Preventing Roof Leaks in Blue Bell: A Guide

Roof tiles are overlapping tiles designed mainly to keep out precipitation such as rain or snow, and are traditionally made from locally available materials such as clay or slate. Later tiles have been made from materials such as concrete, glass, and plastic.

Roof tiles can be affixed by screws or nails, but in some cases historic designs utilize interlocking systems that are self-supporting. Tiles typically cover an underlayment system, which seals the roof against water intrusion.^[1]

There are numerous profiles, or patterns, of roof tile, which can be separated into categories based on their installation and design.

One of the simplest designs of roof tile, these are simple overlapping slabs installed in the same manner as traditional shingles, usually held in place by nails or screws at their top. All forms of slate tile fall into this category. When installed, most of an individual shingle's surface area will be covered by the shingles overlapping it. As a result of this, flat tiles require more tiles to cover a certain area than other patterns of similar size.^[2]

These tiles commonly feature a squared base, as is the case with English clay tiles, but in some cases can have a pointed or rounded end, as seen with the beaver-tail tile common in Southern Germany.

The imbrex and tegula are overlapping tiles that were used by many ancient cultures, including the Greeks, Romans, and Chinese. The tegula is a flat tile laid against the surface of the roof, while the imbrex is a semi-cylindrical tile laid over the joints between tegulae.

In early designs tegula were perfectly flat, however over time they were designed to have ridges along their edges to channel water away from the gaps between tiles.^[3]

Similar to the imbrex and tegula design of tile, mission tiles are a semi-cylindrical two-piece tile system, composed of a pan and cover. Unlike the imbrex and tegula both the pan and cover of Mission tile are arched.

Early examples of this profile were created by bending a piece of clay over a worker's thigh, which resulted in the semi-circular curve. This could add a taper to one end of the tile.

Pantiles are similar to mission tiles except that they consolidate the pan and cover into a single piece. This allows for greater surface area coverage with fewer tiles, and fewer cracks that could lead to leakage.

These tiles are traditionally formed through an extruder. In addition to the S-shaped Spanish tiles, this category includes the Scandia tiles common to Scandinavia and Northern Europe.

Dating to the 1840s, interlocking tiles are the newest category of roofing tile and one of the widest ranging in appearance.^[4] Their distinguishing feature is the presence of a ridge for interlocking with one another. This allows them to provide a high ratio of roof area to number of tiles used. Many distinct profiles fall into this category, such as the Marseilles, Ludowici, and Conosera patterns.^[5]

Unlike other types of tiles, which can in some cases be produced through a variety of methods, interlocking tiles can only be manufactured on a large scale with a tile press.

In many cases interlocking tile is designed to imitate other patterns of tile, such as flat shingles or pantiles, which can make it difficult to identify from the ground without inspecting an individual tile for a ridge.^[6]

The origins of clay roofing tiles are obscure, but it is believed that it was developed independently during the late Neolithic period in both ancient Greece and China, before spreading in use across Europe and Asia.^[7]

Fired roof-tiles have been found in the House of the tiles in Lerna, Greece.^[8][9] Debris found at the site contained thousands of terracotta tiles which had fallen from the roof.^[10] In the Mycenaean period, roof tiles are documented for Gla and Midea.^[11]

The earliest roof tiles from the Archaic period in Greece are documented from a very restricted area around Corinth, where fired tiles began to replace thatched roofs at two temples of Apollo and Poseidon between 700 and 650 BC.^[12] Spreading rapidly, roof tiles were found within fifty years at many sites around the Eastern Mediterranean, including Mainland Greece, Western Asia Minor, and Southern and Central Italy.^[13] Early Greek roof-tiles were of the imbrex and tegula style.^[14] While more expensive and labour-intensive to produce than thatch, their introduction has been explained by their greatly enhanced fire-resistance which gave desired protection to the costly temples.^[15]

The spread of the roof-tile technique has to be viewed in connection with the simultaneous rise of monumental architecture in Ancient Greece.^{[citation needed]} Only the newly appearing stone walls, which were replacing the earlier mudbrick and wood walls, were strong enough to support the weight of a tiled roof.^[16] As a side-effect, it has been assumed that the new stone and tile construction also ushered in the end of 'Chinese roof' (Knickdach) construction in Greek architecture, as they made the need for an extended roof as rain protection for the mudbrick walls obsolete.^[17]

