at kabul�*s airport in the hope of fleeing the new taliban rulers. us department of defense officials said it would still take several days to fly out the 6000 troops deployed to secure and run the airlift. the british prime minister is due to chair a virtual meeting of leaders from g7 countries. it's expected he'll ask the us president to delay the withdrawal of american troops from afghanistan. the taliban have warned there'll be "consequences" if the us and its allies extend their presence into september. the iranian government has said it's prepared to ship more fuel to lebanon to ease their continuing energy crisis. the move would be in defiance of a united states embargo on iranian exports. petrol shortages are paralysing much of lebanon's economy and threatening essential services. now on bbc news: three

engineers leading the field in clean energy solutions come together for a special event presented by kevin fong at the victoria and albert museum, london. hello, i'm kevin fong, and welcome to the engineers: clean energy. we are here at the victoria and albert museum in london with a socially distanced public audience, a virtual audience from around the globe, and three of the world's leading engineers. now, the climate catastrophe threatens all of us. but these engineers are at the forefront of providing our world with real solutions. applause. please welcome henry snaith. he's professor of physics at oxford, and through his

engineering of low—cost photovoltaics, henry discovered a thin film of solar cells made of perovskite. it could be a hugely significant discovery, as henry hopes it will eventually double the efficiency of solar power and halve the cost. danielle merfeld is an electrical engineer who is chief technology officer and vice—president of ge renewables. ge is the biggest creator of wind turbines worldwide, and she and her team currently have over 40,000 wind turbines out in the field. she'sjoining us by video link from north carolina, usa. kristian eikeland holmefjord is here from norway after braving 10 days�* quarantine on arrival in the uk. kristian is at the forefront of efforts to develop battery—powered ships as project director of fuel cells at corvus energy. wind, solar batteries, ships — please welcome our panel.

applause. so, we're going to start with talking about where we are now, and i wanted to start with you, danielle. so, before we get started on the solutions, can we outline the challenge here? the international governmental panel on climate change has said that in order to avoid the worst ravages of the heating associated with climate change, we need renewable resources like solar and wind to provide 85% of global electricity by 2050. but where are we now, and what's the scale of the challenge that faces us? so, danielle, tell me a bit about how close we are to that 85% target? well, the good news is that wind and solar power have doubled in the last five years due to their plummeting costs. now, nearly one tenth of the world's electricity comes from wind and solar together. but if i think about it from the wind perspective, at roughly 8%, we have to get 40—plus, 40—50%. that's a huge leap from where we are today, to meet our net zero goals by 2050.

so lots of work yet to do. let me turn to henry, let's talk a bit about solar here. solar panels use silicon. can you explain how that technology works, and what its limitations are in helping us reach the goal danielle just outlined 7 so, silicon is a semiconductor. that's the material that's used to absorb sunlight and generate electricity in a solar cell. it works by absorbing sunlight, particles of sunlight, that we call photons, they carry energy, they're absorbed in the silicon and what they do is give electrons in that silicon extra kinetic energy, the energy from the photons transferred to the electrons, and those electrons, with that energy, can move around and they're freed from the lattice — they're freed from being bound and localised. and that's the current, in essence, those moving electrons, that if we contact the silicon on either side we can extract in an external circuit and generate current and voltage from the material.

now, in terms of the limitations, if we look at what's the optimum efficiency a single solar absorbent material could be, like silicon, they top out at about 25%. that's really the practical limit for an actual solar panel with today's silicon technology. so, i'm hearing 6%, 7%, 8% from danielle. i'm hearing 20% from you. we're not quite at that 85%. and all of this energy we generate needs storing, doesn't it? so, kristian, i know that you're a man of the fjords and boats and ships have been a constant thread throughout your life, even before you became a marine engineer. so, 90% of the world's trade travels by sea, as well as 3% of the world's greenhouse gases, it's estimated nearly half a million people die prematurely every year from the air pollution created by ships. your company created the world's first fully electric ship, a battery—operated ferry which has travelled the equivalent of eight times around the equator since

it was launched in 2015. but what are the challenges in scaling that up to ships that actually circumnavigate the globe? one of the key challenges i there is being able to fit that amount of energy or batteries you need inside a vessel. - what we've done now, we started with the smaller vessels, - the vessels that go back and forth a lot, such- as this ampere ferry, j that ferry in itself has the same amount of| battery as 25 teslas. and that's not a lot - of battery, but it's enough to go back and forth _ across a fjord and charge every time you go back and forth. now, this is fairly unique to ferries, going back- and forth, and a lot of larger ships are travelling - longer distances. so you need to scale up - the battery, becoming more power—dense inside a vessel, and then you also need - to look at other energy. solutions, you're looking at hydrogen—based fuel coming off the energy from wind - or solar, and then you employ| both the batteries and the fuel and fuel cells together.

