Warming Thoughts© #7—Transporting Energy—Part B, Electricity basics, power plants, Westinghouse/Tesla vs Edison and why we need to really worry about electrical transmission.
By James F. Lavin, CEO Electron Storage, Inc.
Introduction:
The electrical grid is man’s largest and most complex machine. We should all gasp with astonishment every time we turn on a light, an electric motor turns, and our air conditioner turns on. We are at the start of a massive experiment, changing generation, transmission, distribution and use, while massively growing the energy demands on this machine. If we fail, society collapses, either because the grid collapses, or because global warming accelerates.
With the exception of certain geographically favored locations, yes you California, power production is going to become more centralized, not less, and this essay will deal with the complexities of long distance transport of electrical energy via electrical transmission lines.
To move significant amounts of electrical energy long distances, you want to use High Voltage Direct Current (HVDC) transmission lines. Currently we move energy primarily with High Voltage Alternating Current (HVAC) transmission lines, and generally for shorter distances. With AC long distance transport we actually “wheel” the power, A generates power and delivers it to B which uses the power to feed its grid so it can send its freed up power on to C and so forth. We currently don’t directly move substantial electrical power over long distances because fossil fuel powered generation plants exist at A, B and C and because we use fossil fuels for heat and transportation.
Transmission lines are expensive requiring large towers, expensive cables, and long and wide contiguous rights of way, and usually move 1-2 gigawatts, the output of 1-2 large power plants. Underground lines are possible, but lower capacity, 4-8x as expensive and harder to maintain. The New England Clean Energy Connect project had a $950MM budget, a capacity of 1.2 GW and was to run for 145 miles. It is usually cheaper to move fossil fuels over the lifetime of a power plant and burn it at one of the 6,000+ electrical generation plants in the US, than to convey it by power line. As we close these power plants, we will have to move a lot more energy a lot further. As will be discussed below HVDC transmission, while technically better, poses significant societal and routing challenges, but first back to basics.
When you are moving energy, the energy (watts) is the product of how many electrons are moving (current, measured in amperes with the symbol I) and how much pressure or push each electron has (voltage V). You can increase voltage and reduce current or increase current and reduce voltage to get the same wattage. However, to move more electrons (amps) you need a thicker conductor, or more wires in parallel, because the more room the electrons have to move around in, the less they collide with the atoms of the conductor generating heat, ie, resistance, and voltage drops with resistance, so the longer the wire and the more the total resistance the more the voltage and power drop.
Using larger conductors to reduce resistance is expensive and you want to move as few electrons as possible since resistance goes up as a square power of the current; double the current, quadruple the losses. Therefore, you try to move the energy at as high a voltage as possible, as voltage goes up the needed current and therefore losses and conductor size goes down. But we can’t plug our lamps into a 768 Kilovolt wall outlet.
When you have a rotating mass from a turbine engine, you can use it to generate Alternating Current (AC) or Direct Current (DC). Alternating current as its name implies has voltage and therefore power flows cycle up and down, in the US 60 times/second and in most of the rest of the world, 50x/second. Given a choice we would like to run most things on DC because the constant voltage switching of AC causes vibration and the interaction of the 60-cycle current with our own heart electricity makes it much more dangerous. There are a number of other efficiencies, and we waste a lot of energy converting AC to DC as our electronics and batteries and LED’s run on DC. (I spent 3 painful years and almost $10MM dollars trying to create an ultraefficient, single chip converter from AC to DC, but that is another story). Edison championed DC. But Westinghouse won out as we all know, and our electrical systems conduct AC current. Why, and why does this matter to a decarbonized future?
Edison championed DC power. It worked better with arc lamps and it worked better with his incandescent lights which would last longer without the subtle vibrations of AC. However, converting high voltage DC to low voltage DC that could be used in homes wasn’t feasible. All the power had to be sent at low voltages, and the maximum practical wire sizes reduced the usable distance from the power plant to around one mile.
Tesla recognized this problem, and Westinghouse made it happen by championing AC power back in the 1880’s. Transformers are almost magical. By simply putting two coils of wire surrounding iron cores next to each other with different numbers of turns of the wire in each coil, voltage is magically transformed into higher and lower voltages with corresponding changes in the amps flowing through the wires. 13,200 volts at a low amperage converts to 480 volts with 27 times amperage with very little loss. The same can be done the other way, converting high amperages to high voltages. But it only works with AC.
By using transformers, you can send out power from a generating plant at a high voltage over smaller wires, and then transform it as needed to practical voltages at homes and factories. Today most overhead distribution wires along suburban streets are carrying electricity at 4,800 or 2,400 volts and pole mounted can transformers change it to the 240 or 208 entering our homes. Similarly, substations receive their voltages at 13,200 or 28,000 and transform it down to the distribution voltages cited above.
High power DC voltage conversion across wide voltage ranges and into AC has only recently become feasible with the development of IGBT’s, a form of high-power rapidly switching transistor that facilitates power conversion. Which brings us to extra high and ultra-high voltage transmission lines (345,000 volts and above, and 1.1 million volts and above respectively). For the reasons cited above, the higher the voltage, the less cable you need.
