Why Are Solar Panels so Inefficient? (Need To Know!)

Solar panels are made up of cells, each cell having an “active” surface area of around 60.0 cm². The cells are made up of semiconductor material that converts sunlight into electricity via the photovoltaic effect.

However, due to a phenomenon known as internal recombination, the cells can convert only a theoretical maximum of 33.16% (±0.5%) ^1 of the energy carried by photons with energy more significant than the bandgap into electricity.

For more energy to be converted into electricity, multiple cells must be connected, increasing cost and lowering efficiency.

In this article, we’ll cover some key points like:

  • What is solar panel efficiency?
  • How to increase solar panel efficiency.
  • Why solar panels are so inefficient.

You’ll be surprised how low the efficiency of most solar panels is. Read through the article to find out more.

Power Control Panel No Power
Power Control Panel No Power

What is solar panel efficiency?

Solar panel efficiency is the percentage of the sun’s energy that is converted into electricity. It is the ratio of power out divided by power in. for example, a 100-watt panel with an efficiency of 16% would have an output of 16 watts.

The efficiency of the single-junction cell has limited the efficiency of solar panels.

The theoretical upper limit for high-efficiency solar cells is about 33.16% (±0.5%).

There are currently commercially available multi-junction photovoltaic cells with efficiencies over 44%.

NASA is working on a variety of technologies to achieve efficiencies greater than 100%. But in practice, most installed solar panels have an efficiency between 10 and 20%.

Why are solar panels so inefficient?

While there are many different types of solar cells available today, with efficiencies ranging from 10% to 45%, most commercially available solar cells have average efficiencies between 17-20%.

This means that if you place enough of them side by side, they will be more efficient than an array with 20% efficiency because it produces more energy given a particular area.

A fundamental limit is that no single cell will ever convert more than 33.7% of incoming photons into electricity.

This would completely unbind electrons from their nuclei – thus creating an electric current without moving any charge between electrodes. Today’s most efficient solar panels use highly purified silicon with extremely sharp crystal boundaries.

These semiconductor layers can convert 41% of all available energy in photosynthesis into electricity by simply moving charges through the material (not requiring chemical reactions as plants do).

This allows for an overall power conversion efficiency of 90%.

But even if we were to take pure crystalline silicon as our starting point, there are still many other factors involved in solar panels which prevent perfect efficiency.

Solar panels do not have the best area ratio to electrical power output – they absorb less light than a flat surface with the same area.

This is due to only a specific wavelength range absorbed by silicon and other materials used for solar cell production.

It’s also because multiple technologies must be used together to reach their maximum potential: photovoltaic cells can convert sunlight into electricity but need inverters to change direct current into alternating current, and an array of capacitors will store excess energy until it is required.

Inverter losses account for another 7% on average, meaning that at 20% efficiency, we could have an array capable of generating electricity at 97% efficiency – but this is not the case.

Solar panels are designed for maximum output during peak sun hours, which coincides with peak demand times in most places.

Thus, solar companies design their panels to maximize the amount of power you can expect to generate between 10 AM-2 PM; so, despite being able to use them all day long, you’d only receive ~80% capacity because they were designed to operate at high efficiencies during these ideal times.

Many components are also left out of cheaper products to keep costs down, such as bypass diodes, increasing panel efficiency by 2%.

Can solar panels be 100% efficient?

Solar panel efficiencies are limited by the single-junction cell. Solar panels act more like a valve for sunlight, allowing photons to enter but not allowing them to leave.

Photons with an energy larger than the bandgap are absorbed and create mobile electrons that can be used to create an electric current.

However, internal recombination occurs because there are electrons in states within the forbidden gap at about the middle of the solar spectrum; these act like tiny antennas absorbing specific wavelengths of light and sending the energy as heat rather than converting it into electricity.

For more energy to be converted into electricity, multiple cells must be connected, increasing cost and lowering efficiency. The current commercially available multi-junction photovoltaic cells have efficiencies of over 44%.

