PV Plant Technologies. Pv power generation

How a Photovoltaic Power Plant Works? Construction and Working of a Solar Power Plant

What is Solar Power Plant?

The solar power plant is also known as the Photovoltaic (PV) power plant. It is a large-scale PV plant designed to produce bulk electrical power from solar radiation. The solar power plant uses solar energy to produce electrical power. Therefore, it is a conventional power plant.

Solar energy can be used directly to produce electrical energy using solar PV panels. Or there is another way to produce electrical energy that is concentrated solar energy. In this type of plant, the radiation energy of solar first converted into heat (thermal energy) and this heat is used to drive a conventional generator. This method is difficult and not efficient to produce electrical power on a large scale.

Hence, to produce electrical power on a large scale, solar PV panels are used. In this article, we will explain details about solar PV plants and PV panels. Below is the layout plan of photovoltaic power plant.

Photo Voltaic (PV) Principle

Silicon is the most commonly used material in solar cells. Silicon is a semiconductor material. Several materials show photoelectric properties like; cadmium, gallium arsenide, etc.

Electron-holes pairs are created in solar cells. The PV materials have the property to absorb photons of sunlight. The valance Band electrons of semiconductor material are at lower energy and the electrons of conduction Band are at a higher energy level. The difference between this energy level is known as bandgap energy Eg.

When sunlight falls on solar cells, the difference between photon energy E and bandgap energy Eg is absorbed by the cell. And it excites some electrons to jump across the bandgap. These electrons move from the valance Band to the conduction Band and create holes in the valance Band.

Therefore, if the potential difference exists within the cell, the electrons of the conduction Band and holes of the valance Band made the flow of current in the circuit.

According to Max Plant, the energy of photons is directly proportional to the frequency of radiation.

• EP = Energy of Photon
• h = Plank’s Constant = 6.62×10.34 J s = 4.135×10.15 eV s
• v = frequency of radiation (Hz)
• C = speed of light ≈ 3×10 8 m/s
• λ = Wavelength of radiation (μm)

substituting these values in the above equation;

Components of Solar Power Plant

The major components of the solar photovoltaic system are listed below.

• Photovoltaic (PV) panel
• Inverter
• Energy storage devices
• Charge controller
• System balancing component

Photovoltaic (PV) Panel

PV panels or Photovoltaic panel is a most important component of a solar power plant. It is made up of small solar cells. This is a device that is used to convert solar photon energy into electrical energy.

Generally, silicon is used as a semiconductor material in solar cells. The typical rating of silicon solar cells is 0.5 V and 6 Amp. And it is equivalent to 3 W power. The number of cells is connected in series or parallel and makes a module. The number of modules forms a solar panel.

According to the capacity of power plants, a number of plates are mounted and a group of panels is also known as Photovoltaic (PV) array.

The output of the solar panel is in the form of DC. The most of load connected to the power system network is in the form of AC. Therefore, we need to convert DC output power into AC power. For that, an inverter is used in solar power plants.

For a large-scaled grid-tied power plant, the inverter is connected with special protective devices. And a transformer is also connected with the inverter to assures the output voltage and frequency as per the standard supply.

Energy storage devices

The batteries are used to store electrical energy generated by the solar power plants. The storage components are the most important component in a power plant to meet the demand and variation of the load. This component is used especially when the sunshine is not available for few days.

For example, a battery having 100 AH battery can supply 1 Amp current for 100 hours or 100 Amp current for 1 hour.

For a long life of a battery, never fully discharge a battery. And in case, if a battery is fully discharged, never keep fully discharged battery for a long time.

The capacity of a battery is affected by the temperature. There is a reduction of 0.6% of capacity for every degree Celsius rise in temperature more than 25˚ C.

There are two types of batteries used in the solar power plant;

Charge Controller

A charge controller is used to control the charging and discharging of the battery. The charge controller is used to avoid the overcharging of the battery. The overcharging of a battery may lead to corrosion and reduce plate growth. And in the worst condition, it may damage the electrolyte of the battery.

Sometimes, the charge controller is termed a solar battery charger. There are many technologies used to make a charge controller. For example, the most popular technique is the MPPT charge controller that is known as “Maximum Power Point Tracking”. This algorithm is used to optimize the production of PV cells.

System balancing component

It is a set of components used to control, protect and distribute power in the system. These devices ensure that the system working in proper condition and utilize energy in the proper direction. And it ensures maximum output and security of other components of a solar power plant.

Blocking diode

The solar PV panels are connected with a battery. And these panels are used to charge the battery during sunlight is available. During charging of the battery, the current flows from panel to battery. But when the sunlight is not available, the current can be flow in a reverse direction and it may harm the solar panel. So, the blocking diode is a diode that is connected between the battery and panel to avoid reversal current from battery to panel.

Voltage regulator

The output of solar panels depends on sunlight. And the sunlight is not constantly available. It is continuously varying. Similarly, the output of the solar panel is also varying with respect to sunlight. This results in fluctuation in load current. The voltage regulators are used to maintain fluctuation within an acceptable range.

Performance of Solar Cell

A solar cell is nothing but a PN junction. The plot of short-circuit current (ISC) and open-circuit voltage (VOC) describes the performance of the solar cell. This plot is shown in the figure below.

As shown in the above graph, Initially, the short-circuit current remains constant with an increase in voltage. And a further increase in voltage results in a Rapid decrease in current.

The power developed by the solar cell is calculated by multiplying current and voltage. And from that, we can draw a graph of power developed. As shown in the graph of developed power, at point P, the power is maximum. And we try to operate the panel at this point. This point is known as the maximum PowerPoint. And the algorithm used to track this point is known as maximum power point tracking (MPPT). The voltage at which the power is maximum is considered as maximum voltage (Vm) and maximum current (Im).

The factor which is used to describe the performance of the solar cell is known as the fill factor. The value of the fill factor remains between 0 to 1.

The equivalent circuit of solar cells is as shown in the figure below.

