There are four major factors that affect solar panel performance:
1) length of day, 2) angle of sunlight relative to the solar panel, 3) sunlight intensity and 4) temperature.
The more hours of sunlight there are in a day, the more energy the panel produces: Energy = panel power x peak sunlight hours.
The angle of sunlight is important as the amount of energy received on a solar panel is highest when the sunlight is perpendicular to the panel and lowest when at a grazing angle. The sun’s angle is lowest in winter, so unless the panels are tilted steeply to compensate for this, winter solar panels receive significantly less light.
Winter brings snow covered panels and cloudier weather. When solar panels are covered with snow, they don’t make any power. Cloudy weather reduces sunlight intensity, in turn reducing the amount of energy produced.
The only benefit of winter conditions is that solar panels are more efficient the colder they are!
All these factors result in a significant reduction of energy during winter months. A rough rule of thumb is that wintertime production is about one third of summertime production while spring and fall production is about two thirds of summertime production.
Since it’s so cloudy in the winter, will my solar panels produce any electricity at all?
Yes, your solar system will produce power during cloudy weather. How much power depends on the degree of cloudiness, but even under solid cloudy skies, a solar array will produce between 10 — 30 percent of its power rating.
What if it snows?
Snow completely blocks the solar cells from receiving any sunlight; therefore, they produce no power when covered by snow.
There are strategies to deal with snow, such as mounting panels at steeper angles, but generally grid-tied solar panels are mounted flush with the roof slope, which is typically not very steep, so snow tends to linger.
The good news is that for grid-tied, net-metered systems, the goal is simply to produce the maximum amount of energy on an annual basis. Lower sloped arrays produce the most amount of energy over the year and will more than compensate for the impact that snow can have on production.
How do I remove snow from my system in the event of a big snow dump?
It is almost never a good idea to attempt to remove snow from an array; doing so will likely take a lot more energy, risk or expense than the value of the energy gained. Wait for the sun to come out and do the melting thing which tends to allow the snow to slide off quickly.
A lot of snow means heavy weight on the array and the roof connections. This is one of the critical considerations when designing the array structure and evaluating the ability of the roof to handle the array.
A lot of snow will mean a longer stretch of no production which may tempt owners to try to remove the snow. Other than a soft roof rake, there are no safe ways to remove snow from an array. Wait for a sunny day to melt the snow enough so it slides off.
These same considerations apply for flat roofs.
About the only time it’s worth trying to remove snow is for off-grid systems where daily energy production is critical. When the only energy you have is the energy you make, getting snow off the panels makes a big difference.
How do I minimize the risk of snow sliding off my panels in dangerous areas?
Snow guards and rail systems are one way to alleviate snow sliding off arrays. But these features can be unsightly or challenging to install on certain roofs.
Certain rail systems will accommodate snow clips that provide some holding purchase which tends to hold snow from all out avalanching and instead break apart progressively.
If possible, it is best to avoid installing solar arrays over sensitive areas or where people travel.
What effect does night and day temperature variance have on a solar system / solar panels?
Large night and day temperature shifts, especially in winter when the swings can be really large, create the most stress for a solar system. Solar panels are designed to handle these stresses and have proven themselves over many decades in the field. The electronic components in optimizers and micro-inverters (components of some solar systems), due to their myriad tiny soldered connections, are much more vulnerable to temperature swings than solar panels. (It is for this reason, we at IPS stay away from these devices except when dealing with very shady conditions where the decreased component reliability is worth the added production.)
An IPS customer enjoys his off-grid cabin high in the snowy Rocky mountains: http://solaripsdev.wpengine.com/2016/04/high-altitude-rocky-mountain-off-grid-solar/
To talk with one of our friendly technicians about solar for your home, contact us.