To Track or Not To Track

[Bigwheel]

Hi everyone,  

As I sit here and ponder my thoughts, I'm looking for a little guidence on the use of a solar tracker.  I have aquired all the materials to build my top mount(pole) solar array.  So before I finalize my design, I'm looking to others with simular set ups and geography.  Here's the scoop.  I'm going to mounting six evergreen 180's and grid tie those in to the home.  This is just a starter setup, so when finances allow I may add another pole.  I'm located in southwest lower michigan with an average of 4.2 hours of sunlight per day.  I have read some of the pro's and cons to a tracker setup, but am really unsure if is worth doing.  A couple hundred more and I've got a single axis tracker, but where I'm located is it worth it?  Or is it just better to adjust the angle spring and fall and leave it facing true south.  I have a pretty good vantage point from 10am to 6pm is when the sun shines on the location where the array is going to be placed.  Mind you this is what I've been monitoring for the last month or two.  I have yet to see what the gloomy days of winter have in store for me.  The way I look at it, For the money you spend on the equipment you want to make my dollar go as far as it can. Thanks again for your input.  Chad

[wpowokal]

Chad, for me its a no brainer, there is so much to be gained on the sholder periods, before 10 am after 2 pm.

Take one panel connect an amp metre point it directly to the sun from sunrise to sunset at say hourly intervals. Measure the short circuit amps, brief readings only (for your metres sake).

Then repeat with the panel in a fixed position, and you will have your answer.

allan down under

[David HK]

Best thing I have ever done was to track the sun for as much power as my photovoltaics could get from it.

I shall be converting my prototype arrangement to a permanent garage roof system in the next few weeks

David HK

[Volvo farmer]

What are the cons of a tracker? Added complexity perhaps? If the thing ever fails, you've still got a fixed array.  

I'm a firm believer in tracking, scroll down a dozen posts or so to see my latest project. I don't think I'd be so hot on trackers if I actually had to buy a manufactured one. I've built two pretty big ones now for about $100 each in materials. At that price, I think it's a no-brainer.

For your application, if you're thinking about building a tracker from an old c-band dish, I'd worry a little about having six big panels on it. I did an area calculation on mine, it had an 8' solid dish, which comes out to about 50 square feet. My four 170W panels ended up being about 55 square feet, so I figure I'm within the designed wind load for the mount. Things do get a little shaky with the standard (3.5"?) pole too. If you could find a mount for a 10' solid (not mesh) dish, and beef up the pole a bit, you might be able to put all six of those panels on a homebrew tracker.

[Mary B]

The mesh dishes are equivalent to a solid dish at higher wind speeds so the mount from a mesh dish would work.

[GaryGary]

Hi,

The NREL Redbook gives tables of solar radiation for tracked and untracked collectors for a lot of US locations.  Just download the one for your state, and pick a nearby city.  They have a table for fixed collectors and one for single axis tracking -- just compare the two.  

One characteristic of tracking systems is that they do provide more summer benefit than winter benefit -- so look at each month.

It sounds like you might have some obstacles blocking part of the sun in the winter?

You can easily work out how much this blockage will be for any time of year with this Solar Site Survey -- only takes an hour, and its fun and free

http://www.builditsolar.com/SiteSurvey/site_survey.htm

If you are going to do single axis tracking, you might consider the ridge style soft concentrators to further increase your output:

http://www.builditsolar.com/Projects/PV/pv.htm#Tracking

Gary

[TomW]

Farmer of Volvos;

I agree with your dissection of the issue. Despite the bad advice and wrong numbers that inundate the 'Net with regard to tracking, only a feeble mind would not strive to do it if they have more than a few watts installed.

My personal C band dish based tracker mount had a sticker that claimed it was rated for a 1500# dish.

Not being a rich volvo farmer, I will never afford to load it up with that much solar. It did not have an area rating just weight. the rack I added could easily hold a Kenworth conventional tractor, too.

Cheers.

TomW

[DamonHD]

Hate to disagree with with you Tom, but even for my modest sub-100W system though I'd love to have a mechanical tracker I have several limitations:

1. Lack of clear space.  I have a tiny amount of south facing area and there's barely space for the panels never mind clearance to swing 'em.  And If I put them on a pole they'd probably be nicked by the local youf or I'd be told that I would need planning permission and get turned down.  In other words space and stealth...
   
2. Lack of full-day sun in summer, not much angle at dawn/dusk from south in winter.  I'm obstructed by my house from the east except in the winter, when the entire width of the sun's arc barely warrants a tracker so far as I can see, and when I most need to optimise performance.
   
3. Lack of DIY skills.  Biggie.
   
4. A small child running around...  Littlie.  B^>
   
   

My next system will use an MPPT system to at least track electrically!

Rgds

Damon

[ghurd]

Track if you can.

