Rooftop Solar PV Systems: Definition and Different Types

A rooftop solar photovoltaic (PV) system uses solar panels mounted on the roof of a building to convert sunlight into electricity. Rooftop solar systems rely on the photovoltaic effect, where cells generate electricity in response to sunlight. A rooftop solar system is an array of solar panels installed on a roof, each containing several solar cells that absorb sunlight and create an electric field across each panel.

Roof-mounted solar systems are more discreet than solar setups installed at ground-level because they are hidden from view, and they save space on the property. Structures with smaller roofs, like sheds, cabins, and RVs, are all good candidates for rooftop solar panels.

Rooftop solar PV systems are able to power a range of appliances, from washing machines to computers. In theory, any electrical appliance is able to run on solar power. In reality, some appliances are 'heavy draw', meaning they use too much energy for it to be realistic or sustainable for solar panels to power them outside of peak sun hours.

Solar panels are able to power large household appliances like washing machines, dryer machines, refrigerators, and dishwashers, as well as smaller devices like cable boxes, DVD players, computers, and televisions. Additionally, solar systems are able to power heating, ventilation, and air conditioning (HVAC) systems that are responsible for regulating the temperature in a building.

The electricity generated by the solar panels has to be converted from direct current (DC) into alternating current (AC) by the solar inverter before it is sent to the electrical panel of the building and used to power appliances.

The three main types of rooftop solar PV systems are off-grid rooftop solar systems, on-grid rooftop solar systems and hybrid solar systems (grid-tied with battery). Off-grid rooftop solar systems include a solar battery to store excess energy, so owners have backup power during periods of low sun. On-grid rooftop solar systems rely on the electric grid, so the building has no alternative source of power when the supply is disrupted due to bad weather conditions, damaged equipment, or scheduled grid maintenance.

Hybrid solar systems represent the best of both worlds because they include a battery to store excess power for backup and are connected to the electric grid. Owners of hybrid systems are able to sell back electricity they generate that they don't need.

Rooftop solar systems entitle owners to many financial benefits, like saving money on electricity bills, increasing the value of the property, and receiving tax credits. Rooftop solar systems enable property owners to be partially or fully ‘energy independent,’ switch to renewable energy, and reduce carbon emissions. Many property owners are opting for rooftop solar systems, but that doesn't cancel out the disadvantages that they are costly to install, not feasible for every roof, hard to remove, prone to leaks and predisposed to 'hot spots'.

What Is a Rooftop Solar PV System?

Rooftop solar photovoltaic (PV) systems convert sunlight into electricity through solar panels mounted on the roof of a building, secured using heavy concrete blocks serving as anchors or using racking bolted to the rafters through the roof. Rooftop solar systems are less conspicuous than solar systems mounted on poles or racks at ground level because they are hidden from view, but they also save space by taking up less room on the property.

Rooftop PV systems are used on residential and commercial buildings, but traditional brick-and-mortar buildings are not the only candidates for rooftop solar installations. Structures whose roofs have smaller surface areas, like sheds, cabins and RVs, are able to support rooftop solar systems fitted to their size.

Rooftop solar systems are suitable for both off-grid and on-grid properties. Off-grid rooftop solar systems include solar batteries to store excess energy generated by the panels because the building doesn’t have access to the electric grid for power, whereas owners of on-grid rooftop solar systems send excess energy to the electric grid for discounts on their electricity bills.

What can Rooftop Solar PV Systems power?

Theoretically, any electrical appliance is able to run on solar power. In reality, some appliances use an amount of energy that is not realistic or sustainable for solar power to provide. It is important to pay attention to the peak sun hours in the area where the solar system is located, how much energy the solar system needs to produce to meet the power requirements of the property, and whether the backup energy from the system is finite (solar batteries) or infinite (electric grid).

Solar panels on roofs can power large household appliances like washing machines, dryer machines, refrigerators, and dishwashers. However, some household appliances like electric ovens and water heaters are ‘heavy draw,’ meaning they require a lot of power to run, so owners are advised to limit their usage of them to peak sun hours. This approach avoids using energy from the solar battery or having to draw energy from the electric grid. Rooftop solar systems are able to power cable boxes, DVD players, computers, and televisions.

