Solar panels use the sun’s rays to generate electricity that can power our lives. Learn more about the history of solar cell technology, how solar panels convert sunlight to electricity, and how a solar energy system powers a home or a business.
A BRIEF HISTORY OF SOLAR ELECTRIC POWER TECHNOLOGY
The sun’s energy is critical to all life on earth, and humans have always found ways to harness solar energy. Solar photovoltaic (PV) technology as we know it today has been around since Bell Labs created the first silicon cell in 1953. By the end of the decade, solar cell efficiency had improved from 4% to 14% (source: DOE).
The solar energy industry expanded throughout the following decades. Solar technology improved thanks to research & development investment. Federal and state governments established regulatory frameworks for solar interconnections. These policies included policies such as tax credits, rebates, and renewable energy standards.
By 1999, cumulative installed solar capacity had reached 1,000 megawatts (MW). In 2000, while astronauts were installing solar panels on the International Space Station, Sandia Laboratories invented the modern inverter that improved system safety during power outages. In the almost two decades since then, solar panel costs have fallen dramatically due to innovations in solar panel design and improvements in racking systems that have made installations easier and faster.
As solar panel prices fall, the amount of solar installed globally has grown dramatically, from just over one MW in 2000 to more than four gigawatts (GW) in 2017 (source: Wikipedia).
The future of innovation in solar technology is likely to focus on new materials beyond or in addition to silicon. For example, recent breakthroughs with perovskites may lead to higher efficiency panels and the ability to coat various surfaces with solar as easily as painting or spraying.
Given that the amount of sunlight that reaches the earth every hour is enough to power the entire globe’s electricity use for a year, we know that the potential for solar power is unlimited.
WHAT IS A SOLAR PANEL?
A solar panel is a collection of solar PV cells that absorb sunlight and convert that light into electricity. For most installations, multiple solar panels are connected to create a solar array. The components of a solar panel include the solar cells, glass casing, backsheet, metal frame, and cabling to transmit electricity.
Solar cells are made from silicon and are built with a positive layer and a negative layer to create an electric field, similar to a battery. Here are a few fun facts about silicon:
- Silicon (Si on the periodic table) is a metalloid chemical element, which means it has properties of both metals and nonmetals.
- Silicon is a semiconductor, with conductivity between that of an insulator and most metals, which makes it useful for most electronic circuits
- More than one-quarter of the earth’s crust is comprised of silicon (by mass).
- Silicon is the second most abundant element after oxygen.
Most solar panels are made from either monocrystalline or polycrystalline silicon:
- Wafers are cut from a block of a single crystal of silicon, and cells form a distinctive shape – small black squares with notched corners.
- Monocrystalline solar panels have a more uniform appearance
- These panels perform better in high temperatures and shaded conditions, making them higher efficiency.
Polycrystalline (or multicrystalline) silicon
- Silicon fragments are melted together to form a large cell that typically has a multifaceted blue appearance.
- Polycrystalline solar panels are less efficient but are less expensive.
- There is less waste in the manufacturing process of polycrystalline cells.
The solar cells are covered by a glass casing, generally made from anti-reflective glass to increase sunlight absorption and improve solar panel efficiency, and they are protected by a backsheet.
HOW SOLAR PANELS WORK
The sun releases tiny packets of energy called photons, which travel to earth. When photons hit a solar cell, they knock electrons loose from their atoms. If conductors are attached to the positive and negative sides of a cell, it forms an electrical circuit. When electrons flow through the circuit, they generate electricity.
Solar panels create direct current (DC) electricity, a circuit in which electrons flow in a single direction (similar to a battery powering a lightbulb).
The electricity we use from the grid today, including our lights, appliances, and devices (anything that gets plugged into a wall outlet) use alternating current (AC) electricity. With AC electricity, the electric charge can flow different directions.
Thomas Edison developed DC electricity, which was the standard in the United States until the 1880s. Nikola Tesla believed that AC was a better solution because it could easily be converted to different voltages, making it easier to transport over long distances. The tide began to turn when Tesla’s technology was chosen for the Chicago World’s Fair in 1893, and AC electricity became the standard for the electric power grid in the United States (source: DOE).
Thus, an inverter is required to convert the electricity generated by solar panels from DC to AC current. The AC current is then routed to the electrical panel, where it can be used directly by a home or business, connected to an onsite battery, and/or connected to the electric grid.
TYPES OF INVERTERS
Another key part of a solar electric power system is the inverter technology. There are three main types of inverters:
- String inverter: The DC electricity from all of the panels on the array is routed through a single inverter that is then connected to your electrical panel. String inverters are the least expensive inverter solution, but they can make it more difficult to assess performance issues with individual panels.
- Microinverter: Micro-inverters are attached on the back of each individual panel. These tend to be more expensive but enable panel-level monitoring.
- Hybrid: This offers a middle-ground solution that combine a centralized inverter with power optimizers on each panel. Power optimizers are a DC-to-DC converter technology that improves performance by tuning each panel’s output to match the inverter. This technology is intended to offer some of the system performance benefits of microinverters but at a lower cost.
Inverters provide additional features beyond converting the electric current for our use. Inverters also offer ground fault protection and provide intelligence regarding energy production and maximum power point tracking.
HOW SOLAR PANEL SYSTEMS WORK
Here is an example of how a solar power system works.
- Sunlight shines on solar panels installed at your home or business.
- Your solar panels convert the sun’s energy to electricity.
- Electricity flows through conduit to an inverter.
- The inverter converts the electricity from DC to AC current.
- That electricity then flows to your electricity meter and is used to power your home or returned to the electric grid.
When the sun is not shining, your home continues to be powered from the electric grid. If your solar panel system generates more electricity than you are using at any given moment, that electricity will flow out of your home back into the grid. Many utilities have net metering policies that credit you for the excess solar power you generate.