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Corporate project team consisting of Zurich University of Applied Sciences (ZHAW) and Furtwangen University (HFU) analysed and examined the energy usage and its flow in a common household with a Photovoltaic (PV) plant and a battery as storage of the generated PV power. The aim was to optimise the power usage in a configuration with the battery. The energy generated by the PV plant and stored in the battery is quite valuable in terms of efficiency and environmental friendliness. The problem which rises here, however, is the best usage of the power. The common approach is that based on certain parameters the inverter decides when to draw power from the battery. Important parameters for this decision are the actual load current based on electrical devices used in the household and the state of charge (SOC) of the battery. The main problem is disproportional power loss in the inverter by low-load currents drawn from the battery. Measurements of the battery made by the ZHAW demonstrated this problem. The idea is to use the battery power only for high-power devices with knowledge of the usage routine of the devices. So, the determining factor is not the load current but the recognition and usage-prediction of specific devices, such as a stove or water kettle. Only such high-power devices should be powered by the battery so that the losses in the inverter are driven to be negligible., To identify single devices, the load current must be measured. For the sake of simplicity and economy, only one measurement is installed. With digital signal processing and an adapted algorithm, it has been shown that devices can be identified in many cases. The consumption of individual devices is determined by a non-intrusive load monitoring (NILM) system from the total consumption (more details to follow below). An innovation resulted from combining typical energy-system challenges (e.g. minimising losses) which are common for individual PV plants at private homes. With a simple device the efficiency of existing batteries can be improved significant.

Corporate project team consisting of Zurich University of Applied Sciences (ZHAW) and Furtwangen University (HFU) analysed and examined the energy usage and its flow in a common household with a Photovoltaic (PV) plant and a battery as storage of the generated PV power. The aim was to optimise the power usage in a configuration with the battery. The energy generated by the PV plant and stored in the battery is quite valuable in terms of efficiency and environmental friendliness. The problem which rises here, however, is the best usage of the power. The common approach is that based on certain parameters the inverter decides when to draw power from the battery. Important parameters for this decision are the actual load current based on electrical devices used in the household and the state of charge (SOC) of the battery. The main problem is disproportional power loss in the inverter by low-load currents drawn from the battery. Measurements of the battery made by the ZHAW demonstrated this problem. The idea is to use the battery power only for high-power devices with knowledge of the usage routine of the devices. So, the determining factor is not the load current but the recognition and usage-prediction of specific devices, such as a stove or water kettle. Only such high-power devices should be powered by the battery so that the losses in the inverter are driven to be negligible., To identify single devices, the load current must be measured. For the sake of simplicity and economy, only one measurement is installed. With digital signal processing and an adapted algorithm, it has been shown that devices can be identified in many cases. The consumption of individual devices is determined by a non-intrusive load monitoring (NILM) system from the total consumption (more details to follow below). An innovation resulted from combining typical energy-system challenges (e.g. minimising losses) which are common for individual PV plants at private homes. With a simple device the efficiency of existing batteries can be improved significant.

Nominal power measurements of individual PV modules are needed to quantify the critical modules of PV plants offering lower energy production than expected. Today’s state of the art procedure of shipping a small number of modules to a laboratory is time- and cost intensive and it bears the chance of accidental damage. The Portable LED Flasher (PLF) was developed to require no dismounting of the modules. The quality of the PLF was tested on three PV plants in Switzerland. Additionally, ten PV modules of each plant were measured in the certified indoor laboratory of SUPSI, resulting in a maximum deviation of 3% of the STC values. Furthermore, a round robin test on a single crystalline silicon reference module at 25°C was performed at the JRC’s ESTI laboratory, the Swiss Mobile Flasher Bus and SUPSI resulting in a maximum deviation of the mean values below 1% compared to the PLF. A throughput of up to 150 modules or 500 modules respectively per day is expected and the total measurement costs are estimated to be about a tenth of the costs compared to an indoor laboratory. Module temperature measurement is crucial for a low total uncertainty. Thus, methods such as pre-shadowing of the module and approximation of cell temperature are the current focus of further improvement of the PLF measurement method.

An existing off-grid irrigation system of a 12’000 ha farm in Patagonia today powered by electrical pumps and diesel gensets, will be extended by a PV plant and a battery system to improve ecological ratings of the products and reduce energy costs. An optimal photovoltaic plant and a battery energy storage system had to be designed. The compiled hourly demand profile served as input to a simulation model of a photovoltaic diesel battery hybrid system. With the given assumptions the PV array should be oriented to north at an inclination of 30°. The analysis of electricity cost indicated the optimal system size of 1800 kWp PV nominal power and 500 kWh of battery capacity. With this system 55.2% of the energy used for irrigation will be provided by the photovoltaic plant in the first year. The electricity cost amount to $0.136 per kWh electrical energy compared to the $0.432 per kWh electrical energy currently produced by the diesel-only system. Further analysis showed high dependency of the electricity cost on the time until connection to the utility grid and its electricity price and future diesel price.

Nominal power measurements of individual PV modules are needed to quantify the critical modules of PV plants offering lower energy production than expected. Today’s state of the art procedure of shipping a small number of modules to a laboratory is time- and cost intensive and it bears the chance of accidental damage. The Portable LED Flasher (PLF) was developed to require no dismounting of the modules. The quality of the PLF was tested on three PV plants in Switzerland. Additionally, ten PV modules of each plant were measured in the certified indoor laboratory of SUPSI, resulting in a maximum deviation of 3% of the STC values. Furthermore, a round robin test on a single crystalline silicon reference module at 25°C was performed at the JRC’s ESTI laboratory, the Swiss Mobile Flasher Bus and SUPSI resulting in a maximum deviation of the mean values below 1% compared to the PLF. A throughput of up to 150 modules or 500 modules respectively per day is expected and the total measurement costs are estimated to be about a tenth of the costs compared to an indoor laboratory. Module temperature measurement is crucial for a low total uncertainty. Thus, methods such as pre-shadowing of the module and approximation of cell temperature are the current focus of further improvement of the PLF measurement method.

An existing off-grid irrigation system of a 12’000 ha farm in Patagonia today powered by electrical pumps and diesel gensets, will be extended by a PV plant and a battery system to improve ecological ratings of the products and reduce energy costs. An optimal photovoltaic plant and a battery energy storage system had to be designed. The compiled hourly demand profile served as input to a simulation model of a photovoltaic diesel battery hybrid system. With the given assumptions the PV array should be oriented to north at an inclination of 30°. The analysis of electricity cost indicated the optimal system size of 1800 kWp PV nominal power and 500 kWh of battery capacity. With this system 55.2% of the energy used for irrigation will be provided by the photovoltaic plant in the first year. The electricity cost amount to $0.136 per kWh electrical energy compared to the $0.432 per kWh electrical energy currently produced by the diesel-only system. Further analysis showed high dependency of the electricity cost on the time until connection to the utility grid and its electricity price and future diesel price.