Some intro notes on the grid

I started digging into the grid with help of a very famous academic

I’ve been looking awhile for a way to start digging properly into the energy field, and more specifically the electricity sector, and lo and behold, the gods have answered my prayers.

Source: Twitter

Professor Jenkins runs the Zero Carbon Energy Systems Research and Optimization lab (ZERO) at Princeton, so I can’t think of a better primary source to reference as I dive deeper into this field. I first came across this work through an Ezra Klein interview, which I can’t recommend enough as a comprehensive overview of the decarbonization playbook.

Initially, I had some trouble determining the best way to roll out this blog - should I do a deep dive in an energy source like solar or geothermal, run out an analysis on a public utility like FPL, do a project finance run through - but I think the best analysis requires context to frame everything in, and context is something I should clarify before diving in.

There’s 23 lectures here, but for now, I’ll focus on the first one here. The first lecture is linked here; the PPT as you’ll see has some bullets on there, but for each relevant slide, I’ll add commentary and my own research to fill it in.

My notes on Lecture 1: Intro to course

(Slides 19-31)

Source: Intro to course, slide 21-22

The North America power grid consists of two major and three minor alternating current interconnecting power grids

• Major

  • Eastern Interconnection (Stretches from Central Canada to the Atlantic Ocean)

  • Western Interconnection (Stretches from West Canada to Baja, California)

• Minor

  • Alaska Interconnection

  • Texas Interconnection

  • Quebec Interconnection

Each local power grids are connected to the other for reliability and commercial uses to make up these larger, 5 interconnection; even the infamously independent Texas Interconnection, managed by the Electric Reliability Council of Texas (ERCOT), carries some high-volatile direct current ties to the Easter and Western major interconnections¹. The design is to allow power to flow freely though multiples avenues; this redundancy provides a lower risk of power failures. Because of this, the total scale itself in these machines, in sum, is frightening: to go from the empty husk of Yukon, Canada to Baja, Mexico is a serious feat in infrastructure outlay.

As noted above, these interconnections have >100,000 miles of transmission, but millions of miles in distribution. The difference is that transmissions are the interstate highway of electricity delivery, moving electricity from power plants (individual generators) over long distance; distribution is more focused on distributing energy locally. Transmission are by and large (ha) the bigger structures compared to distribution lines; you might have seen them like this:

Source: PJM

Transmission lines carry higher voltage levels than distribution lines; on average, transmission lines have voltages² beyond 100 kV (100,000 volts), while distribution lines have 13 kV. Sequentially, power from transmission lines are stepped down via transformers to distribution lines, where it is then fed into houses for daily use.

Regarding some of the other bullet points here….

• Distributed Generators

  • Distributed generators are touched upon in the slides above as well; unlike power plants, which are centralized and distribute power via transmission lines across large distance, DG products such as rooftop panels sit on site to the user of the power. They make up a growing portion of energy sources now given the focus on renewables; their advantages include less energy loss (energy sent over long distances through transmission lines leads to loss, while situating it closer to the usage site is more efficient), and improved grid stability, as DG sources can provide backup in case of outages.

• Hertz

  • This is a measure of frequency of Alternating Current (AC) waves that cycle per second. The US and Canada set their grid at 60 HZ, which is standardized throughout to prevent mismatching grids and blackouts; other countries like China set theirs at 50 HZ. Electrical devices are then set at these frequencies to match the respective grids.

(Slides 26-27)

Source: Intro to course, slide 26-27

Sankey Diagrams are used to visualize the flow of data within systems, so there’s no better way to visualize the flow from energy generation to energy usage in this country than the ones attached above.

A couple notes:

• The key figure to realize is that “Electricity Generation” here is the midpoint for several use cases; some energy sources are used to make electricity, which is then used to power homes, businesses, and transportation (think electric cars), while some of them are directly sent to be used for the uses cases as well, such as petroleum to transportation (think ICE engines that most cars use today). However, it’s important to not count electricity as a final use case, as otherwise that would be double counting our energy consumption.

• “Primary Energy Consumption” is the total energy used by a country from all energy sources. Here, it is the 100.3 quads of energy³ used in 2022 in America, generated from the sources (solar, petroleum etc) on the left of the chart

  • Electricity generation in America in 2022 was 38% of primary energy consumption, and as noted, 90% of coal goes into generating electricity

    • Coal-fired power plants burn coal to make steam, which turn turbines, to generate electricity. In 2022, coal accounted for 19.5% of US electricity generation.

• “Final Energy Consumption” represents consumption by all final consumers (in this case, the pink boxes on the right representing residential, commercial etc)

  • The 17% of final energy consumption on slide 27 represents the 13.3 quads flowing from electricity generation to the pink boxes of residential, commercial, industrial and transportation, which total to 76 quads.

• Rejected energy is energy wasted - heat waste, for instance, from ICE engines and fossil fuel plants. 2/3 of primary energy consumption is simply shunted away and lost through the use of inefficient fossil fuels; it’s never needed in the first place When we talk about replacing all of our energy needs, we only need to think about the 33.0 quads found in the bottom right for energy services - the 67.3 quads of rejected energy is therefore not energy that needs to be replaced by renewables, but will instead not be needed at all.

I feel like this video below does a good job highlighting this phenomenon

And so too does this article from Michael Liebrich, founder of New Energy Finance (now with Bloomberg)

A third example. Heating the average US home requires 57 million British thermal units per year. If you are heating with gas or oil, after adjusting for 15% upstream losses and 90% furnace efficiency, that comes to 21 MWh per year. Switch to a heat pump with a year-round coefficient of performance of 4, allow 10% for grid losses, and your energy use is reduced to 4.6MWh. Powering a heat pump with clean electricity can reduce your Primary Energy Demand by 78% and eliminate CO2 emissions (and methane leaks) from space heating – with no reduction in comfort.

See the pattern? The transition is not about replacing all of Primary Energy Demand with something cleaner, it just needs to deliver energy services, a vastly smaller quantum, in a clean way.

Each year Lawrence Livermore National Lab produces a wonderful Sankey Diagram, showing how the U.S.’s Primary Energy flows through its energy system. Fully two thirds ends up as “rejected energy”, the majority of it waste heat from fossil-fueled power stations and transportation – in other words from burning stuff: the exact same process as produces CO2 emissions. Only one third ends up as the “Energy Services” actually used by American consumers and businesses.

You can see this renewable shrinking effect in slide 35 and 37 here:

Source: Intro to course, slide 35-37

As we switch to renewables from the frozen policy scenario (where we hold to status quo) to net zero, increased efficiency from greater weighting of renewable energy sources will lead to a reduction in final energy consumption in 2050 (70 Quads to ~50 Quads).

1. Because the Texas Interconnection does not breach state borders, it is solely under the jurisdiction of ERCOT, which operates the grid. The Federal Energy Regulatory Commission (FERC) does not govern this grid, since it only focuses on interstate commerce.

2. Technically speaking, voltage is the difference of potential energy between two points; in other words, it is the pressure of energy

3. A quad is a unit of energy that is 10^15, or a quadrillion British Thermal Units (BTUs).