Achieving Fossil-Free Electricity — Infographic Glossary

The following glossary provides definitions, additional information, and resources for the infographic in the Asia Gas Factsheet #3: No Gas Needed.

ENERGY EFFICIENCY: described by the International Energy Agency (IEA) as “the first fuel of a sustainable global energy system.”In its 2022 Energy Efficiency report, the IEA stated that “the largest energy efficiency opportunities of the future will be found in emerging and developing countries.” Using energy more efficiently increases energy security and lowers costs for consumers. The most significant areas for improvement are generally in buildings and transport.

MARKET & GRID DESIGN & INFRASTRUCTURE: Achieving the first 30-50 percent of renewable energy penetration requires redesigning electricity markets and their operating rules. These measures support greater renewable energy adoption and increased flexibility and interaction between power generation resources. These power market and grid design shifts are the fundamental basis of the transition to clean energy.

Power Market Design

Legislative & Executive Policy & Goals: Setting renewable energy targets for the short, medium, and long term has been shown to support renewable energy adoption. Policies that make clear the government’s ambition over the long term send clear signals to investors and companies that they can safely invest in renewable energy. 
Accurate Regulatory Requirements & Pricing: Prices set by regulators must avoid supporting fossil fuel capacity that is not needed. 
Systems & Standards Setting: Standards set by regulators need continuous reassessment to ensure that they reflect technological innovation and market developments and are not so demanding that they lead to investments in costly generation capacity that is rarely used.

Smart Grids – A smart grid is an electricity network that uses digital and other advanced technologies to monitor and manage the transport of electricity from all generation sources to meet the varying electricity demands of end users.

EVs – Vehicle to Grid: Also known as V2G. A smart charging system that allows car batteries to send back power to the grid. It enables EV batteries to act as storage cells for the electrical grid to help balance wind and solar on the grid.
Demand Response – Residential & Commercial: Provides an opportunity for consumers to reduce or shift their electricity usage in response to time-based rates or other forms of financial incentives in order to flatten demand peaks and help balance renewable energy production. 
Grid-Forming Inverters: As conventional generators decline, their role in providing frequency response also declines. Plan now for an increase in inverter-based resources (wind,  solar & batteries) and utilize emerging tools for inverter-based frequency response.   
Integrate Distributed VRE: Wind, solar, and battery systems operated by households and businesses can be integrated into a smart grid to support the grid’s operation and provide services such as frequency and demand response.

Advanced Forecasting: Big Data and AI

Advanced Generation & Demand Forecasting: Use technology and data to enhance demand forecasting to improve system design and ensure accurate allocation of resources.
Weather – From minutes to months: Meteorological tools capture real-time site-specific weather data. Algorithms then produce advanced forecasts for solar and wind output. This can help maximize the utilization of renewable energy. 
Increase Time Granularity of Markets: Allocating system access to generators in time increments of 15 minutes or less helps better manage the uncertainty in matching power demand and supply in a system with a high share of VRE through electricity prices that better reflect the system conditions in real time.

Transmission

Connect Remote VRE to Demand Centers: Build high-voltage transmission lines to bring electricity from windy and sunny areas to demand centers. 
Interconnection (Countries or Regions): Transmission lines that connect grids in different regions or countries, enabling the sharing of renewable energy and helping to increase flexibility and balance systems.
Overbuild VRE: Studies show that it may be cheaper to build several times more wind and solar capacity than demand peaks imply than to build out large amounts of storage or maintain fossil fuel plants as a backup.

NON-VARIABLE RENEWABLE ENERGY

Geothermal: energy produced from tapping into heat within the earth. 
Conventional: Generally limited to seismically active sites with abundant shallow hydrothermal resources provided by natural fractures.
Enhanced (and Advanced): Drilling deeper than conventional to access heat available at the continental crust. Some techniques use fracturing, which may cause environmental harm and is still at the research and pilot project stage.   
Ultra Deep: Currently experimental. Using millimeter-wave drilling to drill up to 20 km below the surface would enable geothermal energy access almost anywhere in the world. This would potentially allow existing thermal generation units (coal and gas) to operate without fossil fuel, requiring little additional infrastructure. We could see the first plant in operation by 2028.

Marine/Ocean: using energy generated by the ocean’s waves, tides, and currents to produce electricity. 

