Home

Year to year variability in PVsyst

Project design > P50 - P90 evaluations - PVsys

  1. When the variations of annual meteo data is of the order of 3-4% (RMS), the variability of monthly data from year to year is much higher, and defining a probability profile for each month will give erratic results
  2. ation The annual variability (sigma value) will be do
  3. NB: The simulation for a given year takes the average loss calculated mid year. For example for the 10th year of operation, the ageing loss factor will be calculated over 9.5 years. For the usual simulations of PVsyst (first year) we should indeed consider the degradation after 6 months (0.2% in our example). This is usually neglected

What is the P50-P90 probabilistic production ? - PVsyst's

  1. - TArray Aver = Array temperature average over the whole year, weighted by GlobInc, i.e.: TArray Aver = Σ hours (GlobInc * TArray) / Σ hours (GlobInc) Mathematically, if the TArray Aver is calculated with the same data, the yearly PR(corr) value should be equal to the yearly PR. We have implemented this in the PVsyst version 6.74
  2. Generic Year 1990; Grid current in tri-phased configuration; Incidence_Angle; Inverter: power overcharging; Inverter: voltage limits; License file; Licensed mode; LOL Loss-of-load probability (Pumping) LOL Loss-of-load probability (stand-alone) Longitudinal_Incidence_Angle; Plane azimuth; Plane orientation; Plane tilt; PROFESSIONAL; Profile.
  3. g/cooling in the TIO corresponds to more significant surface temperature and precipitation anomalies in Asia during 1981-2016 (Sun et al. 2019). The positive anomalies in western Nepal during 2000-2013 in PC2 can be related to SST variability in the TIO
  4. Bruno Wittmer. Post subject: Re: P50 -P90 probabilities. PostPosted: Fri Sep 05, 2014 2:36 pm. Joined: Thu Oct 03, 2013 7:03 am. Posts: 91. To be able to interpret the simulation output as P50 value, one has to use an average over many years as meteorological input, not the data of a specific year. The PVsyst default is to use Meteonorm data.

Ageing, PV modules degradation - PVsys

  1. us 1°C. 3.
  2. e whether year-to-year fluctuations in PSA levels are due to natural variation and render a single PSA test result unreliable. Design, setting, and participants: Five consecutive blood samples were obtained during a 4-year period and were assessed for total and free PSA levels
  3. The value provided presently with the PVsyst results uses the definition of the Monofacial systems, so that the bi-facial gain comes as an increase of this ratio. NB: The main objective of the PR is to find an indicator for comparing real and simulated data, therefore which may easily be evaluated using simple (and primary) measured data
  4. Other option is using a Time series file, from which several separated one year periods for specific years can be created in PVsyst weather database. Importing Solargis weather info contained in csv hourly files when working with PVsyst takes only few seconds (tested in version 7.1): Go through Databases to access the Meteo database

The historical period used for calculating the inter-annual variability may have some influence, although it is observed to be quite small (e.g. if we compare results from 10 years of data with results from 20 years of data). The expected difference for GHI would be less than 1% (depends on the climate zone) Modeling Maxim Solar Cell Optimizers in PVSYST Maxim Integrated | 9 The annualized performance improvement of the VT8012 panels was greater than 6%, outperforming the 4% estimate for a typical meteorological year (TMY) estimated by PVSYST. We conclude from this case study that the PVSYST modeling methodology presented provides Up to now, we have developed 3 strategies in PVsyst: the storage for enhancing the self-consumption of the PV system owner. a storage for ensuring peak shaving, when the possible power injected into the grid is limited. a storage for the continuity of the user's electricity feeding, when the grid is weak and often unavailable

Project design > Results > Performance Ratio PR - PVsys

The mean centre variability is the average of the year-on-year difference for each centre and the standard deviation (Std. dev.) is a measure of the spread of the variation - a lower standard.. P90 values are obtained by simulating a system's production over multiple years, determining how much variability there is from year to year, primarily driven by the weather (measured by the standard deviation) and then calculating the haircut necessary to outperform the estimated value 90% of the time The ENSO Cycle refers to the evident and sometimes very strong year-to-year variations in sea-surface temperatures, convective rainfall, surface air pressure, and atmospheric circulation that occur across the equatorial Pacific Ocean. El Niño and La Niña represent opposite extremes in the ENSO cycle The present study describes the observed sea surface salinity (SSS) interannual variability in the Bay of Bengal over the 2009-2014 period. It is based on an original compilation of all available in situ SSS observations in that region, assembled in a 2°-resolution trimonthly gridded field. We find that year-to-year SSS variability is particularly strong in the north-eastern part of the bay Long-term variability of bioassessments has not been well evaluated. We analyzed a 20-year data set (1984-2003) from four sites in two northern California streams to examine the variability of bioassessment indices (two multivariate RIVPACS-type O/E scores and one multimetric index of biotic integrity, IBI), as well as eight metrics

