The Engineering Challenges of Renewable Energy

Engineering has given a lot to the world. It's transformed the nature of work, improve sanitation and help create vital infrastructure. The bad news is that to power the tools and processes behind those developments, we've relied on non renewable fuels, the kind that get produced at a much slower rate than we use them. As the name implies, non renewables won't be around forever. Resources like oil and natural gas might be gone in just half a century. And using them has been, frankly, pretty terrible for the environment. 87% of the harmful carbon dioxide emitted by humans in the last 50 years has come from burning fuels such as coal, oil and natural gas, known collectively as fossil fuels. It's been terrible for the atmosphere, in oceans, and is changing our climate in dangerous ways. Whether we like it or not, we're going to have to find new ways to power our world, despite their terrible effects on the environment and limited supply. For now, non renewables do a really good job of meeting our energy needs. In 2017, 80% of the power used in the United States for supplied using fossil fuels. And the need for energy doesn't appear to be shrinking any time soon. Another 9% is delivered from nuclear vision, the process of splitting atoms, which releases far less CO2. Unfortunately, fission produces radioactive waste and also relies on non renewable fuel sources such as uranium and plutonium. All of these methods operate on broadly the same principle, essentially operating as a heat engine. A working fluid, often water, is heated by the fuel to expand and do work turning the blades of a turbine. The turbine is connected to an electrical generator that converts the rotational motion of the blades into electrical power, which has then fed into the grid. So what about the remaining 11% of power that came from renewable energy sources, the kind that are generated about as fast as we use them. Some of the major renewable energy sources come from processes that are naturally occurring on earth, wind power, solar power, hydropower, which is based on flowing water, and geothermal power, which uses the heat of the earth deep underground. None of these sources, the things will run out of We have a good few billion years left of sunlight, E.G. And what's more, renewable energy tends to release fewer harmful byproducts like carbon dioxide, into the environment. Take hydro power, e.g., which converts the kinetic energy from the motion of running water into electrical power in a fast flowing river Run of river power plant diverts, part of the rivers flow, sometimes through a tunnel to turn the turbines of a generator. That works well in some places. But the problem with this approach is that it's tricky to control the generation of energy to meet demand. You don't want to put lots of power into the grid when it won't get used, and you want to be able to ramp up the supply when the demand suddenly spikes, like during the half time break, when the English football team that sockety you Americans played Columbia in the 2018 World Cup, a huge number of people in the UK open their refrigerators to grab a drink or a snack, causing the compresses inside them to turn on. Then there were the people who had already had a bunch of drinks. All those people simultaneously flushing their toilets