While south facing pv systems produce more power overall than west facing pv systems from a utility standpoint the impact of the losses in overall pv production of west facing systems are likely to be more than offset by the value of the reduction in the peak load.
South facing roof.
Based on the movements of the sun passive solar buildings typically have windows glazing on the southern facing side of the building in order to absorb the sun s heat energy to warm a building during the winter.
If the panels face west instead they get more energy during the afternoon an evening.
West facing skylights provide afternoon sunlight and heat gain.
For the northern hemisphere south facing roofs will give you the best results from solar panels.
For north american solar systems facing directly south an azimuth of 180 degrees is ideal.
Many roofs are multi faceted and if your roof is mostly west and east facing you re likely to only see a 10 20 percent reduction in the amount of energy you re generating.
Therefore directions like southwest or southeast are fine.
South facing skylights provide the greatest potential for desirable winter passive solar heat gain than any other location but often allow unwanted heat gain in the summer.
An easy way to determine the direction that your roof faces is to use google maps.
There are three main factors which go in to the calculation of how much sun a roof receives.
Solar panels are most effective when installed on south facing roofs.
On a south facing roof the panels produce energy when the sun is high in the sky but as the evening sets in that production decreases.
There is an optimum angle for solar panels on a roof.
Then roofing shingles in a multicolored color blend may or may not be a good choice depending on how large or busy the pattern of bricks is.
Panels mounted on a standard pitch roof facing east or west will produce approximately 15 less output than panels mounted on a south facing roof of a standard pitch.
If your panels face due east or west you will loose about 9 over what the south facing panels would provide.
However solar panels can be orientated on any roof that faces south of either east or west.
Consider your roof other factors.
Solar panels should face south for any home in america to obtain maximum power generation.
Since rachel asked about roof slope i will focus on this one aspect.
Those on east facing roofs provide maximum light and solar heat gain in the morning.
Not having a south facing roof is not a deal breaker however.
The direction that your roof faces also referred to as the azimuth angle is the primary factor determining how much sunshine your solar panels will see over the course of the day.
Orientation south facing windows passive solar houses typically have windows on the southern side of the building.
Similarly if your facing is a stone veneer of very large randomly sized and multicolored fieldstones roofing shingles with a prominent texture or multiple colors are likely to compete or clash.