Solar Trackers

[BigInch]

I've been doing some rough studies concerning the economic feasibility of using solar panels mounted either in a fixed tilt position on close-to-ground supports, or mounted on 1 or 2 axis elevated solar tracking structures. The extra costs of the tracking structures and mechanisms supposedly can be balanced by higher daily energy production and the resulting income from grid power sales, but so far I have not been able to prove there is a positive return on the required incremental investment for the trackers. I think this is curious, since many projects appear to be using trackers. I am wondering if there is something missing in my analysis. I have included some cost reduction for smaller plot plan footprint of the trackers, but even that doesn't seem to be sufficient to justify their use. Is there an increase in generated power due to the elevation of the trackers and their being more exposed to cooling effects and a consequential reduction in operating temperature that I need to consider? Or ...is the use of trackers just a sales gimick of some kind? Has anybody been able to economically justify the use of solar trackers for a ground based pv installation?

http://virtualpipeline.spaces.msn.com

 

[Compositepro]

From what I have seen flat panel collectors do no use trackers. Focused collectors must use trackers in order to work at all.

The extra power collected by tracking with a flat panel would only be a benefit in early morning and late afternoon. The total available power at those times is not high to begin with so the benefit is low.

 

[BigInch]

Thanks for the comment. It is exactly what I am seeing. Some of these tracker structures cost $5000 and only hold 8 panels, so its in the range of $3/Wp.. almost as much as the panels themselves. With an average of say 25% increase in power capacity, its just not enough to warrant their purchase. I haven't considered a concentration option yet, but I am expecting those to have a similar result for ground based work, but I do want to confirm that thought. Its a 20 MWp installation, so the tracker increment is a hefty chunk of change. Fixed systems so far appear to be a no-brainer, but I'm seeing a lot of projects with trackers and that has me a bit worried. Perhaps it is as I thought, some sales gimick. Most of the projects I've noted are oriented towards sale of individual 100 kWp subsegments to individual investors and I am thinking trackers just might be some market oriented ploy using attractive packaging offered especially for the gizmo freaks with more money than brains.

http://virtualpipeline.spaces.msn.com

 

[BigInch]

... but I have been known to out-think myself from time to time.

http://virtualpipeline.spaces.msn.com

 

[cranky108]

For what it's worth, years ago I read that for a single axis tracker, that there is only about a 15% gain.
I don't remember the exact book that I read it in, or if it is even true.

 

[LionelHutz]

Homepower magazine @

http://www.homepower.com

is a RE publication written from the home user perspective. The trackers you are talking about seem to fall into the home use category. The general consensus at the magazine seems to be that trackers are not cost effective. The panels should be set-up so that they are aimed directly at the sun at the middle of the day when the sun is the highest in the sky. This means they should be able to tilt so that you can change the angle as the seasons change.

You could contact the editor and see if he has some comments or further information. It's Richard Perez.

 

[BigInch]

Thanks. I have seen the homepower website and agree there is very little to be gained from using trackers over using a fixed installation... unless you are above the Arctic Circle. At most latitudes it appears that trackers can provide up to 40% more for a few hours a year, but the power gain is not nearly enough to offset the relatively tremendous costs of the trackers. There may be some advantages to adjusting the tilt angle manually every couple of months, if you don't have many panels and labor cost is cheap. For a large array it appears best to optimize the tilt angle for single value giving the max produced power over the entire year. My conclusion so far is that trackers are for the excessive-compulsive that want to always have max possible power output regardless of cost and for gizmo loving propeller heads. They are not economically viable in an on-the-ground application.

http://virtualpipeline.spaces.msn.com

 

[bonzoboy]

I think the interest you are seeing on those tracking systems is a) they are big b) they are getting big subsidies. They don't pay for themselves, but if the price of power is high (and growing) and the subsidy is good, they can just about break even. And then some accountant can claim credits for the CO2 not generated when the power is produced.

World is upside down from where I am....

 

[BigInch]

I think its a marketing ploy. Its looks better to show an investor they own those 10 trackers right here than it is to point to some corner of a field with 150,000 panels on it and say, "your panels are over there... somewhere".

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

 

[Warpspeed]

Trackers are an interesting development, but it is not only the first time cost, but long term maintenance that can be problematic. There is simply more to go wrong, and it usually does.

