Description: Electric energy storage technologies for electric power applications with benefits for renewables integration; ancillary services; time arbitrage of on- and off-peak energy; and capital deferral at the grid connected, distribution, and customer levels are becoming better understood. Pumped hydro storage (generation from hydro sources is described under category 2) is the most prevalent storage technology at present, with 40 plants operating in the United States and capacity totaling more than 22 gigawatts (GW). Compressed air energy storage (CAES) technologies store ambient air at pressure in underground caverns. CAES produces electricity by releasing the air through a turbine-driven generator. Adiabatic CAES can achieve higher efficiency by recovering the heat of compression. Battery technologies vary tremendously in their underlying design and performance characteristics but hold great promise to allow for increased penetration of variable and distributed power resources. They also are used to provide other services including peak shaving, ramping, spinning reserve, and backup for specific uses such as data centers.

Technology Barriers: There is a need for cycle-testing protocols for grid-scale storage. Once such protocols are developed, there will be a need to test single-cell and multi-cell systems under real-world conditions. Key needs are to reduce response times to demand and increase the total storage capability in order to make stored electricity dispatchable. Decreasing internal losses and improving calendar life are also important.

Commercialization Barriers: Electricity storage is not a mainstream technology considered in planning, building, and operating electric power infrastructure. Several regulatory, policy, financial, and awareness issues will have to be addressed before it can be accepted and exploited as part of the electricity supply chain. The most effective technology for large-scale electric energy storage at this time continues to be pumped hydro. Although that technology is relatively mature, the availability of new sites is extremely limited.

Description: Large conventional hydro generation (greater than 30 megawatts [MW]) had an installed capacity in the United States of approximately 79,000 MW as of 2014, with the technical potential to double large (as well as small) hydro capacity. However, this expansion will likely not be realized by 2035 because of regulatory and financing constraints. MHK power technologies are still in various stages of development. Technologies to utilize ocean currents are in the proof-of-concept and laboratory demonstration phases. Wave, tidal, and ocean thermal technologies have components that have gone as far as open-water operation, although none have undergone array testing, and many wave and tidal technologies are still in the demonstration phases.

Technology Barriers: Improved operational performance of turbine runner and major components; improved flow measurement and control to reduce turbulence and increase energy conversion; fish passage/protection and environmental management; enhanced dam safety; development of room temperature superconductors (RTSs), precisely above 0° C. Some MHK technologies still require significant technology development. None have yet undergone array testing. Critical barriers include developing advanced controls and power take-off technologies, and optimizing device structures to improve energy capture, decrease mass, and improve system reliability.

Commercialization Barriers: Long-term financing for capital projects; long timeline for licensing and relicensing projects; low natural gas prices for competing generation; financial markets for hydro to benefit from providing ancillary services support.

Description: Triple-junction photovoltaic (PV) devices exist and have achieved efficiencies of ~43 percent under concentration with very advanced fabrication technology (the highest efficiencies were obtained with structures based on stacks of epitaxial III-V compounds), but represent the first actual devices to demonstrate very high efficiency potential.

Technology Barriers: Multijunction cells (e.g., the incremental gain from adding another cell to a stack of N junctions is theoretically proportional to 1/N(squared); therefore, after including the per-junction losses (electrical and optical) in a practical device, the expected net gain from adding cells is close to zero after the 4th).

Commercialization Barriers: Needed cost reductions associated with each cell junction addition; utility-scale solar power generation assets depreciated as 5-year property.

Description: Concentrating solar power (CSP) encompasses a variety of configurations, including parabolic troughs, heliostats, and linear Fresnel

Technology Barriers: Cost-effective thermal energy storage; low-cost solar fields; high-temperature receivers; advanced power block technologies; high-temperature heat transfer fluids with low melting points.

Commercialization Barriers: Financing; land use; siting issues in environmentally sensitive areas; transmission; regulatory framework; manufacturing; utility-scale solar power generation assets currently depreciated as 5-year property; supply chain.

Description: Solar thermal heating is used primarily for producing residential hot water, for space heating, and for heating pools. Use in North America has declined because of the high cost compared with other technologies, although use for pool heating remains quite cost-competitive. Solar thermal technologies continue to do well outside of North America where conventional fuels such as natural gas cost more. China remains the largest solar thermal market, with a preponderance of low-cost thermosiphon-type systems. Solar thermal for process applications is another area of great potential.

