SOUTH PORTLAND — City officials are moving forward with a cost-saving plan to build a solar power array on the former municipal landfill off Highland Avenue. ReVision Energy of Portland has sweetened the terms of its proposal to build the solar facility, reducing the price that the city would pay for electricity generated by the array from 12 cents to 10 cents per kilowatt-hour under a power purchase agreement. ReVision revised its offer after legislation to reform Maine’s solar regulations failed last spring, causing several communities to pull back from solar proposals without the means to make them financially viable. “I think ReVision was really willing to work with us,” said Julie Rosenbach, the city’s sustainability coordinator.