You need to think about the size and wattage of the solar panels, the angle and orientation of your roof, and the quantity of available space to figure out how big a solar system you can place on your roof.
The wind load on your roof should also be taken into account. Leave 200–400 mm between the gutter and the top ridge. The number of solar panels that fit on your roof can be multiplied by each panel's wattage, typically approximately 400 watts.
How many solar panels will I be able to fit on my roof?
Roof space is becoming more and more valuable as it will house the engines of the future to energise your smart home. The question may arise ‘ How many solar panels can I fit on my roof?’ for a 6.6 kW system. The answer usually varies by a few square meters, depending on which panel model you choose and the corner angles of your roof.
Rooftop solar power systems have multiple solar modules linked together to form one sizeable photovoltaic generator. When you combine solar panels and connect them in a string, you will use the same model in one system, meaning all panels should have the same wattage class and size.
Also, it depends on which specific solar panel you propose to put on your roof. When I started in the industry in 2006, panels were about 167 – 175 Watts. Usually about one and a half meters tall and about 80 centimetres wide. The system installed below shows these solar panels, a 1,575-watt system in Sydney. So you are generating, on average, 6.3 kWh daily, which supplies approximately 30% of the daily use.
They were 12-15 kilograms and easy to get on the roof. They also allowed some flexibility in the installations as smaller panels allow one to fit them on small roofs easily. In square meters, they took up about 1.2 m2
The new generation
In 2011 – 2012, a new generation of panels was brought to the market. These solar panels were more extensive and had more wattage, usually 250W. They were typically 1.6m high × 0.95 cm wide, meaning they took up approx 1.5 m2 and weighed 18 to 20 kg.
Today the average solar panel has dimensions of around 1.8m in height and 1.10 m wide, with outputs ranging from 370 to 420 watts. The weight is now always over 20 kg and as heavy as 24kg per panel. In addition, they are making it more difficult for a single installer to carry the panel onto a roof via a ladder. The roof area one needs per solar panel is about 2 square meters.
So if you know the available roof space, you can work out approximately how many solar panels you will fit. You will also need to consider that you need at least 200 -400 mm clearances from the gutter a – as per the above image – and the same from the top ridge of the roof because of the wind loading.
The wind load is much higher, close to the gutter and at the roof’s gable, so avoid going right to the edge in case of severe storms.
What should you be looking out for?
In general, a solar panel with a Southern orientation will still generate about 65% of the output of a panel facing ideally North.
But at the moment, look at your Easterly, Westerly, and North-facing roofs to determine how many squares of two meters by one meter you can fit into these areas. That way, you can work out how many panels can fit. Then you multiply that panel number by around 400 Watts. This will then give you the maximum solar system size you can fit.
Example of a required solar system
In a specific sample, a residential roof has 21 m2 facing West, 21 m2 Facing East, and 42 m2 facing North. Approximately one-third of each roof area is at an angle that does not allow a 2m x 1 m solar panel to be fitted. Therefore the number of panels that can go East is 7, West is 7, and North is 14.
The total of 28 panels will allow 28 x 400W = 11,200 Watts. So the maximum size solar system that will fit on the sample roof will be 11,2 kW. If located in Melbourne such a system, using the Your Energy Output Calculator, you will see that such a system without shade will generate 15,000 kWh per year and, on average, 41 kWh per day.
Now that the panels have increased, fitting them has become more difficult for installers, as the latest generation solar panel’s larger footprint will not fit in particular roof space edges. In contrast, an older style smaller solar panel could have.
So how many solar panels will fit?
Many installers have expressed dismay with these developments, and manufacturers, in their mission to achieve efficiency savings, have forgotten the interests of one of their biggest clientele – household solar installers.
There are also solar panels available capable of generating 500W and more. You might see some advertised. It is not recommended that you make a purchase based on the claimed wattage of the panels. Usually, these are for commercial solar systems and are much larger and heavier again. In addition, they look unsightly on a residential roof.