during the break created an increased demand for power on the local pumping stations that maintain pressure in the water system. The total increase in demand was measured to be 1200 mw. That's an extra demand for power equivalent to several power plants. With fossil fuels, you can control the amount of fuel being burned and therefore the amount of power being produced. One of river power plants struggle with this because the amount of power they generate depends on the flow of the river, which in turn depends on things like the rainfall during the time period and even the temperature, both things we can't control. To get around this, the more common form of hydropower is a hydroelectric dam. In this case, you can install a dam that floods an area and creates a huge reservoir of water. The water then falls through the generators turbines at the bottom of the dam, which turn the water's kinetic energy into power. If you install an intake valve that opens or shots to control the water flow through it, you can even manage the production of energy to meet the changing demands of the electrical grid. Unfortunately, flooding an area with water isn't consequence free, changing the environment so suddenly and preventing the natural flow of water downstream can have devastating consequences for the local ecology. There's also the risk of the dam breaking if it was built improperly. Despite those challenges, hydropower has been enormously helpful in recent years. It produces as much as 16% of the world's energy and up to 70% of all the world's renewable energy. The other renewable energy source that works in a similar way to hydro power is wind power, which also uses turbines. The main difference is that the flu don't work on the wind turbines is air instead of water. One of the biggest engineering challenges here is designing the turbine blades to efficiently extract energy from that air. As we saw were fluid mechanics, Predicting the flow of a fluid around an object can get seriously tricky. Blades have to be engineered to withstand the stress the subjected to, while also allowing the wind to efficiently rotate them to power the generator. It's as complicated as designing an airplane wing. Once again, you run into the problem of demand. You can't control the strength of the wind to increase or decrease power generation as you need it. Even if that were possible, you'd still have to transport it from the sparsely populated open plains, where the wind blows more easily, to dense urban centers with low amounts of wind, but high demand for power. Transporting that power becomes even trickier over long distances, because you lose some energy as the electricity travels through the wires. For that reason. In others, engineering considerations often play a big role in deciding where wind farms, as a collection of turbines is known, should be built. So wind power has only generated 4% of the world's total power supply in recent years. Location also plays an important role in another renewable energy source geothermal power. Like conventional power plants, geothermal power relies on steam as the working fluid on the turbines connected to the generator. But in this case, you don't need fuel to generate the steam. You can drill into underground deposits of hot volcanic rocks, normally near the Earth tectonic plate boundaries, to