When planning a solar panel system for your home, the first consideration for any solar designer is the tilt and orientation of your roof areas. We need to know which roof(s) will ensure the most optimum solar output – which translates to the best Return on Investment. For us here in Maryland, the most optimum solar roof orientation is Due South at 180 degrees. Of course, not everyone has this perfectly oriented roof and our customer base consists of homes that have South, West, East and everything-in-between orientations. Occasionally we even install on North-facing roofs if the pitch of the roof is low enough that panels are close to flat, or can be tilted southerly.
For homes that face East-West, you may be wondering which roof would best suited for solar. This is a good question given the fact that the output of your solar panels is directly related to your Return on Investment and how quickly the panels can pay for themselves.
If either East or West favors a more Southerly angle, then that would likely be a more favorable roof. Assuming that there aren’t issues related to shadingor obstructions caused by chimneys, vents, skylights and other roof-placed items.
If the house has a perfectly split East-West orientation, with all things equal – the next consideration would be roof angle; the lower the tilt (i.e. closer to horizontal) – the more solar energy will be generated over the course of the day. If the tilt on either side is the same then we would usually favor the West facing side. Here in Maryland, DC and Virginia we tend to have cloudier mornings, and sunnier afternoons going into dusk. Therefore we want to capture the late afternoon sun (west facing) more than early morning sun (East facing). Of course, should you happen to have a tree, chimney or other obstructing factor(s) on the West roof – we’d favor the East.
Homeowners looking at an East-West installation often have concerns as to whether or not their system will be profitable enough, compared to its south-facing counterparts. Disqualifiers for cost-effective solar systems include shading and limited available roof space. Rarely, however, is a home found unsuitable due to a Non-Southerly facing roof alone.
To illustrate, following is a comparison of a 10kW system’s output respective to East, West and South facing orientations. Data compiled using the National Renewable Energy Laboratory (NREL) weather data patterns for Baltimore, MD –
10kW system installed on a 20 degree pitched roof with zero shade
|SOUTH (180 degrees)||WEST (270 degrees)||EAST (90 degrees)|
|ANNUAL OUTPUT||13,224kWh||11,389kWh||11,328 kWh|
|*Annual $avings||$1853 per year||$1594 per year||$1586|
*Savings based on a conservative $3.00/watt installation, and $0.14/watt BGE rate
Data from PV WATTS
As illustrated, although perfectly South would be ideal, the East and West orientations provide a competitive amount of solar and would add only a few months to the payback period. If you were choosing between East and West (as opposed to installing on both), the difference is nominal. The choice of which roof may come down to aesthetic preference, distance to utility meter and regional weather patterns.