Rooftop solar systems are able to power heating, ventilation, and air conditioning (HVAC) systems. The HVAC system regulates the temperature of a building by moving heated and cooled air through it, from homes to offices to stadiums. Switching to solar-powered HVAC protects the property from disruptions in the electric grid, reduces its carbon emissions, and decreases the cost of electricity bills. Solar-powered HVAC systems require a large solar installation and a warm local climate.

How does a Rooftop Solar PV System work?

Rooftop solar systems work by harnessing the photovoltaic effect. This phenomenon occurs when sunlight hits the multiple cells within solar panels, generating an electric current. By placing panels on a rooftop, solar panels are optimally exposed to sunlight and produce enough electricity to power homes and buildings.

First, a group of solar panels is installed on a roof, typically at an angle to absorb maximum sunlight. When the sun shines on the solar panels, the semiconductors within the cells absorb the photons of sunlight and produce an electric current. This is a natural phenomenon known as the photovoltaic effect. Next, the resultant flow of electric current is sent to a solar inverter, which converts it from direct current (DC) to alternating current (AC). Lastly, once the electricity has been transformed into alternating current (AC), it is sent to the building’s electrical distribution panel for common use.

What are the different types of Rooftop Solar PV Systems?

The three main types of rooftop solar systems are listed below.

1. Off-Grid Rooftop Solar System

Off-grid rooftop solar systems are installed on the roof of a building, shed, or even campervan to generate power without relying on the electric grid. The difference between off-grid solar systems and on-grid solar systems is the inclusion of a solar battery. Off-grid rooftop solar systems include a solar battery to store excess energy, as it is the owner’s only backup power for periods of low sun during the night, in gloomy weather, and throughout the winter months.

Off-grid rooftop solar systems are self-contained, meaning they aren’t connected to the national electric grid or a utility company overseeing their usage. Owners of on-grid solar systems are able to produce their own energy and supplement their supply from the electric grid, but they have no way to store it. Owners of an off-grid rooftop solar system to reduce their carbon emissions by switching to renewable energy, become self-sufficient through ‘energy independence’, and avoid increasingly costly electricity bills.

Rooftop solar installations come with their own set of problems that shorten the lifespan of the system, like the fact that the holes made in the roof to attach the racking are prone to leaks, and the limited airflow between the solar panels and the surface of the roof increases the likelihood of ‘hot spots’ forming. Additionally, solar batteries degrade faster than the rest of the components, so they have to be maintained more frequently and replaced sooner.

Off-grid rooftop solar systems have a higher upfront cost because of the additional equipment that they require, which increases as the energy needs of the property increase, meaning the amount of time it takes to recoup the cost of installing the system (solar payback period) is longer. Off-grid rooftop solar systems are a necessity for properties that are too remote for power lines to reach, but owners of off-grid solar systems who actively made the choice to transition are proud to be self-sufficient. Owners of on-grid solar systems are reluctant to make the leap to being off-grid due to concerns about the solar battery being able to power their property on its own during the winter months.

2. On-Grid Rooftop Solar System

On-grid rooftop solar systems are tied to the electric grid, meaning the property owner is able to rely on energy from a utility company during periods of low production and send excess energy back to the electric grid for financial benefits (net metering). The electric grid serves as the ‘battery’ of on-grid solar systems because they send excess energy they generate back to it, and it provides backup energy when they are not producing enough.

On-grid rooftop solar systems are praised for a number of reasons. Firstly, they save space on the property by installing it on the roof rather than the ground. Second, they allow homeowners the option to sell energy back to the electric grid for a discount on their electricity bill. Thirdly, they provide power for appliances that are too expensive to run on solar energy. Additionally, having an on-grid rooftop solar system means system owners are able to power their property when their solar panels are not producing enough energy. This sometimes occurs in solar panels due to technical malfunctions or periods of low sun.

The average price of an on-grid solar system is between $14,600 and $21,700 for a 6kW system and between $29,200 and $43,500 for a 12kW system. The exact price typically varies depending on the type of solar panels used, your location, the size of the solar system, the cost of the installation, and whether you opt for battery storage. On-grid solar systems entitle owners to claim federal tax credits of up to 30% off the cost of the solar system). Sometimes, property tax is waived if installing solar panels increases your home’s value. Note that contractors charge more to install solar panels on steep roofs because it is harder to do.

