I think the problem of putting electricity back on the grid is easily solved - solar cell panels have been doing this for years. I don't know the details though.

From a recent Applied Physics Letter (v84 p.2700, April 2004) by the group:

One of the major drives for thin-film SOFC development is the interest to reduce operating temperatures. Toward this end, the thin-film fuel cells were operated over a reduced temperature range of from 480 to 570 \ufffdC. The relationship of YSZ-based fuel cell performance with temperature is shown in Fig. 3a. The cell open-circuit voltage was over 0.8 V when connected to a testing circuit with thin gold wires, and the maximum cell output power increased with an increase in temperature varying from 30 mW/cm2 at 480 \ufffdC to a maximum power output of ~110 mW/cm2 at 570 \ufffdC. The relationship between maximum cell output and operating temperature is shown in Fig. 3b. The increase in output current with temperature indicates a semiconductorlike cell internal resistance, which decreases substantially with increasing temperature. Improving the electrolyte conductivity would be productive for the thin-film fuel cell, particularly after the electrodes and the electrode interfaces are improved.

They only present lifetime data out to 6 hours. It looks promising, but still has to be proven. Manufacturing costs may still be an issue - the raw materials aren't cheap.

The fuel cell is made of a YSZ (yttria stabilized zirconia - Y2O3+ZrO2) electrolyte deposited on a nickel foil substrate, covered with with a La0.5Sr0.5CoO3 (LSCO) cathode layer. The nickel has small holes etched in it to allow the natural gas to diffuse through the device.

As the electrons come from (or are transported by) the hydrogen in the natural gas, a larger current will require a higher natural gas flow.

More on natural gas fuel cells is [link|http://www.pnl.gov/fta/5_nat.htm|here].

Cheers,
Scott.