Did you know that the amount of sunlight that reaches the Earth in a single hour would be enough to power the entire world for a whole year if we harnessed it all? Solar electric technology is transforming the way we think about energy and has been for some time – but how much do you know about this kind of solar technology?
We’re looking at how solar panels convert sunlight into usable electricity for homes and businesses, reducing their reliance on the aging electrical grid and providing a reliable, clean, and sustainable energy source.
The Solar Energy Process
There are five basic steps in the solar electric generation and transmission process:
- First, sunlight hits a solar panel, creating an electric field.
- The solar panel then generates an electrical current, which travels in conductive wires through and then out from the panel.
- The wire transports the electricity to the inverter. Here, the DC electricity is transformed into AC electricity – the kind of electricity you’re used to coming from standard wall outlets in your home or business.
- From the inverter, more wiring moves the AC electricity from the inverter to an electrical panel or breaker box. From there, the electricity gets distributed throughout the home or business as needed.
- In most grid-connected solar panel systems, any “extra” electricity passes through a special two-way utility meter, where it then moves into the electrical utility grid. Whenever this is happening, the meter actually spins backward – in other words, you receive a credit for the electricity your solar panels are providing to the electrical grid. This process is called “net metering” and is available for most grid-connected systems.
What Do Solar Panels Do?
To understand how solar panels work to provide electricity, we have to talk about science. The science of solar power dates back to the 1830s, when French physicist Alexandre Edmond Becquerel observed a process called the photovoltaic effect, in which exposure to light (photons) produces voltage and electric current in certain materials.
Solar PV panels (PV standing for photovoltaic) feature numerous small photovoltaic cells – often 60 or 72. The cells on solar panels are made of semi-conductive materials, such as silicon. This means they can conduct electricity and maintain an electrical imbalance simultaneously, essential in creating an electric field.
A solar panel works by absorbing photons from the sun. This causes electrons to become “loose,” drifting freely throughout the cell. Because a PV cell is designed with positively and negatively charged semiconductors layered together, an electric field helps guide the electrons towards the cell’s conductive metal plates. This movement of electrons is an electric current – specifically a direct current (DC) because the electrons are all moving in the same direction.
Once the DC current reaches the metal plates, it moves into the conductive wires. Then it flows to the solar inverter.
How Do Solar Panels Generate Electricity?
The DC electricity that reaches the solar inverter is not yet usable as electricity to power our appliances, electronics, lights, and other devices. So even though solar panels technically produce electricity, it’s the inverter that converts it into the kind of usable energy our household appliances need.
What the inverter actually does is convert the incoming DC electricity into alternating current (AC). Once that process is complete, the AC electricity goes to a breaker box/electrical panel. From there, it can be distributed throughout the building where and when it’s needed.
What Happens to Unused Solar Energy?
Any electricity not needed by the outlets connected to the electrical panel moves into the utility grid, passing through a two-way utility meter. The meter tracks how much electricity is transmitted between the system and the grid and vice versa. So when your solar power system produces more energy than you use, the meter runs backward. As a result, in most US states, you would receive credit for the excess energy (net metering).
Alternatively, if you have opted to go off-grid, you will use an energy storage solution (deep cycle batteries) to store the excess electrical energy. You can draw from this energy “reservoir” if and when you need it, such as during nighttime hours or excessively cloudy periods.
How Do Solar Panels Work on a House?
It doesn’t matter what type of property is utilizing solar panels – whether it’s a home or business, the process is the same. Of course, because the energy requirements of each are different, the actual solar setup will vary. For example, a small home requires less energy than a large office building, so the number of solar panels will differ considerably. But regardless, how solar works remains the same.
Oftentimes the way the solar panels are mounted is on the roof of a home. For sites that have a lot of land, you may opt to do a ground mount. Both systems have a design tool that helps you figure out the components needed for your solar panel mount, mostly dependent on the number of solar panels that are in your system.
What Happens When the Electric Grid Goes Down – Will My Solar Panels Still Produce Power?
