Virtual Power

The Future of Energy Flexibility

William Angel

• Éditeur: New Degree Press
• Année: 2020
• ISBN:
  9781641374255
• Édition: 1
• Sujet: Tecnologia e ingegneria
• Sous-sujet: Risorse energetiche rinnovabili

Electric utilities in the United States spent almost $60 billion on grid modernization in 2019 and will spend trillions in the coming decades to keep the lights on. We’re facing a global challenge to make humanity’s presence on this planet sustainable. The electrical grid is undergoing an energy transition from fossil fuels to renewable energy, but it needs to become more flexible to supply and sustain our needs. Amazing work is being done with renewable energy to decarbonize the electrical grid, but the grid is not yet flexible enough to become carbon-neutral. Yet. Virtual Power details how energy storage and virtual power plants will enable the electrical grid to become more sustainable, affordable, and resilient. In this book, you'll discover:

• How grid scale energy storage in Australia reduces costs and keeps the lights on
• The Duck Curve: how virtual power plants made from charging electric vehicles are keeping solar energy from destroying California’s electrical grid
• How businesses and governments are saving billions of dollars by investing in flexibility and storage

These stories give us hope and provide reasons to be optimistic about our ability to make our energy consumption more sustainable in the future. If you are passionate about sustainability, the environment, or technology, Virtual Power is for you!

6

Energy Storage Technologies

It’s still magic even if you know how it’s done.

—Terry Pratchett, A Hat Full of Sky

Being able to store energy for future consumption makes the grid more flexible, which allows for intermittent renewable energy to be fully utilized without the need for conventional hydrocarbon generation to bridge the gap between renewable supply and total demand. Understanding the different types of energy storage technology in operation is important to see how storage currently fits into the electrical grid and how it will fit into the more flexible and distributed electrical grid of the future.

There are as many different ways to store energy as there are different kinds of energy, with the primary types of energy used for storage being chemical, mechanical, electrical, and thermal. Different technologies have different performance in terms of cost, power output, power density, and risks. Even within specific categories of storage technology, there are wide differences in performance depending on the details of implementation.

Chemical Storage

Chemical energy storage currently only has a few large-scale commercially used technologies for bulk electrical storage: electrochemical batteries, synthetic fuel synthesis, and hydrogen electrolysis. There are numerous types of batteries used for grid-scale storage and even more kinds used for smaller electronic devices. The synthesis of chemical fuels for energy storage is not currently popular due to high costs and the extremely competitive low cost of fossil fuels.40 In the future, however, the synthesis of carbon-neutral hydrogen fuel or methane may become popular as a fuel source. For hydrogen production coupled with a gas turbine or hydrogen fuel cell, this could make an effective source of grid-scale energy storage. Currently, batteries are the most popular electrochemical storage.

Batteries are electrochemical devices that store charge by moving ions between an anode and cathode using an electrolyte. In the context of energy storage, batteries refer exclusively to secondary batteries that can be recharged hundreds or thousands of times unlike primary batteries, which cannot be recharged. Most battery installations consist of dozens of battery packs, which are made up of thousands or tens of thousands of smaller battery cells. There are many different kinds of battery systems, but because each battery cell is usually small, systems can be highly modular to optimize for the duration of discharge—the total amount of energy stored—or speed of discharge, the maximum power that the system can produce. There are many factors to consider when picking a battery chemistry and system design:

• Specific Energy—kWh/Kilogram

• Energy Density—kWh/Liter

• Charge/Discharge Speed

• Battery Lifetime—Number of charge/discharge cycles before performance is reduced

• Self-discharge Rate—How fast an unused battery loses charge

• Environmental Tolerances—Acceptable temperature/humidity

• Efficiency—Percent of stored energy lost

• Safety

• Cost Per Stored Energy—$/kWh

• Cost Per Power Output—$/kW

All of these factors depend on battery chemistry and system design, as well as a system’s operational requirements. Several of these factors are limited by chemistry and the laws of physics: there is a maximum amount of energy released when a lithium atom is oxidized within a battery, which puts a theoretical limit on specific energy given the weight of the chemically relevant materials in a battery. Other factors such as cost and safety are primarily determined by system design, industrial processes, and economies of scale. There are several different types of chemistry that are worth going over.

Lithium-ion batteries are the most common type of electrochemical storage system utilized in the United States and consisted of 85 percent of installed operating battery storage plants in the United States in 2017.41 Lithium-ion is popular because it is usually the cheapest and fastest option to deploy (Tesla’s Hornsdale Power Reserve used lithium-ion batteries). Lithium-ion batteries are energy dense and offer some of the highest performance to weight and performance to size of any commercially available bulk electrochemical storage technologies. These cost reductions have only happened recently, and other storage chemistries and technologies have a great deal of promise.

