Category Archives: Climate Change

Getting more energy from the sun: how to make better solar cells

Global demand for energy is increasing by the hour as developing countries move toward industrialization. Experts estimate that by the year 2050, worldwide demand for electricity may reach 30 terawatts (TW). For perspective, one terawatt is roughly equal to the power of 1.3 billion horses.

Energy from the sun is limitless – the sun provides us 120,000 TW of power at any given instant – and it is free. But today solar energy provides only about one percent of the world’s electricity. The critical challenge is making it less expensive to convert photo-energy into usable electrical energy.

To do that, we need to find materials that absorb sunlight and convert it into electricity efficiently. In addition, we want these materials to be abundant, environmentally benign and cost-effective to fabricate into solar devices.

Researchers from around the world are working to develop solar cell technologies that are efficient and affordable. The goal is to bring the installation cost of solar electricity below US$1 per watt, compared to about $3 per watt today.

At Binghamton University’s Center for Autonomous Solar Power (CASP), we are investigating ways to make thin film solar cells using materials that are abundant in nature and nontoxic. We want to develop solar cells that are reliable, highly efficient at converting sunlight to electricity and inexpensive to manufacture. We have identified two materials that have great potential as solar absorbers: pyrite, better known as fool’s gold because of its metallic luster; and copper-zinc-tin-sulfide (CZTS).

Seeking the ideal material

Today’s commercial solar cells are made from one of three materials: silicon, cadmium telluride (CdTe) and copper-indium-gallium-selenide (CIGS). Each has strengths and weaknesses.

Silicon solar cells are highly efficient, converting up to 25 percent of the sunlight that falls on them into electricity, and very durable. However, it is very expensive to process silicon into wafers. And these wafers have to be very thick (about 0.3 millimeters, which is thick for solar cells) to absorb all of the sunlight that falls on them, which further increases costs.

Silicon solar cells – often referred to as first-generation solar cells – are used in the panels that have become familiar sights on rooftops. Our center is studying another type called thin film solar cells, which are the next generation of solar technology. As their name suggests, thin film solar cells are made by putting a thin layer of solar absorbent material over a substrate, such as glass or plastic, which typically can be flexible.

A CASP center fabricated CZTS solar cell on a flexible glass substrate made by Corning.
Tara Dhakal/Binghamton University, Author provided

These solar cells use less material, so they are less expensive than crystalline solar cells made from silicon. It is not possible to coat crystalline silicon on a flexible substrate, so we need a different material to use as a solar absorber.

Although thin film solar technology is improving rapidly, some of the materials in today’s thin film solar cells are scarce or hazardous. For example, the cadmium in CdTe is highly toxic to all living things and is known to cause cancer in humans. CdTe can separate into cadmium and tellurium at high temperatures (for example, in a laboratory or housefire), posing a serious inhalation risk.

We are working with pyrite and CZTS because they are nontoxic and very inexpensive. CZTS costs about 0.005 cents per watt, and pyrite costs a mere 0.000002 cents per watt. They also are among the most abundant materials in the Earth’s crust, and absorb the visible spectrum of sunlight efficiently. These films can be as thin as 1/1000th of a millimeter.

Testing CZTS solar cells under simulated sunlight.
Tara Dhakal/Binghamton University, Author provided

We need to crystallize these materials before we can fabricate them into solar cells. This is done by heating them. CZTS crystallizes at temperatures under 600 degree Celsius, compared to 1,200 degrees Celsius or higher for silicon, which makes it less expensive to process. It performs much like high-efficiency copper indium gallium selenide (CIGS) solar cells, which are commercially available now, but replaces the indium and gallium in these cells with cheaper and more abundant zinc and tin.

So far, however, CZTS solar cells are relatively inefficient: they convert less than 13 percent of the sunlight that falls upon them to electricity, compared to 20 percent for more expensive CIGS solar cells.

We know that CZTS solar cells have a potential to be 30 percent efficient. The main challenges are 1) synthesizing high-quality CZTS thin film without any traces of impurities, and 2) finding a suitable material for the “buffer” layer underneath it, which helps to collect the electric charges that sunlight creates in the absorber layer. Our lab has produced a CZTS thin film with seven percent efficiency; we hope to approach 15 percent efficiency soon by synthesizing high-quality CZTS layers and finding suitable buffer layers.

Structure of a CZTS solar cell.
Tara Dhakal/Binghamton University, Author provided

Pyrite is another potential absorber that can be synthesized at very low temperatures. Our lab has synthesized pyrite thin films, and now we are working to layer those films into solar cells. This process is challenging because pyrite breaks down easily when it is exposed to heat and moisture. We are researching ways to make it more stable without affecting its solar absorbency and mechanical properties. If we can solve this problem, “fool’s gold” could turn into a smart photovoltaic device.

