Is energy storage.
Energy grids across the world are struggling to cope with a surge in demand for electricity and increasingly volatile supply from renewable power sources.
In the UK, where the government is committed to stringent carbon dioxide reduction targets. These can only be met by massively increasing electricity use - which currently accounts for about a third of all energy consumption - from renewables at the expense of oil and gas.
Peak demand on the UK grid is currently 60GW, but by 2050, the government estimates this will increase six-fold as demand for electric cars and household heating soars.
To meet this demand, more pylons and cabling will be needed, adding up to £1,000 a year to consumer bills, according to power services company S&C Electric.
And it's not just about higher demand and cost, as renewable power sources such as wind and solar are, by their very nature, variable - when the wind doesn't blow and sun doesn't shine, little or no power is generated.
Countries the world over, and particularly those investing heavily in renewable energy, are facing the same problem, and solutions are few and far between.
Increasing fast-acting generation in order to fill energy gaps is one answer, but as most generators of this type, such as diesel turbines, emit CO2, they are somewhat counterproductive.
Another way is to increase connectivity with other countries, but in a world in which national energy security is high on political agendas, this is far from ideal. And besides, as many weather patterns are regional, this is hardly a winning solution.
But there are two ways to help solve this critical problem that should work, both of which are attracting huge sums of money from governments and companies.
The first is energy storage - simply storing energy generated during periods of low demand to use during periods of high demand. Sounds simple enough and, as Anthony Price at the UK's Electricity Storage Network says, it's something that was commonplace 100 years ago.
Not only does storage help overcome the problem of variable supply from renewable energy sources, but it allows electricity grids to operate more efficiently and cost effectively, says Mr Price. This is simply because storage allows "the system to be run at average load rather than peak load", he says.
It would also end the absurdity of paying for wind turbines to be shut down when demand is being satisfied.
And the cost savings could be huge - Imperial College London's Energy Futures Lab has estimated that energy storage technologies could generate savings of £10bn a year by 2050 in the UK.