How Solar Panels Work & How Many You Need to Power a Home
How do solar panels work? This is a question we're asked a lot — and it's not surprising.
As we move toward more sustainable ways to create electricity, solar energy is at the top of the list. In the words of Elon Musk:
"If it wasn’t for the sun, we’d be a frozen, dark ice ball. The amount of energy that reaches us from the sun is tremendous. It’s the 99 percent-plus of all energy that Earth has."
And we agree.
Solar energy — energy from the sun — is the future. And it's becoming more and more accessible to people who want to experience the benefits for themselves.
If you're considering solar panels to power your home, and you want to know how it works, you're in luck. Today, we're sharing an in-depth look at how solar panels work, the science behind them — and how many you'll need to power your home.
How Do Solar Panels Work?
The simple answer is that solar panels convert particles of light into electricity. But, if you're asking this question, chances, are you know this already.
So here's the long answer:
The Composition of Solar Panels
Before we can understand how solar panels work, we need to look at how they're constructed.
Each solar panel consists of photovoltaic cells (also known as solar cells). This sounds complicated. But the word 'photovoltaic' originates from the Greek words for "light" (phōs) and "volt" — meaning "to create electricity from light".
These photovoltaic cells contain two sheets of silicon or another semiconductor. The use of these materials in solar panels is important. This is because — like most electrical appliances — we need something that will conduct electricity, but only partly. If we used full conductors, the cells would convert a large amount of the energy to heat rather than electricity.
According to the Office of Energy Efficiency and Renewable Energy, 90% of the solar panels sold today use silicon. This is for a few reasons:
The structure of crystalline silicon cells increases the efficiency of the light-to-electricity conversion.
They are relatively inexpensive when compared to other suitable semiconductors.
They are long-lasting — we can expect them to function well for at least 25 years.
After silicone, the most common material used is cadmium telluride (CdTe). This is a low-cost semiconductor but it's not as efficient or long-lasting as silicone.
For the rest of this post, we will assume the photovoltaic cells use silicone. But the science is the same, regardless of the semiconductor used.
Creating an Electric Field
But the composition doesn't end there. In order to create electricity, we need an electric field. This is created during the manufacture of the photovoltaic cells.
Remember we mentioned the two layers of silicone? Manufacturers combine each layer with a different material, in a process known as doping. This either adds extra electrons to the layer or takes them away with the following end results:
When the material (e.g. phosphorous) adds electrons, it will create a positive electrical charge.
When the material (e.g. boron) removes electrons, it will create a negative electrical charge.
This creates an electric field between the two layers of silicone.
The Other Components of Solar Panels
As well as the photovoltaic cells, solar panels contain electrical contacts. These are thin metal contacts, carefully constructed so they do not block sunlight from reaching the cells.
The electrical contacts connect the individual photovoltaic cells and carry the electrical current.
The cells are also coated to prevent the loss of sunlight due to reflection. Silicone is a naturally reflective material and can lose more than 30% of the sunlight that hits it without an anti-reflective coating.
The final component of the solar panels we need to consider is the protective casing. This is most often made from glass and protects the silicon cells from the elements. It is important to clean this glass casing regularly — build-up can reduce efficiency by up to 30%.
The casing also provides insulation, which means your solar panels remain effective despite any fluctuations in external temperatures.
How Solar Panels Create Electricity
Now that we understand the composition of solar panels, we can move onto the fun part:
How do solar panels work?
Sunlight consists of photons. These are essentially tiny particles of light, which travel from the sun to the Earth.
When photons land on the solar panel, they displace electrons from the positively charged layer of the photovoltaic cell.
The electrons then land on the electrical contacts, which act as a conductor. The electrons travel down the thin metal plates into wires. And the process of creating electricity from sunlight is complete.
From here, the electrical current flows to an inverter. This converts the electrical energy into the alternating current (AC) we use to power our homes.
Once this process is complete, one of two things can happen:
It's used to power your home.
In the case of excess energy, it may flow back into the electrical grid for other families to use.
The Benefits of Sending Power Back to the Grid
If you live in an area that receives a lot of sunlight, sending power back to the grid can have enormous benefits for your family.
Put simply, the grid distributes your excess energy to other households in exchange for credits.
These credits can then be used when your solar panels don't produce enough electricity, further reducing any energy costs incurred by your household.
And this brings us onto the next question we're asked regularly...
How Many Solar Panels Do You Need to Power a Home?
