When you are assessing the suitability of solar power, you need to survey the site where you are planning to install your solar panel array. You are looking for answers to two questions:
– Where can I position my solar panel array?
– Will I have problems with shading at any point during the year?
Positioning your solar panel array
Solar arrays can be mounted onto the walls or roof of a building, or be mounted onto a free-standing structure, pole or frame.
Location for your solar panel array
You are looking for a location that is south facing (or north-facing if you live south of the equator). You can orientate your panels anywhere from due east to due west, but to capture the sunlight at its most powerful, the closer your panels face towards the south, the more energy you will collect. As a rough rule of thumb, you will reduce the capacity of your system by 3% for every 10 degrees away from the south that your panels are facing.
brackets and cabling
Photovoltaic panels are not lightweight: including mounting brackets and cabling, you need to factor around 10kg or 22 pounds for every 100Wp of photovoltaic you are installing. If you are installing a single small solar panel on the roof of a shed, then that probably isn’t an issue, but a mid-sized 21/2kWp grid-tie solar array is going to weigh around 250kg or 550 pounds. If you are going to be installing a solar array onto the roof of your house, do not just assume that you will be able to do it: get your roof structurally surveyed to ensure the roof structure can handle this weight.
out of reach
You also need to take into account that when solar panels are in direct sunlight, they can get exceptionally hot and can cause severe burns. If you are mounting them on ground-mounted frames, you must make sure they are out of reach of animals and small children.
Because of this heating issue, you will need to put an air gap between the panels and the structure you are connecting them to. This obviously is not an issue with a dedicated solar mounting frame where there is free airflow around the panel, but when mounting on a roof of a house or a shed, you have to factor in the risk of ‘lift’, where the wind blows between the panel and the roof and the pressure build-up is enough to pull the roof upwards. In an extreme storm, this lift could rip the roof off a shed or a tiny home. If in doubt, seek advice.
The direction of your solar panel array
you need to ensure that all the solar panels within your array are facing in the same direction and can capture the same amount of sunlight at the same time.
Positioning your solar panel array
The ﬁnal thing to consider with the positioning of your system is the length of your cable runs. In an ideal world, your cable runs would be as short as possible in order to reduce loses through resistance. In the real world, this is not always possible, and you need to make sure that your cable runs are safe and secure.
The single biggest issue for a solar array is shade. When a solar panel, or part of a solar panel, becomes shaded, the energy production drops dramatically.
There are two types of shade. ‘Soft’ shade occurs when the overall intensity of light is reduced, such as on a hazy day or when there is very thin cloud overhead. ‘Hard’ shade occurs where a solid object is placed in front of the solar panels, creating a deﬁnable shadow.
When a solar panel is subjected to soft shade, the power generation drops in proportion to the strength of the shade. It is not a signiﬁcant problem in itself and solar calculators take into account that there will be a certain number of days in the month when you are likely to encounter hazy conditions.
Hard shade, however, stops the current ﬂowing through the affected cells. In effect, the entire solar panel can stop collecting energy. Have multiple solar panels connected in a string, and all the panels will stop collecting energy.
reduce this problem
Solar panel manufacturers have worked hard to reduce this problem and do so by having silver wires imprinted across each cell so that the charge can be carried across the silicon by the silver wires if a cell is in the shade. This does not eradicate the problem, but it does reduce the impact of shade: you do get some energy production, but much less than you would get from having no shade at all.
Consequently, it is essential to ensure that your chosen location is not affected by shade throughout the day. Check for tall trees and nearby buildings. Take into account that the sun is much lower in the sky in the winter than it is in the summer. If you have some shade to the east or the west, then this may well be acceptable because power generation is weaker at the start and the end of the day, but if you have any shading issues in the 45 degrees between south-west and south-east then you may need to ﬁnd a different location for your panels.
If you cannot avoid shading at your chosen location, you will need to factor in the loss of production into your system due to shade. The table below shows the reduction in efﬁciency for every hour that your solar energy system is in full or partial shade throughout the day:
The performance of solar panels particularly mono and polycrystalline solar panels are affected by temperature: the cooler the temperature, the better they perform. Unfortunately, as solar panels are black or dark grey and are designed to capture as much sunlight as possible, they tend to heat up quite considerably: it is possible for a solar panel to reach 80-90°C (160-175°F) in a hot climate, particularly if there is an insufficient air gap behind the panel to help release the hot air.
Most solar panel manufacturers provide information that shows the effect of temperature on their solar panels. Called a temperature coeﬁicient of power rating, it is shown as a percentage of total power reduction per 1°C increase in temperature.
Typically, this ﬁgure will be in the region of 0.4- 1.1%, which means that for every 1°C increase in temperature, you will lose 0.4-1.1% efficiency from your solar array, whilst for every 1°C decrease in Temperature you will improve the efﬁciency of your solar array by 0.4-1.1%.
Assuming a temperature coefﬁcient of power rating of 0.5%, this is the impact on performance for a 100Wp solar panel at different temperatures:
information in the sheet of your solar panel array
Then you look at the speciﬁcation sheet for a solar panel; you will see a Normal Operating Cell Temperature (NOCT) rating. This shows what the temperature of your solar panel is likely to be running at on an ‘average’ day where the intensity of the sunlight (solar insolation, which we cover later in this chapter) is at around 80%, the ambient temperature is 20°C [68°F) and there is a very light breeze. In most cases, this normal operating cell temperature rating will be around 45-50°C (113-122°F). In other words, even in a comparatively temperate climate, your system is likely to lose around 10-13% of its rated performance.
In many climates, the temperature issue can be mitigated by ensuring there is sufficient airﬂow underneath the panels, particularly if mounting the panels on a roof. A gap of between 7-10cm (3″-4″) on a large panel [150Wp and above) and between 1-5cm (1/2″-2″‘) on a small panel is usually sufficient.
In hotter climates, such as the southern states of America and in Africa, India, Australia, and the Middle East, where temperatures are signiﬁcantly above 25°C (77°F) for much of the year, the temperature of the solar panels may be an important factor when planning your system. Your air gaps should be larger, and you may wish to consider ﬁtting heat sinks to your solar panels in order to increase cooling. You will also need to downgrade the expected performance of your system to take into account the temperature of the panels.
In order to ﬁnd out if you need to worry about temperature efficiencies, look up the average monthly temperatures for where you are. Multiply these temperatures by 2.2 to allow for the heat build-up on the panel itself and then work out what the likely impact is going to be on solar panel performance.