Category Archives: Renewable Energy

How renewable are renewables really?

Renewables are on the rise. The International Energy Agency (IEA) forecasts global capacity of wind, solar and hydropower will grow 43% in the next five years. Such technologies are called renewable since their source of energy (e.g. sun, wind or flowing water) naturally replenish themselves. This can be contrasted with fossil-fuel generation, whose fuels (e.g. coal or gas) can be depleted and take millions of years to regenerate.

The classification into renewable and non-renewable refers only to the process of electricity generation. Over their whole lifecycle, renewable technologies use resources that can both be depleted and lead to greenhouse gas emissions in their extraction process. Furthermore, they need a lot of them: per unit of electricity, wind turbines require 6-14 times more iron and 11-40 times more copper than fossil fuels. Meeting one quarter of global electricity demand from wind by 2050 would require an additional 1 million onshore and 100,000 offshore wind turbines, and the IEA estimates that decreasing energy related greenhouse gas emissions by 50% doubles the material requirements per unit of electricity. Obtaining the additional materials required may negatively impact the environment in their extraction and in their processing.

Furthermore, renewable energy production requires materials that may be scarce, toxic, or required for domestic electronic devices. An important example is the lithium and cobalt required for lithium ion batteries. The demand for these is expected to grow exponentially because of their use in portable electronics, electric cars and storing renewable electricity (see a previous article on this topic). Both metals are available only in a small number of countries, with cobalt a particular concern; more than half of world supply comes from DR Congo, a country infamous for its political instability and plagued by civil war. The combination of high demand and supply uncertainty has even lead to deep-sea mining pilots, worrying many environmentalists. Clearly, the environmental impacts of a massive renewable transition should be considered carefully — we must be careful that one source of environmental damage (greenhouse gases emissions) is not substituted for another.

Figure 1: Lifecycle greenhouse gas emissions per unit of electricity generated for different renewable and non-renewable energy sources. Source: IPCC, 2011 Special Report on Renewable Energy Sources and Climate Change Mitigation (Chapter 9).

In this backdrop, shrinking renewable technologies’ material requirements is a key priority. Many approaches fall under the age-old mantra Reduce, Reuse, Recycle. One strategy is to design new technologies that require fewer scarce resources. The lithium ion battery is itself an improvement on its lead acid predecessor, and the race to build a new battery, free of lithium and cobalt, is in full swing. Another is to increase the effective lifecycle of existing technologies. As everyone with an old mobile phone recognises, battery performance declines over time, and this is usually the first reason to discard an otherwise working model. The same applies to wind power: the harsh conditions experienced by turbine blades, including lightning strikes, storms and ice, decreases the efficiency of wind turbines 60% in their first 15 years of operation. Replacing blades periodically or making them more resilient lowers material requirements, but comes with considerable technical challenges.

A third option is to recycle materials. The first generation of large-scale renewable projects built in the 1990s are reaching the end of their lifetimes, meaning millions of tonnes of old wind farm and solar panel materials will be decommissioned. Estimates suggest that by 2030, there will be 300,000 tonnes of waste from old wind turbines annually in Europe alone, and most of these parts are made from costly unreformable plastic that cannot be melted down or given a second life. Reusing components both reduces demand for mining and prevents costly materials ending up in landfill sites. Examples include a planned recycling centre in Texas where old wind turbines are cut up and given a second life in composite panels and a French chemical firm building blades from reformable plastic. In the EU, research funding and targeted landfill bans have lead to pilot projects into the recycling of solar panels and batteries. Some of these batteries have even been given second lives in grid-scale storage. However, recent attempts have been slow to get off the ground, and for many of these technologies, mining new materials remains cheaper than recycling. Furthermore, recycled materials typically cannot be reused in renewable technologies again and must be sold to other sectors.

Many of the issues outlined above relate to the fact that these technologies are still in their infancy. Fossil fuel technologies have been the dominant energy source for more than a century, and trillions of dollars have been invested to maximise their efficiencies. If and when such sums start being spent on renewables, technologies are expected to improve significantly. These improvements have already sent the price of renewables plummeting, and they may make the renewable resource question disappear altogether in the future.