There are numerous types of lithium-ion battery chemistries, all of which have different performance characteristics and material costs. Some like lithium-polymer batteries are used when performance per weight and performance per volume are prioritized over cost and longevity—though the useful lifetime of a battery can also be improved with better materials and better manufacturing. Most modern personal electronics like phones, tablets, and laptops use lithium-polymer batteries because they offer high-energy densities. By using a dry polymer or polymer-gel electrolyte instead of a liquid electrolyte, the weight and volume are lower and the battery can store more energy. These high-energy densities are desirable in all applications—except the Samsung Note 7.

Sodium batteries are the second most popular electrochemical storage technology currently in use, making up 9.5 percent of operational grid-scale battery storage in the United States in 2017. Most of these are molten sodium-sulfur batteries that use the chemical energy released by converting sodium metal into sodium salts. This reversible chemical reaction between sodium and sodium polysulfides (the salts formed when reacting sodium with sulfur) can be used to efficiently store excess energy and has been used with commercial success.

The Presidio Battery Project in Presidio, Texas, was completed in 2010 and has been providing energy storage and voltage regulation services to improve grid stability. This battery has been a commercial success and allowed Electric Transmission Texas, the project’s owner, to defer $15 million in infrastructure upgrades by almost ten years.42 The $25 million 14 MWh molten-sodium sulfur battery received a software upgrade in 2017 to allow it to provide frequency regulation services to the electrical grid, unlocking additional revenue streams for the battery facility.43 The battery also had enough storage capacity to power the city of Presidio for almost eight hours, which allows the utility to reduce maintenance costs and increase safety by switching the city to battery power when doing repairs on the long-distance transmission lines that normally power the city.

Sodium batteries are popular for long-duration storage projects. The United Arab Emirates (UAE) has installed almost 650 MWh of sodium-sulfur batteries.44 The fifteen storage systems distributed around Abu Dhabi make up 108 MW of total capacity and can be used independently or as a single virtual power plant entity. The investment in storage will allow the UAE to defer investment in new thermal generation—conventional fossil fuel power plants—and will allow diesel generation during peak hours to be reduced while still meeting demand. The sodium-sulfur batteries will also provide frequency regulation, voltage control, and operating reserves to make the grid more stable. Sodium-sulfur batteries were selected for this project because of the lower cost expected for the long term (six hours of operation) discharge requirement and because of sodium sulfur’s endurance in hot climates: lithium-ion batteries perform worse by losing efficiency and total capacity in hot weather and age faster when cycled under high temperatures. Using lithium-ion batteries in conditions and climates that are too hot or cold requires additional environmental controls to increase system life and performance, which increases costs and can make them less desirable than sodium-sulfur batteries.

Redox flow batteries are currently deployed in large-scale trial projects in the United States and made up 2.5 percent of storage in 2017. These batteries are almost closer to fuel cells than the classic rechargeable battery cells that resemble larger consumer batteries, as they store the liquid components of the battery in separate tanks and pump them over a membrane to charge or discharge the battery. Flow batteries are exciting because they lack almost all of the disadvantages of lithium-ion and other purely electrochemical batteries: they are generally safer and lose less capacity over time. They are also more flexible because the total storage can be expanded by adding additional liquid storage tanks, which is far cheaper than the new batteries that are required to expand a conventional battery system. The downsides of redox flow batteries is that they generally have lower power capacities, and it is expensive and difficult to increase their power output. The energy density is typically worse than other battery chemistries, which results in larger and heavier systems.

Nickel and lead-acid batteries made up 1.4 percent and 1.2 percent of the total storage capacity of grid-connected electrochemical systems in the United States in 2017. These storage systems are grid-scale pilots. There is only one grid-scale nickel battery currently connected to the grid. The 40 MW/11 MWh Nickel Battery Energy Storage System in Fairbanks, Alaska, was the largest grid-connected battery in the world when it opened in 2003. The system provides enough backup power during power outages so that the Golden Valley Electric Association Utility can start up backup thermal generation to prevent outages. The 1,500-ton battery has an expected lifespan of twenty to thirty years and is still going strong sixteen years into operation: the battery has responded to an average of fifty-two power outages per year since opening, and in 2018 prevented 309,000 Golden Valley customers from losing power during some of the fifty-nine outages the battery responded to.45

Lead-acid batteries, like larger versions of the batteries in internal combustion engine-powered vehicles that power the starter motor, have also been used for grid-scale storage. Lead-acid has traditionally had lower performance and far more expensive costs than lithium-ion, as well as far higher operational costs. Lead-acid batteries have helped in some places: Kodiak Island in Alaska was able to ...