Large corporations are turning into the biggest solar consumers. Last year, 25 of the biggest companies in the U.S. cumulatively installed nearly a half a gigawatt of solar at stores, warehouses and manufacturing plants.

With solar costs continuing to fall, the technology is a no-brainer for companies looking to do something for the environment, right? Well, it all depends on where they’re located.

The map below, put together by the data crunchers at Energy Points, compares the efficiency of the local grid to the average efficiency of solar, with regional solar resources layered on top.

In the Southwest, which has the best insolation and a heavy dependence on coal, on-site solar beats the grid in efficiency by a significant margin. But in the Northwest, where efficient hydropower is abundant and solar resources are mediocre, the grid beats solar in efficiency. Elsewhere throughout the country, solar performs pretty well — particularly in the regions most reliant on coal:

Of course, there are lots of other considerations for investing in distributed energy: diminishing price volatility, increasing power reliability, or even boosting public relations. But the map provides a useful guide when considering the net energy benefit of installing solar.

The information comes from Energy Points’ database of source energy, which compiles factors such as resource availability, the local generation mix, environmental conditions and the lifecycle energy use of different technologies. The startup uses that data to help commercial or industrial customers evaluate onsite energy decisions by modeling source energy against a company’s billing and consumption data. The model could also help governments determine where to focus efforts in resource conservation and energy-related programs.

“We see ourselves as a big calculation engine,” said Ory Zik, founder and CEO of Energy Points. “The end goal is to be the calculation that everyone uses in order to know their source energy.”

The map below shows another one of Energy Points’ metrics: electricity per gallon, or EPG.

The EPG metric pulls together every imaginable resource factor into one, theoretically allowing a customer to know what energy technologies will have the biggest environmental impact. The company also does the same for water resources.

Energy Points only has “tens of customers,” but is developing relationships with hotels, consulting firms and manufacturers looking holistically at energy use. It is also working on some white-labeled mobile products that show consumers the energy and resource implications of their buying choices.

“Most companies only focus on what they consume onsite. But the market is tied together,” said Zik. “We bother to do the calculation on the real energy return on energy invested.”