A Greek roof tile was responsible for the death of Molossian Greek king Pyrrhus of Epirus in 272 BC after a woman threw one at the king's head as he was attacking her son.^[18]

Roof tiles similar to Greek designs continued to be used through the reign of the Roman Empire. They were a common feature in Roman cities, despite the fact that a single tile would often cost the equivalent of 1.5 day's wages. Tiles were commonly used as improvised weapons during citizen uprisings, as they were one of few such weapons available to city-dwellers of the time.^[19]

Roman imbrex and tebula roofs generally avoided the use of nails and were instead held in place through gravity, it is possible that this was one of the reasons their tile was found on low pitched roofs.^[20]

The Romans spread the use and production of roofing tile across their colonies in Europe, with kilns and tile-works constructed as far west and north as Spain and Britain. Early records suggest that brick and tile-works were considered under the control of the Roman state for a period of time.^[21]

It is believed that the Romans introduced the use of clay roof tile to Britain after their conquest in AD 43. The earliest known sites for the production of roof tile are near the Fishbourne Roman Palace. Early tiles produced in Britain followed the Roman imbrex and tebula style, but also included flat shingle tiles, which could be produced with less experience.^[21]

For a while after the dissolution of the Roman Empire, the manufacture of tile for roofs and decoration diminished in Northern Europe. In the twelfth century clay, slate, and stone roofing tile began to see more use, initially on abbeys and royal palaces. Their use was later encouraged within Medieval towns as a means of preventing the spread of fire. Simple flat shingle tiles became common during this period due to their ease of manufacture.^[22]

Scandinavian roof tiles have been seen on structures dating to the 1500s when city rulers in Holland required the use of fireproof materials. At the time, most houses were made of wood and had thatch roofing, which would often cause fires to spread quickly. To satisfy demand, many small roof-tile makers began to produce roof tiles by hand. The Scandinavian style of roof tile is a variation on the pantile which features a subdued "S" shape reminiscent of an ocean wave.^[23]

In Britain, tiles were also used to provide weather protection to the sides of timber frame buildings, a practice known as tile hanging.^[24] Another form of this is the so-called mathematical tile, which was hung on laths, nailed and then grouted. This form of tiling gives an imitation of brickwork and was developed to give the appearance of brick, but avoided the brick taxes of the 18th century.^[25]

Clay roof tiles are the main form of historic ceramic tilework in China, due largely to the emphasis that traditional Chinese architecture places on a roof as opposed to a wall.^[26] Roof tile fragments have been found in the Loess Plateau dating to the Longshan period, showing some of the earliest pan and cover designs found in Asia.^[7] During the Song dynasty, the manufacture of glazed tiles was standardized in Li Jie's Yingzao Fashi.^[27] In the Ming dynasty and Qing dynasty, glazed tiles became ever more popular for top-tier buildings, including palace halls in the Forbidden City and ceremonial temples such as the Heavenly Temple.

Chinese architecture is notable for its advancement of colored gloss glazes for roof tiles. Marco Polo made note of these on his travels to China, writing:

The roof is all ablaze with scarlet and green and blue and yellow and all the colors that are, so brilliantly varnished that it glitters like crystal and the color of it can be seen from far away.^[26]

Japanese architecture includes Onigawara as roof ornamentation in conjunction with tiled roofs. They are generally roof tiles or statues depicting a Japanese ogre (oni) or a fearsome beast. Prior to the Heian period, similar ornaments with floral and plant designs "hanagawara" preceded the onigawara.

Onigawara are most often found in Buddhist temples. In some cases the ogre's face may be missing.^[28]

In Korea the use of tile, known as giwa, dates back to the Three Kingdoms period, but it was not until the Unified Silla period that tile roofing became widely used. Tiles were initially reserved for temples and royal buildings as a status symbol.

The designs used on giwa can have symbolic meanings, with different figures representing concepts such as spirituality, longevity, happiness, and enlightenment. The five elements of fire, water, wood, metal and earth were common decorations during the Three Kingdoms period, and during the Goryeo dynasty Celadon glaze was invented and used for the roof tiles of the upper class.

