In an interview with the New York Times today, Steven Chu said that major breakthroughs are required in biofuels, batteries and solar. He said that solar needs to get ''five times better,'' which I interpret roughly as follows: Industry sources say that photovoltaics have cost between $3 and $4 per Watt in recent years, which is three or four times higher than the breakeven level with coal-generated electricity. One company, First Solar, claims that it will be able to get PV module production costs down to $1/W in five years. But historical data for recent years''the dollars spent on new PV installations, divided by their total megawattage''suggest that real-world PV costs are still in the vicinity of $6 or $7 per Watt.
So if you take an average of industry claims and historic data, you get a current cost for photovoltaics of about $5/W. Improving on that by Chu''s ''factor five'' would give you breakeven.