Use case

For this use case we would like to calculate the conversion efficiency of 2 PV-Modules that are part of a 12 module PV-string. The PV-system is connected as one string to the inverter.

The conversion efficiency is defined as follows:

$$\eta=\frac{ P_{out}}{P_{in}}$$

Here $P_{out}$ is the DC power of PV-module $[W]$ and $P_{in}$ is the solar power which is defined as:

$$P_{in}=AG$$
$A$ is the PV-module area$[m^2]$ and $G$ is the in-plane irradiance$[Wm^-2]$

We will need to measure the DC output power of the two modules and the in-plane irradiance (POI). We will setup a PV-Blocks system that will allow for these measurements.

Each PV-Blocks system uses the PV-Base pack. We will start the configuration by adding that.

PV-Base pack

The PV-Base pack is the heart of any PV-Blocks system. It is responsible for computing(PV-LINK), power(PV-PSU) and communications(PV-BASE). Without these 3 DIN-rail components a PV-Blocks system cannot be used.

PV-Blocks to use

DC Output

The first parameter to measure is the DC output of both PV-modules. To measure this DC output, we will use two ReRa Solutions PV-MONs. The PV-MON is a high precision instrument that can be connected directly to a PV-module even when it is part of a larger string (up to 1500V). It will measure the current and voltage continuously. The PV-MON has a fixed temperature sensor that can be used to measure the PV temperature.

The PV-MON is connected to the PV-Blocks system using a PV-MOD-DC block. Up to 12 PV-MON’s can be connected to one single PV-MOD-DC. For this use-case we need two PV-MON-DC blocks and one PV-MOD-DC.

Configuration

We will add the PV-MOD-DC and 2 PV-MON DC meters to the system:

Irradiance

To measure the irradiance there are several possibilities. First we have to choose between a pyranometer, a Si-pyranometer and a silicon reference cell. There are several reasons why you would choose one over the other. For now the decision about the irradiance sensor type is left to the user, of course you can contact us directly to help you select the best irradiance sensor.

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.

PV-Blocks to use

For this system we will use a Si-pyranometer(ML-01) from EKO Instruments. As this is an analog sensor, we will have to add a PV-IRR PV-Block to the system. The PV-IRR PV-Block can measure up to 4 analog sensors, but for this use case we will only use one input.

Configuration

We will add the irradiance measurement to the solution:

Configuration

This results in the following configuration:

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. Developer 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.