Category Archives: Energy Storage

Addresses aspects of storing energy in batteries, flywheels, pumped storage, etc.

Man Bites EV: Will EV Bite Back?

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[An expanded treatment of some of this material appears in Appendix section D.3 of the Energy and Human Ambitions on a Finite Planet (free) textbook.]

electric_car

Electric Car: They Might Be Giants

Some time ago, the Chevy Volt attracted my attention. I think the plug-in hybrid concept hits the sweet spot for American drivers, and the Volt’s 35–40 mile electric-only range seemed to be the perfect number. A pure electric vehicle (EV) would not permit my wife’s periodic work-related jaunt to Pasadena, so any battery-powered solution for us must be of the plug-in hybrid electric vehicle (PHEV) variety. The problem, ultimately, was the high price tag (and the hump in the middle of the back seat occupied by the battery). Although I don’t self-identify as being in the “upper class,” our income edges us into the top quintile in the U.S. So for us to decide that the Volt costs too much—despite genuine enthusiasm—seemed to spell trouble (indeed, the average income of Volt owners was claimed to be $175,000). My conclusion was that electric/plug-in cars are out of reach, and could well remain so.

In April of this year, I became aware of the Ford plug-in, called the C-Max Energi (yes, with an “i” at the end!). The C-Max Energi has a 21 mile electric-only range, and gets an EPA rating of 43 miles per gallon (2.3 gal/100 mi; or 5.4 L/100 km). The price tag is approximately $6k cheaper than the Volt, and the back seat passed my wife’s approval. Nonetheless, after carefully considering the C-Max Energi as a replacement for our increasingly ailing car, we decided against springing for one: still too expensive. I was all set to write a Do the Math post to the tune of “Almost bit on a PHEV again.”

But the fact remained that our 11-year old 28 MPG car (bought used) has been costing us a fair bit in maintenance, its reliability increasingly dubious. Replacement loomed. Motivated by an upcoming long-haul road trip, we explored options again, looking at hybrids and the C-Max Energi. In the end—aided by a federal tax credit, a California rebate, and an unfathomably good offer that together knocked $9k off the MSRP—we drove an Energi off the lot under battery power.

It turns out that:

  • the lifetime cost for the PHEV is still higher than other options we considered, but not prohibitively so given credits, rebates, and discounts;
  • the CO2 emissions are cut in half in electric mode (considering upstream electricity production in our region);
  • batteries still stink compared to liquid fuel, and likely always will.

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Death of a Battery

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Four 150 A-h 12-V golf-cart batteries

Four golf-cart batteries used in my off-grid home PV system. Each is 12 V, 150 A-h, thus 1.8 kWh of storage.

All the metrics looked great. The 2.7-year-old lead acid batteries in my off-grid photovoltaic system appeared to have settled into a consistent mid-life performance. Monthly maintenance (equalizing, adding distilled water) promised to keep the batteries in prime condition for some time to come. Based on cycle depth, I expected another 2.5 years out of the present set of batteries. Life was good.

Then, during my absence over the course of Thanksgiving weekend, one of the batteries expired. No forewarning. Just gave up. A previous post expressed an overall disappointment in batteries, now reinforced by this sudden nosedive.

In this post, I’ll show the metrics on my system detailing the demise of “Battery E.” The gruesome graphics are intended for mature audiences.

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Blow-by-Blow PV System Efficiency: A Case Study for Storage

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A short while back, I described my standalone (off-grid) urban photovoltaic (PV) energy system. At the time, I promised a follow-up piece evaluating the realized efficiency of the system. What was I thinking? The resulting analysis is a lot of work! But it was good for me, and hopefully it will be useful to some of you lot as well. I’ll go ahead and give you the final answer: 62%. So you could peel away now and risk using this number out of context, or you could come with me into the rabbit hole…

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Battery Performance Deficit Disorder

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Batteries fail—as certainly as death and taxes. Rechargeable batteries at least offer the possibility of repeating the cycle, so are in this sense more like recurrent taxes than death. But alas, the story cannot repeat indefinitely. One cheerful thought after the other, yes?  But wait, there’s more… Add to their inevitable demise an overall lackluster performance in battery storage technology, and we have ourselves the makings of a blog post on the failure of batteries to live up to their promises.

To set the stage, the specific energy of gasoline—measured in kWh per kg, for instance—is about 400 times higher than that of a lead-acid battery, and about 200 times better than the Lithium-ion battery in the Chevrolet Volt. We should not expect batteries to rival the energy density delivered by our beloved fossil fuels—ever.

A recent article in APS News reported on an emerging view that batteries are failing to live up to our dreams in the electric car realm:

Despite their many potential advantages, all-electric vehicles will not replace the standard American family car in the foreseeable future. This was the perhaps reluctant consensus at a recent symposium focused on battery research.

