A rooftop solar system looks simple from the street, but it is really a small power plant made of several connected parts. Understanding those parts, how they connect to your home and the grid, and what changes the amount of electricity they produce can help you make a more confident decision.

Short version: Panels make DC electricity, inverters turn it into AC for your home, and permits plus utility approval are required before the system can operate. Sunlight, orientation, shade, and temperature all affect output.

The Main Parts of a Rooftop Solar System

According to the U.S. Energy Information Administration, a photovoltaic cell, commonly called a solar cell, is a nonmechanical device that converts sunlight directly into electricity. Sunlight is made of photons, or particles of solar energy. When a cell absorbs enough sunlight, electrons are dislodged from the material’s atoms and create an electrical imbalance that produces voltage.

One cell only produces a small amount of power, so cells are connected inside a weather-tight panel, sometimes called a module. The EIA explains that panels can be connected in groups to form an array. The number of panels in an array determines the amount of electricity the array can generate.

Panels Make Direct Current

The EIA states that PV cells generate direct current, or DC, electricity. DC electricity can charge batteries and power some devices, but nearly all electricity supplied through transmission and distribution systems is alternating current, or AC. That is why a rooftop system needs more than panels.

Inverters Convert DC to AC

The U.S. Department of Energy says inverters convert the DC electricity generated by solar modules into AC electricity, which is used for most appliances in homes. A PV system either has one central inverter that converts electricity from all the modules, or microinverters attached to each individual module.

The DOE notes that a single inverter is generally less expensive and can be more easily cooled and serviced. A microinverter allows each panel to operate independently, which is useful if some modules might be shaded. The DOE also says inverters are expected to need replacement at least once in the 25-year lifetime of a PV array.

Mounting, Wiring, and Balance of System

The Hong Kong Electrical and Mechanical Services Department describes the balance of system, or BOS, as the components required to make up a photovoltaic system apart from the photovoltaic array. The BOS includes combiner boxes, charge controllers and storage batteries for standalone systems, inverters, mounting structures, wiring, switchgear and fuses, surge arrestors, and earth-fault protection devices.

The Pennsylvania Public Utility Commission fact sheet explains that a residential solar system consists of solar cells connected to form panels, which are connected to form arrays. Other BOS equipment may include ground-fault protection, overcurrent protection, surge protection, and disconnect devices. The fact sheet adds that batteries are optional and can store excess power for backup during outages.

How a Rooftop System Connects to Your Home and the Grid

The U.S. Department of Energy explains that permitting and inspection are required before a solar array is allowed to produce electricity on the grid. Generally, local governments require solar installers to obtain a permit for rooftop panels before they can be installed. After installation, a professional from the local government inspects the new array to ensure safety codes have been followed. The utility then connects the system to the grid, and it can begin generating power.

The DOE says local governments have different rules for permitting and inspection, and details and fees may vary across jurisdictions. The permitting and inspection process helps ensure that a building is safe for solar panels and that the system is properly installed. Administrative errors and backlogs can cause permitting delays.

Anything connected to home wiring or the grid is done by licensed professionals with permits and utility approval. The DOE recommends working with a qualified professional who holds a certification and works with high-quality solar panels. The industry-standard certification is awarded through the North American Board of Certified Energy Practitioners, or NABCEP.

What Affects Rooftop Solar Output

Several factors change how much electricity a rooftop array produces. The EIA says solar energy is a variable and intermittent energy source, and the availability and intensity of solar radiation varies by time of day and location.

Sunlight and Location

According to the EIA, the intensity of solar radiation at any location is greatest when the sun is at its highest apparent position in the sky, at solar noon, on clear, cloudless days. Latitude, climate, and weather patterns are major factors that affect insolation, which is the amount of solar radiation received on a given surface area during a specific amount of time. Locations in lower latitudes and in arid climates generally receive higher amounts of insolation than other locations.

Orientation and Shading

The DOE says PV arrays must be mounted on a stable, durable structure that can support the array and withstand wind, rain, hail, and corrosion over decades. To obtain the highest annual energy output, modules in the northern hemisphere are pointed due south and inclined at an angle equal to the local latitude.

The DOE homeowner guide adds that solar panels perform well on south-facing roofs with a slope between 15 and 40 degrees, though other roofs may be suitable too. The EIA notes that buildings, trees, and mountains may shade a location during different times of the day in different months of the year. If trees near your home create excessive shade on your roof, rooftop panels may not be the most ideal option.

Temperature and Weather

The EIA explains that clouds, dust, volcanic ash, and pollution in the atmosphere affect insolation levels at the surface. The Pennsylvania Public Utility Commission fact sheet says that on cloudy days or under shade, cells produce less electricity than if the cells are exposed to full sun. Electricity is not produced when there is no sunlight exposure, such as at nighttime.

Estimating Production for Your Roof

The DOE homeowner guide says the National Renewable Energy Laboratory developed a tool called PVWatts for estimating energy production. The guide describes PVWatts as a tool that estimates the energy production and cost of energy of grid-connected PV energy systems for any address in the world. It allows homeowners, small building owners, installers, and manufacturers to develop estimates of the performance of potential PV installations.

PVWatts is run by the National Laboratory of the Rockies, formerly known as NREL. The DOE recommends using such tools for getting started, but also says to work with a solar installer for a custom estimate of how much power your solar energy system is likely to generate.

Roof Age and Suitability

The DOE homeowner guide says solar panels are built to work in all climates, but in some cases rooftops may not be suitable for solar systems due to age or tree cover. The size, shape, and slope of your roof are also important factors to consider. You should consider the age of your roof and how long until it will need replacement.

If a solar professional determines that your roof is not suitable for solar, or you do not own your home, you can still benefit from solar energy through community solar. Community solar allows multiple people to benefit from a single, shared solar array that can be installed on- or off-site.

Parts, Jobs, and Homeowner Questions

Part Job Homeowner question
PV cells and panels Convert sunlight into DC electricity How much roof area with good sun exposure do I have?
Inverter or microinverters Convert DC to AC for home use Will shading affect some panels more than others?
Mounting and racking Hold the array at a fixed angle and withstand weather Is my roof structure stable and in good condition?
Wiring and protection devices Connect components and protect the system Will the installer handle permits and inspections?
Optional battery storage Stores energy for later use or backup Do I want backup power during outages?

Frequently asked questions

Do I need a battery with rooftop solar?

No. The Pennsylvania Public Utility Commission fact sheet describes batteries as optional. A grid-tied rooftop system can operate without batteries, while batteries can be configured to meet needs such as backup during power outages. The DOE says storage allows you to save energy and use it later, such as when the power goes out.

Can I install rooftop solar myself?

The DOE recommends installing solar through a qualified professional who holds a certification and works with high-quality solar panels. Permitting, inspection, and utility connection are required before a solar array is allowed to produce electricity on the grid, and local governments generally require solar installers to obtain a permit before panels can be installed.

Why does my roof direction matter?

The DOE says modules in the northern hemisphere are pointed due south and inclined at an angle equal to the local latitude to obtain the highest annual energy output. The DOE homeowner guide adds that panels typically perform well on south-facing roofs with a slope between 15 and 40 degrees, though other roofs may be suitable too.

To compare rooftop solar with other ways to connect a home system, see types of home solar systems. For a broader look at equipment and planning, start with the home solar systems section or the rooftop solar category page.

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