Photovoltaic system performance

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The SR30 pyranometer is an example of an PV monitoring sensor, which can be used in two orientations (horizontal and in plane of array) for measuring irradiance. SR30 pyranometer field use.jpg
The SR30 pyranometer is an example of an PV monitoring sensor, which can be used in two orientations (horizontal and in plane of array) for measuring irradiance.

Photovoltaic system performance is a function of the climatic conditions, the equipment used and the system configuration. PV performance can be measured as the ratio of actual solar PV system output vs expected values, the measurement being essential for proper solar PV facility's operation and maintenance. The primary energy input is the global light irradiance in the plane of the solar arrays, and this in turn is a combination of the direct and the diffuse radiation. [1]

Contents

The performance is measured by PV monitoring systems, which include a data logging device and often also a weather measurement device (on-site device or an independent weather data source). Photovoltaic performance monitoring systems serve several purposes - they are used to track trends in a single photovoltaic (PV) system, to identify faults in or damage to solar panels and inverters, to compare the performance of a system to design specifications or to compare PV systems at different locations. This range of applications requires various sensors and monitoring systems, adapted to the intended purpose. Specifically, there is a need for both electronic monitoring sensors and independent weather sensing (irradiance, temperature and more) in order to normalize PV facility output expectations. Irradiance sensing is very important for the PV industry and can be classified into two main categories - on-site pyranometers and satellite remote sensing; when onsite pyranometers are not available, regional weather stations are also sometimes utilized, but at lower quality of data; the Industrial IoT-powered sensorless measurement approach has recently evolved as the third option.

Sensors and photovoltaic monitoring systems are standardized in IEC 61724-1 [2] and classified into three levels of accuracy, denoted by the letters “A”, “B” or “C”, or by the labels “High accuracy”, “Medium accuracy” and “Basic accuracy”. A parameter called the 'performance ratio' [3] has been developed to evaluate the total value of PV system losses.

Overview

Photovoltaic system performance is generally dependent on incident irradiance in the plane of the solar panels, the temperature of the solar cells, and the spectrum of the incident light. Furthermore, it is dependent upon the inverter, which typically sets the operating voltage of the system. The voltage and current output of the system changes as lighting, temperature and load conditions change, so there is no specific voltage, current, or wattage at which the system always operates. Hence, system performance varies depending on the time of day, amount of solar insolation, direction and tilt of modules, cloud cover, shading, soiling, state of charge, temperature, geographic location, and day of the year.

Performance by system type

Solar PV parks

Solar parks of industrial and utility scale may reach high performance figures. In modern solar parks the performance ratio should typically be in excess of 80%. [4] [5] Many solar PV parks utilize advanced performance monitoring solutions, which are supplied by a variety of technology providers.

Distributed solar PV

In rooftop solar systems it typically takes a longer time to identify a malfunction and send a technician, due to lower availability of sufficient photovoltaic system performance monitoring tools and higher costs of human labor. As a result, rooftop solar PV systems typically suffer from lower quality of operation & maintenance and essentially lower levels of system availability and energy output.

Off-grid solar PV

Most off-grid solar PV facilities lack any performance monitoring tools, due to a number of reasons - including monitoring equipment costs, cloud connection availability and O&M availability.

Performance monitoring

Rbee Solar, PV monitoring with solar irradiance measurement Schema PV-monitoring Mesure-de-l'irradiation.png
Rbee Solar, PV monitoring with solar irradiance measurement

A number of technical solutions exist to provide performance monitoring for solar photovoltaic installations, differing according to data quality, compatibility with irradiance sensors as well as pricing. In general, monitoring solutions can be classified to inverter manufacturer-provided logger and monitoring software solutions, independent data-logger solutions with custom software and finally agnostic monitoring software-only solutions compatible with different inverters and data-loggers.

