For those of you who have spent any length of time living in the northern latitudes, you know first hand just how much of a mixed bag outdoor life can be. The days can be long and hot in summer and the nights cold and seemingly never-ending in winter.
Take your weekly commute for example. How many times during the winter have you driven into work in the dark, only to have your return trip home also be in the dark? One can easily assume that solar panels would be less productive in these types of conditions – and that assumption would be correct.
The ability of a solar panel to produce electricity depends on the duration and the quality of sunlight striking the panel. In other words, the longer a panel is exposed to unobstructed direct sunlight, the more power it will produce.
Unfortunately, winter tends to bring both short and cloudy days – both of which reduce a solar panel’s ability to work efficiently.
So while solar panels do work in the winter, they will most likely produce less energy than they would on a long summer day.
Daylight Hours (Duration)
Daylight hours is probably the easier of the two variables to understand with regards to solar panels and their productivity. It’s fairly obvious that the more sunlight a panel is exposed to, the more opportunity it has to work. But what can be surprising is just how much daytime varies from summer to winter – especially in the northern latitudes.
For example, where I live, daylight duration is a little over 9 hours a day on Jan 1st. Fast forward to June 1st and that changes to a little over 15 hours a day. In other words, June offers an additional 6 hours a day or 42 hours a week more than January. Clearly, summer has a notable difference in production time over winter.
While the amount (duration) of sunlight hours and the corresponding impact to power production is obvious, the quality of sunlight plays an equally critical part of power production – while being somewhat more fickle in nature.
The key to remember is that solar panels operate most efficiently when the sunlight strikes directly. And while this may be a easy concept to state, it can be very challenging to employ as there are two variables that are constantly moving to thwart production. These are orientation and obstruction.
- Orientation – For those of us who ever had a solar powered calculator, you are probably familiar with having to hold the device directly up to the light after it sat in a dark place for too long. Being situated in a position where it can maximize contact with direct light provides a boost for the calculator to charge up.
In order to maximize output, solar panels need to be oriented in a position where they can fully capitalize on the amount of sunlight coming into contact with them. For those of us living in the northern hemisphere, this means not only having the panels facing south (to track the sun as it moves from east to west), but with their standing angle set to ensure that sunlight is striking evenly across the entire panel.
To picture this, take a flashlight and hold it in one hand with your elbow on the table. Then place a DVD case or book cover flat on the table, (keeping it at arm’s length away from the flashlight with your other hand). The flashlight, in this example, represents the sun as it hangs in the sky and the hardcover a solar panel.
With the hardcover laying flat on the table, you will observe that the light from flashlight strikes the hardcover, but does so unevenly – with more light striking the edge of the cover that is closest to the flashlight. This is the equivalent of having a solar panel laying flat on the ground.
Now, with the hand that is not holding the flashlight, slowly tilt the hardcover towards the light, careful to keep one edge on the surface of the table. As the hardcover begins to angle upwards, it should be observed that more of the light from the flashlight is able to shine evenly across the surface of the hardcover. This simulates mounting a solar panel on an angle.
With a little experimentation, you should quickly find the optimal angle necessary to maximize direct contact with the light from the flashlight. In this same manner, a quality solar installer will work to ensure solar panels are mounted at the proper orientation and at just the right angle in order to maximize direct contact with the sun.
Unfortunately, for most of us, the sun doesn’t hang at the same angle in the sky all year round. This is because of our planet tilting on its axis.
To simulate this, simply lower the flashlight to five inches or so, off of the table. You should find that as the flashlight comes down, the angle of your hardcover is no longer optimal and needs to be increased (tilted towards the light-source) to match the lowering light.
This mimics the actions of the sun in the winter, as the winter sun hangs lower in the sky.
Sadly, with the majority of solar panels being mounted in a fixed fashion, they are unable to tilt to the angle that is necessary for direct contact with sun – meaning they are no longer orientated for optimal performance.
For a better understanding of this, check out: https://www.youtube.com/watch?v=G01A51L-5Vc
- Obstruction – Regardless of how much careful attention is given to the orientation of your solar panel, it will all be for naught if a cloud rolls in. I have personally observed my solar array go from generating 6kW of energy down to 1.2kW in a matter of about 15 seconds. In this particular case, a dark rain cloud was the culprit.
And clouds aren’t the only thing that can come between your panels and the sun. Three inches of wet snow can completely prohibit your panels from generating energy. Fog or even a heavy mist can wreck havoc on your solar day.
A good test that I have discovered regarding unobstructed sunlight is the stare test. If the sun is too bright to stare at safely, then it’s reasonable to assume that quality sunlight is available. However, if you can look directly towards the sun with no discomfort/risk to your eyes, then its fair to assume that conditions are poor for generating solar power.
For example, this past winter I was enjoying what appeared to be a bright sunny day. The curtains were all pulled back illuminating the interior of the house quite nicely and I felt assured that things were going to be good. However, when I went out to check on my power generation, I was shocked to observe very little energy being produced.
Initially, I thought something must be malfunctioning as clearly the outdoors were bright. But as I walked outside to look at the sun, I observed tiny ice crystals hovering in the air. These glistening little jewels were effectively acting like miniature mirrors deflecting sunlight in countless different directions. So while the outdoors were bright and well light, direct sunlight was impossible.
Solar panels tend to get a bad rap when it comes to winter. But the reality is, a solar array will work just fine in the winter season, provided it has the proper orientation and clear skies to work with. And this is something I can attest to personally.
Even with our smaller array of 7.8 kW, poor orientation of about 20 deg. and shorter daylight hours, we can easily run everything in our house – including laundry, vacuuming, dishwasher and electric heat… IF direct sunlight is available. However, direct sunlight in my area is not a common thing for winter weather. Consequently, this results in lower performance.
Fortunately, home solar is continuing to do what it already has for so long – improving in both capability and cost. And this is lessening the negative attributes of the winter season.
As the unstoppable progress of solar power continues, better and better home solar systems are coming online… ones that are able to thwart the dark and gloomy skies of the winter season.
Tools To Help
A great tool for learning about the quality of sunshine for your specific area can be found here: https://www.suncalc.org/
Start by typing in your area code and then look for two specific numbers:
- Daylight duration – which will give you a solar panel’s production time.
- Altitude – which will give you the sun’s angle in the sky.
Once you find these two variables, then utilize the calendar function to compare Jan 1st and Jul 1st. This should give you a fairly good understanding of just how much things change from summer to winter.