Transmission & Markets
We usually build power plants near large concentrations of power users. But wind and solar must be generated where those resources are readily available.
As such, high-voltage transmission infrastructure to move power efficiently from where it’s generated to where it’s used is critical to ensuring that grid operators can provide reliable service while reducing overall carbon emissions.
The current electric grid in the U.S. is a balkanized system with limited regional capacity. The regional transmission planning that does occur usually focuses on ensuring reliability and replacing aging assets within a utility’s service area. While these are important considerations, large-scale transmission planning should expand to account for other key criteria, including: 1) economic efficiency (for example, reduced congestion and curtailment), and 2) climate and other policy benefits. Current planning practices do not prioritize clean energy or effectively allow for higher penetration of renewable energy sources like wind and solar.
States have always had authority over the permitting of transmission lines, and interstate transmission projects are still subject to permitting and zoning approval by local and state government entities. In some instances, one local government has blocked the development of a multi-state transmission project that would bring renewable energy to a major population center. While the federal government has backstop siting authority that could address these barriers to transmission permitting, it has never been used.
Disagreement on Fair Cost Allocation
Transmission lines require significant capital and will only be developed if project costs can be recovered in a reasonable timeframe. Most lines follow the regulated cost-recovery model, whereby utilities and developers get state or Federal Energy Regulatory Commission (FERC) approval to charge a certain rate to customers based on their costs. But it can be difficult for stakeholders to agree on these costs, especially in the case of multi-state lines. Not everyone may agree on the net benefit of reducing emissions and share costs accordingly.
Technology Innovation Examples
Technological advances in high voltage DC (HVDC) and superconducting materials provide opportunities to build low-cost, long-distance transmission lines, including underground lines. HVDC and superconducting lines have lower losses and lower heat production than AC lines. As a result, they can achieve higher current over long distances at a lower cost, both above ground and underground.
While ambient air cools above-ground transmission lines, underground power lines can overheat if they are not designed to dissipate or withstand the heat generated by resistive losses. This limits the current they can carry.
Some companies are working on next-generation technologies using high-voltage DC (HVDC) technology to dissipate heat and reduce the cost of underground lines significantly. The conductor and insulation for underground cables can be optimized for the thermal characteristics of the soil they are passing through. (525-kiloVolt cross-linked polyethylene insulated cables enable much higher line ratings, for instance, which means a single cable can deliver many more GW.)
Solar, batteries, and some types of wind generators produce DC power that is converted to AC. The growth of these resources increases the need for new mechanisms for maintaining grid stability. Enhanced power converters will play an important role. Today’s converters follow frequency and voltage signals on the grid that are set by conventional AC power plants. Parts of the grid using large amounts of renewable energy sources and few conventional power plants are reaching reliability constraints that limit the addition of new wind and solar generators. Advanced converters can overcome these limits by contributing to grid control.
Grid control technologies, such as dynamic line ratings and power flow control, can deliver more energy over existing lines with speedy, low-cost installations. Dynamic line ratings use real-time temperature measurements to keep lines from overheating and causing long-term damage. Power-flow control technologies can also optimize transmission by increasing flow over less used lines. Deploying these technologies can result in significant cost savings and increased energy delivery.