LATEST NEWS & INFORMATION

​

5 Photovoltaic Cell Basics

When light shines on a photovoltaic (PV) cell – also called a solar cell – that light may be reflected, absorbed, or pass right through the cell. The PV cell is composed of semiconductor material; the “semi” means that it can conduct electricity better than an insulator but not as well as a good conductor like a metal. There are several different semiconductor materials used in PV cells.

When the semiconductor is exposed to light, it absorbs the light’s energy and transfers it to negatively charged particles in the material called electrons. This extra energy allows the electrons to flow through the material as an electrical current. This current is extracted through conductive metal contacts – the grid-like lines on solar cells – and can then be used to power your home and the rest of the electric grid.

The efficiency of a PV cell is simply the amount of electrical power coming out of the cell compared to the energy from the light shining on it, which indicates how effective the cell is at converting energy from one form to the other. The amount of electricity produced from PV cells depends on the characteristics (such as intensity and wavelengths) of the light available and the multiple performance attributes of the cell.

An important property of PV semiconductors is the bandgap, which indicates what wavelengths of light the material can absorb and convert to electrical energy. If the semiconductor’s bandgap matches the wavelengths of light shining on the PV cell, then that cell can efficiently make use of all the available energy.

Learn more below about the most commonly used semiconductor materials for PV cells.

 

 

 

 

SILICON

 

Silicon is, by far, the most common semiconductor material used in solar cells, representing approximately 95% of the modules sold today. It is also the second most abundant material on Earth (after oxygen) and the most common semiconductor used in computer chips. Crystalline silicon cells are made of silicon atoms connected to one another to form a crystal lattice. This lattice provides an organized structure that makes the conversion of light into electricity more efficient.

Solar cells made out of silicon currently provide a combination of high efficiency, low cost, and long lifetime. Modules are expected to last for 25 years or more, still producing more than 80% of their original power after this time.

THIN-FILM PHOTOVOLTAICS

A thin-film solar cell is made by depositing one or more thin layers of PV material on a supporting material such as glass, plastic, or metal. There are two main types of thin-film PV semiconductors on the market today: cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS). Both materials can be deposited directly onto either the front or back of the module surface.

CdTe is the second-most common PV material after silicon, and CdTe cells can be made using low-cost manufacturing processes. While this makes them a cost-effective alternative, their efficiencies still aren’t quite as high as silicon. CIGS cells have optimal properties for a PV material and high efficiencies in the lab, but the complexity involved in combining four elements makes the transition from lab to manufacturing more challenging. Both CdTe and CIGS require more protection than silicon to enable long-lasting operation outdoors.

PEROVSKITE PHOTOVOLTAICS

Perovskite solar cells are a type of thin-film cell and are named after their characteristic crystal structure. Perovskite cells are built with layers of materials that are printed, coated, or vacuum-deposited onto an underlying support layer, known as the substrate. They are typically easy to assemble and can reach efficiencies similar to crystalline silicon. In the lab, perovskite solar cell efficiencies have improved faster than any other PV material, from 3% in 2009 to over 25% in 2020. To be commercially viable, perovskite PV cells have to become stable enough to survive 20 years outdoors, so researchers are working on making them more durable and developing large-scale, low-cost manufacturing techniques.

ORGANIC PHOTOVOLTAICS

Organic PV, or OPV, cells are composed of carbon-rich (organic) compounds and can be tailored to enhance a specific function of the PV cell, such as bandgap, transparency, or color. OPV cells are currently only about half as efficient as crystalline silicon cells and have shorter operating lifetimes, but could be less expensive to manufacture in high volumes. They can also be applied to a variety of supporting materials, such as flexible plastic, making OPV able to serve a wide variety of uses.

QUANTUM DOTS

 

 

 

 

 

 

 

Quantum dot solar cells conduct electricity through tiny particles of different semiconductor materials just a few nanometers wide, called quantum dots. Quantum dots provide a new way to process semiconductor materials, but it is difficult to create an electrical connection between them, so they’re currently not very efficient. However, they are easy to make into solar cells. They can be deposited onto a substrate using a spin-coat method, a spray, or roll-to-roll printers like the ones used to print newspapers.

Quantum dots come in various sizes and their bandgap is customizable, enabling them to collect light that’s difficult to capture and to be paired with other semiconductors, like perovskites, to optimize the performance of a multijunction solar cell (more on those below).

MULTIJUNCTION PHOTOVOLTAICS

 

 

 

 

 

 

Another strategy to improve PV cell efficiency is layering multiple semiconductors to make multijunction solar cells. These cells are essentially stacks of different semiconductor materials, as opposed to single-junction cells, which have only one semiconductor. Each layer has a different bandgap, so they each absorb a different part of the solar spectrum, making greater use of sunlight than single-junction cells. Multijunction solar cells can reach record efficiency levels because the light that doesn’t get absorbed by the first semiconductor layer is captured by a layer beneath it.

