long, 6 feet wide

Step 4:  (no picture)

Array Size   576 square feet, 24 X 24 feet

Mirrors:  (96) 36 inch X 24 inch to

(192) 18 inch X 24 inch (depends on desired amplification)

Array and Equipment Weight:  about 3000 lbs.

Trailer Size:  dual axle, 20 feet long, 8 feet wide

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FIGURE 1:  First (Small) Test Rig, folded down for travel

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FIGURE 2:  Elevated at site.







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FIGURE 3:  Expanded with fold-out wings.






[Bruce S]

Phil ;

  Great to see that you're still working at this!!

On the garge opener, the only thing I see of the newer ones, not sure which year make/model you have, is; the internal gear will not hold up to the shear loads.

I have helped replace a good 1/2 dozen of these here in St. Louis this year alone while people were trying to close theirs during the high winds and they weren't even close to the 70Mph.

ALL of the ones I've helped with name brand ones and they ALL have plastic/rosin gears instead of the good brass gears that they used to have.

Good read on the design too, kinda wierd that part of the text went to 2 point size down from say 10 point type size but still readable

Hope this helps

Bruce S

[Phil Timmons]

Thanks on the G-door opener advice.  Not real keen on it myself, just like to ponder / brainstorm with an open mind to the world of possibles.

Had to take a break for a bit and did a project with the big evil utility company in the meantime, while the mirrors kept piling up.

Dunno about the text part.  It looks all the same on my screen, but now I see the last two figures are not showing up on mine.  I really hate the software they run here, but hey, it is free, huh?

[Spdlmt150]

A garage door opener doesn't last very long just lifting a garage door. My first thought would be a servo motor. I have seen 24vdc servo motors on cnc machines that can run a ridiculous load & have yet to see one go bad (keep in mind that I do crash repair on machines on a regular basis) Might be a bit higher price than planned, but as a business venture, I would think reliability would be a key factor.

Definitely a cool idea overall. I have had similar ideas, but not yet had the time to explore them.

[thefinis]

A few things come to mind.

One is that you will need a way to clean the mirrors easily while at the location if a Texas dust/mud storm comes up.

Two is lifting mech kind of for when the arrays get larger. You might could use a 12 volt hydraulic system like the tommy gates use for folding unfolding and tracking. I have been seeing some smaller units that are for raising and lowering convertible tops that are more reasonable in price. Even a compressed air system might work but it would seem to take more power but might be feasible to use a prefilled air tank and top it off ever so often. One nice thing about using an air tank is there is little to steal.

Three is you could have it fold up when the sun goes away or when a storm cloud/rain reduces the light to a set point. This might save it from storm damage and from vandals at night.

Great stuff and I am in the same fix in that it costs an arm and a leg for power and to back feed the grid they want the other arm and leg in equipment safeguards and insurance. Still trying to track down a smaller unit already set up for under/over voltage frequency etc.

Keep up the good work.

Finis

[thefinis]

After rethinking it I don't think air is a good bet as it does not have the fine control of a hydraulic system.

[scottsAI]

Hello Phil Timmons,

Not sure I understand:

What type of concentrator, shape?

Looking for single axis or two to move?

What will you do with the heat? Mention electrical power how?

200 sun makes it hot, to what benefit?

Where goes the heat receiver?

Have fun,

Scott.

[Phil Timmons]

Hey Finis,

Thanks for the review and mentioning the cleaning issues.  Had pondered that a bit, and am chatting with some window cleaning guys about "best" designs.  If anyone here has any clever ideas for washing the mirrors, those are welcome, too.  I guess I should build that into the array, huh?

I met the window cleaning guys while shopping for "human fly" type hand grip suction cups that I have been using to handle all the mirrors.  Those are pretty neat toys.  Been using two pair of double 4" inch suction cups and I can pick 4 x 8 or 5 x 10 feet mirrors right off the wall for salvage.

But back towards the window (and mirror) cleaning -- I was thinking some sort of "spider" that climbs up them and washes them during the "off" hours.  I am chatting with the window washer folks to see what would also be useful to them for irregular and dangerous locations so they could use such a spider as well.  

As far as connecting your equipment to the grid and insurance requirements -- Most folks I have worked with in Texas have some sort of insurance as property owners.  Usually the grid-tie connection agreement requires US$1,000,000 General Liability with the utility listed as an "additional insured."  Typically all that makes the owner's liability insurance costs go from around $700 a year to $1000 or so per year.  (to anyone reading this -- those are very general numbers only, and check with both your utility and insurance company before beginning to build and buy equipment).  

In my case, I am a Texas licensed Electrical Contractor and already carry $1,000,000 General Liability.  Its listed coverage is "wiring in buildings" but also covers external features such as lighting, site generators, solar equipment, on and on.  I think the "in buildings" part is to differentiate from aircraft or marine electrical work.  