On the other hand, the higher the voltage the more it tends to arc across long distances to fry people, start fires, and other nasty things and therefore the wider the clear area around the transmission lines. We run 4,800 volts down our suburban streets near trees, but we need 200 ft clear rights of way to run an extra or ultra-high voltage transmission line. If you step back and think that these wires are carrying the energy from the burning coal or gas driving an entire gas or coal burning power plant, or dozens of 300-meter-high windmills, it makes sense not to get too close.
How do you convince communities to accept 200 ft clearings and high, ugly transmission towers? The answer is you bribe them. Want to get permission to run an UHVAC line through someone’s’ town? You offer to install a transformer and provide them with low-cost power. That bribe was the key to the electrification of the west and the development of long-distance transmission lines.
UHVDC better for long distance transport, but it has problems. Transforming million-volt DC power to something usable is extremely expensive, like $150 MM expensive at each end of a power line. You simply can’t afford to offer that local town, or state part of your power. So why should they cooperate and let you deface their town? Maine voters stopped the New England Clean Energy Connect Project this fall. It was a HVDC line and provided almost no benefit to Maine.
So why HVDC and UHVDC instead of the more flexible HVAC? And why, despite this should you consider investing, if possible, with companies along the HVDC supply chain? One, if you are running power lines along distances under the ocean you need to use DC. Offshore windfarms, unless close to the shore, have massive and expensive electrical concentration platforms that the individual turbines connect to, and where the electricity generated (which is usually AC) is converted to high voltage DC and sent to shore. It is then converted to AC to integrate with existing electrical grids. You can’t use AC underwater because the electromagnetic waves created by alternating current find a lot to interact with in salt water and this interaction drains power from the electrical lines. The planned 3 GW, 2,400-mile underwater power line from Australian solar farms all the way to Singapore is HVDC and there will need to be hundreds more of such lines.
Above ground, HVDC transmission creates fewer problematic interactions with the surrounding environment, you don’t have something called corona discharge, you have less interaction with moisture in the air and insulators, and need a less extensive right of way. You need less material since the constant flow of electrons (it is actually the electrical field that moves, individual electrons hardly move at all) allows you to utilize all of the wire’s capacity, whereas with AC since its power fluctuates, 71% of the wire’s capacity is the maximum that can be used. You need two wires for DC and not the 3 wires used for moving the 3 phases of high-power AC current. All these advantages are not enough to overcome the costs of creating the high voltage DC on one end and converting it at the other end, except over long distances. At long distances AC has another serious problem.
AC has a phase problem. Like all waves, if another wave interacts at an opposite phase angle, the wave is disrupted. AC electrical grids need all the power feeds to come in at the same wave, ie, the same positive or negative voltage at the same time. Synchronizing this is difficult. It is possible with inductors and capacitors to change the timing and recreate the synchronous wave, but it is not simple nor cheap. The problem come in with distance. Electrical transmission is fast, 50% or more of the speed of light. Assume it’s the speed of light, 300,000 km/second. Electricity would travel 2,000 KM’s in 150/th of a second, but the sine wave of electricity is changing 60x per second, and the electricity from the transmission line will be around a 3rd out of phase. Synching a distant electricity source delivered via an AC line to another point in the grid is difficult and expensive.
With DC to AC conversion, which is part of every solar power array attached to the grid, there is a device called an inverter that listens to the power line AC and creates an artificial sine wave when feeding power into the AC circuits so that the sine wave is synchronized. HVDC lines do the same thing using the very expensive endpoint equipment to reduce the voltage and create the wave. Since they are synching to the local grid, there is no phase problem.
We need to transfer large amounts of electrical power long distance via high voltage DC lines. We need transfer large amounts of energy because windy areas (on shore or offshore) are concentrated in certain locations around the globe. The tropics, for example, don’t have much wind. If you want them to benefit from wind resources, you need to connect to them over extremely long distances.
If you feel that distributed solar is the answer, try that in northern Minnesota in the winter when the panels are covered in snow. Solar isn’t distributed and we will need even longer transmission lines. The solar distribution map for the US and Europe below illustrates the magnitude of the mismatch. You simply can’t power northern Europe or northern North America without long distance transmission, and no one want those lines, particularly DC lines running overhead. Wind helps, but there are greater limits on wind resources than solar—and as Europe is currently finding sometimes the winds don’t blow.
China has UHVDC lines from distant solar and wind farms to its industrial heartlands. The US has almost none and the reason is rational NIMBYism. At least in the US we have no legal framework other than trampling property rights to get around this problem. We can reduce the conflicts by cutting through national parks and forests and along scenic rivers and it is one of the many ugly tradeoffs we aren’t discussing frankly. Without a brutal blow to private property rights, we won’t be able to realize the dreams of renewable energy
We haven’t had a truly serious problem until now because there are a great number of power plants. As stated above 6000+ in the US alone, and the fossil fuels to power them are widely distributed or easily shipped. Where there were large concentrations of power plants, it was usually in sparsely settled areas out west where running power lines was less of a problem. We have to triple our electrical grid capacity overall---and increase our transmission capacity by a great deal more. That will be unpopular. And no technical solution is on the horizon, much as I wish room temperature superconductors were a reality, quantum mechanics keeps throwing a wrench into the power line. I consider moving energy the hardest problem and we will discuss non-electric clean energy transportation in an upcoming essay.