I was against it before, except for large systems.  When PVs were cheap, another panel sounded like the best option.  Besides, most systems I do get the battery pretty much get to regulation voltage in a day.

Your system is large, and the 'battery' will never be full.

G-

[Volvo farmer]

Not to pick nits here, but I've seen a whole lot of C band dishes, and not one of them even approached 300 lbs, much less 1500. Why would the manufacturer build something rated to carry five times the intended load? Something doesn't add up. You sure you weren't reading the sticker on the linear actuator? Those are usually rated for a lb load.

Maybe there is no area rating but I worry that a 40MPH gust might take my precious silicon and make a $3000 pile of broken glass and twisted aluminum on the ground. 50 square feet is a considerable amount of sail, and if it's early or late, the array is pretty much vertical. I seriously considered putting six panels on one of these mounts and my gut instinct was that it was not a good idea, no matter what the sticker said :-)

[TomW]

Damon;

Obviously, local physical limitations must be factored in. I tend to forget that not everyone has acres of room, is retired with no children and has full southern exposure and, best of all, no silly codes and associations dictating use at least with it designated as agricultural use there are no restrictions. I don't think the footprint changes much on mine and in fact, I think it is actually less at both ends.

Typical of my posts, I insulted someone by just stating what I mean outright without thinking how it could offend someone.

Cheers.

TomW

[mungewell]

I would agree with the comments so far.

Most importantly do a site survey. There is no point building/buying a tracker if your panels will be shaded early morning or late afternoon. Even some shading can kill production.

Also consider the winter sun arc, up here in southern Alberta we get considerably less daylight in the winter.

During the summer I predicted that I would get almost twice the amount of power with a 2 axis tracker, however being off grid I have no where to actually store it. I could make use of some of it with electric cooking perhaps....

The big consideration for me was the wind. I just felt that it was too risky placing my panels on a tracker. If (quite often) gets gusting over 100km/h due to the Chinook winds, too much risk to have 9 sq.m of panels on a single mount.

Simon.

[DamonHD]

No offence at all.

What I am interested to learn, and haven't found the answers to yet, is the maximum extra output that mechanical tracking might buy in midwinter in the south of England (near London) in mid-winter when available solar energy is minimum and equipment output should be maximised to avoid too much over-spec for summer.

I hear numbers of ~20% tracker energy gain (over fixed-due-south) for summer when the east-west angle swept by the sub is at its largest, but what is realistic for winter?  1%?  5%? 10%?

Rgds

Damon

[TomW]

Volvo;

Well, I may have misled on the source of my polar mount. It originally came from a commercial cable TV dish farm. Old one and it had a huge fiberglass dish mounted on it. Later I used it for years with a mesh C-band dish.

The weight rating was on a sticker on the saddle of the mount but is from memory so maybe I mis remembered. 4" heavy steel pole set in a hole in concrete 5 feet down to our "bedrock" with about 7 feet out of the hole. I doubt any wind will tip it over or suck it out of the hole. I always set things like this in bell shaped holes so the concrete slug is bigger than the main hole at the bottom. Just a good practice IMHO. The weak spot would be the jack or actuator. The 3"X3" .25" thick angle iron rack will outlast everything else. I "only" have 4 Siemens SP75 panels. So about 32 square feet of area. I would add another 4 of these with no qualms about safety.

Just to clarify.

Cheers.

TomW.

[GaryGary]

Oops -- forgot to give the link for the NREL Redbook:

http://rredc.nrel.gov/solar/pubs/redbook/

Gary

[Mary B]

The weight rating could reflect the windload, and a 10 foot diameter dish is 78 square feet of load and depending on where you are the tracking on those gets close to vertical at the ends,

[RP]

Not that I know anything about it but I have to wonder what a C-band dish with a foot of snow on it would weigh...

[scottsAI]

I have not built, in the same stage as you.

Have four 25 watt panels, plan on a tracker.

If you DIY, then trackers are cost effective.

Looking over the charts 16% in Jan gets better from there.

I like Gary's suggestion of the soft concentrators.

For the winter you can't go wrong! Might want to monitor temperature.

Have fun,

Scott.

[TomW]

RP;

Would depend on the snow. About 50.24 cubic feet per foot of depth [8 foot dish] could add up quick with wet snow like we see occasionally. My math sucks so if thats wrong on figuring the area of a circle which I used rather than a hemisphere, blame my feeble math skills. The weight of a 2 inch accumulation of ice from an ice storm that occurs occasionally I think would be about 8.4 cubic feet of water say 60 odd gallons and getting up to 500 pounds rough figures. Ice is much heavier than snow per inch of depth.

This mount I have is pretty stout with a 3/4 inch bolt thru brass bushings for the pivot and the steel is all 1/4 inch and well engineered. I am confident it can handle anything likely to occur here.

Cheers.