Furthermore, despite the hefty material requirements, a study by the Norwegian University of Science and Technology estimates that the planet has enough resources to support the large-scale transition to renewables, and it’s not the case that fossil fuels don’t use any materials for their infrastructure — imagine, for example, the amount of metal and energy required to build on oil rig. In terms of lifecycle greenhouse gas emissions, renewables are a clear improvement on non-renewables (see Figure 1). However, having enough resources for the foreseeable future does not mean this will be the case forever.

Becoming a truly renewable society requires not just the adoption of renewable technologies, but also their improvement. Otherwise, it may be that in solving one sustainability issue, we are creating another.

Adriaan Hilbers – PhD student researching Mathematics of Power Systems at Imperial College London

Mariana Clare – PhD student researching numerical fluid and sediment transport models at Imperial College London

What’s the Deal with Nuclear?

Some people think nuclear is the best solution for climate change, and others want it gone tomorrow. What’s the deal? Source: Burghard

As the world strives to reduce its carbon emissions, massive efforts are being undertaken to decarbonise electricity. In most developed countries, fossil fuels like coal are on the way out, being gradually (albeit slowly) replaced by renewables such as solar and wind. However, keeping the lights on while generating most power from weather-dependent renewables comes with significant challenges (see a previous article that discusses this in more detail). The key difficulty arises because electricity supply and demand must always match perfectly. Traditionally, this involved adjusting power plant output to meet demand, including rapid spikes or dips. In fact, grid operators tune in  to popular TV shows to ensure supply is increased exactly as thousands of people turn on their kettle at the end of an episode.

A famous graph showing total UK electricity demand during the 1990 World Cup Semi-Final against Germany, with spikes at times when watchers massively turned on their kettles. Source: National Grid

Weather-dependent renewables make this balancing act more difficult since generation levels are controlled by e.g. the wind or sun and cannot be adjusted as required. In fact, the supply-demand balance requirement means that, in countries without the possibility of hydropower (requiring mountainous and rainy terrain) or geothermal power, it is virtually impossible to go 100% renewable without drastically increasing electricity prices. This is sometimes referred to as the energy trilemma: in most regions, only two of supply security, affordable energy and environmental sustainability can be satisfied. Two of the most promising solutions, grid-scale storage (storing excess renewable production at times of high supply and using it when supply is low) and carbon capture-and-storage (storing carbon emissions before releasing them into the atmosphere), are unproven and not yet economically viable. For this reason, most countries still generate most of their electricity from fossil fuels — it’s too difficult or expensive to match supply and demand any other way.

In this backdrop, nuclear power seems perfect: fully controllable output levels without any greenhouse gas emissions. It’s also a proven technology, generating electricity from the United States to Pakistan. Nonetheless, the future of nuclear power is a contentious issue. From this author’s personal experience, the UK energy community seems to be in a perfect dichotomy between those who think nuclear power should be the strategy to mitigate climate change (at least in the short term) and those who think all reactors should close tomorrow. Why all the disagreement? This article hopes to give a balanced account of the advantages and disadvantages of nuclear power, and the controversy surrounding it.

Firstly, there are ethical arguments. Current nuclear technology produces poisonous nuclear waste that must be stored safely for thousands of years. Nuclear detractors question the morality of leaving behind toxic material for future generations to take care of, while nuclear supporters opine that the social costs of unmitigated carbon emissions are much higher.

Secondly, there are political factors. For a number of reasons, decisions regarding atomic energy are typically made at government level. The first is scale; nuclear power plants are so expensive that energy companies are unable or unwilling to take the risk building them. They are usually built either by governments themselves or involving some government financial support. And even when market players do build new plants, the extensive planning permissions mean that, in the end, it is usually the government who decides. For this reason, decisions regarding nuclear power are susceptible to the whims of political sentiment, and this explains many of the trends in the sector.

Politicians (especially in democracies) are concerned with public opinion, and the general perception of nuclear power is a complicated topic. It’s reputation has been tarnished by a number of high-profile disasters, most notably Chernobyl (former USSR, currently Ukraine) and Fukushima (Japan). Both contaminated the surroundings, left areas uninhabitable for decades and required hefty cleanup costs. The United States had its own accident at 3 Mile Island, of comparably smaller impact but nonetheless negatively affecting the perception of the safety of nuclear power.

