One Black Coral smart-technology investment is Digital Lumens of Boston, which makes high-efficiency, low-cost LED lighting for warehouses and factories. Software and controls are embedded in the fixtures, which can cut lighting bills by 90 percent, providing customers a two-year payback, says Day.

U.S. venture capital investment in cleantech companies hit $4.9 billion last year, down 4.5 percent in dollar terms but flat in the number of transactions, according to Ernst & Young LLP, which analyzed data from Dow Jones VentureSource. Cleantech companies raised 29 percent more capital last year than in 2009, E&Y said recently.

Most of that decline, however, came from less investment in sectors that were once hot.

Investment in energy and electric generation, including solar businesses, fell 5 percent to $1.5 billion, while that of industry products and services companies plunged 34 percent to $1 billion, according to E&Y's analysis of equity investments from venture capital firms, corporations and individuals.

The energy efficiency category leads the diverse industry in deals with 78 transactions worth $646.9 million. Energy-storage companies raised $932.6 million, a 250 percent increase and 47 percent deal increase.

Stop Juggling That Handful of 401(k)s and IRAs

The Retiree's New Pastime: Cutting Costs

REITs Still Offer Shelter from the Storm

Time to Bail Out on Treasurys?

Running the Show for Mom and Dad

More Portfolio Tune-Up