Many post-war Korean roofs feature giwa and a common ornamental symbol is the Mugunghwa, South Korea's national flower.^[29]

Neolithic sites such as Alamgirpur in Uttar Pradesh provide early evidence of roof tiles.^[30] They became more common during the iron age and the early historic period during the first millennium BCE.^[31] These early roof tiles were flat tiles and rounded or bent tiles, a form that was widespread across the Ganga Valley and the Indian Peninsula, suggesting that it was an essential architectural element of this period.^[31] This early form of roof tiles also influenced roof tiles of neighboring Nepal and Sri lanka.^[31]

Metal roof tiles made of gold, silver, bronze and copper are restricted to religious architecture in South Asia. A notable temple with golden roof tiles is the Nataraja temple of Chidambaram, where the roof of the main shrine in the inner courtyard has been laid with 21,600 golden tiles.^[32]

Tapered flat roof tiles have been used in Thailand, Laos and Cambodia since at least the 9th or 10th century CE, with widespread adoption after the 14th century, commonly to roof traditional Buddhist temple architecture.^[33] These shingle tiles have flat elongated bodies with a bent upper end for hooking at the roof and a pointed lower end.^[33]

In Indonesia, approximately 90% of houses in Java island use clay roof tile.^[34] Traditionally, Javanese architecture use clay roof tiles.^[35] However, it was not until late 19th century that houses of commoners in Java and Bali started using roof tiles.^{[citation needed]} The Dutch colonial administration encouraged the usage of roof tiles to increase hygiene.^{[citation needed]} Before the mass usage of roof tiles in Java and Bali, commoners of both of islands used thatched or nipa roof like the inhabitants of other Indonesian islands.^{[citation needed]}

In the Philippines, aside from various thatching methods, a native roof tiling technique is the kalaka which uses halved bamboo sections fitted together.^[36] During the Spanish colonial era of the Philippines, colonial-era bahay na bato architecture (which mixes native and Spanish architecture) also extensively used the Spanish-style Monk and Nun tiles, known natively as teja de curva.^[37]

Roof tiles were introduced to North America by colonizers from Europe, and typically were traditional designs native to their original country.

Pieces of clay roof tile have been found in archeological excavations of the English settlement at Roanoke Colony dating to 1585, and in later English settlements in Jamestown, Virginia and St. Mary's, Maryland. Spanish and French colonists brought their designs and styles of roofing tile to areas they settled along what are now the southern United States and Mexico, with Spanish-influenced tile fragments found in Saint Augustine, Florida, and both Spanish and French styles used in New Orleans, Louisiana.

Dutch settlers first imported tile to their settlements in what are now the Northeastern United States, and had established full-scale production of roofing tiles in the upper Hudson River Valley by 1650 to supply New Amsterdam.

Clay roof tiles were first produced on the West Coast at the Mission San Antonio de Padua in 1780. This Spanish-influenced style of tile remains in common use in California.

One notable site of roof tile production was Zoar, Ohio, where a religious sect of German Zoarites formed a commune in 1817 and produced their own roofs in a handmade German beaver-tail style for several decades.^[38]

From the 1700s through early 1800s, clay roofing tile was a popular material in colonial American cities due to its fire-resistance, especially after the establishment of urban fire-codes.

In spite of improving manufacturing methods, clay tile fell out of favor within the United States around the 1820s, and cheaper alternatives such as wood shingle and slate tile became more common.^[39]

Beginning around the mid-1800s, expanding industrial production allowed for more efficient and large-scale production of clay roofing tile. At the same time, increasing city growth led to rising demand for fireproof materials to limit the danger of urban fires, such as the Great Chicago Fire of 1871.

These conditions combined to bring a significant expansion in the use of roof tile, with a shift from regional and hand-produced tile to patented and machine-made tile sold by large-scale companies.^[40]

The Gilardoni brothers of Altkirch, France were the first to develop a functional interlocking roof tile.^[41]

The Gilardonis' design marked a significant shift in the design of roofing tile. Prior to this tile most roofing tile profiles could be hand made without the need for large-scale machines, but the new interlocking tiles could only be produced with a tile press and were more cost effective than comparable vernacular styles. Through the rest of the 19th century many companies began refining and developing other versions of interlocking tiles.^[41]

The Gilardoni brothers began making their design in 1835 and took out a patent on their first design of interlocking clay tile in 1841, with a new design patented ten years later. The Gilardonis shared their patent with six other French tile manufacturers between 1845 and 1860, contributing greatly to the spread of interlocking tile usage throughout France and Europe. Their company built additional factories and continued to operate until 1974.^[41][42]

