Global Progress Toward Renewable Electricity: Tracking the Role of Solar

—Renewable electricity is growing rapidly, with solar electricitygrowingrelativelyfasterthananyotherfuelsourceinthelasttenyears.Astheworldacceleratesitstransitiontocleanenergy, itisusefultotracktherateofgrowth,butthedataaretrackedindifferentwaysfromdifferentsources.Thisperiodicpublication collectsdatafrommultiplesourcesandpresentsitsystematicallyasaconvenientreferenceforIEEEJPVreaders.

growth in total global electricity generation from all fuels in that same time frame went from 11 957 to 26 823 TWh, a factor of about 2.3 [1].
The goal of this article is to present data, in both graphical and tabular form, on the global progress toward renewable energy.Tracking progress over time provides not only important history but also a basis for anticipating future milestones and transitions.Multiple entities and institutions provide this global energy data on a yearly basis.This article seeks to assemble a set of key sources to track both long-term trends and yearly changes.Different institutions may have variations in original sources or methodologies and may change methodologies over time.We hope it will be valuable, therefore, to assemble a collection of frequently used and cited sources so that these variations can be appreciated in context relative to overall trends.
We present the following three sets of graphs: 1) annual generation by broad fuel source for global electricity (Section II); 2) yearly generation and newly installed capacity for specific fuel sources with a focus on renewables (Section III); 3) generation and capacity over time with a more detailed breakout of fuel sources including PV (Section IV).Data are summarized from six primary sources: the Statistical Review of World Energy, published yearly by BP [2]; the international data presented by the U.S. Energy Information Administration (EIA) [3]; the World Nuclear Association (WNA) [4], the International Energy Agency (IEA) [5]; the International Renewable Energy Agency (IRENA) [6], and REN21 [7].Short summaries of the mission and history for these six organizations are provided in the Appendix.We will make yearly updates and provide the PV community with a consistent source of data and figures to monitor and present progress over time.As applications and sector coupling increase, the report may be expanded to include PV sectors (e.g., utility, commercial, residential, building integrated, agriPV, etc.) and critical related technologies (e.g., storage).circles used to mark the other data sources.One sees that source variations, although of interest for detailed understanding and analysis, are not significant when assessing major trends over time.

