Solar panels are more effective in colder weather.
Yes, really. But first, the basics…
How latitude affects efficiency of solar panels
Solar energy is not equally distributed across the Earth.
Although plenty of northern regions get a lot of sun, it would seem that in general, solar panels are less effective the further north you go.
Why is this?
Angle of solar impact
The Southern Hemisphere receives more energy during December (southern summer) than the Northern Hemisphere does in June (northern summer) because Earth’s orbit is tilted. 
One factor influencing solar radiation intensity is the angle of impact. For harvesting solar energy from cells, the optimal angular impact is 90 degrees perpendicular.
In northern latitudes, because because the angle of impact is less direct than it is at the equator, it is spread over a greater surface area and therefore you get a less concentrated energy output per unit area.
And unfortunately, this also means that solar panels are less effective during the months that Earth is tilted away from the Sun, during the winter months.
To make up for this, solar panels are often tilted based on the location on Earth as well as time of year.
The angular tilt of solar panels to maximize efficiency is greater the further north you go as well.
In addition to the sun’s rays being spread over a wider surface area, there is a second factor that latitude influences.
Absorption scattering of UV rays
As we see in Figure 1 below, the distance that solar radiation must travel through the atmosphere is further.
A wider band of atmosphere through which the rays pass means there is more absorption scattering of sunlight in the atmosphere.
UV rays comes into contact with the nitrogen, oxygen, carbon dioxide, and other gases in the atmosphere over a wider area, so more is absorbed.
Because a large amount of UV rays have been scattered and absorbed, they are less intense once they reach Earth’s surface
The combination of absorption scattering in the atmosphere as well as the angle of impact suggest that in general, we would expect solar panels to be less efficient during the winter time in each respective hemisphere.
However, as mentioned at the beginning of this post, there is a third factor that influences solar panel efficiency – temperature.
Solar panel efficiency in cold temperatures
Yes, cold weather does increase the efficiency of solar cells, if everything else is constant. 
This means that cold weather (with sunshine) are the ideal conditions for solar cells.
The reason is that low temperatures decrease the solar cells’ internal energy leakage.
In cold temperatures, electrons are less active. At higher temperatures, electrons are more active.
With lower electron activity, energy can be stored and moved across wires and batteries more efficiently. 
According to phys.org, solar cell efficiency decreases by 0.3% for each temperature degree increased. 
This means that a warmer region, while perhaps sunnier, is not necessarily going to be an optimum place for solar energy generation.
This is good news for the northern regions of Earth.
While northern latitudes may be at a disadvantage for reasons based on the first two factors mentioned the earlier section of this post, we can make the case for solar energy in cold, sunny places!
Of course, snow and ice can be a problem for solar panels, and attempting to scrape it off could damage or break the components.
If the ice is translucent, the solar panels may be able to generate a continued output of energy.
Solar in Germany
Germany is the leading country in Europe for solar deployments.
Germany is further North than most people realize. Berlin, Germany occupies the latitudinal region of 52 degrees N (Berlin).
By comparison, the latitude of Calgary, Canada is around 51 degrees N.
It is inspiring to see a country as far north as Germany have so much success with solar, and Germany should perhaps serve as a model for other nations.
If a northern, Temperate country like Germany can prove the viability of solar, surely countries further south can too, with even greater ease.
Still, we’re not at 100% sustainable energy yet.
In order to meet 100% of its electricity needs with solar, Germany would need to significantly increase its solar photovoltaic capacity to between 303 GW and 446 GW.
Given the three factors covered above that impact solar panel efficiency, equatorial areas are not necessarily going to be the only places (or even the best) where solar will work.
Eventually, the world will need to transition to 100% sustainable energy. We cannot survive off of fossil fuels and coal forever, as these reserves will eventually run out.
This post isn’t meant to provide a more realistic approach and help people understand how solar can help while supplementing other energy sources in order to maximize the amount of sustainable energy for the grid. It should be mentioned that wind, nuclear energy, hydroelectric, and more could also help transition the world to sustainable energy.
For example, as solar is added to the grid, it reduces the net demand for electricity in the middle part of the day (when the sun is most radiant).
And if we assume there is no storage of excess energy during peak hours, solar output during the night is pretty much zero.
Perhaps off-grid regions of the world, such as research bases in Antarctica or remote areas of Alaska, could fulfill their own power demands via solar systems during the summer. 
For now, perhaps solar energy could be a viable way to reduce diesel, at least during the daytime.
With improvements in battery technology paired with a greater number of solar panels across the globe, perhaps humans can one day capture and store enough solar energy that we can sustain our energy requirements all hours of the day and night.
And if land is abundant, as it is in the United States, perhaps the most reasonable way to increase the percentage of renewable energy that we consume is to simply build more solar panels.
- PR aka Performance Ratio for photovoltaic performance https://www.nrel.gov/docs/fy13osti/57991.pdf
- hong kong observatory http://www.hko.gov.hk/en/education/edu06nature/ele_srad.htm#