• Isc = Source current generated by the sunlight
• Ij = Junction current
• I = Current passes through the load
• RL = Load resistance

The relationship between current and voltage at the PN junction is given as the equation below.

• I0 = Saturation current
• V = Junction voltage
• e = electron charge = 1.602×10.19 J/V
• k = Boltzmann’s constant = 1.381×10.23 J/K
• T = Temperature (K)

Solar Cell Efficiency

The solar cells are a device that used to convert the photon energy into electrical energy. The efficiency of solar cells equates as below;

Quantum Efficiency QE,

Factors affecting the efficiency of solar cells

Theoretically, solar cells are used to operate at maximum efficiency. The main factors affecting the efficiency of solar cells are listed below.

Due to the intrinsic characteristic of the semiconductor material, the efficiency of solar cells is highly impacted by temperature. The solar cells cannot operate efficiently at a higher temperature. And the efficiency of solar cells is high with lower temperatures.

Sun Intensity

The sun’s intensity varies throughout the day. In the afternoon, the sun intensity is maximum. During this time, the efficiency of solar cells is maximum. During evening and morning time, the sun intensity is not at peak level. Hence, during this time, the efficiency is lower compared to around afternoon time.

Solar Shading

The efficiency of solar cells is highly dependent on solar sheading. During a cloudy atmosphere, the solar cells are not capable to generate more energy. During the rainy season, the efficiency of solar cells decreases due to shading.

The solar cell collects photon energy. But the efficiency of cells will decrease if the cells reflect light away from the surface. Untreated silicon surface reflects light up to 30% of incident light. To avoid this situation, an anti-reflection coating is used on the surface of the solar cells. Due to this coating, the solar cells appear dark blue or black.

Types of Solar Power Plant

The solar power plant is classified into two types according to the way load is connected.

Standalone System

The stand system is an independent power plant. It is not connected with a grid. It is directly connected with the load. This type of plant is used in a place where a grid is not available like forest, hilly area etc.

This type of plant can be used as a power backup plant when the power of the grid is not available, this plant is used to supply the load. A battery and charge controller is an optional part of this system. But in most cases, the battery and charge controller is used with this system to increase reliability.

DC loads can directly connect with this plant. But in the case of AC load, the inverter is required to convert DC power into AC power. Generally, this type of system is not used to generate electrical power in bulk amounts. This type of plant use to operate small loads or in emergency conditions only.

The block diagram of this system is shown in the figure below.

The standalone system can be categorized as below.

• Direct-coupled standalone system
• Standalone system with battery storage
• Standalone system with batteries and charge controller
• Standalone system with AC and DC loads
• Hybrid standalone system

Direct-coupled Standalone System

In this type of system, the solar panels are directly connected with the loads. This system is not suitable for AC load as this system does not have an inverter. So, DC loads are directly supplied by the solar panel.

This system cannot woks during the night or when sunlight is not available. Generally, this type of system is used for agriculture purposes to operate pump sets and other agriculture auxiliaries. The block diagram of this system is shown in the figure below.

Standalone System with Battery Storage

This type of system can be operating while sunlight is not available. During the daytime when sunlight is available, the solar panel is used to charge the battery. And the battery is used to supply power during the night. This system is cheap as it is not using a charge controller. But, in this system, the battery may overcharge or fully discharge and it reduces the life of the battery. The block diagram of this system is shown in the figure below.

Standalone System with Battery and Charge Controller

The charge controller is used to control the charging and discharging of the battery. The cost of this system is high. But, the life of this system is high. Due to the charge controller, the battery works efficiently compared to the standalone system without a charge controller. The block diagram of this system is shown in the figure below.

Standalone System with AC and DC Loads

The output of the solar panel is in the form of DC power. Hence, DC load can directly connect with the solar system. But if you need to connect the AC load, the inverter is necessary to convert the DC power into AC power. Generally, this plant is connected with other AC sources also. And this source is used to charge a battery during sunlight is not available. The block diagram of this system is shown in the figure below.

Hybrid Standalone System

In this type of system, more than one source is connected with the load. These sources may be a diesel generator, small water turbines, fuel cells, etc. This will increase the reliability of the system and reduce the battery capacity. The block diagram of the hybrid standalone system is as shown in the figure below.

Grid-connected System

This type of system is used to generate bulk power and transmit it to the load by a grid. Hence, this plant is known as a grid-connected power plant. In this system, a greater number of solar panels are used to generate more power. And it requires a large area to build a power plant.

The grid power is in the form of AC. And if we need to supply power to the grid, we need the output of solar plants similar to the power of the grid. In this system, the most important condition is that the output frequency and voltage must be matched with the grid’s frequency and voltage. And also, the power quality maintains the grid standard. The block diagram of this system is shown in the figure below.

Types of Solar Panels

• Monocrystalline Solar Panels
• Polycrystalline Solar Panels
• Thin-film Solar Panels

Monocrystalline Solar Panels

This is the oldest type of solar panel. The monocrystalline solar panel is the most developed and very efficient type of panel. The efficiency of the latest monocrystalline panel reaches up to 20%.

The cells are made of pure silicone and it is the purest form of solar panel. These panels look uniform in dark color. The shape of the cells of this panel is a round corner (oval shape). And it recognizes by appearance. This type of panel has high power output and occupies less space compared to a polycrystalline panel. But the cost of these panels is high.

The main advantage of this panel is that it slightly less reacts at high temperatures compared to a polycrystalline panel.

Polycrystalline Solar Panels

Polycrystalline panels use melted silicon. This process is faster and cheaper compared to the monocrystalline panels. The shape of the solar cell is rectangular with a sharp corner. Generally, this panel looks blue color because of the impurities added to the silicon.

The efficiency of this type of panel is slightly less compared to the monocrystalline panel. The efficiency is around 15%. And the life span of this panel is also less compared to the monocrystalline panel.

Thin-film Solar Panels

This type of solar panel is manufactured with one or more films of photovoltaic material. The polycrystalline panel is less expensive as the process to make this panel is easy. The major advantage of this panel is that it is a flexible panel. As the name suggests, thin-film panels, this panel is approximately 350 times thinner compared to the monocrystalline and polycrystalline panel.