How can we increase solar panel efficiency?

NASA is working on a variety of technologies to increase solar cell efficiency. One of the most promising approaches would use multiple thin-film tandem cells stacked in layers, with each layer designed for a different part of the solar spectrum. This approach employs co-evaporation

To create semiconductor layers that have different bandgaps, ensuring that photons always encounter a material whose bandgap energy is smaller than their photon energy.

The top cell in a triple-junction cell can be tuned to capture mainly blue and green light; this cell would be several thousand angstroms thick because it needs only to absorb short-wavelength light.

Each subsequent cell absorbs progressively longer wavelengths; thus, current technology implementations consist of about 20 semiconductor layers, each a thousand angstroms or so thick.

The result is an overall thickness of about 30 to 60 micrometers – thin enough for large-scale deployment on rooftops or in power plants.

How close are we to making 100% efficient solar panels?

The closest scientists have come so far would be by using multi-junction photovoltaic cells with efficiencies over 44%.

NASA is working on various technologies to achieve efficiencies greater than 100%, but most installed solar panels have an efficiency between 10 and 20% in practice.

This means that if these panels were placed side by side, they would create more energy than the same number of panels, with an average efficiency of 20%.

Overall, the best commercially available solar panels have efficiencies between 17 and 20%.

While several promising technologies are in development, none of them will be ready for commercial use until around 2020. In the meantime, other approaches could increase efficiency without requiring any new technology.

One solution would be to add tiny nanocones or nanowires to existing cells, which would scatter light into sideways paths that would otherwise not be collected by normal flat cells.

This approach is desirable because it can be applied cheaply and efficiently at the manufacturing stage, even to old panels – and it should work with almost any type of cell.

A coating could also absorb some wavelengths better than others due to its chemical composition, requiring scientists to fine-tune the spectrum of light absorbed.

Either approach could enhance the efficiency of solar panels on rooftops by 30%. Still, it would probably first be implemented on solar farms, where the greater surface area means more significant cost savings.

How do you calculate solar panel output?

To calculate the output of a solar panel, you ideally need to know which part of the color spectrum and thus which wavelength range your cell is most sensitive to.

Some manufacturers state this explicitly in their datasheets or webpages, but if not, you can find out by testing it yourself.

A multimeter with a photovoltaic function would be sufficient for measuring VOC (open-circuit voltage) and JSC (short-circuit current). These values can then be used to calculate your power output.

As long as we know our short circuit current value (JSC) and one other value, such as open-circuit voltage (VOC), we can quickly determine how much power (AC) our panel puts out.

Once we know the AC output value, we can also calculate the percentage of light our solar panel can convert into electricity (% VOC).

This value is highly dependent on your panels’ spectral response curve, which you would have to derive yourself or find in the datasheet.

What is the most efficient solar panel?

There are a lot of factors that influence which solar panel is the most efficient one. For instance, there are different kinds of silicon cells with drastically different efficiencies:

• monocrystalline Si has efficiencies from 16 to 18%
• multi-crystalline Si has efficiencies from 13 to 15%
• thin-film technologies have achieved up to 20%, but they currently have low market penetration.

The leading companies in the solar industry are becoming more and more efficient at making silicon cells.

Industry leader SunPower recently claimed a new record with an efficiency of 24%.

Panasonic is also one to watch. It is currently developing a cell that will absorb 44% of the energy from sunlight, nearly doubling the amount of light absorbed by existing cells.

So far, there aren’t any significant manufacturers that have achieved efficiencies higher than 32%; however, their research indicates that they should reach 40% within the next five years.

What are the factors affecting solar panel efficiency?

The efficiency of a solar panel is determined by:
• the material used
• the type of cell (amorphous, monocrystalline, and polycrystalline cells)
• how it was manufactured.

Silicon is currently the most used semiconductor in solar cells; however, other materials such as gallium arsenide or cadmium telluride exist.

Silicon has to be treated with boron and phosphorus atoms to create an abundance of free electrons (electrons that can move freely through the material).