This is a common question and/or misconception. When the utility power goes out, people with solar panels may assume they will still have electricity. Unless you have an energy storage system (ie. batteries that will store the power generated from the solar panels), for safety reasons, the solar array on the home or business will shut down, so line workers can stay safe when working on the grid.
More on the Photovoltaic Effect and Solar Panels
When photons from sunlight are absorbed by a semiconductor material (usually silicon), they knock negatively charged electrons loose from their atoms. The electrons flow from the negative to the positive side of the PV cell to recombine with available holes. This creates a direct current (DC) flow. We can then use this flow of electrons to power a DC device directly (generally simple devices like pumps or fans) or charge a battery bank – or we can convert it to AC power to use in your home.
Silicon solar cell components
Each individual solar PV cell generates about ½ volt. That’s not much for practical use. So multiple cells are wired together in series to create higher voltage, creating a solar module, commonly referred to as a solar panel. A typical 24 Volt (V) solar panel has 72 cells. The larger a solar cell is, the higher the current. So the cells of a 400 Watt (W) panel are generally bigger than a 300W panel. You might be asking “Doesn’t 72 cells times ½ V per cell equal 36V, not 24V?” Your math is correct; see the “Nominal Voltage of Solar Panels” section below for an explanation.
Silicon cells combined to make solar module
The more solar cells wired in series, the higher the voltage of the solar panel. You can see the difference in the look of a 36-cell 12V module compared to a 72-cell 24V module. As with anything, there are exceptions, but this is an excellent general rule.
12V solar module vs. 24V solar module
Nominal Voltage of Solar Panels
Nominal voltage is a way to categorize battery-based solar equipment. Because a higher voltage is required to charge a battery, nominal voltages help see what equipment goes with what. A nominal 12V panel has a Voc voltage of around 22V and a Vmp of approximately 17V. This difference often confuses people when they try to measure the voltage of a solar panel when it’s not connected to anything but a voltmeter. If you count the number of cells, it will likely have 36 cells wired in series.
Likewise, a panel designed to charge a 24V battery bank will have a Voc of around 44V and a Vmp of approximately 36V. Counting the cells will come up with 72, twice as many as a 12V panel. If you wire two 24V panels in series or four 12V panels in series, you can charge a 48V battery bank.
This was all well and good for battery-based systems, but then along came grid-tie systems, and since they don’t use batteries, so DC voltages like 12V, 24V, and 48V aren’t relevant to them. So the industry sort of standardized on 60-cell, 20V nominal panels. Alone, they are too big to charge a 12V battery and too small to charge a 24V battery. MPPT charge controllers solves that by reducing the voltage down to the required range and, in doing so, increasing the current output, so you are not losing power. With very few exceptions, you still need to make sure the nominal voltage of the solar array is higher than the battery bank. You can see more on MPPT charge controllers in our MPPT vs. PWM Charge Controller video.
The demand for higher wattage solar panels has been increasing. Many manufacturers are achieving that by increasing the number of cells and, in turn, increasing the voltage of the panels. As you may recall, Watts equals volts times amps, so increasing the volts while maintaining the same amps increases the Watts. As such, there are now 96-cell panels available these days.
If the panel you select doesn’t specify its nominal voltage, you can look at the specificationsf (for help with this, learn how to read solar panel specifications). A 24V panel has a Voc of about 46V, whereas a 20V nominal panel has a Voc of around 38V. You’ll need to know the nominal voltage of a panel when you are designing an off-grid solar system to ensure the input voltage is high enough to charge the battery bank and determine what type of solar charge controller you need. Be sure to check out our article on sizing MPPT charge controllers in our DIY Solar Resources Library.
Make the Switch to Solar with Quality Components from altE
Are you searching for the best solar panels for your home or business? There are high-quality options to suit a broad range of needs and budgets, and you can find them all through altE.
altE is a solar equipment provider that helps you save time and money by eliminating the middleman and offering you solar panels and other equipment for sale. Whether you’re going to build a DIY solar energy system or simply sourcing your components for professional installation, we have you covered with the best brands in the business.
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