Molten metal batteries: Holy Grail for solar power protagonists?

Molten metal batteries: Holy Grail for solar power protagonists?

By Jack Ward, MD of power provisioning specialist, Powermode.

News about a revolutionary, high-capacity molten metal battery, claimed to be the Holy Grail of cheap, long-lasting power storage devices, has hit the headlines.

The invention is funded by Bill Gates and others who know something about developing technologies. The battery, currently in prototype, is unlike any other and comes in the form of an insulated, sealed metal casing the size of a pizza box. Within the ‘box’ are layers of floating reactive molten metals of different densities one on top of another – much like a layer cake.

Antimony, a lustrous gray metalloid, is the base layer, an electrolyte such as sodium sulphide is next and magnesium (the ninth most common element in the universe) is at the top. At maximum efficiency, the batteries operate at high internal temperatures – some say as high as 700 degrees C - which will be reached as a result of the internal chemical reactions associated with repeated charging and discharging.

The efficiency numbers currently quoted for the prototype are in the 69% region, typical for any kind of rechargeable battery. It appears as if the approximately 30% energy lost during the charge/discharge cycle should, if retained via insulation (instead of deliberately dissipated as is typical for low-temperature batteries) be sufficient to keep the battery operating at just about any temperature required.

The batteries are modular, so they can be stacked vertically and horizontally to form giant-sized devices. They are also cheap, less than a third of the cheapest (lead-acid) batteries available on the market today. And they will last significantly longer – around 10 to 15 years is an early estimate.

The result is an unusually resilient device that can quickly absorb large amounts of electricity. The electrodes can operate at electrical currents tens of times higher than any battery that's ever been measured, according to Donald Sadow­ay, a materials chemistry professor at MIT and one of the battery's inventors.

The new battery’s development flies in the face of mainstream battery research which has, up to now, focused on small and light (and ambient temperature) batteries for electronic gadgets and cars. Lithium has been the (costly) medium of choice.

The real breakthrough associated with the molten metal battery is not in size or weight, but cost as it applies to the battery’s materials and its simple manufacturing process.

While the battery’s dimensions and high internal temperatures rule it out of any role in the consumer market - where ‘small’ and ‘light’ are the watch words - it makes it an ideal option for power storage at wind and solar power generating plants where its application is currently targeted.

So, will the new batteries be able to help mankind throw off the shackles of the petroleum industry and slay the dragon of global climate change?

According to the inventors, a container-load of connected batteries would be able to service around 200 average households assuming the neighbourhood has enough solar PV panels in a generating plant or on its roofs to meet its electricity requirements. Even so, it will need significant storage capacity to see it through an overcast week or a stormy weekend.

This will encourage the local generation of electricity and if (or when) the legal hurdles are overcome, any surplus could be fed into a national electricity grid to supply electricity to other homes and businesses and generate additional revenue for the neighbourhood.

Wind and solar power have a clear future mapped out for them, if the German experience is any yardstick. Today, Germans are paying less per kw/h for electricity (thanks to solar and wind generation) than their French counterparts pay for nuclear generated electricity. Makes you think...