The main disadvantage of this pane is that it requires more space. And this issue makes this panel unsuitable for residential applications. The life span of this panel is short compared to monocrystalline and polycrystalline panels.

Advantages and Disadvantages of Solar Power Plant

The advantages of solar power plants are listed below.

• Solar energy is a clean and renewable source of energy which is an unexhausted source of energy.
• After installation, the solar power plant produces electrical energy at almost zero cost.
• The life of a solar plant is very high. The solar panels can work up to 25 years.
• This plant is not causing pollution.
• There are no moving parts in solar cells. So, maintenance is not needed to keep a solar plant running.
• It does not produce any noise.
• For a bulk generation, this plant can be installed in any land. So, there are no specific site selection criteria like thermal and hydropower plants.
• The solar plant can be installed on the house or flat. So, it reduces the transmission cost as it generates energy near the load center.
• In a grid-tied power plant, the electrical generate power can directly transfer to the grid and this will reduce the burden of conventional power plants.

The disadvantages of solar power plants are listed below.

• The initial cost of a solar panel is very high.
• It requires large land to produce electrical power in bulk amounts.
• The solar plant is only installed in countries where sunline is available efficiently.
• During a cloudy atmosphere, the solar plant cannot operate efficiently.
• The efficiency of a solar panel is very less.
• This plant generates electrical energy when sunlight is available. During the night, this plant cannot generate electrical power. Hence, if you need to use electrical power at night, you have to install a battery and charge controller. That increases the cost and maintenance of the plant as the life of a battery is very short.
• In a grid-tide power plant, the inverter is required, which is costly and needs skilled manpower and new technology to make sync with grid power quality.

PV Plant Technologies

Grid-connected photovoltaic (PV) systems cover a wide range of applications. Most PV systems are residential (up to several kW) and commercial scale (up to several MW) connected to distribution networks. However, many PV systems are large generation facilities (some exceeding 100 MW) and are connected to the transmission system. NERC Reliability Standards require that power flow and dynamics models be provided, in accordance with regional requirements and procedures. Under the existing WECC modeling guidelines [ 3 ] all PV power plants with aggregated capacity 20 MVA or larger must be modeled explicitly in power flow and dynamics. This means that these plants must not be load-netted or modeled as negative load. Manufacturer-specific dynamic models commonly provided for interconnection studies are not adequate for regional planning. For this application, WECC requires the use of approved models, that are public (non-proprietary), are available as standard-library models, and have been tested and validated in accordance to WECC guidelines. Approved models are listed in the WECC Approved Dynamic Model List.

Architecture

Solar power plants are different than conventional power plants. The interface to the grid is an inverter connected to a PV array. Inverters are required to transform the DC output of the solar arrays to alternating current (AC) electricity compatible with the electric grid. One of the inverter functions is to control the DC voltage to ensure that the PV array operates at maximum power. Inverters also incorporate grid compatibility functions such as anti-islanding, and reactive support.

Inverters are characterized by low short circuit current contribution, lack of mechanical inertia, and high-bandwidth (fast) controls. A primary function of the inverter controls is to make the most efficient use of available energy being produced by the PV array, while ensuring that the magnitude of AC current does not exceed the rating of the inverter. PV plants do not have any inherent inertial or frequency response capabilities.

Large PV plants typically have several medium voltage radial feeders. The PV inverters are connected to the feeders via step-up transformers, with several inverters sharing one step-up transformer. Some plants designs include capacitors or other reactive support systems that work in conjunction with the inverters to meet reactive power capability and control requirements at the point of interconnection. A plant controller provides the power factor reference to the inverters and plant-level reactive power support equipment, if present. The plant controller processes measurements at the point of interconnection and commands issued from the fleet remote operations center or directly from the transmission system operator.

Small PV systems are deployed in customer premises and are connected directly to distribution service voltage. These systems do not typically have a plant controller, and the inverter manages the grid interface. Some PV systems as large as 20 MW are connected directly to distribution substations using a dedicated medium voltage feeder.

PV plants are considered non-dispatchable because the energy source (solar irradiance) is variable. However, reactive power is dispatchable within the capability of the inverters and plant-level reactive compensation.

Types of PV Arrays and Tracking Systems

Photovoltaic systems use semiconductor cells to convert solar radiation into DC electricity. The three most common types of PV technologies are crystalline silicon (c-Si), thin-film technology, and concentrating PV. Crystalline silicon solar cells are by far the most common technology for the solar cell market today [ 4 ]. Current reporting on efficiency of thin-film cells are in the area of 11% whereas c-Si cells come in around 20% [ 5 ]. Thin-film technology can also use Si as the semiconductor (usually amorphous Si) but have also used other materials such as cadmium telluride (CdTe). Concentrating PV technologies utilize lenses or mirrors to FOCUS sunlight on a small area of highefficiency cells. Demonstrations of concentrating PV show large-scale system efficiencies of 25% [ 6 ]. In addition to the semiconductor technology, there are different ways that a system can optimize energy capture. The arrangement and angle of the PV cells can play an important role in the total energy capture of the plant. While it is more common for PV arrays to have fixed mounts, some PV arrays use one-axis tracking systems to enhance energy production.Tracking systems are required for concentrating PV.

Inverters and Other Balance of Systems

Inverters are required to transform the DC output of the solar arrays to alternating current (AC) electricity compatible with the electric grid. One of the inverter functions is to control the DC voltage to ensure that the PV array operates at maximum power. Inverters also incorporate grid compatibility functions such as anti-islanding, and reactive support.The rating of power converters for large-scale solar plants today is typically 250 kW;however,1-MW converters are just starting to appear.

Solar is now ‘cheapest electricity in history’, confirms IEA

The world’s best solar power schemes now offer the “cheapest…electricity in history” with the technology cheaper than coal and gas in most major countries.

That is according to the International Energy Agency’s World Energy Outlook 2020. The 464-page outlook, published today by the IEA, also outlines the “extraordinarily turbulent” impact of coronavirus and the “highly uncertain” future of global energy use over the next two decades.

