The biggest machine on Earth delivers more than $400 billion of electricity a year across nearly 7 million miles (11 million kilometers) of transmission and distribution lines. It’s the U.S. power grid, an interconnected system of generating plants, wires, transformers and substations that keeps the lights on for the homes, offices and factories of the world’s largest economy. Now, President-elect Joe Biden wants it to be carbon-free by 2035 as part of his ambitious plans to confront climate change. Reaching this target will require replacing about 60% of the country’s fossil-fuel based power supplies with emissions-free energy. The endeavor will also require a grid upgrade described as “one of the most radical infrastructure overhauls in U.S. history,” by Ed Crooks, an energy analyst at research firm Wood Mackenzie.

1. What would it look like for the grid to go green?

The U.S. grid was designed for the one-way flow of power from big, centralized fossil-fuel plants to homes and businesses. That will need to change as those big generators are replaced with lots of smaller, cleaner power sources. The clean-energy grid therefore will need to be decentralized in a way that allows for power to flow in multiple directions. For example, an increasing number of consumers will install solar and batteries, turning their homes into mini-power plants that can sell power back to utilities. Corporations and cities may also create their own self-contained power networks using solar, batteries and software controls that will also connect to the larger grid. And new power lines will have to be built to connect all of that green power to towns and cities.

2. What needs to change for that to happen?

The grid will need to get a lot “smarter” and more flexible, says Ethan Zindler, head of BloomberNEF’s research in the Americas. A carbon-free power network will have to handle instantaneous shifts in both electricity supply and demand. That will require major upgrades (read investments) in grid communications and computer-based control systems to make sure everything works together.

3. What does that mean for consumers?

They’ll also need to become more flexible in their power use. For example, utilities may need homes to ramp down their electricity consumption when the grid is stressed and solar power wanes. This can done with programmable thermostats and other smart home appliances that can vary their energy use based on signals from the grid. There will also have to be a lot more energy storage or other carbon-free resources available that can back up wind and solar, whose production varies with the weather and the time.

4. Does that mean solar panels on every roof?

Probably not. While solar is getting cheap enough that many more homes and businesses will be adding it (along with batteries), not everyone will be able to afford it or live in a place where they can use it. Utilities say that the cheapest and most cost-effective way to add lots of renewable energy to the grid is by connecting to large solar fields and wind farms. That’s likely how most of the new clean power will be added.

5. What stands in the way of a green grid?

The main obstacles will be cost and feasibility. Wind and solar only work when the sun shines or winds blow. So they need help from big batteries or power plants that stand by to run when needed. While batteries have fallen in price, they remain an expensive way to back up clean power. In addition, batteries have yet to be tested on a large scale on the grid. Still, a recent study by the University of California at Berkeley’s Goldman School of Public Policy found that reaching 90% zero-carbon electricity by 2035 could be feasible and economic by using mostly solar, wind and batteries.

6. What about the last 10%?

Eliminating the last of the carbon from the grid will likely prove difficult -- and very expensive -- unless there is a technological breakthrough. Those could include advances in carbon capture and storage, small nuclear reactors and hydrogen.

7. How would that all be stitched together?

The U.S. can produce a lot of wind power in the Midwest and solar energy in the Southwest, but it will still need to deliver that electricity to distant cities. That will require building high-voltage transmission lines, something that has so far proved to be a bureaucratic nightmare. Big projects often get delayed and face local opposition. There have been efforts to streamline the permitting process and construction of interstate transmission, but those steps have yet to spur the kind of build-out that will be needed.

8. Have any countries gotten further on this?

A few smaller countries such as Iceland and Paraguay have nearly carbon-free grids, but that’s by virtue of them having access to home-grown renewable resources such as geothermal energy (Iceland) or hydro-power (Paraguay). Some coal-heavy European countries have made progress in cutting emissions from their grids, although the U.K. has run into some challenges as it switches over to using more wind power. In the U.S., California is a leader in clean electricity, but endured blackouts last summer in part because the older natural that backed up solar had been closing.

9. What are other drawbacks and benefits, besides less carbon?

Adding a lot of new communication technology to the grid could make it more vulnerable to cyberattacks. Grid managers and utilities will need to take extra precautions to prevent bad actors from infiltrating critical infrastructure. Building a clean grid, however, could create a lot of new jobs. Workers would be needed to build and install solar and wind farms, string up power lines and design new control systems. The Biden administration says transforming the U.S. electricity system represents the biggest job creation opportunity of the 21st Century.

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