II. TRACKING PROGRESS TOWARD RENEWABLE ELECTRICITY
Electricity generation, a measure of energy provided, is presented in TWh, where 1 TWh = 3.6 x 10 15 J. Installed nameplate capacity, commonly reported in W, MW, or GW depending on system size, is the rated output of a generator or other electric power production equipment under specific conditions designated by the manufacturer.The "capacity factor" is the ratio of the actual output of a system or collection of systems under true operating conditions (reflecting e.g., variable resource, facility downtime, performance variations, large scale climate effects, etc.) and the output of that electricity source operating continuously at its commercial product or plant rating.Capacity factors for electricity generating technologies can vary significantly, both within a technology depending on the performance, and between technologies as determined by the physics of the particular energy conversion process.Actual electricity generation [Fig.1(a)] is the most relevant to understand and track the evolution of the energy system in terms of contributing fuel sources.Capacity [Fig.1(b)] allows one to understand and track global installations and new technology investment.
Different organizations report their source data using different fuel subcategories.In Fig. 1, the BP values for fossil generation and capacity are determined by summing component data for oil, gas, coal and "other" (where "other" is pumped hydro, nonrenewable waste, and statistical discrepancies) [1] to obtain a total fossil value.Nonhydro renewable totals are calculated by subtracting the sum of total fossil, nuclear and hydro from the total electricity value.This addresses the fact that individual values for certain nonhydro renewable components (PV, wind, concentrating solar power, geothermal, etc.) were not uniformly reported in earlier years, though that situation is evolving rapidly.The EIA values are taken directly from the website [9] by selecting the desired categories.
Several recent transitions are worth noting in Fig. 1.Electricity generation from combined nonhydro renewables (primarily PV and wind) reached and exceeded generation from nuclear power sources in 2019 and is poised to exceed electricity generated from hydropower worldwide in the next few years.The combined capacity for nonhydro renewables now exceeds both conventional hydroelectric power and nuclear, reflecting the rapid growth in PV and wind installation.Finally, continued projected growth in nonhydro renewables, compared to the growth rate in total electricity, suggests major potential for future electrification of other energy sectors, with corresponding benefits to overall efficiency and decarbonization.The pie charts illustrate themes from the introduction: a massive system, dominated by fossil energy [Fig.2(a)], undergoing a rapid rate of change [Fig.2(c)].We plot electricity generation, generating capacity, and net capacity expansions (new installation minus any decommissioning) to highlight both where we stand and the rate of change that will drive the future electricity generating mix.Combined renewables (solar, wind, hydro, geothermal, and biomass) constitute more than 50% of capacity expansions for the past five years.PV and wind combined alone are more than 50% of capacity expansion for the past four years.Although the fractional global contribution of PV to electricity generation, growing from 1.1% in 2015 to 3.4% in 2020, is still relatively small, the relative rate of change is large, representing a tripling in just five years.These trends have continued despite the impact of the global pandemic, and policy and emerging technology issues including tariffs, local price structuring, and the growing role of storage and sector coupling.
IV. TRACKING THE ROLE OF PV Fig. 3 again shows yearly global electricity generation (a) and generating capacity (b) from 1990 to 2020, but this time breaking out the contributing technologies to the "nonhydro renewables" from Fig. 1.Source data are presented in Table VIII and IX, respectively.In Fig. 3(a), the solid lines again represent data from [1], with open circles used to mark other data sources.For Fig. 3(b), solid lines represent the data in bold in Table IX, with open circles used to mark the other data sources.As mentioned previously, different organizations have different mission goals and focus and report source data using different fuel subcategories.By looking at these in combination, one can track a wide range of trends over time.We note again that source variations, although of interest for detailed understanding and analysis, are relatively minor when assessing major trends over time.
The rapid growth in solar PV and wind since 2000, reflected in the pie charts for 2016-2020, has led to several milestones in the last few years.Combined wind and solar PV global capacity exceed 1 TW and are contributing ∼9% of global electricity.With regard to fossil fuels, electricity generation from natural gas has increased, generation from coal has flattened and generation from oil has decreased.For nonhydro renewables, every technology -wind, solar PV, biomass, geothermal and concentrating solar power (CSP) -is increasing in magnitude of electricity generated.
Five different sources for solar (BP, EIA, IEA, IRENA, and REN21) are presented in Table IX and utilized in Figs. 2 and 3. Variations in these values can arise for multiple reasons.Among these are as follows: 1) variations in reporting PV capacity as W dc or W ac ; 2) differences that arise in reports of PV shipments versus installations, variations in cross-border electricity accounting, or handling of the balance between new and retired resources; 3) changing methodologies in source reporting.Those with interests in pursuing these variations can find further details in the primary sources.
We also note that reporting of solar electricity and capacity can be composed of contributions from both PV and CSP, depending on the source.Data available from IEA [10] show that the magnitude of electricity generated from CSP exceeded that from PV in the period from 1990 to 1999.Since that time, the rapid growth in PV has made PV the dominant contributor to solar-generated electricity.Using that same data source, we find that PV was ∼98% of the solar total reported for 2018.Tables VIII and IX indicate whether solar data are a combination of these technologies or PV only.These tables also indicate our assessment of which data are W dc or W ac .However, we note that there may be inconsistencies in the documentation of dc and ac PV ratings and that some sources may include a mixture of data.
V. CONCLUSION 2020 was a watershed year globally for many reasons.In the midst of the global disruption associated with the pandemic, new installation of renewable energy electricity generating capacity continued to represent a majority of expansion, and electricity generated from PV globally now exceeds 3%.This reflects large variations in the use of the solar resource and PV technology around the globe, suggesting both the challenge and the opportunity ahead.The continued growth of both wind and PV point to a future where synergies between these two technologies, with growing impact of storage, can lead the way to a clean, sustainable energy system as well as increased electrification and efficiency across all energy sectors.The rapid rate of change continues.
The broad PV research and development community has played a significant role in the trajectory of renewable energy and particularly PV represented in Figs.1-3.This progress has been driven by a combination of decreased costs, increased performance, and increased reliability.These advances have enabled a growing global industry and supply chain to both respond to and drive increasing demand.Sustaining future growth will require continued progress in all these areas as we continue to track progress in renewable energy as a whole, PV as a key technology, and the rate of change that will determine our future.

