Two Triangle energy-services companies have swapped a $4 million solar-energy venture in a deal that shows how the solar industry is expanding into ever-bigger projects that can be difficult for smaller installers to finance and develop.

Southern Energy Management, a privately-owned Morrisville business, sold its commercial solar power installation unit to PowerSecure International, a publicly-traded Wake Forest company that specializes in energy services and consulting for electric utilities and large industrial clients.

The sale will transfer about 50 employees to the new PowerSecure subsidiary, reducing Southern Energy Management’s workforce by about half. The asset sale includes an ongoing 4.5-megawatt solar farm project in North Carolina, the largest to date attempted by Southern Energy Management.

Solar energy has soared in North Carolina with projects of progressively increasing size as the cost of solar panels has plummeted and combined state and federal incentives cover more than half the cost of the projects. The biggest proposed to date in North Carolina is a 40-megawatt solar farm at Apple’s data center near Charlotte, and 5-megawatt projects are now routine, whereas just several years ago 1 megawatt was seen as an insurmountable price barrier.

PowerSecure cited the “new, significantly improved economics of distributed solar energy systems” as a rationale for the acquisition. Southern Energy Management will retain a 10 percent ownership stake in the new solar venture, called Southern Energy Management-PowerSecure. PowerSecure has an option to buy the remaining 10 percent state in two years. PowerSecure shares closed Wednesday up 10 cents at $4.61. The stock is down 7 percent this year.

Staff writer John Murawski