It is important to regularly inspect the racking system to extend the lifespan of a rooftop solar installation. Solar panels not securely mounted to the roof are susceptible to becoming loose, moving around, and falling off entirely. Although debris naturally falls off solar panels installed on sloped roofs or is washed off their surface by rainfall, it is crucial to clean rooftop solar panels at least once a year to ensure their full surface absorbs sunlight.

3. Grid Tied With Battery – Hybrid

Grid-tied solar systems include a battery to store backup power; meaning owners are able to fall back on solar energy during national power outages, periods of low sun, and peak demand hours when electricity is the most expensive. Hybrid solar systems have a battery for energy storage and are connected to the electric grid, meaning they are incredibly efficient because the owner is able to rely on the electric grid for power during periods of low sun and store excess energy generated by the solar panels.

Maintaining a hybrid solar system requires cleaning of the solar panels once to twice a year, checking of the batteries to ensure they are storing energy efficiently and keeping a watchful eye on the hybrid inverter (as it is responsible for switching between the solar batteries and the electric grid).

As of February 2024, the average cost of a hybrid solar system is $30,000. That said, the cost of hybrid solar systems varies depending on the specific components, the number of batteries, and the installation cost. Hybrid solar systems, which are grid-tied with batteries, tend to be more expensive than grid-tied solar systems. This is due in equal part to the added cost of solar batteries and the added cost of a hybrid inverter. Owners of hybrid solar systems cite net metering for money off their electricity while storing excess energy to use during peak hours as a winning combination.

Hybrid solar systems allow owners to enjoy the benefits of on-grid solar systems and off-grid solar systems at the same time. Owners of hybrid solar systems are able to fall back on the electric grid for power when there is less sunlight, and they are also able to sell energy back to a utility company in exchange for discounts on their electricity bills. Hybrid solar systems are able to power a property using solar energy when the electric grid is down due to bad weather, damaged equipment, or grid maintenance.

What are the advantages of Rooftop Solar PV Systems?

Rooftop solar systems are a great option for property owners who want to switch to renewable energy, save money on electricity bills and increase their energy independence - while not sacrificing outdoor space.

Below are the 6 main advantages of rooftop solar systems.

• Save money on electricity bills: Rooftop solar systems lower the cost of monthly electricity bills, by enabling owners to generate energy without having to rely on the electric grid, and by giving them the option to sell excess energy back to their utility company.
• Increase home value: Installing a rooftop solar system increases the value of a property, meaning the owner is able to put it on the market at a higher price when they choose to sell it. Additionally, solar-powered buildings are becoming more and more desirable, as buyers are starting to prioritize sustainability and renewable energy in real estate.
• Enable energy independence: ‘Energy independence’ refers to the extent to a property’s energy needs are met by an energy source outside of the electric grid. Rooftop solar systems allow property owners to (partially or fully) produce their own electricity, increasing their energy independence, enabling them to be self-sufficient and freeing them from reliance on the electric grid.
• Require minimal maintenance: Solar panels, regardless of whether they are installed on a flat roof or a sloped roof, need to be cleaned once every 6 months. Rooftop solar systems require minimal maintenance because most of the debris which falls on them either slides off or washes off with rainfall.
• Decrease carbon emissions: Rooftop solar systems provide clean, emissions-free, and renewable energy. The electricity provided by utility companies is generated by burning fossil fuels like oil and coal, which release large amounts of carbon dioxide in the process.
• Entitle owners to financial incentives: The Solar Investment Tax Credit (ITC) entitles owners of solar systems across the country to claim 30% of the total cost of their residential solar system, in the form of a dollar-for-dollar reduction, off their taxes the following year. Each state offers different financial incentives to encourage residents to switch to solar energy. Refer to the online Database of State Incentives for Renewables & Efficiency (DSIRE) to check what you are eligible for, or use SolarCompares solar incentive finder to get an idea of exactly how much your home is eligible for in Federal and State incentives.

What are the disadvantages of Rooftop Solar PV Systems?

Rooftop solar systems are versatile, space-saving, and discreet, but they are not a perfect solution.

Below are the 6 main disadvantages of rooftop solar systems.

