Will Solar Panels Work on East Facing Roof?
We all know how important it is to choose the perfect number of solar panels and the type of solar panels for installation. Similarly, the placement and orientation of solar panels are also important factors to be considered while installing solar panels. When placed perpendicularly, solar panels will absorb the most power. The general rule of thumb for solar panel orientation is that in the northern hemisphere solar panels should face true south and in the southern hemisphere, the solar panels should face true north. This is the best direction as the panels will receive direct sunlight throughout the day.
Magnetic vs Geographic orientation
The magnetic south is generally considered to be the earth’s magnetic pole south. The geographic south is the earth's south pole location. So, when installing solar panels, the geographic orientation (i.e., true north / true south) needs to be considered for both north and south hemispheres instead of the magnetic north/south. Some other terms to be aware of are the tilt angle and the azimuth angle.
Figure 1: The difference between Earth's North and South Magnetic pole and Geographic North and South pole can be seen.
Tilt angle is the angle of the panel relative to horizontal. If the panels are parallel to the surface, then the angle is 0. If the panels are standing straight up then it is perpendicular to the surface The Azimuth angle is like a compass direction with North = 0° and South = 180°. For example, in countries like the USA which is in the northern hemisphere, the sun spends most of the time in the southern half of the sky. It’s for this reason, that the solar panels are pointed directly south in the northern hemisphere. This will yield more electricity generation. In the southern hemisphere, in countries like Australia, the sun is in the northern part of the sky, so the panels are usually fixed facing the true north.
To track the movement of the sun and absorb more energy, trackers are installed this allows your solar panels to follow the sun’s path in the sky. Solar trackers are usually paired with ground-mounted solar panels but recently, rooftop solar panels have come onto the market. In tracing systems there are active and passive trackers. Single axis trackers follow the sun from east to west. These are usually used in utility-scale projects. This increases the production up
to 40 %. The dual axis tracker follows the sun's movement from east to west and also from north to south.
Figure 2: Single axis tracker on a horizontal axis.
Cloudy days can impact the solar performance a lot when compared to a clear sunny day as the irradiance from eh sun doesn’t directly reach the solar panels but gets scattered by clouds in the atmosphere. Solar panels can generate power on cloudy days too but the power output will be reduced when compared to power generated on a sunny day.
The Cloud Edge Effect
The cloud edge effect is a well-known phenomenon but its effects on PV plants haven’t been thoroughly understood. This effect is caused by a sudden increase in irradiance due to the reflection of the passing cloud focusing more sunlight on the array. Solar panel manufacturers don’t necessarily take these into conditions while manufacturing solar panels. In general, monocrystalline solar panels are considered to be good for cloudy days compared to multi-crystalline panels. Although they are a bit expensive compared to thin-film / multi-crystalline panels they tend to perform better in low light conditions as they usually have a high efficiency compared to their other counterparts.
Figure 2: Basic representation of the solar radiation components Source: Tiepolo et.al, .; National Space Research Institute
When installing solar panels on the east-facing roof you need to take the local weather pattern and the climate into consideration. The paper “A multi-objective assessment of the effect of solar PV array orientation and tilt on energy production and system economics” published in the journal solar energy takes a comprehensive look into the question of what directions should solar panels face. The researchers took the effect of the placement (azimuth and tilt) of fixed solar PV systems on their total energy production, peak power production, and economic value given local solar radiation, weather, and electricity market prices and rate structures into consideration. A model was used to calculate the output of solar PV systems across a range of azimuths and tilts to find the economically optimal placement. They concluded that the optimal placement can vary with a multitude of conditions, and challenges the default due-south placement that is conventional for typical installations