Monitoring solutions by inverter manufacturers

Dedicated performance monitoring systems are available from a number of vendors. For solar PV systems that use microinverters (panel-level DC to AC conversion), module power data is automatically provided. Some systems allow setting performance alerts that trigger phone/email/text warnings when limits are reached. These solutions provide data for the system owner and/or the installer. Installers are able to remotely monitor multiple installations, and see at-a-glance the status of their entire installed base. All the major inverter manufacturers provide a data acquisition unit - whether a data logger or a direct means of communication with the portal.

These solutions have the advantage of providing of a maximum information from the inverter and of supplying it on a local display or transmitting it on the internet, in particular alerts from the inverter itself (temperature overload, loss of connection with a network, etc.).

Some of those monitoring solutions are:

Independent data logging solutions connected to inverters

Generic data logging solutions connected to inverters make it possible to overcome the major drawback of inverter-specific manufacturer solutions - being compatible with several different manufacturers. These data acquisition units connect to the serial links of the inverters, complying with each manufacturer’s protocol. Generic data logging solutions are generally more affordable than inverter manufacturer solutions and allow aggregation of solar PV system fleets of varying inverter manufacturers.

Some of those monitoring solutions are:

Independent monitoring solutions

The last category is the most recent segment in the solar photovoltaic monitoring domain. Those are software based aggregation portals, able to aggregate information from both inverter-specific portals and data loggers as well as independent data loggers. Such solutions become more widespread as inverter-specific communication to the cloud is done more and more without data loggers, but rather as direct data connections.

Energy generation data availability and quality

An essential part of PV system performance evaluation is the availability and the quality of energy generation data. Access to the Internet has allowed a further improvement in energy monitoring and communication.

Typically, PV plant data is transmitted via a data logger to a central monitoring portal. Data transmission is dependent on the local cloud connectivity, thus being highly available in OECD countries, but more limited in developed countries. According to Samuel Zhang, vice president of Huawei Smart PV, over 90% of global PV plants will be fully digitilized by 2025. [6]

Weather data sources

On-site irradiance sensors

On-site irradiance measurements are an important part of PV performance monitoring systems. Irradiance can be measured in the same orientation as the PV panels, so-called plane of array (POA) measurements, or horizontally, so-called global horizontal irradiance (GHI) measurements. Typical sensors used for such irradiance measurements include thermopile pyranometers, PV reference devices and photodiode sensors. To conform to a specific accuracy class, each sensor type must meet a certain set of specifications. These specifications are listed in the table below.

Table 5 - Sensor choices and requirements for in-plane and global irradiance cited from IEC 61724-1 [2]
Sensor typeClass A

High accuracy

Class B

Medium accuracy

Class C

Basic accuracy

Thermopile pyranometerSecondary standard per ISO 9060

or

High quality per WMO Guide (Uncertainty ≤ 3% for hourly totals)

First class per ISO 9060

or

Good quality per WMO Guide (Uncertainty ≤ 8% for hourly totals)

Any
PV reference deviceUncertainty ≤ 3%

from 100 W/m2 to 1500 W/m2

Uncertainty ≤ 8%

from 100 W/m2 to 1500 W/m2

Any
Photodiode sensorsNot applicableNot applicableAny
The VU01 pyranometer ventilation unit with SR20, with heater and ventilation, is an A-class compliant pyranometer according to the IEC 61727-1 VU01 pyranometer ventilation unit SR20.jpg
The VU01 pyranometer ventilation unit with SR20, with heater and ventilation, is an A-class compliant pyranometer according to the IEC 61727-1

If an irradiance sensor is placed in POA, it must be placed at the same tilt angle as the PV module, either by attaching it to the module itself or with an extra platform or arm at the same tilt level. Checking if the sensor is properly aligned can be done with portable tilt sensors or with an integrated tilt sensor. [7]

Sensor maintenance

The standard also specifies a required maintenance schedule per accuracy class. Class C sensors require maintenance per manufacturer's requirement. Class B sensors need to be re-calibrated every 2 years and require a heater to prevent precipitation or condensation. Class A sensors need to be re-calibrated once per year, require cleaning once per week, require a heater and require ventilation (for thermopile pyranometers).

