Mexico City - Mexico's government awarded 18 solar and wind projects last week in its first electricity auction under the 2013 energy sector overhaul, a bidding round that is to generate $2.6 billion in total investment.

The 11 winning bidders won contracts to build 12 solar plants and six wind farms and the rights to supply a combined 5,402.8 gigawatt-hours of renewable electricity annually over 15 years to state-owned electric utility CFE, the sole buyer in this initial private auction after the broad 2013 energy reform.

Among other things, that overhaul opened up Mexico's electricity system, which previously had been almost entirely owned and operated by the CFE.

Those 18 projects also were awarded a total of 5.38 million Clean Energy Certificates, or CELs, per year. Under Mexican law, CELs are issued for each megawatt-hour of electricity that is generated without using fossil fuels.

"It's 2 percent of total (electricity) generation, a figure that may seem small for a process of this magnitude, but it's important for the system because it's clean energy," Deputy Electricity Secretary Cesar Emiliano Hernandez said.

Initially, the organizers of the auction had said Tuesday that 11 projects were awarded to seven different companies. But on Wednesday, they provided the new total, blaming the discrepancy on a flawed bid by one participant and the need to evaluate other proposals.

With this initial auction of long-term contracts to supply electricity to the CFE, Mexico aims to make strides toward its pledge to reduce its greenhouse gas emissions by 25 percent by 2030.

"The private projects will help diversify the clean energy portfolio so that by 2024 35 percent of the country's energy" comes from renewables, said the CFE's director general, Enrique Ochoa.

The projects awarded to domestic and foreign companies are spread out over seven states: Guanajuato, Coahuila, Yucatan, Jalisco, Tamaulipas, Aguascalientes and Baja California Sur.

"They are located in areas with notably high energy costs, such as the Baja California Peninsula and Yucatan Peninsula," Hernandez said, adding that around 85 percent of the electricity supply contracts and clean energy certificates on offer were awarded and that the prices are "very competitive by international standards."

The winning bidders included companies from the United States, China, Italy and Spain, while the projects are expected to come online starting March 28, 2018, and provide "the system with cleaner and cheaper energy," Hernandez said.

The 18 renewable projects are expected to be built at a combined investment cost of $2.6 billion, Energy Secretary Pedro Joaquin Coldwell said.