雖然讓太陽能電池板和風力渦輪機啟動並運行以產生電力相對容易，但 "當太陽不照耀和風不吹時，你如何保持燈光？"BBC的環境記者Matt McGrath說。
Researchers in Finland have installed the world's first fully working "sand battery" which can store green power for months at a time.
The battery is charged up with heat made from cheap electricity, like solar energy from the sun or wind power.
Developers say the battery could provide energy all year round, storing heat at around 500C, which can then heat water and houses in winter when it costs more to keep homes warm.
Finland is a northern European country where winter is long and very cold and temperatures often drop to around, or below, freezing for several months.
The new technology, developed at Vatajankoski power plant in the town of Kankaanpää in western Finland, involves 100 tonnes of builder's sand piled high inside a tall storage container known as a silo.
The researchers responsible for the sand battery hope that it will provide a more reliable alternative to green or renewable energy.
While it is relatively easy to get solar panels and wind turbines up and running to generate electricity, but "how do you keep the lights on when the sun doesn't shine and the wind doesn't blow?" says Matt McGrath, the BBC's environment correspondent.
"The most obvious answer to these problems is large scale batteries which can store and balance energy demands as the grid becomes greener," says Matt, explaining how the batteries can store the green energy that has already been generated - so there isn't a problem when the sun isn't shining or the wind turbines aren't turning.
Sand is very effective at storing heat and loses little over time. The developers say that their device could keep sand at 500C for several months.
"Whenever there's like this high surge of available green electricity, we want to be able to get it into the storage really quickly," said Markku Ylönen, one of the two founders of Polar Night Energy who have developed the product.
So when the cost of keeping homes warm is higher, the battery can give off hot air which warms water which is then pumped around homes, offices and even the local swimming pool in the nearby area.
"It's really simple, but we liked the idea of trying something new, to be the first in the world to do something like this," said Pekka Passi, the managing director of the Vatajankoski power plant.
"It's a bit crazy, if you wish, but I think it's going to be a success."
Development of the battery comes at a time when Finland and many countries around the world are looking to reduce the use of greenhouse gases and fossil fuels because of climate change.
It also comes at a time when Finland is having to reduce its reliance on gas supplied by Russia because of the war in Ukraine.
Finland, which is in the European Union, has the largest land border with Russia of any EU country and has also applied to join Nato, an organisation that brings together the armies of various countries.
As a result, Russia has stopped supplies of gas and electricity going into Finland.
Now, "one of the big challenges is whether the [sand battery] technology can be scaled up to really make a difference." says the BBC's Matt McGrath.