I went into the GridWeek conference last week assuming that nuclear power advocates needn’t worry about all of these SmartGrid initiatives and that there was a great deal of hype about this that was overblown and not viable economically. I left with a much better understanding of some of the fundamentals of the issues around electricity across the country. AND a feeling that too much time and effort was being centered on the consumer end of the grid.
Yesterday, I wrote an overview of the issues facing the electrical power industry in the 21st century. in the area of the grid. Today, I am going to pick on one aspect of the grid – power generation. While at first blush generation would not seem to be a part of the grid, it is the point at which the process starts. If the power being generated is unreliable or too slow to respond, nothing later in the grid can fix that.
As discussed in my prior post, generation in the US works on a demand basis. That means that electricity is only generated when it is demanded. There is no direct storage of electricity, except in capacitor banks that give the grid operators time to spin up or down other generation options. That brings us to the first area that is encompassed in SmartGrid.
There are other storage options, of course. The rest convert electricity into other energy forms more amenable to storage, like mechanical or chemical potential then convert it back. The chart below, from Secretary of Energy Steven Chu identifies many storage systems by relative power and duration. Most of these options have limited use today or are still in early stages of development and deployment.
These storage options become even more critical when the renewable portfolio standards (RPS) recently passed by congress come into play. While solar and wind energy sources have successfully campaigned for their status as ecologically good electricity sources, the fundamentals of their technology add even more volatility to the electricity infrastructure today.
For the moment, we’ll ignore the idea that end users might have solar panels or wind mills pumping power back into the grid and concentrate solely on industrial scale renewable installations, those generating at least 10 MW of electricity from one installation. Again, in Dr. Chu’s opening remarks at grid week he presented two charts that brought home the point about both solar and wind.
In the first chart, power generation from a solar array in Colorado is shown for a single day. I expected to see the first part of the curve. As the sun rose the power output of the panel increased to a fairly steady state peak with a few hours and was operating smoothly and predictably at that level. Easy to manage and providing power during the higher usage periods of the day, all good things. What happens in the mid-afternoon was something I had not appreciated before. Clouds, probably generated by the day’s heating began passing between the sun and the solar panels. These were scattered clouds, so as one passed the sun would again shine on the panels, This causes huge jumps and drops in the electrical output of this solar array. It occurs late in the afternoon, just when the demand on the grid is peaking; adding even more stress to an already burdened system.
The second chart shows the projected impact on generation over the course of a typical week. I know, the chart is too small to read. Here’s a link to the original presentation. The critical observation here is that the more green you see, the more complex the energy response of other sources becomes. At even 11% renewables in the mix, coal (grey in the chart) begins to be forced to respond when the wind is generating too much power at a lull period. As the amount increases to 23 and 35% more and more complexity is called for. At 35%, even nuclear plants are required to modify operation.
While proponents of solar and wind see this as a reduction in the use of coal and/or nuclear, the realities of the current response based system and the physics of spinning up or down the large turbines associated with base load coal and nuclear plants mean that, in reality the system is operating increasingly inefficiently. Coal and other carbon fuels is still burned at almost the same rate as before. The turbines are still spinning, they just aren’t putting electricity to the grid.
This is where SmartGrid generation options come into the big potential pay-off. If the county really wants renewable energy sources, then using excess capacity during lower power demand periods to store energy that can then be siphoned off during high demand or low availability of so-called “green sources.” The scale of storage is far beyond anything currently on the grid in terms of both power and duration.