Originally Posted by Tommycat
Because the difference in power required for the Apollo capsules required less energy than even the cheapest Nokia cell phone. It's still a developing technology. Would the Apollo computer be practical for surfing the web?
That wasn't the reason. It was that fuel cells provided more energy per unit of weight than batteries or solar panels. One other advantage often overlooked was that the byproducts of the fuel cells, water, was provided for the crew. That meant they utilized the weight of the oxygen, hydrogen, and fuel cells much better than if they installed solar panels + a few hundred kg of drinking water.
This was the reason for having fuel cells on spacecraft; because they are more effective for their weight to power ratio than solar panels over short periods. The shuttle and apollo had fuel cells because they weren't designed to fly for more than two weeks at a time, but it makes more sense for satellites in orbit for much longer than that to use solar panels.