The Electrical Grid Needs Fattening Up

Heimlich was the caterpillar from one of my kids’

favorite movies, A Bug’s Life. He ate and ate because

he needed to store energy. When the time came to

metamorphose into a butterfly, he would need to

convert that stored energy to forms his body could

use. We need the same thing for our national

energy grid.

When presented with food, you can convert it all to energy (stuff your face), or can save some for later (leftovers). We can make use of much food over time and not lose any of its energy, most of the food won't spoil before tomorrow or the next day. Likewise, your body can store energy it takes in, some as glycogen, and some as fat. We can go back later to burn the fat when we need extra energy – although we usually don’t.

This isn’t the case with the national energy grid. Whatever energy is generated, it goes directly into the copper wires of the transmission network. This is fine most of the time, because you can run more or fewer generators, and they can be made to work at higher or lower efficiency to meet immediate needs.

The real problem comes when we try to be green. Some fuel for generators can be used when needed, but other sources of energy have to be used when they are available. For example, it doesn’t matter whether you burn coal today or ten years from now, you still get the energy from it.

But think about wind power. If you don’t generate electricity from the wind as it blows, then you can’t go back later and use it – it’s gone with the wind. Same with solar energy, if you don’t harvest today’s sunshine, you can’t come back tomorrow and find it. Sure, you can use tomorrow’s sunshine, as long as it’s sunny – but not everyday is sunny.

As more and more electricity is generated from green sources, we need to harvest as much of it as we can when we can. This means that we need to be able to store energy in some form. This large-scale energy storage is the focus of much current research and even more construction.

If we can’t store electricity as electricity, it means we have to convert (transduce) it to some form of potential energy. Research and engineering is showing that we can do this in several ways. Let’s look at a few:

Compressed air storage – One source of potential energy is air under pressure. Of course, it would have to be a whole bunch of air, like an abandoned mine volume of air - or one speech from a politician. Several of these large-scale energy storage mechanisms have been set up in Europe, using mines or caverns.

Here is a schematic for compressed air storage of

energy. The compressor motor uses energy from the

grid to pump air into a huge space – maybe somewhere

that has given up its natural gas. Then when it escapes,

it runs turbines that return electricity to the grid. I bet

fracking opponents might have a problem with this as

well – geologically speaking.

Some caverns are better than others. Salt caverns (McIntosh, Alabama) are good because the crystal is flexible without being porous; no reaction occurs between the walls and the oxygen. When there's less demand on the grid, air compressors use the extra electricity to pump air into a sealed mine. Newer proposals seek to use pipelines to store the compressed air.

Under pressure, the air can remain as a source potential energy for an undetermined time. When the grid needs more electricity, the pressurized air is allowed to escape, passing across turbine blades and turning a generator. Basically, it’s electricity to wind to electricity.

Compressed air storage is about 45% efficient. If you use the heat created by compressing the air (pushing the molecules together creates friction and heat) to heat the air when it expands (usually it cools greatly, like when you spray off your computer keyboard with that can of air and the long red straw), you can increase the efficiency to about 70%. That ain’t bad.

Hydrogen – Hydrogen gas is a very dense fuel source, meaning that you get a lot of energy for the amount of fuel you use. However, you first have to produce the hydrogen. One way is to split water, just like plants do during photosynthesis. While plants use the power of the sun to split water, we can use electricity – this is called power to gas generation. Gas generated is usually hydrogen from water, but methane can also be produced from carbon dioxide plus water.

The hydrogen gas produced is then stored, similar to the compressed air storage described above. For more efficiency in storage, the hydrogen can be cooled and pressurized to be stored as a liquid. When electricity needs to be generated, the gas can be burned to heat water for conventional turbine generators, or it could be put through large fuel cells, as we discussed two weeks ago.

Caverns and mines can be utilized for storage, but Germany uses mostly hydrogen pipelines for storage, and has done so for many years. In fact, German hydrogen storage is some 5000x greater then their pumped water storage capability. I’d worry about explosions. Remember the Hindenburg - that was hydrogen gas.

This is how pumped water storage works. They

picture shows the direction for daytime and nighttime,

but it could be anytime energy is excess or needed. The

reason for day and night labels is that you can make it

in the day when more is needed and store it at night,

when energy usage is lower. In addition, using electricity

at night is cheaper (less demand = less cost).

Pumped Water - A new pumped water storage facility is near the approval stage in Montana. The Gordon Butte project will build a pair of 1.3 billion gallon (6.4 billion liter) reservoirs, one atop the butte and one 1025 ft (312 m) below, at the bottom of the butte. The U.S. and China have many of these facilities, the largest of which is located on the Virginia, West Virginia border (Bath County, 3 GW).

