In its annual ranking of world businesses based on their environmental policies, Greenpeace gave Amazon a so-so rating. Greenpeace said Amazon lags behind Apple, Facebook, and Google in terms of its renewable energy promises and projects. Not happy about being slapped around in public, Amazon has decided to ramp up its commitment to rooftop solar at its more than 50 worldwide operations centers.

The global e-tailer will begin with its 15 largest shipping and sorting centers in the US and plans to convert them to mostly solar power by the end of 2017. Combined, they will have an output capacity of about 41 megawatts. The homegrown electricity means electricity won’t be purchased from local utility companies, most of which rely on fossil fuels like natural gas or coal to generate their electricity, or on nuclear power, which has its own set of environmental detriments.

Those who are not advocates of solar power often carp about how it places an unwarranted strain on the utility grid, but that argument fails to account for the benefits that flow to the surrounding community from breathing cleaner air that is not contaminated by the byproducts of combustion and to the utility by not needing to expand the grid further. Electricity that is created by sunlight and consumed close to its source pays dividends to all stakeholders.

The Amazon solar installations are expected to provide about 80% of the electrical energy needed to operate each of the 15 US facilities. The reduction in energy costs should nearly offset the cost of installation of the systems over time.

Reduction in energy costs? Of course — solar power is now cheaper than everything but wind power in the US, on average. That would be utility-scale solar power, but rooftop solar power still beats the price of retail electricity in many or most places.

One US site affected by the program will be Amazon’s fulfillment center in Patterson, California, where over 75% of the building’s 1.1 million square feet of roof will be covered  in solar panels, which will provide most of the power needed by the hundreds of Amazon sorting robotics inside.

Amazon is proud to be going green, highlighting, “Amazon was the leading corporate purchaser of renewable energy in the US in 2016, according to according to the 2017 State of Green Business report.” But hey, it’s pretty easy to go green when doing so saves you money, isn’t it? Too bad more companies don’t realize what Amazon realizes.