There Is Massive Potential for Reducing CO2 Emissions (Without Losing Reliability)
It makes sense that higher percentages of renewables would decrease emissions. The NREL study, however, does a great job of mapping out the precise implications for carbon in the charts below:
As you can see, under the baseline scenario (BAU) we are in big trouble, with CO2 emissions rising. However, the higher the penetration of renewables in the electricity mix, the more dramatic the implications for lowering carbon. Here’s another way to put that data:
The big takeaway here is that under the 80 percent renewables scenario, natural gas-fired and coal-based electricity generation also declined by about 80 percent by 2050. Consequently, so did emissions.
Overcoming Obstacles: Grid Flexibility and New Transmission
The study evaluates renewable energy penetration scenarios with several variables; including constraints on transmission, flexibility, and resources. Each of these constraint scenarios had implications for how exactly renewables were utilized.
For instance, a constrained transmission scenario favored resources that don’t require transmission like rooftop PV. Constrained flexibility meant more reliance on non-variable renewables, like CSP, and less on utility-scale PV and wind. Under the constrained resources scenario, biopower, geothermal, and hydro (which you can’t find everywhere) were limited; whereas CSP and onshore wind reached high levels of penetration.
What does this have to do with obstacles? Well, system planners, operators, and Public Utility Commissions that want to hit high renewable targets will have to harness different technologies based on their constraints. We can’t do much about the resource constraints issue, but we can do something about flexibility and transmission nationwide. Here’s a little more background on why that’s necessary and what it would entail.
Grid flexibility, or the ability of the grid to meet demand in a variety of changing circumstances, is a crucial component of an efficient and useful power system. As higher percentages of renewables are incorporated, however, some have expressed concerns that the grid will not be flexible enough to meet demand. This is largely because supply and demand must be balanced in real time.
The NREL study acknowledges this concern and explains how 80 percent renewables still allow for a flexible grid.
First, the 80 percent renewable scenario must provide adequate generation capacity to meet demand. The NREL study showed that the 80 percent renewable scenario provided more than enough capacity to meet demand — even under times of system stress. Storage technology and transmission infrastructure would also chip in massively. In other words, the lights would still stay on.
In addition to being able to meet generation capacity requirements, the system must have a certain amount of energy on standby, also known as an “operating reserve.” The NREL study found that the 80 percent scenario was more than sufficient to meet these requirements. In their words: “integrating high levels of variable generation is not an insurmountable task even under relatively conservative assumptions for transmission and institutional flexibility.”
“the supply- and demand-mix, planning and operating reserves, and transmission system predicted by ReEDS under the scenarios analyzed were sufficient to meet load on an hourly basis, and that hourly mismatches between supply and demand on a regional basis were therefore not anticipated.”
Share the Wealth- Building New Transmission
Getting to 80 percent renewables efficiently suggests the need for construction of 110-190 million miles of new transmission and 47-80,000 miles of new intertie capacity across the three interconnections. This would cost anywhere from $6.4 to $8.4 billion annually. However, this is in line with recent annual investments of $2 billion to $9 billion annually from 1995-2008. So, the new infrastructure demands are well in line with our national trajectory.
An interesting implication for transmission, though, is that NREL found its use would increase by 8 percent (from 32 to 40 percent) with the 80 percent scenario. This is what enables every region to significantly contribute to renewable energy supply. For more on the transmission issue, you can see the fourth volume of the NREL study here.
The report offers a great blueprint for thinking about our energy future. It once again shows that a renewables-dominant energy system is not a technical challenge, but an engineering and creativity challenge.
This post was originally published by Climate Progress.
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