Remote site. Solar panel tilt?

[PNW_Steve]

Hey everyone,

I need to pull together a solar design for a location that is unreachable parts of the year.

New to me is the complete lack of access. I have ridden my share of road graders and snow cats to sites. I don't have those options for this site so performance in snowy condition is a necessity.

They will be ground mounted.
I will need to use AGM or LFP batteries. Size TBD.

It occurred to me that if I were to mount panels at a severe tilt, almost vertical, I would think that would keep them clear of snow. Solar performance would suck but I can oversize the array to accommodate.

I was also contemplating a like set of panels connected in parallel and at optimum tilt for Summer.

Any thoughts or suggestions on dealing with the snow?

[Mike90250]

If you use LFP batteries, in snow, what is your plan to keep them above 40F ?

[peakbagger]

Ideally mount them vertical, if there is snow on the ground it reflects the sunlight very effectively. BTW even with vertical panels, they can still build up snow in the right conditions.. I have several tracking arrays in my area of northern NH..They default to a full vertical mode in snow conditions and I have seen a few snow events where the panels are completely sealed over with snow yet they are tracking from east to west at full vertical for a couple of days (burning up AC power to run the tracking). I do have a set of panels mounted on a wall under an overhang and the overhang makes a big improvement on snow buildup. I cant put my panels full vertical to be completely under the overhang as they are over a bay window but expect with a straight vertical wall a slight overhang above the panels would work the best. I do have a bit of shading in the early morning and later afternoon during summer when the sun rises and sets north of west.

[bob-n]

Vertical may be a really good idea for snow. Just for my own information, I wanted to know how much vertical affects production, so I ran an experiment on PVWatts. I entered a random place in New Hampshire, and compared production from a random south-facing 4kW array at 30 degrees and 90 degrees.

production.jpg

In short summary, going vertical really hurts you in terms of energy output in the long term, and doesn't buy much even in the winter. If you could build an array that could be rotated in October while you can still get up there and then rotated back in April after the snow clears, you might gain a bit and also solve the snow problem.

Now it's up to you to decide if it is worth the extra construction effort and the trips up and back, vs the cost of adding extra panels and accepting suboptimal output.
Also, what angle would be optimal for snow shedding vs production? There's nothing stopping you from building with the panels at an angle greater than or less than 90 degrees and elevating them high enough so they are always above snow line.

Let us know what you decide.

[J.P.M.]

First, if the array will be inaccessible for periods of time, plan on making it as simple a design as possible for the duty and in so doing decrease the probability of failures that lead to down time or worse, particularly when unattended. Simple stuff fails less. Seems like that may be a more critical a consideration if no one is around to fix stuff when it fails.

Since you're asking:

I'd check into/snoop around for info on designs for remote sites. (S.K. - you still out there ? Any tips to share ?)

Also, mount the array with sufficient ground clearance such that snow buildup stays below the array level Maybe 3X the greatest recorded 48 hr. snowfall ?

Elevated arrays with high aspect ratios may need extra attention paid to structural design as it is impacted by wind loads.

As Mike points out, how do you plan to keep the batteries warm, including a back up plan ?

To increase annual system yield (if that's a consideration) consider an array with seasonally adjustable tilt. Not tracking - just 3 different tilt angles, one winter, one summer and a third for spring/fall.

Winter irradiance enhancement from snow boosted albedo can help winter energy harvest, particularly if the winter array tilt angle is higher than what solar models such as PVWatts will come up with.

But maybe not as much as you might be led to believe.

From my past experience, which I must say was not as detailed or extensive as it would be now, for higher array tilt angles of, say, latitude +15 degrees or more - including vertical orientation, expectations of day long totals of irradiance enhancements of more than, say, 10 % or so under bright sun and fresh snow conditions vs. bare ground conditions for most any array tilt are the stuff of dreamers and peddling con men.

On the other hand, vertical surface irradiance in the winter in northern climates is probably within, say, 5 - 10 % (less) than a latitude + 15 degree orientation, so, a vertical orientation may be worth the tradeoff. Just make sure of the duty - that is - pad it less, or use less oversizing, and then make the array larger.

FWIW, when I lived in Buffalo, I did some modeling and measurement of irradiance on south facing surfaces at both at a 60 deg. tilt and a vertical tilt. On very clear days, with fresh snow and bright sun (which, BTW, happened on average about 15-20 days per winter season), a vertical surface came out slightly ahead of the 60 deg. surface for day long irradiance totals. The rest of the time in winter - which was most of the time - with mostly cloudy conditions and with ground snow that had a lot less albedo, the 60 degree tilt orientation won out. The 60 deg. tilt modeled (and measured) more irradiance on typical days and also modeled more total winter surface irradiance.