Nuclear power: contentious around the world. Source: capotian

Nuclear proponents sometimes argue that the technology’s nature gives it an intrinsic disadvantage in public opinion. Disasters can be of almost biblical scale, and images of atomic explosions or radioactive ghost towns appeal to human emotion more than e.g. a gradual rise in temperature or the lives lost each year in coal mine accidents. Furthermore, public perception of nuclear energy is often based on emotive imagery as much as reasoned analysis. One US study indicates that support is higher among those either better informed about it or living in close proximity to a nuclear power plant, and that the majority of opposers can be convinced of its merit just by telling them that it is the “only electricity source that provides both clean air and 24-7 electricity”.

When nuclear power goes wrong, it really goes wrong, as the ghost town of Pripyat (near Chernobyl) shows. Source: Amort1939

The effect of public sentiment can be seen in Germany’s 2011 decision to phase out nuclear power, taken in the wake of the Fukushima disaster. While widely supported politically, energy scientists point out that it delayed Germany’s energy transition multiple years by requiring coal plants (with the highest carbon emission of all major generation technologies) to stay open. For this reason, despite a slightly higher renewable electricity production, Germany’s carbon emissions per unit electricity are around twice as high as the UK, where coal power has almost totally disappeared.

Despite all this, nuclear’s high cost is broadly considered the main driver behind its decreasing role in world energy supply. For the Hinkley Point project, aiming to build the first new UK plant in decades, the government has agreed to purchase electricity at around twice the current average price. This has been described as “ridiculously expensive”, especially in the face of plummeting renewables costs. Supporters argue that the ability to generate when needed (as opposed to only at sunny or windy times) justifies the higher price, but the fact remains that nuclear power cannot compete on a pure cost basis . Furthermore, its economics worsen in combination with renewables. Nuclear power plants are expensive to build, but cheap to run, so should be run as often as possible. Since renewable-heavy grids only need backup power at times of low renewable output, it becomes more difficult for nuclear plants to “earn back” their considerable construction expense with low generation costs.

Nuclear power — on the way out? Even while global electricity demand has grown, nuclear production has stalled since around 2000. Source: World Nuclear Association

A fantastic website, electricitymap.org, shows real-time greenhouse gas emissions from electricity generation in many parts of the world. The data displayed serves as a good indication of the present reality. There are essentially two ways to generate power without emitting greenhouse gases. The first is hydropower, which countries like Norway use for almost all their electricity needs. The second is nuclear. Indeed, the only country with a population over 10 million people consistently emitting less than 100g CO2 per KWh of electricity without major hydropower is France, which generates between 60% and 80% of its power from atomic fission. For many countries, going nuclear is the only way to decarbonise electricity.

The greener the country, the lower the carbon emissions per kWh of electricity. Only three countries in Europe are really green: Norway (majority hydropower), France (majority nuclear power) and Sweden (combination of  hydropower and nuclear power). Source: electricitymap.org

However, something currently being true does not mean it will be forever. Much of the difficulty in nuclear decisions relates to uncertainty about the future. With Hinkley Point, the UK government agreed to pay, for multiple decades, a price that may seem unjustifiably high. Nobody knows what will happen in those decades. If breakthroughs in grid-scale storage or carbon capture-and-storage allow rapid decarbonisation of electricity, then Hinkley Point will probably be viewed as a mistake. If not, its construction may prove essential to meet climate goals. Some of the uncertainty comes from uncertain future developments of nuclear technology itself. One example is the development of small modular reactors (SMRs), essentially mini-reactors, that are easier for private companies to finance and build. Another is to (finally) harness the power of nuclear fusion, which produces almost no nuclear waste but has been “ten years away” since the 50s. The commercialisation of either of these may yet provide a nuclear resurgence.

All in all, a Grantham Institute briefing on UK nuclear power perhaps summarises the future of the technology most aptly:

“Nuclear power will be essential for meeting the UK’s greenhouse gas emissions reduction target, unless we can adapt to depend largely on variable wind and solar, or there is a breakthrough in the commercialisation of carbon capture-and-storage. […] We may regret building nuclear power stations if the cost of renewables continues to fall and we find solutions to the problem of the variability of these generation sources. On the other hand, if progress in reducing the costs of energy storage is insufficient, we may not be able to achieve climate targets without new nuclear generation capacity.”

