Solar Panel Performance vs Panel Tilting

[CA_Traveler]

The following chart reflects solar panel performance for Denver, CO for the Summer Solstice on 6/20/16. The calculations are based on the USNO sun data which includes sun elevation and azimuth. The solar panel is also set to a given elevation (0 = vertical and 90 = flat) and azimuth. The RV Education website equations were used to calculate the suns angle on the solar panel and the power calculated based on 100W. The calculations do not reflect any parameters like air mass, atmosphere, temperature, shadows, etc. The calculations include the elevation and azimuth of both the sun and the panel.

The maximum sun elevation is 74 degrees and the sun azimuth is then 185 degrees. The solar panel orientation was set to the same values for the chart below. The chart shows the wattage for the day. Notice that for the early and late hours there is no panel output because the sun is behind the panel.



The total wattage for the day is 846Wh.

The following chart shows the Sun elevation and azimuth for the day. The right hand scale is for the azimuth.



The suns azimuth changes 243 degrees during the day.

[CA_Traveler]

Summary for Denver – 40 degrees latitude

Spring Vernal Equinox 3/19, elevation 50 degrees from vertical, 764W, flat 587W, 0 declination, Fall Autumnal Equinox 9/22 similar

Summer Solstice 6/20, elevation 74 degrees from vertical, 846W, flat 881W, max declination

Winter Solstice 12/21, elevation 27 degrees from vertical, 751W, flat 271W, min declination

Tilt the panel to or near the maximum sun elevation. Using latitude is less desirable and doesn’t account for the earth declination which varies 47 degrees during the year.

The calculations used for this thread do not account for air mass, atmospheric conditions, etc that effect solar panel and that effect can be greater in the morning and afternoon.

[mchero]

Put 1k of panel on my roof flat.

[JiminDenver]

CA Traveler wrote:
And for Jim's pesky Denver noon time clouds rotating the panel 45 degrees to a azimuth of 133 degrees yields this chart. 🙂



But not much afternoon power from the sun. 😞

It's a choice of morning sun or afternoon clouds, it doesn't take much to hold float in the afternoon.

[JiminDenver]

It's easy to say add another panel but for some of us it isn't quite that simple.

My roof is maxed out without racking to avoid obstacles with the fourth panel. I wouldn't get much out of a fourth panel except for a hot controller as it would be over paneling most of the time. So after racking the panels and replacing the controller, I'd need to find a match to my high voltage panels or risk confusing the controller. Were I not able to find a match, I'd have to buy a new set. Might as well upgrade to the next size up since I racked them, right.

So after a small fortune and a lot of effort, I could go from 750w to over 1700w and avoid tilting. 🙂

[Ro_n_Joe]

Golden_HVAC wrote:
I don't tilt my panels anymore because I don't want to risk damage to my roof, or breaking my leg either.

It is now cheaper to get an additional panel than to tilt and worry about your time on the roof.

I can recall my first 90 watt system with controller, mounts, wiring, ect. for $750. Then upgrading in 96 with a 75 watt panel for $375 - only $5 per watt! Later in 99, I installed some 120 watt for $429. Now you can get 140W for $229. Much less expensive than the original prices, and wages have gone way up, so what would have taken a couple weeks pay can now be paid off in one day's work.

Good luck,

Fred.

2X here. Add more solar and don't worry about it

[gatorcq]

Repeat of many test done in the pass.

That is why I have 1000 watts, so I do not have to geton roof and tilt.

Sorry

[CA_Traveler]

And for Jim's pesky Denver noon time clouds rotating the panel 45 degrees to a azimuth of 133 degrees yields this chart. 🙂



But not much afternoon power from the sun. 😞

[CA_Traveler]

The following chart reflects solar panel performance for Denver, CO for the Winter Solstice on 12/21/16. The maximum sun elevation is 27 degrees and the sun azimuth is then 178 degrees. The solar panel was set those same values for the chart.

This chart shows the wattage for the day based on 100W.



The total wattage for the day is 751Wh. This is only 11% less than the 846Wh for the Summer Solstice. Panel tilting makes this possible.

The following chart shows the Sun elevation and azimuth for the day. The right hand scale is for the azimuth.



The suns azimuth changes 119 degrees during the day.

[CA_Traveler]

ktmrfs wrote:

I disagree that tilting doesn't make a difference in the summer. Further south, likely, but up north, it does. Not near as much as fall/winter/spring but it does.

I see about 20% increase in output in the summer between a flat panel and one tilted properly at 45 degrees north.

Easy way to set panel optimally

hold a empty TP or paper towel tube perpendicular on the panel
Adjust for zero shadow.
Done.

If I'm not around for the day, I set it for ideal around mid day.

To be clear I was referring to the Summer Solstice in Denver and per the above post the panel is set to the maximum sun elevation which is only 16 degrees from being flat. Under those conditions tilting doesn't buy much on that day. Different days and locations merit their own consideration for tilting.

[N-Trouble]

Golden_HVAC wrote:


It is now cheaper to get an additional panel than to tilt and worry about your time on the roof.

^^THIS^^

[Golden_HVAC]

I don't tilt my panels anymore because I don't want to risk damage to my roof, or breaking my leg either.

It is now cheaper to get an additional panel than to tilt and worry about your time on the roof.

I can recall my first 90 watt system with controller, mounts, wiring, ect. for $750. Then upgrading in 96 with a 75 watt panel for $375 - only $5 per watt! Later in 99, I installed some 120 watt for $429. Now you can get 140W for $229. Much less expensive than the original prices, and wages have gone way up, so what would have taken a couple weeks pay can now be paid off in one day's work.

Good luck,

Fred.

[ktmrfs]

CA Traveler wrote:
Summer tilting makes little difference and leaving he panels flat is close to optimal. And panel azimuth makes virtually no difference.

I'm working on the winter charts where tilting is very beneficial. Also advancing the panel azimuth can help compensate for those noon clouds. 🙂

I chose Denver not for the weather but because it's about mid latitude for the lower 48.

I disagree that tilting doesn't make a difference in the summer. Further south, likely, but up north, it does. Not near as much as fall/winter/spring but it does.

I see about 20% increase in output in the summer between a flat panel and one tilted properly at 45 degrees north.

Easy way to set panel optimally

hold a empty TP or paper towel tube perpendicular on the panel
Adjust for zero shadow.
Done.

If I'm not around for the day, I set it for ideal around mid day.

[CA_Traveler]

Summer tilting makes little difference and leaving he panels flat is close to optimal. And panel azimuth makes virtually no difference.

I'm working on the winter charts where tilting is very beneficial. Also advancing the panel azimuth can help compensate for those noon clouds. 🙂

I chose Denver not for the weather but because it's about mid latitude for the lower 48.

[JiminDenver]

That can't be Denver, there are no clouds at noon. lol

Tilting in the summer cost you early and late, plus doesn't benefit much at noon over flat. Tilting in the winter makes much better sense due to limited loss early and late and a large benefit over flat at noon.

Now unless we are in a drought year, if you come here in the summer, tilt to the south east. Take advantage of the morning sun before the clouds roll in between 11 am and 1 pm and drop them flat after that.