Technology Barriers: Low-cost systems with plug-and-play installation for residential and commercial use; large field integration for industrial applications; measurement of solar thermal output.

Commercialization Barriers: Incomplete value chain; lack of knowledge among building owners and/or operators; insufficient incentives to adopt new technology; split incentives between building owners and operators.

Description: Biomass power production, frequently referred to as biopower, refers to power generation from biomass sources such as grasses, straws, forest products, and energy crops. Pretreatment processes such as leaching and torrefaction help eliminate deleterious components from biomass and increase the energy density of biomass, making it more suitable as a fuel whether direct- or co-fired. Wood is the most common biopower fuel, generating more than 42 gigawatt hours (GWh) of electricity in 2015 (nearly twice the electricity produced by utility-scale solar PV).

Technology Barriers: Leaching/torrefaction plant demonstration projects; pilot burning tests using leached plus torrefied biomass in existing boilers; power production (e.g., distributed bipower systems, high-efficiency conversion technologies); feedstock development (e.g., efficient forest-thinning techniques, higher-yield crops/trees, improved biomass upgrading technology).

Commercialization Barriers: Cost of leached + torrefied biomass 3 times higher than that of coal on a per million British thermal units (MMBtu) basis; lack of leaching + torrefaction demonstration plants large enough to support pilot burning tests; high cost of delivered feedstock.

Description: Margin stimulation is being examined for the purpose of converting dry in-field wells that were originally deemed failures, while a hot dry rock method is also being considered to access existing subsurface heat in a wide geographic area by using water or supercritical carbon dioxide (CO₂).

Description: New wind generator technologies include advanced direct-drive permanent magnet generators (ADDPMGs), high-temperature superconducting generators (HTSCGs), and room-temperature superconducting generators (RTSCGs). Their development could reduce the levelized cost of electricity, increase capacity factors, reduce generator weight, and support the search of the wind industry for larger-scale wind

Technology Barriers: ADDPMGs—structural robustness, long-term reliability, scale-up to 10 megawatts thermal (MWt); HTSCGs—industrialization of cryocoolers/low maintenance/higher efficiencies; RTSCGs—development of RTSs, precisely above 0° C.

Commercialization Barriers: Competitive capital cost and efficiency of commercial units; no evaluation of independent demonstration projects, including transportation, field assembly and operating performance; high perceived risk increase financial costs.

Description: Integrating a large amount of distributed resources into the power grid in an economical and sustainable way while ensuring system reliability will require new tools and methods. Understanding of the impacts on the rest of the power system, planning to ensure that the power system infrastructure can accommodate high penetrations of variable generation, and development of the operational tools needed to manage some of the unique aspects of wind and solar PV are needed. The scale of integration matters for both large-scale and distributed systems. Integrating distributed resources to supply more than 15 percent of the load will require smart inverters that enable distributed energy resources to provide voltage and frequency support and to communicate with energy management systems. It will also require distribution management systems and ubiquitous sensors so operators can reliably integrate distributed generation, storage, and end-use devices while also interconnecting those systems with transmission resources in real time.

Technology Barriers: Variability and uncertainty of production, limiting the penetration in certain areas because of a lack of system flexibility. Inverter-based nature of the technology, limiting instantaneous penetration in the system (more than 50 percent not currently possible in a synchronous system). Distributed nature resulting in less visibility and control and potential reliability impacts.

Commercialization Barriers: Distributed PV may reduce utility revenue while still requiring significant transmission and distribution upgrades; lack of additional revenue streams for variable generation; large balancing costs imposed on variable generation.

Description: Although it is not cost-competitive at present, CO₂ capture and storage can work in fossil fuel power plants. There is also room for substantial improvement. Current technologies use three times the theoretical minimum energy to capture and compress CO₂, and efforts to prove and improve CO₂ capture and storage are in the early stages. Pipeline transportation of CO₂ in the United States is quite mature, with 50 individual pipelines spanning more than 4,500 miles.

Technology Barriers: Need to better understand long-term issues related to storage: impact on water tables, caprock, injection operations, liability (see Chapter 5 section on “Key Nonmarket Barriers”).

