Warming Thoughts© 8: Transporting Energy, Part 3
The distribution grid, an analogy from the water system and an illustration of changes and complexity coming from a local street.
By: James F. Lavin, CEO Electron Storage, Inc.
In the previous essay I discussed the need for, and problems associated with, building long distance transmission lines. In this essay I want to make an analogy to water distribution systems to start to illustrate the complexities we are introducing into the grid distribution of power and discussing some of the new complexities in a local street. I am planning for Warming Thoughts 9 to cover substations and the need for and uses for advanced sensing and switching throughout the grid. Then we can discuss moving energy in other forms.
Grid Basics and Increasing Complexity:
The simplest place to start is to think of the grid and (electricity) in the same way you do a water system. In this type of system, there is a water source, say a reservoir with a water pump (generator), a series of interconnected pipes, with big ones (transmission) branching down into small ones (distribution), with perhaps a major connection point (substation) with pipes from two sources, and lots of smaller branch lines coming out of it. Water only flows when you open a faucet (the load): maybe a big one to fill a pool, maybe a small one at your bathroom sink.
If there’s no open faucet (no load), the water pump (generator) has to stop because water is incompressible. Increase the flow and the water pumps work harder. Lots of flow (load) may mean the pump (generator) can’t keep up, causing water pressure to drop (voltage reduces), and voids to form, causing the flow (frequency and amperage) to collapse.
This is a very hierarchical one-way flow, and the amount of work at the water pump is determined by the flow of water out of the faucets. Because water is incompressible, the source flow and the end user flow must balance. But the water system has an advantage, there are water tanks and reservoirs for storing water, particularly at high places so gravity can assist or replace the pump, they can act as buffers and pressure limiters so the generation and use don’t have to match in real time. And backflow doesn’t (usually) kill your workers.
When there was a water pipe break, you could find the nearest valve upstream and close it so that no water would be flowing downstream, facilitating repair. There may be electronically controlled valves along the way, but in general there are not a lot of control points or active sensing along the water distribution system – shockingly there isn’t a lot more along the electrical distribution system. We have been successfully running water systems for hundreds of years (thousands if you include the Romans or examine the water tunnels that fed the ancient temple in Jerusalem).
We have been successfully running electrical systems since the 1880’s with the same essential characteristics. Load and generation must balance, the load determines how much is generated, the generation occurs at a centralized plant(s), and the power flows in one direction, with reducing power (pipe size) at each stage as it flows from generation to end user load.
There are differences of course; the voltage and cycle phases from each electrical generator must synchronize. But once synced, generators tend to stay in sync. The generators were rotating masses with a lot of inertia and were powered by water, steam, or burning natural gas. The inertia kept the voltage up and the frequency in sync when loads suddenly changed. We have had experience in keeping rotating masses rotating at the same speed since the invention of the steam engine in the 1700’s. We still had to fiddle a bit, and there are capacitors that store and release small amounts of power quickly, impedance coils to help with surges and managing frequency, filters to reduce harmonics, and load centers, essentially giant toasters to add load, all to maintain stability, but essentially one-way flows made life predictable.
Let’s look at a couple more characteristics of the grid as it was before we started to transition it to distributed energy resources and modern loads. One, load increased 1-2%/year and utilities were able to plan for this and keep adequate reserves. Short term load changes and, thereby, generation were also reasonably predictable, allowing generators to be spun up in preparation for anticipated load. Loads were understood well enough that additional generation was ready for half-time at televised English football matches when everyone put on their tea kettles. The water systems were not so well prepared for the simultaneous flushing of toilets, but that is a messy story for another day.
Two, generators had copious energy storage on hand in the form of coal (primarily), oil, and water behind a dam. Combined with the reserve capacity, generator plants could deliver the necessary power without expensive electrical storage devices except for pumped hydro and dams.
With that we can close the background…but wait there’s more! Water and electricity companies are generally regulated utilities. They don’t operate like other business because they must operate within constraints set by utility regulators, usually appointed by politicians and whom may have various degrees of competence and technical expertise. These regulators decide directly and indirectly on power rates, generator buildout, capacity, what investments are made, i.e., “smart meters” or more electric lines, sensors, or no sensors, as they have the ability to dictate what assets get a guaranteed return and which don’t.
Since electricity grids interconnect, you also have a variety of federal regulatory bodies like FERC, NERC, and of course the EPA if you want to build anything. Plus, you have the various independent system operators, PJM, ERCOT, CAISO, NEISO, etc. that coordinate power flows between the different utilities in region. It is an environment that favors lawyers as executives, not technical experts.
Some Challenges starting at the Local Level:
Let’s start at an endpoint: a cul-de-sac in an affluent suburb in sunny California. In the past, every house had its own load, greater or lesser depending on the time of day, who was home, and the temperature, but always a load. Now many of the houses have solar panels on the roof, some have electric cars with level 2 charging stations, most have electric heating and, of course, air-conditioning. A couple of the houses may have battery storage systems and a couple others may have backup diesel or natural gas-powered generators. All depend on the grid for power at times, usually at night, and in the morning and evening when load is high and solar power is very low, and of course on cloudy winter days. Hopefully a third family doesn’t move in with an electric car, otherwise the entire street grid may collapse due to an electric line or transformer overload. Our simple neighborhood just got complicated.