The somewhat unsatisfying answer is that decisions made about nuclear power now can’t be evaluated for years. One the one hand, massive investments now will look foolish if technological breakthroughs allow power systems to decarbonise by other means or if a major nuclear disaster occurs. On the other hand, not investing will be a mistake if it turns out carbon emissions can’t be reduced without it, and the effects of climate change really start to hurt. Simply waiting is not an option: nuclear power plants take more than 10 years to build, so decisions must be made now to ensure carbon emission reduction targets are not missed. For the future climate, electricity bills, and the challenge of keeping the lights on, the next few years will be telling.

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.

Money blowing in the wind

I bet you’re not looking forward to receiving your monthly electricity bills. Can you predict how much you’ll be charged this time? Short answer: assume that more than you’d be willing to pay. Long answer: spend a couple of years studying how electricity prices evolve in time. Yes, that’s exactly what my PhD is about.

Power markets are surprisingly complicated. Trading energy is a relatively new idea, increasingly important because of the gradual liberalisation of the EU electricity industry. Not only do market rules in various countries differ significantly, but relevant laws change frequently. Therefore if you’re interested in any details, please don’t rely solely on my article, but refer to the website of the appropriate market (eg. European Power Exchange).

From the mathematical point of view, modelling any financial processes is an extremely difficult task. Stock values change in unpredictable ways, they also strongly depend on political events and human behaviour. Because of that, financial mathematics attracts increasing numbers of mathematicians with different backgrounds. Actually, not only mathematicians. For example, a building block for many financial models is a so-called Brownian motion, first used by physicists to describe chaotic movement of particles. The tools we can use are limited only by our imagination!

Energy markets are problematic, as they behave differently than traditional stock exchanges, so we have to come up with completely new ideas to model them. The main difference is that the supply and demand for electricity must always match. Storing electricity is almost impossible, in the best case very expensive, so we cannot produce (or buy) more and leave it for later. On the other hand, the supply is inelastic, because industry and citizens require a specific amount of power for their regular activities. You don’t like blackouts, do you? And they happen exactly as a result of a significant imbalance in the energy market.

Thankfully many people work very hard (this is how I like to think about myself) to make sure that you don’t have to dig out these candles too often. Mathematical models help producers decide how much energy to generate and traders to buy and sell its appropriate amounts. Most of trading takes place in electricity markets.

Two main types of contracts are traded. First, spot contracts (traded at noon) oblige producers to deliver a specified amount of energy for 24 hours, from midnight of the following day. Second, one can also trade futures contracts for a specified delivery period: a week, a month or a year. For example, if a producer signs a “2 months ahead” contract today (June 2017), she or he would have to deliver the electricity between 01/08/2017 and 31/08/2017.

However, predicting the prices so far in the future is a difficult task. We don’t know the general state of economy or if Donald T. decides to build a *huge* bridge from New York to the Moon (which would require a lot of power, I guess). And, what interests me most, what the weather will be.

Weather conditions significantly influence electricity prices, both the demand and supply. In countries like the UK or Germany, in general the demand is higher in cold months, when we need to heat our houses and offices, as well as use more light due to shorter days. In warmer places, also in the summer a lot of energy is needed for air-conditioning. On the other hand, renewable energy production strongly relies on the weather. We can’t generate wind energy without wind!

This is why in my models I have to take into account weather forecasts. As you know, they’re pretty useless a few weeks in advance, not to mention a few years. Therefore the models need to account for uncertainty related to these forecasts.

You might wonder if these factors really matter. They actually do! Now many markets even allow the prices to be negative, which means that we get paid for the electricity usage. It happens rather rarely, so you won’t even notice. However, it’s interesting to note that almost all negative prices are observed in early morning hours after a windy night. This means that a high level of wind energy generation, combined with a low demand (most factories are closed at night, we also tend to sleep), can significantly decrease electricity prices.

In other words, the chance for a lower electricity bill is literally blowing in the wind.

Source: https://paularowinska.wordpress.com/2017/06/11/money-blowing-in-the-wind/