thank you. now, danielle, i want to come back to you to hear about your latest prototype wind turbine, the haliade—x, unveiled in 2019. it is a monster of a machine, this thing. and i want you to describe for me its scale and efficiency, and how you get it to work. so, the haliade—x is the world's most powerful wind turbine in operation today. it's offshore, it has a iii—megawatt capacity, and the rotor — so, the distance from blade tip to blade tip — is 220 metres. so each blade is longer than the wingspan of the largest aircraft in the world. each spin of one of those blades can power a typical household for more than two days. so, a typical wind farm can power about a million households. and so this is incredibly

important in terms of being able to move to more wind power, more efficient offshore wind, and with every one of these turbines that goes out, you're saving about 52,000 metric tons of c02, which is like taking 11,000 vehicles off the road. wow, that is pretty, pretty impressive. henry, look, i want to turn back to solar for a second. perovskite is the material you've been working on. what is it, how does it work, and why is it such an improvement and such a possibility for the revolution of solar power? perovskite is a crystal structure. one of the unique aspects of them is because they're composed of three different ions, we can actually change the composition of these ions and that changes the optical properties and electronic properties of this material. this means instead of using a single material to absorb the sunlight, we can actually tune the perovskite to absorb in different regions and stack these materials on top of each other. now, this stacking of solar

cells on top of each other we call multi—junctions, and the simplest multi—junction is a tandem cell, two solar cells on top of each other. and the perovskite we tune to match perfectly silicon. it absorbs only the visible light and we let the silicon absorb all the infrared. and in doing that we actually fundamentally improve the efficiencies. if we made a perfect perovskite on silicon tandem cell, that would top out at about 45%. so we've fundamentally lifted the ceiling. and if we went one step further to anotherjunction, triple junction, three junctions, that would top out at just above 50%. so what perovskite does is lift the ceiling for potential efficiency and gives us a new path forward to go to higher and higher efficiency. so, i mean, substantial gains in efficiency here. how close is this really to being a real technology? is this now, or this is far—flung future? this is very near term.

you can't go out today and buy perovskite solar cells, but we're building a production line at the moment. we're talking about next year, the first cells and modules will be in production, and start to be deployed in the world. so this is all fantastic, this is state—of—the—art technology and engineering that is market ready or nearly market ready. so is the message i should get that you are going to gallop to my rescue when it comes to climate change? that i can carry on with my life as i always have, and everything is going to be fine, because the engineers are going to sort it all out? henry, i want to start with you. is that what i should be taking away from this? that is not what you should be taking away, but you should feel encouraged that there can be solutions. but we all need to... it's a challenging road ahead. there's a lot of scale that needs to happen from the industry, and we all need to embrace it, and embrace this change. the technology's there, but if it doesn't get

employed and deployed, then it's not going to work. thank you. kristian? yeah, i think accepting - what is happening on that side, as henry mentions, is crucial. and then an aspect that. i would emphasise as well is that we have to look at wasting energy - as unacceptable. we can't waste energy in any form of action. i so when the energy is. going to be challenging to harvest at large—scale, we're solving parts - of harvesting as much energy as we can in good ways, - and then we have - to use that energy as efficiently as possible. and before we open it up to questions, danielle, when it comes to the threat that climate change presents to us, who is going to do the heavy lifting? is it going to be the engineering or is it going to be the individuals? i think the biggest changes will happen at the country level. there's going to be a need for us, in terms of our public policy, to support these kind of technologies at scale. it will certainly develop and deliver lower—cost

