Case Studies

Control Your Power – Frequency Shift

System in co. Sligo consists of 4x200Ah lifepo4 batteries (10kWh usable capacity), 5kW Victron inverter charger, 3kW Fronius solar inverter with 11x285Wp Perlight modules and recently installed VAWT. Owner has also 30kWh capacity in his car.

As can be observed on graph system has been independent for over 12 days. Energy consumption is between 5 to 10 kWh per day. Only when load is higher than 5.5kW internal relay of Victron Multi connects to ESB grid supply.

Energy consumption sources:

On graph below we can see solar and wind inverters on separate graphs. Notice: the last few days were windy. Last week was sunny but hopefully spring will come…

Solar (top) and wind (bottom) generation - last 12 days

Maybe it is not the best wind spot in terms of average production as it is very dependent to wind direction but turbine works very well, and when it is windy it produces energy day and night (if it is windy from the west – 5.3kW of power was recorded during storms from there!).

On windy day, when battery is getting full, we can connect an electric car charging at 3.7kW (how many times energy was converted at this stage?) and discharge system a little bit, but if you do not want to do it frequency shift mechanism will start work. After the battery reaches to absorption voltage battery has to be topped up gently. At this stage, we do not need all the power from the wind turbine or solar (off grid situation with surplus power).

Victron is increasing our micro grid frequency… Wind and solar inverter have grid settings set up to work with that frequency rise (that is my own grid code). Whenever GTI (grid tie inverter) can see grid frequency going up, he will reduce output to keep system in balance.

AC output frequency (island frequency) and the state of charge of the battery (bottom)

Maybe it is not the safest solution for the wind turbine as 4kW resistor heater kicks in at 530V DC rectifier output – so at pretty high rpm… but it works fine. The heater has not melted yet and the turbine is still there on 10m tower.

VE Configure frequency shift Victron settings
ABB Aurora Manager TL wind inverter settings

Last graph below… The area under will get bigger than area above red line. Note: it is much more efficient to use energy directly from the wind and sun before it goes to the battery (energy is converted only once).

AC Output Power History
AC energy direction of flow (above the ax demand, below excess that is going to battery)

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