Our sun is a naturally occurring nuclear reactor. It releases tiny packets of energy called photons, which travel the 93 million miles from the sun to Earth in about eight-and-a-half minutes. Every hour, enough photons impact our planet to theoretically satisfy global energy needs for an entire year. However, solar-generated power currently accounts for just four-tenths of one percent of the total energy consumed in the United States. Solar technology is improving and costs are dropping rapidly, though, so our ability to harness the sun’s abundance of energy is on the rise. In fact, a report from the International Energy Agency indicates that solar energy could become the largest global source of electricity by 2050. In the coming years, we will all be enjoying the benefits of solar-generated electricity in one way or another.
So how does solar power work?
Photovoltaic solar panels
Photovoltaic (PV) solar panels are made up of many solar cells. Solar cells are made of silicon, like semiconductors. They are constructed with a positive layer and a negative layer, which together create an electric field, just like in a battery. 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 such a circuit, they generate electricity. Multiple cells make up a solar panel, and multiple panels (modules) can be wired together to form a solar array. The more panels you can deploy, the more energy you can expect to generate.
Basics of electricity
PV solar panels generate DC (direct current) electricity. With DC electricity, electrons flow in one direction around a circuit. This example shows a battery powering a light bulb. The electrons move from the negative side of the battery, through the lamp, and return to the positive side of the battery.
With AC (alternating current) electricity, electrons are pushed and pulled, periodically reversing direction, much like the cylinder of a car’s engine. Generators create AC electricity when a coil of wire is spun next to a magnet. Many different energy sources can “turn the handle” of this generator, such as gas or diesel fuel, hydroelectricity, nuclear, coal, wind, or solar.
AC electricity was chosen for the U.S. electrical power grid, primarily because it is less expensive to transmit over long distances. However, solar panels create DC electricity. How do we get DC electricity into the AC grid? We use an inverter.
A solar inverter takes the DC electricity from the solar array and uses that to create AC electricity. Inverters are like the brains of the system. Along with inverting DC to AC power, they also provide ground fault protection and system stats including voltage and current on AC and DC circuits, energy production, and maximum power point tracking.
Central inverters have dominated the solar industry since the beginning. The introduction of micro-inverters is one of the biggest technology shifts in the PV industry. Micro-inverters optimize for each individual solar panel, not for an entire solar system, as central inverts do. This enables every solar panel to perform at maximum potential. One solar panel won’t drag down the performance of entire solar array, as opposed to central inverters that optimize for the weakest link.
Putting it all together
Here’s an example of how a residential solar energy installation works. First, sunlight hits a solar panel on the roof. The panels convert the energy to DC current, which flows to an inverter. The inverter converts the electricity from DC to AC, which you can then use to power your home. It’s beautifully simple and clean, and it’s getting more efficient and affordable all the time.
However, what happens if you’re not home to use the electricity your solar panels are generating every sunny day? And what happens at night when your solar system is not generating power in real time? At this point, we don’t store solar-generated energy for later use, so it flows back into the grid. But don’t worry, you still benefit through a system called “net metering.”
A grid-tied PV system has no batteries. So when the sun is shining and the solar user doesn’t use up all the energy generated in a day, excess power is sent out of the house to neighbors’ houses. This is called “back feeding” the grid. At night, the grid will provide energy for lights and other appliances as usual, so solar users are covered in exchange for the excess energy they shared with the grid during the day. A net meter records the energy sent compared to the energy received from the grid.
There are now over 20,000 megawatts of cumulative solar electric capacity operating in the United States. Around 650,000 homes and businesses have now gone solar. In 2014, a new solar project was installed every two-and-a-half minutes. The growth of solar capacity is projected to double in the next two years. Solar energy is truly the wave of the future, and we at SunPower believe the sun belongs to everyone. We’re committed to unlocking its vast energy so all of us can enjoy the freedom it provides. It all starts with a single solar cell.