Solar Trust of America's decision to pull the plug on its flagship concentrated solar power (CSP) project sends another tremor through the US CSP sector. As demonstrated by the announcement, solar technologies-CSP, photovoltaic (PV), and concentrated photovoltaic (CPV)-are increasingly squaring-off in a solar-on-solar competition in the US Southwest. But as long as undemonstrated CSP technology solutions remain on the drafting table, the CSP sector will increasingly struggle in direct competition and will be forced to seek out hybrid thermal solutions and other markets.