PVsyst 7 Hel

The annual variability is the RMS of the normal distribution of your annual data. If you have 10 years of meteo data for your site, you can import them (create 10 *.MET files in PVsyst - each MET file is for one year). Then since version 6.37, you have a new tool in Meteo tables and graphs > button Compare, for comparing different meteo. Quantifying the Variability in Solar PV Production Forecasts ASES National Solar Conference May 17 PVsyst, Polysun, etc), but •Th. e TMY databases refer to the Typical Meteorological Year.

Dominant pattern of year-to-year variability of summer

  1. year over the plant's 20- to 30-year life. Exceedance probabilities have been widely used in the wind industry to describe the probability that a particular lo­ cation will experience sufficient wind speeds for a proposed . wind farm to be financially sound. Banks and investment firms working on wind farm projects often require P50 an
  2. PVSyst Solar project simulation report in pdf, and project file exported to PVSyst format. Simple horizon and far shading simulation. P50-P90 simulation and Additional 8760´s hourly file for financial analysis if requested. 5 or more Simulation Options that let you optimize and analyze the Solar Plant. Loss diagram over the whole year
  3. Time Losses: System Degradation. Suggested Values: 0.3%/year for high-end modules; 0.5%/year for monocrystalline; 0.6%/year for polycrystalline; You can also use manufacturer production guarantees for a conservative estimate - for example, if a manufacturer guarantees that their panels will have 80% production after 25 years, that is 20%/25 years = 0.8%/year degradation
  4. Currently, PVsyst is one of the most common software used by . developers, installers and consultants and has become the industry standard in the U.S. for the simulation of utility-scale PV systems . PVsyst is the [3] focus of this research. The development of PVsyst started in 1992 at the University of Geneva and is now managed by PVsyst SA [4]

P50 -P90 probabilities - PVsyst's foru

  1. PVsyst TRIAL PVsyst TRIAL PVsyst TRIAL PVsyst TRIAL 30/12/20 PVsyst V7.1.2 VC0, Simulation date: 30/12/20 12:10 with v7.1.2 Project: 5 Kw On-Grid Solar System Variant: New simulation variant SARN SOLAR SOLUTION PVT.LTD. PVsyst Evaluation mode Main results System Production Produced Energy 7.79 MWh/year Specific production Performance Ratio PR.
  2. for traditional PR evaluated over one full year, by compensating for seasonal variation. Digital twins Analysis is increasingly based on modelling of the entire power plant using more complex models, such as the Sandia PV Array Performance Model (SAPM), the System Advisor Model (SAM) and PVsyst. These models no longer work with G i
  3. PVsyst HOMER RETScreen Sunny Design Version assessed 5.51 2.68 beta 4 2.01.0R Commercial licensed software Y N N N Meteo. data input 1 year of hourly data 1 year of hourly data 1 year of monthly average data Not possible Irradiance Model [3] Hays and Davis model Hays and Davis model Isotropic Sky model private Array perf. Model [3] one

Video:

The 5-year data from two field sites in this study provided a natural experiment that monitored intra- and inter-annual variation in prairie productivity (warm vs. cool years and wet vs. dry years) using satellite remote sensing. Different vegetation indices provided complementary information in vegetation productivity estimation Production variation Discount rate Income dependent expenses Income tax rate Dividends Depreciation Depreciable assets Salvage value Depreciation period Financing Own funds Loan 25 years Aging tool results 29.0 0.40 1.00 Aging tool results 4.00 0.00 0.00 80˜900˜000 0.00 15 16˜460˜000 65˜840˜000 W/m2K %/year %/year %/year % %/year %/year. Considering a 10-year payback period, monitoring costs are equal to an eleventh (9.09%) of the maximum allowed costs for mitigation. So the maximum allowed costs are equally divided between the purchase of soiling monitors (occurs only once) and each of the 10 years in which soiling mitigation is performed. ii In PVsyst location of geographical site was selected so from meteonorm monthly meteo values for whole year are generated as shown in table 1 3. GRID CONNECTED SOLAR PV SYSTEM 1 MW grid connected solar PV power plant is installing the energy production, economic feasibility of the place of shapur village at Gujarat using PVsyst Software