Trackers will also be much more vulnerable to high winds and storm damage than rigidly mounted flat panels.

 

[bonzoboy]

And a lot of panels go on top of roofs. WalMart probably wouldn't want their roof crashing in on them if their solar panels were too heavy because of the additional weight (I use Walmart as an example, because somewhere I heard a factoid that if all Walmart stores were covered with PV panels, they could supply a couple % of the US generation demand)

 

[danw2]

Anyone here have the photovoltaic solar panel rules-of-thumb with which to test Bonzoboy's factoid?
"if all Walmart stores were covered with PV panels, they could supply a couple % of the US generation demand"
(Does 1 sq ft of solar panels use 1 sq ft of roof space? If not, ? ?)

For Walmart roof area, I found these facts on Walmart's web site,

http://www.walmartfacts.com/articles/2502.aspx

1,000 discount stores in the United States.
Discount stores average 107,000 square feet.

107,000 * 1,000 = 107,000,000 sq ft of roof top (on average)

Supercenters today number more than 2,300 nationwide.
Supercenters average 187,000 square feet.

2,300 * 187,000 = 430,100,000 sq ft.(on average)

430,100,000 sq ft + 107,000,000 sq ft = Walmart's potential roof area = 537,100,000 sq ft of roof space.

Dan

 

[Warpspeed]

Here we go:

Average insolation values for north American cities:

http://www.porta-energy.com/Insolation_USA.htm

Assuming average photovoltaic panels are 10% to 15% efficient.

A wild guess 5KwH per day x 12% = 600 watt hours per sqM

 

[MikeHalloran]

Random thoughts:

Maintenance is a real cost for anything that moves. A big, new installation should need very little... at first, which can be a problem, because you'll need to create/expand the maintenance crew when things start failing, at which time you may have lost much of the needed documentation/ skills.

If you've got a 'farm' of articulated panel assemblies, you only need one that actually tracks the sun; the rest could be slaved to that.

Actually, in theory, you don't need a sun tracker at all; a modest computer with a real time clock should be able to point the array to where the sun _should_be_ at any given time.



Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

"537,100,000 sq ft of roof space."

1 square foot = 0.093 square meter

537,100,000sqft x 0.093 = 49,950,300m²


"600 watt hours per sqM/day"

49,950,300m² x 600Whr/m²/day = 29,970,180,000Whrs/day => 30GWhrs/day





Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Warpspeed]

Mike, I had often thought a solar tracker could be purely mechanical. Just a synchronous motor and an equatorial mount. moving 180 degrees in exactly twelve hours should track the sun, even if/when below the visible horizon.

The equatorial mount itself could also be driven to vary it's tilt throughout the seasons. As the earths tilt is 23.5 degrees, this could be adjusted with a crank and connecting rod coupled to a one year per revolution gearbox.

The whole mess could just grind away slowly, day and night, slewing back and forth to where the sun should be. No need for anything fancy, just some dumb gears, cranks, and connecting rods, and a bit of imagination.

Bravo Itsmoked, I was trying to work it out on my fingers, but quickly ran out of fingers.

 

[MikeHalloran]

Yeah, Warp, it's an elegant thought.

One tricky part is getting the synchronous motor to 'catch up' after an outage.

I guess if you used slip rings, the continuous rotation in azimuth wouldn't be a problem.




Mike Halloran
Pembroke Pines, FL, USA

 

[Warpspeed]

I guess it depends where you are. Near the equator, the tracking motor could probably just go into reverse at night.

At very high latitudes, where the sun never sets in the summer months, continuous rotation would be preferable.

As the effective gearbox torque multiplication would be fairly enormous, the motor drive power should be minimal. A crystal oscillator backup, and battery power could keep the gears grinding away during short power outages. The power grid as a frequency source has the very great advantage of constant frequency correction.

The whole thing could be made less crude with stepper motors and an off air broadcast time/frequency standard. But the idea of constant angular rotation, without having to play hide and seek with the sun in cloudy conditions appeals to me.

 

[itsmoked]

You want simple.. Just use a thermal tracker. They're solar driven!

http://www.emarineinc.com/products/mounts/tracker.html

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jghrist]

Total US consumption in 2006, 3,816,845 Gwh ÷ 365 = 10,457 GWh/day

http://www.eia.doe.gov/cneaf/electricity/epa/epates.html

30 GWh/day = 0.29%