Reflecting this uncertainty, this year’s version of the highly influential annual outlook offers four “pathways” to 2040, all of which see a major rise in renewables. The IEA’s main scenario has 43% more solar output by 2040 than it expected in 2018, partly due to detailed new analysis showing that solar power is 20-50% cheaper than thought.

Despite a more Rapid rise for renewables and a “structural” decline for coal, the IEA says it is too soon to declare a peak in global oil use, unless there is stronger climate action. Similarly, it says demand for gas could rise 30% by 2040, unless the policy response to global warming steps up.

This means that, while global CO2 emissions have effectively peaked, they are “far from the immediate peak and decline” needed to stabilise the climate. The IEA says achieving net-zero emissions will require “unprecedented” efforts from every part of the global economy, not just the power sector.

For the first time, the IEA includes detailed modeling of a 1.5C pathway that reaches global net-zero CO2 emissions by 2050. It says individual behaviour change, such as working from home “three days a week”, would play an “essential” role in reaching this new “net-zero emissions by 2050 case” (NZE2050).

Future scenarios

The IEA’s annual World Energy Outlook (WEO) arrives every autumn and contains some of the most detailed and heavily scrutinised analysis of the global energy system. Over hundreds of densely packed pages, it draws on thousands of datapoints and the IEA’s World Energy Model.

The outlook includes several different scenarios, to reflect uncertainty over the many decisions that will affect the future path of the global economy, as well as the route taken out of the coronavirus crisis during the “critical” next decade. The WEO also aims to inform policymakers by showing how their plans would need to change if they want to shift onto a more sustainable path.

This year it omits the “current policies scenario” (CPS), which usually “provides a baseline…by outlining a future in which no new policies are added to those already in place”. This is because “[i]t is difficult to imagine this ‘business as-usual’ approach prevailing in today’s circumstances”.

Those circumstances are the unprecedented fallout from the coronavirus pandemic, which remains highly uncertain as to its depth and duration. The crisis is expected to cause a dramatic decline in global energy demand in 2020, with fossil fuels taking the biggest hit.

The main WEO pathway is again the “stated policies scenario” (STEPS, formerly NPS). This shows the impact of government pledges to go beyond the current policy baseline. Crucially, however, the IEA makes its own assessment of whether governments are credibly following through on their targets.

“The STEPS is designed to take a detailed and dispassionate look at the policies that are either in place or announced in different parts of the energy sector. It takes into account long-term energy and climate targets only to the extent that they are backed up by specific policies and measures. In doing so, it holds up a mirror to the plans of today’s policy makers and illustrates their consequences, without second-guessing how these plans might change in future.”

The outlook then shows how plans would need to change to plot a more sustainable path. It says its “sustainable development scenario” (SDS) is “fully aligned” with the Paris target of holding warming “well-below 2C…and pursuing efforts to limit [it] to 1.5C”. (This interpretation is disputed.)

The SDS sees CO2 emissions reach net-zero by 2070 and gives a 50% chance of holding warming to 1.65C, with the potential to stay below 1.5C if negative emissions are used at scale.

The IEA has not previously set out a detailed pathway to staying below 1.5C with 50% probability, with last year’s outlook only offering background analysis and some broad paragraphs of narrative.

For the first time this year, the WEO has “detailed modelling” of a “net-zero emissions by 2050 case” (NZE2050). This shows what would need to happen for CO2 emissions to fall to 45% below 2010 levels by 2030 on the way to net-zero by 2050, with a 50% chance of meeting the 1.5C limit.

The final pathway in this year’s outlook is a “delayed recovery scenario” (DRS), which shows what might happen if the coronavirus pandemic lingers and the global economy takes longer to recover, with knock-on reductions in the growth of GDP and energy demand.

The chart below shows how the use of different energy sources changes under each of these pathways over the decade to 2030 (right-hand columns), relative to demand today (left).

Left: Global primary energy demand by fuel in 2019, million tonnes of oil equivalent (Mtoe). Right: Changes in demand by 2030 under the four pathways in the outlook. Source: IEA World Energy Outlook 2020.

Notably, renewables (light green) account for the majority of demand growth in all scenarios. In contrast, fossil fuels see progressively weaker growth turn to increasing declines, as the ambition of global climate policy increases, from left to right in the chart above.

Intriguingly, there are signs that the IEA has been giving greater prominence to the SDS, a pathway aligned with the “well-below 2C” Paris goal. In the WEO 2020, it features more frequently, earlier in the report, and more consistently through the pages, compared with earlier editions.

This is shown in the chart below, which shows the location, by relative page position, of each mention of “sustainable development scenario” or “SDS” in the WEOs published over the past four years.

Mentions of “sustainable development scenario” or “SDS” in the last four WEO reports, by relative page position. Source: Carbon Brief analysis of IEA World Energy Outlook 2020 and previous editions. Chart by Joe Goodman for Carbon Brief.

Solar surge

One of the most significant shifts in this year’s WEO is tucked away in Annex B of the report, which shows the IEA’s estimates of the cost of different electricity generation technologies.

The table shows that solar electricity is some 20-50% cheaper today than the IEA had estimated in last year’s outlook, with the range depending on the region. There are similarly large reductions in the estimated costs of onshore and offshore wind.

This shift is the result of new analysis carried out by the WEO team, looking at the average “cost of capital” for developers looking to build new generating capacity. Previously the IEA assumed a range of 7-8% for all technologies, varying according to each country’s stage of development.

Now, the IEA has reviewed the evidence internationally and finds that for solar, the cost of capital is much lower, at 2.6-5.0% in Europe and the US, 4.4-5.5% in China and 8.8-10.0% in India, largely as a result of policies designed to reduce the risk of renewable investments.

In the best locations and with access to the most favourable policy support and finance, the IEA says the solar can now generate electricity “at or below” 20 per megawatt hour (MWh). It says:

“For projects with low-cost financing that tap high-quality resources, solar PV is now the cheapest source of electricity in history.”