Satellite remote sensing of irradiance

PV performance can also be estimated by satellite remote sensing. These measurements are indirect because the satellites measure the solar radiance reflected off the earth surface. In addition, the radiance is filtered by the spectral absorption of Earth's atmosphere. This method is typically used in non-instrumented class B and class C monitoring systems to avoid costs and maintenance of on-site sensors. If the satellite-derived data is not corrected for local conditions, an error in radiance up to 10% is possible. [2]

Equipment and performance standards

Sensors and monitoring systems are standardized in IEC 61724-1 [2] and classified into three levels of accuracy, denoted by the letters “A”, “B” or “C”, or by the labels “High accuracy”, “Medium accuracy” and “Basic accuracy”.

In California, solar PV performance monitoring has been regulated by the State government. As of 2017, the governmental agency California Solar Initiative (CSI) provided a Performance Monitoring & Reporting Service certificate to eligible companies active in the solar segment and acting in line with CSI requirements. [8]

A parameter called the 'performance ratio' [3] has been developed to evaluate the total value of PV system losses. The performance ratio gives a measure of the output AC power delivered as a proportion of the total DC power which the solar modules should be able to deliver under the ambient climatic conditions.

See also

Related Research Articles

<span class="mw-page-title-main">Photovoltaics</span> Method to produce electricity from solar radiation

Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially used for electricity generation and as photosensors.

<span class="mw-page-title-main">Solar inverter</span> Converts output of a photovoltaic panel into a utility frequency alternating current

A solar inverter or photovoltaic (PV) inverter is a type of power inverter which converts the variable direct current (DC) output of a photovoltaic solar panel into a utility frequency alternating current (AC) that can be fed into a commercial electrical grid or used by a local, off-grid electrical network. It is a critical balance of system (BOS)–component in a photovoltaic system, allowing the use of ordinary AC-powered equipment. Solar power inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection.

A pyranometer is a type of actinometer used for measuring solar irradiance on a planar surface and it is designed to measure the solar radiation flux density (W/m2) from the hemisphere above within a wavelength range 0.3 μm to 3 μm. The name pyranometer stems from the Greek words πῦρ (pyr), meaning "fire", and ἄνω (ano), meaning "above, sky".

<span class="mw-page-title-main">Automatic weather station</span> Meteorological instrument

An automatic weather station (AWS) is an automated version of the traditional weather station, either to save human labour or to enable measurements from remote areas. An AWS will typically consist of a weather-proof enclosure containing the data logger, rechargeable battery, telemetry (optional) and the meteorological sensors with an attached solar panel or wind turbine and mounted upon a mast. The specific configuration may vary due to the purpose of the system. The system may report in near real time via the Argos System, LoRa and the Global Telecommunications System, or save the data for later recovery.

<span class="mw-page-title-main">Solar panel</span> Assembly of photovoltaic cells used to generate electrical power

A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a frame, and a neatly organised collection of PV panels is called a photovoltaic system or solar array. Solar panels capture sunlight as a source of radiant energy, which is converted into electric energy in the form of direct current (DC) electricity. Arrays of a photovoltaic system can be used to generate solar electricity that supplies electrical equipment directly, or feeds power back into an alternate current (AC) grid via an inverter system.

<span class="mw-page-title-main">Solar tracker</span> Device that orients a payload towards the sun.

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<span class="mw-page-title-main">Stand-alone power system</span>

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<span class="mw-page-title-main">Simple Model of the Atmospheric Radiative Transfer of Sunshine</span>

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<span class="mw-page-title-main">Rooftop solar power</span>

A rooftop solar power system, or rooftop PV system, is a photovoltaic (PV) system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. The various components of such a system include photovoltaic modules, mounting systems, cables, solar inverters and other electrical accessories.

The Open Solar Outdoors Test Field (OSOTF) is a project organized under open source principles, which is a fully grid-connected test system that continuously monitors the output of many solar photovoltaic modules and correlates their performance to a long list of highly accurate meteorological readings.

