Why Renewables Are Difficult

Renewable energy represents one of the most promising solutions to climate change since it emits no greenhouse gases. However, it poses some difficulties for power systems. Source: U. Leone

The issues of climate change and sustainability seem to be everywhere throughout politics, media and public sentiment, and represent a significant challenge for current and future generations. Making our lifestyles sustainable will require, among other things, drastic reductions in worldwide greenhouse gas emissions. One of the biggest sources of such emissions is the generation of electricity, and this proportion is expected to increase as electric cars, heating and the internet-of-things takes off. “Greening up” power supply is essential. The good news is that it is possible to generate electricity without any emissions whatsoever through renewables. Examples include wind turbines and solar panels, which are called renewable since their source of energy (wind and sun respectively) do not run out. This can be contrasted with fossil-fuel generation, which uses finite fuels such as coal, oil or gas, and emits greenhouse gases.

Renewable technologies have been around for years, and public awareness of the need to reduce greenhouse gas emissions since around the 80’s. However, most countries still generate the vast majority of their electricity from non-renewables that emit carbon or damage the environment in other ways (e.g. nuclear waste). Why, after decades of both the problem and a solution being known, haven’t renewables taken off yet? This article hopes to give the reader a sense of why renewables are “difficult”, and how the world can keep the lights on into the future in a cheap, secure, and sustainable way.

Until recently, the primary reason for the slow uptake of renewables was economical. It was impossible to build wind turbines and solar panels cheaply enough to compete with fossil fuel technologies, which had become highly cost effective after more than 100 years of use. While there was some effort, governments were not willing to spend billions on subsidising renewables when electricity could be generated cheaply in other ways. Mark Rutte, the Dutch prime minister, frequently claimed in debates between 2010 and 2014 that “windmills are only powered by subsidy” (link in Dutch). However, as time passed, improved manufacturing methods, economies of scale and increased competition has sent prices plummeting. The price of solar panels has decreased by a factor over 100 in the last 40 years, and generation through many renewables is now cheaper than fossil fuels.

So, is it just a matter of time before fossil fuel electricity disappears? Why are societies still so hesitant to go 100% renewable? To understand why, a quick introduction to power systems (meaning the industries, infrastructures and markets based around electricity) must be given.

At their core, power systems are simply supply & demand problems. Industries and consumers use electricity that is provided by generators. One key feature distinguishes power systems from other economic markets: there is virtually no means of storing it at large scale (with the notable exception of hydropower, discussed below). This implies that supply & demand must be continuously matched exactly, and makes managing the grid both complicated and essential. Usually, some independent party, called a system operator, is issued this task.

(As an aside, in the UK, there is a fantastic website, called Drax Electric Insights, in which the total UK electricity demand, and exactly from which sources it is being generated, can be browsed through in real time as well as historically. Looking through it for a few minutes will give a better feel for how power systems work than any blog post can).

A still from Drax Electric Insights, where electricity demand and generation levels can be browsed through, both in real time and historically. Source: Drax Electric Insights

Before renewables, most electricity was generated by fossil fuel plants. Fuel (e.g. coal or gas) could be burnt at different rates, and level of electricity supply was directly adjusted to meet demand. One caveat to this is that output levels in some types of plants cannot be adjusted arbitrarily quickly. To combat this, planners use baseload generation to generate most electricity, and peaking plants, whose output could be varied rapidly, to meet short-term fluctuations in demand. For example, the UK’s system operator had to deal with a massive demand spike just after the royal wedding, as millions turned on their kettles at the same time. Throughout the rest of the article, the term conventional generation will refer to generation through fossil fuels for which the output levels can be directly controlled.

A famous graph showing total UK electricity demand during the 1990 World Cup semi-final against Germany, with spikes at times that viewers turned on their kettles en masse. System operators had to rapidly adjust supply to ensure the lights stayed on. Source: National Grid

With renewables, the single biggest difficulty is that their production levels typically can’t be controlled. It’s not always windy or sunny, and times of high renewable output do not always align with times of high demand. How does one ensure the lights stay on on a cloudy day or when the wind tails off?