The IEA says that new utility-scale solar projects now cost 30-60/MWh in Europe and the US and just 20-40/MWh in China and India, where “revenue support mechanisms” such as guaranteed are in place.

These costs “are entirely below the range of LCOE [levelised costs] for new coal-fired power plants” and “in the same range” as the operating cost of existing coal plants in China and India, the IEA says. This is shown in the chart below.

Estimated levelised costs of electricity (LCOE) from utility-scale solar with revenue support, relative to the LCOE range of gas and coal power. Source: IEA World Energy Outlook 2020.

Onshore and offshore wind are also now assumed to have access to lower-cost finance. This accounts for the much lower cost estimates for these technologies in the latest WEO, because the cost of capital contributes up to half of the cost of new renewable developments.

When combined with changes in government policy over the past year, these lower costs mean that the IEA has again raised its outlook for renewables over the next 20 years.

This is shown in the chart below, where electricity generation from non-hydro renewables in 2040 is now seen reaching 12,872 terawatt hours (TWh) in the STEPS, up from 2,873TWh today. This is some 8% higher than expected last year and 22% above the level expected in 2018’s outlook.

Global electricity generation, by fuel, terawatt hours. Historical data and the STEPS from WEO 2020 are shown with solid lines while the WEO 2019 is shown with dashed lines and WEO 2018 as dotted lines. Source: Carbon Brief analysis of IEA World Energy Outlook 2020 and previous editions. Chart by Carbon Brief using Highcharts.

Solar is the largest reason for this, with output in 2040 up 43% compared with the 2018 WEO. In contrast, the chart shows how electricity generation from coal is now “structurally” lower than previously expected, with output in 2040 some 14% lower than thought last year. The fuel never recovers from an estimated 8% drop in 2020 due to the coronavirus pandemic, the IEA says.

Notably, the level of gas generation in 2040 is also 6% lower in this year’s STEPS, again partly as a result of the pandemic and its long-lasting impact on economic and energy demand growth.

Overall, renewables – led by the “new king” solar – meet the vast majority of new electricity demand in the STEPS, accounting for 80% of the increase by 2030.

This means they overtake coal as the world’s largest source of power by 2025, outpacing the “accelerated case” set out by the agency just a year ago.

The rise of variable renewable sources means that there is an increasing need for electricity grid flexibility, the IEA notes. “Robust electricity networks, dispatchable power plants, storage technologies and demand response measures all play vital roles in meeting this,” it says.

Revised outlooks

The lower costs and more Rapid growth for solar seen in this year’s outlook means there will be record-breaking additions of new solar capacity in every year from 2020, the IEA says.

This contrasts with its STEPS pathway for solar in previous years, where global capacity additions each year – net of retirements – have flatlined into the future.

Now, solar growth rises steadily in the STEPS, as shown in the chart below (solid black line). This is even clearer if accounting for new capacity being added to replace old solar sites as they retire (gross, dashed line). Under the SDS and NZE2050, growth would need to be even faster.

Annual net additions of solar capacity around the world, gigawatts. Historical data is shown in red while central outlooks from successive editions of the WEO are shown in shades of blue. The WEO 2020 STEPS is shown in black. The dashed line shows gross additions, taking into account the replacement of older capacity as it retires after an assumed lifetime of 25 years. Source: Carbon Brief analysis of the IEA World Energy Outlook 2020 and previous editions of the outlook. Chart by Carbon Brief using Highcharts.

The story of raised outlooks for solar – thanks to updated assumptions and an improving policy landscape – is directly contrasting with the picture for coal.

Successive editions of the WEO have revised down the outlook for the dirtiest fossil fuel, with this year seeing particularly dramatic changes, thanks in part to a “structural shift” away from coal after coronavirus.

The IEA now sees coal use rising marginally over the next few years, but then going into decline, as shown in the chart below (red line). Nevertheless, this trajectory falls far short of the cuts needed to be in line with the SDS, a pathway aligned to the “well-below 2C” Paris target (yellow).

Historical global coal demand (black line, millions of tonnes of oil equivalent) and the IEA’s previous central scenarios for future growth (shades of blue). This year’s STEPS is shown in red and the SDS is in yellow. Carbon Brief analysis of the IEA World Energy Outlook 2020 and previous editions of the outlook. Chart by Carbon Brief using Highcharts.

This year’s outlook makes particularly drastic changes for India, where the use of coal in electricity generation is seen growing far more slowly than expected last year.

In the STEPS, coal-fired power capacity would grow by just 25 gigawatts (GW) by 2040, the IEA says, which is 86% less than expected in the WEO 2019. Rather than nearly doubling in size from 235GW in 2019, this means that India’s coal fleet would barely grow over the next two decades.

Similarly, growth in the amount of electricity generated from coal in India is now expected to be 80% slower than thought last year, according to the IEA figures.

India will build 86% less new coal power capacity than expected last yr

Long seen as driving global coal growth, IEA now says India will add just 25GW by 2040

The IEA expects continued Rapid retirements of old coal capacity in the US and Europe, which would by 2040 close 197GW (74% of the current fleet) and 129GW (88%) respectively.

Taken together, and despite a Rapid expansion in southeast Asia, this means the outlook – for the first time – sees the global coal fleet shrinking by 2040.

Energy outlook

Taken together, the Rapid rise of renewable energy and the structural decline for coal help keep a lid on global CO2 emissions, the outlook suggests. But steady demand for oil and rising gas use mean CO2 only flattens off, rather than declining rapidly as required to meet global climate goals.

These competing trends are shown in the chart, below, which tracks primary energy demand for each fuel under the IEA STEPS, with solid lines. Overall, renewables meet three-fifths of the increase in energy demand by 2040, while accounting for another two-fifths of the total. Smaller increases for oil and nuclear are enough to offset the decline in coal energy use.

Global primary energy demand by fuel, millions of tonnes of oil equivalent, between 1990 and 2040. Future demand is based on the STEPS (solid lines) and SDS (dashed). Other renewables includes solar, wind, geothermal and marine. Source: IEA World Energy Outlook 2020. Chart by Carbon Brief using Highcharts.

