and we haven't really had a way of storing solar energy until very recently. but, over there, ten buildings full of batteries. so, it's a start. a pretty good one, too. babcock has the largest combined solar and storage facility in the us. the batteries can store a0 megawatt hours of electricity, which is enough to keep around 2,000 average us homes alight for four hours. of course, lithium batteries are just one way of storing energy to use later, and we've seen other methods before. there's electric mountain in wales, which holds water at a top reservoir until power is needed. it then releases it back down to a lake below. switzerland's air cave fills itself with compressed air and then blows it out to turn turbines. well, now, over in california, kate russell is on track to see a new solution. since the oil crisis of the 19705, california has invested heavily into wind and solar power,

with the latest state legislation calling for 50% renewable energy by 2030, and all new homes must have solar within two years. the state is way ahead of its target, so much so that they've had to start paying neighbouring states to take some of the energy from them. as we've heard before, the problem is storage. the grid was built to handle fossil fuel—generated power and storage solutions like hydroelectric dams are in short supply. batteries too are very bad for the environment, turning unused renewable energy into not such a green solution. california—based company aries have come up with one alternative. aries was really an attempt to think of a way to use the inexhaustible, always reliable power of gravity. right? we know gravity is going to be there for us. we don't have to worry about shortages or any of that.

so, how do we use gravity to store and then discharge power when we need it? one of the most efficient ways to move mass known to man, which people have spent billions of dollars to perfect, are railroads. right? 150 years of experience, incredibly efficient, steel wheels on steel rails are one of the most efficient ways to move mass. dubbed "the gravity train", energy is stored using electricity to push its weight uphill. when you want to take the energy out, you let gravity pull the train back down, using the friction of braking to slow the train in order to make power. it's the same way hybrid electric cars like the prius work. you see those wind turbines there behind me, they're completely still, even though there is clearly plenty of wind right now. it's not because they're broken, it's because there's no more room to store the energy they would create. and that's a problem the gravity train will solve. when you're into excess energy production, use it to power

the train up a hill, and when you want the energy back, you just send the train back down again. this demo train carries almost five tonnes uphill, storing energy as it goes. a full—scale installation will return 80% of the stored energy, which is not quite as efficient as a huge dam, but has a lot less impact. the amount of energy we store is the weight of the train times the height of the hill. simple mathematics. so the more weight and the higher the hill, the more energy we can store. we need long, gently sloping plains. but we had clients who approached us and said, "well, i only have steep, rocky, craggy mountains," so we've developed a new variation on the aries technology at almost vertical. in october, the company breaks ground on the first full—scale aries in the state of nevada. it'll be used to fine tune

the inconsistent energy flows that are a natural part of using solar and wind power. minute by minute, it will trim the imbalance between load and generation on the grid, so our trains may need to go uphill for a minute, they may need to go downhill for five minutes, they're constantly acting like a large flywheel, that allows the grid to stay at exactly 60 hertz. it's early days yet and the concept has still to be proved in nevada, but it could help solve one of the renewable industry's biggest conundrums right now, balancing the ebb and flow of nature—made energy in a more sustainable way. after we run 30 or a0 years providing energy storage and helping people, we can remove all of our facilities very quickly, 96% of them can be either repurposed or recycled, so only 4% of our facilities could ever go into a landfill. and we're trying to reduce that.

and we can then plant some native vegetation and six months later, you never know our facility was there. that was kate on a roll in california. back at babcock, i'm going for a solar—powered spin in an autonomous shuttle with its chief financial officer. so, i guess the motivation for having these autonomous vehicles is that you're encouraging families here not to have as many cars. correct. yeah, i think our thought is that over time, most families in the us have a two—car family. and so our hope is that we can get from a two—car to a one—carfamily, where you have your car for the family, perhaps, but if you have a car for a commuterfor work, you won't need it anymore, you can take an autonomous shuttle or an autonomous vehicle to work. and so, over time, which will take a long time, perhaps there are no cars. but i think, realistically, within the next 10—15 years,

