OREES is an optimization scheme that surrounds a load flow and dispatch model of the Swiss transmission grid. The optimization allows to find the best generation portfolio of, for example, PV and wind energy, given a flexibly defined objective function. The optimal power flow algorithm in the load flow and dispatch model ensure that the generation portfolio is functional with respect to the transmission grid, and under the capabilities of hydropower plants and international electricity exchanges. The portfolios explored by OREES are constrained by a 50-meter resolution geographical analysis of land use. If the required input data is available, the objective function can for example be defined to optimize for economic goals, or social acceptance, or grid stability, or balancing requirements. The response of the hydropower infrastructure, of the grid and international exchanges can be analyzed to quantify the various impacts of the tested portfolio. The simulations are performed at hourly resolution, and the spatial resolution of the installations maps of the portfolio are currently 1.6x2.3 km for PV installations and 1.1x.1.1 km for wind turbines. This resolution will be increased during SWEET EDGE to reach 100 meters.