In 2022 Chile produced about 18% of its electricity from solar power, up from 7% in 2018. Chile produces the highest percentage of its electricity from solar in the world. As of year end 2018, it had 2137 MW of solar PV capacity. In July 2020 installed solar capacity had risen to 3104 MW, with another 2801 MW under construction. At the end of 2021 Chile was ranked 22nd in the world in terms of installed solar energy.

<span class="mw-page-title-main">Tigo Energy</span>

Tigo Energy is an American private corporation, headquartered in Campbell, California, United States. It provides products, technologies, software, and services to installers, distributors, and original equipment manufacturers within the photovoltaic industry. It specializes in module-level power optimizers and smart module power electronics.

<span class="mw-page-title-main">Morgan Solar</span>

Morgan Solar, Inc. is a Canadian solar power and optical technology company based in Toronto, Ontario. Since 2017, the company has specialized in urban sunlight management, led by its SPOTlight platform. The company also produces in situ IV curve tracers and optical film technologies.

<span class="mw-page-title-main">Solmetric</span>

Solmetric Corporation, based in Sebastopol, California, is a manufacturer of solar test and measurement equipment and developer of solar design software. It was founded in 2005 and is best known for its shade measurement tool, the SunEye, and its I-V curve tracer, the PV Analyzer. The award-winning SunEye shade tool is used primarily by residential solar installers. It tells the user when and where shadows will fall so that solar modules can be placed to maximize energy harvest. The PV Analyzer is an I-V curve tracer. It is used for commissioning and troubleshooting commercial and utility scale PV systems.

<span class="mw-page-title-main">Photovoltaic module analysis techniques</span>

Multiple different photovoltaic module analysis techniques are available and necessary for the inspection of photovoltaic (PV) modules, the detection of occurring degradation and the analysis of cell properties.

Soiling is the accumulation of material on light-collecting surfaces in solar power systems. The accumulated material blocks or scatters incident light, which leads to a loss in power output. Typical soiling materials include mineral dust, bird droppings, fungi, lichen, pollen, engine exhaust, and agricultural emissions. Soiling affects conventional photovoltaic systems, concentrated photovoltaics, and concentrated solar (thermal) power. However, the consequences of soiling are higher for concentrating systems than for non-concentrating systems. Note that soiling refers to both the process of accumulation, and the accumulated material itself.

References

  1. ↑ Myers, D R (Sep 2003). "Solar Radiation Modeling and Measurements for Renewable Energy Applications: Data and Model Quality" (PDF). Proceedings of International Expert Conference on Mathematical Modeling of Solar Radiation and Daylight. Retrieved 30 December 2012.
  2. 1 2 3 4 IEC 61724-1:2017 – Photovoltaic system performance – Part 1: Monitoring (1.0 ed.). International Electrotechnical Commission (IEC). 2017 [1998-01-01]. Archived from the original on 2017-08-25. Retrieved 2018-05-16.
  3. 1 2 Marion, B (); et al. "Performance Parameters for Grid-Connected PV Systems" (PDF). NREL. Retrieved 30 August 2012.
  4. ↑ "The Power of PV – Case Studies on Solar Parks in Eastern" (PDF). Proceeding Renexpo. CSun. Archived from the original (PDF) on April 8, 2022. Retrieved 5 March 2013.
  5. ↑ "Avenal in ascendance: Taking a closer look at the world's largest silicon thin-film PV power plant". PV-Tech. Archived from the original on 22 February 2015. Retrieved 22 April 2013.
  6. ↑ Predicting the future for smart PV. PV Magazine. 25 June 2020.
  7. ↑ "SR30 pyranometer | compliant with IEC 61724-1 Class A requirements". www.hukseflux.com. Retrieved 2018-05-16.
  8. ↑ https://www.energy.ca.gov/sites/default/files/2020-06/PMRS_Certification.pdf [ bare URL PDF ]
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