Off grid different than on grid for location

49 Posts
Feb 20, 2011 09:10 pm
Off grid different than on grid for location

  I would like to know what people think on where to mount the panels. example- on a grid system you would always point the panels to the south. On an off-grid you only have so much storage so if there all south when you use energy around suppertime you wouldn't gain as much in the evening for your batteries to last through the night. I have 3 220w facing south and 3 facing mostly west, my batteries are charged enough in the day for the generator not to kick in then in the evening the batteries are charged more. does this make sense.
97 Posts
Feb 20, 2011 11:44 pm
Re: Off grid different than on grid for location

Interesting query, James.  I have an off grid system for household, with 2kw of solar, and 2.5kw of wind.  In the summer, the sun rises and sets on a sweep of over 180 degrees, so I have a bank of panels on the east for morning sun, a bank to the south for midday sun, and a bank on the west for evening sun.  For year round optimal angle, the panels are set to the same inclination as my latitude........44 degrees. I have no generator, but use twice as much battery capacity as i would normally need. I am located in the midwest and get most of my power from wind, however, being next to the Dakota's.  I have often wondered if a solar tracking system would give me better performance or simply be another load circuit to drain my resources.  Anyone have some input about that?  Jon C.
99 Posts
Feb 21, 2011 12:26 pm
Re: Off grid different than on grid for location

I have my house and panels pointed to magnetic south.  Here in PA, that's about 15 degrees east of solar south.  I did that on purpose because the batteries will drain and the house will cool overnight, so I want to get them charged up first thing in the morning, not wait until mid-day.  If my batteries are full long before supper, that's ok, they'll hold me through the night.  A westward facing bank of panels at that point wouldn't do me much good other than maintain full batteries.  Most of the energy would probably go to waste.  The worse case is to have an overcast day then go through the night and not take advantage of first light to charge up again.

As far as vertical orientation, I pointed mine at 60 degrees to get the most direct exposure on the shortest day of the year.  This is important when off-grid, but not such much when grid-tied.  I may get much less power in the summer (and therefore for the year) than I otherwise could, but it's still much more in the summer than the winter.  The steep angle flattens out the seasonal curve to ensure I get decent power all year long.  It also deflects hail and snow this way.

A tracker sounds enticing to solve these issues, but I figure for the cost of a tracker, I could buy a lot more solar panels, so what really is the payoff?  I'd rather have the reliability of solid-state panels than a complex mechanical/electronic device.
49 Posts
Feb 21, 2011 06:53 pm
Re: Off grid different than on grid for location

 Wouldn't pointing them more east charge them up earlier
 I noticed here in Wisconsin the winter mornings are usually clear then it clouds up later.
99 Posts
Feb 21, 2011 09:31 pm
Re: Off grid different than on grid for location

Wouldn't pointing them more east charge them up earlier?

Yep.  The same reason you need breakfast in the morning, your off-grid system needs morning sun.  After the night, you're more likely to need to fill up your batteries than in the evening.  That's why I think photovoltaic panels' marginal utility is higher by pointing them slightly east.  But that's only true for off-grid.  For grid-tie, pointing them at solar south is better because you'll get greater total energy from them and there is no storage issue.

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