On Wednesday, August 16, 2017 at 5:04:17 PM UTC-4, micky wrote:


How much sun does the north side of a roof in your area get
even in summer?

Whatever Derby Dad's page said.

It's not about summer just summer
months, it's about how much sun falls on a given roof face
during the entire year.

It depends on what you mean by "it". You appear to be talking about the
annual solar input, but I was talking about "The sun is overhead in the
summer".

Do people typically buy these systems based on it's output versus
it's cost savings based on the summer only or on a whole typical
year?





South facing is best, sw is still
very good. North, forget about it. I've never seen an array
facing north, have you?

I have. Did you read Dad's page. It's not such a bad idea,depending on
the latitude and slope of the roof, and maybe there were other factors.

I just read it now. Let's start with this:

How much worse are north-facing solar modules?

"We start with a typical residential system in Charlotte, North Carolina. We designed and modeled the system in HelioScope, our sales and design software platform. With a 2/12 pitched roof...."


So, they don't start with a "typical residential system", unless 2/12
roofs are typical in NC. Are they typical in MD? They aren't typical
here, 6/12 would be typical. Then they say that if it were a shallow
pitched roof of 1/12. WTF? 2/12 is already shallow. If it's close
to flat, then orientation doesn't matter. Finally they
start to get to reality, 4/12 is 29% less efficient when facing north.
I'm not going to bother with the calculator to find out how bad it gets
when you reach 6/12 pitch, but from the shallow 2/12 roof to a 4/12 roof
the efficiency loss doubled, so draw your own conclusions on what
happens as you get closer to a typical roof. Even at 4/12 you're
29% worse off and that's in NC, if you go further north it gets worse
too. The economics already
need subsidies to make them practical and that's for a normal install.
If you want to put one on a typical roof that faces north, you can
but the economics get much worse. That is why I don't see them on
north facing roofs here.