Using Batteries as a Renewable Energy Source

By Vernon Trollinger, February 6, 2017, Green

Welcome to Exploring Renewable Energy Technology from Bounce Energy! Because the ERCOT portion of Texas can be thought of as a “walled garden,” renewable energy sources in Texas now make up a significant portion of the energy supply mix. It’s also a dynamic technology with new innovations, discoveries, and issues arising every week. Each month, we will examine the latest news in the industry to better understand what (if any) changes might come to the Texas energy supply.

Batteries Required —Part One

If you’ve ever heard a discussion about renewable energy, you’ve probably heard someone retort, “What are you going to do when there’s no sun or the wind doesn’t blow?”

One answer is to use batteries. While that might have sounded ludicrous a decade or two ago, grid-scale battery development has become one of the key innovations that is helping expand Texas renewable energy. Admittedly, renewable systems like wind and solar are intermittent supplies. In west Texas, solar farms don’t make much electricity on cloudy days and make zero at night. Wind farms only produce energy when the wind blows —which is typically at night but that’s when demand is low. Consequently, these two can’t be relied on all the time.

Grid-scale battery storage changes all that. While the batteries don’t look very exciting, most are just intermodal containers, they are helping the Texas grid work better.

Exploring Renewable Energy Technology — February, 2017

Currently, most of the largest utility scale battery installations are lithium ion. This is the same technology that powers your laptop battery or phone battery or just about any other gadget in your home — only they’re much bigger and there’s more of them all wired together. While storage capacity in these batteries isn’t anywhere big enough to power a city like Austin, having grid scale batteries in place can help smooth-over fluctuations in grid voltage such as when sunshine dims or wind speed drops or demand spikes. Not only do grid batteries improve local grid reliability, but they do it without polluting emissions or the use of water. Recently, AEP Texas North Company (TNC) petitioned the Public Utility Commission of Texas to install lithium-ion batteries at Woodson and Paint Rock to improve the reliability of its distribution system. One new record-sized battery installation in California will be used to store energy when it’s cheap and then power the grid when rates spike.

Not all of these big battery sets are lithium ion. For example, the first utility-scale battery in Texas was a 4 MW sodium-sulfur (NAS) energy storage system in Presidio, Texas. NAS batteries are molten systems that operate around 660°F but are long-lived and are better than 85% efficient. Once the battery is heated to operating temperature, the heat from the charging and discharging cycles is enough to maintain the process.

Exploring Renewable Energy Technology — February, 2017

Lead acid batteries, like those in your car, were also used by Duke Energy at its 36 MW Notrees Battery Storage Project in 2013 to support its 153 MW wind farm. Used primarily for frequency regulation, the round-the-clock charge and discharge usage reduced the battery life. The lead acid batteries were replaced with lithium-ion batteries about two years later.

Which brings us to the basic problem facing all battery research right now—getting beyond lithium ion. Currently, lithium ion batteries provide the most bang for the buck. However, as with lead acid batteries, lithium ion batteries also don’t last long during intensive charge/discharge cycling. This kind of stress reduces charge capacity. What’s needed is a battery that can charge/discharge rapidly, last long time, and is cheap. These are some of the new battery technologies under development:

Flow batteries  currently the preferred type for utility scale. Flow batteries are essentially electrochemical batteries just like a lemon battery that use electrolyte solutions (containing vanadium, chromium, iron, and zinc) instead of solid metal poles (like the copper and zinc nails in a lemon battery). The electrolyte solutions are pumped into container divided by an ion-selective membrane. The membrane lets electrons flow from electrolyte solution pole to the other and this creates an electrical current. The electrolyte solutions are circulated out of storage tanks which allows the solutions to be changed out and refilled with fresh electrolyte. This way, flow batteries bypass the wear-problems from intensive charge/discharge cycling. While the load to run pumps cuts a little into overall efficiency, replenishing the electrolytes makes their lifespan arguably limitless. The drawback is the price of electrolytes isn’t cheap and is arguably a fuel cost.

Exploring Renewable Energy Technology — February, 2017 | Direct Energy Blog

Lithium-sulfur batteries These have three times the output of a lithium ion battery. They also do well in cold weather but not as well in hot. Cost is low due to abundance of sulfur which keeps the cost moderate, around $250/kWh. Their drawback is they have a short charge/discharge cycle life. Experiments with graphene might bring some enhancements.

Lithium-air batteries — This type promises to store far more energy than is possible with current lithium-ion battery. Each cell can voltages of between 1.7 and 3.2 volts. That doesn’t sound like much but when you load up a 40’ trailer with racks and rack of cells, all that power adds up fast. The drawbacks are that it doesn’t perform well in cold temperatures and charge/discharge cycle also remains very low.

Magnesium-Pyrite battery  Nicknamed the “Fools Gold Battery” for using iron pyrite as the cathode (or negative pole), this battery delivers energy densities comparable to commercial Li-ion batteries. Costs are low because it is built with abundant elements: iron, sulfur, sodium and magnesium. It’s also safer because magnesium isn’t as flammable as lithium. Cycling lifespan is promising; the lab-tested model withstood 40 charge/discharge cycles without losing performance. Other batteries mentioned usually begin degrading at this point.

Exploring Renewable Energy Technology — February, 2017 | Direct Energy Blog

Sodium-ion batteries Essentially, this is a saltwater battery. Possibly, the lowest-cost, most environmentally friendly alternative. These batteries can be completely discharged without facing stresses common to other battery systems. Costs are similar to the lead acid battery. In general, problems still exists in that the battery tends to swell when charged and the charge/discharge cycle needs improving. Aquion Energy is developing grid level salt batteries and recently installed a 55kW model at Kruger National Park in South Africa.

What would you like to see us discuss in future installments of Exploring Renewable Energy Technology? Please share with us in the comments!

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A native of Wyomissing Hills, PA, Vernon Trollinger studied writing and film at the University of Iowa, later earning his MA in writing there as well. Following a decade of digging in CRM archaeology, he now writes about green energy technology, home energy efficiency, DIY projects, the natural gas industry, and the electrical grid.

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