solar power only when it's sunny, wind power only when it's windy and wave power when the sea's not too rough.

I'm Russell Beard and I've come to the south of Spain to visit Gemasolar,

the first solar power-tower station that can produce electricity 24 hours a day

but in order to get a real sense of the scale of this place I need to get a little bit higher

My heart is in my mouth a little bit but it's incredible

and I can't believe I'm flying this plane.

Sam just spotted the tower up ahead so he said just point at the tower and carry on.

OK here's Gemasolar. You can see it just below us now.

Thousands of these heliostats,

these revolving mirrors.

It's just amazing. It feels like we're looking into the future.

Photovoltaics are one of the fastest-growing energy sources

in the world at the moment but these aren't photovoltaics, are they?

No, not at all. They are not photovoltaics at all. They are just glass. They are mirrors

and they are reflecting the light to the top of the tower.

The reflected sunlight from the 2,650 heliostats

combined can generate enough electricity to power 25,000 homes

but only if they're pointing in exactly the right spot

Santiago has brought along one of these miniature parabolic mirrors

which I guess is almost like a perfect scale model of your solar tower.

Yes. I mean the tower is in the middle of a circle of heliostats

and every heliostat is taking a different angle

to reflect the light on top of the tower and

then to concentrate all the energy on a single spot. So let me try.

Oh wow! You can see it catching fire. It's so sensitive.

Like one tiny degree out and it stops burning.

I mean this must be the challenge that you're facing.

Exactly. Exactly what we have to be doing. We have to be very precise in moving the heliostats

into the right position

to concentrate the light there.

Sunlight is reflected from each heliostat to the central receiver

at the top of the tower. Sodium and potassium nitrate salts are pumped from the

cold salts tank up to the receiver where they absorb the concentrated solar

thermal energy

reaching temperatures of up to 565 degrees C.

The heated salts are then pumped into the hot salts tank where they can be

stored in a molten state or used to generate electricity

via the heat engine.

This is the hot

molten salt tank that contains the molten salts

at 565 degrees C.

This is like a big battery but it is a

thermal battery

it is not an electrical battery. In fact, the energy

that is accumulated here is enough to

continue operating the turbine for 15 hours

at full speed.

So this is what distinguishes this from other solar towers around the world.

It is actually that storage.

Exactly. To store energy this way means that solar power can for the first time

be provided 24 hours a day

not just when the sun's shining. This is the vessel in which the water turns to steam.

In fact, you have water

at maybe 500 degrees C

at already 100 bars of pressure.

This is incredible. So what Santiago's telling is

despite how futuristic this all looks

the actual business end where they create the electricity

is much the same as any other coal-fired or even nuclear power plant. It's a steam-driven power plant.

Wow! Wow! This is what I'm talking about. Now this looks like a power station. And it is.

This technology's been around for hundreds of years. So really out there is the only sci-fi part of this building. By the time the power comes down from the molten salt we're talking about good old-fashioned steam turbines. That's what we can hear now coming out of those chimneys at the top.

We are going to be reducing our costs but also due to

oil prices going up

it will make it impossible to burn gas to produce electricity

and then our plant will continue to be delivering cheap and clean energy

to our children, let's say.