• Expensive to install: Installing a rooftop solar system benefits property owners in the long run, but it has a high up-front cost. Users have to accept that they will only recoup the cost of the solar system 6 to 10 years after buying it. The period between installing the solar system and recouping its cost is known as the solar payback period.
• Unsuitable for every roof: Not every building can support a rooftop solar system. Buildings with overly sloped roofs (more than 40 degrees), roofs with only space on the north side, and roofs made from weak materials (like wood and slate) are not suitable for a rooftop solar system.
• Complicated to remove: Rooftop solar systems are time-consuming and expensive to uninstall, which makes it complicated (and generally not worthwhile) to relocate them. Rooftop solar systems are an investment in the structure or property they’re added to, moving them often causes damage to the roof and many solar technicians will refuse to do so for fear of breaching the warranty.
• Dependent on sunlight: The efficiency of a rooftop solar system depends entirely on the amount of sunlight it receives. Rooftop solar systems generate significantly less energy during periods of low sun - during the night, in gloomy weather, and throughout winter months - so they are unable to guarantee a steady supply of power.
• Prone to leaking: Some rooftop solar systems require the installer to drill a hole in the surface of the roof to attach the racking system to the rafters. The holes left in the roof by solar system installation are susceptible to leaks, even when they are reinforced with metal.
• Susceptible to developing ‘hot spots’. The space between the solar panel and the surface of the roof is much smaller in rooftop solar installations than in solar setups mounted at ground level (on poles or racks), which limits the airflow. Panels in rooftop solar systems are prone to developing 'hot spots' because of the limited airflow to cool down their surface.

How to Install a Rooftop Solar PV System?

Below are the 12 steps to installing a rooftop solar system. The steps vary slightly depending on the material used and the slope of the roof.

1. Check that the roof is able to support the solar system: The most important thing to do for a successful installation is to check beforehand that the building is able to support the weight of the solar system. Check that the roof is able to support the added weight of the solar panels and racking system before proceeding with the installation.
2. Take necessary precautions: There are three things to check before starting to install a rooftop solar system: the manufacturer's guidelines on the racking, the local regulations for solar systems, and the necessary safety precautions for the specific type of roof. Familiarize yourself with the manufacturer guidelines so that the racking system is installed properly, ensuring that the warranty is not voided and safe. Additionally, tall buildings with high roofs require workers to take extra safety precautions for fall protection, like safety lines (to attach harnesses) and guardrails.
3. Gather the materials: Gather the materials from the solar panel mounting system, making sure you also have the tools on hand to install it. These tools include a drill, a drill bit, a pencil, a chalk line, a tape measure, and a ladder on hand to install the rack. Solar panel mounting systems typically come with brackets, clamps, strut channels, and screws.
4. Identify the location of the rafters: Consult the blueprint of the building or use a stud finder to identify the location of the rafters on the roof. The mounts, also known as L-feet, standoffs, or stanchions, are drilled into the rafters through the roof to attach the racking system.
5. Plan the layout of the mounts: Plan the layout of the mounts, positioning them so the bolts bear into the rafters when they penetrate the roof. Ensure that the vertical distance between the mounts for the top rail and the mounts for the bottom rail is equal to the distance between the mounting holes on the back of the solar panel frame. Ensure that the horizontal distance between each mount is at least four feet.
6. Drill holes into the rafters: Carefully drill the holes for the mounts into the center of the rafters, taking care not to split or damage them. Use a chalk line to mark a straight line upwards from each of the mounts for the bottom rail to check that the hole for the top rail is properly positioned.
7. Install the roof flashing: Adding roof flashing is an important step for installing solar racking systems on shingle roofs, as it directs water away from holes and prevents leaks. Apply flashing to the holes made in the roof for the mounts by peeling up the shingle and sliding it underneath so that the premade holes in the material line up with the holes in the roof.
8. Install the mounts: Place the mounts over the holes drilled in the roof and secure them to the rafters using steel bolts. Use a torque wrench to tighten the bolts instead of a power tool, avoiding overtightening them and bending the flashing.
9. Secure the rails to the mounts: Cut the rails (also known as strut channels) to length if necessary, so they are able to accommodate all of the solar panels in the array. Secure the rails to the mounts using the screws which come with the racking system. Ensure that the rails are parallel by measuring the diagonal distance between the left corner of the top rail and the right corner of the bottom rail and vice versa. Use a level to check that the rails are perfectly horizontal on the roof.
10. Seal the holes: Seal the hole with polymer, silicone and butyl, as these are strong enough to prevent leaks through the lifespan of the array. Sealing the holes drilled in the roof is a crucial part of installing solar systems, because failing to do so makes the building vulnerable to leaks, and compromises the ‘thermal envelope’ which keeps heat inside.
11. Slide the solar panels onto the rails: Attach the solar panels to the rails, adding a clamp (or retaining clip) to each of the rails after every panel, as well as at the start and the end of the rail.
12. Connect the solar panels to the electrical system: Shut off the power supply to the building to ensure safety before doing electrical work on a rooftop solar system. Take the wires from each solar panel and connect them to the solar inverter, which converts the electricity generated by the array from DC into AC, and then connect the solar inverter to the electrical panel.

