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Low voltage DC-bus link for efficient photovoltaic production and local battery storage

Integration of local storage in a PV-plant via DC-bus link

This project is carried out with the support of  Logo d'Energies Sion Région (ESR) et lien vers le site web., Logo des Forces Motrices Valaisannes (FMV), The Ark Foundation and HES-SO (ED2050).

Based on the advantages of the DC-bus technology to link various producers and consumers the existing Photovoltaic test plant of the HES-SO Valais-Wallis, ISI, has been extended to a power of about 11 kWp installed PV-power and linked via the DC-bus power link at 700 Volt to a battery system (Lithium & Lead-Gel) and the in-house DC/AC converter. Again the high-efficiency individual DC/DC-converters for each PV-module have been built based on the in-house design via an external supplier, installed and tested. The wireless communication of the relevant PV-data (current, Voltage, temperature, panel-ID) is as well entirely developed inhouse, based on low power bluetooth.

Due to the permanent transmission of the relevant PV-data an online supervision of the produced power in realtime under real operating conditions with a time resolution of 10 seconds has been established. An evaluation of the performance of individual modules is thus possible, and has therefore been adapted at the PV-Lab in Neuchâtel as well.

The extensed DC-bus linked PV-plant of more than 10 kW consists of 30 crystalline PV-modules and 15 thin film micromorph modules. The upgrade with a local battery storage system on the DC-side of the DC/AC converter allows direct local energy storage and thus smoothening of the PV-production profile according to parameters which can freely be choosen.

The entire operational system forms the basis to be extended to a fully operational DC-microgrid, with many additional beneficial features like production and injection forecast, smoothening of power profile, guaranteeing a precisely defined power profile, integrating all kinds of consumers directly into the DC-bus (for example variable frequency motor drives), providing regulation power to GRD’s, etc.

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In order to integrate the battery (either Li or Pb) a precharing unit is required which guarantees perturbation free connection of the battery system.

Typical shape of the power profile of two micormorph silicon and five crystalline silicon PV-modules. The clearly distinct power curves proof that each module is individually optimized in power.