Meteo data Kind Specific year Year Synthetic Specified Deviation Year deviation from average 0.0 % Year-to-year variability Variance 5.8 % The probability distribution variance is also depending on some system parameters uncertainties Specified Deviation PV module modelling/parameters 1.0 % Inverter efficiency uncertainty 0.5 The variation of temperature and solar (MW) in April from 7.4% a year ago due to increased capacity and lower electricity consumption by states. The decline in consumption in certain north Indian states was due to a weak intra-state network for dissemination the PVSYST[4] modeling software has been used, and a design with a new concept. In PVSyst this is Earray or Energy Injected into the grid Case study on comparison of yield from alternative sources. Problem is that there is more variation from different sources than comes from the year by year variation

Multiple location and no map function - USD 1,700/INR 115,000 PER YEAR. Multiple location + map function + direct normal radiation data (DNI) - USD 3,600/INR 241,500 PER YEAR. 30 -days Free Tria Importance: Accumulating evidence indicates that higher blood pressure (BP) variability from one physician office visit to the next (hereafter referred to as visit-to-visit BP variability) is associated with poor outcomes. Short-term measurement (throughout 1 year) of visit-to-visit BP variability in high-risk older patients may help identify patients at increased risk of death

Variation of serum prostate-specific antigen levels: an

This paper specifically discusses the issue of longer-term variability of renewables over months, years and decades in systems with relatively high penetration of VRE (namely, > 20% of energy) Near shading impacts from tree heights and clearing setbacks can be dialed in within the 3D shading scene within PVsyst. Although time consuming to set up within in PVsyst, an accurately modeled near shading scene will pay dividends later in the form of improved performance estimates Forcing PVSyst to account for rolling terrain variation in this way only facilitates a rough estimation of losses based on the shading factors. Plus, the labor-intensive manual process takes several hours per block — which amounts to several days of work for each utility-scale project The global horizontal irradiation (GlobHor) is 1762.0 kWh/m2/year. The horizontal diffuse irradiation (DiffHor) is 822.04 kWh/m2. The overall global incident energy on the collector plane is 1855.5 kWh/m2. Table 6 shows the detailed monthly average system losses in kWh. Module quality loss ( Mod Qual) is 802.14 kWh/year PVsyst TRIAL PVsyst TRIAL PVsyst TRIAL PVsyst TRIAL PVSYST 7.0.17 24/11/20 Grid-Connected System: Simulation parameters PVsyst Evaluation mode Project : ITI Geographical Site ITI Country India Situation Latitude 22.48° N Longitude 88.35° E Time defined as Legal Time Time zone UT+5 Altitude 10

Tambacounda (62.7 MWh/year) and Ziguinchor (59.3 MWh/year) is entirely self-consumed. The annual performance ratio are 0.796 at Dakar, 0.795 at St Louis, 0.775 at Tambacounda and 0.792 at Ziguinchor. The results obtained follow the variability of the solar resource. This variability is often impacted by th In addition to the annual average PV output and the average irradiation, PVGIS also reports the year-to-year variability in the PV output, as the standard deviation of the yearly values over the period with solar radiation data in the chosen solar radiation database. You also get an overview of the different losses in the PV output caused by. FPV is growing fast and is expected to have an average growth rate of above 20% in the next five years due to extremely low costs (with an FPV bid recently coming in for a system in Thailand at. thermal loss factors in PVsyst, for the modules of four different PV technologies experiencing hot-desert climate conditions by statistically correlating a year-long monitored data. Thermal models help to effectively quantity factors influencing module temperatures to estimate performance and energy models