In most countries, this is not yet a problem since renewable capacity is small and their output never exceeds demand. Renewables produce whatever electricity they can, and the rest is picked up by conventional generation. Two complications warrant mentioning.

Firstly, the flexibility required from the grid increases. As well as just demand fluctuations, systems must also be able to deal with renewable output variability. To prevent blackouts, conventional generation (fossil-fuel power plants whose output can be controlled directly) must be able to ramp up quickly enough to meet a simultaneous demand spike and rapid drop in wind levels. In the Netherlands, in May 2018, the domestic grid was unable to respond quickly enough to an unexpected drop in wind-speeds and associated wind power, and required emergency imports from Belgium at high cost (link in Dutch).

Secondly, the advent of renewables changes the economics of power markets. Power plant owners tend to have a standard business model: build an expensive power plant and pay off the investment cost using the proceeds from the sale of electricity. For this to work, electricity prices need to be high for a large proportion of the time. When renewables are added to the grid, this changes: at times of high wind or sun, they produce electricity virtually free, pricing out conventional generation. This means that investing in a conventional power plant, or keeping an old one open, may no longer be economical. However, if this happens, when renewable output is low, there is no conventional generation left to provide power! To counteract this effect, many countries, including the UK, host capacity auctions, in which they subsidise producers to meet demand when necessary. In this way, while renewables displace conventional generation, they tend not to allow for the permanent closure of conventional plants. Note that this economic reality applies to renewables too: the more wind is added to the grid, the more it pushes electricity prices down at windy times, thus eating into its own profits.

(Two additional complications, which will not be discussed at length here, are the issues of transporting electricity from windy areas to demand centres, and frequency stability through inertia. In Germany and Ireland, these issues have already led to multiple occurrences of wind curtailment, in which wind farm owners are paid to turn off their turbines).

The issues of both flexibility and supply security will intensify as more renewables are added to the grid. Thankfully, there are a few ways that society can both use renewables and keep the lights on in the future. They fall broadly into two categories.

The first is electricity storage. With grid-scale storage, excess electricity production on windy or sunny days can be stored and used in times when renewable output is low. Besides adding to supply security, this would enhance the economic picture for renewables since storage owners buy up electricity when price is low and sell it when price is high, evening out price jumps. At present, the reason storage plays only a small role is economical. Battery prices still have to drop significantly before they can be used at large scale.

The second possible solution is by interconnecting different countries better and allowing them to share electricity. When it is wind-free in London, the chance is high it is in Scotland as well. However, it may be windy in Germany or Spain. Transporting electricity around could help alleviate supply insecurity. The UK currently has interconnections with France, the Netherlands, and Ireland, and more are in the pipeline. This may eventually become what has been termed the European Supergrid, where electricity can be transported across Europe to balance out regional renewable supply peaks and troughs.

There is one important exception to storage being uneconomical: hydropower. It has been around since the early 1900’s, and typically involves a high dam being built in a river, creating an artificial lake and an elevation difference on either side of the dam. Water is allowed to flow down the dam, powering a turbine to generate electricity in the the process. The generation levels can be controlled by adjusting the flow level, and there is a natural storage function: when demand is low, water is allowed to accumulate in the lake. In this way, the lake is “charged” by nature when it rains and water from the mountains flows into it.

Hydropower provides an economical option to store electricity, but requires mountainous terrain. Source: skeeze

Hydropower is a great form of electricity since its output can be controlled and has no associated greenhouse gas emissions. Norway, for example, generates virtually all its electricity from such dams and exports power to other countries when their demand is low. A difficulty is that hydropower requires mountainous and rainy terrain, which not all countries have.

(Since hydropower is so convenient, some developed countries are attempting to engineer their own forms of hydropower even without the above-mentioned terrain. In the UK, a notable example is tidal power, in which an artificial lagoon is constructed that water can enter and exit through turbines, generating power. At present, there are fierce discussions about the economics of such a project.)