use them as a heat source for a power plant. Then all you need is to pump water to that location and create another channel for steam to rise through to do work on the turbines. The biggest problem comes with setting up a geothermal power plant in the 1st place. It can be expensive to drill and explore for underground conditions that are exactly right, and is only really possible in certain parts of the world, like Iceland and Italy. But there's one source of renewable energy that's so abundant and easily accessible you only have to step outside on a bright, sunny day to see it, solar energy. In fact, the amount of sunlight the Earth receives in just a single year is twice the total amount of energy that will ever be extracted from fossil fuels and the uranium used in nuclear fission combined. The challenge is finding efficient ways to harness that energy, because turning sunlight into electricity isn't simple. The most promising technology we have is called the photo voltaic or simply PV cell. Most people know them by the name given to many cells arranged together solar panels. Unlike everything else we've looked at, there's no trace of a turbine wine here. Instead, as we saw when looking at semiconductors, solar panels used two different semiconducting pieces to set up an electrical field that biases the movement of free electrons inside the material in a particular direction. In short, the materials encourage an electrical current to flow when they receive energy, which then travels through the circuit, delivering power to whatever is connected to the PV cell. That means solar panels can deliver power directly to the grid. Between that and the abundance of sunlight, it seems like there shouldn't be an energy shortage problem at all. But as we've seen for the other energy sources, costs, fluctuating demand, location and transmission, all factor in here. For starters, solar cells aren't all that efficient. The very best solar cells can convert 40% of the energy they absorb into electrical power. But they're expensive to produce because of the high quality of silicon needed in manufacturing, among other reasons. On average, industrial PV cells were about 17% efficient. Once you factor in the cost of making the cells and energy storage, solar power ends up being anywhere between three and six times as expensive to produce. Is that from fossil fuels. Increasing solar panels efficiency would bring this down dramatically. Another big challenge for solar power is that, like with the hydroelectric dam, you need a way to store energy, to control the production. In line with power demands, you won't generate much solar power on a cloudy day, whereas you might have a surplus on sunny days, but you can't store sunlight directly. Instead, engineers are working on ways to temporarily store that extra solar power. These include solutions like batteries, or even pumping water up a column to later give up its energy as hydro power during periods of high demand. Once again, though, efficiency plays a big role in making both these methods a suitable form of energy storage. Despite the efficiency and storage problems, there is one major advantage to solar panels. They can be deployed pretty much anywhere. Rather than having to transmit power across long distances, solar panels can simply be installed on smaller scales, close