solutions that are good for the individual, but the biggest challenge ahead of us isn't technology, it's public acceptance. it's support for improved permitting and collaboration on changes to ensure that migration patterns for birds are known, and we don't site wind turbines in those areas or wind farms in that space. but there can'tjust be a wholesale rejection of this technology because of the threat of something that would be negative. that collaboration is the real opportunity for us to work together. so it's a partnership, really, it's you delivering the technologies that make the future possible, and us adopting them and making the right choices to protect us from this growing threat. thank you so much. we're going to move to questions now. this is the engineers: clean energy. we've been discussing the future of solar energy, wind power and electrical storage, and i'm going to ask

who would like to ask a question of any of our clean energy engineers. hi, i'm ajay gambier, - iworkjust around the corner at the grantham institute for climate change - and the environment at imperial college. i i would like to ask, i is it a surprise to any of you that we are now in this world where we are seeing i cost—competitive clean energy that can compete with fossil . fuels, or was that, _ in your mind, an inevitability, and if so, why? i'm going to offer that to danielle. so, danielle? thank you, yes. i think it was inevitable, and one of the reasons why most in this space would say that is that we can see these learning curves of cost reduction over time, over decades of time. in solar, in wind, in battery, in most technical arenas, where the certain doubling, for example, the volume of this technology being put out into the world comes out

with a cost reduction. so each curve will have a different rate of learning. solar was a 24% learning curve rate, meaning for every doubling of solar power volume out in the world, it'd be 24% reduction in cost. and as you continue to see volume increase in these technologies you will continue to see cost reduction. thank you so much, danielle. so we are now going to go to scotland, to alastair, who has a question about nuclear energy. alastair? hello, today we've got representatives of wind and solar, which are often portrayed as the two examples of clean energy. but there are still huge challenges with the amount of land required and energy storage required — challenges which aren't faced by existing nuclear power technology, something i would argue we really need to prioritise. i wonder if you think nuclear should form a key part of the clean energy mix, and should be a large part of the discussion today, and if not, how do we ensure we invest in and choose the most effective technologies that are going to make the biggest difference to stopping climate change? i'm going to give that one over to kristian here. nuclear, it's a fair point, isn't it? we've talked about wind,

we've talked about solar, we've talked about ways of storing, but nuclear is here, and could do thejob. why aren't we talking about that? well, the major worst—case scenario is something - that we always look at, - and worst—case on a solar panel installation, let's say, i very worst—case could be a house burning down. worst—case on a windmill could be it tipping over. and crashing something. worst—case. and i'm not saying we don't... we engineer a lot of good safety barriers, safety - solutions, but worst—case is still a massive - nuclear reaction. there are, however, being done tremendous effort and work- on looking at nuclear options where that is not— the worst case. so the effort being done - there is going to bring nuclear towards a more realistic part i of that energy mix, but i think we've seen so many of thesej worst—case scenarios happen that the public- acceptance to it is going to take a long time. you need a long time to be i fully sure that the worst—case scenario is no longer a nuclear reaction that scales up - in a massive meltdown. thank you.

and henry, i have to briefly dive out to you because i know you used to formerly — well, you still identify as a physicist, albeit recently you've seen the light and come over to engineering. what do you think about nuclear? why did you go for solar physics rather than nuclear physics? well, on a personal note, i considered nuclear fusion, i considered working in fusion rather than solar at the outset, but itjust seemed too much of a long—term challenge, still too far off really mainstream use, and it remains today. nuclear fission works, works well. the big challenge is actually one of economics. it doesn't compete on cost. they have to be massive national projects — firstly have to be done at scale, you can't do a small nuclear plant, it's gotta be a large one, what do you think about nuclear? why did you go for solar physics rather than nuclear physics? well, on a personal note, i considered nuclear fusion, i considered working in fusion rather than solar at the outset, but itjust seemed too much of a long—term challenge, still too far off really mainstream use, and it remains today. nuclear fission

works, works well. the big challenge is actually one of economics. it doesn't compete on cost. they have to be massive national projects — firstly have to be done at scale, you can't do a small nuclear plant, it's gotta be a large one, they're big long—term projects and they don't compete on cost. the cost of electricity from nuclear is the only technology that keeps going up, so the plants are getting safer and safer, but with that, the cost is actually increasing, so it will cost a lot. then you can ask the question, well, even though it costs a lot, do you still need it? because we can do it. another challenge with nuclear is it produces constant power very well so doesn't actually do so well at offsetting peaks and troughs of solar and wind. so, my slightly biased opinion is we need to generate most of our power from solar and wind — certainly hydro where it's in existence — and then use production of hydrogen or fuels and power gas—fired turbines if we need them. if they can fill the gap for winter power, for instance,

