It's a statement of the obvious, but solar panels do their best work during the day, specifically noon and early afternoon when the sun is at its strongest.
The trouble is, this rarely tallies with when energy use is at its highest--typically in the evening, when everyone gets home from work.
The solution to bridging this offset supply and demand is energy storage, and the metal vanadium could be instrumental in our future storage needs.
Vanadium's unique properties make it highly useful for developing stable batteries--ones that can be charged thousands of times without suffering degradation or capacity loss.
As the BBC reports, vanadium can lose or gain electrons very easily.
Vanadium (Image: Flickr user fdecomite, used under CC License)
This same process can be demonstrated on a much larger scale, in a battery.
Called a Vanadium Redox Flow Battery, it consists of two tanks of different solutions of vanadium separated by a membrane.
As fluid is pumped past electrodes on either side of the battery, current is produced. Electrons are released by one side and received by the other--changing the color of the solution as they do so. And these electrons generate the current.
The battery chemistry, of course, doesn't really affect the job the battery does--the aim here is to store solar energy during the day. You could do this with a lithium-ion battery--indeed, old lithium batteries from electric vehicles are often used in such a manner.
It's the vanadium battery's long life that makes it useful here.
They can be charged and discharged 20,000 times without loss of performance--about ten times that of Li-ion batteries. And they're thought to last decades--though they've not been around long enough for this to be demonstrated in practice.
Downsides? The batteries are expensive, since vanadium is expensive. That's mainly a symptom of its popularity within the steel industry as a hardening compound, and the steel industry accounts for around 90 percent of demand for the metal.
Photovoltaic solar panels on roof of Honda Smart Home at UC-Davis, California
The batteries are also huge--think shipping container sized, right now. So they're strictly static only--don't expect to see them in electric cars. Or even your garage--these would effectively be used by electrical utilities, so there's hope for them yet even if an entire neighborhood opts for solar power...
Solar power is generated at fairly low voltage, so German renewable energy entrepreneur Alexander Voigt believes the batteries' best application is on a local level--placed at transformer stations to harness energy produced during the day for use later at night.
They're quite adaptable, too. While it increases the batteries' size further, more storage can be achieved by adding larger tanks of electrolyte. And they're happy to discharge slowly, as needed to serve the community's power needs.
Perhaps the biggest issue though is vanadium supply.
For one, China's rapid, resource-heavy growth is also increasing demand for vanadium in steel. And vanadium used in steel is effectively written-off for use in batteries--it isn't economically viable to recover it when the steel is recycled.
But, as with other metals used in batteries, an increase in demand will no doubt lead to more companies willing to extract it from the ground.
And eventually, every neighborhood in sunny regions could have a vanadium battery nearby--holding enough energy to supply a street with enough power for its TVs, ovens and electric cars every night.
[Hat tip: Ned]