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The Alternative Energy Matrix

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[An updated treatment of this material appears in Chapter 17 of the Energy and Human Ambitions on a Finite Planet (free) textbook.]

Breathe, Neo. I’ve been running a marathon lately to cover all the major players that may provide viable alternatives to fossil fuels this century. Even though I have not exhausted all possibilities, or covered each topic exhaustively, I am exhausted. So in this post, I will provide a recap of all the schemes discussed thus far, in matrix form. Then Do the Math will shift its focus to more of the “what next” part of the message.

The primary “mission” of late has been to sort possible future energy resources into boxes labeled “abundant,” “potent” (able to support something like a quarter of our present demand if fully developed), and “niche,” which is a polite way to say puny. In the process, I have clarified in my mind that a significant contributor to my concerns about future energy scarcity is not the simple quantitative scorecard. After all, if it were that easy, we’d be rocking along with a collective consensus about our path forward. Some comments have  asked: “If we forget about trying to meet our total demand with one source, could we meet our demand if we add them all up?” Absolutely. In fact, the abundant sources technically need no other complement. So on the abundance score alone, we’re done at solar, for instance. But it’s not that simple, unfortunately. While the quantitative abundance of a resource is key, many other practical concerns enter the fray when trying to anticipate long-term prospects and challenges—usually making up the bulk of the words in prior posts.

For example, it does not much matter that Titan has enormous pools of methane unprotected by any army (that we know of!). The gigantic scale of this resource makes our Earthly fossil fuel allocation a mere speck. But so what? Practical considerations mean we will never grab this energy store. Likewise, some of our terrestrial sources of energy are super-abundant, but just a pain in the butt to access or put to practical use.

In this post, we will summarize the ins and outs of the various prospects. Interpretation will come later. For now, let’s just wrap it all up together.

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Pump Up the Storage

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If we adopt solar and wind as major components of our energy infrastructure as we are weaned from fossil fuels, we have to solve the energy storage problem in a big way. An earlier post demonstrated that we do not likely possess enough materials in the world to simply build giant lead-acid (or nickel-based or lithium-based) batteries to do the job. Comments frequently pointed to pumped hydro storage as a far more sensible answer. Indeed, pumped storage is currently the dominant—and nearly only—grid-scale storage solution out there. Here, we will take a peek at pumped hydro and evaluate what it can do for us.

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Got Storage? How Hard Can it Be?

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The recent city-wide power outage in San Diego made me appreciate my small off-grid photovoltaic system using four golf-cart batteries to store energy for use at night. Unlike most San Diegans, I did not immediately eat the ice cream in my freezer, which trucked along under stored solar energy just like it does every night. Energy storage becomes more important as we transition away from fossil fuels—already its own energy storage medium—to more intermittent sources. But besides batteries—which offer a limited number of cycles and for some types require monthly maintenance—what other non-fossil in-home energy storage alternatives might we consider, and how much energy might we expect to store in each case? We will look at gravitational storage, flywheels, compressed air, and hydrogen fuel cells as possible options. Some might even cost less than $100,000 to implement in your home.

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Power Out, People Out

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Yesterday at about 15:40 local time, San Diego lost power—along with many other parts of Southern California, Arizona, and Mexico. Our power was out for 11 hours. The experience was fascinating for me, because it changes the rules of the game suddenly, and exposes certain fragilities in our system. This is a brief account of what I learned from the experience. Continue reading →

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A Nation-Sized Battery

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As we look to transition away from fossil fuels, solar and wind are attractive options. Key factors making them compelling are: the inexhaustibility of the source with use (i.e., renewable); their low carbon footprint; and the independence that small-scale distribution can foster (I’ll never put a nuclear plant on my roof, even if it would make me the coolest physicist ever!).

lovely future of solar, wind, and honking-big battery

With full-scale solar in the desert southwest, and wind in the plains states, we're going to need a big battery (items not to scale!).

But solar and wind suffer a serious problem in that they are not always available. There are windless days, there are sunless nights, and worst of all, there are windless nights. Obviously, this calls for energy storage, allowing us to collect the energy when we can, and use it when we want.

Small-scale off-grid solar and wind installations have been doing this for a long time, typically using lead-acid batteries as the storage medium. I myself have four golf-cart batteries in my garage storing the energy from eight 130 W solar panels, and use these to power the majority of my electricity consumption at home.

It’s worth pausing to appreciate this fact. Compare this scheme to the dream source of fusion. Why do people go ga-ga over fusion? Because there is enough deuterium in water (sea water is fine) to provide a seemingly inexhaustible source of energy, and there are no atmospheric emissions in the process. Meanwhile, solar provides a source that will last longer (billions of years), produces even less pollution (no radioactive contamination of containment vessel), and is here today! It’s even affordable enough and low-tech enough to be on my roof and in my garage! People—we have arrived!

Storage works on the small scale, as many stand-aloners can attest. How would it scale up? Can it? Continue reading →

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