When there is excess energy in the grid, it will automatically be used to power pumps that will move water from the lower reservoir to the upper. This mass of water, positioned in the top reservoir is a powerful source of potential energy.

During peak usage hours, the water is allowed to fall to the lower reservoir, through a turbine that then powers a generator. At this point, the system acts exactly like a typical hydroelectric plant. These mechanisms are very efficient, returning 75-85% of the energy invested in them. The problems: you need sufficient space at two nearby locations, but at very different elevations, and two, reservoirs are very expensive to dig. I wonder if drought would be a problem.

The real advantage to pumped water storage over other large-scale storage methods is the timing. Pumping or generating can begin within just 5-7 minutes of declared need, while compressed air storage facilities take more than 30 minutes to ramp up.

Electric vehicles will need be chargeable wherever they

are if we are to make them a source of energy storage

for the grid. Here is the new thing – wireless rechargers.

The top image shows them implanted in parking spots,

while the lower images has them embedded in the

parking blocks. Yes those concrete obstructions in

parking lots are called parking stops or parking

blocks – bet you didn’t know that.

Electric Cars – One intriguing idea is to use privately and publicly owned electric vehicles as a storage dump for energy. The batteries of such cars can be connected to the grid in a two-way fashion. You plug them in at night to recharge the battery, but a V2H (vehicle to home) system also allows you to draw energy from the car battery in case your house power lines are down.

A study from 2011 used mathematics (eww!) to estimate the viability of electric vehicles as a large scale energy storage mechanism. In general, two things will have to happen. One, 10 million or more people (in U.S.) need to own these cars. And two, they have to be able to plug in their cars at work. Only with work and home charging will enough cars be plugged in at any one time so that a grid need will be met, either by pumping more energy into the car batteries or taking a bit of energy from each car.

There are several other methods – large, rechargeable batteries are starting to be used. Painesville, OH has a 1 MW vanadium battery in use, as well as large flywheels, or thermal storage. You can investigate these yourself and figure out how best to make green energy pay off in the long run..

Contributed by Mark E. Lasbury, MS, MSEd, PhD

As Many Exceptions As Rules

F. K. Tuffner, Member, IEEE, and M. Kintner-Meyer, Member, IEEE (2011). Using Electric Vehicles to Mitigate Imbalance Requirements Associated with an Increased Penetration of Wind Generation Power and Energy Society General Meeting, 2011 IEEE , 1-8

What It Takes To Kill A Watt

From space, the view at night gives a good indication of how

much electricity we humans use. With the exceptions of

North Korea and Antarctica, you can’t find many places on

Earth that don’t glow at night. But even at that, it would

take 20 years for us to produce the same amount of energy that

shines on the Earth from the Sun in one day.

Christmas has just passed and everyone has new phones, PlaySatations, drones and other gadgets. Unless your phone is nuclear or solar, it also came with a recharging cord because these tool/toys work on electricity, the very lifeblood of modern society. To illustrate - the total amount of electricity generated in the U.S. in 2012 was 4,047,765,000,000 kilowatts.

For something so important to commerce, entertainment,medicine – just about anything you can name – the average person knows shockingly little about how it comes to them. Let’s take some time to acquaint ourselves with something called the National Grid of electrical generation and distribution. Let’s consider power generation this week.

There are a couple of ways to directly generate electricity from a potential energy source. Solar photovoltaic cells turn solar radiation directly into electricity.  These technologies have been around for several decades. However, even though sunlight has many wavelengths of light, most photovoltaic cells only harvest a fraction of them. Historically, this has made solar energy inefficient to use.

New cells use several different semiconducting materials, each absorbing a different wavelength of light. According to 2014 research, these new cells achieve an efficiency of 44%, meaning that 44% of the energy that strikes the surface is converted to electricity. This is pretty good compared to single junction cells that have about a 25% efficiency.

Fuel cells generate electricity by moving hydrogen ions across a catalyst. The metal catalyst strips electrons from the hydrogen and these electrons form an electrical current. The resulting positive hydrogen ions combine with oxygen on another catalyst to produce water as the only by product. The problem is that the materials (exchange membranes or electrolytes) to move the positive hydrogens to the oxygen are every expensive.

Fuel cells produce water as their only byproduct. When the

catalyst strips hydrogen of its electron, this flows as

current, and is then replaced by an electron from oxygen.

Most cells differ only by the electrolyte used. Upps now has

a fuel cell on the market to power your smart phone for a

week. I wonder how you don’t end up with a soggy phone.