The prospect of combining hydropower and interconnections between countries is tempting, since it means countries with lots of wind but little storage capacity, like Germany or Denmark, could “use Norway as a battery” by exporting their excess wind power to Norway in windy periods, who allow their dams to accumulate water. In calm spells, the hydropower generation levels could be increased and excess electricity exported back the other way. Making this work will require significant increases in Norwegian hydropower infrastructure, interconnection lines and international cooperation.

The batteries in electric cars can be used for grid management provided that owners agree to this. Source: Marilyn Murphy

Another creative solution to the storage problem is to use the big and expensive batteries in electric cars. Electric car uptake will lead to demand spikes when people return from work and plug them in to charge. An electric car owner could get the option of cheaper electricity if it means her car’s battery is not charged, or even emptied, during demand spikes and recharged when demand is lower. This presents interesting dilemmas: suppose you arrive home from work at 6pm and will leave again the next morning at 8am. Would you accept a cheaper charging price, if it meant your car might not be charged if you had to leave unexpectedly at 8pm?

Current power systems are not yet ready to use renewables for the majority of their electricity supply. However, the immediacy of the climate change danger means business-as-usual is not an option, and a total energy revolution is required, including in the electricity sector. Presently, the most realistic short- and medium-term solution is the use of renewables. This article hopes to give the reader a sense of the problem, why renewables are “difficult” and some the possible solutions. It is an exciting time to be in energy, and nobody knows how the power system of the future will look. But everyone agrees it will be very different.

FAQ: Why do HFCs and CFCs contribute more to warming?

This question came from a young relative of mine doing a school project on climate change and it’s a really interesting one, bringing in a lot of important concepts about the climate that aren’t explained as much as they should be. Here we go!

Ultimately, it’s the sun that warms the planet. Well, okay, there’s some heat coming from the core, but the crust’s rock layer does quite a good job insulating so we can pretty much neglect it. I think we can agree that the sun is the hot thing – much much hotter than the ground.

As the sun heats up Earth, Earth needs to be being cooled down in some other way, otherwise it’d just get indefinitely warmer. There’s enough heat coming in from the sun that if we didn’t lose any, the surface of the planet would get considerably hotter every day!

We lose it through “earth-shine” or outgoing long-wave radiation, in the proper lingo. In the same way that the sun gives off light and heat we can feel when we go outside, the earth is giving off its own electromagnetic waves, just at a wavelength we can’t see. Wavelength is like colour: red, blue and yellow light are all different colours, but so are x-rays and radiowaves and what wifi and cell phone signals are transmitted through.

https://marine.rutgers.edu/cool/education/class/josh/em_spec.html

But since the sun-shine and earth-shine are at different wavelengths, they’re blocked by different things. Glass isn’t see-through to all light and nor is the atmosphere. Let’s take a close look at the diagram below:

http://cybele.bu.edu/courses/gg312fall01/chap01/figures/

The wavelength is measured in micrometers, which are million times smaller than a meter. The middle of the sun’s shine (“black-body”) curve is in visible radiation, very little of which is absorbed by the atmosphere (see the same region on the lower plot). For the earth-shine, it’s not so lucky. About 80% of the outgoing earth-shine doesn’t make it out – it gets trapped and re-emitted by the molecules in the atmosphere.

Those molecules work to block radiation because of their specific shape and how well they resonate (match) with the light at each wavelength. Water is really really good at it absorbing radiation at loads of wavelengths, but CH4 (methane) and CO2 (carbon dioxide) do a reasonable job too. They all block the outgoing radiation and make the surface of the earth heat up, like the glass in a greenhouse lets sunlight in but keeps heat from going out. That’s why we call them greenhouse gases.

Water has a special place because there’s so much of it coming in and out of the atmosphere in clouds and rain. We think of it as a response rather than a cause because you can’t inject it into the atmosphere and have it stay. The same is absolutely not true for carbon dioxide, methane and HFCs (hydro-flouro-carbons) and CFCs (chloro-flouro-carbons). They get added to the atmosphere by some natural processes and, unfortunately, by humans who have use them for fire extinguishers and refrigerants, and once they’re there, they stick around, blocking the earth-shine and changing the natural balance.

