A photovoltaic (PV) distributed energy resource (DER) was established to support the Tennessee Valley Authority's Green Power Switch program, which allows utility customers to purchase blocks of electricity generated by solar resources. The PV DER was also used to study the potential shading benefits of roof-mounted PV systems for commercial buildings. Test data derived by monitoring an offset-mounted PV array shading a built-up low-slope roof system shows that the annual savings per square foot of low-slope roof can be as high as $0.18 ($1.95 per square meter) in Phoenix, AZ.