TomW

[Fiddlehead44]

    (SPMT)    Spouse Powered Manual Tracker!

 My wife (a sweet person) loves to watch TV. I told her that the electricity

 for her set was directly connected to the solar tracker and if it wasn't

 adjusted at least every 1/2 hour, her TV would fail. So, during comercials,

 she trots out and adjusts the knobs. When I'm outside and handy to the tracker,

 I will give her a break and do it for her. She's happy, I'm delighted and it

 costs me nothing.    Fiddlehead the Redneck

[altosack]

Hello Bigwheel,

Tracking is not a "is it worth it or not in every instance" question, and I have not heard in the comments above what I feel to be the important questions.

Basically, (daily) tracking will help you a lot more in the summer than in the winter, because of the angles of the sun. Depending on your latitude (and assuming you have a full solar window), tracking will help 5-20% (50-30 N or S Latitude) in the winter and 30-40% in the summer. For Michigan, you are probably looking at 10% or less in the winter.

Most of the time, people with an off-grid system are hurting for energy in the winter and have plenty in the summer, so tracking may give you a lot more energy in the time that you need it the least and only a little more when you need it the most.

There are some scenarios where tracking will be a big help:

1. You are grid-tied and net-metered.
   
2. You pump a lot of water in the summertime (or some other reason your summer electrical load is much higher than in the winter).
   
3. You have a solar/wind setup (primarily wind-powered), but the wind is calm in the summer and you are depending primarily on your solar input.
   
4. You live closer to the equator than 30-35 Latitude, and you have sized your system marginally.
   
5. You want to have a tracker just because it's so cool (particularly if you build it yourself, and don't underestimate this one; this is one the best reasons to do anything).
   
   

I would go ahead with your pole setup and see if you have enough energy. If you don't (and most of us don't because we always underestimate our electricity usage) then you can upgrade to a tracker later with little lost.

Best of luck,

Dave Voss

[finnsawyer]

He's probably at 43 degrees north latitude.  The 45 degree line runs through the northern part of the lower peninsula of Michigan.  I'm at 47 degrees north myself.  If I were to invest big in solar I would want tracking due to the long summer days.  Also, Michigan does have a net metering law, so that's something to consider.  I would have to be concerned about snow loads in the winter and he may have to too, since he may be near Lake Michigan (I'm a mile from Lake Superior).  Considering that most of Europe is at a more northern latitude than he is, one would like to know what the experience of our European Brethren has been?

[TomW]

fiddlehead;

Woohoo! My kind of logic.

It does make a difference and I used to manually track myself with a switch to run it back n forth right at the mount. I don't really care about the numbers I see quoted. I see full power all day if sunny and with fixed it gradually built up to full power then dropped off to nothing. This makes me "feel" like I am getting maybe 2 or 3 times as much over fixed. Regardless of the numbers, I find it worthwhile to do, if only "in my head".

Cheers.

TomW

[Bigwheel]

Hi to everyone,

And a big thanks to all who replied.  I'm located about 42 degrees 40 minutes and a 1/2 mile off lake michigan.  So, depending on the storms we do get lake affect.  Other times generally about 7 miles in land is where the biggest amout starts to form.  Anyhow.  I spent the better half of last night getting paid to ponder what to do.  From what I read yesterday, I've decided to make the tracker.  I figured out a simple pivot that should work out (at least on paper).  If something is to fail, it can still produce in the fixed position.  I look forward to posting some art if I can figure out how to get the pictures croped and down loadable.  My electric loads are alot higher than the average jo.  Running a open loop Geothermal setup.  I've seen usage in the winter up to 2.5MW.  Mind you I'm not using any gas or wood for heat.  But the monthly average runs about 1100kw/month or $150.00. I've learned to live with it and the three other hell raisers that contribute to it.  The lights finally turned on and the days of my childhood make me realize that I needed to make a change.  That thinking lead me to the path of RE and simpler days of the past.  I plan on grid tieing the system into the house and eventually the enertech 1800 sitting in the attic of the barn.  After getting quotes for batteries and getting sticker shocked, I chose grid tie in.  In the past 7 years we've never been without power longer than 6 hours.  Seeing, that michigan allows grid tie in, it makes the setup more simplified and cheaper to install.  The only drawback is the paperwork!!  

