Two grass-roots coalitions that want a say in Long Island’s energy future are supporting polar-opposite alternatives to achieve their goals.

In Southampton, a new nonprofit group called Peak Power Long Island eschews any form of fossil fuel-derived power, working instead to persuade homes and businesses to cut power use, chiefly during the peak summer times.

Executive director Lynn Arthur plans to recruit thousands of home and business owners in the town to use advanced thermostats that cut energy use.

The Peak Power group, which grew out of Southampton Town’s sustainability committee, is negotiating with a funding source and plans to launch in June. “We can solve the 2017 power problem,” Arthur said.

Each 1,000 customers outfitted with the new thermostats, which automatically adjust central air conditioning systems to save power during peak times, can save the utility about 1 megawatt of power. PSEG estimates the 2017 shortage is 8 megawatts. The thermostats can save customers up to 15 percent off their energy bill and pay for themselves in a year.

In Coram, meanwhile, a group called the Coalition for a Brighter Long Island held a rally Tuesday to demand that Gov. Andrew M. Cuomo and PSEG build the proposed 750-megawatt Caithness II gas-fired plant in Yaphank. About 100 people, most in building trades, said the plant would bring needed construction jobs, tax payments for schools and services, and a more modern power infrastructure.

Daniel Tomaszewski, executive director of the coalition and president of the Longwood Central School District, said the plant “absolutely has to be built” to modernize the antiquated Long Island fleet. The plant would make $20 million a year in payments in lieu of taxes, including $13 million to the Longwood school district, Tomaszewski said.

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PSEG has said that the plant would raise rates 6 percent and that no new major power sources are needed until 2028. The utility has said it plans to release results of its broad analysis of the Island’s energy resources by the end of June.

“The analysis is in the final stages and we look forward to sharing the results and gathering feedback on the options when the study is complete,” spokesman Jeff Weir said.

Meanwhile, PSEG has been soliciting bids to address power needs such as those on the South Fork and in western Nassau. Results of the South Fork request for proposals will be released in July. People briefed on the matter say semifinalists include a 90-megawatt wind farm proposed by Deepwater Wind, two large battery-storage proposals, and a combination demand-reduction, solar, battery-storage and mobile generator proposal by Anbaric Microgrid II, a fuel-cell proposal and a biodiesel peaking plant.