Solar Power Shed Project

[Rob-D]

I'm building a solar tracker for my panels. Sensing will be from cells that equalize at the point of greatest sun light. Micro controlled for aberrations of clouds. To keep it as storm safe as possible the frame will be extra robust. I don't see much else you can do especially in my wind area and the fact that the panels will be in an open field which I actually like better as there is less chance of trees and flying 'stuff' slamming into them. Also an open field yields maximum sun

The frame won't be a single pole. I just weighed one of my panels and it is about 37.5 pounds so figure 40 to round it off times 8 panels and just the panels alone and you're dealing with 320 lbs. My frame will be similar to a saw horse with the two front legs shorter for winter summer solar angles.

I haven’t decided yet whether to build two trackers to cut the weight and also have a better chance of surviving flying debris. I figure damage will only take out half my system with a little luck!

 

[patrick_g]

Defective, I will think about your suggestion but on the surface I have objections on aesthetic grounds.

Pat

 

[patrick_g]

I'm building a solar tracker for my panels. Sensing will be from cells that equalize at the point of greatest sun light.

Ham radio folks have built trackers to aim an antenna array at the moon for EME (Earth-Moon-Eatrh), i.e. moon bounce communications. You might want to look at some of those designs. Pretty clever and they have been perfected.

I had a solar aiming design that used a couple light sensitive diodes (IR spectrum so as to work through an overcast) and a small opaque object to cast a shadow. When the device (solar panel) is aimed directly at the sun both photo diodes are just barely in the shadow of the opaque thingy. If there is a small allignment problem one of the diodes is in the light and the motor moves the array until the diode is in the shadow again. You have to pretty grossly misallign a solar panel to lose very much conversion efficiency. This is why a lot of folks only change the vertical adjustment a couple times a year.

Micropositioning of a solar panel has no payoff since the fall off in capture is a sine/cosine thing and it takes several degrees of error to ammount to much difference in energy capture.

Q: What is the cosine of theta when theta is zero?

A: 1.000

Q: When theta is 5 or 10 degrees?

A: 0.9962 and 0.9848 respectively

Q: How much aiming error does it take to reduce insolation (solar flux exposure ) by 10%?

A: 25 degrees

So there isn't much to be gained by getting too nitnoid about super accurate aiming of the array. This is why some trackers use opposing globes filled with a low vapor point liquid and a pneudraulic ram. The globes (small pressure vessels) are partially shadowed by the array. When the array is not alligned one globe is shadowed more and the other less. This generates a differential in pressures piped to the double sided ram which moves to realliign the array and ballance the pressures.

Pat


Pat

 

[patrick_g]

I'm building a solar tracker for my panels. Sensing will be from cells that equalize at the point of greatest sun light.

Ham radio folks have built trackers to aim an antenna array at the moon for EME (Earth-Moon-Eatrh), i.e. moon bounce communications. You might want to look at some of those designs. Pretty clever and they have been perfected.

I had a solar aiming design that used a couple light sensitive diodes (IR spectrum so as to work through an overcast) and a small opaque object to cast a shadow. When the device (solar panel) is aimed directly at the sun both photo diodes are just barely in the shadow of the opaque thingy. If there is a small allignment problem one of the diodes is in the light and the motor moves the array until the diode is in the shadow again. You have to pretty grossly misallign a solar panel to lose very much conversion efficiency. This is why a lot of folks only change the vertical adjustment a couple times a year.

Micropositioning of a solar panel has no payoff since the fall off in capture is a sine/cosine thing and it takes several degrees of error to ammount to much difference in energy capture.

Q: What is the cosine of theta when theta is zero?

A: 1.000

Q: When theta is 5 or 10 degrees?

A: 0.9962 and 0.9848 respectively

Q: How much aiming error does it take to reduce insolation (solar flux exposure ) by 10%?

A: 25 degrees

So there isn't much to be gained by getting too nitnoid about super accurate aiming of the array. This is why some trackers use opposing globes filled with a low vapor point liquid and a pneudraulic ram. The globes (small pressure vessels) are partially shadowed by the array. When the array is not alligned one globe is shadowed more and the other less. This generates a differential in pressures piped to the double sided ram which moves to realign the array and ballance the pressures.

Pat

 

[Rob-D]

Pat,

I did some experimenting with my panels and sunlight. While I think you're right about not gaining much by constantly having the panel dead on, 20 degrees off axis makes a big difference in usable power and solar trackers do yield 25 to 35% greater efficiency by tracking the sun.

Lots of people put them on their roofs, I guess, because of simple real estate problems but that's a lot of loss.

Also I'm using an MPPT so I'm going to get everything possible out of my very expensive 175 watt panels.

By the way I do know about moon bounce. Never did it but built lots of transmitters as I have an Extra Class lic.

Rob-D

 

[Rob-D]

ps,
If I remember the rule is to add another panel after three for equal power as a tracker.