in the uk where we use the stored hydrogen, use that as a power source. so it's traditional power stations, but using green hydrogen as the power source. thank you. i'm going to look for another question in the room here at the v&a. hi, my name is shivika from imperial college. i just want to know about the future regarding the airborne wind turbines. what do you think that in the near term there is a future for airborne because google investing in airborne wind turbine system, we've seen one — first wind turbine system in germany. so what is the future of that technology? so, we've had land, we've had sea and now we're asking about air turbines. i'm fascinated to hear the answer to this. for those who haven't heard about this concept — the airborne—based wind farms are essentially like kites or tethered aeroplanes that are released up into the very high atmospheres, essentially at a very high altitude.

they circulate and move around in the sky and generate electricity through their motion. generally they're much more costly than traditional wind or solar, and there's the challenge of taking an efficient power off of that kite or aircraft. so i think there will be a niche for this. certainly i don't want to depress anyone�*s ideas about going after new technologies, but it's very much a smaller opportunity in terms of new potential cost reductions and scale. thank you. and we're now going to go to indonesia, a question about geothermal energy. yes, in indonesia there's a lot of volcano. so, how is the potential to tap energy from this volcanic chain, from the island, from sumatra for power, and what is the risk of injecting water to get steam from the magma inside?

so i think... oh, this is an interesting question, isn't it, about the ultimate energy store here, really, other than the sun. you know, geothermal energy, kristian, this is really the mother of all batteries in many ways. so, what is its potential and why, really, haven't we spoken about it much today? well, it definitely has i geographical potential. so the locations where it. exists and is easy to enter into and harvest, so, for instance, iceland| is a great example i of geothermal power. they are very close to that. and, as you say, in indonesia, there's a few different . geographical places that are well—suited and those i will employ that geothermal power, but it will be i a challenge to get it up to a scale where that power also is transmitted to all. other places in the world. so having solar panels, - wind power located more spread around the world compared to what you have _ with geothermal power. so i think we'll see more - and more geothermal power on the various locations -

where it's possible to have it. the risk is, as you mentioned, it's a challenge, _ an engineering challenge, - to handle that amount of heat and amount of energy, - but it's still fairly solvable, it's solved in a lot of power plants, so i think we'll see| more and more of them, i but the scale is really hard. it's hard to scale that up to cover huge amount i of the world's energy needs. you'll cover percentages, but you're not going - to cover 100% of the world. the world is a big battery, but it's hard to harvest it. | thank you so much. i'm going to come back to the room here at the victoria & albert museum and see if there are any questions. and there's one over to my right there. thank you.

jane sutton from the royal academy of engineering. just on your point about balancing demand. a few years ago, there was a lot of chat about a european super grid to share renewable electricity, and we've even had a presentation from somebody who was looking at a global super grid. do you think that's possible? would it be helpful to balance demand in different parts of the world? i actually want to let danielle take that one. a global super grid sounds like your sort of scale with your quarter of a kilometre wind turbines. yes, thank you. what do you think? i'm so glad this question was asked because that's one of the... there's actually two components to the rollout of a significant scale of renewable energy that we haven't talked about. one is the ability to balance those demand changes over time and balance the geography and the weather patterns over space by connecting more of our regions together. so the super grid idea, evenjust regionally

connecting within a continent, gives us so much more flexibility and resilience and reliability of our grid and reduces the total amount of capacity that we need to have installed, because we're seeing variation that we can tap into — if the sun is not shining here, the wind is blowing there. if it's very hot and sunny here, you've got hydropower or wind power, in another region. connecting us will be a very big part of that. the second part that's quite related is demand response. so how can those who are transmitting and distributing this electricity get signals back from industry or homes that they can, without the user noticing, reduce the load, either change the — turn off the defrost cycle of the freezer for 15 minutes, not even noticeable. 0r reduce the temperature of a cooling. these are the types of responses that we are going to have to get used to, it's not central hub and spoke, we're all part of this new electrical system together

