Electric Transmission 202: Integrating Variable Renewable Resources

Twenty-nine states and the District of Columbia have renewable portfolio standards which require a minimum percentage of electricity to be produced from renewable resources, and federal standards are under consideration. This new focus on remote, clean energy sources will require that the existing high-voltage transmission network be expanded and upgraded. Accommodating the variability of potentially vast wind and solar resources requires transmission planners and operators, as well as renewable energy developers, to prioritize and manage interconnection requests, to aggregate generators over large areas, to improve system balancing techniques and coordinate operation of diverse kinds of generators, to study projected levels of renewable penetration in the market, to devise new market rules, to re-think allocation of related transmission costs, and to update technical requirements or seek any necessary changes in applicable regulations. Solutions may vary among markets or regions or among the affected resources.

On April 26, 2010, the Environmental and Energy Study Institute (EESI) and WIRES (Working group for Investment in Reliable and Economic electric Systems) held a briefing on the integration of renewable resources into the electric grid. The current grid was developed at a time when power came from conventional fuel resources that could be stored and used as needed for reliable service. But renewable resources will require new transmission infrastructure and new operations and strategies to ensure that the power system remains reliable, efficient, and low-cost. This briefing addressed various factors that can help bring location-constrained renewable electricity, including power from resources often characterized by variable outputs, to distant markets.

This briefing was the fifth in a series co-sponsored by EESI and WIRES. The other briefings were "How the Grid Works", "Policy Challenges to Grid Expansion", "Upgrading the Grid", "Cost Allocation" and "Planning to Expand and Upgrade the Grid".

• Grid reliability requires delivery of the right amount of energy, at the right time, at the right location, with the right power qualities. To achieve this reliability in a cost-effective manner, we need a diversity of energy technologies located in a diversity of geographic areas.
• Maintaining reliable electricity service will benefit from smart grid technologies, energy storage innovations, more efficient customer control over when electricity is used, and new power system software tools for decision-making.
• The conventional grid is like a marching band -- highly regimented and controllable. The renewable grid will require a symphonic approach, the ability to continually harmonize different categories of energy generation.
• Pumped storage is a good resource to balance variable energy resources, but there are only nine pumped storage facilities in the United States.
• The National Renewable Energy Laboratory’s Eastern Wind Integration and Transmission Study found that the eastern United States could get 20 to 30 percent of its electricity from wind by 2024, with significant expansion in transmission infrastructure. In the four scenarios analyzed (including varying combinations of onshore and offshore wind development), transmission costs were a small minority of total annualized costs.
• Texas is leading the nation in renewable electricity with over 9,000 MW in operation (roughly 20 percent penetration at lower load levels). The state has had a Renewable Portfolio Standard (RPS) in effect since 1997, has already surpassed the 2015 standard (5,880 MW) and expects to exceed the 2025 requirement (10,000 MW) within next few years.
• Obstacles to more extensive integration of wind energy include the lack of a federal Renewable Portfolio Standard and the lack of process for multi-region planning for HVDC Lines.
• Workforce needs are drastic; 45 percent of power engineers are retiring over the next five years.
• In January 2010, the Federal Energy Regulatory Commission published a Notice of Inquiry for input on rules and procedures affecting the integration variable energy resources.
• While the recession has depressed energy demand in the present, it will undoubtedly rebound in the future. Major new transmission investments will be required whether renewable generation is brought online or not.