How Solar Panels Work
How Solar Panels Work
Solar panels generate electricity directly from sunlight using what is known as the photovoltaic (PV) effect. The first solar panels were invented in the 1950s and the basic operating principle is still the same, however, the efficiency has increased significantly over the last decade. Solar panels are a relatively simple device made up of a series of solar cells sandwiched between a front glass plate and a rear plastic back-sheet, supported within an aluminium frame.
Sunlight is made up of parcels of energy known as photons and when these hit the solar cells they release electrons which flow into an electric circuit. The amount of electricity a solar panel generates is proportional to the amount of sunlight or more accurately irradiance, so naturally, during cloudy weather, the solar generation will decrease. It is often mistaken that solar panels work using heat, but this is incorrect, higher temperatures actually reduce the power output by a small amount. Solar panels only require sunlight but they still produce a small amount of electricity even during very poor weather but the lighter the clouds the better.
Power vs Energy ⚡️⚡️⚡️
Electrical power is how much a solar panel (or system) produces at any given time, and is measured in Watts or W (a 1000 Watts is called a kilowatt or kW). A solar system’s potential power is also measured in kW. For example, a 10kW solar system is a system with panels that can produce up to (and sometimes slightly more than) 10kW of DC electricity.
Electrical energy is measured in Watt-hours or Wh (a 1000Wh is equal to 1.0kWh). The amount of electricity that you use at home is measured in kWh on your electricity bill. The amount of electricity that your solar system produces, or is capable of producing, in a given period of time is also measured in kWh.
The amount of energy that any given solar panel can produce depends on the location of the system, and specifically the amount of sun that location gets. For example, a 10kW solar system in southern Australia, or northern USA, with a perfect installation, may expect around 35kWh of energy on average per day throughout the year. Whereas a 10kW system in northern Australia or southern USA may expect to produce up to 55kWh a day, on average throughout the year.
Main factors that affect solar panel power output:
Sunlight - PV (or photovoltaic panels) require light to produce energy. Factors that decrease sunlight are:
Dirt - Dirty panels obstruct sunlight and reduce power output.
Shade - Trees or buildings can get in between sunlight and your panels.
Heat - You might expect heat to help in solar production, actually heat is detrimental to the output. The best conditions are lots of light, and low heat.
Position of the solar panels - The angle relative to the suns path, and the azimuth (direction the panels face) are a big factor in the ability of the panels to produce power.
How are solar panels made?
Solar photovoltaic cells, or PV cells are made using silicon crystalline wafers which are similar to the wafers used to make computer processors. The silicon wafers can be either polycrystalline or monocrystalline and are produced using several different manufacturing methods. The most efficient type is monocrystalline (mono) which are manufactured using the well known Czochralski process. This process is more energy-intensive compared to polycrystalline (poly) and therefore more expensive to produce. Read the full Solar Panel Construction article.
Polycrystalline wafers are slightly less efficient and are made using several purification processes followed by a simpler, lower cost, casting method. Cast monocrystalline or cast mono cells have also been gaining popularity due to the lower-cost casting process used to make cast mono cells. However, cast-mono wafers are not quite as efficient and pure mono wafers made using the Czochralski process. Read the Solar PV Cell Construction article.
Monocrystalline silicon cells - Highest efficiency and highest cost
Cast monosilicon cells - High efficiency and lower cost
Polycrystalline silicon cells - Lower efficiency and lowest cost
Is my roof right for solar?
To determine whether your rooftop is suitable for solar there are a few key considerations you first need to assess:
Do you own your own roof space?
Does part of your roof face north, west or east in the Southern Hemisphere, or south, west or east in the Northern Hemisphere? And is that roof space unshaded for the majority of the day, for most of the year?
Is there enough unshaded area to fit 8 or more solar panels? (Approx 12 sq. meters, or 130 sq. feet)
If you answered yes to all of the above, you can probably install a productive solar system on your house. However, there are a few other factors that may influence the viability or cost of install. We should also take a closer look at some of those questions.
In the southern hemisphere, a north-facing roof is optimal for solar production throughout the entire day (south-facing in the northern hemisphere). Depending on the pitch of the roof, a west or east-facing roof will decrease your solar output across the day by about 15% compared to the optimal. Having solar on an east or west-facing roof is not ideal if you are home all day to use your solar power, or if you receive a nice feed-in tariff (or net metering, see next chapter for more on that). However, it’s also not a deal breaker if you only have an east or west-facing roof, because 15% is not a massive amount, plus solar panels are pretty cheap these days so you can always oversize the inverter (put up greater kW of panels than the inverter size) in order to go some way to counter the loss from the roof direction.
Furthermore, if you do not get paid much for the solar that you export, and you aren’t home throughout the day, then you may in fact prefer to have solar installed on your east or west-facing roof. That is because the sun rises in the east and sets in the west (in both hemispheres), which means an east-facing solar system will produce more power in the morning and a west-facing system will produce more in the evening. Therefore if you use most of your power in the morning and evening, you will consume more of your own solar power if you have an east and/or west facing install.
Solar panel installation angle plays an important role in the performance of a solar system. Generally, solar panels are mounted flush to the roof and so, the roof angle determines the angle of the panels. This is generally adequate, providing the roof is facing roughly in the right direction (as explained in the previous section). However, if you have a relatively flat roof then the panels should be installed on tilt frames that can be positioned to face the desired orientation. As a general guide, the minimum tilt angle solar should be 15 degrees from horizontal to allow water to run off which also helps to wash off any dust, dirt or leaves.
The optimum tilt angle for maximum performance throughout the year is typically determined by the latitude of your location. For example, Sydney Australia has a latitude of about 34º, so the optimum tilt angle is roughly 30º to 35º. The further you are from the equator the greater the optimum tilt angle. This becomes more and more important once you pass 40º latitude as the amount of sunlight decreases dramatically during the winter months and the sun is much closer to the horizon, even in the middle of the day, so the greater the tilt angle the better the winter performance.
There is a lot that can be said about shading, however the most important thing you need to know is that your solar panels will not generate power when they are shaded. If you have big beautiful trees surrounding your house that provide lots of shade in summer, then buying a solar system would likely be a waste of money.
If partial shading is a problem, there are several clever add-on devices that can help overcome any associated performance issues.
The calculations are too complex to go into here as to whether or not the shade on your house is a deal breaker or not. It is suffice to say that if you get a decent amount of sun on some of your roof for most of the year, then it is worth getting an assessment from a solar provider. Any decent solar company should be able to give you an accurate idea of how much energy your system will produce, and how much it will be affected by shade.
If partial shading is a problem, there are several clever add-on devices that can help overcome any associated performance issues. In most solar installations the panels are linked together in what is known as a string. Strings of solar panels work together, but unfortunately due to the electrical characteristics of solar cells, any shaded panels will reduce the power output of the whole string, even if only half of one panel is shaded. Luckily, there are several ways to get around this problem. The most common way is to use a device known as a power optimiser, these are small add-on devices that are attached to the rear side of a solar panel and essentially bypass the shaded panels. If the shading is more severe, then the next best option is to use micro inverters which enable every panel to operate independently.
Type of roof
Installers can install a solar system on most types of roof material, however there are some roofs that are unsuitable. Slate for example can prove difficult, and fibreglass is generally not possible.
The pitch of your roof can also lead to additional costs during installation. If you have a steep roof, it can be dangerous to install on, which means the installers may need special access and safety equipment (this can add hundreds of dollars). Likewise, if the roof is difficult to access, the installers may need special access equipment or cranes. If the roof is flat, or nearly flat, you will likely require extra tilt racking in order to face the panels in the direction of the sun.