A unit of National Grid plc filed a plan to invest in renewable generation, electric vehicle infrastructure and energy storage, as well as hike rates to cover the cost of the initiatives, as the utility looks to adapt its system to emerging technologies and cut emissions of greenhouse gases. To pay for the program, National Grid subsidiary Narragansett Electric seeks to boost revenues by $31.4 million, or 11.2 percent, for the three-year term starting Sept. 1, with hikes for natural gas rates as well, according to a June 5 filing with the Rhode Island Public Utilities Commission. Low-income customers would benefit the most under the plan with a 15.7 percent cut to electric bills in the first year. The plan, reached under a settlement, also provides for performance incentives associated with the capital investments and clean energy investments.