Storing Electricity

The US has plentiful sources for generating electricity.  Unlike parts of Asia and Europe our self-sufficiency does not force us into precarious positions such as needing to import natural gas (as does Ukraine) carried by hostile pipeline operators. Nor do wo we need to rely on transoceanic tankers for liquefied natural gas supply (as do Japan, South Korea and China). We do not need to import vast amounts of coal to generate electricity, as does China.  Nevertheless, like most countries, the US relies on fossil fuels for 67% of its electric energy generation (33% gas, 33% coal, and 1% petroleum).  Although nuclear is the cleanest of all generation sources, it has raised worries over potential accidents that may stem from design or maintenance failures.  The US obtains 20% of its electric power from nuclear generation. 

That leaves 13% of our electricity generated by renewable sources.  Hydroelectric and geothermal provide 6.4% of the electricity.  Wind turbine provides 4.7%, biomass and other (wave generated power, tidal flow generation) provide 1.6% and solar provides 0.6%.  Renewables may be, arguably, regarded as clean for the environment, but they are interruptible sources of electricity that require special provisions to cover those periods when the sun is occluded, the wind is calm, when ocean waves are calm, between tidal flows, or when hydroelectric dams are low on water.  For many years, renewable energy has been subsidized to encourage gaining familiarity with how to engineer more efficient uses.

The most common “special provision” is a battery that stores excess from an active generation period to be drawn down when the generation is not active.  The amortized capital cost of the equipment that generates renewable power plus the maintenance have dropped over the years.  Countries that rely heavily on renewables have much higher energy prices than in the US and Canada.

On a large scale, batteries are a cure for interrupted generation.  On a small scale, Lithium ion batteries work best for consumer devices that would normally use a power cord into the electrical network (e.g. smartphones, tablets/PCs, digital cameras,  and power tools), and for powering electric automobiles because of Lithium’s high energy density and light weight.

Lithium ion batteries to store energy, however, present some challenges. Certain types are prone to fire and explosion when pierced or recharged rapidly; the manufacturing process can pollute, and they are expensive.  Lithium ion batteries are wholesale priced at near $200 per kilo Watt hour (kWh).  A kWh is an amount of energy, roughly as much as running a toaster for 1 hour would consume.  A Tesla Model-S needs batteries with a 65 kWh capacity.  A Chevy Volt needs just 16 kWh of battery capacity.  Northvolt, a competitor to Tesla’s battery operations, expects wholesale Lithium ion battery prices to drop from $109/kWh in 2015 to $73/kWh by 2030.  That will cut the cost of electric vehicles substantially since the batteries are about one-third of an electric vehicle’s price.

A battery-design called a “flow battery” is more suited to the massive storage context of the electric grid.  Charges are stored in liquid electrolytes that sit in external tanks and flow on either side of a membrane.  The ions pass electric charges between the solutions in the tanks.  When the process is reversed (i.e., when the battery is charged), the ions return to the other tank.  Because those tanks have no size limit, the storage capacity of a flow battery can be scaled up as needed. 

Hopefully, in the future, we can expect to see flow batteries provide the off-hours power from renewables whenever the sun, water or wind cannot generate power.  Lithium ion batteries have special significance for some consumers because lower battery prices help renewables lower costs relative to fossil fuel generation, and lower cost Lithium ion batteries could make electric cars more affordable.