Others have mentioned the varying thickness of the atmosphere that the sunlight has to pass through, but cloud cover is the more important factor. The map you are looking at seems to include cloud cover in its calculations.

The suns rays go through less atmosphere near the ~~poles~~ equator. Not to scale, but should show the overall concept.

Lie on the beach in winter: the sun is pathetically un-warm.

Adjusting the angle at which you recline won't make the sun any warmer.

So your intuition is off here.

Imagine someone puts an opaque shell around the earth at cruising altitude, and cuts a metre-square window in it.

Put that window directly over the equator, wait for noon. You will have a metre-square patch of sunlight on the ground.

As the sun heads towards the horizon, the patch of sunlight stretches into a long east-west tail, just like a long shadow.

The same amount of energy is coming through the window, but it's spread over a much larger area on the surface, so there's fewer watts-per-square-cm hitting the ground.

Now move that window north 30 degrees. Wait until noon, and the patch is already smeared into a long tail north-south, and that's before applying any east-west smear. As the sun heads for the horizon, it's going to be even more spread out into a great big enormous oblong, extended in both directions.

Now, entirely replace that shell with windows, and through the raytracing gets more involved, the same principles are at work.

That's why mornings and evenings are cold, that's why winter is cold, that's why it gets colder towards the poles. You're getting a smaller and smaller share of the sunlight hitting the area where the earth is.

It's not just the cloud cover and going through more atmosphere, it's also the amount of energy per square meter hitting the ground. But a large part of it is most solar panels aren't tracking and even if they are it's usually in the horizontal and not in the vertical.

It's impractical to mount solar panels at such an extreme angle, but it also won't help very much since the sun is so close to the horizon shadows will be terrible. Imagine two rows of panels, once you set up the first one almost vertical, the second row won't get any sun. And that's if there is even a clear view to the horizon, in most places that's not true. It's also very hard to mount panels at such an extreme angle because the wind will catch it more easily. Mounting flush to the roof is usually preferred, or at a fixed angle with struts for flat roofs.

Because the panels don't track, higher latitudes are less efficient, as the sun varies more in angle during the year. From just peaking out over the horizon in winter, to high in the sky in summer.

There's several factors here.

The most important probably being the energy per square meter. Higher latitudes gets less energy per square meter than equatorial latitudes.

There's also the mentioned cloud cover and atmosphere density.

The climate it's also important. As higher latitudes tends to be more cloudy.

And sun hours, here is not about the total energy but how it's distributed. As sun hours are more estable near the equator (12 hours light 12 hours dark) while in higher latitudes you can get 4 hours light some times of the year that can't amount to nothing, and 20 hours of day other times of the year which are nice, but there's no way to store that energy for the winter lack of sunlight.

I see what you're getting at here. The solar constant is the solar constant. If you've got a perfect angle to the sun, you should be getting the same amount of power regardless of latitude. I mean I suppose it's possible there might be a slight attenuation with the sun at a lower angle due to there being more atmosphere to traverse? Otoh solar panels don't function as efficiently at high temperatures, so it's possible they may be more efficient in some cases.

But you have to consider that averaged out, you're looking at shorter daylight hours overall at high latitudes, even if there are periods in mid-summer when days can be super long, so that's a consideration. So yes, the panels should pull in similar amounts of power while the sun is up, but it's not up as much.

Solar panels are more efficient closer to the equator because of the most direct light from the sun. At higher or lower latitudes, there is more atmosphere for the light to pass through. The actual distance from the sun is basically irrelevant without an atmosphere. There might be a measurable difference based on distance alone but not much.

Efficiency does not generally equate to optimal power generation. There are probably hundreds of other variables that directly translate to maximum power production.

Assuming an ideal mounting angle...

Near the equator, sunlight has less distance of atmosphere to travel through than at higher or lower latitudes, generally speaking.

Then there's also the average of the weather patterns for different areas, like some areas get way more cloud cover and rain than others.

And then there's also the air pollution factor, and since significantly more people live in the northern hemisphere than the southern, of course the northern hemisphere has more air pollution.

I hope my insight on this has been helpful.

I'm no specialist, but (1) don't most solar panels have a fixed inclination and orientation? Depending on the location that will not be as optimal at each day of the year because of the tilt of the earth. (2) The weather/cliimate will have an effect too. Your 2nd image is apparently showing kWh/kWp - so the longer term yield (h=hours) divided by the theoreticall maximum (p=peak). So it shows longer term efficiency , vs the yield at a certain moment like you appear to be focusing on.