Wave: harnessing the kinetic energy of ocean waves to generate electricity. While variability exists, it is highly predictable, making wave energy a reliable energy source. 
Tidal: harnessing the kinetic energy from the gravitational forces exerted by the moon and the sun on the oceans. Potential tidal resources are unevenly distributed worldwide, concentrated in Argentina, Central America (Atlantic), France, North America (both coasts), the Republic of Korea, the Russian Federation, and the UK.
Ocean Current: Currently the least developed ocean energy source, but shows promising potential with highly reliable and continuous energy flows.  

Hydro

Existing: Large hydropower dams have harmed communities and caused environmental destruction worldwide. There should not be any new dams built. Existing hydropower provided 15 percent of global power generation in 2022, which is fossil-free power that can be used to support wind and solar. Hydropower is well-suited to support VRE because turbines can quickly start or stop in response to demand. However, climate change threatens the reliability of hydropower as prolonged drought reduces water availability for power generation.
Retrofit: Retrofit, where appropriate, existing dams that were built for flood control, irrigation, or recreational purposes to generate electricity.
Micro: small hydroelectric generators that do not require dams and can power households, businesses, or small communities. They can be part of microgrids.

ENERGY STORAGE: storing surplus renewable energy for when not enough is generated to meet demand. 

SHORT DURATION (1-4 hours)

Lithium Batteries: Lithium-ion battery technology dominates today but is only suitable for short-duration storage and is associated with the environmental impacts of lithium mining and associated rare earth mineral mining. 

Front of Meter (Utility Scale): large-scale battery storage plants operated by utilities. Increasingly, these are designed together with wind and solar plants and can enable those plants to operate as a dispatchable generation. 
Behind the Meter (Residential/Commercial): batteries installed by homeowners or businesses to store distributed renewable energy or serve as a backup when the grid requires it.

LONG DURATION (5 hours +…) 

Mechanical / Kinetic

Gravity-Based: storing energy by lifting weights with surplus energy and generating energy on release.  
Compressed Air: based on the gas turbine cycle. Surplus power is used to compress air using a rotary compressor and then store it, often in an underground chamber. When the power is required, it is released from the chamber and passed through an air turbine that generates electricity from the flow of high-pressure air.
Liquid Air: uses surplus electricity to cool air until it liquefies, then stores the liquid air in a tank or underground cavern. The air is then decompressed and heated to drive a turbine to generate electricity. 
Pumped Storage (Hydro): uses the difference in elevation between two reservoirs to pump water uphill with surplus electricity and flow to the lower reservoir to generate power when it is needed. As with large hydroelectric projects, land use and community impacts can be issues that must be avoided. 
Carbon Dioxide: similar to the compressed air system. Using CO2 in a closed loop system (i.e., no emissions) requires less energy as CO2 moves between gaseous and liquid phases without the need for cryogenic temperature extremes. So, CO2 is compressed during the charge phase and is released through a turbine to generate energy in the discharge phase without ever leaving the system.

Thermal: storing energy as heat and then releasing the heat to generate electricity

Sensible Heat (Molten Salt / Rocks): storing heat in a liquid or solid storage medium—such as water, molten salts, sand, or rocks and then using the heat to make steam to drive a turbine.
Latent / Thermochemical Heat: storing heat in phase change materials and then releasing the heat to make steam.

• Electrochemical (Batteries)Flow Batteries: liquid electrolytes stored in tanks outside of the cell. No rare earth minerals or lithium are required. Uses abundant, relatively low-cost minerals, such as iron and vanadium. 12-hour storage is typical. 700MW of projects recently announced, mostly in China.
  Metal-Air: capable of much higher energy density compared to lithium-ion. Uses iron or zinc in a “reversible rust” cycle. Low cost and abundant materials, no fire risk. 
  Sulfur-based: Sulfur is highly abundant and cheap and can replace nickel, cobalt, and/or manganese in lithium-based batteries, with a high energy density potential. 
  Conductive Polymer: Free of heavy metals and rare earth minerals and without fire risk. Polymers are made from oil but could be plant-based in the future. 
  Green Hydrogen: Manufacturing hydrogen using electrolysis powered by renewable energy. There are issues around safety and efficiency, particularly with hydrogen storage and transportation. Converting electricity to hydrogen and back again is inherently inefficient, and adding long-distance transportation to the process greatly increases inefficiencies. Hydrogen should be manufactured, stored, and converted back to electricity, all at the same location, to limit inefficiencies and leakage risks. Storage facilities must be closely monitored to prevent hydrogen from escaping into the atmosphere, as it is a potent greenhouse gas.