Picture a sunflower field, only shinier and less likely to give you hay fever. That’s sort of what a large scale solar farm looks like from the sky. But beneath that sun drenched expanse, the number that matters most comes down to acres.

You might be surprised to find out that you normally need between 5 and 10 acres for every megawatt (MW) of solar power. To put this in real world terms, you would need an area the size of around eight football fields to power about 200 U.S. dwellings (the rough output of 1 MW). The U.S. Department of Energy normally maintains that photovoltaic (PV) systems need 6 to 8 acres for per MW. However, some solar projects need less acreage or even more space. Fixed-tilt and tracking technologies change the game since trackers need room to move.

What is it about that terrain that makes it different? Putting panels close together like sardines isn’t enough. Engineers figure out how far apart the rows should be so that the panels don’t block the sun. They also check to see that there is enough room for batteries, inverters, and substations. You might think that site is good for building on, but you need to avoid floodplains, fragile wildlife habitats, and complications with city zoning. Not all “open space” is as open as it seems, it turns out.

There have been some large undertakings in the last few years that clearly exemplify what I mean. The Solar Star project in California, for instance, covers more than 3,200 acres and can produce 579 MW. That is bigger than most small towns yet smaller than many major airports. Sometimes, projects with even superior layouts make good headlines for the media, but this is not always the case.

Don’t forget to ask where: The land in the American Southwest is frequently vast and flat, which is perfect for solar arrays to stretch out. There is a lot of sun there. In the Northeast or the Midwest? There are more trees and less room. Some layouts are tighter, and other times there are creative answers, such putting “floatovoltaics” on reservoirs.

The idea is that there isn’t a single answer that works for everyone. Where a project located, what technology is accessible, and even local politics can all affect it. But as a general rule, you should plan on 5 to 10 acres for each kilowatt. When you fly over those blue geometric patterns again, try to envision how big each one truly is.