ST. PAUL — Minnesota regulators voted 4-0 Thursday to give a tentative go-ahead to a proposed large-scale solar energy project that would generate power for Xcel Energy but also authorized the utility to negotiate deals to meet some of its needs for more power from natural gas.

Edina-based Geronimo Energy wants to build 20 large solar power arrays next to Xcel substations across Minnesota at a cost of $250 million. The 100 megawatts would represent a sevenfold increase in the state’s solargenerating capacity.

Environmentalists hailed the Public Utilities Commission’s decision to direct Xcel to negotiate a power purchase agreement with Geronimo Energy. Jessica Tritsch of the Sierra Club’s Beyond Coal campaign called it a major win.

“This investment in clean energy means instead of shipping our hard-earned dollars out of state to buy fossil fuels, our money can support our local economy,” Tritch said in a statement.

The PUC also directed Xcel to negotiate power purchase agreements for one or more of three proposed natural gas power projects that have been under consideration.

The PUC asked energy developers for competing bids last year because Xcel and state experts projected a need for more power in 2017-2019, after the utility retires the two remaining two coal-burning units at its Black Dog plant in Burnsville.

Xcel’s three gas options were to add a gas unit at Black Dog, or buy the power from Invenergy Thermal Development, a Chicago-based company that would expand its existing Cannon Falls plant, or Houston-based Calpine, which proposed another unit at its Mankato plant. At least one of those three projects will still go forward.

The decision marks the first time solar and gas have competed head-to-head on price before the PUC. Renewable energy advocates backed Geronimo’s solar project. One of them testified Tuesday that state law requires the PUC to favor renewable energy over fossil fuel.