This talk by Jesse Jenkins at UPENN is one of the best looks at what doing deep decarbonization of the grid really looks like. Jenkins is a PhD candidate at MIT researching realistic paths to get our electricity sector down to zero carbon emissions.

Price vs. Value

He starts with the common and simple refrain we all have, which is that research investments in solar have driven down the cost below that of fossil fuels, that cross over point has happened, and renewables will just take off and take over.

But that’s the wrong model. Because of the intermitency of Wind and Solar, after a certain saturation point the wholesale value of a new MWh of their energy keeps decreasing. This has already been seen in practice in energy markets with high penetration.

 Sources of Energy

The biggest challenge is not all sources of energy are the same.

Jenkins bundles these into 3 categories. Renewables are great at Fuel savings, providing us a way not to burn some fuel. We also need a certain amount of fast burst on the grid, today this is done with Natural Gas Peaker plants, but demand hydro and energy storage fit that bill as well. In both of these categories we are making good progress on new technologies.

However, in the Flexible base camp, we are not. Today that’s being provided by Natural Gas and Coal plants, and some aging Nuclear that’s struggling to compete with so much cheap Natural Gas on the market.

How the mix changes under different limits

He did a series of simulations about what a price optimal grid looks like under different emissions limits given current price curves.

Under a relatively high emissions threshold the most cost efficient approach is about 40% renewables on the grid, some place for storage. The rest of the power comes from natural gas. 16% of solar power ends up being curtailed during the course of the year, which means you had to overbuild solar capacity to get there.

Crank down the emissions limit and you get more solar / wind, but you get a lot of curtailment. This is a 70% renewable grid. It’s also got a ton of over build to deal with the curtailment.

But if you want to take the CO2 down further, things get interesting. 

Because of the different between price and value, relatively high priced Nuclear makes a return (Nuclear is a stand in for any flexible base source, it’s just the only one we current have in production that works in all 50 states). There still is a lot of overbuild on solar and wind, and huge amounts of curtailment. And if you go for basically zero carbon grid, you get something a little surprising.

Which is the share of renewables goes down. They are used more efficiently, there is less curtailment. These are “cost optimal” projections with emissions targets fixed. They represent the cheapest way to get to a goal.

The important take away is that we’re in this very interesting point in our grid evolution where cheap Natural Gas is driving other zero carbon sources out of business because we aren’t pricing Carbon (either through caps or direct fees). A 40 – 60% renewables grid can definitely emerge naturally in this market, but you are left with a lot of entrenched Natural Gas. Taking that last bit off the board with renewables is really expensive, which means taking that path is unlikely.

But 100% Renewables?

This is in contrast to the Mark Jacobson 100% renewables paper. Jenkins points out that there have really been two camps of study. One trying to demonstrate the technical ability to have 100% renewables, the other looking at realistic pathways to zero carbon grid. Proving that 100% renewables is technically possible is a good exercise, but it doesn’t mean that it’s feasible from a land management, transmission upgrade, and price of electricity option. However none of the studies looking at realistic paths landed on a 100% renewables option.

Jenkins did his simulation with the 100% renewables constraint, and this is what it looked like.

When you pull out the flexible base you end up with a requirement for a massive overbuild on solar to charge sources during the day. Much of the time you are dumping that energy because there is no place for it to go. You also require storage at a scale that we don’t really know how to do.

Storage Reality Check

The Jacobson study (and others) make some assumptions about season storage of electricity of 12 – 14 weeks of storage. What does that look like? Pumped hydro is currently the largest capacity, and most efficient way to store energy. Basically you pump water behind a dam when you have extra / cheap energy, then you release it back through the hydro facility when you need it. It’s really straight forward tech, and we have some on our grid already. But scale matters.

The top 10 pumped hydro facilities combined provide us 43 minutes of grid power.

One of the larger facilities is in Washington state it is a reservoir 27 miles long, you can see it from space. It provides 3 1/2 minutes grid average power demand.

Pumped hydro storage is great, where the geography supports it. But the number of those places is small, and it’s hard to see their build out increasing dramatically over time.

Does it have to be Nuclear?

No. All through Jenkins presentation Nuclear was a stand in for any zero carbon flexible base power source. It’s just the only one we have working at scale right now. There other other potential technologies including burning fossil fuels but with carbon capture and storage, as well as engineered geothermal.

Engineered Geothermal was something new to me. Geothermal electricity generation today is very geographically limited you need to find a place where you have a geologic hot spot, and an underground water reserve, that’s turning that into steam you can run through generators. It’s pretty rare in the US. Iceland gets about 25% of it’s power this way, but it has pretty unique geology.

However, the fracking technology that created the natural gas boom openned a door here. You can pump water down 2 miles into the earth and artificially create conditions to produce steam and harvest it. It does come with the same increase in seismic activity that we’ve seen in fracking, but there are thoughts on mitigation.

It’s all trade offs

I think the most important take away is there is no silver bullet in this path forward. Everything has downsides. The land use requirements for solar and wind are big. In Jenkins home state of Massachusetts in order to get to 100% renewables it would take 7% of the land area. That number seems small, until you try to find it. On the ground you can see lots of people opposing build outs in their area (I saw a Solar project for our school district get scuttled in this way).

In the North East we actually have a ton of existing zero carbon energy available in Hydro Quebec, that’s trapped behind not having enough transmission capacity. Massachusetts just attempted to move forward with the Norther Pass Transmission project to replace shutting the Pilgrim Nuclear facility, but New Hampshire approval board unanimously voted against it.

Vermont’s shutdown of their Yankee Nuclear plant in 2014 caused a 2.9% increase in CO2 in the New England ISO region, as the power was replaced by natural gas. That’s the wrong direction for us to be headed.

The important thing about non perfect solutions is to keep as many options on the table, as long as you can. Future conditions might change in a way where some of these options become more appealing as we strive to get closer to a zero carbon grid. R&D is critical.

That makes the recent 2018 budget with increased investment credits for Carbon Capture and Storage and small scale Nuclear pretty exciting from a policy perspective. These are keeping some future doors open.

Final Thoughts

 

Jenkins presentation was really excellent, I really look forward to seeing more of his work in the future, and for a wider exposure on the fact that the path to a zero carbon grid is not a straight line. Techniques that get us to a 50% clean grid don’t work to get us past 80%. Managing that complex transition is important, and keeping all the options on the table is critical to getting there.