Maryland has adopted a renewable portfolio standard that requires the state’s electricity suppliers to generate increasing percentages of their electricity from renewable sources beginning in 2006. The legislation, which passed by a veto-proof margin in April by the House and the Senate, was signed by Governor Robert Ehrlich on May 26, 2004. The law requires that electricity suppliers produce 1 percent of their electricity from “Tier 1” renewable resources in 2006; the portion of renewables required rises by 1 percent every two years, reaching 7 percent in 2017. Tier 1 renewable resources include solar, wind, ocean, qualifying biomass, geothermal, landfill or wastewater methane, renewably-fueled fuel cells, and small hydroelectric plants. The law also requires that 2.5% of the portfolio each year be produced through either Tier 1 or “Tier 2” resources, until 2017, when all renewable generation must be from Tier 1. Tier 2 includes hydroelectric power, incineration of poultry litter, and waste-to-energy.