Getting the most out of your solar power system is hard, but isn't impossible. The amount of power solar panels produce depends on three important factors: the size of the panel, its efficiency, and the amount of sunlight the panel gets.
Everything around us is energy: the sound we hear, the heat we feel, and the light we see. Solar panels perceive the former – a stream of tiny particles called photons. Each photon has its energy, mass and impulse. One of the most powerful sources of photons is the Sun. It radiates energy 24/7, whatever the weather. That is what makes solar power systems so effective.
Solar panels are made up of smaller units called solar cells. They are usually made of silicon – a semiconductor that is the second most abundant element on Earth. In a solar cell, crystalline silicon (depletion layer) is sandwiched between two conductive layers. N-type silicon has extra electrons, while P-type silicon has extra spaces for electrons, so called holes. Where the two types of silicon meet, electrons can wander across the P/N junction, leaving a positive charge on one side and creating negative charge on the other.
When a photon of light strikes the silicon cell with enough energy, it can knock an electron from its bond, leaving a hole. The negatively charged electron and location of the positively charged hole are now free to move around. However, the electric field at the P/N junction leaves them with no choice: the electron is drawn to the N-side, while the hole is drawn to the P-side.
The mobile electrons are collected by metallic conducting strips at the top of the cell. From there, they flow through an external circuit, doing electrical work, like powering a lightbulb. After that they return through the conductive aluminum sheet (substrate base) on the back. A single silicon cell can't really do any usable work, but you can string them together in modules to get more power. For example, twelve photovoltaic cells are enough to charge a cellphone, and it takes many modules to power an entire house.
The number of solar cells determines how much power solar panels produce. A typical residential photovoltaic panel consists of 60 cells aligned in 6 columns of 10 cells each and generates about 320W. The dimensions are generally 65 inches by 39 inches with slight variations among manufacturers. Solar panels also come with 72 and 96 cells, growing in size and capacity as solar cells add up.
There are also 120 and 144-cell panels which, believe it or not, are the same size as 60 cells and 72 cells respectively. Such compactness is achieved with the help of the half-cell technology, which cuts full cells into half, reducing their resistance. Lower resistance means more energy is being captured and produced. So, half-cell technology provides higher power output ratings (380-400W).
Two panels with the same number of cells can produce different amounts of electricity. Let's compare two 60-cell panels: Mission Solar Panel 310W and Solaria 355W Solar Panel.
Mission Solar 310W 60 Cell Solar Panel MSE310SQ8T
Cell number: 60 cell
Rated Power Output: 310 W
Cell Type: Monocrystalline
Rated Efficiency: 18.5%
Solaria 355W Solar Panel AC Module 60 Cell XT-355R With Enphase IQ7+
Cell number: 60 cell
Rated Power Output: 355 W
Cell Type: Monocrystalline
Rated Efficiency: 19.6%
All other things being equal, the power output rates differ greatly because of the difference in efficiencies. Solar panel efficiency shows solar panel's ability to convert sunlight into usable electricity. Given the same amount of sunlight shining for the same duration of time on two different solar panels, the more efficient panel will produce more electricity than the less efficient one.
Most solar panels are between 15% and 20% efficiency, but high-quality solar panels can exceed 22%. There are several factors that contribute to this:
• Material (monocrystalline or polycrystalline silicon)
• Wiring and busing (busbars)
• Reflection (glass layer on top of silicon solar cells).
These factors largely influence the price, so high efficiency solar panels tend to be 20-50% more expensive than their less efficient counterparts. However, they will allow you to economize in the future. Firstly, they are high quality panels with low degradation rate. Secondly, they'll save you some valuable space on your roof. Finally, they can be all arranged on the south-facing side of the roof to harvest the most power.
The power output you find in the specifications is basically the peak wattage – the amount of DC power a panel produces at standard test conditions (solar irradiance – 1,000 W per square meter, the cell temperature – 77 F).
Unfortunately, these exact conditions don't occur that often in the real world.
Peak sun hours help estimate how much power solar panels produce per day. Peak sun hours (PSH) describe the intensity of sunlight in a specific area, defined as an hour of sunlight that reaches about 1,000 watts of power per square meter (around 10.5 feet).
The number of peak sun hours you get per day depends on your location. The closer you are to the equator, the more PSHs you have. For the US, the average number is something between 4 or 5. For example, a 1kW solar power system (3 panels 330W each) installed in California will produce from 4.5 to 5 kWh per day.
Peak sun hours are something you can't change, but knowing them will give you an idea of what capacity solar system to install. What you can influence are shading conditions. Trees, buildings, and even small obstructions, like a leaf, can cast a shadow and deprive your solar panels of valuable solar radiation. So, try to set up your home solar panels where there is no shade and clean them timely.
With a degree in Linguistics, Tatiana uses her vast experience in technical translation to deliver complicated concepts in simple words. She joined the company in 2020 as a contributing writer to become the person to influence Blog’s development.
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