Do you plan to use solar panels to significantly reduce your family's electricity costs? If so, it's important to consider how many solar panels you will need to power your home.
There are a few factors we need to consider when answering this question. The answer will vary depending upon the equipment used, the size of your home, and your energy requirements.
Here are the main things you need to consider:
How Much Energy Do You Use?
A lot of people assume the size of the home is the most important factor. But it's not.
The most important factor, by far, is the amount of energy you currently use to power your home. This will determine how much energy output you need from your solar panels, which will help you figure out how many you need.
For example, consider the following families:
The first is a professional couple with no children. They spend long days in the office, with regular trips away from home. When they're not working, they like to eat out and socialize with friends. They don't own a TV.
The second family has two young children. The father works in sales. He spends half of his time visiting clients, and the other half working from his home office. The children's mother stays at home to take care of the children.
They may live in the same area and their houses may be the same size — but the first family will use considerably less energy.
To find a breakdown of your electricity usage, take a look at your recent bills. For the most accurate picture, it's useful if you have access to a year's worth of data. This will help you account for seasonal fluctuations when making your predictions.
How Much Sunlight Will They Receive?
It is also necessary to consider how much sunlight the panels will receive. This varies depending on location.
Our work in Southern California takes us to different areas but for the most part, our customers get a lot of sun.
On average, summers are warm and dry with plenty of sunlight. Winters are pretty mild compared to elsewhere in the USA. This makes Southern California an excellent location for people wishing to use solar panels to power their homes.
But the amount of sunlight still varies within the state. For example, homeowners in the desert will need fewer solar panels than homeowners living in coastal areas.
Are you reading this from another state? Homes closer to the Canadian border will receive less sunlight than homes on the Mexican border — and therefore need more solar panels to achieve the same output. This is due to the different positions on the Earth, and the impact this has on how sunlight reaches your home.
The positioning of your solar panels makes a difference too. Even homes on the same street differ in terms of their solar exposure and the amount of shade that covers their property.
How Will Your Needs Evolve Over Time?
Solar panels can be a significant investment, so it makes sense to factor in how your needs might evolve over time. For example, if you plan to have children soon or spend more time in your home, it's likely your needs will increase.
This doesn't mean you necessarily need more solar panels now, but you should consider your options for scaling. Also, don't forget, many suppliers enable you to send excess power back to the grid in exchange for credits.
If you anticipate your needs will change in the future, this could be a good way to create a buffer and offset any future costs.
You should also think about how much of your electricity use you'd like to cover with your solar panels. Do you want to create 100% of the electricity your family uses — or would 50% be enough?
What Equipment Do You Plan to Use?
Before making a commitment, it's important to investigate all the options available to you. Each solar panel on the market has a slightly different power output. Once you have all the necessary information about your property, you'll be able to figure out which are best suited to your needs.
Do you have a small amount of roof space available and limited sunlight? You'll need to find solar panels with high power output.
But if you live in the middle of the desert and have a large amount of roof space available — with no shade — you're free to choose panels at the lower end of the spectrum.
We recommend you speak to a range of suppliers and gather as much information as possible. This will enable you to compare costs and find the equipment that's right for you.
Once you've made a decision, you'll be able to crunch the numbers to find out exactly how many panels you will need.
For example, the average family home in the US uses somewhere in the region of 10,000 kWh per year. In California, this requires a system with a 7kW output.
Once you have this information for your household, and you've chosen the equipment, you can use it to work out exactly how many solar panels you'll need.
Assuming you choose a solar panel with a standard power output of 1kW per day, in the example given above you would need around 28 solar panels to cover 100% of your electricity usage.
Already Have Solar Panels But Need to Increase Your Power Output?
Over time, it's natural for your power output to reduce slightly as the components begin to degrade. But this should only account for small fluctuations in the electricity generated.
Most people assume any drops in output are a sign their solar panels are becoming less effective. But this isn't always the case.
When did you last clean your solar panels?
As we mentioned earlier, regular cleaning can increase the output of your solar panels by up to 30%.
It may be that your photovoltaic cells are still functioning exactly as they should — it's just that less sunlight is reaching them.
And it's not just because of dirt, either. If you have attempted to clean your solar panels yourself, build up from the water can block photons from getting through the glass casing.
Thankfully, there's an easy solution — and that's where we come in.
We offer solar panel cleaning services to ensure you get the most from your equipment. Looking to maximize your power output without the need to buy more panels? Get in touch with us via the contact page to find out how we can help.