Rooftop solar power
A rooftop solar power system, or rooftop PV system, is a photovoltaic system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. The various components of such a system include photovoltaic modules, mounting systems, cables, solar inverters battery storage systems, charge controllers, monitoring systems, racking and mounting systems, energy management systems, net metering systems, disconnect switches, grounding equipment, protective devices, combiner boxes, weatherproof enclosures and other electrical accessories.
Rooftop mounted systems are small compared to utility-scale solar ground-mounted photovoltaic power stations with capacities in the megawatt range, hence being a form of distributed generation. A comprehensive life cycle analysis study showed that rooftop solar is better for the environment than utility-scale solar. Most rooftop PV stations are Grid-connected photovoltaic power systems. Rooftop PV systems on residential buildings typically feature a capacity of about 5–20 kilowatts, while those mounted on commercial buildings often reach 100 kilowatts to 1 megawatt. Very large roofs can house industrial scale PV systems in the range of 1–10 MW.
As of 2022, around 25 million households rely on rooftop solar power worldwide. Australia has by far the most rooftop solar capacity per capita.
Installation
The urban environment provides a large amount of empty rooftop spaces and can inherently avoid the potential land use and environmental concerns. Estimating rooftop solar insolation is a multi-faceted process, as insolation values in rooftops are impacted by the following:- Time of the year
- Latitude
- Weather conditions
- Roof slope
- Roof aspect
- Shading from adjacent buildings and vegetation
Components of a rooftop solar array
The following section contains the most commonly utilized components of a rooftop solar array. Though designs may vary with roof type, roof angle, and shading concerns, most arrays consist of some variation of the following components- Solar panels produce carbon free electricity when irradiated with sunlight. Often made of silicon, solar panels are made of smaller solar cells which typically have six cells per panel. Multiple solar panels strung together make up a solar array. Solar panels are generally protected by tempered glass and secured with an aluminum frame. The front of a solar panel is very durable whereas the back of a panel is generally more vulnerable.
- Mounting clamps generally consist of aluminum brackets and stainless steel bolts that secure solar panels to one another on the roof and onto the rails. Clamps often vary in design in order to account for various roof and rail configurations.
- Racking or rails are made of metal and often lie in a parallel configuration on the roof for the panels to lie on. It is important that the rails are level enough for the panels to be evenly mounted.
- Mounts attach the rails and the entire array to the surface of the roof. These mounts are often L brackets that are bolted through flashing and into the rafters of the roof. Mounts vary in design due to the wide range of roof configurations and materials.
- Flashings are a durable metal plate that provide a water resistant seal between the mounts and roof surface. Oftentimes, caulk is used to seal the flashing to the roof and it resembles a metal roof shingle.
- DC/AC wiring for inverters connect wires between panels and into a micro inverter or string inverter. No cables should touch the roof surface or hang from the array to avoid weathering and the deterioration of cables.
- Micro inverters are mounted to the bottom of the panel and convert DC power from the panels into AC power that can be sent into the grid. Micro inverters allow for the optimization of each panel when shading occurs and can provide specific data from individual panels.
Finances
PV system prices (2022)
| Country | Cost |
| Australia | 1.0 |
| China | 0.8 |
| France | 1.1 |
| Germany | 1.2 |
| India | 1.0 |
| Italy | 1.3 |
| Japan | 1.2 |
| Pakistan | 0.6 |
| United Kingdom | 1.2 |
| United States | 1.1 |
| Country | Cost |
| Australia | 0.85 |
| China | 0.64 |
| France | 0.9 |
| Germany | 0.9 |
| India | 0.75 |
| Italy | 0.9 |
| Japan | 0.95 |
| United Kingdom | 1.0 |
| United States | 1.0 |
Incentives
United States
Solar incentives by state in the USA can help offset the initial cost of installation and make solar power more affordable. In the United States, each state has its own set of incentives and rebates for solar energy, including tax returns, tax credits and net metering for grid connected solar power systems.Cost trends
In the mid-2000s, solar companies used various financing plans for customers such as leases and power purchase agreements. Customers could pay for their solar panels over a span of years, and get help with payments from credits from net metering programs. As of May 2017, installation of a rooftop solar system costs an average of $20,000. In the past, it had been more expensive.Utility Dive wrote, "For most people, adding a solar system on top of other bills and priorities is a luxury" and "rooftop solar companies by and large cater to the wealthier portions of the American population." Most households that get solar arrays are "upper middle-income". The average household salary for solar customers is around $100,000. However, "a surprising number of low-income" customers appeared in a study of income and solar system purchases. "Based on the findings of the study, GTM researchers estimate that the four solar markets include more than 100,000 installations at low-income properties."
A report released in June 2018 by the Consumer Energy Alliance that analyzed U.S. solar incentives, showed that a combination of federal, state and local incentives, along with the declining net cost of installing PV systems, has caused a greater usage of rooftop solar across the nation. According to Daily Energy Insider, "In 2016, residential solar PV capacity grew 20 percent over the prior year, the report said. The average installed cost of residential solar, meanwhile, dropped 21 percent to $2.84 per watt-dc in the first quarter of 2017 versus first quarter 2015." In fact, in eight states the group studied, the total government incentives for installing a rooftop solar PV system actually exceeded the cost of doing so.
In 2019, the national average cost in the United States, after tax credits, for a 6 kW residential system was $2.99/W, with a typical range of $2.58 to $3.38.
Due to economies of scale, industrial-sized ground-mounted solar systems produce power at half the cost of small roof-mounted systems.
Feed-in tariff mechanism
In a grid connected rooftop photovoltaic power station, the generated electricity can sometimes be sold to the servicing electric utility for use elsewhere in the grid. This arrangement provides payback for the investment of the installer. Many consumers from across the world are switching to this mechanism owing to the revenue yielded. A public utility commission usually sets the rate that the utility pays for this electricity, which could be at the retail rate or the lower wholesale rate, greatly affecting solar power payback and installation demand.The FIT as it is commonly known has led to an expansion in the solar PV industry worldwide. Thousands of jobs have been created through this form of subsidy. However, it can produce a bubble effect which can burst when the FIT is removed. It has also increased the ability for localized production and embedded generation reducing transmission losses through power lines.
Solar shingles
or photovoltaic shingles, are solar panels designed to look like and function as conventional roofing materials, such as asphalt shingle or slate, while also producing electricity. Solar shingles are a type of solar energy solution known as building-integrated photovoltaics.Hybrid systems
A rooftop photovoltaic power station can be used in conjunction with other power components like diesel generators, wind turbines, batteries etc. These solar hybrid power systems may be capable of providing a continuous source of power.Advantages
Installers have the right to feed solar electricity into the public grid and hence receive a reasonable premium tariff per generated kWh reflecting the benefits of solar electricity to compensate for the current extra costs of PV electricity. In countries with unstable or relatively expensive grid electricity, rooftop systems are also more viable.For consumers, a solar PV system can help them reduce their reliance on fossil fuels by using the sun’s free energy to produce electricity that they can use in their home. Solar PV can therefore help homeowners lower their carbon footprints as well as saving money with their utility bills.