How to Keep the Lights On When the Fossil Fuels Are Gone

This guest post is by Jonathan Trinastic, a physics graduate student interested in renewable energy and the pursuit of safe, sustainable energy policy. He maintains the blog Goodnight Earth, which reviews current research on these topics, and can be followed on Twitter @jptrinastic.

If you're behind the times, they won't notice you. If you're right in tune with them, you're no better than they are, so they won't care much for you. Be just a little ahead of them.

-- Shel Silverstein

Imagine a 540-foot tower spiking through the flat Nevada horizon, storing energy as thousands of surrounding mirrors reflect sunlight to heat molten salt inside.¹ Or how about solar cells on individual homes in constant electronic communication with utility companies to tailor energy needs? And then there's the molecule that stores energy by changing its atomic structure when light hits it²!

All these ideas and more promise to change how we think about energy storage and distribution in the next few decades to establish a world fueled by renewables. But why do we need new technology in order to use solar and wind power, touted for their renewability and minimal environmental impact, when we can already disseminate energy from fossil fuels to millions of homes? To answer this question, we must understand how the typical electrical grid works and how its fundamental operations need to change to accommodate new energy sources.

A centralized web

A typical electrical grid works like this. Centralized power plants collect huge amounts of coal (or natural gas). The coal is heated and converts water to steam over 1000° F. This steam rapidly spins a turbine connected to a magnetic generator inside an electrical coil. As the turbine spins the magnet, Faraday tells us that this will induce an electric current in the coil wires. Electrons speed through this coil and into transmission wires, leaving the plant for the long journey to our homes. (Note that water is a crucial resource for current power generation - another reason for water conservation!)

If that's not enough of an engineering feat, consider the infrastructure to send these electrons where they're needed. The US alone has 450,000 miles of transmission lines snaking across the country³ to connect the power plant to distribution systems and individual homes, as shown by the various colored lines below (other developed countries have similar grids):

So you can think of the grid as an assortment of webs originating from centralized power plants. If this system works for fossil fuels, why can't we just hook up our solar panels and wind farms to the existing grid? We can, and countries are increasing their renewable capacity in this way; however, a problem arises if we want an electrical grid completely supported by renewables.

The energy expectation

The problem lies in how the grid deals with changing consumption. Coal can be stored because it exists in an easily-handled, solid form. Even natural gas can be compressed in tanks or liquefied for long-term storage. Storage is crucial because the amount of consumer-demanded electricity, or load, varies substantially from day to day and season to season. Daily peaks occur between 3-8pm as folks return home from work, turn on the lights, cook dinner, and fire up the TV. Huge seasonal peaks are seen in red-hot summer months or ice-cold winter months when cooling and heating are required, as seen in this hypothetical sketch of daily demand:

The grid handles peak loads by having plants on reserve, turned off until they're needed to throw loads of energy at the grid, providing a straightforward way to deal with variability in consumption. This method has its inherent disadvantages, including the huge capital cost and maintenance for plants that sit idle most of the year.

On the other hand, solar and wind are inherently ephemeral - we can't grab a sun ray like we can a piece of coal. And they're intermittent. Solar power peaks only when the sun is shining bright, which we can't control. Wind provides power as long as it's, well, windy, which we can't control. So the power source and consumer consumption are variable. If these two factors don't happen to vary coincidentally, we're in trouble. Families at home will be demanding the next episode of Scandal, and the solar panels and wind farms won't be able to give it to them on a dark and calm evening.

With fossil fuels, power companies always maintain a reserve load 8-15% above peak to maintain a stable grid, but this isn't always possible with renewables because we lack the technology to store and release energy from these sources quickly. But change is on the way! Two significant advances will change how we think about accessing and storing electricity: 1) the smart grid, and 2) novel energy storage technology.

(As a side note, there's a psychological argument to this issue as well - we've come to expect stable electricity when and where we want it. I could imagine a renewably reliant society that learns how to use energy when it's available and accept when it's not. That's another story worth thinking about...)

Modernizing and decentralizing the grid

The current grid is massive and antiquated, slowly extended in patchwork since its birth at the beginning of the 20^th century. The centralized hierarchy of power generation, with coal plants at the top, is an inflexible, one-way design. Energy moves from source to user, but utilities are blind to real-time, dynamic changes in demand, leading to wasted energy.

The so-called smart grid changes this relationship. Analog meters would be replaced with digital ones. Digitized information processing at every level of the grid would allow utilities to change energy distribution and cap consumption as needed, based on continuous knowledge of local demand. More importantly, this smart grid can take advantage of decentralized power generation⁴, such as residential solar cells. Every home can generate their own power and send excess back to utilities to help satisfy peak demand elsewhere, decreasing the enormous capital costs required for new power plants. Smart grid infrastructure will allow for this reciprocal relationship. Using the two-way grid, power companies could monitor energy needs of homes, giving and taking energy as needed.

