Today, at least a fifth of the world’s electricity is produced by renewable energy, motivated by unprecedented drops in production costs and developments in technology such as resilient, high-capacity storage batteries. Meanwhile, innovative approaches to renewable energy infrastructures, such as growing crops beneath solar panels to farm food provide added incentives to switch to renewables. But how does energy from those solar farms arrive at our homes? How is electricity from renewable sources discerned from traditional sources such as fossil fuels or nuclear power? To answer these questions, we need to take a closer look at the ubiquitous power lines, transmission towers, and generators that we call the grid. The power grid can be divided into four sub-categories: generation, transmission, distribution, and utilization of electricity. The first step is generation: electricity is produced historically at large-scale hydrocarbon (coal, petroleum, and natural gas) or nuclear power plants, though in recent years production has been augmented by wind and solar farms. In the transmission phase, electricity is moved, often across vast distances, from generators to distributors. Depending on how the energy market is set up in your country, distribution and retail might go hand-in-hand. But at its core, distribution is about the movement of electricity from transmission networks to consumer networks, while retail deals with billing and interacting with consumers themselves. For the scope of this post, we’ll be focusing mostly on the transmission and distribution stages.

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 Transmission
Power stations tend to be outside of cities for a variety of factors. Thus, electricity generated from these plants usually need to travel vast distances to meet demand. The most common way to deliver this energy is through three-phase and single-phase alternating current (AC) transmission lines (distinctions between the two can be found here.) Because traditional generators are not the most efficient at converting fuel into electricity (coal power plants are about 33% efficient), meticulous care is taken to minimize energy loss during transportation. One way to reduce energy loss is by transmitting electricity at high voltages — anywhere from 115 kV or above. That’s at least 100,000 volts! In comparison, most houses in North America are wired at 120 volts. The justification for this lies in the formula P = VI where P is power, V is voltage, and I is current. Increasing the voltage leads to a proportional decrease in current, and vice versa. This is important because according to Joule’s Law, energy losses are directly proportional to the square of the current. An example of how higher voltage minimizes energy loss is as follows: if the voltage is increased by 2, the current is halved. This means that energy loss is minimized by a factor of 4! Electrical substations make this voltage manipulation possible. Transformers located at platforms close to power generators help step up, or increase voltage for delivery. Substations closer to consumer networks help step down voltage for eventual usage.  Not all substations carry transformers, however. This is because some suppliers transmit their energy through High-Voltage Direct Current, or HVDC. Transformers, built for AC, have no effect on direct current (DC) electricity. Instead, specialized circuit breakers are needed to enable similar functionality. Although this results in added complexity, it is offset by the fact that HVDCs are more efficient across extraordinarily long distances and for underwater electricity transmission — a thousand-mile HVDC line carrying thousands of megawatts might lose 6 to 8 percent of its power, compared to 12 to 25 percent for a similar AC line. Regardless, beyond the specific electrical devices used, the general architecture of AC transmission lines and HVDC technology remain relatively the same. At the final leg of the supply chain, high-voltage electricity is stepped down and passed into lower-voltage power lines that deliver the final product to end-users.

Distribution
Because electricity generated from coal, nuclear, oil, natural gas, wind, and solar all go through the same grid lines, there is ultimately no distinction regarding where a certain amount of electricity is produced. Fortunately, measures to track clean energy do exist by other means. In the United States, the EPA created Renewable Energy Certificates (REC). For the EU, Guarantees of Origins provide information to electricity customers on the source of their energy. The UK equivalent is the Renewable Energy Guarantees of Origin. These certificates are generated per specified unit of electricity, and are tradable through various markets. This makes it possible for homeowners and businesses to support clean energy. For example, in 2017, Google was able to buy on an annual basis the same amount of megawatt-hours (MWh) of renewable energy as the amount of MWh of electricity they had consumed around the world. Direct access to renewable sources, meanwhile, can be achieved through proximity to a clean energy generator (such as installing solar panels in your home) Since natural gas plants are still the dominant source of energy for some countries, power grids are not completely clean yet — but clean energy, particularly energy from wind, is getting cheaper than ever and even undercutting natural gas power plants, while problems that used to plague renewable energy generators are now being addressed by technological advancements. In addition, suppliers are being pressured by corporations and individuals alike to consider these alternate options — accelerating infrastructural and cultural changes needed for a modernized, responsive, and environmentally responsible grid.
This is the first of a series of blog posts under the theme of “Untangling the Power Grid”.