Author Topic: Tilting (at) solar panels  (Read 4257 times)

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Offline SomeoneTopic starter

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Tilting (at) solar panels
« on: August 06, 2016, 10:23:54 am »
Running the numbers for installing some solar systems in Melbourne (37.5 degrees south) comes up with some interesting optimisations for positioning. The "default" annualised daily generation factor suggests 32 degrees off level:

But this is simply to globally maximise energy generation for a fixed system. Peak power delivery can be shifted several hours into to the afternoon without measurable losses by rotating the panels mounting in the direction of the setting sun, but this has seasonal limitations and vertical tilt has seasonal variations. These for a north facing array and are normalised to the 25 years of historical average insolation data from the Australian Bureau of Meteorology to include climatic/seasonal/local variations and assume a perfect sky view with no shadowing:

Back from the "Direct" 100% fill in the case of a perfect 2 axis tracker, the fixed possibilities average around 70% of the perfect tracking. Sticking to an optimal fixed 30 degree install averages an annual load factor of 24% which is achievable and proven in installations.

But if the mounts were adjustable and you manually changed the tilt with the season you could get 5% more energy for a two angle schedule, or 7% more for a 3 angle schedule. Seems like its worth the couple of hours a year to shift the panels and keep them clean.
 
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Offline Seekonk

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Re: Tilting (at) solar panels
« Reply #1 on: August 06, 2016, 03:07:43 pm »
Seldom can panels be idealized unless you live in the middle of nowhere.  My panels are fixed and lay almost flat, about 10 degrees.  Like to keep a low profile because all my panels are not even on my own land.  I am almost a batteryless system and prefer more even power throughout the day rather a higher daily total.
 

Offline mtdoc

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Re: Tilting (at) solar panels
« Reply #2 on: August 06, 2016, 05:55:50 pm »
I have 2 solar arrays. One is an 1800 watt array on a pole mounted 1 axis tracker.  I manually adjust the tilt twice a year (spring and fall) to eack out a bit more production - but honestly the gains are minimal.  My other array is 2700 watts on a fixed south facing 45 degree tilt on a shed (I live at 48 degrees North).

NREL has an excellent online tool.  Their PV Watts Calcuator lets you set your location, array size, etc and then adjust tilt to see how theoretical output (based on historical solar insolation data) changes.

 

Offline SomeoneTopic starter

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Re: Tilting (at) solar panels
« Reply #3 on: August 06, 2016, 11:18:04 pm »
Did you try to use some of those sun path tools? (btw, I think the Y scale is in error, should be 0.1kWh to 1.2kWh)
Its all using sun paths, otherwise you cant optimise the panel facings. The vertical axis is correct in its maximum of 12 kWh/m2/day or 12000 Wh/m2/day peak insolation.
I have 2 solar arrays. One is an 1800 watt array on a pole mounted 1 axis tracker.  I manually adjust the tilt twice a year (spring and fall) to eack out a bit more production - but honestly the gains are minimal.  My other array is 2700 watts on a fixed south facing 45 degree tilt on a shed (I live at 48 degrees North).
Like trackers there is this weird intermediate system size around 10-100kW where it makes sense to adjust the tilt seasonally. The amount needed to adjust the tilt between seasons is similar for most latitudes.
NREL has an excellent online tool.  Their PV Watts Calcuator lets you set your location, array size, etc and then adjust tilt to see how theoretical output (based on historical solar insolation data) changes.
I'm not sure where they pull their numbers from but they estimate a 10% load factor for Melbourne, which is much less than half the achievable performance, perhaps there is a large derating factor for shading to keep the public consumers happy? And it may not be doing full path tracking since it doesnt match the relative changes between 30 and 60 degree mountings in my fully worked example.
 

Offline Red Squirrel

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Re: Tilting (at) solar panels
« Reply #4 on: August 07, 2016, 04:05:48 am »
I always thought it would be neat to setup an array like space stations, but it would have to be very strong if there is a wind gust.  Basically it would deploy upwards in the morning and face east, and slowly turn and track the sun. Then at night it would retract. This would also keep the snow off.  You'd only get one axis of tracking but you'd get exposure throughout the whole day.

I also wonder how well mirrors could work to boost solar output, you don't want to cook them, but maybe just one line of flat mirrors that reflects more sun to the panels.  I guess where you can put the mirrors you can just put more panels.  More expensive but more output.
 

Offline SomeoneTopic starter

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Re: Tilting (at) solar panels
« Reply #5 on: August 12, 2016, 03:19:42 am »
Tidying off with some examples of changing the direction the panels are pointing its surprising to see how little is lost when turning them away from the optimal facing. Many installs in local suburbs face whichever way the roof points with no effort to match any angles and its not as bad as you might first think when angled at a typical 30 degrees to the ground:


And optimisation of rotating the facing to shift generation to the evening peak, assuming the array is small enough that you will self consume all the power it generates in the evening peak:

At typical price differentials of 1:3 or 1:4 its already a substantial change in orientation.
« Last Edit: August 12, 2016, 03:22:45 am by Someone »
 

Offline poida_pie

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Re: Tilting (at) solar panels
« Reply #6 on: September 13, 2016, 04:33:04 am »
But if the mounts were adjustable and you manually changed the tilt with the season you could get 5% more energy for a two angle schedule, or 7% more for a 3 angle schedule. Seems like its worth the couple of hours a year to shift the panels and keep them clean.

Or buy one or two more panels and forgetaboutit?

Like you I modeled tilt angle and found there was not a lot of difference in any angle over the year.
The result freed me up to build the panels at about a 15 deg tilt which was optimal for the area I had available to cover (a double space carport roof. I spent a lot of time fretting over the installation details of the 3kW system.
2 years later I found a source for another 3kW of 1 year old used panels at $130 each (compared with $300 each for the new ones) and now I think "just put them on the roof, and get it over with". It's funny how my attitude to this has changed.

I do not care to maximise the peak power output, even 3kW is enough when the sun is out. But I also live in Melbourne and the sun is not out most days. Having the new 3kW array facing East will in no way diminish the new array's benefit since I want more power in cloudy days and orientation is nowhere nearly as important with the diffuse light provided by cloudy skies.

Cleaning panels is not quite worth the effort I have found. I have some trees that shade one or two of the panels and trimming them is the only reason I get on the carport roof.


 
 


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