We all know that in order for solar panels to make us electricity, sunshine is must! Clouds, snow, ice… they’re all a bunch of killjoys when it comes to the solar party. But interestingly enough, just because the official sunrise time has arrived, this doesn’t mean that your solar panels are ready to go.
As a general rule, solar panels will work 90 minutes less than total daylight hours for your specific location.
Remember, photovoltaic cells require direct sunlight in order to function at their optimum. And direct sunlight doesn’t happen the instant the sun comes over the horizon. Nor does sunlight stay at maximum brightness all the way to sunset.
We have found that our solar panels will start to work well about 45 minutes after the official sunrise. Likewise, they will decline quickly about 45 minutes before official sunset.
Using this behavior, we can roughly calculate total hours of power production by taking our seasonal allotment of daylight hours and subtracting 90 minutes.
Solar Panels & Sunrise
Unlike the rooster who crows at the crack of dawn, solar panels need a little ‘coffee time’ in order to get going. But this doesn’t mean that they aren’t stirring.
As someone who is up early to care for our flock, it is not uncommon for me to hear our charge controllers (the computers directly tied to the panels) clicking on and off, trying to engage, as the growing sunlight starts to feed the panels.
What’s interesting about this ‘wake up’ time, is that the charge controllers will often start trying to engage before the official sunrise. This is generally because the skies are clear and sunlight is finding its way over the horizon ahead of the sun’s entrance.
Solar Panels & Sunset
Unlike the small child who protests bedtime because ‘the sun is still up’, solar panels have no problem knocking off early and going to bed.
This is because solar panels require direct sunlight in order to work at optimum. And even though the sun may still be visible, because it is so low on the horizon, unless your panels are pointed directly at the setting sun, then sunlight will not be directly striking them – hence, there won’t be enough power for the charge controllers to stay engaged.
I can tell you from personal experience, it can be fairly surreal to be working outdoors trying to get one more thing done while it’s still light enough, only to note that my solar array has already shut down and called it a day!
It’s worth stating that so long as the controllers stay engaged, the panels are officially working. So one could argue that the panels could work from sunrise to sunset. However, it should be understood that the amount of power being produced in that 45 minutes leeway from sunrise and to sunset, will be negligible.
For example, our current array is rated at 7.8kW – or 7,800 watts of power production.
The charge controllers will engage at fairly low levels, with our readings showing .1kW or 100 watts.
100 watts of power production is pretty abysmal when your capacity is 7,800 watts. Point of fact, 100 watts doesn’t really run a whole lot, not when you have a fairly normal house that is relying on off-grid power.
I can tell you, 100 watts will not run the dishwasher… nor the air-conditioner… nor the water pump, or anything else except the modem and maybe a few lights. So while the panels may be technically on, from a practical standpoint, they are NOT!
However, should the skies be sunny, it only takes a little less than an hour for production to go from .1kW to 4.8+kW. And that is production that will carry us through the day!