The space needed for solar electric installations depends on your building’s energy needs. Energy Trust of Oregon recommends planning on 100 square feet for 1 kilowatt of solar panels, which will generate 1,000 kilowatt-hours per year. You can scale your system to meet only part of your load.

Online map measures roof area and solar potential
The City of Portland provides an online solar map that lets you zoom in on a satellite image of your rooftop to determine whether it’s a good candidate for solar panels. It estimates the usable roof area for solar and calculates an estimate of your roof’s solar energy potential.

Orientation and shading
Both orientation and the angle of PV panels will affect the electrical production, so both should be considered when evaluating your site’s solar potential and sizing up your system. Solar modules can be put on rooftops or on the ground using a fixed mount or a tracking mount that follows the sun.

Solar installations require a southern exposure for maximum output, although east or west orientation may be suitable. For best performance, there should be little or no shading year-round. Even partial shading on one portion of a panel can seriously degrade its output. An evaluation tool, such as the Oregon Department of Energy’s sun chart worksheet (PDF), can estimate the impact of shading and panel orientation on the annual performance. Typically, your solar contractor will perform a site analysis.