Cars once jammed the parking lots at Evergreen Solar Inc.’s 23-acre manufacturing complex in the former Fort Devens.

But that was before the company, heralded by green energy fans as a Bay State success story with state tax breaks and grants, shuttered its solar panel manufacturing operation last year after being undercut by China.

Having barely finished constructing a 300,000-square-foot plant in April 2008, the Marlborough-based manufacturer of photovoltaic panels announced it was expanding to 450,000 square feet. Jobs grew from 350 to 760. Workers’ cars quickly flooded an auxiliary parking lot leased next door.

Machines inside worked at the blink of an eye, stacking batches of new photovoltaic cells. Eight-foot-tall robots swung their arms like dinosaurs, shifting panel laminates and framed panels.

Back then, photovoltaic panels – or “modules” – sold for an average of $4 per watt. Still spending $4.35 per watt to make the panels, Evergreen knew mass production was the key to lowering costs. The race was on: Make more. Sell more.

Science was on Evergreen’s side. With the exclusive rights to String Ribbon, a trademarked technology developed at Massachusetts Institute of Technology in the early 1980s, the company could make wafers – the component in solar panels that produce electricity – with half the silicon used by competitors.

Slicing is the conventional method of making wafers from big silicon blocks, but it loses half of the expensive material to sawdust.

String Ribbon wafers, however, are made by spreading hot, liquid silicon between two parallel strings, the way soapy water expands inside a bubble wand. It cools off and hardens into a thin strip of silicon wafer, wasting nothing.