What are the things to consider before installing Rooftop Solar PV Systems?

The 5 main things to consider before installing a rooftop solar PV system are given below.

• Impact of solar energy on the environment: Solar energy has a positive impact on the environment because it is a renewable source of energy, reducing the reliance on fossil fuels and decreasing greenhouse gas emissions, but solar panels contain hazardous materials like lead and cadmium which pollute soil when they are not correctly disposed of.
• Impact of snow and rain on solar panels: Solar panels are built to withstand harsh weather like snow and rain, but they are unable to produce energy when snow builds up on their surface. Solar panels stop generating electricity when snow accumulates on their surface, but they generally slide or melt off after a short period of time.
• Feasibility of installing solar panels without a contractor: It is not feasible to install solar panels without a contractor on some types of roofs, like slate roofs or extremely steep roofs, because it is technically challenging. Solar installers are not cheap because the cost covers design services, labor, and maintenance, so it is important to think about the added expense of hiring a technician before installing a rooftop solar system.
• Maintenance of rooftop solar systems: Rooftop solar systems require minimal maintenance, cleaning the surface twice a year to remove any dirt or debris, but it is still important to consider upkeep when installing a rooftop solar system. Most of the grime which accumulates on solar panels is washed off by rain, but some solar system owners still have to hire a professional to clean their panels..
• Return on investment of solar systems: Return on investment (ROI), or the solar payback period, is an important consideration before installing a solar system because it is considerably longer for off-grid solar systems than on-grid solar systems. Off-grid solar systems are more expensive, due to the added component of the solar battery, so it takes longer for the owner to recoup the initial cost.

Do Rooftop Solar PV Systems have an impact on the environment?

Yes, rooftop solar systems have a positive impact on the environment because they reduce the number of consumers who rely on the electric grid, which reduces the amount of fossil fuels burned by utility companies to generate electricity. Rooftop solar systems are good for the environment because they allow property owners to reduce their carbon emissions by switching to renewable energy.

Are snow and rain a potential issue for Rooftop Solar PV Systems?

No, snow and rain are not typically an issue for rooftop solar systems because they are designed to withstand water and weather conditions. High-quality and properly installed solar panels are resistant to severe weather conditions like rain, snow, and hail. The rain actually provides the benefit of cleaning solar panels.

Do I need a contractor to install Rooftop Solar PV Systems?

No, you don’t necessarily need a contractor to install a rooftop solar system, as it’s possible to do it yourself with the right equipment and strong knowledge of electrical wiring. Hiring a solar panel installer is always the best bet, to ensure the rooftop solar system is efficient, reliable and follows local (building, electrical, safety) regulations.

Is Rooftop Solar PV Systems high maintenance?

No, rooftop solar systems are not high maintenance because they only need to be cleaned twice a year. Most debris on roof-mounted solar panels slides off naturally or is washed off by rainfall.

Is it worth it to install Rooftop Solar PV Systems?

Yes, installing a rooftop solar system is a worthwhile investment because the lifespan of solar panels is longer than the amount of time it takes for the property owner to recoup their investment. Usually, it takes 6-10 years to pay off a solar system (called the “payback period”), whereas solar panels last up to and beyond 25 years. Once the panels are paid off, the property owner can look forward to many years of reduced electricity bills.