Another popular early interlocking tile pattern was the Marseilles design invented by the Martin Brothers in Marseille, France as early as the 1860s. The Marseilles tile pattern is distinguished from other designs by its diagonal notches on its side rebate, as well as the teardrop-shaped end of its middle-rib.^[41]

While the Martin Brothers invented the design, its widespread use was more due to the pattern's adoption and international production after its original patent expired. The Marseilles tile was widely exported, especially in European colonies in South and Central America, Africa, and Australia.^[41]

French-manufactured Marseilles tiles were imported to Australia by 1886 and New Zealand by 1899.^[43][44] Many New Zealand railway stations were built with them, including Dunedin.^[45][46] Large scale production of Marseilles tiles by Wunderlich began in Australia during war-time import shortages in 1916.^[43] From 1920, factories at Pargny-sur-Saulx exported tiles to England.^[47] By 1929 Winstone were making them at Taumarunui, in a tile works established about 1910, which was replaced by Plimmerton in 1954.^{[48][49][50][51]}

In 1881 Wilhelm Ludowici developed his own interlocking tile, an improvement upon the earlier designs which incorporated a double-rebate on the side, double head-fold at the top of the tile, and a strategically designed surface pattern for repelling water and melting snow from the top of the roof. Unlike other designs, Ludowici included his tile's central rib for functional reasons rather than aesthetic.^[41]

Ludowici's design was mass produced in Germany and later the United States by the Ludowici Roof Tile company, who advertised the pattern as French tile.^[52]

Many tiles found in the Mangalore region of India are derived from or made in this pattern. Clay roof tiles had been produced in the region since missionary Georg Plebst set up the first factory at Mangalore, Karnataka, India, in 1860 after finding large deposits of clay by the banks of the Gurupura and Netravati rivers. The initial tiles they produced were similar to the Gilardoni brothers' design, but later tiles adopted Ludowici's pattern. Over the years ten companies produced Mangalore tiles, which were exported around the Indian Ocean and subcontinent.^[53]

The Conosera tile was developed by George Herman Babcock in 1889, and was unique due to its diagonally interlocking structure and design allowing for more installation flexibility than other interlocking tile designs. Babcock designed the pattern with towers and spires in mind, since his design significantly reduced the number of graduated tile sizes needed to roof a cone.^[54]

Conosera was initially manufactured and sold by the Celadon Terra Cotta Company of Alfred, New York. After a merger formed the Ludowici-Celadon Company in 1906 the group continued to produce Conosera tile for special orders.^[55]

The earliest known concrete tiles were developed in the 1840s by Adolph Kroher. While visiting Grassau, Bavaria, Kroher learned about locals' use of regional minerals to create stucco and began to experiment with the material, developing a diamond-shaped interlocking pattern of concrete tile which became one of his company's primary profiles. He also manufactured a concrete pantile similar to the Scandinavian style of clay tile.

In order to reduce the high shipping cost for his tile, Kroher adopted a 'do-it-yourself' method of tile manufacture for some time, where he sold a supply of cement and the necessary tools for a home-builder to create their own tiles. This had the disadvantage that cement was prepared by amateurs and did not always have consistent or correct mixing preparation.

Concrete tiles became more widespread in Germany over the next few decades after manufacturers such as Jörgen Peter Jörgensen and Hartwig Hüser began producing interlocking and overlapping designs.^[56]

The concrete tile industry grew and spread internationally through the early 20th century, driven by its cheapness to produce at scale.^[57] Researchers considered concrete tile inferior to clay tile, largely due to its fundamental weaknesses of porosity and color impermanence.^[58][59]

Glass tiles, also referred to as skylight tiles, are used as accessories alongside clay roof tiles. These were first developed in the 1890s and designed to allow light into spaces roofed with interlocking tiles, such as warehouses and factories.^[41]

It is uncommon for a roof to be completely covered in glass tiles however there are a few exceptions, such as on the tower of Seattle's King Street Station.^[60]

Plastic tiles, marketed as composite or synthetic tiles, became available towards the end of the 20th century. Their exact invention date is unclear, but most became available around the year 2000.^[61][62]

Plastic tiles are generally designed to imitate slate or clay tiles, and achieve their color through synthetic dyes added to the plastic. They are produced through injection molding.^[63]

