A Bloom Box is a hydrogen fuel cell. It’s popular among many Fortune 500 companies in particular thanks in part to generous incentives that have made its economics very attractive over the last five years. But there’s more to the story.It is an interesting piece of energy innovation. You put natural gas in and it spits out electricity. Unlike a traditional natural gas power plant, no combustion takes place, just the silent separation and recombination of protons and electrons.The critical piece to a fuel cell is something called a catalyst. For Bloom, the unique catalyst they have pioneered is their critical piece of intellectual property. What the catalyst does is split hydrogen ions off from the natural gas molecule. These ions are positively charged, so electrons will work hard to unite with them. And they will flow thought your lights, your motors, and anything else in your building that runs on electricity to get to that proton.While the devices are technically sound, there are a few problems to be cautious of, in particular price and environmental impact.When you tear hydrogen out of natural gas, carbon dioxide is created. So unlike solar power, Bloom Boxes are not a carbon free source of electricity. Specifically, a Bloom Box emits 773 pounds of CO2 per megawatt-hour (MWh) of electricity. For a typical large office building that ran entirely on a bloom box, it would emit the pollution equivalent to about 2 barrels of oil every day. Not terrible, but not great either. The Bloom Box is about 50% efficient, which is pretty good, but still less efficient than a new central station natural gas plant. There are losses in transmission of natural gas and electricity that factor into these calculations, too, about overall environmental impact. Some companies buy biogas certificates to make their power cleaner, but there have been verifiability problems in this market.On the financial side, Bloom Boxes suffer from the challenge faced by fuel cells for decades: cost. A Bloom Box costs around $7,000 per kilowatt (kW), and Bloom Boxes sell in increments of 100 kW. Depending on what state you’re in, there are incentives that dramatically change the economics of bloom boxes. These incentives come and go and will eventually disappear, so a key question is will Bloom boxes be cost effective once the rebates are gone? If a 100 kW Bloom Box installation costs $700,000 and the purchaser takes out a loan at 4%, assuming maintenance costs of 3% per year, and you buy gas at $0.90 a therm, then the device will give you power at around $0.17/kilowatt-hour (kWh). The US average is about $0.10/kWh. So it’s close, but it’s not quite there.In short, the Bloom Box is an innovative technology that does emit carbon dioxide and is still expensive: about twice as expensive as retail coal power, and about 25% more expensive than retail solar power. Unlike solar power, the Bloom Box creates carbon emissions, but also unlike solar, the Bloom Box can generate electricity at night. So it has plusses and minuses, and as with so many energy technologies, as to whether it will help you achieve your energy and sustainability goals, the devil is in the details.