For electrical equipment of all kinds power quality, a nice sine wave with a predictable smooth 60 cycles per second and corresponding voltage change, is critical for reliable, efficient, low loss, vibrationless operation. Over the past decade, we have shifted to direct current (DC) digital power supplies because our electronics run on DC. We use brushless DC motors because they run more efficiently and precisely on DC, and we convert AC to DC to charge batteries in our laptops and phones. Our incandescent lights were simple resisters, but our LED bulbs run primarily on DC, converting AC to DC at multiple points or with AC to DC power supplies controlling a bank of LED lights. We are now converting AC to DC at a hundred points.
Converting from alternating current to direct current grabs power from the sine wave. This distorts the power curve and creates harmonics (ripples superimposed on the sine wave). They radiate not just inside each of these houses, but also back down the power lines to the street and other houses, and ultimately back into the grid. I mentioned in an earlier post that a company I founded failed in its attempt to create a single chip high power AC to DC converter. What we failed at was not the ultraefficient conversion, but at controlling the harmonics generated in the process.
On the roof of many of our cul-de-sac’s houses are solar panels. As the sun comes up, they start to generate electricity, increasing as the sun rises, decreasing then, increasing as a cloud passes over, going to zero if covered with snow and ice, and decreasing to zero at night. The electricity a solar panel generates is DC, but it must feed into the AC current in the house synchronized to the power lines outside. An inverter which converts the DC from the panel to AC, listens to the grid sine waves and starts chopping and shaping the DC current until it resembles a matching sine wave and feeds it into the house. Even though it resembles the wave, it still adds its own degree of distortion to the sine wave. And the sine wave it is trying to match is itself distorted by all the digital power supplies chopping away at it.
The specifications and testing of inverters for rooftop solar have improved dramatically in the past few years, but some of our panels were put in place by trendy Californians a while ago. How good are the inverters? How many of the new ones will precisely meet specifications in five years? The current reality is that in many of these streets, power quality is already awful. Of course, on a sunny day with no one home the solar panels are generating a lot of excess power and the helpful politicians have made it mandatory for the utilities to accept this power. The power quality problems radiate outwards, quite possibly damaging transformers.
The power being generated also radiates outward. The system design that keeps lines and transformers from overloading wasn’t designed for two-way power flows. There is no real protection for the electric system and effectively no sensing of local overloads. The current grid truly doesn’t have the capability to handle thousands, hundreds of thousands, millions and tens of millions of separate generation systems.
Wait you say, doesn’t the power company have any control over the power being fed into the lines from all these household power sources. No, it doesn’t. Don’t the “smart meters” provide lots of dynamic information to assist in control? No, they don’t. The power company usually knows your power is out when you call to report the outage, power quality monitoring is non-existent, and there are very few control and monitoring points at the local level. If and when we do create both detailed sensing and controls we introduce another problem, a massive increase in the vulnerability of the electric system to collapse due to accidental or deliberate software problems.
Utility systems above all are supposed to ensure a reliable supply or reliable power. Their revenues are being removed by solar panels during the day as they are not selling power and are often forced to accept it at rates higher than their costs of generation. They can’t operate power plants, especially non-polluting nuclear ones, economically without steady demand, yet they still have to support peak demand. They were relying on gas peaker plants which can come online very quickly, but mandates and pipeline restrictions are taking them away. Battery storage has a long way to go and can’t currently provide power for more than a handful of hours. We are rapidly facing a power reliability and power quality crisis even in our local neighborhoods, even while steadily increasing our dependence on electric power for heating, cooling, hot water, and transportation.
Safety:
The power goes out in our neighborhood due to a tree touching a feeder line and it needs repair. In the old days, it was a simple matter of opening a switch further upstream and safely depowering the line—similar to closing the valve upstream in our water system example. Now, because power can feed into the line from multiple sources, a lineman must carefully find every possible disconnect into the feeder and open them all to ensure his or her safety if the repair can’t be done hot. They may get shocked by power coming from a solar panel, a battery system not fully islanded (isolated from the power grid connection), or a generator system.
When the distribution system was built, it didn’t assume multiple sources of power, so the number of openable switches is limited and there may not be one between our cul-de-sac and the line needing repair. But wait, aren’t there built-in interrupts to ensure power isn’t being fed into the lines from a battery system or a solar panel array when there isn’t a power sine wave to sync to? Want to bet your life on a dozen different installations over a dozen years? A lineman doesn’t want to bet his life either.
Nor do firemen or firewomen; they don’t like being shocked and tumbling off roofs. My former head of sales at Fireaway is currently working for an Australian company, PV-Stop, which has the only solution for another safety problem. If the sun shines, a solar panel generates electricity. If it’s feeding a battery system without a proper automatic disconnect, it is feeding power into the battery array and reenergizing any fire that may have started there. Solar panels on rooftops can be damaged by hail and other storms and create sparks.
A standard part of firefighting is chopping a hole in a house roof to vent the fire. Firemen are increasingly refusing to get up on these rooftops or fight battery fires connected to a solar array and are instead fighting fires “defensively.” That is another word for letting it burn down your house and just trying to prevent spread to your neighbors’ home. Insurance companies are noticing the problem and may be raising insurance rates as a result. PV-Stop is a spray on film that blocks light transmission and deactivates the panel. It can also be peeled off without damage afterwards. Another problem and opportunity with the changes to the grid on a local level.
If you are interested in information about PV Stop, send me a note.
This essay just touches on the complexity of the new electric grid, one that is being asked to dance quickly and gracefully---but never fall.