This thesis presents a method for islanding detection of single-phase micro-grids including solar micro-inverters. Solar panels in Building Integrated Photovoltaic (BIPVs) applications are often connected to an ac grid using ac module micro-inverters that are usually operate at power ratings less than 0.3kW. The solar micro-inverters are basically single-phase inverter units that connect each panel to the grid separately and in a parallel configuration. Safety requirements of building necessitate immediate disconnection of the micro-inverters when the main ac line is disconnected. Such a situation is called islanding and standards require detection and disconnection of micro-inverters in less than 2 seconds. Several methods including passive and active methods have been suggested and tested to comply the islanding detection standards. Passive methods are established based on monitoring of voltage (frequency) of the grid at the point of common coupling (PCC) and they work based on detection of the PCC voltage (frequency) deviations using an over/under voltage (frequency) relays. This method can fail when there exist a balance between loads and photovoltaic power generation at the islanding moment that is called non-detecting zone (NDZ). To enhance the islanding detection capabilities, active method with smaller NDZ are suggested in which a perturbing signal is injected to the system and this signal will make the inner control loop of the inverter unstable as soon as the islanding phenomenon occurs. Sandia Voltage and frequency methods are two examples of active methods for islanding detection in three-phase micro-grids. The thesis addresses the islanding phenomenon in single-phase micro-grid and presents an impedance method for detection of islanding phenomenon in signal and multi-inverter photovoltaic power systems. The method is established based on injection of a harmonic current to the grid and on-line measurement of impedance seen from the PCC. The grid is modeled as a sinusoidal source behind an impedance and when islanding phenomenon occurs, the measured impedance is significantly changed if the frequency of the injected current is selected appropriately. The performance of the method is investigated for both signal- and multi-inverter using the IEEE UL1741 standard circuit based on several time-domain simulations and experiments. The investigations also cover the effect of a non-linear load (full bridge rectifier) in a signal-phase system. The test results show that in all tests the suggested impedance method can detects the islanding phenomenon significantly faster than conventional approach especially in NDZ situation. The limitations of the suggested method are: 1) it needs a precise voltage sensor to be able to measure the small harmonized PCC voltage; and 2) it can fail at blind frequency that is a frequency in which the islanding and grid connected mode impedances are the small or too close together to be detected. To address the second limitation, a method in which two harmonized current with different frequencies are injected, is suggested and it has been shown that this method can completely remove NDZ. However, this method still needs highly precise voltage sensor which can be a practical limitation due to increasing the final manufacturing cost of micro-inverters. Keywords: Islanding Detection, Micro Grid, Renewable Energy, Solar Micro-Inverter, Impedance Island Detection Methods.