In a recent study, researchers at Stanford University and the University of California at Berkeley estimated that solar power could provide up to 45 percent of U.S. electricity by 2050. To meet that target, we need to keep driving down the cost of solar power and find ways to make solar cells more sustainably. We believe that abundant, nontoxic materials are key to realizing the potential of solar power.

The Conversation

Tara P. Dhakal, Assistant Professor of Electrical and Computer Engineering, Binghamton University, State University of New York

This article was originally published on The Conversation. Read the original article.

Should fracking decisions be made locally?

The future role of gas in the UK is the subject of significant debate. There is controversy about how much gas we could use and for how long, and whether this will be compatible with statutory climate change targets. As North Sea supplies decline, there are also starkly differing views about whether some of the gas we will need in future should come from domestic shale gas resources.

Despite the number of headlines about shale gas, there has been very little development activity so far. Fracking for shale gas has only been carried out at one site near Blackpool, where operations by Cuadrilla caused minor earthquakes in 2011. This means that it is almost impossible to determine whether significant UK shale gas production would make economic sense. The recent falls in oil and gas prices have added to this uncertainty, but are likely to make commercial viability more challenging.

During the recent 14th licensing round for onshore oil and gas, 159 areas were awarded licenses for development – 75% of these were for unconventional oil and gas extraction, which has sparked local debates in many of the affected areas.

Two planning applications submitted by Cuadrilla for exploration at sites in Lancashire were recently turned down by the local council on the grounds of noise and traffic. One of these was refused against the advice of council officers. An appeal by Cuadrillia is currently underway. Whether or not it goes in favour of the council or the developer, it raises broader questions about the role of local democracy and decision-making.

Last August the government announced the introduction of fast-track planning regulations designed to limit the length of local planning processes for unconventional oil and gas operations. Greg Clark, the secretary of state for communities and local government, also said he expects to have the final say over the Lancashire applications.

What is Fracking?

This intention to constrain local planning processes has understandably led to concerns about local democracy. It is not the first time national government has tried to intervene in local decision-making, especially when it comes to the development of new large-scale infrastructures or natural resources.

While national government may emphasise a particular course of action, like the development of shale gas, there is no guarantee that local decision-makers will simply agree. Furthermore, selective limits on local planning risk exacerbating public mistrust. A Sciencewise project on public engagement with shale gas and oil, commissioned by the government, revealed significant unease among participants about decision-making processes.

A waste of energy?

Given that large-scale changes to energy infrastructures are very likely to be required across the UK as the energy system decarbonises, this issue goes well beyond shale gas. Local opposition has also been significant for other energy developments such as wind farms, solar farms, gas storage sites and electricity transmission lines.

The government’s approach to different energy sources appears to be inconsistent – most notably between onshore wind and shale gas. In contrast with the approach for shale, local planners will determine whether new onshore wind projects go ahead or not. Ministers have defended this situation on the grounds that a lot of wind farms are already being deployed, while shale gas is at a very early stage.

Although the government’s regular energy opinion poll no longer asks specific questions about onshore wind, other polls suggest it still has significant public support – as well as being the cheapest low carbon electricity generation technology.

Where should our energy come from?

The focus on shale and wind could also be a missed opportunity for a broader conversation about the UK’s sustainable energy transition. This conversation should not be restricted to which technologies or resources should be used, and what they might cost. Previous research from the UK Energy Research Centre suggests that people are also interested in how energy systems can reflect values such as fairness, sustainability and efficiency. A focus on individual sources like shale gas in isolation leaves little space for this broader conversation to be held.

The Conversation

Jim Watson, Research Director, UK Energy Research Centre

This article was originally published on The Conversation. Read the original article.

Tipping point: how we predict when Antarctica’s melting ice sheets will flood the seas

Antarctica is already feeling the heat of climate change, with rapid melting and retreat of glaciers over recent decades.

Ice mass loss from Antarctica and Greenland contributes about 20% to the current rate of global sea level rise. This ice loss is projected to increase over the coming century.

A recent article on The Conversation raised the concept of “climate tipping points”: thresholds in the climate system that, once breached, lead to substantial and irreversible change.

Such a climate tipping point may occur as a result of the increasingly rapid decline of the Antarctic ice sheets, leading to a rapid rise in sea levels. But what is this threshold? And when will we reach it?

What does the tipping point look like?

The Antarctic ice sheet is a large mass of ice, up to 4 km thick in some places, and is grounded on bedrock. Ice generally flows from the interior of the continent towards the margins, speeding up as it goes.