The dashed lines in the chart above show the dramatically different paths that would need to be followed to be in line with the IEA SDS, which is roughly a well-below 2C scenario.

By 2040, although oil and gas would remain the first and second-largest sources of primary energy, there would have been declines in the use of all fossil fuels. Coal would have dropped by two-thirds, oil by a third and gas by 12%, relative to 2019 levels.

Meanwhile, other renewables – primarily wind and solar – would have surged to third place, rising nearly seven-fold over the next two decades (662%). The SDS sees smaller, but still sizeable increases for hydro (55%), nuclear (55%) and bioenergy (24%).

Together, low-carbon sources would make up 44% of the global energy mix in 2040, up from 19% in 2019. Coal would fall to 10%, its lowest since the industrial revolution, according to the IEA.

Despite these Rapid changes, however, the world would not see net-zero CO2 emissions until 2070, some two decades after the 2050 deadline that would be needed to stay below 1.5C.

This is despite the SDS including “full implementation” of the net-zero targets set by the UK, EU and most recently China.

(These targets would be only partially implemented under the STEPS, based on the IEA’s assessment of the credibility of the policies in place to meet the goals. For example, table B.4 of the report says that under the STEPS, there is only “some implementation” of the UK’s legally binding target to reach net-zero greenhouse gas emissions by 2050.)

Net-zero numbers

The NZE2050 “case”, describing a route to 1.5C, has been published for the first time this year, because the WEO team agreed “it was time to deepen and extend our analysis of net-zero emissions”, according to IEA director Fatih Birol, writing in the report’s foreword.

Over the past 18 months, major economies announcing or legislating net-zero emissions targets include the UK and EU. Most recently, China announced its intention to reach “carbon neutrality” by 2060. [Forthcoming analysis for Carbon Brief will explore the implications of this goal.]

Carbon Brief analysis of the last four WEOs shows that these developments – along with the publication of the Intergovernmental Panel on Climate Change (IPCC) special report on 1.5C in 2018 – have been accompanied by a significant uptick in coverage of these topics in the WEO.

Whereas the WEO 2017 used the phrase “1.5C” less than once per 100 pages, this increased to five uses in 2019 and eight uses per 100 pages in 2020. The usage of “net zero” is up from once per 100 pages in 2017 and 2018, to six in 2019 and 38 per 100 pages in this year’s report.

However, the NZE2050 case is not a full WEO scenario and so it does not come with the full set of data that accompanies the STEPS and SDS, making it difficult to fully explore the pathway.

This seems “bizarre”, says Dr Joeri Rogelj, a lecturer in climate change and the environment at the Grantham Institute at Imperial College London and a coordinating lead author of the IPCC 1.5C report.

The IEA already publishes lengthy annexes, with detailed information on the pathway for different energy sources and CO2 emissions from each sector, in a range of key economies around the world, under each of its main scenarios. (This year these are the STEPS and SDS.)

Rogelj, who last year joined scientists and NGOs calling for the IEA to publish a full 1.5C scenario, tells Carbon Brief that “all underlying data of the NZE2050 case should be made available with the same detail as the other WEO scenarios”.

Carbon Brief has asked the IEA for such data and will update this article if more details emerge. Rogelj adds:

“The main question, of course, is how the NZE2050 intends to reach its objective of net-zero CO2 emissions in 2050. Of particular interest here is how much and which type of CO2 removal [negative emissions] the scenario intends to use and how it intends to do so while ensuring sustainable development.”

The WEO devotes a full chapter to the NZE2050, with a particular emphasis on the changes that would be needed over the next decade to 2030.

(It also compares the pathway to those set out in the IPCC special report, saying that the NZE2050 case has a comparable CO2 emissions trajectory to the “P2” scenario, which stays below 1.5C with “no or low overshoot” and has relatively “limited” use of BECCS.)

THREAD: The @IEA now has an aggressive 1.5°C scenario, reaching net-zero by 2050.

It builds on the Sustainable Development Scenario, strengthening reductions in power end-use, but with new behavioural measures.

The chart below shows how CO2 emissions effectively plateau to 2030 in the STEPS, remaining just below the level seen in 2019, whereas the NZE2050 case sees a decline of more than 40%, from 34bn tonnes (GtCO2) in 2020 to just 20GtCO2 in 2030.

Global CO2 emissions from energy and industrial processes, 2015-2030, billion tonnes of CO2 (GtCO2), under the STEPS, SDS and NZE2050. Coloured wedges show contributions to the additional savings needed for the SDS and NZE2050. Source: IEA World Energy Outlook 2020.

The power sector contributes the largest portion of the savings needed over the next decade (orange wedges in the chart, above). But there are also important contributions from energy end-use (yellow), such as transport and industry, as well as from individual behaviour change (blue), explored in more detail in the next section.

These three wedges would contribute roughly equal shares of the extra 6.4GtCO2 of savings needed to go from the SDS to the NZE2050 in 2030, the IEA says.

The NZE2050 case would see low-carbon sources of electricity meeting 75% of demand in 2030, up from 40% today. Solar capacity would have to rise at a rate of around 300 gigawatts (GW) per year by the mid-2020s and nearly 500GW by 2030, against current growth of around 100GW.

CO2 emissions from coal-fired power stations would decline by 75% between 2019 and 2030. This means the least efficient “subcritical” coal plants would be phased out entirely and the majority of “supercritical” plants would also close down. The WEO says the majority of this decline would come in southeast Asia, which accounts for two-thirds of current global coal capacity.

Although nuclear would contribute a small part of the increase in zero-carbon generation by 2030 in the NZE2050, the IEA notes that the “long lead time of large-scale nuclear facilities” limits the technology’s potential to scale more quickly this decade.

For industry, CO2 emissions would fall by around a quarter, with electrification and energy efficiency making up the largest shares of the effort. than 2m homes would get an energy efficiency retrofit during every month this decade, in “advanced economies” alone.

