solar concentration from water and ice

[clarsondd]

I was thinking about putting some solar panels along the shoreline of my lake.  And, I was wondering if I should have any concerns about solar concentration from the water and ice.

panels solar track, so i would guess the most concentration would occur when the sun is low in the sky (mornings, evenings, and winter).

I'm guessing that the most concentration possible would be a factor of 2.  And, that would only occur when the sun is at certain positions in the sky and if the water/ice was a perfect reflector.  So, does anyone know what percentage would reflect off water or ice.?

I'm also thinking that the randomness of the wave action (usually waves of only a few inches) would keep any hot spots from occuring, but ice and snow does move all that much.  So, should I have any concerns about some areas of the panel receiving more light then others?

Any information, thoughts, or sharing of experience in this regard would be apprecitated.

[TomW]

clarsondd;

Personally, I think it is a non issue. Might be a rare occasion where it gets 2 solar discs worth of light but they will be short lived and pretty rare. Even then, I doubt it would actually achieve 2X the light. Thousands of panels survive years in snow country with no problems. The other factor is it is cold so that will tend to offset any damage concerns. You will see a bit of gain in incoming amps I think over non reflective.

Do not mistake me for any kind of expert. I seem to recall this being discussed some months ago.

Cheers.

TomW

Cheers.

TomW

[DanG]

You do not state where in the snowy cold world you are located. PV panel output goes up as it gets colder - add in panels aimed close to the horizon in upper northern latitudes and that reflected light might very well push an over voltage condition on your inverter or charger. System parameters should be tuned to such weather, to include PV panel make & model and charger/inverter or MPPT charger & inverter models.

The thought of a two-axis tracker calibrated to harvest the low levels of rising & setting sunshine boosted by water bounced light is interesting, though snow and ice has so many variables from one day to another it may be much harder to account for - somewhere out there is general percentages for reflections off the different flavors of snow but I have not googled it for you...

[vawtman]

Ive been thinking about adding a solar array to my ice fishin shack.One can get a nice tan in very low temps.Never tried a full body tan though:>)

 Nice post.

[clarsondd]

You do not state where in the snowy cold world you are located

lets say 45 degrees latitude.  

System parameters should be tuned to such weather

I thought it would be helpful to do so also.  That is why i'm asking before making a purchase.  

somewhere out there is general percentages for reflections off the different flavors of snow

It seems the reflectivity of snow/ice is in the 80-90% range.  while the ice is pretty flat, the snow surface (if there is any), is depends on which way the wind has been blowing.

sunshine boosted by water bounced light is interesting

I would say that water isn't going to be all that good of a reflector, ie water does warm up in sunlight meaning at least some absorption is taking place

[ghurd]

While the peak operating voltage increases, the amps decrease. Less AH per day when AH are needed most.

Any controller worth the shipping cost would take that into consideration in it's ratings.

Two axis trackers don't gain much over 1 axis at higher latitudes.

G-

[clarsondd]

> While the peak operating voltage increases, the amps decrease

I'm hardly an expert, but what i've read it seems with most panels that at -25 C there can be a 25% voltage increase as well as a 25% decrease at 75 C.  and while the current does vary with temperture it is much smaller, along the size of 1-2%.

It would seem like i co uld expect a 25% voltage increase (and power) because it is very cold out. But, i'm sure the important temperture is of the silicon and to a lesser extent the ambient outdoor temperture.  and, i'm not sure how much warmer the silicon will be once the sun hits it.

>Less AH per day when AH are needed most.

as far as i know the sun is more intense in the winter, ie earth is closer to the sun, less water vapor in the because it is colder, etc.  And, the only reason there is fewer ah is because the there is fewer hours of daylight.  Which of co urse is why the ah are needed more, the lights are on more.

>Two axis trackers don't gain much over 1 axis at higher latitudes

from what i've read, a two axis tracker gives a about a 10% increase, depending on how often you adjust it.  which means it all depends on how much you spend on  your panels (and if you like making the adjustments manually) weather it is cost effective or not.

[ghurd]

The voltage increase isn't a problem, or there would be lots of stories about blown up controllers every winter.

The amp decrease seems to run about 4 to 5% on the data sheets I just checked.

Unless the controller is MPPT, the 25% voltage increase won't make an increase in usable power. The panels won't operate higher than the battery voltage plus a couple tenths for losses. The amps into the battery will still be less, meaning less usable power.

It would be better to think in amps or amp-hours of power, instead of rated or peak-power watts.

The sun is less intense in the winter.

Partly due to increased scattering and absorption as the light must pass farther through the atmosphere to reach the ground, and partly due to increased reflection by the upper atmosphere at winter angles.  The same reasons a panel won't make the same power an hour after sun up as it does at noon.

Water vapor probably depends on where the system is located.

Here, the sun is about to vanish until late January or February when the Great Lakes freeze.

G-

[clarsondd]

Thanks very much for your input and allowing to me to benifit from your experience.

you must get alot of lake effect clouds.  Myself, I live in minnesota and november is our cloudest month, followed by december.

Thanks again for sharing your knowledge.

[clarsondd]

here is some information i found at:

http://www.theweatherprediction.com/habyhints2/463/

METEOROLOGIST JEFF HABY

An object with a high albedo reflects a significant amount of the incoming light. An object with a low albedo does not reflect much light. With an albedo of 100% all incoming radiation is reflected while it is 0% if it is all absorbed. In almost all cases the albedo will not be perfectly 100% or 0%. Water has an interesting property in that the amount of reflection depends greatly on the state (liquid or frozen) and the angle the radiation is striking it.

Liquid water has a higher albedo when the sun angle is low. For example, just after the sun rises the sun angle will be low and much of the radiation will be reflected by the water. This has important implication in locations the sun angle is low such as in high latitudes. High latitude locations where the sun is near the horizon will reflect more solar radiation away than at low latitude locations. This is one reason that high latitude locations are colder (with the main reason being that the sun's energy is spread over a larger surface area in high latitude regions).

When the sun is well above the horizon (30 degrees to directly overhead) then water has a low albedo and absorbs a great deal of solar radiation. The middle latitude and tropical oceans absorb an enormous amount of solar energy.

Ice is a good reflector of solar radiation especially if it is a fresh snowfall. The albedo decreases as the age of snow increases.

Here is a guide to the albedo of water at various states and sun angles:

fresh snow: 80%

sun near the horizon on water: 65%

old or dirty ice: 40%

water with a sun angle 30 degrees or more above the horizon: 8%