The question of how bad a particular greenhouse gas is is a difficult one. The first is whether it’s doing a job nothing else can do. The atmosphere has a lot of carbon dioxide and water in it, so adding a little more doesn’t make as much difference as adding something which absorbs in the gaps. If you look at the diagram below, you can see that CFCs (and the same is true for HFCs) absorb in the ‘atmospheric window’.

https://www.sciencedirect.com/science/article/pii/S0007091217334049

This means that every molecule added absorbs some radiation that would otherwise have gone through. Methane is powerful like that too. For CO2, a molecule added doesn’t have so much power – there’s already a lot of them so that each additional molecule doesn’t go so far. This is measured in the radiative efficiency.

The other thing that makes a molecule strong is how long it sticks around for (the lifetime). Methane turns into CO2 after a little while (10 years) in the atmosphere thanks to the active chemistry (driven in part by the sunshine) that goes on up there. Some CFCs and HFCs stick around much longer – check out the IPCC table here.

Now, suppose you put different things in the atmosphere and wanted to know how bad they are. You’ve got to combine two things: one is how much of a difference they make themselves (that is, how good they are at blocking earth-shine and whether anything else would have been blocking it anyway) and the other is how long it sticks about. That’s why we think about global warming potential.

From the EPA glossary

Global warming potential (GWP): A measure of how much heat a substance can trap in the atmosphere. GWP can be used to compare the effects of different greenhouse gases. For example, methane has a GWP of 21, which means over a period of 100 years, 1 pound of methane will trap 21 times more heat than 1 pound of carbon dioxide (which has a GWP of 1).

It adds up how much damage each gas does times how much of it is around over the course of 100 years. Take those together and you get a table like the one here. CFCs and HFCs come out pretty badly, with a GWP in the thousands!

But there is good news: we don’t make as much of them as some of the less nasty things, especially since the Montreal Protocol which came in in 1989. That’s one big success for global political agreements to curb climate change!

 

A puzzle: 100 year timeline over which to calculate global warming potential doesn’t do such a good job of taking into account your great-grandchildren! Over the molecule’s lifetime, something long-lived (like CO2) might do a lot more harm than something short-lived (like methane). So what should we prioritise?  Comparing 100-year global warming potentials or calculating warming per molecule over the molecule’s entire lifetime?

 

Eco-espresso?

3LpAs of 2011, the top five biggest commodities in the world were (in descending order) crude oil, coffee, natural gas, gold and Brent oil. As a first note, the presence of three fossil fuels in this list means that there is still a long way to go in the transition to a low carbon economy. But, yes, what I was actually trying to point out is that coffee is the second biggest commodity in the world. An estimated 1.6 billion cups of coffee are consumed worldwide every single day, with an estimated 55 million in the UK.

As former president of the University of Manchester Coffee Connoisseurs Club (UoMCCC), I set out to try and establish what kind of impact drinking coffee has on the environment, whether it is an issue that so much of the stuff is consumed every day and to what extent it can be sustainably sourced.

Fair Trade coffee has become widely available in recent years, with many big brands displaying the Fair Trade logo on their packaging. In the UK, almost 25% of total coffee sales are Fair-trade – a proportion which is steadily growing. This is certainly a step in the right direction regarding the coffee industry’s treatment of humans. Regarding treatment of the environment, on the other hand, it is not so obvious that improvements are being made.

 

Can’t see the woods for the lack of trees

Coffee is naturally found and traditionally grown, in tropical and subtropical regions of the world, in forested and often mountainous areas. Under the canopy of trees, the coffee plant is sheltered from constant direct sunlight. The rich biodiversity means the soil in which it lives is healthy and, further, there are few pests which are able to damage the crop before being swooped up by a predator. A human seeking to harvest coffee beans from such a plant cannot expect to get the greatest yield for a unit area, but at least the crop was grown in keeping with nature and without any need for pesticides or herbicides.

Since the 1970’s, monoculture and sun-grown coffee have become the norm. It was recently reported that

“By the end of the 1990’s, sun or reduced-shade cultivation systems accounted for almost 70% of Colombia’s land area devoted to coffee and 40% of Costa Rica’s.”

