Bloom Energy today formally unveiled its energy server, an industrial solid oxide fuel cell that can convert natural gas or other hydrocarbons into electricity pretty much on demand. 

And in the process, the company has ignited a debate over which of the alternatives to coal, nuclear and centralized natural gas plants might be best. Can we answer it today? No -- one of the pivotal factors will be how Bloom's servers (formerly known as Bloom Boxes) perform over time. Board member Colin Powell said at the unveiling that the company doesn't have twenty years of user data.

But we can speculate and compare. And here are some of the key things to keep an eye on.

Versatility and Up-Front Cost: A 100-kilowatt Bloom server array costs around $700,000 to $800,000, or $7,500 a kilowatt, after incentives that cover around 50 percent of the costs. The company hopes to have home versions that generate a few kilowatts and cost about $3,000 in ten years, but they don't exist now.

Bloom, however, doesn't scale down yet. It sells its 25 kilowatt boxes four units at a time. Home and small businesses need not apply just yet. Solar systems span the kilowatt and megawatt range. Ergo, when it comes to financing and flexibility, solar wins for now.

Can fuel cells scale down? Yes. Panasonic started selling home fuel cells in Japan last year that generate around 1 kilowatt, not enough to power a complete household, for $30,000 before incentives, or $15,000 if you factored in U.S./California incentives. ClearEdge Power has a 5 kilowatt fuel cell that costs $56,000 and drops to the $30,000 to $25,000 range after incentives. (Side note: Bloom's fuel cell produces mostly electricity and a little heat, while heat consists of half or more of the power from the Panasonic and ClearEdge fuel cells. Electricity is more valuable than heat, so for Bloom to be equivalent in price or less than these guys would be a victory for Bloom.) We're guessing Bloom is aiming for around $1,000 a kilowatt, which won't be easy. Ceres Power in England will come out with a fuel cell made in part with diesel components next year.

Energy costs: CEO and Founder K.R. Sridhar said the Bloom server will produce power for 9 to 10 cents per kilowatt hour after incentives in California. This price includes service, maintenance, gas and all of the other costs associated with running it. Commercial solar installations in California, when incentives and external costs are added, generate power for around 10 cents a kilowatt hour, according to Shayle Kann at GTM Research. Residential solar generates power for around 19 cents a kilowatt hour and utility-scale solar costs around 11 cents a kilowatt hour. Cutting-edge wind turbines can generate power for costs five cents a kilowatt hour after incentives, according to the American Wind Energy Association. Kann says that on average, wind costs a little less than solar.

Wind, thus, still wins this contest, and solar and Bloom are about tied. Bloom server buyers will have to contend with fluctuating gas prices: the box does not work if you don't put gas into it. If methane and biogas rise in price, so will the cost of running the box. Buyers, however, can likely insulate themselves with long-term gas contracts.

Cost reductions: This is a big question mark. Solar and wind are somewhat mature technologies. Nonetheless, incremental advancements -- better solar racking, cheaper thin films, more efficient turbines -- continue to bring down the cost of both solar and wind. Bloom is just starting out. Three years ago, the same box that now produces 25 kilowatts of power only produced 5 kilowatts. Scott Sandell, a Bloom board member and a partner at NEA, said the costs for Bloom have gone down 25x in just a few years.

Bloom, therefore, may have an advantage, because costs always drop the fastest in the beginning. On the other hand, Bloom is outnumbered. Thousands of engineers in various segments of the solar industry are working on dropping those costs. Do you believe in individual genius or crowdsourcing? That is the dynamic at play here and this will be one of the more interesting races to watch.

Maintenance. Solar wins here. Solar panels require a minimum of maintenance. Dust them occasionally and wipe off the snow and you are done. Bloom servers will be monitored closely by their initial buyers. The servers also contain fans and other mechanical objects. More handholding and repairs seem inevitable.

One of the big hurdles that Bloom will have to cross is the reliability of the ceramic/zirconium plates inside the fuel cell. These plates, which convert gas to electricity, must operate in an 800-degree Celsius environment without becoming distorted or corrupted. User data will be heavily scrutinized. Sources say that the plates have a lifetime of five years: replacement at this pace is contemplated in the 9 to 10 cents a kilowatt hour price. If replacement occurs at a faster rate, it could throw off the costs.

Warranty. Solar systems have warranties that last 20 years or more. Bloom currently offers a 10-year warranty. That discrepancy will definitely raise eyebrows.

Testing and certification. Solar and wind both have an advantage here. Underwriters' Laboratory and hundreds of utilities have tested and tinkered with photovoltaic panels and wind turbines for years. Getting a solar field approved mostly revolves around obtaining financing. Bloom will have to go through the proctology exam of utility reliability testing. That could take a few years. On the other hand, if Bloom passes these tests well, sales will zoom.

Carbon emissions. Solar and wind win again. It takes about four years to work off the carbon footprint of a solar panel. The Bloom server continually emits carbon dioxide. The Bloom server emits about half of the carbon dioxide that would be generated if you bought power from a power plant, but it's still carbon dioxide. Consumers can reduce their carbon footprint by stoking the box with biogas, but biogas remains an exotic substance. Most of the industrial gas sold and shipped in pipelines in the world comes from wells deep in the ground, not landfills or manure digesters.

Bloom's patents discuss converting the waste carbon dioxide into a methane-like fuel by running the carbon dioxide through the fuel cell and adding water. It's a fascinating but extremely challenging idea. Effectively, that would be like making energy from Gerolsteiner bubbly mineral water and some power. In today's press conference, Sridhar downplayed the carbon dioxide-to-fuel idea, which makes it sound like the idea might be on the far back burner. Still, Bloom represents a step forward compared to power plants.

Availability: This is Bloom's biggest selling point. The box can produce power 24 hours a day in a completely predictably fashion. Solar panels only produce during the day and wind turbines are only active about 30 percent of the time. Worse, wind turbines in many areas generate most of their power at night.

Storage: Advantage Bloom again. Fuel cells are by their very nature electricity storage devices. Power doesn't get made until gas gets released into the fuel cell stack. General Electric and others are trying to build sodium or lithium battery packs to store power at wind and solar fields but these are in the experimental stage.

Sridhar also mentioned that in about ten years, Bloom will add plumbing and other technology to its servers so that the boxes can convert water into hydrogen for more energy storage. Pulling this off will require electricity from an outside source, preferably from solar panels. Don't be surprised to see them team up with Sun Catalytix, an MIT spin-off with a catalyst for splitting water.

Competition: Bloom will have to face an array of competitors: General Electric, Siemens, Philips, Areva, you name it. The relatively small company will have to run fast to stay ahead of industrial giants or else face getting acquired. Solar and wind have already gone through this process. Solar and wind companies again can also license ideas and leverage partnerships. Bloom right now is sort of on its own.

Manufacturing footprint: The solar industry continues to work off a glut of excess factory capacity. Bloom needs to build its up. Solar, thus, wins for now, but for painful reasons. Although Bloom has raised around $400 million, it will need to raise more to build up factory capacity. As other companies have found, finding financing still remains tough.