Commercialization Barriers: Lack of regulatory and economic drivers (see

Description: Advanced natural gas technologies, such as a new power generation concept based on the “Allam Cycle,” could provide power at a thermal efficiency exceeding 50 percent. Heat rates for other advanced technologies are approaching 5,400 Btu/kilowatt hour (kWh). Combined heat and power (CHP), a technology of interest to large industrial organizations with a significant demand for thermal energy (steam or hot water), is another promising technology. Current installations are almost universally large and custom designed. Small-scale systems are not as well developed. Small-scale users would benefit from the development of modular “plug and play” thermal appliances.

Technology Barriers: Need to prove the system (e.g., that it can operate as a whole while responding to typical demands of a natural gas-fired power plant); for micro-CHP, lack of availability of “plug and play” thermal appliances (most CHP installations need to be custom engineered).

Commercialization Barriers: In the long term, a continued preference for natural gas as a fuel source will pose a barrier to lowering GHG emissions.

Description: Water withdrawals and the treatment of wastewater are important limiting factors in the construction and operation of power plants. Conventional processes for generating desalinated (and deionized) water include reverse osmosis (RO), multistage flash distillation (MSF), and multiple effect desalination (MED). RO involves the use of membrane to generate pure water from salt water by applying a pressure higher than the osmotic pressure. MSF and MED involve thermal evaporation of water. In membrane distillation (MD), a heated aqueous solution passes through a hydrophobic membrane and is partially transformed to water vapor and collected as pure water. Electrodialysis (ED) transports salt ions through ion-exchange membranes under the influence of an applied electric potential

Technology Barriers: RO—high power consumption and limitations of high salt concentration and fouling; MSF and MED—high investment, corrosion, energy cost; MD—availability of membrane with high flux; ED—energy-intensive, high treatment cost (which depends on salt concentration), competitive with RO in some cases (particularly for brackish water applications), fouling; FO—separation of draw solutes and high-flux membranes. The economics of FO are as yet unclear. Some studies argue that FO is economically/technologically less attractive than RO, while others argue the opposite. FO membranes are of insufficient permeability, and higher-permeability membranes are needed. Moreover, solute crossover limits use of FO for potable water production. In addition, draw solution requires regeneration, which adds to the overall cost. As in the case of RO, fouling and mineral scaling are of concern, and experience with FO systems in this regard is currently limited.

Commercialization Barriers: RO—development of membrane with less fouling; thermal distillation processes—predominantly large investment and energy costs; MD—need for significant improvements in pure water flux, probably by an order of magnitude, and need to prove cost and advantages through extensive field demonstration; ED—more complex to deploy for very large-scale systems, opportunities for integration of RO and ED for high--

Description: Advanced reactor designs are intended to provide increased safety margins, reduce costs, and extend the length of useful life for nuclear power plants. A large number of systems are under development, including several that use gas, molten salts, or liquid metals for cooling instead of light water. There has been much development activity in the field of advanced nuclear power plant systems over the past 15 years, but a great deal of additional work will be needed for commercialization of these systems. Given the likely importance of very low-carbon or zero-carbon dispatchable power sources, the continued development of these systems is of high priority. The committee recognizes developments around the world that are under way that employ various technologies.

Technology Barriers: Need to develop materials capable of withstanding high neutron flux densities; no demand pull; spent fuel issue (see Chapter 5 section on “Nuclear Innovation Prospects and Obstacles”).

Commercialization Barriers: Commercializing nuclear-related innovations is an expensive, lengthy, and risky process; need to develop regulations tailored to new technology systems (see Chapter 5 section on “Nuclear Innovation Prospects and Obstacles”).

Description: Small modular reactors (SMRs) are smaller in size (300 MW or less) than current-generation baseload plants (typically 1,000 MW or larger). There are several systems under development across the world based on both light water and advanced designs. The committee recognizes developments around the world that are under way that employ various technologies.

Technology Barriers: Designs need to be tested and proven (e.g., development of assessment methods for evaluating advanced SMR technologies and characteristics; development and testing of materials, fuels, and fabrication techniques; development of advanced instrumentation and controls and human-machine interfaces) (see Chapter 5 section on “Nuclear Innovation Prospects and Obstacles”).

Commercialization Barriers: Cost and lack of experience; commercializing nuclear-related innovations is an expensive, lengthy, and risky process; need to develop regulations tailored to new technology systems (see Chapter 5 section on “Nuclear Innovation Prospects and Obstacles”).

