Plans for large solar farms sprouting in Mass.

Solar energy systems could grow in a big way this year in Massachusetts — and not just in number.

New state incentives and regulations are making it possible for the construction of large solar “farms” on tracts of land or very large rooftops, a scale familiar to neighboring states but rare in Massachusetts.

Local developers have already proposed construction of at least 10 megawatts of solar — enough to power 10,000 houses — in a handful of projects, and solar installers across the state are talking with commercial building owners about large systems on rooftops that could add several more megawatts.

If these projects, ranging in size from 500 kilowatts to 2 megawatts, are successful they would dwarf the size of Brockton Brightfields, a 425-kilowatt solar farm constructed on a city-owned brownfield and currently the largest solar system in the state.

While the project, constructed in 2006, took nearly six years to permit, developers say many of the challenges the project encountered in permitting were alleviated by the overhaul of Massachusetts’ energy laws in 2008.

“Today the opportunities far outweigh the challenges,” said Lori Ribeiro, project manager for Brockton Brightfields and a consultant to renewable energy developers. “You’ll see more city-owned projects, but you’ll see more third-party developers that can take advantage of federal tax credits for construction as well as sell renewable energy credits to retail electricity providers and utilities. People are definitely champing at the bit.”

The limiting factor for large solar farms has been financial. Incentives for installation under the state’s flagship Commonwealth Solar program were capped at 500 kilowatts and solar installers said the most financially feasible projects were between 100 kilowatts and 120 kilowatts. But changes to state energy regulations effective this year make it possible to structure loans for megawatt-size projects.

The most recent change is to the solar incentive program itself. After it ran out of funding late last year, Commonwealth Solar was mostly replaced by a solar renewable-energy credit incentive program starting Jan. 1. The program works by requiring utilities to buy a certain percentage of their power from owners of qualifying solar systems through the creation of special solar renewable energy credits. The credits would have a price floor of $300 per kilowatt hour, nearly 10 times as much as the going rate for other renewable energy credits utilities must buy. Those that do not meet the requirements would have to pay the state $600 per kilowatt hour.

Developers, who can use these credits to create a credit profile, already are using the program in conversations with customers and banks.

“There’s a lot of interest in the marketplace and the new regulations have an invigorating effect,” said Steve Black, project developer for Borrego Solar Inc. in Lowell. “It’s early on in this process ... but we’re actively engaged in a lot of conversations with our customers.”

In Fairhaven, renewable energy project developer Blue Sky Power LLC is in final negotiations with the town to build a 500-kilowatt array on a closed landfill. The project was on the verge of stalling when the old Commonwealth Solar rebate program ran out of money, but the new program “basically restored our project to being financially feasible,” said Jack Eggleston, owner of Blue Sky Power. The project’s planners hope to break ground this summer.

In Salisbury, True North LLC has plans to build three separate 2-megawatt projects. Developers there like the concept of a solar-credit incentive system, but wonder if it will provide long-term price stability.

“The program works like a charm if supply is equal to demand. The question is if there’s more supply than demand, how do you make sure all of those credits are purchased? Utilities are not going to buy more than one year’s worth of credits at a time,” said Mark Kalpin, a WilmerHale LLP attorney representing True North.

Yet state officials have structured the program assuming 40 megawatts of solar capacity will be on line this year — nearly double the amount installed at the end of 2009. Not all of that capacity will come from independent developers. The Green Communities Act allows utilities to own up to 50 megawatts of solar and Western Massachusetts Electric Co. plans to announce the site for its first 1.5 megawatt project in the coming weeks.

To be sure, there are additional challenges to building large-scale solar in Massachusetts. First is the amount of land or flat rooftop needed to build a project — the rough minimum needed for 1 megawatt of power is 5-to-7 acres on the ground, or 100,000 square feet of flat rooftop.

Developers also have to go through permitting hurdles subject to the vagaries of local boards. But if the Brockton project and the proliferation of solar on homes and businesses are any indication, the process could be easy-lifting compared with the regulatory burdens of developing wind projects.