of an attack at kabul airport and advised their nationals not to travel there. the warning comes 2a hours after president biden highlighted the danger posed by extremists linked to the group calling itself islamic state. the pace of the airlift at kabul airport continues to pick up — with dozens of military flights ferrying close to 20,000 people out of afghanistan in the past 2a hours. the us has insisted american efforts to help people leave the country will continue past the august 31st deadline. a study in britain indicates that protection from catching covid—19 given by two doses of the pfizer and astrazeneca coronavirus vaccines starts to wear off within six months. the study�*s authors underlined the importance of getting vaccinated — but urged the government to make plans for boosterjabs. 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 us all. 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 thin film 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 ten 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 going 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 absorber 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 our 85%. and all of this energy we generate needs storing, doesn't it? so, kristian, i know 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, and 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 . here is being able to fit that amount of energy or batteries you need inside a vessel. - what we've done now, - we've started with the smaller vessels, the vessels that go back and forth a lot, - such as this ampere ferry. 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 over- 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 needl to scale up the battery, becoming more power—dense inside the 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 that 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 can 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 that 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 got to 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 already 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 and albert museum and see if there are any questions. and there's one over

to my right there. thank you very much. 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 will 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. we just had the hottest day of the month on wednesday. and it was western scotland the place to be. looks lovely in the sunshine and temperatures reached 27 celsius. now, it won't get as hot as that again through the rest of the month because we've got this weather front moving down toward the southwest of the uk. it's bringing in cloud, one or two spots of rain just for a while, and as that weather front moves through, so we introduce a cooler wind off the north sea. that's blowing in cooler air and it's dropping the temperatures as well. we start with some fog, though, quite extensively across northern ireland in the morning. not so much fog in scotland. the fog will lift. the cloud that we start with in wales and the southwest will break up. sunshine for many western areas. but the wind will continue to blow in more cloud to the eastern side of the uk. should get more sunshine, though, for the northern isles, some areas of cloud lingering across some easternmost parts of scotland.

much of the country, though, seeing the sunshine and temperatures 23, maybe 2a in the west of scotland this time. could make 22 or 23 in fermanagh and tyrone. always warmer for wales, western parts of england. down the eastern side, a lot of cloud, a cooler wind as well. and around the coasts in particular, temperatures could be no better than 16 or 17 degrees. there could be a hint of sunshine now and again, but generally it's going to be pretty cloudy at headingley for day 2 of an exciting test match. not quite so chilly on friday. by this stage, the cloud is pushing more towards wales and western parts of england, and that means we should get a bit more sunshine for the eastern side of england. there will be some areas of cloud for scotland and northern ireland, some spells of sunshine too, and temperatures are back down to around 19 or 20 degrees typically, perhaps a little lower than that in the far north and east of scotland. heading into the weekend, big area of low pressure is bringing lots of showers into central europe. they're not far away from the southeast on saturday, but over the weekend, it's high pressure that should tend to dominate. always a wind coming in from the north sea, some brisk winds for the southeast of england.

should be a fair bit of sunshine, though, i think, on saturday, some patchy cloud bubbling up here and there. and in the sunshine, again, across western scotland, we could see temperatures up to 22 degrees. second half of the weekend, still dry, high pressure around, bit breezy and cooler around some of those north sea coasts, a bit more cloud perhaps coming into scotland and northern ireland, sunshine for england and wales and temperatures typically 19 or 20 celsius.

you're watching bbc news — i'm rich preston — our latest headlines. the united states and britain warn their citizens to stay away from kabul airport — amid fears of a potential terror attack. but the scramble to flee the country continues — thousands of people remain at the airport — desperate to leave. is it worth it? is it betterjust staying here in afghanistan for the moment? translation: there's | no way we can stay here. the americans should shoot us or let us through. researchers say booster shots of the covid vaccine may be needed — in the wake of a study suggesting protection wanes after six months. and — a warning that the summer of devastating wildfires underlines the need for radical shifts in behaviour to tackle global warming.