For those of you who have built there own,  how satified have you been with the redock controller??  Has anyone ever used the one's from the AnalogGuy.  Found his add in the back of Home Power Mag.

  http://www.theanalogguy.com/

"Thanks TomW,  it is as easy as falling off a bar stool"

A little more pricey, he does have a couple different models.  And come in a sealed housing. Thought I'd share the info.  I will have to get the actuator on order.  Being a small grid tie system,  I'm going to need to send all the extra dc voltage to the inverter inorder for the system to run.  My thought's are to pick up a small panel with a built in charge contoller to keep the battery for the actuator topped off.  Simular to that of the Lorentz trackers.  Just wanted to thank all you for your input on this topic,  Know it's time to Fab.  thanks again  Chad

[hydrosun]

I've been happy with the redrok tracker circuit. But I always ask for the modified circuit with a 90 second delay before changing direction. That keeps the tracker from shuddering back and forth.    I didn't like the last circuit I recieved that also delayed between each pulse of movement in the same direction. It makes  it  time comsuming to adjust.  So talk or email to Duane exactly what you want.

 I've commented before about  the advantages of trackers for increasing the output of the panels  and spreading the output over the whole day instead of a large peak in the middle of the day when you may not need the extra power.

Chris

[wpowokal]

Here is a link to my diary with results of a test I did between fixed and tracked.

http://www.fieldlines.com/story/2005/2/1/0713/31693

[Volvo farmer]

I've also been happy with my Redrok trackers. Like Chris, I've started ordering the RI (reverse inhibitor) models. They're ten bucks more than the basic one, but I also had problems with my array trying to go back and forth in half-second increments until I got the RI circut added.

I've bought six of them now. One blew up one day for some unknown reason, the one that's replaced it had worked flawlessly for about ten months now. I also destroyed one on my garage array because I let rain get down into the jar.

Rather than build something from scratch, you really should take a drive in the country and look for a c-band dish in someone's yard. Hardly anybody uses them anymore and you could likely get it for free. The pivots are heavy duty, you'll get the linear actuator instead of having to spend $100 on one, and they are really really simple to adjust for the seasons. It's literally a one-minute job with a couple of crescent wrenches.

[TomW]

volvo;

Good points on the old polar mounts for C band dishes. They are a bit more rare here lately, at least standing in yards. Probably stashed in the iron pile.

Cheers.

TomW

[Bigwheel]

Hi, That was some impressive data.  Somewhat what I've been looking for, thanks for sharing.  Well, got some news.  Last night got the frame work finished for the tracker,  just neet some time to paint the steel.  I'll try and post some pictures of the post and pivot bracket.  Got about 7 hours into it and cost--freebees-- minus a couple of beers.  The only cost will be the actuator, controler, and concrete.  It will be interesting to see how it does for wind loading.  Were talking about 120 sq/ft that at the top is about 12' off the ground.  I'm woundering if I should allow a gap in between the panels to allow air to flow through?  Seems logical to do.  

Ok another question for those with the old C dishes.  Are those acutators 12v or 36 volt?  What are you guys using to power those actuators up.  DC to DC converter??  I've keeping an eye out for 12v one, but I may stumble across the 36v models and needed some powering ideas.  Thanks for the scoop on those redock controllers, And thanks for the input.  Chad

[Volvo farmer]

I believe the actuators are mostly 36V. However, if you wade through Duane's site long enough, he explains somewhere that they actually work pretty well on 12V. The motor just moves slower, but this is not a problem, and may actually be a benefit while trying to track something slow moving, like the sun.

I did have a problem with my array on 12V but I'm not using a regular linear actuator, mine's a worm drive. Anyway, my array is a little imbalanced at the extreme east and west limits and the motor wouldn't pull it up from the limit at 12V. I rewired for 24V and everything's been fine ever since, this would likely not have been an issue with a linear actuator.

[cyplesma]

just my .02, well maybe a nickels worth

I'm over on the east side of MI, in the lower part of the thumb, somewhere around 43 mark.

right now I'm tossing 3 trickle chargers to keep a varity of batteries charged up.

when I leave them on the ground they do fairly well in keeping a 12 car battery and 2 lawn tractor batteries above 13v.

when I move them every hour or so. it'll keep a pair of 6v golf cart batteries above 12.8

right now I still need to plug in a couple of 1 amp wall chargers to keep these really full, but I have those rigged to my combiner panel and feed into my solar charge controller.

this is all on a bright sunny summer day of course. during the winter I keep the panels inside and move them around to keep them pointed at the sun. this winter I hop to mount them on a small tri leg base with a lazy Susan under that.

but I would say if your not sure about the panels staying mounted to the tracker then just hard mount them for now. I'm not sure if it will make that big a difference on the net metering (IMHO). but if you work out of the home during the day and most everything is off then you may get your meter to go backwards during those hours.

[RP]

Have you considered adding a simple couterweight to the back of the array to balance it?

[Volvo farmer]

Well, yeah, I considered it. Duane told me the same thing. I'm just stupid thinking in three dimensions I guess. If I look at something like this:

It's really hard for me to understand why a balance weight is going to help. If I put it north, how does that affect the balance when the thing is cranked over that far? If I put the balance east or west, it exasperates the problem on the other end. I'm not adverse to the idea, maybe you can explain it to me, because I sure don't understand it now.