How far away from north facing slope is ok for solar?

Hi, I'm looking at a 100 acre property with a flat building site but has a hill on the south part. In the attached contour map, each contour line represents 15 feet elevation. Point A would be my proposed building site. Point B is an example of a bad place to build because it is too close to the north slope.

Point A seems far enough away from the hill at 600 feet. But how do I determine just how far away from the slope I can be to still get good sunlight for solar panels?

Thanks!

Aldo Caine wrote:Hi, I'm looking at a 100 acre property with a flat building site but has a hill on the south part. In the attached contour map, each contour line represents 15 feet elevation. Point A would be my proposed building site. Point B is an example of a bad place to build because it is too close to the north slope.

Point A seems far enough away from the hill at 600 feet. But how do I determine just how far away from the slope I can be to still get good sunlight for solar panels?

Thanks!

what latitude is the property located at?

Are you talking about a North facing slope?
Where is north on the photo, to the top of the page?
What hill are you talking about being 600ft from Point A?
Essentially you need  a place where the sun has maximum number of hours landing on the solar panel.
Without numbers on the contours is difficult to read the land shape.
I am guessing perhaps the dark spot is lake, pond or dam?

I have worked it out, I thought the distaNCE LINE WAS actually pointing to Point A.
And I have realised how the contours are rising from the creek bed and the lake.
So Point A on the south facing slope is much better than point B.
Is the N-W corner of the block excised from the property?
I am guessing from the contours that some of those slopes are quite steep, am I correct?
What would you do on the land out of interest?

Of course there are many other considerations to take into account;
- access, is there a road adjacent to point A?
- water supply, I encourage rainfall collection. Look at my signature.
- soil quality

You can calculate sun angles for your location throughout the year at this site:
https://www.sunearthtools.com/dp/tools/pos_sun.php

I believe this calculator assumes flat land. I'm not sure how to precisely calculate the effect of a north slope. I think it creates an artificial horizon, essentially mimicing a more northerly latitude. This means fewer minutes of direct sun, and less production.

I wonder if you could put in stakes at a "maximum sun" location and at Point A, and mark where the morning sun and evening shade hits them. This might give you a rough-and-ready correction factor.

I advocate the empirical approach, and just put out a sheet of plywood, or some other flat surface, and watch how the sun plays against it.  Figure that in the middle of winter, the sun will be about 30-35 degrees lower in the sky then right now.  That shouldn't be too hard to eyeball.

Here is something to think about in the design phase.  Modern MPPT charge controllers act like a transformer, taking raw high voltage solar and transforming down to battery voltage, making extra amps out of the extra volts.  What that means in the real-world is that you can now wire your panels in series to get high-voltage, then transform it down to battery voltage right at the controller.  Then you can position your array wherever you please and transmit the power to your system with little or no power lose.

Here is what I am doing.  I've wired four 30V 250W grid-tie panels in series to get 120VDC.  I run this ~130' from the array to the utility room where the solar electronics are.  My Midnight200 controller takes the 8A at 120V, and transforms it down to ~38A at 25V to charge my 24V battery bank.  Using 10 gauge solar cable, I see zero voltage drop at 130'.  

For you, you don't need to worry about shadows from the north hill.  Just build an array in the sunniest spot within a few hundred feet of your building, then run 10 gauge wire from your array to your batteries.  You can use this voltage drop calculator to predict exactly how much a certain distance will cost you.  https://www.calculator.net/voltage-drop-calculator.html

BTW, you don't want to do this with 12V panels.  You get far better results with high-voltage grid-tie panels, which are available on Craigslist right now for ~4W/$.  12V is just too expensive.

The Midnight200 charge controller is a bit pricy, so you might want to look at other controllers that can handle 200+V.  Take a look at Epever's Tracer 5420AN, which can also handle high voltage but is significantly less expensive.

Douglas Alpenstock wrote:You can calculate sun angles for your location throughout the year at this site:
https://www.sunearthtools.com/dp/tools/pos_sun.php

I believe this calculator assumes flat land. I'm not sure how to precisely calculate the effect of a north slope. I think it creates an artificial horizon, essentially mimicing a more northerly latitude. This means fewer minutes of direct sun, and less production.

I wonder if you could put in stakes at a "maximum sun" location and at Point A, and mark where the morning sun and evening shade hits them. This might give you a rough-and-ready correction factor.

Thanks, that is getting close to what I am looking for. If I had better access to the property I would try the stake idea - I'm just a few hours away and besides would like to come up with a generic method for solving this problem. We know the contour interval, and the distance, so it should just be geometry. Just stuck on the sun angle, as it is elliptical and the amount of useable solar over a given time period something worth optimizing in my climate (northeast).

Agreed, it's basic celestial mechanics and adjustments for the contour of the land at a specific location.

I'll bet there's a more precise calculator available somewhere, provided you know the specific lat/lon GPS coordinates.

Try this
how-solar-irradiance-is-calculated-

This is a software system which speeds up the mathematics, which is complex.
What is Solar Irradiance?
Irradiance is a measure of solar power. Because power refers to the rate of energy transfer over time (not the total amount of energy delivered),
another way of thinking of irradiance is that it quantifies the amount of solar energy that arrives in a particular area in a given moment [Watt/m2].

The web site above hs this note
"As a help, we’ve gathered links to some excellent resources for solar irradiance maps that you can find here:
- NREL’s (National Renewable Energy Laboratory) Global Horizontal Irradiance Map
- Global Solar Atlas Map
- Solargis Solar Resource Maps of the World
- Solcast Solar Irradiance Maps"

Some of this may help.
But I have just realised you really may need information about what angle to tilt your panels at, and will Point A get any radiation at all.
This may help solar-panel-angle-tilt-calculation/
it has this comment; "The optimum tilt angle is calculated by adding 15 degrees to your latitude during winter, and subtracting 15 degrees from your latitude during summer."

We've got a really good site calculator in NZ but it only works in our corner of the Pacific. Even plots sun paths with local topography. I haven't found one quite this cool anywhere else yet:

NIWA Solarview

Here's a good one that produces polar charts without topographic info and works globally (I think):

University of Oregon Solar Radiation Monitoring Laboratory

Phil Stevens wrote:We've got a really good site calculator in NZ but it only works in our corner of the Pacific. Even plots sun paths with local topography. I haven't found one quite this cool anywhere else yet:

NIWA Solarview

Here's a good one that produces polar charts without topographic info and works globally (I think):

University of Oregon Solar Radiation Monitoring Laboratory

Ok, I think I got it by using the uoregon link. I should just be able to point my clinometer at the highest point on the south facing horizon (the hill) and reference the chart that site produces. Feeling very optimistic. Sorry for not responding to everyone that posted, I have read your replies and have lots to think about. Thank you for giving me new ideas