hydrogen fuel cells combine hydrogen and oxygen to create a flow of electrons around a circuit to power a motor. and as we all know, hydrogen plus oxygen equals h20. the problem is... we can't do much about the fundamental properties of hydrogen. volumetrically, we need to compress it to get sort of in the ballpark of not quite a third of the efficiency of fuels that we use. that means that we need often very large, very heavy tanks, because they need very thick walls to deal with the incredibly high pressures we need them at. what you end up with is an aeroplane that can't have any passengers in. this is the challenge faced by zeroavia, one of several companies working to make hydrogen—powered flight a reality. they retrofit existing planes with hydrogen engines. the company had several successful test flights with this plane last year.

in the original frame, we would be able to fly about 19 passengers. it looks like a lot of kit in there. how would you fit in 19 people? yeah, so in the retrofitted configuration, it will be about a dozen people. daniela is one of the engineers working on the engine. actually, the fuel cells are this one. the power is created in these small layers. so you have to build up your layers to create the power to take off an aircraft. this engine could almost provide enough power to get you from london to glasgow, but not quite. if you wanted to scale it up for international flights, would you just make the same thing bigger or is it a totally different exercise? it is scalable until a certain power, but then we'll have to change technology. getting this high power density system that will allow to have a lot of power but minimal weight to be integrated on an aircraft is really a challenge.

and that probably means completely redesigning the plane. everything will be shrunk. some parts of the engine, of the fuel cell, will be sitting inside of the nacelle, and also the storage tank, which is, uh, going to be probably the largest, uh, you know, piece of equipment they will actually bring outside, 0k? right. so either on the side of the fuselage, or we will hang it on the wing. making everything fit isn't the only challenge, though. you need to have the maintenance and repair organisation. the whole process needs to be certified. we need to provide the hydrogen infrastructure to the, uh, to the aircraft. zeroavia has a plan for that. in its vision, hydrogen would be produced on site at airports using renewable energy before being processed and transported out to the plane. but what about the cost of all this? at the moment, liquid hydrogen is significantly more expensive

than conventionaljet fuel, but backers of hydrogen planes believe it will eventually become cheaper than traditional flight. zeroavia isn't the only company racing to reimagine air travel, though. aerospace giants like airbus and boeing are also developing hydrogen planes. but there are still questions over how sustainable they'll actually be. we're going to be using some fairly exotic materials that are very energy intensive to arrive at. what energy are you using to build the fuel cell? what materials are you using? how much energy are we sinking into this technology to get something out? zeroavia has the backing of the uk government and big investors and has over 2,000 pre—orders from airlines. so there seems to be significant belief in hydrogen despite all of the challenges. but what i really want to know is... are we going to be able to jet off

to spain anytime soon in a hydrogen plane? history shows that you need to start small and grow big. and that growth would take a while. but if this could be scaled to the largest of planes, then the difference to emissions would bejumbo. you know, it sounds like, if they can get it right, hydrogen planes could be a massive deal. yeah. it's as much about the infrastructure, though. they've got a lot to do. right, 0k, noted. 0k, we're going from the air to the sea now. you might not think of the world's oceans as a great source of green energy, but when you think about it, the tides move an enormous amount of water around the globe every single day, and we are discovering new ways to harness this tidal power. and adrienne murray has been to the remote faroe islands, which are between scotland and norway, to see what they're doing to help harness renewable energy.

rugged and remote, the faroe islands are an isolated archipelago found in the north atlantic. powerful currents flow around its 18 islands, and in this sea channel called the vestmannasund, mechanical creatures lurk beneath the water's surface, called dragons. designed by swedish marine energy firm minesto, it's among a wave of new technology that hopes to revolutionise tidal power. this huge yellow thing behind me is a tidal kite. it looks a bit like a glider because it's designed to fly through the water, and once it's installed on the sea bed, it will be generating electricity using the current that flows through this stretch of water. weighing 28 tonnes and with a 12—metre wingspan, the newest dragon can deliver 1.2 megawatts of power.

it's sort of like kitesurfing, but underwater. so we tether it off to the sea floor, foundation on the sea floor, and then it flies in a figure of eight. as underwater currents flow by, the kite's wings generate a hydrodynamic lift force, spinning the turbine and generating electricity. this design�*s very different to other types of tidal technology. so what's the advantage of a design like this one? we can install and operate and produce power in low flow currents with lightweight machines. although it looks big to the eye, this is actually a very small tidal turbine. we've designed the system as such to be maintenance friendly — you simplyjust tow them in, replace modules and then put them back in. we've also, over the years, removed more and more components from the system and fit them onshore instead. the less old components you have that could become damaged, it's easier to access it and it's much cheaper also.

