Racking challenge

ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
We have a potential customer who wants to put something on the order of 20kW of PV on the roof of his business. His roof is flat and there are no trees or other buildings obstructing solar incidence onto the building. It is a multi level roof, and most of the sections are pretty small, but the main contiguous section is roughly square and is about 190 m^2, so we should be able to get fairly close to his 20kW request if there were no other problems.

There is a problem, though. The section of roof in question has a 56" concrete wall around it. Here in Austin, a sun chart shows that the solar elevation at 9 AM and 4 PM on the winter solstice is just a smidge over 16 degrees. If we set back from the wall on three sides (the edges of the roof are very close to N-S and E-W) to allow for full sun down to the deck from 9 AM to 4 PM on Dec 21, that 190 m^2 of roof area is reduced to something less than 375 m^2. Ouch.

Some of the ideas I have been tossing around are raised racking, module level MPPT tracking a la Solar Edge, Tigo, etc., or microinverters, and raised racking AND module level MPPT.

Any other ideas?


  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Racking challenge

    you have another problem besides that concrete wall for the pvs themselves will have height to harvest the winter sun and will cast a shadow to the next pv or string of pvs behind it. you may need to raise some of the pvs that are to be shadowed up higher and do it like you would for bleacher seats at a ll baseball game. the ones in the very front can be on their own inverter or as you say using the enphase type, but it's not for me to debate that point for now as either way pvs and inverters would be idle if not raised.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Racking challenge

    If you are going to cover most/all of the roof, then I would go with raised (and probably tiered as neil said) in order to leave crawl space below the PV modules in case of a leaky roof that needs a bit of goop, or whatever.
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