How Many Hours Of Sunlight Do Solar Panels Need?

Until you’ve lived on off-grid power, you really won’t appreciate just how beautiful a sunny day can be. Sunshine on your solar panels can make your whole day – or if it’s the middle of a gloomy winter, your whole week!

At our house, we go nuts when the sun is shinning in January. The dishwasher will run, even if it’s only half full, every scrap of laundry gets washed and the entire house gets vacuumed; whether it needs it or not.

Why? Because we don’t often see the sun in winter. And what sunlight we do get, is generally short when it comes to the daylight hour count.

Which leads to the question, just how many hours of sunlight do you need to power a house?

In general, if your array is sized properly, your solar panels will need at least 3 hours of quality sunshine to power your home for 24 hours.

To be clear, there are a host of variables that play into this. The two most obvious being the quality of the sunlight and the house load for any given day. But I can tell you from personal experience, our battery bank is almost always topped off after 3 hours of good sunlight – no matter how low they were at the start.

Solar Panels & Quality Sunlight

Photovoltaic panels require direct sunlight to perform at optimum. But unfortunately, while the sun is always shinning, there are things that can get in the way.

Clouds are notorious power disruptors!

Right now, as I am writing this, it is 2:30 in the afternoon and our array of 7.8kW is only generating 1.2kW of power.

Why so little?

Because it’s cloudy.

The sun is still out there doing its thing, but cloud cover is blocking/defusing the sunlight before it can strike our solar panels. Consequently, power generation is severely reduced.

In this situation, it is easy to see that 3 hours of reduced power generation will not be enough to get our home through 24 hours of normal use.

By way of comparison, a typical clear summer day will generally provide us with our 3hr sunshine requirement before noon – leaving the panels to sit mostly idle until sunset.

#Note#

It should be noted that the home power system mentioned above is an off-grid system – meaning that there is no connection to the electric utility.

With solar panels that are grid-tied – meaning connected to the electric grid – power generation is generally continuous as they are not limited to the size of a local storage system (battery bank) but rather instead, feed any extra power back into the utility. In this way, smaller arrays can actually generate more power, year over year, as they are not restricted by the limits of a energy storage system.

Solar Panels & House Load

If you’ve spent any time shopping for a solar power system, chances are when you’ve asked that infamous question, ‘how many solar panels do I need?’ you’ve gotten that ridiculously non-informative answer, ‘depends.’

While this answer may be incredibly frustrating as it tells you absolutely nothing, there is good reason for it.

House load – the amount of energy a house uses – will vary, not only from house to house, but from user to user. Consequently, when a solar professional is asked, ‘how much do I need?’ it is pretty much futile to give any kind of realistic answer, as they do not know how much energy you are in fact using.

And this can vary a lot more than you think.

Take for example, the difference between an electric and gas ranges.

On average, the top burners on an electric range will pull between 1500 and 1800 watts per burner, while the actual oven will pull considerably more at around 3000 watts (actual ranges vary from model to model). So if you are cooking dinner, with the oven and two burners all going simultaneously, you can see how the electrical load quickly adds up.

Now compare this to a gas range which uses virtually no electricity and there is an enormous difference between the electrical power requirements, even with the entire rest of the house being the same.

The same thing can be said about hot water heaters. Some electric hot water heaters will have dual 4000 watt elements (8000 watts total).

So consider just how much electricity your home would require if the hot water heater was engaged at the same time you were cooking dinner (8000 watts for the water heater and 4500 + watts for the range = 12, 500+ watts)

To put that into perspective, my solar array is rated at 7.8kW or 7800 watts.

In other words, the combination of an electric range and a electric hot water heater could easily exceed the power capacity of my array of solar panels.

Conclusion

Solar power systems can be fairly costly, with out-of-pocket costs quickly exceeding $15k. Ensuring that you’ve done your homework properly can make an enormous difference on just how well the panels meet your expectations.

For those of you who are blessed to live in an area with lots of good sunshine, you could probably back away from the larger array necessary to power your home on just 3hrs of good sunlight.

The same thing can be said for those whose panels are grid-tied (connected to the electric utility) as your panels will be able to operate without the constraints of onsite battery storage.

However, if you plan to live off-grid and reside in an area that sees significant seasonal cloud cover, then it would be to your benefit to plan on a larger array.