to areas of demand, even on the roof of an individual home. But manufacturing the panels themselves brings its own set of issues. One of the more materials used to currently make solar panels is caught, which has to be processed to produce the high quality silicon needed for making PV cells. This itself is an energy intensive process, which offsets some of the total energy production of solar panels across their lifetime of usage. Even worse, processing courts can often produce toxic by products like tetcher chloride, which can end up spilling into the environment and causing damage to soil. That all sounds a little bleak, but the most difficult challenges in engineering are often the most important ones. In fact, the National Academy of Engineering in the US has identified making solar energy more economical is one of the grand challenges that engineers in the 20 onst century need to solve. Future engineers have lots of ways to contribute towards making solar more feasible. Currently, researchers are looking at new storage systems, such as using solar power to drive hydrogen fuel production, which can be burned later on with no carbon dioxide emissions. More on that next time. Engineers are also introducing new materials into production of solar panels and improving the ways in which PV cells themselves are linked and arranged on the panels. There are even experimental methods being developed that use new structures on a molecular level called nano crystals. These increase the amount of energy given to the electrons and the material when light is absorbed, instead of losing the energy is heat. So that could drive the efficiency high enough to make it economically competitive with current power sources and increase the adoption of solar worldwide. So there are lots of challenges ahead in bringing renewable energy sources to the forefront of electrical power production, but that's all the more space for future engineers to have an impact and create new solutions to the world's energy needs. In this episode, we looked at renewable energy sources and why we need them. We looked at how hydropower, wind, geothermal and solar power are used to produce electricity. Some of the challenges face in doing so. In the areas engineers are working on to make their use more widespread. And our next episode will see how engineers have moved beyond natural processes to invent entirely new ways of generating power. Critical engineering has produced in association with PBS Digital Studios, which also produces Ions, a series that journeys through the history of life on Earth, with paleontology and natural history. Ions takes you from the dawn of life to the so called age of dinosaurs, and right up to the end of the most recent ice age crash. Course, is a complexly production, and this episode was filmed in the Doctor Charles c Kinney studio, with the help of these wonderful people, and our amazing graphic team. Is Thought Cafe. 

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                可再生能源的工程挑战

