Screen capture by Martin LaMonica/CNET

To get the benefits of fuel cells in portable electronics, Apple engineers think they need to work well with batteries.

In newly published patent applications today, Apple describes a way for fuel cell power sources to be designed into electronics, such as a laptop, and controlled to optimize their performance without adding a lot of extra weight.

In one patent application titled simply a Fuel Cell System to Power a Portable Computing Device, Apple says there is "increasing awareness and desire" among consumers to use renewable-energy sources. Fuel cells are compelling technically because of their energy density, or ability to pack a lot of energy into a relatively small package compared to a battery.

"Fuel cells and associated fuels can potentially achieve high volumetric and gravimetric energy densities, which can potentially enable continued operation of portable electronic devices for days or even weeks without refueling," according to the patent application. The challenge has always been keeping electronics portable and cost-effective, Apple said in the application.

Indeed, there have been a number of products developed for charging electronics, but they have yet to really take off. Typically, fuel cells for electronics are designed for portable charging, where a person carries a fuel cartridge, which could be a cylinder the size of a roll of coins, to recharge a phone or music player.

By contrast, Apple envisions fuel cells integrated right into the electronics. Much of one patent application describes a control system for optimizing energy flow from the fuel cell stack, which produces power, from a dedicated communications system.

The second patent application describes how this fuel cell would work in tandem with a rechargeable battery, so the fuel cell could charge the battery and vice versa. "This eliminates the need for a bulky and heavy battery within the fuel cell system, which can significantly reduce the size, weight and cost of the fuel cell system," according to the patent application.

These aren't the first fuel cell patent applications Apple has filed. Patently Apple notes that in October a newly published patent application from Apple was for fuel cell plates that focus more on power generation from within a portable device.

As for the fuel itself, one of Apple's patent applications said that a variety of fuels could provide the source of electric power. Among them are sodium borohydride powder mixed with water. These are still considered experimental and do not appear to be commercially available.

A fuel cell works by passing hydrogen through a membrane, where oxygen from the air mixes with the hydrogen to produce water vapor and electricity. Apple's patent applications describe fuel cells where the hydrogen is derived from solutions that contain sodium borohydride or similar materials.

One of the barriers to portable fuel cell chargers is having a sales channel to purchase and recycle fuel cartridges. Although it makes no mention of its stores in its patent applications, Apple's retail outlets could make fuel cell use far more approachable.