According to the latest IEC 61724 standard series The new IEC 61724 Photovoltaic system performance series of standards is the best available source that defines parameters such as performance ratio and performance index. The purpose of this document is to clarify the logic behind IEC 61724 and its vocabulary. For brevity sake we do not mention all parameters and performance. Heterogeneity and Variability in Pressure Autoregulation of Organ Blood Flow: Lessons Learned Over 100+ Years Crit Care Med. 2019 Mar;47(3):436-448. doi: 10.1097/CCM.0000000000003569. Authors Lingzhong Meng 1 , Yingwei Wang 2 , Lina Zhang 3 , David L McDonagh 4 Affiliations 1 Department of. ∑N) to output variability of the same PV fleet concentrated in 5one single location (equal to σ∆ ). The relative output variability quantifies the noise reduction associated with the dispersion of the fleet over a region. Relative Output Variability ranges between 0 and 100 percent PVsyst is a famous solar photovoltaic system design software for simulation design and data analysis, developed by PVSyst from Switzerland. As a fully-functional photovoltaic system simulation software, it is able to carry out modeling and simulation of the photovoltaic power generation system, analyze various factors affecting the electric energy production, and finally calculate the.

Meteonorm, developed by Meteotest, is a widely used and accepted solar radiation data source in the solar energy industry. It has been around for 30+ years (first released in 1985), and became the standard meteorological database for solar energy simulations After candidate location from PVsyst. determination must be make simulation by Sketchup Energy produced for the full year = peak power × software. SketchUp is a 3D modeling computer peak sun hours × days of years = 4655.8 kWp × 4.4 program gives us the tools to create all kinds of 3D hours × 365 days = 7.477GWh/year For example, in PVsyst the NASA data available globally has a 20+ year record but hasn't been updated since 2005. Meteonorm offers 30+ years of data, but its records end in 2010. Climate changes at your location in the last decade will not be captured by these data sets

Original PVsyst database Manufacturer Canadian Solar Inc. Sub-array Sub-array #1 Number of PV modules In series 17 modules In parallel 2 strings Total number of PV modules Nb. modules 34 Unit Nom. Power 320 Wp Array global power Nominal (STC) 10.88 kWp At operating cond. 9.76 kWp (50°C) Array operating characteristics (50°C) U mpp 559 V I. to Shading in PVsyst, v6 PVsyst stochastically given their intrinsic variability and uncertainty •Should there be ways to translate derate/loss factors to out to however many year, or should this change due to higher array to inverter ratios? 28 Working Grou Time series data is a historical record of weather data for a specified location. Time series of solar radiation and meteorological variables are used during the simulation of energy production of solar power plants to understand expected year-to-year variability, seasonal or intra-day energy generation profile, and for calculation of energy estimates for P90 or other probabilistic scenarios

How is calculated the PR (Performance Ratio) ? - PVsyst's

Interannual variability. It considers the variations that can occur year by year and that can deviate from the long-term average. Also this parameter is indicated in the report delivered by the data provider. The longer the period of available data, the lower the variability is PVsyst is the most widely used solar simulation software for the energy yield estimation and For optimal design of solar power plants. PVsyst makes use of the extended knowledge of PV Technology, Meteorological irradiation resources data and PV sy.. This online training course is divided into 4 parts: 1) Understanding the Key Fundamentals of Off Grid Solar PV Plants. In this part of the course, we will learn about analyzing the load profile at an hourly basis, understanding the daily variation of solar generation, and the dynamic interaction between solar generation and the load

Solargis data in PVsyst Solargi

Combining model uncertainty and uncertainty because of

Persistent 400,000-year variability of Antarctic ice volume and the carbon cycle is revealed throughout the Plio-Pleistocene Download PDF. Published: 02 January 2014; Persistent 400,000-year. Year-over-year (YOY) is a method of evaluating two or more measured events to compare the results at one period with those of a comparable period on an annualized basis. YOY comparisons are a. Gary Schnitkey • Focus soon will turn to 2017 yield estimates as USDA will release their first estimates of national and state yields on August 10th. In preparation for this release, national corn yields from 1972 to 2016 are shown in this article. These national trends illustrate that corn yields have been above trend in all years since 2013. Also, maps are shown giving county yield.