工程给世界带来了很多。它改变了工作的性质，改善了卫生条件，帮助建立了重要的基础设施。坏消息是，为这些工具提供动力在这些发展背后的过程中，我们依赖的是不可再生燃料，这种燃料的生产速度要慢得多然后我们使用它们。顾名思义，非可再生能源不会永远存在。像石油和天然气这样的资源可能在半个世纪内就会消失。坦率地说，使用它们对环境非常糟糕。在过去50年里，人类排放的有害二氧化碳中有87%来自燃烧煤炭、石油和天然气等统称为化石燃料的燃料。这对大气和海洋来说都是可怕的，并且正在以危险的方式改变我们的气候。不管我们喜欢与否，我们都必须找到新的方式来为我们的世界提供动力，尽管它们对环境造成了可怕的影响，而且供应有限。目前，非可再生能源在满足我们的能源需求方面做得很好。2017年，美国80%的电力供应来自化石燃料。而且对能源的需求在短期内似乎不会减少。另外9%来自核视觉，即原子分裂的过程，释放的二氧化碳要少得多。不幸的是，裂变会产生放射性废物，并且依赖于不可再生的燃料来源，如铀和钚。所有这些方法的运作原理大致相同，本质上就像热机一样运作。一种工作流体，通常是水，被燃料加热膨胀并做功转动涡轮机的叶片。涡轮机与发电机相连，发电机将叶片的旋转运动转化为电能，然后送入电网。那么剩下的11%的电力来自可再生能源，这种能源的产生速度和我们使用的速度一样快。一些主要的可再生能源来自于地球上自然发生的过程，如风能、太阳能、水力发电(基于流动的水)和地热能(利用地下深处的地球热量)。这些资源都不会用完，我们还有几十亿年的阳光更重要的是，可再生能源倾向于释放更少的有害副产品，如二氧化碳，进入环境。以水力发电为例，它在湍急的河流中将流水运动的动能转化为电能。河流发电厂使部分河流改道，有时通过隧道来转动发电机的涡轮机。这在一些地方很有效。但这种方法的问题在于，它很难控制能源的产生以满足需求。你不想在电网不用的时候向电网投入大量电力，你想在需求突然激增的时候增加供应，比如在中场休息期间，当英国足球队在2018年世界杯上击败你们美国人对阵哥伦比亚队时，英国有很多人打开冰箱拿饮料或零食，导致冰箱里的压缩装置打开。还有一些人已经喝了很多酒。所有这些人都在休息期间同时冲洗厕所，这增加了当地泵站的电力需求，以维持供水系统的压力。据测量，总需求增加了1200兆瓦。这对电力的额外需求相当于几个发电厂。有了化石燃料，你就可以控制燃烧的燃料量，从而控制发电量。其中一个河流发电厂与此斗争，因为它们产生的电量取决于河流的流量，而河流的流量又取决于时间段内的降雨量甚至温度，这些都是我们无法控制的。为了解决这个问题，更常见的水力发电形式是水电站大坝。在这种情况下，你可以建一个大坝，淹没一个地区，形成一个巨大的水库。然后，水通过大坝底部的发电机涡轮，将水的动能转化为电能。如果你安装一个可以打开或关闭的进气阀来控制流经它的水流，你甚至可以管理能源的生产，以满足不断变化的电网需求。不幸的是，用水淹没一个地区并不是没有后果的，如此突然地改变环境，阻止水的自然流向下游，可能会对当地的生态造成毁灭性的后果。如果修建不当，大坝还存在溃坝的风险。尽管存在这些挑战，水力发电近年来还是大有帮助。它生产的能源占全球的16%，可再生能源占全球的70%。另一种与水力发电原理相似的可再生能源是风力发电，它也使用涡轮机。主要的区别是流感对风力涡轮机不起作用的是空气而不是水。这里最大的工程挑战之一是设计涡轮叶片以有效地从空气中提取能量。正如我们在流体力学中看到的，预测物体周围流体的流动是非常棘手的。叶片的设计必须能够承受承受的压力，同时还要允许风有效地旋转叶片，为发电机提供动力。这就像设计飞机机翼一样复杂。你又遇到了需求的问题。你不能根据需要控制风力来增加或减少发电量。即使这是可能的，你仍然需要把它从人口稀少的开阔平原运输到人口密集的城市中心，那里风更容易吹，但风力较少，但对电力的需求很大。长时间输送电能变得更加棘手距离，因为当电流通过导线时你会损失一些能量。因为这个原因。在其他情况下，工程方面的考虑往往在决定风力发电场(一组已知的涡轮机)应该建在哪里时起着重要作用。因此，近年来风力发电仅占世界总电力供应的4%。地理位置在另一种可再生能源地热发电中也起着重要作用。与传统发电厂一样，地热发电厂依靠蒸汽作为与发电机相连的涡轮机的工作流体。但在这种情况下，你不需要燃料来产生蒸汽。你可以钻到热火山岩的地下沉积物中，通常在地球构造板块边界附近，把它们用作发电厂的热源。然后你所需要做的就是把水抽到那个位置，创造另一个通道，让蒸汽上升，对涡轮机做功。最大的问题是首先要建立一个地热发电厂。钻探和勘探地下条件的成本可能很高，而且只有在世界上的某些地方才有可能，比如冰岛和意大利。但有一种可再生能源非常丰富，而且很容易获得，你只需要在阳光明媚的日子走到外面就能看到它，那就是太阳能。事实上，地球在一年内接收到的阳光是从化石燃料和核裂变中使用的铀中提取的总能量的两倍。挑战在于找到有效的方法来利用这种能量，因为将阳光转化为电能并不简单。我们拥有的最有前途的技术被称为光伏电池或简称PV电池。大多数人都知道它们是由许多排列在一起的电池组成的太阳能电池板。不像我们看过的其他东西，这里没有涡轮酒的痕迹。相反，正如我们在观察半导体时看到的那样，太阳能电池板使用两种不同的半导体片来建立一个电场，使材料内部的自由电子向特定方向运动。简而言之，当材料接收到能量时，就会产生电流，然后通过电路，将能量传递给连接到光伏电池上的任何东西。这意味着太阳能电池板可以直接向电网输送电力。再加上充足的阳光，似乎根本不应该有能源短缺的问题。但正如我们所看到的其他能源，成本，波动的需求，位置和传输，都是这里的因素。首先，太阳能电池并不是那么高效。最好的太阳能电池可以将吸收的能量的40%转化为电能。但它们的生产成本很高，因为制造过程中需要高质量的硅，还有其他一些原因。工业光伏电池的平均效率约为17%。一旦你考虑到制造电池和能量储存的成本，太阳能的生产成本最终将是太阳能的3到6倍。是来自化石燃料。提高太阳能电池板的效率将大大降低这一比例。太阳能发电的另一个巨大挑战是，就像水电站大坝一样，你需要一种储存能量的方法，来控制生产。根据电力需求，在阴天你不会产生太多的太阳能，而在晴天你可能会有盈余，但你不能直接储存阳光。相反，工程师们正在研究暂时储存额外太阳能的方法。这些解决方案包括电池，甚至将水抽到一个柱子上，然后在高需求时期将其能量转化为水力发电。然而，再一次，效率在使这两种方法成为合适的能量存储形式方面起着重要作用。尽管存在效率和存储问题，但太阳能电池板有一个主要优势。它们几乎可以部署在任何地方。太阳能电池板可以简单地安装在更小的范围内，靠近有需求的区域，甚至安装在单个家庭的屋顶上，而不必长距离传输电力。但是制造太阳能电池板本身也带来了一系列问题。目前用于制造太阳能电池板的更多材料之一是捕获，它必须经过加工才能生产出制造光伏电池所需的高质量硅。这本身就是一个能源密集型的过程，它抵消了太阳能电池板在其使用寿命期间产生的一些总能量。更糟糕的是，加工法院往往会产生有毒的副产品，如氯离子，最终会泄漏到环境中，对土壤造成破坏。这一切听起来有点凄凉，但工程中最困难的挑战往往是最重要的挑战。事实上，美国国家工程院(NationalAcademyofEngineering)已经确定，使太阳能更加经济是21世纪工程师需要解决的重大挑战之一。未来的工程师有很多方法可以使太阳能变得更可行。目前，研究人员正在研究新的储存系统，比如利用太阳能驱动氢燃料的生产，氢燃料可以在以后燃烧而不排放二氧化碳。下次再详细讲。工程师们还在太阳能电池板的生产中引入了新材料，并改进了光伏电池本身连接和排列在电池板上的方式。甚至有正在开发的实验方法，在分子水平上使用称为纳米晶体的新结构。当光线照射时，这些增加了给予电子和材料的能量吸收，而不是失去的能量是热。因此，这可以将效率提高到足以使其在经济上与现有的能源竞争，并增加全球对太阳能的采用。因此，在将可再生能源推向电力生产的前沿方面，我们面临着许多挑战，但这也为未来的工程师提供了更多的空间，他们可以发挥影响，为世界能源需求创造新的解决方案。在这节课中，我们探讨了可再生能源以及我们为什么需要它们。我们研究了水电、风能、地热和太阳能是如何被用来发电的。这样做会面临一些挑战。在这些领域，工程师们正在努力使它们的应用更加广泛。下一集我们将看到工程师们如何超越自然过程，发明全新的发电方式。《关键工程》是与PBS数字工作室合作制作的，PBS数字工作室还制作了《离子》系列节目，讲述了地球上生命的历史，包括古生物学和自然史。离子带你从生命的开端到所谓的恐龙时代，一直到最近一次冰河时代崩溃的结束。当然，这是一个复杂的制作过程，这一集是在查尔斯·c·金尼医生的工作室拍摄的，得到了这些了不起的人的帮助，还有我们出色的图像团队。是思想咖啡馆。