Still, and depending on your site conditions and particulars, if it was me and I couldn't find any other way to meet the duty, I'd go with a seasonally adjustable tilt array with maybe a latitude + 25-30 deg. tilt or so winter array orientation, keep the bottom of the array maybe 3X the worst recorded 48 hr. snowfall, be careful and conservative with the mechanical design, particularly with respect to wind loads, with particular all around attention to the KISS principle and accessibility for service, and by all means careful attention to ensuring the battery bank is protected from cold temperatures.

Welcome to the neighborhood.

[bcroe]

Hey everyone,

I need to pull together a solar design for a location that is unreachable parts of the year.
They will be ground mounted.

It occurred to me that if I were to mount panels at a severe tilt, almost vertical, I would
think that would keep them clear of snow. Solar performance would suck but I can
oversize the array to accommodate.

I was also contemplating a like set of panels connected in parallel and at optimum tilt for Summer.
Any thoughts or suggestions on dealing with the snow?

All the above is good advice, you might get some ideas from this construction, with similar
requirements.

To minimize snow accumulation, and making it easier to slide off. It uses landscape mounting,
and a big gap, so snow will not need to slide far. Ground clearance of over 40 inches keeps it
clear of any ground accumulation here. It may easily be set seasonably to vertical for snow, or
a good summer angle the rest of the time.

At the angle shown, I find just a few taps may be sufficient to cause all snow to fall off, some
day I might try building a tapper which also needs a remote camera to observe results. This
designed by an electrical type, a mechanical will probably make improvements. Bruce Roe

TiltPV2.JPGarray20R2.JPG

[peakbagger]

FWIW My experience is PV Watts does not deal well with snow.My guess is the data sites were at airports so not representative of typical installation conditions.

[KarlieBoe2]

Vertical may be a really good idea for snow. Just for my own information, I wanted to know how much vertical affects production, so I ran an experiment on PVWatts. I entered a random place in New Hampshire, and compared production from a random south-facing 4kW array at 30 degrees and 90 degrees.

production.jpg

In short summary, going vertical really hurts you in terms of energy output in the long term, and doesn't buy much even in the winter. If you could build an array that could be rotated in October while you can still get up there and then rotated back in April after the snow clears, you might gain a bit and also solve the snow problem.

Now it's up to you to decide if it is worth the extra construction effort and the trips up and back, vs the cost of adding extra panels and accepting suboptimal output.
Also, what angle would be optimal for snow shedding vs production? There's nothing stopping you from building with the panels at an angle greater than or less than 90 degrees and elevating them high enough so they are always above snow line.

Let us know what you decide.

ooooh thank you for taking the time to put that table together. It helped build on my intuition a lot. If only solar panel systems were as simple as blacksmith hammers. I have spent weeks researching solar panels, and like 30m upgrading my blacksmithing setup.

[PNW_Steve]

WOW!

Thank you all for all of the responses. It will take me a bit to digest it all.

[J.P.M.]

FWIW My experience is PV Watts does not deal well with snow. My guess is the data sites were at airports so not representative of typical installation conditions.

Not only does it not deal well with snow, it only considers snow to the extent the snow covers an array and only then as a gross reduction to annual output. See the PVWatts help screens.

The PVWatts model also has a fixed value of 0.2 for albedo, winter and summer. That 0.2 (20%), BTW, does not mean that 20 % more irradiance hits an array as reflected from the surroundings. Depending on which irradiance model is used (PVWatts use the Perez model for estimating irradiance, which is actually among the less conservative methods).

The way things work, that 0.2 usually works out to something between 0 and ~ 0.10 (0% to 10%) more irradiance hitting the array than the simple P.O.A. irradiance. That %age varies by hour and day, as well as array orientation, the nature of the surroundings and something called view factors that you probably learned about when studying undergrad heat transfer. It's not a linear number. 0.4 for example, doesn't get you twice as much irradiance hitting the array as 0.20.

As for sites being at airports, that doesn't matter much. Reason: Dirty little secret - Most all the MEASURED data from the TMY tables that most models including PVWatts and SAM use is from the original 26 station SOLMET data done years ago. All the other sites use synthetic (modeled data) generated from those 26 sites for weather, atmospheric and irradiance data. See the TMY manual for details as well as the tables themselves for which data is modeled and which is not. Most any site in the TMY tables is modeled. Fortunately, the modeling seems to fairly reliable for long term averages.

See the Perez algorithm or SAM for more details on how it handles albedo. Or, for that matter, see/run SAM to model an array to estimate the effects of albedo changes incurred by snow or other effects.