By 2050 vast photovoltaic arrays in the Southwest would supply electricity instead of fossil-fueled power plants and would also power a widespread conversion to plug-in electric vehicles. Excess energy would be stored as compressed air in underground caverns. Large arrays that concentrate sunlight to heat water would also supply electricity. A new high-voltage, direct-current transmission backbone would carry power to regional markets nationwide. The technologies and factors critical to their success are summarized at the right, along with the extent to which the technologies must be deployed by 2050. The plan would substantially cut the country’s consumption of fossil fuels and its emission of greenhouse gases (below). We have assumed a 1 percent annual growth in net energy demand. And we have anti­cipated improvements in solar technologies forecasted only until 2020, with no further gains beyond that date.  —K.Z., J.M. and V.F.  

Technology Critical Factor 2007 2050 Advances needed

Photovoltaics Land area 10 sq miles 30,000 sq miles Policies to develop large public land areas

Thin-film module efficiency 10% 14% More transparent materials to improve light transmission; more densely doped layers to increase voltage; larger modules to reduce inactive area

Installed cost $4/W $1.20/W Improvements in module efficiency; gains from volume production

Electricity price 16¢/kWh 5¢/kWh Follows from lower installed cost

Total capacity 0.5 GW 2,940 GW National energy plan built around solar power

Compressed-air energy storage (with photovoltaic electricity) Volume 0 535 billion cu ft Coordination of site development with natural gas industry

Installed cost $5.80/W $3.90/W Economies of scale; decreasing photovoltaic electricity prices

Electricity price 20¢/kWh 9¢/kWh Follows from lower installed cost

Total capacity 0.1 GW 558 GW National energy plan

Concentrated solar power Land area 10 sq miles 16,000 sq miles Policies to develop large public land areas

Solar-to-electric efficiency 13% 17% Fluids that transfer heat more effectively

Installed cost $5.30/W $3.70/W Single-tank thermal storage systems; economies of scale

Electricity price 18¢/kWh 9¢/kWh Follows from lower installed cost

Total capacity 0.5 GW 558 GW National energy plan

DC transmission Length 500 miles 100,000- 500,000 miles New high-voltage DC grid from Southwest to rest of country