APPENDIX
This appendix describes the sources of the data reported in Figs.1-3.
The Statistical Review of World Energy is compiled and published by BP and publicly released in the summer of each year.Its history goes back to 1952, initially called the Statistical Review of the World Oil Industry.The name was changed in 1981 to its present title, with a corresponding expansion to provide information on fuels other than oil [8].The report provides tables summarizing global data in ten major categories (coal, electricity, hydroelectricity, key minerals, natural gas, nuclear energy, oil, primary energy, renewable energy, and CO 2 emissions).BP makes available the full report edition for download, as well as PowerPoint slides and Excel spreadsheets of the source data.
The EIA is a U.S. government agency located within the Department of Energy.It was officially created in 1977 as the primary federal government authority on energy statistics and analysis.EIA information is disseminated in a variety of ways, including reports, web products, press releases, data browsers, and maps.Reports are issued on varying time scales; EIA is generally the last to present data for each year.While EIA has, arguably, the most comprehensive data set, it is also the least timely in tracking global data.Both U.S. and international data sets are available, and many are available in Excel spreadsheet form for download.
The IEA was created in 1974 as an international forum for energy cooperation.Today it has 30 member countries and eight association countries.IEA provides a wide range of data products.Their time series goes back to 1971 and reflects input from over 150 countries.Data can be charted real time in various ways and chart data are available for download in Excel format.Data can be sorted by category (e.g., supply, consumption), indicator (e.g., fuel type) and country or region (e.g., world, Europe, France).
The IRENA was officially founded in 2009 and has over 180 countries engaged in its activities.It is an international organization designed to assist countries in their transition to a sustainable energy future.IRENA provides a range of products, including renewable energy capacity statistics.They produce periodic publications and have their complete capacity data set from 2000 onward available for download.
The WNA is an international organization representing the global nuclear industry and composed of members from nuclear utilities, reactor vendors, engineering firms, and a range of companies involved in the nuclear supply chain.The WNA tracks year to year nuclear electricity production and nuclear generating capacity in their World Nuclear Performance Report [11].
REN 21 (Renewables Now) was founded in 2004 and is an international network with a focus on renewable energy policy.They "collect, consolidate and synthesize" data on renewable energy.REN 21 publishes a yearly report, the Renewables Global Status Report (GSR).The GSR is a crowd sourced report, covering market and policy trends, and released midyear.The full report and an associated data pack are available on the REN 21 site for download.
The data obtained from the above organizations and presented in Figs.1-3 are tabulated in Tables I-IX.The selection of data for Tables III-VII has little effect on the creation of Fig. 2(a) and (b) but can have a greater effect on the appearance of Fig. 2(c).While we were forced to mix data from different sources to create Fig. 2, we attempted to be consistent from year to year in our methodology so that the trends would be clear.The electricity data in Fig. 2(a) and Tables III-VII were taken from BP except the biomass and geothermal data, which were taken       from REN21.The capacity data in Fig. 2(b) and Table II used WNA data for nuclear, BP data for wind and solar and REN21 data for hydro, biomass, and geothermal.The fossil capacity data were taken from EIA for the earlier years and estimated for the later years by noting the REN21 assessment of the fraction of capacity additions that could be related to fossil.

Fig. 1
Fig. 1 shows yearly global electricity generation (a) and generating capacity (b) from 1990 to 2020.Source data are presented in Tables I and II, respectively, in the Appendix.Data from the Statistical Review of Energy, now in its 70th edition and representing the longest running compilation of global energy statistics [8], are indicated in Fig. 1(a) by solid lines, with open circles used to mark other data sources as indicated.For Fig. 1(b), solid lines represent the data in bold in Table II, with open

Fig. 1 .
Fig. 1.(a) Annual electricity generation and (b) electricity generating capacity.Data are tabulated in Tables I and II with lines for the bolded data and open circles for the other sources.
III. TRACKING THE RATE OF CHANGEIn Fig.2(a)-(c), we plot data for the past five years (2016-2020) for (a) global fraction of electricity generation, (b) global fraction of electricity generating capacity, and (c) global fraction of net expansions of electricity generating capacity for the given year.Data for fossil, nuclear, and hydro are drawn from Table I and are summarized by year in Tables III-VII.Data for wind, solar, and other technologies are drawn from Table VIII and also summarized in Tables III-VII, with the electricity generation data in Fig. 2(a) taken from Tables I and VIII and the electricity-generation capacity data in Fig. 2(b) taken from Tables II and IX.The net expansions of the electricity-generating capacity data in Fig. 2(c) are obtained by subtracting the data in Fig. 2(b) for each year from the following year.The choice of data sets to use for Fig. 2 and tabulated in Tables III-VII is detailed in the Appendix.Some values in Tables III-VII are not directly available and were derived indirectly from the references as described in the Appendix.

Fig. 2 .
Fig. 2. (a) Pie charts showing global share of electricity generation by technology for the indicated years.Data taken from Tables I and VIII and summarized in Tables III-VII (see Appendix).The "other" category includes biomass and geothermal.(b) Pie charts showing global share of electricity-generation capacity by technology for the indicated years.Data taken from Tables II and IX and summarized in Tables III-VII (see Appendix for additional details).(c) Pie charts showing global share of net expansions of electricity-generation capacity by technology for the indicated years.Data taken from Tables II and IX and summarized in Table III-VIII (see Appendix for additional details).

Fig. 3 .
Fig. 3. (a) Annual electricity generation.(b) Electricity generating capacity by fuel.Data are tabulated in Tables VIII and IX (see Appendix) with lines for the bolded data and open circles for the other sources.
Table II, with open

TABLE I GLOBAL
ELECTRICITY GENERATION BY TECHNOLOGY CATEGORY (TWH FOR INDICATED YEAR)

TABLE III GLOBAL
2016 DATA SUMMARY FOR CREATING PIE CHARTS IN FIG. 2 * Biomass and Geothermal

TABLE IV GLOBAL
2017 DATA SUMMARY FOR CREATING PIE CHARTS IN FIG. 2 * Biomass and Geotherm

TABLE V
GLOBAL 2018 DATA SUMMARY FOR CREATING PIE CHARTS IN FIG. 2 * Biomass and Geothermal

TABLE VI GLOBAL
2019 DATA SUMMARY FOR CREATING PIE CHARTS IN FIG. 2 * Biomass and Geothermal

TABLE VII GLOBAL
2020 DATA SUMMARY FOR CREATING PIE CHARTS IN FIG. 2 * Biomass and Geothermal