While all solar cells with more than one bandgap are multijunction solar cells, a solar cell with exactly two bandgaps is called a tandem solar cell. Multijunction solar cells that combine semiconductors from columns III and V in the periodic table are called multijunction III-V solar cells.

Multijunction solar cells have demonstrated efficiencies higher than 45%, but they’re costly and difficult to manufacture, so they’re reserved for space exploration. The military is using III-V solar cells in drones, and researchers are exploring other uses for them where high efficiency is key.

CONCENTRATION PHOTOVOLTAICS

Concentration PV, also known as CPV, focuses sunlight onto a solar cell by using a mirror or lens. By focusing sunlight onto a small area, less PV material is required. PV materials become more efficient as the light becomes more concentrated, so the highest overall efficiencies are obtained with CPV cells and modules. However, more expensive materials, manufacturing techniques, and the ability to track the movement of the sun are required, so demonstrating the necessary cost adva

ntage over today’s high-volume silicon modules has become challenging.

 

Learn more about photovoltaics research in the Solar Energy Technologies Office, check out these solar energy information resources, and find out more about how solar works.

 

 

I

As Rooftop Solar Grows, What Should the Future of Net Metering Look Like?

Almost every state has been weighing changes to how homes with solar are compensated for electricity they send to the grid. The results will impact solar growth.

Like solar installers across much of America, Mark Hagerty is adapting to drastic changes in the economics of his business. His state, Michigan, is one of many that are cutting the rates rooftop solar owners receive for selling excess power to the grid.

“We’re going to do fewer jobs, and each job is going to be a smaller size,” said Hagerty, president of Michigan Solar Solutions, a solar installer based northwest of Detroit. His comments echo concerns now being voiced by solar installers in many states as new rules take effect.

Read More

 

 

 

 

 

 

Home battery comparison: Tesla Powerwall, Generac PWRcell, LG Chem RESU, Sonnen Eco, Enphase Encharge

Reading Time: 6 minutes

Now more than ever, home batteries are becoming a smart purchase either with or without a solar panel system. Batteries offer many benefits, from electricity bill savings to resiliency against grid outages and more.

There are plenty of companies offering energy storage solutions, including both established manufacturers and up-and-coming smaller players offering unique products. In this article, we’ll review some of today’s most popular home battery options to see what sets them apart.

Read More

 

 

 

 

 

 

 

AC vs. DC solar battery coupling: what you need to know

Reading Time: 4 minutes

Solar batteries are becoming popular additions to solar energy projects of all scales. When it comes to the way your solar panels, batteries, and inverters are all wired together on your property, there are two main options: alternating current (AC) coupling and direct current (DC) coupling. Both AC and DC coupling have advantages and drawbacks that are dependent on the specifics of your solar plus storage installation.

AC vs. DC coupling: what’s the difference?

The key distinction between an AC-coupled and DC-coupled system lies in the path electricity takes once it is produced by solar panels. Solar panels generate DC electricity that must be transformed into AC electricity for your home’s appliances. However, solar batteries store electricity in DC form.

In an AC-coupled system, DC solar electricity flows from solar panels to a solar inverter that transforms the electricity into AC electricity. That AC electricity can then flow to your home appliances, or go to another inverter that transforms the electricity back to DC for storing in a battery system. With AC-coupled systems, any electricity that is stored in the battery system needs to be inverted three separate times before use.

​

​

​

​

​

​

​

In a DC-coupled system, DC solar electricity flows from solar panels to a charge controller that directly feeds into a battery system, meaning there is no inversion of solar electricity from DC to AC and back again before the electricity is stored in the battery. Any electricity produced by the solar panels will be inverted only once (from DC to AC), either as it flows from batteries to your home electrical setup or out to the electrical grid.

​

​

​

​

​

​

Historically, AC-coupled battery storage setups have been more common for residential and commercial solar installations, but as more DC options become available, DC coupling is gaining in popularity.

Read More

 

 

 

 

 

 

 

 

 

 

Solar 101

 

How does a photovoltaic solar cell work?

Reading Time: 4 minutes

You’ve probably seen solar panels on rooftops all around your neighborhood, but do you know how they actually work to generate electricity? In this article, we’ll take a look at what a photovoltaic solar cell is – the technology behind a solar panel that makes it possible to create energy from the sun. Specifically, we’ll examine the science of silicon solar cells, the solar cells making up the vast majority of solar panels.

Solar cells produce energy in three steps

A solar photovoltaic (PV) cell works in three general steps:

1. Light is absorbed and knocks electrons loose

2. Loose electrons flow, creating a current

3. The current is captured and transferred to wires

The photovoltaic effect is a complicated process, but these three steps are the basic way that energy from the sun is converted into usable electricity by solar cells in solar panels.

Solar cells are the building blocks of solar panels

A solar panel is made up of six different components, but arguably the most important one is the photovoltaic cell, which actually generates electricity. The conversion of sunlight into electrical energy by a solar cell is called the “photovoltaic effect”, hence why we refer to solar cells as “photovoltaic.”

read more

​