Features - PVsys

The response of the Greenland ice sheet to global warming is a source of concern notably because of its potential contribution to changes in the sea level. We demonstrated the natural vulnerability of the ice sheet by using pollen records from marine sediment off southwest Greenland that indicate important changes of the vegetation in Greenland over the past million years On the other hand, a cutoff point of 74 years of age is a determinant of vitamin D status. A BMI ≤ 32.7 and an age > 74 years also predict a 90% probability of vitamin D deficiency and 10% of insufficiency, while an age < 74 years is a predictor of 70% insufficiency versus 20% deficiency status (Figure 4) Variability is the extent to which data points in a statistical distribution or data set diverge from the average, or mean, value as well as the extent to which these data points differ from each.

Is there more variability in the heights of 2-year-old girls or 14-year-old girls? Is there more variability in the heights of 20-year-old girls or 20-year-old boys? Ann E. Watkins Cal State Northridge September 2014 6 Estimate the 25th percentile of height for 4-year-old boys. The 50t The objective of this study was to characterize within-person three-year variability of plasma levels of sRAGE. DESIGN AND METHODS: We measured sRAGE in plasma samples from 179 men and women in the community-based Atherosclerosis Risk in Communities (ARIC) Study at two time points, three years apart To examine the trend of CTC variation in survival rates, all live born preterm infants with a GA between 23 0/7 weeks and 31 6/7 weeks born in the entire 10-year study period were analysed. GA-specific survival rates of preterm infants born in 2000-2004 were compared with survival rates of those born in 2005-2009

What is Climate Variability? - Columbia Universit

C6 Corvette: The Best Model Years, Ranked. In just the sixth generation alone, the C6 had numerous different models buyers could go for, so in this list, we rank them worst to best. The C6 Corvette was the sixth generation of the Chevrolet Corvette and lasted from 2005 to 2013. If you are planning to buy a used model, this is a good generation. Seasonal temperature variability over longer timescales could offer new insights into understanding different forcing factors and response processes in the climate system. Here we report an alkenone-based temperature reconstruction for growing season over the past 1600 years from the varved sediment in Lake Sihailongwan, northeastern China

We present a 3 million year record of aeolian dust supply into the eastern Mediterranean Sea, based on hematite contents derived from magnetic properties of sediments from Ocean Drilling Program Site 967. Our record has an average temporal resolution of ∼400 years. Geochemical data validate this record of hematite content as a proxy for the supply of aeolian dust from the Sahara. We deduce. This study explored the development of mood variability in 474 Dutch adolescents (56.8% male, 90.1% medium to high socioeconomic status) from a community sample, followed from ages 13 to 18 years. Three times per year, adolescents reported on daily happiness, anger, sadness, and anxiety for 5 days using Internet diaries (15 assessment weeks. A new study using a reconstruction of North American drought history over the last 1,000 years found that the drought of 1934 was the driest and most widespread of the last millennium. Using a tree-ring-based drought record from the years 1000 to 2005 and modern records, scientists from NASA and Lamont-Doherty Earth Observatory found the 1934.

Used by meteorological organizations around the world for analyzing climate conditions, climate normals are average values of temperature and precipitation over a period of time, typically 30 years, and are updated approximately every 10 years. The approach assumes a stationary climate and came into use about 75 years ago by the World. Desired year in a decimal format to include any fraction of the year that has already passed. The value is the current year plus the number of days that have passed in this year divided by 365. To calculate the decimal year, dyear, for March 21, 2015

Coastal foredunes are topographically high features that can reduce vulnerability to storm-related flooding hazards. While the dominant aeolian, hydrodynamic, and ecological processes leading to dune growth and erosion are fairly well-understood, predictive capabilities of spatial variations in dune evolution on management and engineering timescales (days to years) remain relatively poor Using an empirically motivated conversion from submillimeter variability to variation in mass accretion rate, six sources (7 % of our full sample) are predicted to have years-long accretion events during which the excess mass accreted reaches more than 40 % above the total quiescently accreted mass: two previously known eruptive Class I sources. 80 years. Day-to-day temperature variability was seen to have . 22,850 MOBERG ET AL.: DAY-TO-DAY TEMPERATURE VARIABILITY TRENDS decreased in the Northern Hemisphere. To place these recent changes in a longer context than a part of the twentieth century, it is important to consider earlier periods when. Abstract: A temperature variation with a time period of a few decades has been previously reported [1] and observed in SST data. In this post, a 60 year oscillation with an amplitude of 0.1C is identified in the HadCrut global temperature data[2] and will likely cause a halt in global warming over the next decade or so