Rooftop PV systems around the world: Bensheim, Germany (top-left), Berlin, Germany (top-right), Kuppam, India (bottom-left), Greencap Energy solar array on Eton College, United Kingdom (bottom-right)

A rooftop solar power system, or rooftop PV system, is a photovoltaic (PV) system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure.^[1] 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.^[2]

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^[3] showed that rooftop solar is better for the environment than utility-scale solar.^[4] 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 (kW), while those mounted on commercial buildings often reach 100 kilowatts to 1 megawatt (MW). 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.^[5] Australia has by far the most rooftop solar capacity per capita.^[6]

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^[7]

There are various methods for calculating potential solar PV roof systems including the use of lidar^[8] and orthophotos.^[9] Sophisticated models can even determine shading losses over large areas for PV deployment at the municipal level.^[10]

The following section contains the most commonly utilized components of a rooftop solar array. Though designs may vary with roof type (e.g. metal vs shingle), roof angle, and shading concerns, most arrays consist of some variation of the following components

1. 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.^[11] The front of a solar panel is very durable whereas the back of a panel is generally more vulnerable.
2. 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.^[12]
3. 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.^[13]
4. 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.^[12]
5. 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.
6. DC/AC wiring for inverters connect wires between panels and into a micro inverter or string inverter.^[13] No cables should touch the roof surface or hang from the array to avoid weathering and the deterioration of cables.
7. 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.^[13]

^{[needs update][citation needed]}

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.^[14]

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.^[15]

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."^[15] Most households that get solar arrays are "upper middle-income". The average household salary for solar customers is around $100,000.^[15] 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."^[15]

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."^[16] 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.^[16]

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.^[17]

Due to economies of scale, industrial-sized ground-mounted solar systems produce power at half the cost (2 c/kWh) of small roof-mounted systems (4 c/kWh).^[18]

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.^[2]

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 (BIPV).^[19]

A rooftop photovoltaic power station (either on-grid or off-grid) 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.^[2]

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.^[2]

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.^[20]

An electrical power system containing a 10% contribution from PV stations would require a 2.5% increase in load-frequency control (LFC) capacity over a conventional system^[jargon]—an issue which may be countered by using synchronverters in the DC/AC-circuit of the PV system. The break-even cost for PV power generation was in 1996 found to be relatively high for contribution levels of less than 10%. While higher proportions of PV power generation give lower break-even costs, economic and LFC considerations impose an upper limit of about 10% on PV contributions to the overall power systems.^[21]

When replacing the asphalt shingle roof the solar panels will need to be uninstalled and taken down to re-shingle the roof and reinstalled after the re-shingling of the roof. Power outages could happen at the house during that time. Solar panel installers would have to come out twice to do the uninstall and re-install at a later date when the roof is finished, and their labor is typically more expensive than asphalt shingle roofers pay rate.^[22]

There are many technical challenges to integrating large amounts of rooftop PV systems to the power grid.

The electric power grid was not designed for two way power flow at the distribution level. Distribution feeders are usually designed as a radial system for one way power flow transmitted over long distances from large centralized generators to customer loads at the end of the distribution feeder. With localized and distributed solar PV generation on rooftops, reverse flow causes power to flow to the substation and transformer, causing significant challenges. This has adverse effects on protection coordination and voltage regulators.

Rapid fluctuations of generation from PV systems due to intermittent clouds cause undesirable levels of voltage variability in the distribution feeder. At high penetration of rooftop PV, this voltage variability reduces the stability of the grid due to transient imbalance in load and generation and causes voltage and frequency to exceed set limits if not countered by power controls. That is, the centralized generators cannot ramp fast enough to match the variability of the PV systems causing frequency mismatch in the nearby system. This could lead to blackouts. This is an example of how a simple localized rooftop PV system can affect the larger power grid. The issue is partially mitigated by distributing solar panels over a wide area, and by adding storage.

Rooftop PV solar operation and maintenance is of higher costs in comparison with ground-based facilities due to the distributed nature of rooftop facilities and harder access. In rooftop solar systems it typically takes a longer time to identify a malfunction and send a technician, due to lower availability of sufficient photovoltaic system performance monitoring tools and higher costs of human labor. As a result, rooftop solar PV systems typically suffer from lower quality of operation & maintenance and essentially lower levels of system availability and energy output.