Description: Research is needed to address the technical bases for decisions regarding the continued high-performance operation of nuclear power plants. The research will need to address aging and life-cycle management, refurbishment and uprate decisions, and opportunities for modernization and performance improvement—especially needed to understand materials degradation and aging. Spent fuel continues to be a challenge, although local solutions—mainly onsite storage—are emerging in the absence of a single, central repository at the national level. The committee recognizes developments around the world that are under way that employ various technologies.

Technology Barriers: Little research on degradation and aging of materials, including concrete; new technologies for online monitoring of critical equipment; new safety and risk analysis tools; integrated life-cycle management data, methods, and tools; enhanced nuclear fuel designs and analysis.

Commercialization Barriers: Development of repair and mitigation tools/technologies; development of accident-tolerant fuels and technologies; plant demonstrations to assess the new technologies; code and regulatory acceptance.

Description: HVDC technology uses two types of converters: line

Technology Barriers: Increase operating voltages and levels of power transmission for VSCs.

Commercialization Barriers: No U.S. companies developing HVDC systems as power grid is almost entirely AC. Investments in R&D.

Description: The electricity industry is the second largest electricity-consuming industry in the United States. The use of electrical energy in the production of electricity, as well as the uses or losses in power delivery (transmission and distribution), contribute to this total. There are opportunities to reduce electricity use in power production and delivery. These opportunities may include advances in control systems for auxiliary power devices and the use of adjustable-speed drive mechanisms (ASDs).

Technology Barriers: Power system designers seldom consider electrical losses in the design of power plants or transmission and distribution systems.

Commercialization Barriers: Retrofitting fossil or nuclear power plants

Description: Encompasses meters, appliances, power sources, phasor measurement units, power flow controls, and system automation. Smart-grid technologies permit systematic and reliable communication between suppliers and users, allowing for time-of-use pricing, peak load curtailment/leveling, smoother demand response, and greater penetration of variable and distributed generation sources.

Technology Barriers: Mitigation of natural disaster impacts; cyber security of resources; accommodate and optimize the use of intelligent devices that reside at different points within the grid; integration of new and legacy technologies.

Commercialization Barriers: Savings may not be directly visible to consumers. Rate-based rate-of-return regulation may not allow for cost of infrastructure. Regulation may not allow for failed investment.

Description: Increasing power flow on existing and new transmission lines and corridors can facilitate greater use of renewable power generation options, enhance reliability, reduce control station power plant emissions, and reduce costs. Several technology options are commercially available, although some would benefit from additional advances. Others are in relatively early TRL stages and in need of continued development.

Technology Barriers: Standards need to be developed.

Commercialization Barriers: Savings may not be directly visible to consumers. Rate-based rate-of-return regulation may not allow for cost of infrastructure. Regulation may not allow failed investment.

Description: Increasing penetration of variable distributed energy resources (DER), especially solar PV systems on the distribution power grid, is creating grid integration challenges for utility engineers. Over voltage, reverse power flow, and excessive switching of capacitor banks and/or line tap changers often occur in circuits with higher penetration of variable generation sources such as solar PV. Some of these technical challenges can be resolved, or at least minimized, by employing the full potential of power electronics inside the inverters interfacing these sources with the electric grid. Inverters with grid supportive functionality, including reactive power support, low/high-voltage ride-through, watt-frequency, watt-voltage, and real power curtailment, can contribute to grid stability and hence help allow a higher adoption rate of variable DER technologies.

Technology Barriers: Need for common communication protocols.

Commercialization Barriers: Absence of widely accepted grid interconnection standards (e.g., Institute of Electrical and Electronics Engineers [IEEE] 1547) and testing standards (e.g., UL1741) to refer to regarding these smart-grid functionalities. There are also some open questions, such as the utility having access to customer-owned inverters, whether PV plant owners will be compensated for providing grid services, and whether a uniform grid code will be enforced.

Technology Barriers: Because of the range of technologies, a full accounting of the technology barriers is difficult to summarize. Most technologies require additional development and refinement to improve their performance profiles. Further electrification would require distribution system upgrades (see categories 18 and 19 and Chapter 6).

Commercialization Barriers: Incomplete value chain; lack of knowledge or disconnected incentives between building owners and operators.