In the transport sector, CO2 would fall by a fifth, not including behavioural shifts counted below. By 2030, more than half of new cars would be electric, up from around 2.5% in 2019.

Behavioural changes

For the first time, this year’s outlook contains a detailed analysis of the potential for individual behaviour change to reduce CO2 emissions. (This is clear even at a simplistic level, with the word “behaviour” mentioned 122 times, against just 12 times in 2019.)

Behavioural shifts, such as cutting down on flights and turning down air conditioning, will play a vital role in achieving net-zero emissions, according to the report.

While the SDS calls for modest changes to people’s lifestyles, such as increased use of public transport, these choices only make up 9% of the difference between that scenario and the STEPS.

By comparison, in the NZE2050 these changes are responsible for nearly a third of the CO2 reductions relative to the SDS in 2030.

The report includes a detailed analysis of estimated emissions savings from the global adoption of specific actions, including a global switch to line-drying laundry, slower driving speeds and working from home.

The authors estimate that 60% of these changes could be influenced by governments, citing widespread legislation to control car use in cities and Japan’s efforts to limit air conditioning in homes and offices.

As the chart below shows, changes to people’s transport choices account for the majority of the emissions savings. Road transport (blue bars) accounts for more than half the savings in 2030 and significantly reducing the number of flights accounts for another quarter (yellow).

Impact of behaviour changes across three key sectors on annual CO2 emissions in the NZE2050 scenario. Source: IEA World Energy Outlook 2020.

Around 7% of CO2 emissions from cars come from trips of less than 3km, which “would take less than about 10 minutes to cycle”, according to the authors. In the NZE2050 scenario, all of these trips are replaced with walking and cycling.

The report estimates that behaviour shifts could cut emissions from flying by around 60% in 2030. These include substantial changes, such as eliminating flights of less than one hour long, as well as reducing numbers of both long-haul and business flights by three quarters.

Even so, due to the growth in aviation that is otherwise expected, total aviation activity in 2030 would still remain around 2017 levels in this scenario.

The remaining savings come from decisions to limit the use of energy in homes, such as turning both heating and air conditioning systems down.

Working from home has the potential to save emissions overall, as the reduction in emissions from commuting is more than three times larger than the increase in residential emissions.

Expert analysis direct to your inbox.

Get a round-up of all the important articles and papers selected by Carbon Brief by email. Find out more about our newsletters here.

Get a round-up of all the important articles and papers selected by Carbon Brief by email. Find out more about our newsletters here.

The report estimates that if the 20% of the global workforce who are able to work from home did so for just one day a week, in 2030 this would save around 18m tonnes of CO2 (MtCO2) globally, as the chart below shows.

In fact, the NZE2050 scenario assumes that all those who are able to do so, work from home three days a week, amounting to a relatively modest 55MtCO2 savings.

Due to wider changes in the energy mix in NZE2050, the emissions impact of widespread home working is small when compared to the current situation, shown in the left-hand column, or STEPS in 2030, shown in the middle column.

Change in annual global energy consumption (left y-axis) and CO2 emissions (right y-axis) if 20% of the population worked from home for one day a week, under three different scenarios. Emissions savings from transport (red and light blue) exceed the increase in residential emissions (purple, dark blue and grey) associated with working from home. Source: IEA.

While the report focuses on CO2 emissions from the energy system, it also alludes to the high levels of methane and nitrous oxide resulting from global agriculture and livestock farming in particular.

It notes that without shifts towards vegetarian diets it will be “very difficult to achieve Rapid emissions reductions”.

The authors acknowledge that universal adoption of the proposed behaviour changes is unlikely, but suggest there are “alternative ways” in which such changes could combine to yield similar results.

For example, though some regions may not introduce tougher speed limits, others might decide to cut driving speeds by more than the 7km/h suggested in the report.

Simon Evans was one of more than 250 external peer reviewers who read sections of the World Energy Outlook in draft form.

The Dark Side of Solar Power

Solar energy is a rapidly growing market, which should be good news for the environment. Unfortunately there’s a catch. The replacement rate of solar panels is faster than expected and given the current very high recycling costs, there’s a real danger that all used panels will go straight to landfill (along with equally hard-to-recycle wind turbines). Regulators and industry players need to start improving the economics and scale of recycling capabilities before the avalanche of solar panels hits.

It’s sunny times for solar power. In the U.S., home installations of solar panels have fully rebounded from the Covid slump, with analysts predicting more than 19 gigawatts of total capacity installed, compared to 13 gigawatts at the close of 2019. Over the next 10 years, that number may quadruple, according to industry research data. And that’s not even taking into consideration the further impact of possible new regulations and incentives launched by the green-friendly Biden administration.

Solar’s pandemic-proof performance is due in large part to the Solar Investment Tax Credit, which defrays 26% of solar-related expenses for all residential and commercial customers (just down from 30% during 2006–2019). After 2023, the tax credit will step down to a permanent 10% for commercial installers and will disappear entirely for home buyers. Therefore, sales of solar will probably burn even hotter in the coming months, as buyers race to cash in while they still can.

Tax subsidies are not the only reason for the solar explosion. The conversion efficiency of panels has improved by as much as 0.5% each year for the last 10 years, even as production costs (and thus prices) have sharply declined, thanks to several waves of manufacturing innovation mostly driven by industry-dominant Chinese panel producers. For the end consumer, this amounts to far lower up-front costs per kilowatt of energy generated.

This is all great news, not just for the industry but also for anyone who acknowledges the need to transition from fossil fuels to renewable energy for the sake of our planet’s future. But there’s a massive caveat that very few are talking about.

Panels, Panels Everywhere

Economic incentives are rapidly aligning to encourage customers to trade their existing panels for newer, cheaper, more efficient models. In an industry where circularity solutions such as recycling remain woefully inadequate, the sheer volume of discarded panels will soon pose a risk of existentially damaging proportions.

