Use case A (Generated Power Monitoring AC/DC)

Compare DC to AC generated power

Use case

For this use case we would like to calculate the conversion efficiency of an inverter. The PV-system is equipped with 12 PV-modules, that are connected as one string to the inverter we want to analyze.

The conversion efficiency is defined as follows:

Eff=100\% \cdot \frac{\text{AC energy [kWh]}}{\text{DC energy [kWh]}}

We will need to measure both the DC output power and the AC output power. 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

The PV-PSU is a high quality 24VDC power-supply. It is used to power the PV-Link computer and all connected PVBlocks.

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The PV-LINK is an industrial computer that runs a robust Linux distribution. All measurements are orchestrated by this component. It runs a local database to store up to 10 years of continuous data (depending on the system size), as well as a webserver that can be used to configure the system. The computer can be connected to the internet to access the pvblocks cloud, however it will run perfectly without an active internet connection as well.

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The PV-Base is the communication gateway to all installed PVBlocks.

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AC Output

The first parameter to measure is the AC output of the system. The AC output has to be measured ‘behind’ the inverter.  PV-Blocks supports 1-phase and 3 phase AC networks. In this use case our inverter generates AC power in a single phase. The AC meter will be a B21-112-100 from ABB (accuracy class 1.0). This meter can be directly connected to the PV-MOD-AC PV-Block by means of its digital interface.

ABB AC meter

ABB AC meter

The PV-KWH-1P is a DIN-Rail device that can be mounted inside the grid connection enclosure close to the inverter. It will measure the generated AC power continuously. The meter is an ABB B21-112-100.

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This PV-Block communicates directly to AC electricity meters that support the RS485 interface.

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We will add the PV-MOD and PV-KWH-1P electricity meter to the system:

DC Output

The second parameter to measure is the DC output of the PV-string. The DC output will be measured ‘before’ the micro-inverter. To measure this DC output, we will use a  ReRa Solutions PV-MON. The PV-MON is a high precision instrument that can be connected directly to a PV-string (up to 1500V) or between a single PV-Module and the rest of the PV-string. 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, however that is not required for this specific use case.

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

The PV-MON is a high precision instrument that can be connected between a PV-Module and the rest of the PV-system. It will measure the current and voltage continuously. The PV-MON has a fixed temperature sensor that can be used to measure the PV-module temperature. There is the possibility to connect an analog irradiance sensor (0..100mV)

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Digital interface between a PV-MON-DC and the PV-Blocks system. Up to 12 PV-MONs can be connected to one single PV-MOD-DC.

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We will add the PV-MOD-DC and 1 PV-MON DC meter to the system:

The resulting system to measure the AC/DC conversion efficiency is now ready to install. It has a PV-BASE pack, a PV-MOD-DC, PV-MOD-AC, PV-KWH-1P and a PV-MON.

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.