Batteries use electrochemical reactions to liberate electrons (electricity). Primary batteries only produce electricity, while secondary batteries can reverse their chemical reactions and store electrons if an electrical charge is applied – these are rechargeable batteries. In most cases, batteries are used on small scales, although we will see in a couple of weeks how they can be used on a very large scale.

These technologies excepted, most electricity is produced from the turning of generator turbines. The turbines spin a coil of wire in a magnetic field. This produces electricity – thank you very much Michael Faraday. The key is how we generate the force that turns the turbine blades that then spin the wire coil. In most cases, we burn some sort of fuel to turn the blades, but in a few cases turbine blades can be turned directly.

The wind turbine is an old technology use to harness the power of air moving from areas of high atmospheric pressure to areas of low pressure (wind). The Europeans used wind power to grind grain into flour (hence the name wind mill) but they have been around since the time of the Greeks. American and Australian farmers use them to pump water, but today we mostly use wind turbines to generate electricity.

Hydroelectric generators use the power of gravity and water under pressure to turn turbine blades. By constructing a dam between an area of high elevation and one of lower elevation, water is put under pressure. Allowing a controlled volume to pass through a turbine will spin it and the associated generator will produce electricity.

The Three Gorges Dam and Hydroelectric Plant in China

(top) was built to be world’s largest hydroelectric generator

system. However, the Itaipu Dam on the Brazil/Paraguay

border (bottom, all generators first online in 1991)

generated significantly more electricity in 2013 and 2014.

Ocean waves can also be used to generate electricity. Whether on the shoreline, near shore or offshore, wave power use the movement of water to turn turbines. There are several different mechanisms to capture the wave motion and transfer it to a turbine, but designing an efficient mechanism has proven to be harder than originally thought. It may be another 30 years before wave power matches the wind power we generate today.

These direct "energy to turbine" mechanisms are helpful, and are becoming larger players in the electricity game (along with solar power and fuel cells). But the burning of fossil fuels - natural gas/petroleum/coal - is still the main way we turn turbine blades turn.

Fossil fuels are non-renewable natural resources and their importance in energy can’t be underestimated, both from the standpoints of how helpful and efficient they are, but also in how dirty they are and how they are running out. However, they aren’t the most important natural resource for the generation of electricity. Can you guess what is?

Believe it or not, water is the resource used in greatest amount so that you can charge your iPhone.  Name an energy generation technique that doesn’t use water – you can’t. Water cools power plants that burn fossils fuels; it cools nuclear reactors too. It is used to water the fields that grow plants for biodiesel. Water is heated for almost all generator turbines. Water is even used to extract petroleum from the ground – ever heard of fracking? A research report in 2008 stated that the U.S. alone uses 500 billion liters (132 billion gallons) of fresh water each day just to produce electricity. 

Frack - expletive, energy process, or jacket? All three, actually.

In dressage, the frack is the dress coat worn in some

competitions. In energy circles, it refers to hydraulic fracturing,

where water, chemicals and sand are injected into shale in order

to fracture it and release trapped crude oil or natural gas. Some

people are against both and use the expletive to show

their displeasure.

Water in liquid form maintains a certain volume, but water in vapor form – steam – takes up a lot more room. The volume expansion of water when boiled creates force; it can make a whistle blow on your coffee pot or it can be used to turn the blades on a generator turbine. So the key to making most electricity is turning water into steam. In truth, it's the kinetic energy of motion from escaping steam that is used to turn a magnet across a coil of copper wire.

How do we produce steam to turn the blades of a generator turbine? Nuclear fission is one way. Decay of naturally radioactive materials in a water bath generates a lot of steam. Other ways include solar thermal energy, where the energy of the sun is directed by mirrors at a large mass of water that then boils, or by burning biomass (wood, sawdust, biodiesel, trash, methane).

It's beyond this discussion to explain how a spinning magnet across a coil produces moving electrons, so you can read about it here. The point is that whatever means is used to spin the turbine, its shaft is attached to the magnet that spins.

In most power stations, one magnet passes three coils on each revolution, so three alternating current lines are produced. This is the three phase generation that will become important when we next week talk about the electrical lines coming to your house.

contributed by Mark E. Lasbury, MS, MSEd, PhD

As Many Exceptions As Rules

Sheng, X., Bower, C., Bonafede, S., Wilson, J., Fisher, B., Meitl, M., Yuen, H., Wang, S., Shen, L., Banks, A., Corcoran, C., Nuzzo, R., Burroughs, S., & Rogers, J. (2014). Printing-based assembly of quadruple-junction four-terminal microscale solar cells and their use in high-efficiency modules Nature Materials, 13 (6), 593-598 DOI: 10.1038/nmat3946