If you are considering solar power for your home or business, one of the first questions you may have is whether your site is good for solar power or not. A very important aspect to consider is the available solar irradiance, which is often measured in kilowatt-hours per square meter per day (kWh/m2/day). To illustrate the importance of solar irradiance, assume you have two sites with identical conditions except for that value::
If you install solar PV systems of the same capacity in both locations, the second one will produce around 50% more energy per year. This will also translate into increased power bill savings and a much faster payback period. Even if you obtain solar energy through a Power Purchase Agreement, you will get higher savings in site #2 because you are getting more kilowatt-hours at a discounted price.
NASA have created an Atmospheric Science Data Center that can be accessed online, where you can input your coordinates to get all sorts of weather data for your exact location, including the incident radiation on solar panels for various inclination angles. Let’s choose two sites from Australia and plug their coordinates into the tool to see what results are obtained:
In this example we’re using their general coordinates from Google, but you can get the exact coordinates of your location with your smartphone. Note that the coordinates must be input in decimal degrees format, where North and East are positive, while South and West are negative.
To start, visit the NASA Atmospheric Science Data Center website (link here), where you will notice there are two blank spaces for latitude and longitude. To obtain solar data for a given location, just follow the steps below:
You will now get a table with solar irradiance values (kWh/m2/day) for horizontal surfaces and various tilt angles between 0° and 90°. In particular, the two final values are very interesting:
In the case of Sydney, NSW, you will find that the optimal tilt angle considering the entire year is 30.2° facing north, and the resulting average irradiance is 5.10 kWh/m2/day. Keep in mind that this is not the actual electricity produced by a solar PV system, since you have to account for the conversion efficiency of the solar panels, and then the losses due to the inverter and other system components. However, it gives you an idea of the available sunshine.
If we repeat the procedure for Broome, WA, we get an optimal tilt angle of 22.9° and a corresponding average irradiance of 6.78 kWh/m2/day. The smaller angle makes sense, since Broome is located farther to the north than Sydney. In addition, the solar irradiance is 33% higher, which makes sense when you consider that northwestern Australia gets more sunshine than the southeast.
As we move closer to the equator, the optimal tilt angle is reduced because the sun is higher up in the sky. In addition, the available solar irradiance increases. On the other hand, as we move farther to the south, the tilt angle is higher and the solar irradiance is lower even at the optimal tilt angle. Let’s try a third location to observe this trend:
Here the optimal tilt angle is 37.4° and the resulting solar irradiance is 4.42 kWh/m2/day. The optimal tilt is steeper than in Sydney, and the average irradiance is lower. Compared with this value, Sydney gets 15% more solar irradiance at the optimal tilt angle for PV panels, while Broome gets 53% more.
Keep in mind that all the values generated with this tool are for a solar panel that is oriented directly in the north-south direction, and tilted towards the north. These values do not apply if you rotate your solar panels west or east. Also consider that the optimal tilt angle is generally easier to achieve with a ground-mounted array or a flat concrete rooftop. In angled rooftops, the tilt angle of the roof itself is normally used.
Keep in mind that many other factors affect performance in an actual PV system, including the presence of shadows and differences in operating temperatures across various sites. Solar panels lose efficiency as their temperature rises; more sunshine equals more energy to convert into electricity, but also less efficiency due to the heating effect.
Sunshine is one of the most abundant resources in Australia, so most solar power sites tend to range from “good” to “excellent”. Unless your property is fully covered with the shadows of trees or surrounding buildings, solar power will likely offer an attractive return on investment. Australia could cover its energy demand 10,000 times with solar power, so the available opportunity is massive.
If you have already taken the decision to install a solar PV system for your property, the best you can do is getting a professional assessment before purchasing anything or signing a PPA. Knowing the solar irradiance available gives you an idea of what productivity you can expect, but site-specific conditions must also be accounted for.