The more free electrons available, the more electricity we will get out of our solar panel. This treatment process is known as “doping” and creates either p-type or n-type silicon (positive or negative).

P-type silicon has an abundance of free “holes,” basically holes in the material filled with electrons. Holes act like positively charged particles and can move through the material just like electrons can.

General Solar Panel FAQ

What Problems Do Solar Panels Solve?

In environmental terms, solar panels can potentially solve a handful of problems, including;
1. Air pollution
2. Water pollution
3. Greenhouse gases
4. Reduction in fossil fuel use

For individuals, solar energy allows you to become completely self-sufficient when it comes to your electricity needs and can save you a lot of money in the long run.

What Are 3 Important Uses Of Solar Panels?

The three most important uses of solar panels are;
1. Solar electricity. This can be used to power almost any appliance in your home, including TVs, computers, and fridges.
2. Lighting. In addition to the use of low-power, LED lightbulbs, solar panels can provide an efficient, low-cost, and environmentally friendly way to provide lighting to homes. 
3. Portable solar. In our modern, always-connected lives, our phones, tablets, and computers are almost always with us, and all run on batteries. Portable PV chargers can help keep our batteries topped up no matter where we are, as long as there is some sun to charge them.

Do solar panels give you free electricity?

Once the cost of the array is paid in full, the energy it produces is free. There are ongoing maintenance costs, too, such as annual panel cleaning, etc. 

How much will my electric bill be with solar panels?

Suppose your solar array includes a solar battery backup system, and it is large enough to fully cover your energy usage per day. In that case, your monthly electric bill will be next to zero dollars, even with a grid-tied system. 

If your solar array does not include a solar battery backup system, then at night, your house or business will use grid electricity. That cost will vary but expect to pay from 1/3-2/3 of your average electric bill, and that cost will fluctuate seasonally. 

Do you save money with solar panels?

The simple answer is, Yes, you save money with solar panels. There is an initial upfront cost, but since solar panels are warrantied for 25 years, you will save money over time. You will also begin to see monthly savings in energy bills, but there are other ways that solar panels pay you back. Those include:
1. Adding value to your home or commercial building 
2. Monthly decreases in energy costs
3. The ability to add more energy appliances without increased monthly costs
4. The potential for tax credits for going solar

Can solar panels power a house 24-7?

Most definitely! Solar panels can certainly power a house 24-7, with the addition of a high-quality inverter and a suitable battery bank, of course. To power, a house under normal usage will require a massive solar array, though, and there will be a very expensive initial financial outlay.

Do I need to tell my energy supplier I have solar panels?

This depends on where you live, but in most cases, it’s not necessary to inform your energy supplier that you have solar panels. That said, you may be producing excess power with your solar system, in which case you may be able to sell that excess power back to energy companies.

In this case, you’ll naturally need to be in contact with them. 

What Are Solar Cells Known as and Why?

Solar cells are also called photovoltaic (PV) cells. They are called so because the term ‘photovoltaic’ literally means light i.e. photo and electricity i.e. voltaic.

These cells generate electricity through the photovoltaic effect. This effect basically causes the generation of free electrons from the semiconducting silicon material of the solar panel when sunlight hits its surface.

What Type of Solar Panels Are Most Efficient and Why?

There are currently three types of solar panels available in the market that are:
1. Monocrystalline
2. Polycrystalline
3. Thin-filmed

Among these, monocrystalline solar panels are known to be the most efficient among all others.

Does heat enter your home through the roof?

Absolutely. Heat enters your home through your roof, and on a hot day your attic can get up to 150 degrees Fahrenheit or more. Through conduction, heat from the sun warms your roof which then warms your attic and the rest of your home.

Sol Voltaics is an affiliate and an Amazon Associate, we earn from qualifying purchases - at no extra cost to you.

FIND WHAT YOU'RE LOOKING FOR

Sol Voltaics Logo Icon green white
SOL VOLTAICS