Where the ice sheet meets the ocean, large sections of connected ice – ice shelves – begin to float. These eventually melt from the base or calve off as icebergs. The whole sheet is replenished by accumulating snowfall.

Emperor penguins at sunrise.
David Gwyther

Floating ice shelves act like a cork in a wine bottle, slowing down the ice sheet as it flows towards the oceans. If ice shelves are removed from the system, the ice sheet will rapidly accelerate towards the ocean, bringing about further ice mass loss.

A tipping point occurs if too much of the ice shelf is lost. In some glaciers, this may spark irreversible retreat.

Where is the tipping point?

One way to identify a tipping point involves figuring out how much shelf ice Antarctica can lose, and from where, without changing the overall ice flow substantially.

A recent study found that 13.4% of Antarctic shelf ice – distributed regionally across the continent – does not play an active role in ice flow. But if this “safety band” were removed, it would result in significant acceleration of the ice sheet.

The Totten Glacier calving front.
Esmee van Wijk/CSIRO

Antarctic ice shelves have been thinning at an overall rate of about 300 cubic km per year between 2003 and 2012 and are projected to thin even further over the 21st century. This thinning will move Antarctic ice shelves towards a tipping point, where irreversible collapse of the ice shelf and increase in sea levels may follow.

How do we predict when will it happen?

Some areas of West Antarctica may be already close to the tipping point. For example, ice shelves along the coast of the Amundsen and Bellingshausen Seas are the most rapidly thinning and have the smallest “safety bands” of all Antarctic ice shelves.

To predict when the “safety band” of ice might be lost, we need to project changes into the future. This requires better understanding of processes that remove ice from the ice sheet, such as melting at the base of ice shelves and iceberg calving.

Melting beneath ice shelves is the main source of Antarctic ice loss. It is driven by contact between warmer sea waters and the underside of ice shelves.

To figure out how much ice will be lost in the future requires knowledge of how quickly the oceans are warming, where these warmer waters will flow, and the role of the atmosphere in modulating these interactions. That’s a complex task that requires computer modelling.

Predicting how quickly ice shelves break up and form icebergs is less well understood and is currently one of the biggest uncertainties in future Antarctic mass loss. Much of the ice lost when icebergs calve occurs in the sporadic release of extremely large icebergs, which can be tens or even hundreds of kilometres across.

It is difficult to predict precisely when and how often large icebergs will break off. Models that can reproduce this behaviour are still being developed.

Scientists are actively researching these areas by developing models of ice sheets and oceans, as well as studying the processes that drive mass loss from Antarctica. These investigations need to combine long-term observations with models: model simulations can then be evaluated and improved, making the science stronger.

The link between ice sheets, oceans, sea ice and atmosphere is one of the least understood, but most important factors in Antarctica’s tipping point. Understanding it better will help us project how much sea levels will rise, and ultimately how we can adapt.

The Conversation

Felicity Graham, Ice Sheet Modeller, Antarctic Gateway Partnership, University of Tasmania; David Gwyther, Antarctic Coastal Ocean Modeller, University of Tasmania; Lenneke Jong, Cryosphere System Modeller, Antarctic Gateway Partnership & Antarctic Climate and Ecosystems CRC, University of Tasmania, and Sue Cook, Ice Shelf Glaciologist, Antarctic Climate and Ecosystems CRC, University of Tasmania

This article was originally published on The Conversation. Read the original article.

Why it makes little sense to regulate rainwater barrels in the dry western U.S.

Many of us never think about who gets to use the drops of rain that fall from the sky. But it’s an increasingly pertinent question as more people look to collect rainwater as a way to conserve water, live off the grid or save money on water bills.

As a result, many states in the arid West are now asking whether rain barrels are allowed under existing law and policy and, in some cases, are setting limits on the practice of rainwater catchment.

Colorado has gone further than any of its neighbors by requiring a permit for any rainwater collection. Meanwhile, Utah put rainwater harvesting rules into effect in 2010 with some restrictions, and Washington legalized rainwater collection in 2009, while leaving the state the “ability to restrict if there are negative effects on instream values or existing water rights.”

Why this worry over rainwater harvesting?

If everyone captures the rain that falls on rooftops and through downspouts of homes, the argument goes, then the water will never reach the rivers and streams. If this happens, existing water users may not be able to access their rights to use the water.

This concern, however, overstates the issue and risks missing more concrete opportunities for water conservation and efficiency. A more effective way to address decreasing water supply would be for states to apply the legal principles prohibiting waste and demanding reasonable water use, which have long been embedded in any right to use water.

