In-depth PV material research

Research institutes, universities and calibration entities require different tools to achieve their PV research objectives. It is common to combine different instruments, dataloggers and software to create a laboratory grade setup. The biggest challenges in these setups are:

• Time synchronized measurements
• Integration of different instruments
• Visualization and data analysis

PV-Blocks is a modular system that is from the ground up developed to solve exactly this challenge. One system to connect all PV related instruments:

• Pyranometers, reference cells both analog and digital
• Temperature sensors
• Electronic Loads to perform IV-curve measurements and MPPT
• AC and DC measurement devices
• Spectro radiometers
• Suntrackers
• Meteo stations

Time synchronized measurements

Outdoor PV-measurements can only be of value when the measured data of the different inputs is synchronized to an identical clock. PV-Blocks uses an internal clock that can be synchronized to any time server on the internet or intranet. The system uses an internal 1 minute heartbeat. By using this heartbeat as a trigger for all PV-Blocks, the researcher can safely process the measurements without aligning different timestamps afterwards.

The measurement resolution is not limited to this 1 minute heartbeat, it is only there to provide synchronization.

Web interface

The operator can setup the PV-Blocks system by means of an ethernet connection using any web browser. Setting up the system in completely handled by the internal webserver. The PV-Blocks system runs standalone and does not need any maintenance besides a regular backup. The measured values are stored locally on the internal computer. Depending on the amount of PV-Blocks connected, about 10 years of data can be stored locally. Measured data can be downloaded from the web-interface directly.

Application Programming Interface (API)

The PV-Blocks system is completely open to developers by means of an extensive API. Developers can create their own programs to retrieve the data and analyze it in any possible way. An example python script is included with the system that should help a developer to get started.

PV-Blocks Cloud

You can use the PV-Blocks cloud to off-load all data automatically online. Dashboards (Grafana) can be build directly and shown to any audience. Of course the cloud solution complies to the highest security standards.

Irradiance

Irradiance can be measured by pyranometers, reference cells, silicon pyranometers or pyrheliometers. The type of light can be direct (DNI), diffuse(DHI) or global(GHI). However, some sensors have to be mounted differently; for example to measure ground reflection or in-plane irradiance. PV-Blocks supports all types of irradiance measurements.

An irradiance sensor can have an analog or digital output. Both types are supported by PV-Blocks.

Analog Sensors:

An analog irradiance sensor is a device that outputs a voltage that represents the irradiance received by the detector. This voltage is measured and converted to irradiance by the PV-Blocks systems. The PV-Block to use for this is the PV-IRR.

Digital sensors:

Digital sensors have gained popularity over the last years as these are less sensitive for noisy environments. A digital sensor communicates over a digital bus to transfer the measured irradiance. Typically multiple digital irradiance sensors can be connected to one bus. The PV-Blocks system supports many digital irradiance sensors for example the MS80S of EKO Instruments. The PV-Block to use for digital irradiance from EKO Instruments is the PV-MOD-MSXXS.

IV-curves and MPPT

The electrical parameters of any PV-device are best characterized by the measurement of an IV-Curve. These curves are typically obtained using an electronic load. The drawbacks of many electronic loads currently available are their high price and the necessity to mount them indoor or at least inside an enclosure.

Nowadays, institutes have one sophisticated electronic load connected to a multiplexer to sequentially measure the PV-devices. Because of the sequential measurement, it is not possible to obtain data of multiple PV-devices simultaneously. This makes it difficult to time-align the IV-curves to other physical parameters like irradiance and temperature.

To overcome these above mentioned problems dedicated IV-Loads are available to be used by PV-Blocks. These IV-Loads can be mounted outdoor and connect directly to a PV-Device. They can be used to measure an IV-Curve, perform Maximum Power Point Tracking (MPPT), apply a fixed voltage bias and switch a PV-Device in open-voltage(Voc) or short-circuit(Isc) conditions.

The IV-Loads are equipped with high precision analog digital converters that measure the voltage and current simultaneously.

The curve sweep can be configured by the user. The curve can be taken in any direction (Voc-to-Isc or Isc-to-Voc). It is as well possible, to sweep in two directions analyze hysteresis.

In numbers:

The standard IV-Load 600 can be used to measure a voltage up to 80V and allows for maximum 20A of DC current. The maximum power for MPPT is 300W continuously, while IV-curves can be taken for devices up to 600W.

IV-Curves are measured relatively fast, therefore the power that can be higher compared to continuous MPPT.

Other voltage and current ranges are available on request. PV-Blocks is actively used for modules up to 800W and cells generating less then 5mW!!