Solar tracking systems

[john p]

What everyone seems to forget about trackers is most of the energy that the panels receive is bewteen 10.30 and 2.30 pm and slight angle variations dont make much difference. Using methods to point them accurately to the sun before and after those times will still generate very little extra.,compared to off axis.

Have a look at any "bell curve" for panels.

[Amarjee65]

Nice post.......

[vinniethePVtech]

What everyone seems to forget about trackers is most of the energy that the panels receive is bewteen 10.30 and 2.30 pm and slight angle variations dont make much difference. Using methods to point them accurately to the sun before and after those times will still generate very little extra.,compared to off axis.

Have a look at any "bell curve" for panels.

Not according to 1000watts/m2. An irradiance meter shows that even off by 1 degree can throw off 2% from pmax. Irradiance can also deflect, reflect, off of tempered glass. The problem is mostly the glass one of the reasons AR coating was used to bring cells closer to achieving max efficiency before glass was applied.

Anyway 10:30 to 2:30 are some pretty bogus hours. Just the AVG in sun hours where I live is 5.4hours. That means from that AVG only half of that is full potential, meaning a little after 12 until about 2:45 is where the most power is made and that will change according to the season.

Trackers were developed to capture every hour of full irradiance, and it is proven to work.

[TnAndy]

Well, in my case, I was going to have to pole mount anyway ( House roof is too shaded and I'm not willing to give up the natural A/C effect ), so to make them track was simply a matter of adding a couple 2" pillow block bearings ( 60 bucks ), a 4' piece of round shaft steel ( 40 bucks ), a linear actuator ( 150 bucks ) and a controller ( 140 bucks ) and some wiring to get 24vDC supply to the pole ( maybe another 50 bucks )......so for less than the price of one 175w panel ( which were 800 at the time ), I figured if I got even 10% more production, I was money ahead.

.....not even factoring in the "coolness" issue......ahahahahaaaaa

[john p]

Vinnie if that degree of accuracy was needed then every fixed panel in the world would be only producing the panels max output for 10 mins for one day of the year. If the 1 deg made 2% difference then there would be just about no output in wintertime if the panels were optimised for middle of summer.
I dont know where you live but where I live we get same output from panels at 11 am as 1 pm.

The most perfectly aligned panel in any part of the world will be producing only a small fraction of its noon output at 9am or 4pm

[TnAndy]

The most perfectly aligned panel in any part of the world will be producing only a small fraction of its noon output at 9am or 4pm

Define "small fraction".


At 9am, given a good sunny day, my arrays produce (2) 1350w and 1900w, ( give or take ) and at noon, about 1550 and 2250 of a potential 1750 on (2) and 2450 on the other. Takes a bit for the dew to burn off the panels. At 4pm, they are pretty close to noon.

I'll turn the power off the big array tracker tomorrow, leave it in the fixed noon position and provide readings at 9, 12 and 4.

[russ]

You apparently have a big meter problem - the insolation data for a location (direct normal radiation) comes in roughly the shape of a bell curve.

There ain't no way to get the same output early and late as at mid day with any tracker.

For example, today the insolation here was at
0900 hours 232 watts/m2,
1000 hours 387,
1100 hours 499,
1200 hours 565,
1300 hours 569,
1400 hours 508,
1500 hours 395,
1600 hours 234
and 1700 hours 55.

For 4 hours it was roughly the same but no tracker will help for 900 hours for example.

[john p]

Tn Andy I think Russ has defined my saying "small fraction".. You can build the best tracker in the world with a .000001% accuracy of the panel facing the sun and at 9am the panels will still be producing sweet FA.

[TnAndy]

OK fellows.....these readings are from the Outback charge controllers, so I have no way of verifying the accuracy, but I assume it's not TOO far off.

The sun tops a ridge to the east of me about 7:50 this time of year, and begins to hit my arrays.

All three arrays were tipped due east this morning ( they reset at night ). The two lower arrays are 10x175w, and the upper is a 10x245w. Weather conditions were BRIGHT clear day ( rain front from yesterday moved out ), temp was 36 degrees F.

The lower arrays move on single axis and are fixed at 37 degrees tilt angle ( my latitude ). The upper array is currently on 45 degrees, it's " near winter" position ( doesn't auto track in tilt, I put a manual control on that part and have to hit a switch to get it to adjust, plan to do that once a quarter...it can go to about 50 degrees.... but it does auto track east/west daily )

At 8:15, the two lower arrays were reading 1222w and 1115w, respectively, on their separate FM60 controllers. Sun is still peaking thru some deciduous trees, leaves gone, but branches still doing some shading on one of the lower arrays.....the reason I put the new, larger one higher on the hill )

The upper array was reading 1770 on it's FM80 controller.

At 8:30, (1) 1288, (2)1250, (3)1840

I moved the upper array to the noon position, walked back down
and read the FM80: 1410w

Loosing 400w by moving it to the noon position, where most fixed panels would be.

9am readings: (1)1404 (2) 1392 (3)1625 (still in the noon position)

Tipping the upper array BACK to the east, reading went to 2075w.

Kwhrs produced today as of 9am: (1) 1.5 (2) 1.4 (3) 2.4

Pic taken at 8:30am



Make of it what you will.....I'm not trying to convert anyone, just reporting what I see.

[Sunking]

Trackers will yield about 18 to 26% more harvest.

[Naptown]

You apparently have a big meter problem - the insolation data for a location (direct normal radiation) comes in roughly the shape of a bell curve.

There ain't no way to get the same output early and late as at mid day with any tracker.

For example, today the insolation here was at
0900 hours 232 watts/m2,
1000 hours 387,
1100 hours 499,
1200 hours 565,
1300 hours 569,
1400 hours 508,
1500 hours 395,
1600 hours 234
and 1700 hours 55.

For 4 hours it was roughly the same but no tracker will help for 900 hours for example.

That is inslolation in it's simple form and not accounting for angle of incidence and reflection increases due to the higher angles. A tracker does not increase insolation but it does reduce dramatically the angle of incidence I agree with Dereck that the harvest is improved.

[vinniethePVtech]

Trackers will yield about 18 to 26% more harvest.

23.4% difference in harvest and that's just in early morning. Amps will typically be higher in the morning as it is cooler than afternoon temps.

[russ]

That a tracker improves harvest has never been in question (I don't think). How much is the question.

More harvest due to improved angle of incidence only. What insolation there is is all that there is. The sun does feel hotter on the skin at midday than at 0900 hours after all.

The insolation number includes any reflected photons.

Outback seems to have come up with a good sales gimmick possibly? The only way to know would be to monitor separately what actually goes to the batteries.

[Sunking]

When it comes to tracking, what it really boils down to is economics, space limitations, and maintenance.

Starting with maintenance you want to avoid tracking systems if possible because like it or not the system will require maintenance, be more prone to wind damage, and equipment/hardware things will fail at some point.

Economic for most battery systems it will be less expensive to just add more panels. Even if not maintenance cost has to be calculated in the long term investment. Fixed systems are not prone to mechanical failures and less susceptible to wind damage.

Restricted space is where tracking systems can be justified economically. Where minimum power requirements must be met on a daily basis tracking system might offer a solution. With that said the window of opportunity is small of about 20 to 25% more harvest.

[russ]

From PV Watts for the Dallas-Fort Worth area for a 1 kW system

no tracking - annual kWh production projected at 1404 kWh

1 axis tracking - 1783 kWh

2 axis tracking - 1876 kWh