Do Solar Panels Need Direct Sunlight?

Solar panels absorb light particles from the sun rays known as photons and convert them into usable electrical energy. Direct sunlight is the most efficient but some particles will still get to the panels even when there is indirect sunlight. Solar panels don’t necessarily require direct sunlight to function, as indirect, diffuse and reflected sunlight can all be converted into energy.

50w Solar panel can operate in a variety of weather conditions, including fog, clouds, rain and snow!

As you can imagine, the amount of power generated when sunlight is restricted in this way is very low – perhaps 10% of the power produced in direct sunlight.

How Much Sunlight Does a Solar Panel Need?

The amount of sunlight that a solar panel requires to perform optimally is determined by various factors:

What Is the Best Roof Angle for Solar Panels?

The table below shows the difference in irradiance levels (peak-sun-hours) in Las Vegas comparing flat panels against a title of 54 degrees:

Insolation by month for Las Vegas, Nv by month (kWh/m2/day - also are known as Peak-Sun-Hours)
	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Flat	2.83	3.64	5.18	6.50	6.73	7.36	7.62	6.22	5.41	4.29	3.14	2.17
54 °	4.63	5.11	6.32	6.70	6.74	6.33	6.27	6.06	6.15	5.85	4.99	4.48

In winter time the tilted panels can generate almost twice as much power when tilted than if mounted flat.

As a general rule, the best tilt angle for any location in the summer months is the location latitude -15 degrees and +15 degrees in the winter.

How Does Solar Irradiance Affect Solar Panels?

Irradiance, or the amount of sun energy, is by far the biggest factor affecting solar power generation. It varies by location across the globe and the differences can be significant – see table below:

City	Chicago, Il	London, UK	Glasgow, UK	Houston, Tx	San Fran., Ca
Irradiance (peak-sun-hours)	4.043	2.374	1.860	4.253	5.699

A solar array in San Francisico generates 3 times more power than a similar power system in Glasgow, UK. Chicago has the average US irradiance of 4 peak-sun-hours.

Does Orientation of Solar Panels Matter?

Orientation means which direction the panels are facing. The very best direction in the Northern hemisphere is due South, and the very worst is due North. (In the southern hemsiphere it’s the opposite way round!)

However, due to the angles of most roofs and the effect of diffuse sunlight, the reduction in power output due to orientation isn’t as much as you might think.

North-facing solar panels suffer from a reduction in output of 16% to 20 percent, while East or West-facing panels generally see a drop of about 15%.

What Affects the Output of a Solar Panel?

There are many factors affecting the power output of a solar panel system.

Panels are rated by manufacturers accord to the STC (Standard Test Conditions). Among other things, it specifies panel output at an irradiance of 1000kWh/m2 at a temperature of 25 degrees C.

Basically, these are ideal laboratory conditions and quite rare in real-life situations.

In fact, a commercial or domestic solar power system has quite a few losses, some are inherent to the system design, while others can be reduced by the user.

The inforgraphic below shows the details of 10 major solar PV system losses.