This paper reports the performance of a 4-kW grid-connected residential Wind-Photovoltaic system (WPS) with battery storage located in Lowell, MA. The system was originally designed to meet a typical New-England (TNE) load demand with a loss of power supply probability (LPSP) of one day in ten years as recommended by the Utility Company The data used in the calculation was wind speed and irradiance of Login Airport Boston (LAB) obtained from the National Climate Center in North Carolina. The present performance study is based on two-year operation. (May 1996-Apr 1998) of the WPS. Unlike conventional generation, the wind and the sunrays are available at no cost and generate electricity pollution-free. Around noontime the WPS satisfies its load and provides additional energy to the storage or to the grid. On-site energy production is undoubtedly accompanied with minimization of environmental pollution, reduction of losses in power systems transmission and distribution equipment, and supports the utility in Demand Side Management (DSM), This paper includes discussion on system reliability, power quality, loss of supply, and effects of the randomness of the wind and the solar radiation on system design.