In today's tight-money environment, energy efficiency financing hovers around $20 billion. But that could grow to as much as $150 billion a year if businesses, banks and other institutions would work together more strategically to unlock funds for green building, according to Capital-E.

Investment at that high level over a decade could lead to savings of $200 billion a year for U.S. businesses and households, in addition to creating more than a million full-time jobs, says a new report from the consulting firm that specializes in cleantech energy innovations and green design.

"This investment gap represents an enormous opportunity to strengthen the economy, increase competitiveness of U.S. businesses while creating jobs and strengthening exports," the report says. "The critical step to close this gap is to make EE financing a mainstream financial asset class with a high degree of standardization, predictability and scale."

Capital-E's report, prepared for the Energy Foundation, explores 11 mechanisms for energy efficiency financing, takes a look at the firms that have put them to work, summarizes pros and cons for each, and offers its view of what it will take to scale up those practices to achieve full investment potential.

Here are the 11 models detailed in the report:

1. Energy Savings Performance Contracting, in which government agencies, hospitals, universities, schools and other entities pay for energy efficiency improvement using savings that result from the work. We've reported on Johnson Controls' and Honeywell's business in this area on GreenBiz. The report highlights efforts by those companies as well.

2. Energy Services Agreements, which build on the idea of power purchase agreements. Such arrangements are frequently seen in solar power installation projects at retailers, schools and hospitals. The firms host solar arrays on their rooftops and benefit from negotiating lower energy rates with the outfits that install, own and maintain the systems and get rights to the electricity they produce. Kaiser and Walmart are among the companies that have installed solar power systems using PPAs.

3. State/Municipal Loan Programs. The programs take several forms and state programs, administered by energy departments, are among the most common. The initial funding pool for such programs can come from the general fund, federal grant allocations or ratepayer funds.

4. Sustainable Energy Utilities, which are set up to administer financing programs, offer technical assistance and provide financial incentives to building owners. Such entities are designed to implement efficiency measures and support renewable energy installations.

5. Carbon Market Funding. The growth of energy management and demand response firms like EnerNOC, Tendril and Efficiency 2.0 are examples of this "new and fast growing pathway to motivate and guide energy efficiency," according to the report.

Next Page: Preferential terms for green buildings, PACE programs for commercial properties and other mechanisms to unlock efficiency financing.