PVsyst - Logiciel Photovoltaïqu

The exact method is compiled from various sources and presented in Chapter 1. In Chapter 2, an HSG record from classic North Atlantic DSDP Site 609 is reconsidered. While the Site 609 HSG record was initially interpreted to exhibit 1500-year variability, it did not actually contain spectral power at the 1500-year band HbA1c variability was evaluated using a mixed effects model to reduce regression dilution bias. Age-specific associations (45- 54, 55- 64, 65- 74 and 75- 84 years) between HbA1c variability and risk of CVD and mortality were assessed by Cox regression, adjusted for patient characteristics and usual HbA1c. Result The recent 20 years (2000-2019) ozonesonde profiles recorded at the Hong Kong Observatory are analyzed to study the Tropospheric Ozone (TropO 3) variability over Hong Kong, South China.The TropO 3 profiles are described without the constraints of traditional monthly averages; they are clustered based on a Self-Organizing Map (SOM) to explore the short-term variability, and separated into two.

Hence, variation in solar radiative output may have contributed to decade-scale rainfall variability in equatorial east Africa. Specifically, highest inferred rainfall of the past 1,100 years. Sun's energy influences 1,000 years of natural climate variability in North Atlantic Date: March 9, 2014 Source: Cardiff University Summary: Changes in the sun's energy output may have led to.

Time Series vs TMY Solargi

Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term is named for Serbian geophysicist and astronomer Milutin Milanković.In the 1920s, he hypothesized that variations in eccentricity, axial tilt, and precession resulted in cyclical variation in the solar radiation reaching the Earth, and that this orbital. Long, continuous, marine sediment records from the subpolar North Atlantic document the glacial modulation of regional climate instability throughout the past 0.5 million years. Whenever ice sheet size surpasses a critical threshold indicated by the benthic oxygen isotope (δ18O) value of 3.5 per mil during each of the past five glaciation cycles, indicators of iceberg discharge and sea. Fewest Category 3+ landfalls in one year: 0 (1981) Most total landfalls over a 10-year period: 177 (1988-1997) Fewest total landfalls over a 10-year period: 120 (1975-1984) Total landfalls 2010.

The most substantial positive shift in isotopes occurs from 5000 to 4300 years BP and is coincident with aridity in India and the Tibetan Plateau. Other proxy records indicate increased ENSO variability and a southward shift in the ITCZ, which has an effect on the strength and onset of the ISM and may account for this change in hydrologic balance OBJECTIVE To determine whether intraindividual variability in fasting glucose (FG) below the threshold of diabetes is associated with cognitive function in middle adulthood beyond increasing FG. RESEARCH DESIGN AND METHODS We studied 3,307 CARDIA (Coronary Artery Risk Development in Young Adults) Study participants (age range 18-30 years and enrolled in 1985-1986) at baseline and. An early warming about 14,000 years ago was associated with ice-free conditions; however, seasonal sea ice was present throughout the Holocene. Variability of sea-ice conditions in the Fram. NOAA found the 2018 annual mean temperature for the contiguous 48 United States was the 14th warmest on record. Warming trends are strongest in the Arctic region, where 2018 saw the continued loss of sea ice. In addition, mass loss from the Greenland and Antarctic ice sheets continued to contribute to sea level rise

Understanding Climate Variability and Change - Climate Future

The 100,000-year problem (100 ky problem, 100 ka problem) of the Milankovitch theory of orbital forcing refers to a discrepancy between the reconstructed geologic temperature record and the reconstructed amount of incoming solar radiation, or insolation over the past 800,000 years. Due to variations in the Earth's orbit, the amount of insolation varies with periods of around 21,000, 40,000. Trade Balance: One can define trade balances as the variation between the value of the exports and the value of the imports in a certain country or a certain economic block through a given period

The annual variability of wind spee

Jamaica is an upper-middle income country with an economy heavily dependent on tourism; it has an average of 4.3 million tourists a year. Politically it is a Commonwealth realm, with Elizabeth II as its queen. Her appointed representative in the country is the Governor-General of Jamaica, an office held by Patrick Allen since 2009 We found invasive species now cost Australia around A$24.5 billion a year, or an average 1.26% of the nation's gross domestic product. The costs total at least A$390 billion in the past 60 years