U.S. water law, east and west

Both the rainwater collectors and the existing water rights holders, such as irrigators or municipalities with water rights to river flows or groundwater sources, believe they have a fully private interest in any water they use.

Throughout the United States, however, the law recognizes the public nature of water. Under the public trust doctrine, each state holds title to the water within the state in trust for the people of the state.

Given the competing demands for water use, principles of U.S. law seek to balance these competing needs and uses to ensure that the public’s rights to water are protected.

In western states, farm owners often have rights to use water which can often be delivered through irrigation ditches, such as this one in Colorado.
question_everything/flickr, CC BY-NC-ND

In the eastern United States, there is the riparian system that protects reasonable use of water among all landowners along rivers or streams. In the western part of the country, the doctrine of prior appropriation requires a permit to use water based on showing that the water will be put to beneficial use without waste.

The public nature of water ensures that individual private interests never fully control who gets access to water and when, where and how water is used. In fact, when an individual has a right to use water, that right is known as a “usufructory” interest – that is, the right to use the water without owning the water itself.

Granting a usufructory interest – something that doesn’t fully privatize a water right – makes good sense when you think about the nature of water.

Short of putting water in a bottle and selling it by the ounce, water is difficult to possess and reduce to ownership. It is a shared resource that is used over and over again as the molecules of water make their way through the hydrologic system.

Water falls from the sky, runs along the ground and percolates into the groundwater system. It is taken up by plants and trees, consumed by people and animals, and eventually makes its way through one mechanism or another, back into the groundwater or surface water sources, only to flow further down the system to be used again or eventually evaporate back into the atmosphere to start the process all over again.

Private ownership of drops of water presents a complex problem not only as a legal matter, but as an ethical public policy choice as well.

The debate over rainwater collection demonstrates this complexity.

Don’t homeowners in Colorado have the right to collect rain that falls on their rooftop? At the same time, doesn’t a senior water right holder have a right to have the rain enter the stream so that their right can be satisfied?

Our legal system evolved ways to deal with this complex reality, with our state governments empowered to manage this resource among competing interests on behalf of all of us.

In the eastern United States where rainfall is plentiful and competing uses for water are rare, the riparian system allows any landowner adjacent to a water source to use its water. If there is a conflict about the quantity of water available for a certain use, that conflict is resolved by using legal standards to sort through the reasonableness of each individual’s use.

In the western United States, where competition among users has always been more commonplace, each individual state requires a permit for water use. These permits are awarded pursuant to the doctrine of prior appropriation. For example, irrigated agriculture often holds senior water rights (issued under state law) and Indian tribes often hold even more senior rights (based on federal law).

When conflict arises, disputes are resolved using the legal principle of first-in-time, first-in-right that protects the most senior, beneficial, nonwasteful uses of water. Or at least that is the theory.

Water waste and powerful interests

So how does this relate to the regulation of rainwater harvesting?

If the primary concern is that somehow rainwater barrels will limit the amount of water in the system, reduce availability of water and potentially impact existing rights, then there may be better ways to address this concern.

Rather than devoting resources to regulating individual rain barrels – a logistically difficult task – it may make more sense for state water agencies to get serious about enforcing principles of waste.

To enforce waste reduction policies, water resource management agencies in each state would need to set standards on how much water is needed to carry out a particular use. They then would need to measure water use to ensure that individual permit holders are not taking more water than what is necessary to accomplish their purpose.

Many longstanding water users take more water than they need, under the principle of use-it-or-lose-it. In western water law, if you don’t use the water, you risk forfeiting your water right. As a result, many users divert the full quantity of their water right whether that amount is needed or not.

If the states crack down on waste, it will bring this longstanding practice into the spotlight. Existing water users may be faced with calls to increase efficiency and to decrease the rate of diversion.

As droughts become more frequent and demands on water grows, states could do more to reduce waste from big water users.
sunlizard4fun/flickr, CC BY

For decades, there has been a persistent reluctance to address waste because it would involve scrutinizing water use practices among some of the most powerful interests in the state.

But by addressing the thorny problem of waste, state agencies could make more headway in securing reliable water supplies and certainly could have a more significant impact on water supply than regulating rainwater catchment.

In the end, we may face tough public policy choices about whether and how to regulate rainwater catchment. But before we go in this direction, policymakers should take a careful look at whether existing larger-scale water users are complying with longstanding principles of nonwaste and reasonableness embedded in U.S. water law.

The Conversation

Adell Amos, Associate Dean for Academic Affairs, Associate Professor of Environmental and Natural Resources Law, University of Oregon

This article was originally published on The Conversation. Read the original article.