By clearing away regions of forest, farmers were able to increase their yield. In Central America alone, 2.5 million acres of forest have been cleared for coffee farming. Clearly, this deforestation results in the utter destruction of ecosystems far older than our society and which are among the most delicate on Earth. In the world of coffee, there is a tragic trade-off between a higher yield and less ecological damage. Needless to say, the cutting down of trees implies a reduced capacity of the natural world to absorb climate warming CO2, especially when applied on an industrial scale.

By removing the other flora and fauna which originally lived in harmony with coffee crops, the soil quality degrades and pests have free reign, meaning fertilisers, herbicides and and pesticides are the commonly used, as in the majority of global agriculture. Clearly, less than perfect handling of these chemicals can lead to further ecological problems such as water pollution and contamination.

IntroToCoffeeBeans_Content2Of course, many of the ecological problems discussed above are not unique to coffee and apply to many other crops grown in hot conditions. One factor that is particularly relevant, however, is waste.

As can be seen in the diagram opposite, the marketable product which is the coffee bean is just one, inner part of the harvested fruit, known as the coffee cherry. As any coffee connoisseur will be aware, there are many different processes by which the pulp is separated from the bean such as honey processing, natural processing, semi-dry/wet-hulled processing, washed processing… The enormous variety of flavours of coffee available on the market may be attributed largely to these different methodologies, which have heritage in different parts of the world from Ethiopia, to Indonesia, to El Salvador. Despite differences in what is done after harvest, each of the methods eventually discards the pulp and many require additional water and labour.

For the coffee connoisseur, the diverse range of coffee processes, origins and formats (from espresso, to siphon, to frappe-latte-mochachino), is astounding. The sad truth is that in order to obtain this diversity, an even richer diversity is often sacrificed – that of age-old ecosystems.

 

In the hands of the consumer

Unlike some crops sold on the international market, which are flown, coffee is usually transported by freighter ship or train, meaning that the environmental aspects of its transportation are not so bad. However, once on the shores of the consumer, yet more problems abound.

Not least of these are the problems of the waste theme, such as disposable coffee cups. An estimated 25,000 tonnes of waste is generated by the coffee industry in the UK alone, with 2.5 billion single-use coffee cups thrown away each year.
Further, if you decide to save money and brew your beverage at home, there are climatic impacts due to the fact that the kettle is a profoundly energy intensive device. Assuming you do not have a renewable power source, a recent investigation at Imperial College London revealed that boiling 1 litre of water in the average electric kettle results in approximately 70g of CO2 being released into the atmosphere. England’s all-time highest TV-related electricity demand surge was during half-time of the 1990 World Cup semi-final with West Germany, when the whole country went and put their kettles on to make a brew.

1990-Semi-Final-Pickups
Electricity demand during 1990 semi-final. Source: national grid.

Now I am not going to propose that everyone should give up coffee and all hot beverages along with it, for the sake of the environment. But there are certainly ways in which changes in the consumer habit could lessen the impact of the coffee industry on the world we inhabit.

In direct terms, only boiling enough water as is needed and carrying a reusable cup are two commonly given, but far less often followed, pieces of advice which need no further explanation.

Sustainable coffee does exist. Recent attempts involve shade grown coffee, which mimics the way coffee grows naturally, in tune with nature. Whilst coffee grown in this way is sometimes more expensive, its environmental impacts are much less than the conventional farming methods, the social responsibility is significantly higher and the benefit for ecosystems is great. The Huffington Post recently reported the head of sustainable agriculture at Rainforest Alliance, Chris Wille, as saying that

“Our scientists say a certified coffee farm is the next best thing to rainforest,”

regarding shaded farms. In some cases, these products are even equivalently priced to sun grown coffees. Surely there is no good reason for an environmentally conscious coffee lover not to consider switching to shade grown coffee.

 

Resources

There are a number of shade grown coffees now on the market, which can be found on coffee-direct.co.uk, naturalcollection.com and birdandwild.co.uk.

Image sources: headergif, demand