An encouraging development is the popularity of net metering policies, which take advantage of this reciprocity by allowing home-generated solar power to offset electrical bills. For this vision to become reality, however, significant investment at the state level is required to upgrade the grid.

Decentralization can take us even further, to the newest idea in grid modernization: microgrids. These smaller, autonomous power distribution centers for communities, hospitals, parks, etc. could operate whether connected to the larger grid or not. Excess power would be fed back to the main grid, using smart grid technology to provide it to other regions that need more. This would provide a tremendous buffer for communities against large-scale failures of the centralized grid. Microgrids also lend themselves to local solar and wind power generation, as smaller-scale storage technology would be adequate for community use.

Sounds wonderful, but the integration of microgrids and local power generation does rely on one area that needs improvement: energy storage technology.

Storing Nature's energy

Solar cells are the sexy energy technology. But they and wind turbines need to be connected to storage devices that can release energy when it's needed, flattening intermittent power generation to provide a stable grid. This makes storage technologies the unsung, under-researched heroes that could transform how renewables penetrate the market. Batteries are ubiquitous for handheld devices and computers, but their poor discharge rates make them inadequate for a grid that often needs flexible and fast access to power. Fortunately, new ideas are here. Here's a small sample of new storage technologies:

1) Supercapacitor⁵: The newcomer that's giving the battery a run for its money. Whereas batteries store energy by intercalating ions deep in electrode structures, supercapacitors rely on electrostatic forces at electrode surfaces. This dependence on electrostatic instead of chemical physics allows supercapacitors to reach much higher discharge rates that, when connected with solar and wind power, will help the grid provide spikes in energy when needed. Look for research in this area to skyrocket.

2) Molten salt tower: Light reflected by surrounding mirrors heats molten salt that can store thermal energy at high temperature for 10-15 hours, solving the problem of solar intermittency and the lack of energy input at night. Molten salt is also non-toxic and earth-abundant, making this a ‘green' technology. It's appearing in Nevada, Arizona, and Spain, and should power at least several thousand homes in each case.

3) Solar thermal fuels²: Remember the molecule I mentioned that changes shape when hit with light? This is a great alternative to solar cells. Direct light energy is stored in the molecule as it changes shape, and the energy can be accessed by heat whenever it is needed. Plenty of similar ideas can use the same principle for fossil-fuel-free storage.

4) Virtual storage: As opposed to the hard storage examples above, virtual storage relies on dynamic building behavior to tailor energy usage. For example, ‘building as battery' designs include white, reflective paint and electrochromic glass that can be adjusted to let more heat inside in the winter and less in the summer!⁶ These extremely low-cost methods act as an effective storage device by changing energy load.

In future posts, I'll spotlight technologies like these in more detail to describe how new research is improving them. They deserve more attention!

What can you do?

So take a moment to imagine the future. Solar panels on individual homes combine with wind farms to produce the majority of power generation. Constant chatter between homes and utilities provide second-by-second updates about who needs power when - energy is distributed only to those that need it and taken from homes that generate more than they need. Advanced supercapacitor and battery technology efficiently store solar and wind power within decentralized microgrids. Taken as a whole, the smart grid mimics an organic creature, healing itself where needed, using energy as efficiently as possible, and protecting against global failure.

Our electrical grid is working now, but we need to be a step ahead of the crisis when fossil fuels become too expensive to extract and we still have billions of people who are accustomed to stable electrical consumption. Policy will be a powerful mover in this regard, and those on the ground can affect policymaking by supporting net metering, smart grid technology, and the devotion of research funds to supercapacitors and storage technology. The time is now. And success is possible - just look at Scotland's aim for a renewable-only electrical grid by 2030!

References

1. Energy Digital. "World's largest molten salt solar tower plant completed." Accessed January 27, 2014
2. Kucharski et al. "Templated assembly of photoswitches significantly increases the energy-storage capacity of solar thermal fuels." Nature Chemistry, 6, 2014.
3. Indiana Energy Association "The Electric Grid System" Accessed January 27, 2014.
4. Farhangi, H. "The path of the smart grid." Power and Energy Magazine, IEEE, 2010.
5. Faraji et al. "The development supercapacitor from activated carbon by electroless plating - a review." Renewable and Sustainable Energy Reviews, 42, 2015.
6. Kraft et al. "Properties, performance, and current status of the laminated electrochromic glass of Gesimat." Solar Energy Materials and Solar Cells, 93(12), 2009.

Photo Credits

Molten storage tower photo: by National Renewable Energy Laboratory
Coal power plant image: by Tennessee Valley Authority
US electrical grid photo: by JMesserly on Wikipedia