“Is having 100% renewable energy for a country feasible?”

This question was recently posed on Thinkable.

Dr. Gene Preston, a man who has been professionally specializing in grid reliability studies since his 1997 dissertation on the subject, answers “Exceptionally unlikely.” He doesn’t stop there; his answer includes enough detail to persuade all but the most fervent believers in the fantasy.

I’ve been fortunate enough to have been reading Dr. Preston’s thoughts and professional investigations into grid reliability planning for a number of years. We communicate via the same closed email list that includes members with a variety of professional backgrounds who share technical interests in electricity production and distribution.

It’s obvious to members of the list that Gene really knows his stuff when it comes to accurately modeling the variables in grid reliability predictions.

It would be useful for more people should have access to his information, so I obtained his permission to republish his detailed answer explaining why it isn’t feasible to attempt to provide 100% of a modern society’s energy demand with power sources that have been branded as “renewable.”

The below is a slightly edited and reformatted version of Dr. Preston’s answer on Thinkable.

100% means all the time, every hour, through good weather years and bad ones.

I do reliability studies that simply ask the question, is there enough capacity every hour to meet the demand. I recently gave a talk to ERCOT, the Electric Reliability Council of Texas, that included scenarios pushing renewables to as high as 75% penetration.

I gave the same talk to some university students on the same day. That talk was recorded and archived, so it includes more details than the slide outline.

ERCOT has quite a lot of wind power and energy, 20,000 MW in a 70,000 MW peaking system with about a 40,000 MW average demand for the year. We are just now beginning to add a lot of solar to our system.

The simulations show that somewhere around 7000 to 14000 MW of solar we will have excess power. We will begin dumping excess energy at times, much as California is having to do right now.

This is wasted energy. And we begin to waste this renewable energy at an early point in the conversion to renewables, maybe around 20% to 30% penetration. I haven’t checked the exact value. In order to stop dumping this valuable energy we will need to store it.

So I add storage to the model and it works fine. There is a table at the end of the presentation showing scenarios of different penetrations and how much storage is needed. At first the storage is useful for just moving energy to peak shaving.

But as renewables pick up more and more of the load the peak shaving is satisfied and now renewables begin to pick up more hours. As you keep on adding more renewables and more storage pretty soon you are seeing renewables picking up nearly all the energy all the time.

But there is a problem. Every once in a while you see energy shortages in renewables production. This is because the wind and solar just have low production days in energy. You already have enough storage to distribute the energy to when its needed. That’s not the problem. The problem is that wind and solar and hydro unavoidably have times when they don’t produce much energy across the entire state.

If you miss a day of production in renewables you have to fire up the gas generators to fill in the demand. So when you run the reliability program I call RTS3, the program forces you to not retire all the gas. In fact you have to keep most of your fossil fuel capacity in standby to fill in when renewables fail to produce enough energy.

So this right here prevents 100% conversion to renewables.

What if we had really long term storage, like the equivalent of a grain silo? Suppose we could create some form of liquids, such as a flow battery, where we could store large amounts of energy in these liquids? We might even store them for years. We could ride through the low production years with enough storage.

But that technology is not yet invented. So until we invent long term storage for electric energy we are not going to be able to achieve 100% renewables. You can download my RTS3 model and run your own scenarios. I could even prepare for you the CAISO data from public sources.

I intend to do just that as soon as I finish my NERC study on the CAISO. They want to finish their report first before we go public. By the way the CAISO has a terrible reliability problem if there is an extended drought which reduces hydro production for years at a time.

Hydro is a blessing and a curse. Its a blessing during rainy years and a curse in dry years. California had the driest years in 2013 – 2015 in the past 1200 years. When is the next drought? What kind of resources do we need to keep working so we can insure the lights will stay on during severe droughts?

Having some nuclear in the mix would make the system more reliable both capacity wise and energy wise. It will also reduce CO2 emissions.

So those are my comments. Please contact me at any time for modeling how we get off fossil fuels. We all have the same goal of getting off fossil fuels. My web page is http://egpreston.com .

Gene Preston, PE PhD