backchannel: why aren’t tilted panel daily harvests higher?

Tilting panel is advantageous when the sun is relatively low in the sky (winter, higher latitudes, morning/afternoon, etc).  The question is how advantageous?

Grand Canyon example

A fellow excitably posted about his increased yield when tilting:

100w panel will be at least 4 times as efficient

That’s clearly not true, panel efficiency is a function of construction and materials, among other things.  Efficiencies in the 15-20% range are pretty typical.  Anyone who could increase efficiency to 60-80% would be a billionaire. It’s clear he meant that in his brief testing tilting resulted in 4x more power at that moment.  That’s certainly possible (I saw 3x late yesterday as the sun was setting) , and makes little practical difference.

According to pvwatts, the difference in daily harvest between flat-mounted panels and optimally tilted panels at that latitude is +32.39%.

Wait.  How can watts be +400% but daily harvest only +32.39%?

limiting factors

A couple things are going on.

  1. Tilt advantage is greatest when power harvest is most limited.  A 100w panel making 15w flat at sunrise  is  still only **60w **tilted. for example.    As the sun gets higher more power is available and the flat-mounts are working better.  This reminds me a bit of running higher voltage strings in low-light;  yes you get more power but in practice the numbers are quite low.

  2. Tilt is most advantageous in clear skies when the sun directly strikes the panels.  Cloudy skies diffuse the light so angle of incidence is less of a factor.

The question is not “does tilt advantage exist?” (yes) but “is it worth it for any particular person to tilt their panels?” (maybe)

Lots of experienced full-timers who stay emplaced for a while have large panels they prop up in the winter.  A +32.39% bump for a few minutes effort sounds like a good deal.  In summer I see most of them stay flat on the roof.

My overall approach has been to overpanel to make up for flat-mounting.  That failed in the forest but tilting would have, too.    In the forest context portability is more important than tilt.