Anyway, since I am planning on keeping listed ownership of this equipment, although it is on customer sites, I think my insurance might cover it.  I am doing yearly audits and renewals for my insurance this week ahead (think liability insurance is a pain?  Try worker's comp -- I hate those people).  I will let you know what they say, and if they cover it and you would like to test some of this at your place, maybe we can get all that taken care of.  What utility area are under?  TXU territory, or some county coop?  Some of the coops can be pains for grid-tie, but some also some are so cheap, that RE cannot compete.    

If none of that works out, we could still use "load shedding" methods at your place.  That is where you take individual 20 amp (or so) circuits and use simple double throw relays as automatic transfer switches to select portions of your load to be fed either from the grid or your RE equipment, with no concern for grid-tie issues.  While you do get roll the meter "backwards," it does allow the maximum use of your RE equipment up to the point of surplus.

 

[Phil Timmons]

Hey Chris --

It is sort of an update, ripoff, and massive expansion of the Teton Engineering flat mirror sectioned Fresnel style collector.

Builder manual and pictures for that is here:

http://www.ida.net/users/tetonsl/solar/solarhom.htm

All built from simple (and very cheap) flat mirror sections.  What Teton understood very well was low, low cost of building makes for a quick and easy payback period.  Very smart business.  That entire concept seems totally lost on much of the commercial RE industry I run across.  

My bias is two axis -- polar coordinate system as it were.  It both pivots on the axle(s) fully towards the East and beyond (morning) and West and beyond (evening).  The elevation portion (figure 2) is so that it covers all day tracking, and all latitudes and seasons from Panama to Canada (range of folks that I have as customers already, if it works out well).

Teton's system was only one dimension with pole mounted tracking, with seasonal adjustments, but my business model does not allow that, as it is meant to go quickly on and off site, and not need to be individually adjusted per site.  It also looks like the hardware model I am looking at has a longer daytime runtime than single axis pole mount.

Uses of the heat -- Different folks I am dealing with have different best uses --

Applications include:

Electricity

Building and Water Heat

Absorption Air Conditioning

Ethanol production

Fresh (distilled) Water.

Pretty much in that order, by stage, as the temp drops.  While I can conceivably get all that from one cycle by starting with the high temps, different applications vary by customer.  Electricity and A/C here (Texas -- high utility electrical prices) and on the islands and Panama.  Ethanol through the Midwest.  Building and water heat from here to the North.  And also fresh water on the islands.

The range of (up to) 200 suns is because differing locations have differing heat levels available (far North drops off) and different applications require differing levels of heat supply.  For example, electricity uses both high temps and large volume.  Alcohol cooking and distillation requires large volume, but not as high of temps.  Absorption A/C is in between.  And fresh water (distillation) is the most flexible on the range of temp and volume.

Conceivably, I could go as high as nearly 600 suns if 1 foot squares were used on the 600 sq ft. model -- but it is hard to effectively move that much heat away into applications.

The heat receiver goes at the focal point (duh, huh? )  While that seems easiest at the center, center, I am still very open to what might fit best for travel, best heat transfer, etc.  The nature of the mirrors all individually being focused (but all moving together with the whole array) gives all that a lot of flexibility, as well.  I have pondered some designs where the target moves and mirrors move minimally for roof top applications -- but that is sort of a different project.  

 

[Phil Timmons]

[edit -- last sentence should have been:]

While you do [NOT] get [TO] roll the meter "backwards," it does allow the maximum use of your RE equipment up to the point of surplus.

[scottsAI]

Hello Phil Timmonsm,

Got it. (duh, huh? ) now that is funny.

Summary of answers below, can supply more detail if interested.

The single focus parabola requires the heat receiver to be moved as the dish tracks the sun.

Using a Spherical mirror the heat receiver can be fixed, better mounting for travel.

Heat receiver is not in the sun's path blocking some of the sun.

For a concentrator using optical tracking is not good. If the direct sun is blocked, reflected sun is not worth chasing. Just stay the course and wait for the suns return.

Mounting two accelerometers (XL) on the dish will allow the system to steer itself without user input.

Trailer must be N-S oriented properly. Unless put a compass in it.

ADXL213 is the most accurate and costly, so use ADXL323 one would work, better accuracy if each XL measured one axis of tilt, 1 deg accuracy should be achievable and more than enough.

With an XL on the mirror, how the trailer is installed will not mater except N-S alignment.

Add GPS for current location and time, it can figure out how to adjust without you doing anything

Park it, start it, and watch. That is it.

This style of tracker meets my liking:

http://www.solar-trackers.com/conc-deu.htm

Use a jack screw to add N-S tilt to it. I like the two points of mounting, just looks stronger.

Hope this was entertaining if not useful.

Have fun,

Scott.