it's the gravitational pull of the moon, and to some extent the sun, which gives the tides their rhythm. and unlike wind, solar or hydro, tidal power isn't reliant on weather. while tidal barrages have been around for decades, their cost and the ecological impact has been a barrier. now, from the scottish islands through to canada, a new generation of tech firms have introduced tidal stream turbines. 0cean energy is still largely untapped, so what are the barriers that have prevented it from taking off? it's a relatively small and new industry, so very few machines in the water, and then you have to compete with wind farms and solar pv, etc. we're now addressing a resource that's so much larger, so we're opening up a market that didn't even exist before. if all goes to plan, there could be arrays of subsea kites around the faroe islands, installed in groups similar to wind farms. so this machine here,

that's the first utility, or the array device. there will be many of these in parks, orarrays, as you call them, uh, around the world. the faroes aren't connected to any other country's power grid, so it has to be self—sufficient. and in the past, it relied heavily on oil imports. now, though, it's going fully green, and this battery station helps to regulate electricity supply. we have the biggest battery, i think, in the danish kingdom. we don't have any subsea cables to neighbouring countries. so we need to maintain the stability of the power system at all points in time on a millisecond level. much of the country's power will come from wind, hydro and solar, but that's also where its experiment with tidal energy comes in. it's predictable. we know exactly when it's there, 100 years ahead. if we install tidal turbines in different spots, we will have a baseload generation from tides, and that is extremely valuable.

if we can unlock the potential, it can really dramatically change the energy mix in the islands. maybe 30 to 40% of the annual usage in the islands could be provided by tides. now this dragon has begun to fly, and it's sending energy to the grid. it's just one machine, but potentially a big leap forward for harnessing energy from our seas. and that's it for the short cut of click this week. more in the full length version which is waiting for you right now on iplayer. . thanks for watching- _ you right now on iplayer. . thanks for watching. we _ you right now on iplayer. . thanks for watching. we shall _ you right now on iplayer. . thanks for watching. we shall be - you right now on iplayer. . thanks for watching. we shall be back - for watching. we shall be back next week.. ,, , .,

hello there. many parts of the uk had some lengthy spells of sunshine on friday, but there were a few showers around. the remain of some of this shower cloud in wolverhampton gave this fine end to the day, a fine sunset, and the majority of the shower cloud through friday afternoon was associated with a stripe of cloud you can see right here. this was actually an old cold front. the significance of that is colder air is behind it. and as we go through the next few hours, that will be pushing in across much of the uk. milder air recirculating around our area of high pressure into northern ireland and western scotland. so it's here through the weekend that we will see the nation's highest temperatures. now on to the next few hours, we're looking at that colder air arriving, a lot of dry weather, a lot of clear skies. and that means it's a recipe for things turning pretty cold. and heading into the first part of saturday morning, we start off with a frost, even some patches of frost, i think, across rural areas of southern england. the lowest temperatures probably down to about —3 celsius or so into rural areas of northern

england and scotland. for saturday, where we get this colder air moving in, for most, it's a glorious start to the day with clear, blue, sunny skies. a bit of cloud coming in to eastern areas of norfolk and suffolk and maybe a bit of cloud developing through the day elsewhere. some splashes of rain possible for the far north of scotland, but otherwise it's dry. the highest temperatures likely in northern ireland. we could see a 17 celsius here in the very warmest spots. for sunday, generally, there's going to be a bit more cloud across parts of scotland, thick enough for some splashes of light rain, fleeting rain, really, a few showers coming in across east anglia and southeast england, where we'll continue to have quite a chilly wind. could be even warmer for northern ireland if we were to get 19 celsius, well, that would be northern ireland's highest temperature of the year. so we'll be monitoring that carefully through the weekend. 0n into next week, high pressure stays to the west of the uk, and we continue to see this feed of cloud coming down the north sea. if anything, the cloud getting a bit more extensive, a bit thicker, and that means there's more likelihood of seeing some patches of drizzle across northern

and eastern scotland and some eastern areas of england as well. the best of the sunshine, probably parts of north west england, wales, south west england, northern ireland might still do 0k, and western parts of scotland, where the sunshine comes out, it shouldn't feel too bad. but if you're in the east where it's going to be quite cloudy with that wind coming in off the north sea, it will probably feel quite chilly. temperatures picking up a little later next week.

live from washington. this is bbc news. world leaders call for calm after us officials say an israeli missile hit iran. a 61—billion—dollar aid ukraine aid package moves one step closer to passing in the us congress. and — the us government is spending hundreds of billions of dollars to boost green manufacturing — we'll look at its impact on the economy. hello. we start in the middle east, following last night's strike on iran, which is widely

considered to have been carried out by israel in response to last weekend's attack by tehran on saturday. the white house has declined to comment on the strike. and despite further questions from reporters, white house press secretary karinejean—pierre said the biden adminstration didn't have "anything to share". earlier, us secretary of state antony blinken repeated calls for de—escalation in the middle east. the united states has not been involved in any offensive operations. what we are focused on, but the g7 is focused on, and it is reflected in our statement ended our conversation is our work to de—escalate tensions, to de—escalate tensions, to de—escalate from any potential conflict. you saw israel on the receiving end of an unprecedented attack, but our focus has been on, of course, making sure that is really —— israel can effectively defend itself, de—escalating tensions, avoiding conflict, and that

remains our focus.