Objective
To demonstrate a grid connected PV system with a new type of inverter. A 77 kWp roof mounted PV array and inverter supplies ac power for a family house in Saarbruecken. Excess power is fed to the grid, which provides back-up when the output from the PV -array is insufficient. The inverter is a new, highly efficient fully electronic, line-communated type, developed and made by the Fraunhofer Institute.
Should the cost of PV modules become low enough, power generation using PV modules will become economically interesting, even in areas already supplied by the grid. The cost of storing electrical energy in batteries is high and in grid connected areas it may be simpler and cheaper to use the grid as a storage system.
Grid connected PV systems need inverters, which to date have often had low efficiencies when operating at partial loads. In this project a new fully electronic inverter, with a high efficiency even at low loads, will be demonstrated. The 7.68 kWp array of AEG polycrystalline modules, type PQ10/40/01, will be integrated into the roof of a single family house in Saarbruecken. The PV modules are arranged in 5 fields so that each field produces a voltage which is a multiple of 14V, ie 14V, 28V, 42V, 84V, and 168V. The array is connected to an electronic inverter, which builds up a sine wave by gradually switching in the different fields. Transistors first switch in the first field of 14V, this is then switched off and the second field of 28V switched on. In this way the voltage is raised to a peak of 322V in steps of 14V. The rate at which the fields are switched in is determined by the inverter which senses the grid voltage. An analog to digital converter scans the grid voltage and converts it into a sequence of binary signals, which are directly used to control the transistors which switch in the PV fields. The inverter thus follows all voltage and frequency fluctuations in the grid.
When power is produced which is surplus to the requirements of the house, it is fed to the grid via the inverter. The 8 kW inverter has an efficiency of greater than 90% for partial loads down to 5%.
This type of system is not competitive with grid produced electricity at the present time, and will not become competitive until there is a very substantial reduction in PV costs.
The monitoring system uses a Krueckmann data acquisition system and Hewlett Packard HP 86Bmicrocomputer. Parameters are read every 10 seconds and averaged and recorded on disc every 15 minutes. Monitoring is carried out since October 1989 in accordance with JRC Ispra guidelines.
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
6600 Saarbruecken
Germany