Solar 101: Home does home solar power work?

Solar has grown an average of 50% every year for the past decade. There’s now more than two million solar installations in the United States. It’s no wonder that more and more people are thinking of adding solar power to their homes.

Solar power isn’t new. Edmond Becquerel first demonstrated the photovoltaic effect way back in 1839. Still, how it actually works in your home to turn sunlight into electricity is a bit of a mystery to many people.

The Solar Nerd has a complete guide to solar power for your home, but if you’re looking for a quick overview, this article will explain the basic parts that make up a photovoltaic (PV) system for your house.

Step-by-step overview of how home solar works:

1. Solar panels, also known as solar modules, collect sunlight and turn that solar energy into electricity via the photovoltaic effect.
2. Your panels can either be mounted on your roof or mounted in your yard on a grount mount. Roof mounted installations use aluminum rails and are the most common and least costly, but ground mounting can be a better option for some situations.
3. Your panels are connected by wires to one or more inverters. Inverters are electronic devices that turn the direct current (DC) power that your solar panels generate into alternating current (AC) that your house can use.
4. From your inverters, wires carry the AC current to your home’s electrical panel. Your existing panel may need to be upgraded to handle this load, and it’s also possible that your installer may identify wiring issues that need to be addressed first.
5. The electric panel distributes this solar electricity for use in your home.
6. Your electric panel also maintains a connection to the electric grid. When your house doesn’t use all of the solar electricity that you generate, the power flows from the inverter into the grid. When your panels don’t generate enough electricity (such as at night), your home is supplied by grid electricity.
7. There will be one or more utility meters that track the amount of electricity that your solar panels generate, the amount of power that you draw from the grid, and the amount that you send back into the grid.
8. Your system will include a monitoring system that lets you keep track of how much power your system generates. This will almost always include a website or a smartphone app that will let you conveniently get real time information.
9. One last small but important detail is a disconnect switch between the solar panels and the electrical panel. This is used to turn off electricity from the system for maintenance or shut down the system in emergencies (such as a fire).

What are the components of a home solar photovoltaic system?

Solar module or solar photovolatic panel

Solar panels are semiconductor devices that turn sunlight into electricity. The typical size of an individual panel for residential use is 65 inches by 39 inches. Each one may generate anywhere from 250 Watts to more than 350 Watts, depending on the efficiency, which can range from around 14% to more than 22%. Higher efficiency generally means higher cost, but it also means that you need fewer high efficiency panels to reach your desired total system output.

Mounting system

In residential systems, panels can be mounted on your roof, which is the most common application, or if you have the space for it, they can also be ground mounted.

Roof mounted systems come in a variety of types, but in all cases they are aluminum components that are bolted to your roof, onto which the panels are then secured. Flashing and sealants are used to maintain the waterproof integrity of your building.

If installed on the ground, the panels will be racked onto either aluminum scaffolding or a pole mounted rack. For an additional cost, a ground mount can include a tracking system that will automatically rotate the panels to follow the sun throughout the day, which will increase the total power generation.

If your roof ever needs servicing, the panels can be removed, but this does come with labor cost.

Photo courtesy Quick Mount PV

Inverters

Photovoltaic cells produce electricity as direct current, but your house and the power grid use alternating current. It’s the role of inverters to do this conversion. Here are the types that are available:

• A string or central inverter is connected to multiple panels in your system and handles their power output. If you have a larger system, you may require more than one inverter. The advantage of this inverter type is lower cost, but the downside with this type of system is if one panel is shaded (say, by trees or leaf fall) the power output of the entire “string” of panels will be curtailed. Whether or not this potential loss of efficiency in your system is worth upgrading to microinverters or optimizers is something you should consult with your installer about. But if you don’t have trees or snow to worry about, then choosing this type of inverter may be a good way to save money.
• Microinverters are another type. With microinverters, there is one inverter per solar module, which is usually mounted to the back of the panel itself. With this type of system, your power output is maximized because the loss of power at one panel doesn’t affect the output of the rest of the system. This will also let you monitor each panel individually and know if there’s a fault in any one. Microinverters are a newer technology, and perhaps because of this, early microinverter systems had a reputation for poor reliability. However, the technology has since matured along with the support provided by manufacturers, who now often provide warranties of 20 or even 25 years. Naturally, because of the higher performance of microinverters, you should expect higher cost as well.
• Power optimizers are something of a hybrid between these two technologies. A power optimizer is a device that, like a microinverter, is paired with a single solar panel, and works with the rest of the system to ensure that a power drop at a single panel does not affect the rest of the system. Power optimizers are typically DC-to-DC devices, and therefore still require a central inverter to work. This gets you benefits to similar to microinverters, but at a cost that is higher than a standard inverter.

Photo courtesy SolarEdge

You can read our guide to inverters to learn more.

Power meter

The vast majority of home solar installations are grid-tied, which means your home will send excess power into the grid, and take power from the grid when your panels are not producing enough. Your utility will install a power meter that measures the amount of power that you draw from the grid, and the amount of excess solar power that your panels put back into the grid.

Example of a solar PV meter.

Monitoring

Any home PV system will provide a way for you to monitor in real-time the amount of energy that your system is producing, usually with a smartphone app or a web interface. Typical features that you’ll find are the ability to view a graph of power for the day and for selected time periods as far back as when your system was switched on.

SolarEdge is one of the major inverter vendors, and they provide a public demo account of their monitoring application that you can try.

Disconnect switch

The disconnect switch is wired between the solar panels and your electrical panel. When you pull the switch, the flow of electricity from your panels into your house and the grid is switched off. This is used when your system is undergoing maintenance, or in an emergency, such as a fire.

You should also throw the switch off during a blackout if you don’t have a system that includes a battery. A properly functioning inverter will do this automatically, but as an extra measure it’s a good idea to make sure that your panels aren’t sending electricity into the grid during a blackout. This is because unexpected electricity flowing into the grid can hurt utility workers who are performing repairs.

Example of a solar PV disconnect switch.

(Optional) Batteries

Due to the wide deployment of lithium-based batteries in everything from smartphones to electric vehicles, economies of scale have allowed the cost of batteries to steadily decline. Because of this, storage batteries paired with home solar is becoming more common. With a battery system, your excess solar power is used to charge the batteries. If the batteries are full, the excess will then go into the grid. At night or at times of high power usage, your home will draw power from the batteries and only use grid power when your batteries are depleted.

To be clear, batteries are not a requirement for home solar. The main application for batteries is to keep your home powered even when grid power goes down. In a grid-tied system, your inverters must synchronize the frequency of their alternating current output to match that of the grid. When the grid goes down, such as during a blackout, the inverters in a system without batteries will automatically shut down. This is also done because you are prohibited from sending power into the grid during a power failure, because it would energize power lines and potentially harm utility workers who are doing repair work.

However, if you have batteries, your house can continue to stay powered even during a blackout.

Another battery application is to have steady electricity in a home that does not have access to grid power, such as with a remote vacation home. In such a case, solar paired with batteries would allow you to run your home with solar power for most of the time, and fall back to a natural gas or diesel generator only in times of high load or during longer cloudy spells.

In spite of the benefits, the cost of a battery system is still pretty high. For example, the Tesla Powerwall is a well-known brand. Their cost estimate for a 30 kWh system that includes two Powerwalls, hardware, and installation is $14,500. Unless you are in a situation with unreliable grid power, this often doesn’t make financial sense for the typical home.

Where to learn more about going solar

This article provides a quick overview into how solar photovoltaic systems work, but if you want to learn everything you need to make a smart decision about whether to go solar, check out our complete guide to home solar. It includes articles about the technical aspects of solar, information about how to make a smart financial decision for you, and important tips on how to find the best solar installer and compare solar quotes.