and having us connected and having there be signals going both ways from generation to load is going to be a part of making it a more efficient global system ultimately. thank you so much. i think that that is it for questions from the audience, both here in the v&a in london and from around the world. thank you so much for those questions. i have one of my own to finish with. very, very briefly, are you optimistic or pessimistic about the gauntlet that is laid down before us of 85% renewable energy to be met in the future — kristian? i'm optimistic we will reach it, but it will require - sacrifices in a lot of aspects of, well, public acceptancel and the technology we need to develop to solve it. - thank you. henry. and i'm, you might argue, over—optimistic. firstly we shouldn't just aim

for 85%, it'll be 100% by 2050, and i see that very feasibly happening. we've got 20 years of continued learning, 30 years by 2050. by the time we get there, the cost of electricity will be so much cheaper than today's cost, including storage and redistribution, that actually we'll see a step up in wealth across the world and many other places coming up to the levels of wealth that we're used to in the uk, so i actually see this as a massively exciting transition. it's a daunting change, but if we embrace it, actually, this is the next transition, next step advancement for society and well— being for humankind. and for the last word, danielle. so i would say i am very optimistic, knowing that prices will continue to come down, there will be more people with access to energy, living better lives, bringing more people out of poverty, because, not in spite of, this growing amount of renewable energy. creating more jobs, internationally.

my only reservation would be that there are so many people in the world who either think this is purely a technology issue, which is separate from their life, or something that they don't need to think too much about or be a part of, and as i mentioned before, the biggest challenge is how the public accepts how we manage to lobby our governments and we think about the priorities that we want to make in our society. and that's it from the engineers: clean energy here at the victoria and albert museum in london. on behalf of the bbc world service, our partners, the royal commission for the exhibition of 1851 and all of us here, a huge thank you to our brilliant engineers, kristian eikeland holmefjord, danielle merfeld and henry snaith.

applause. hello there. county tyrone in northern ireland was the warmest part of the uk on monday. and over the next few days, generally, it's going to be the western side of the uk that sees the highest temperatures and the best of the sunshine. the high—pressure is still in charge of our weather, so essentially it is fine and dry. coming in off the north sea, though, there is this cloud that's pushing towards northern england and eventually it will work towards parts of wales and it could produce a few spots of drizzle, some mistiness over the hills. mist and fog patches and scotland and northern ireland will lift, the sunshine comes out and south of our cloud will get some sunshine across more so than parts of england, as well. let's move northwards though into the northern aisles. cloudy skies here, certainly

pegging back the temperatures. but elsewhere in scotland, many places enjoying lots of sunshine. temperatures in the west getting up to 2a or 25 degrees. sunshine for northern ireland, higher temperatures in the west of the country, more cloud than for northern england and particularly as you head towards them north midlands, lincolnshire affecting mid and north wales. south of that, sunshine, stronger wind through the english channel affecting the south coast of england. many parts of the country and to stay with some sunshine, still some cloud in central areas, more cloud into the northeast as well. that is where we will see the weather front approaching as we head into wednesday. still got high pressure in charge, mind you. still some stronger winds as we head to wednesday across more southern parts of england and through the english channel. we still have this cloud in central areas drifting down perhaps across the midlands, wales, maybe even a little further south, allowing more sunshine in northern england, northern ireland, and in scotland away from the northeast. typical temperatures around about 21 degrees or so. but higher temperatures again across northern ireland, western scotland and this time in cumbria. maybe not quite as warm in yorkshire and headingley, but should be dry for day one of the third test. but more cloud and a cooler feel certainly, i think, for day two on thursday. that is because we will have

a strong wind coming off the north sea behind this weather front here, which is more a band of cloud than anything else that will stretch its way down towards wales and the southwest. that cloud tending to break up through the day. but with the stronger winds down to its eastern side of scotland and particularly eastern england, we will have more cloud feeding in here, much cooler on thursday, down to the north sea coast, up to 15 or 16 degrees. it's out to the west that we'll see the best of the temperatures and the best of the sunshine.

welcome to bbc news — i'm david eades — our top stories... eight days to the evacuation deadline in afghanistan — but can foreign troops stay longer? the taliban suggests it won't allow it. that is a clear violation, one thing. secondly, about consequences, it is up to our leadership how to proceed. g7 leaders prepare to discuss what would happen next if the rescue operation is not complete by the end of the month. if their timetable extends even by a day or two, that will give us a day or two more to evacuate people. because we're really down to hours now, not weeks. lebanon turns to iran to help with an acute shortage of fuel, as the country

continues to spiral from one crisis to another.