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What does your electricity use look like?

Part II of an energy and research discussion for my parents (part I)

We all expect that when we flip the light switch at night, the lights will turn on. We won’t have to stumble around in the dark feeling around for a glass of water or to let the dog out. There are people and algorithms working around the clock to make sure when you and I request power, it is available.

This is exactly what our electric utilities do. They focus on delivering reliable and safe power to meet our “demand”. Because most utilities do such a good job of delivering electricity, we never think about the details.

The chart below gives a good idea of my family’s electricity demand last Thursday, October 24th. You can see there are many spikes as we made coffee and ran the dishwasher in the morning and other larger spikes later when we returned from work. Your energy use probably looks just as spiky though the details will certainly differ.

Cartoon of my family’s energy demand on Thursday, October 24th.

Our household daily usage is fairly similar day-to-day, even if the exact timing of making Henry and myself breakfast can differ quite a bit.

Sharp spikes to smooth curves

If every household has spiky electricity demand, how can our utilities anticipate the amount of power they need to produce at any one moment? Utilities rely on my demand, the demand of all my neighbors, and your demand being similar day after day. This helps them figure out a daily quantity which will likely be requested.

What about the precise timing of our morning coffee, how do they get that right? Utilities rely on having many customers and the law of large numbers. Not everyone makes coffee at 6:00am. Some make coffee earlier, some make it later, some not at all. When the actions of thousands of electricity customers are added together, their small differences smooth out the jagged spikes you see from my household when viewed in isolation. This leads to a very predictable energy demand throughout the day for a utility territory.

The below charts show electricity demand over three October days in 2017. The first is for a small utility with only 26,000 customers. This demand curve is already much smoother than my single household’s usage. And, the total demand across the contiguous United States is even smoother. In both of these cases, the demand has a cyclic peak-and-trough pattern with the lowest demand late at night.

The left figure shows the electricity demand for a small utility with 26,000 customers while the right figure is the total demand for the contiguous U.S. 1 Megawatt = 1,000,000 Watts

Utilities can make accurate forecasts of their territory’s electricity usage 24 hours in advance. Most can predict 24 hours ahead within 3% of the real value. This makes the cyclic peak-and-trough structure of demand very approachable for utilities.

Providing Electricity the Traditional Way

Over the past century, utilities have traditionally built enough coal, gas, nuclear, and hydro plants to match the peak electricity demand for their territory.

When a utility forecasts demand will reach 5,000 Megawatts tomorrow at 5:00pm in their territory, they make sure 5,000 Megawatts of their power plants will be ready to produce at that time. Human errors and mechanical failures can happen, and when they do, they are addressed. But, overall, the traditional system is very predictable.

The large scale introduction of intermittent renewable energy is changing this and will be the topic of the next post. Let me know if you have any questions or would love more detail. Check out the current energy use in your region with this amazing map.

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Why Study Energy?

Part I of an energy and research discussion for my parents

Abundant energy has shaped the modern world. It has enabled wonderful innovations such as rapid and affordable travel, vaccines produced on an industrial scale, fertilizer for our crops, an elevated standard of living for billions of people, and the Information Age just to name a few. Fossil fuel makes up the majority of the abundant, easily accessible energy we have consumed to get here. While our standards of living have been elevated, the aggressive burning of fossil fuels has positioned us on a path for severe climate change [1].

Current technologies exist that can significantly reduce our global energy use while delivering what energy is still needed via clean, carbon free sources. And, yes, this can be done while bringing power to the one billion people currently living in energy poverty.

A Brief History of Energy Use

Energy use has skyrocketed over the past two centuries. Over this same period, the composition of fuels and power sources we use changed significantly. Prior to the 1850s, wood was the main fuel source. For the first half of the 1900s, coal dominated. But coal was quickly outpaced by petroleum with the rise of the automobile. The 1970s saw the introduction of natural gas and nuclear power on a large scale.

From EIA “History of energy consumption in the United States, 1775-2009”

At the start of the 1970s, petroleum was set to continue its exponential climb. Instead, the global energy market was struck by the oil crisis of 1973. The U.S. Federal Government enacted sweeping programs to beat down energy use while keeping the economy humming along. This was the introduction of energy efficiency as a staple of the U.S. energy strategy [2].

Two versions of energy intensity: the cyan “Energy Intensity Index” as developed by the U.S. Office for Energy Efficiency and Renewable Energy and the green ratio of energy use to GPD “E/GDP” – Reference [3]

It is difficult to disentangle the effects of a growing population, an expanding economy, and an economy transitioning away from heavy industry in a single chart. The above chart shows us that the “Energy Intensity” or energy used to create economic value has been decreasing in the U.S. for many years. However, in the 1970s, after enacting aggressive efficiency policies, Energy Intensity fell faster than before.

Another way of viewing energy use is considering the amount of energy used per capita. Historically, the the total energy use per person in the U.S. increased every year until the 1970s. Since then, use per person has been steady or slightly declining.

It is worth noting that the U.S. has outsourced a significant portion of its heavy industry as it transitions towards a service based economy. Regardless, energy use per capita and energy intensity are both helpful indicators of the efficacy of coordinated energy efficiency policy at the national level.

A re-invigoration of coordinated energy efficiency policies would help further decrease Energy Intensity and reduce the energy which we need to supply with carbon free sources.

Carbon Free Energy

Nuclear energy and large scale hydroelectric power have been staples of the U.S. electric system for many decades (see first figure). Solar and wind power are relatively new to the U.S. energy portfolio. These four technologies, plus biofuels, make up two different categories of carbon free energy.

  • Predictable power sources who’s power output can be increased or decreased as needed (nuclear, hydro, biofuels)
  • Intermittent sources who’s output is controlled by weather, not customer needs (solar and wind).

The above chart from the EIA shows carbon free energy production by source and is part of their annual energy review. Solar and wind energy have begun a rapid rise since the turn of the millennium.

The rapid increase in solar and wind energy is on a collision course with the way electric utilities traditionally operate their grid. Intermittent solar and wind challenge operators to deliver continuous, reliable power despite their fluctuations. Batteries and other storage technologies are being researched, developed, and continuously improved to help smooth out these difficulties.

Currently, in places with lots of installed solar power, electricity is stored in batteries when it is sunny and discharged back into the grid when large clouds pass over, reducing solar panel output, or during the night. Many new wind power installations also include batteries to help smooth out fluctuations.

To enable a large scale energy transition away from carbon intense sources towards carbon free sources, we need to figure out the right mix of intermittent renewable energy, other clean sources, and storage technologies to create a reliable grid. This is the central focus of my current research working with Ken Calderia at Carnegie Science.

  • [1] IPCC Working Group 3: Fifth Assessment Report “Summary for Policy Makers” https://science2017.globalchange.gov/downloads/CSSR_Ch1_Our_Globally_Changing_Climate.pdf
  • [2] U.S. Office of Energy Efficiency and Renewable Energy, “Energy Intensity Indicators”, Accessed 14 October 2019, https://www.energy.gov/eere/analysis/energy-intensity-indicators