
How much less efficient are north-facing solar modules? (2016) - curtis
https://www.solarpowerworldonline.com/2016/06/much-less-efficient-north-facing-solar-modules/
======
curtis
I've been wondering for a while if vertical solar panels on the sides of
buildings might make sense. Today (for no reason that I know of) I started
wondering if might even make sense to put panels on parts of a building that
don't directly face the sun at all.

That's what lead me to this particular article, which examines the efficiency
of putting panels on north facing roofs.

I explored the vertical panel idea in a blog post last year:
[http://curtisb.posthaven.com/the-solar-garage-
door](http://curtisb.posthaven.com/the-solar-garage-door). I don't know if
that idea would work, but I was trying to imagine an application of the idea
so absurdly simple that a startup could easily use it to bootstrap into a more
lucrative market.

~~~
Retric
Generally, you don’t run out of roof space before meeting a 2 story buildings
energy needs. On taller buildings installation costs would be significant,
coupled with lower effects and it’s more viable to put them just about
anywhere else.

The garage door is a rather complex place to put them as their are a huge
range of styles and you would need to either fit the opening and replace the
mechanism, or design a door for each existing type sold. On top of that wiring
up solar to your house is the tricky part not putting something on a roof.

~~~
jefftk
Around here (Boston) roofs tend to have a lot of obstructions: dormers,
skylights, chimneys, vent pipes. They're also typically very steep (1:1) so
North-facing isn't an option. Then you lose some space due to shading from
trees and other houses. When we got solar there was only room for panels
covering 1/4 of our electricity usage.

~~~
Retric
That’s an extreme situation as Boston is rather far to the north and has poor
weather for solar. Covering a skylight with solar is a net energy win, as
would taking down the tree(s). Trees are also going to block the front of your
building even more than the southern facing roof.

Getting shade from other buildings on your roof is also unusual for 2 story
buildings.

~~~
gumby
Not sure I would call Boston especially north as it is south of, say, Nice.

~~~
Retric
It’s 42.3601° N closer Toronto at 43.6532° N than New York City at 40.7128° N.

By comparison Miami is 25.7617° N and still above the Tropic of Cancer 23°26ʹ
which is the furthest north you can get where the sun is ever directly
overhead.

PS: Europe is kind of deceptive as the equator is so far down below the bulk
of Africa. But so many maps stop at the top of Africa it’s easy to think of it
as some sort of mid point. Further, due to weather patterns it’s warmer than
you would expect.

~~~
goodcanadian
_It’s 42.3601° N closer Toronto at 43.6532° N than New York City at 40.7128°
N._

It's relative, I suppose. From a Canadian point of view, Toronto is just about
as far south as you can get.

~~~
gumby
What about Turks and Caicos :-)

(Couldn’t understand why you guys weren’t enthusiastic for their offer)

------
DuskStar
I think it should probably be noted that this analysis is for grid-attached
solar, not grid-independent. For the first, you're generally not going to care
about the seasonal power profile (you get paid the same for a kW in June or
January) and so the north-facing array's production being more heavily loaded
into the spring and summer months won't matter. But if you're trying to
actually power your house, you probably want all the power you can get in the
winter months. Optimizing for minimums, not totals, if that makes any sense...

~~~
coldtea
> _But if you 're trying to actually power your house, you probably want all
> the power you can get in the winter months._

Even so, if you can't have a south-facing module, the fact that you don't lose
as much in many circumstances (roof slopes etc) is good to know.

Even when one wants to power their house, there's no need to go in an "all or
nothing" approach.

------
johnhenry
Anyone in the southern hemisphere confused about this?

~~~
FooHentai
Nah, most stuff is written with the assumption of being in the Northern
hemisphere (after all, ~90% of humanity lives up there).

It's the same as having to ROT6 any gardening advice or you'll be planting
things at the worst possible time :)

------
singularity2001
With the price for solar-panels falling exponentially (1/2 every ~6 years),
north facing tiles even in the most extreme examples will become profitable in
a few decades or less.

[0] [http://blog.comparemysolar.co.uk/wp-
content/uploads/2013/03/...](http://blog.comparemysolar.co.uk/wp-
content/uploads/2013/03/10-year-solar-panel-price-forecast-2013-2022.png) etc

------
thedoops
Good rule of thumb is that the best production per panel ratio to get the most
utility consumption offset (so you drop to the lowest tier) will return the
most savings.

Shaded or North facing panels in the northern hemisphere are almost never
worth it. Put what you can on the south and look into a better AC unit, new
windows, LEDs, and insulation first.

------
myroon5
Depends on the hemisphere

~~~
oska
You've been downvoted but I also noticed the "northern-hemispherism" (to coin
a word) in the title. It does get a bit tedious for those of us who live in
the southern hemisphere.

------
foxhop
I live in Connecticut (New England) and most of my panels are positioned
slightly north.

[https://russell.ballestrini.net/fulfilling-childhood-
dreams-...](https://russell.ballestrini.net/fulfilling-childhood-dreams-
solar/)

------
Johnny555
His numbers are overly optimistic in most of the country where a 2/12 pitch
roof is uncommon, 4/12 - 9/12 is more common.

Is 2/12 common anywhere? Certainly not in any place that gets snow.

(he does give some numbers for other pitches in his charts, but in the teaser
paragraph, he uses 2/12)

~~~
Retric
It’s not just the charts, “In Minneapolis, a 10/12 pitched roof that is
perfectly north-south will have a 57% penalty between the south-facing and
north-facing modules.”

Really, you should not complain if you’re badly skimming an article.

~~~
Johnny555
If he gave some context in the beginning of the article where he exclaimed
"Not great, to be sure, but probably not as bad as you might expect!" to say
"But a 2/12 roof is very shallow" (and indeed is the minimum pitch suitable
for shingles), I might agree.

But you shouldn't have to get half way into the article before you find out
that he chose the absolute best case for his example and you're not likely to
see the same results in the real world.

~~~
Retric
The very next paragraph starts with ‘The tilt of the roof matters a great
deal.’ Including a much worse example at 29% worse, but also a better one 1:12
which are not uncommon for that area. He then adds ordination of the building,
and latitude as further examples.

Really, if he had started by showing a huge chart it would have been gibberish
to most people.

------
seymour333
This probably applies more to homes with an East to West facing pitch, but I
find it really odd that it isn't standard issue to have a track system that
moves the solar panels from one side of the roof to the other. A simple track
and something basic like a garage door motor would allow the panels to be in a
more optimal position throughout the day.

------
tejohnso
Slightly off topic, but why is there so much discussion about fixed rooftop
solar compared to a ground based system with tracking? Seems to me a ground
based system would be easier and safer to set up, easier to keep clean, and
easier to keep in an optimal position, even if it didn't have tracking. Why
have this tight coupling to the roofing system?

~~~
bradknowles
It develops that tracking systems are expensive, heavy, and take up a lot of
space.

In fact, so much so that the tracking systems rarely make sense with modern
panels. You would usually be better off spending the money, weight, and space
on more fixed panels than messing with the tracking systems.

~~~
tejohnso
That's disappointing. It's too bad the tracking systems are such a burden.

But what about a simple wooden structure to hold fixed panels oriented
optimally? That's a few thousand dollars at most, for a twenty to sixty
percent efficiency improvement. It would kill me to mount panels facing North
at a 45deg angle.

