Installing Solar Panels: The Importance of Site Conditions
12 October 2020
Considering the abundant sunshine and high electricity prices in Australia, solar panels are among the best building upgrades available. However, building owners must first make sure they have a suitable site for solar power. A photovoltaic array requires a large enough area that is not covered by shadows, and in the case of roof installations, the building must also have enough structural capacity.
Companies can benefit from solar power even when they lack a suitable site. They can sign a solar Power Purchase Agreement (PPA) off-site, which is also known as a front-of-meter PPA. In this case, the client purchases electricity from a solar array that is installed somewhere else. When solar panels are inside the property, the agreement is called a behind-the-meter PPA.
This article will discuss some site conditions that can limit the use of solar panels. To get the best results with solar power, these factors must be considered before installing them.
Having a Large Unshaded Area for Solar Panels
A 60-cell solar panel covers an area of around 1.7 m2, while a 72-cell panel covers around 2.0 m2. The efficiency and wattage of solar panels can vary, depending on their brand and cell material – monocrystalline or polycrystalline silicon. However, you can normally install between 150 and 200 watts of capacity per square metre.
Assuming an average space requirement of 1.0 m2 for every 175 W, you need around 6.0 m2 for a kilowatt, and around 6,000 m2 for a megawatt. However, solar panels cannot be installed continuously: rows must be spaced out for cleaning and maintenance, and not all roof areas can be used. For these reasons, large solar installations may actually need over 9,000 m2 per megawatt.
In addition to having enough space for solar panels, companies also need an area that is free of shadows:
- In most installations, solar panels are connected in string circuits, which are in turn connected to inverters.
- When one panel in the string is shaded, the effect is similar to closing a valve. All solar panels in that circuit have a drop in their power output, even if only one is shaded.
When designing the layout of a PV array, solar engineers consider how shadows behave during the day. Since the sun’s position is constantly changing, the direction in which objects project shadows also varies.
A solar power system can also be designed with microinverters, where each panel is equipped with its own inverter, instead of using large inverters with string circuits. However, this also makes the installation more expensive. In most cases, the best solution is to simply use a solar array layout that avoids shaded areas.
Having Enough Structural Capacity for Rooftop Solar Panels
Just like wattage, the exact weight of solar panels varies depending on the manufacturer and material. However, 60-cell panels normally weigh around 18 kg, while 72-cell panels weigh around 22 kg. Considering their average areas of 1.7 m2 and 2.0 m2, solar panels alone weigh between 10 and 11 kg per m2. However, when racking and other system components are considered, the load can range from 15 to 20 kg per m2.
Before installing a rooftop solar array, the building owner should get the roof inspected by a structural engineer. Reinforcements will be needed if the existing roof cannot carry the additional weight of solar panels. Older properties may have roofing materials that are not suitable for solar panels, and the entire roof may need a replacement in these cases. For example, asbestos cement roofs are too brittle for solar panels, while being a health hazard!
How Roof Orientation Affects Solar Panel Performance
The roof orientation also has an effect on the energy output of solar panels. However, this factor is much less critical than roof shading and structural capacity. In southern hemisphere countries like Australia, solar panels are more productive in north-facing roofs, and less productive in south-facing roofs.
- The difference is small in low-pitch roofs, such as those found in many commercial and industrial buildings, and the productivity loss of south-facing panels may be less than 5%.
- On the other hand, the productivity difference may reach around 25% in high-pitch roofs.
Solar panels have intermediate productivity when installed in roofs that face east or west. In particular, east-facing panels will be more productive during the morning, while west-facing panels will be more productive in the afternoon.
To get the best results with solar panels, a professional assessment of your property is necessary. This will ensure that your solar array has the optimal layout, avoiding shaded areas that affect generation. Also, you can rest assured that the weight of solar panels will not damage your roof.
After the inspection, if solar experts conclude that your property does not have suitable conditions for installing solar panels, you can still sign a front-of-meter PPA. You can also complement solar power by investing in energy efficiency measures, which will also help reduce your electricity bills.