 

[patrick_g]

Rob, I have nothing against trackers, just commenting that the losses for being a few (maybe several) degrees off from perfect doesn't have a giant effect. I doubt you saw much loss at 5 degrees of error which is way easy for a decent tracker to beat. Yeah I left a few things out of the simple analysis. Things like... Front surface reflection with rays normal to the panel is about 11% (unless you get an expensive multi-layer anti-reflection coating on the cover glass you can't beat this) and goes up with greater off axis positioning. It is a chain multiplication of various factors and they all contribute to reduction in Watts out but still it isn't worth being better than 5 degrees or so as the gain is virtually nill and the cost of doing it may be greater by far than the benefit.

A lot of really practical folks do similarly to what you suggest, just add more panels. The cost is similar and the results are about the same except you have much fewer moving electromechanical things to go wrong. A fixed mount can take a heck of a wind without being super expensive to build.

In Baja were our leased recreational property is located in a SOLAR ONLY area you see quite a spectrum of installations from garbage to terrific. Last time I looked there were few trackers and no dual axis trackers (in operation, one dual axis outfit that was hosed up and worked on by an idiot who probably fixed it so it couldn't be fixed.

I have panels on top of my camper and my motorhome. Designed an easy to point holder and then just mounted them flat on the flat roof. In the desert I start getting a trickle charge at dawn and max out at about 12-14 amps for much of the day. We only have 320AH storage at 12 vdc (I keep the parallel 100AH starting batts out of the action) We don't have excess charging capacity. Typically if it is hot enough to need A/C then there is enough sun to run our swamp cooler which works great in the desert. It only takes 6 amps to run it at its fastest speed. We use the entertainment stuff and lights at night with impunity and have never run out of batts. This includes sat tv. I did not install a big inverter to power the microwave. If we just have to use it I hit the genny button. Since my wife loves to microwave stuff the batts get a little charge that way as the charger is on and ready to contribute whenever the genny is fired up. Likewise the house batts get charged anytime the vehicle is fired up.

The frige is a 3 way gas 120vac or 12vdc. For safety at a filling staton we secure the gas frige and not having AC the unit automatically goes to DC and the solar panels run it.

When I was in San Diego several of the repeaters were solar backup (mostly at reduced output.)

EME (in my opinion) is best approached with a large high gain antenna array and not so much brute force in the power amp. It works better since the ant is good for receiving too. Some guys run high power and are heard but then may not hear the other guy. This is just more noise as far as I am concerned.

Pat

 

[Rob-D]

Pat,
My crazy thinking is that I don't buy what I can make and if I can buy a tool to make what I want cheaper then the cost of the item I do it because I figure I'll have a tool at the end that will save on my next project. This, by the way, was my thinking when I shelled out a big chunk of change on my tractor.

As I get older the problem is that you just don't have time to make all the things you 'need' and the tools build up so the only thing you need to buy is steel or the latest logic level MOSFET.

So my thinking with the tracker is this. With all my fancy MIG equipment and my latest digital Tek scope I figure buying the metal will run me about 300 to 400 bucks. ( I can run off the circuit with my EDA program and make the circuit boards here too) so the tracker design is not a long curve to a finished product.

My panels run anywhere from $900 to $1100.00 each and I'd need two to equal the tracker. The home made tracker wins out even in my advancing years.

As an after thought. Getting old has certain benefits, one being that you don't have to make things last forever. When I was twenty I did that. I just built a new garage and I figure buy the time the shingles run out there's a good chance I will if I haven't already. Don't get me wrong, I built a nice garage, it's just not as nice as the house I built 15 years ago!

 

[patrick_g]

Rob, Your thinking is not crazy at all or at least WE have plenty of company. Not that I can't lay out and fab a PCB but for just a couple copies I tend to do otherwise unless there are other factors that push me. I'm not the worlds best logic circuit guy but I manage. I still think in TTL and then translate to whatever modern chips I can get easily. Am I backward or what?

I used to build kits and or scratch build electronic equipment because it was fun. If you actually amortized the time I may have only made 5-10 cents per hour vs just buying the whatever.

The first time I wanted to change my Sumbeam Tiger from racing cam, solid lifters, high rise manifold with 4 bbl carb to cast iron intake with 2 barrel and hydraulic lifters, I got a ball park estimate from a garage and then went to Sears and bought a good socket set and did it myself. Paid for the tools and then when I wanted to revert back to "performance mode" I already had the tools and could switch back and forth pretty much at will. In hi perf mode the car would do 165MPH but it wasn't tame enough for the wife to drive in surface traffic as a daily commuter but with the hydraulic lifters, standard cam, and 2bbl carb it was a ***** cat (snarled a bit) but was OK for stop and go surface traffic.

Just recently I was getting ready to buy the steel and fab a round bale feeder but talked myself into buying a nice factory built and galvanized one since I would have been welding outdoors in 12-20 degrees and manually bending all the materials out there too. I'm not a wimp but I am getting less prone to look for opportunities to be a martyr.

Pat

 

[Little_Grizzly]

I haven't gone back and read the whole thread but I have a quick question I hope hasn't been asked.

What happens to the tracker if a small amount of dirt gets on one of the photodiodes and not the other?