you could see a time when you go from two—car to one car. you think the us government at the moment doesn't understand? i think they get it. i think they're getting it. the government's a little slow to move, typically. but i think in major cities, in major metros, where traffic and pollution are an issue, technology can come in and save a lot of that. i think governments are willing to step up and make sure this comes to fruition. and we're seeing that slowly. what we're hearing and reading about is that a lot of major urban cores are going to become — there'll be restricted access, if you're driving your car and you're trying to get there, you can't get in, up to a certain mile, three miles outside of the city core, you can't get into the city core without being in an autonomous vehicle, for instance. but outside of autonomous vehicles, i mean, building a city or a town that is sustainable, i mean, you're not going to be able to do this in colder, more crowded parts of the world. no, i think that's right. i think this is fairly unique. we've a unique situation here where we have the benefit of scale. there's not a lot people that own 18,000 acres of land. that's a big chunk of dirt. along with autonomous shuttles, babcock has its own water and waste facility, and as well as reclaiming

water, there's a restriction on the amount that you're allowed to use. the tin roofs reflect heat, making homes 10% better at keeping cool, and the ranch's on—site gym is environmentally friendly too, it's powered by the treadmills. 0ne incentive to get off the couch, i suppose. it is a commendable vision to build a town with all these sustainable values but i can't help thinking you can only really do this when you are building a community from scratch. i mean, could you imagine trying to retrofit an existing town with all of these technologies? you'd basically have to tear up the infrastructure and tear down all the buildings and start from scratch anyway. babcock has been built in the style of older towns to attract people who aren't necessarily fans of the new—build feel. hi, are you expecting me? people like the kinleys. mind if ijust step inside your air—conditioning and stay here forever? yeah, yeah.

they've got a robot vacuum cleaner... i just want to kick those things. ..a coffee—making fridge... no, it's set up so it won't spill all over the place. ..and, of course, an electric car. for richard, a self—confessed geek and actual real fan of click, babcock was his calling. just reading tech blogs all the time on the internet, and it sounded fascinating to me. i liked the idea that it was environmentally friendly and was looking forward as far as energy solutions. we — in atlanta — we lived just downwind from one of the biggest coal— polluting plants in the country, and i thought "that cannot be healthy". i think of it as guilt—free living. in the uk, when you have a small town with a central area that you can walk to, it encourages walking, so it's the lifestyle. and while the buildings may look like historic florida, for me, it was also all the technology,

all the — you know, having 1 gigabyte of fibre optic internet to the home... yeah, you like that — you definitely like that. and that's it for the shortcut of our sustainability special. the full—length version is available on iplayer for you to watch right now. check us out on facebook and on twitter at @bbcclick. thanks for watching, see you soon. hello. away from scotland it is a

bank holiday weekend. many of us got off toa bank holiday weekend. many of us got off to a reasonable start with good spells of sunshine this morning. equally we have had a few showers in northern ireland, eastern scotland northern ireland, eastern scotland north and east wales was showers feeding in through the cheshire gap and extending into parts of the midlands and the home counties. this is the weather tomorrow from the early satellite picture. the bank of cloud will be bringing something wet and windy tomorrow. this afternoon and windy tomorrow. this afternoon and this evening most of the showers will slowly start to fade leading the night dry. cloud will build across western scotland, northern ireland, wales and the south—west of england and outbreaks of rain. lows between seven and 11 celsius. we're inforan unsubtle between seven and 11 celsius. we're in for an unsubtle day tomorrow. the frontal system will be working its way eastwards, increasing the cloud

and strengthening the wind and bringing rainfor and strengthening the wind and bringing rain for many during the day. at dry and bright start in the eastern counties of england. rain in the west extending eastwards. some of the rain will be heavy, that italy over the higher ground. dryer in the afternoon. these are the average speeds. perhaps 30 to a0 mile an hour gusts on the western coasts. a damp and blustery day that it will feel fairly cool given the strength of the wind and the rain. it would be with us for a time tomorrow evening. they hang back of rain across scotland tomorrow night. the wins will start to lose their strength. for many will be a bank holiday monday. it looks as if it will be very similar to today with sunny spells and a scattering of showers. warmer with highs between

17 and 22 celsius. some spousal sunshine around with showery rain affecting north and western parts of scotland. that is it from me. goodbye. i'm annita mcveigh live in dublin. the headlines at 6pm... pope francis is in ireland, for the first papal visit in almost a0 years. he's spoken of his shame at the failure of the catholic church to address the abuse of children by priests. translation: the failure of ecclesiastical authorities, bishops, religious superiors, priests and others adequately to address these repellent crimes has rightly given rise to outrage and remains a source of pain and shame for the catholic community. i myself share those sentiments. i'm rebecca jones, the other

headlines this hour.... women in england are to be allowed to take the second of two early abortion pills in their own homes instead of in a clinic. ajewish man, who believes he was one of the people