Solar Powered PC
We all would love solar power to work better, but it's hard to have it make economic sense yet, at least if you're near the grid. A solar panel takes 4 years just to give back the energy it took to build it, and it never pays back the money put in if you compare it to putting the money into the stock market. And that's with full utilization. If you use panels and batteries, any time your batteries are near full the power is being discarded, and you also have to replace your batteries every so often and dispose of the old lead-filled ones. Yuk. A grid-tie can use all the power of a panel but that's an expensive, whole-house thing.
But here's a start -- a solar-using PC power supply. My PCs, like many folks', are on all day, including the peak-demand heat of the day. Desktops draw anywhere from 50 to 200 watts even when idling.
So make a PC power supply that has 3 external connections. One for the wall plug. And two optional ones, one for a 12v solar panel and one for a battery. Then sell it with a 50w or 100w solar panel -- most importantly, the panel should not ever generate more power than the PC uses.
Because of that, during the bright part of the day, the panel will be providing most, or just barely all, of the power for the PC. The wall plug will provide the rest. At night, the wall plug would provide all the power. It's a grid-tie but it doesn't feed power back to the grid, it just reduces demand on it. The 100w panel takes 100w off the grid load during the peak demand times. And we use every watt the panel generates, we never throw any away.
This is all pretty cheap to make. Today switching power supplies, even ones that take DC, are cheap, inexpensive and efficient. This would cost more than a standard power supply, and the panels still cost around $4 per watt at the best prices available.
The battery add-on is optional, but makes this more economical. It's not much more to add the ability to draw from a battery, and to charge it (generally from wall power, not the solar) if it gets drawn down. In effect, with a battery you have a very long-life UPS. Indeed, since the solar panel can almost power the PC, during a sunny day even a small battery (an 18ah can be had for $20) might make up the difference for 6 hours or more. At night, it would drain almost as quickly as any UPS battery, but still be more efficient due to the direct connection.
This ability to have a built-in, long life UPS makes this power supply (without panel) cheaper to buy than a traditional power supply and external, shorter-life UPS. Indeed, throw on a larger battery like an RV battery and you would get a huge lifetime. An 80w PC and a 50w panel and Costco's $45 RV battery would run a PC for almost 16 hours! (Not the monitor, however.)
The thing that would make this would would be the availability of the $4/watt energy rebate in California. Unfortunately, the grid-tie requirement associated with this rebate might not apply to a system like this that combines with the grid and does not feed power back to it. However, it attains all the goals the rebate had in mind -- taking load off the grid and encouraging solar -- just on a smaller scale. With the rebate, this system becomes economical to the buyer. The supply costs only a bit more than a conventional PC and the panel is almost paid for by the rebate. It saves about $14/year on the electricity bill and is actually cheaper than the existing external UPS solution.