To be sure, this is not the story one gets from official industry and government sources. The International Renewable Energy Agency (IRENA)’s official projections assert that “large amounts of annual waste are anticipated by the early 2030s” and could total 78 million tonnes by the year 2050. That’s a staggering amount, undoubtedly. But with so many years to prepare, it describes a billion-dollar opportunity for recapture of valuable materials rather than a dire threat. The threat is hidden by the fact that IRENA’s predictions are premised upon customers keeping their panels in place for the entirety of their 30-year life cycle. They do not account for the possibility of widespread early replacement.

Our research does. Using real U.S. data, we modeled the incentives affecting consumers’ decisions whether to replace under various scenarios. We surmised that three variables were particularly salient in determining replacement decisions: installation price, compensation rate (i.e., the going rate for solar energy sold to the grid), and module efficiency. If the cost of trading up is low enough, and the efficiency and compensation rate are high enough, we posit that rational consumers will make the switch, regardless of whether their existing panels have lived out a full 30 years.

As an example, consider a hypothetical consumer (call her “Ms. Brown”) living in California who installed solar panels on her home in 2011. Theoretically, she could keep the panels in place for 30 years, i.e., until 2041. At the time of installation, the total cost was 40,800, 30% of which was tax deductible thanks to the Solar Investment Tax Credit. In 2011, Ms. Brown could expect to generate 12,000 kilowatts of energy through her solar panels, or roughly 2,100 worth of electricity. In each following year, the efficiency of her panel decreases by approximately one percent due to module degradation.

Now imagine that in the year 2026, halfway through the life cycle of her equipment, Ms. Brown starts to look at her solar options again. She’s heard the latest generation of panels are cheaper and more efficient — and when she does her homework, she finds that that is very much the case. Going by actual current projections, the Ms. Brown of 2026 will find that costs associated with buying and installing solar panels have fallen by 70% from where they were in 2011. over, the new-generation panels will yield 2,800 in annual revenue, 700 more than her existing setup when it was new. All told, upgrading her panels now rather than waiting another 15 years will increase the net present value (NPV) of her solar rig by more than 3,000 in 2011 dollars. If Ms. Brown is a rational actor, she will opt for early replacement. And if she were especially shrewd in money matters, she would have come to that decision even sooner — our calculations for the Ms. Brown scenario show the replacement NPV overtaking that of panel retention starting in 2021.

See more HBR charts in Data Visuals

If early replacements occur as predicted by our statistical model, they can produce 50 times more waste in just four years than IRENA anticipates. That figure translates to around 315,000 metric tonnes of waste, based on an estimate of 90 tonnes per MW weight-to-power ratio.

Alarming as they are, these stats may not do full justice to the crisis, as our analysis is restricted to residential installations. With commercial and industrial panels added to the picture, the scale of replacements could be much, much larger.

The High Cost of Solar Trash

The industry’s current circular capacity is woefully unprepared for the deluge of waste that is likely to come. The financial incentive to invest in recycling has never been very strong in solar. While panels contain small amounts of valuable materials such as silver, they are mostly made of glass, an extremely low-value material. The long life span of solar panels also serves to disincentivize innovation in this area.

As a result, solar’s production boom has left its recycling infrastructure in the dust. To give you some indication, First Solar is the sole U.S. panel manufacturer we know of with an up-and-running recycling initiative, which only applies to the company’s own products at a global capacity of two million panels per year. With the current capacity, it costs an estimated 20–30 to recycle one panel. Sending that same panel to a landfill would cost a mere 1–2.

The direct cost of recycling is only part of the end-of-life burden, however. Panels are delicate, bulky pieces of equipment usually installed on rooftops in the residential context. Specialized labor is required to detach and remove them, lest they shatter to smithereens before they make it onto the truck. In addition, some governments may classify solar panels as hazardous waste, due to the small amounts of heavy metals (cadmium, lead, etc.) they contain. This classification carries with it a string of expensive restrictions — hazardous waste can only be transported at designated times and via select routes, etc.

The totality of these unforeseen costs could crush industry competitiveness. If we plot future installations according to a logistic growth curve capped at 700 GW by 2050 (NREL’s estimated ceiling for the U.S. residential market) alongside the early-replacement curve, we see the volume of waste surpassing that of new installations by the year 2031. By 2035, discarded panels would outweigh new units sold by 2.56 times. In turn, this would catapult the LCOE (levelized cost of energy, a measure of the overall cost of an energy-producing asset over its lifetime) to four times the current projection. The economics of solar — so bright-seeming from the vantage point of 2021 — would darken quickly as the industry sinks under the weight of its own trash.

Who Pays the Bill?

It will almost certainly fall to regulators to decide who will bear the cleanup costs. As waste from the first wave of early replacements piles up in the next few years, the U.S. government — starting with the states, but surely escalating to the federal level — will introduce solar panel recycling legislation. Conceivably, future regulations in the U.S. will follow the model of the European Union’s WEEE Directive, a legal framework for the recycling and disposal of electronic waste throughout EU member states. The U.S. states that have enacted electronics-recycling legislation have mostly cleaved to the WEEE model. (The Directive was amended in 2014 to include solar panels.) In the EU, recycling responsibilities for past (historic) waste have been apportioned to manufacturers based on current market share.

A first step to forestalling disaster may be for solar panel producers to start lobbying for similar legislation in the United States immediately, instead of waiting for solar panels to start clogging landfills. In our experience drafting and implementing the revision of the original WEEE Directive in the late 2000s, we found one of the biggest challenges in those early years was assigning responsibility for the vast amount of accumulated waste generated by companies no longer in the electronics business (so-called orphan waste).

In the case of solar, the problem is made even thornier by new rules out of Beijing that shave subsidies for solar panel producers while increasing mandatory competitive bidding for new solar projects. In an industry dominated by Chinese players, this ramps up the uncertainty factor. With reduced support from the central government, it’s possible that some Chinese producers may fall out of the market. One of the reasons to push legislation now rather than later is to ensure that the responsibility for recycling the imminent first wave of waste is shared fairly by makers of the equipment concerned. If legislation comes too late, the remaining players may be forced to deal with the expensive mess that erstwhile Chinese producers left behind.