Effects of photovoltaic panels on roof heat transfer (2023)

Table of Contents
solar power Abstract introduction section cutouts building and location solar radiation, wind speed and outside air temperature Simulation of the roof heat flow heat flow of the roof discussion and summary thanks references(18) Influence of building-integrated photovoltaics on the microclimate of urban treetops Building and Environment The effects of changing roof albedo on the cooling load of scale model homes in Tucson energy and buildings Rooftop Sun Reflection and Cooling Energy Consumption: Field Research Results from Florida energy and buildings An overview of wind convection coefficient correlations for modeling building envelope energy systems Applied thermal engineering A thermal model for photovoltaic systems solar power Saving peak power and cooling energy from shady trees energy and buildings Peak power and cooling energy savings of high albedo roofs energy and buildings Cited by (80) Influence of different canopy mitigation strategies on near-surface temperature and energy consumption in the Chicago metropolitan area during a heatwave event Thermal and energy benefits of rooftop photovoltaic panels in a semi-arid city during an extreme heatwave event Building PV integration according to regional climate conditions: BIPV regional adaptability extension of the Köppen-Geiger climate classification against urban and climate-induced temperature increases Investigation of the annual output of a building shaded by roof-top PV modules in different climate zones of India Optimization of photovoltaic power generation and roof insulation in existing residential buildings Energy performance of integrated adaptive skin systems for residential buildings Featured Articles (6) Effects of mounting geometries on photovoltaic module performance using CFD and single diode models Determination of the heat transfer coefficient of PV modules Investigating the role of cavity airflow on the performance of building-integrated photovoltaic modules On the effect of roof-mounted photovoltaics on the energy demand of the building A critical analysis of the factors affecting the performance of photovoltaic green roofs Evaluating the Potential Benefits of Solar Photovoltaic Shading in Hong Kong FAQs Videos

solar power

Volume 85, Issue 9,

September 2011

, pages 2244-2255

Author links open the overlay panel, ,


The indirect benefit of rooftop photovoltaic (PV) systems for building insulation is quantified through measurements and modelling. In San Diego, California, measurements were taken of thermal conditions throughout the roof profile of a building partially covered with photovoltaic (PV) panels. Thermal infrared images on a clear April day showed that daytime ceiling temperatures were below thePVArrays were up to 2.5K cooler than under exposed roof. Heat flux modeling showed a significant reduction in daytime heat flux under the PV array to the roof. At night, conditions reversed and the ceiling under the PV arrays was warmer than for the exposed roof, indicating PV's insulating properties. Simulations showed no advantage (but also no disadvantage) of the PV-covered roof for the annual heat load, but 5.9kWhm−2(or 38%) reduction in annual cooling load. The reduced diurnal variation in roof surface temperature beneath the PV array reduces thermal stresses on the roof and results in energy savings and/or human comfort benefits, particularly for rooftop PV on older storage buildings.


Building heating, ventilation and air conditioning (HVAC) is a major contributor to urban energy use. Especially in poorly insulated, single-storey buildings with a large floor area such as warehouses, most of the heat enters through the roof. Increasing the roof albedo (or solar reflectance) reduces the cooling load in sunny and hot climates. Installation of reflective roof membranes resulted in seasonal air conditioning energy savings of 57% in a house in California (Akbari et al., 1997a), 49% in a bungalow, 2-43% in Florida (Parker and Barkaszi, 1997), and 30 Whm−2D−1on a renovation building (Akbari and Rainer, 2000). However, energy saving depends on the insulating properties of the roof. Increasing roof albedo from 0.09 to 0.75 in a building with no insulation resulted in energy savings of 28%, while albedo in a building with R-30 insulation increased from 0.30 to 0.75 (an increase of 5.28 km2W−1of thermal resistance) resulted in savings of only 5% (Simpson and McPherson, 1997).

Shade trees planted near residential buildings resulted in a 30% savings in seasonal cooling energy and savings of 27% and 42% during peak demand in two residential buildings in Sacramento, California (Akbari et al., 1997b).

One rooftop “modification” that has had limited research on its impact on the cooling load is solar photovoltaic (PV). ITRON Inc. (2010) found that after a (non-building-integrated) PV installation, AC energy consumption decreased on days with high degrees of cooling compared to a reference sample. A 1 degree increase in the average daily temperature in the San Diego Gas & Electric (SDG&E) area resulted in households using 0.501 kWh less energy per day after PV with air conditioning. Supportively, a thermal conduction model showed a 65% reduction in the cooling load component through a PV roof compared to a traditional roof with a thermal resistance of R16 (Yang et al., 2001). Wang et al. (2006) modeled a one-dimensional transient heat transfer for a summer day and a winter day in China using four configurations: building-integrated ventilated air-gap PV (BIPV), non-ventilated (enclosed) air-gap BIPV, close-mounted BIPV, and conventional R8 roof with a Solar absorption of 0.9. In summer, the daily heat gain and peak cooling load with ventilated air-gap BIPV decreased by about 50% compared to conventional roofs, while the heat gains and peak cooling loads for closed air-gap and closed-roof BIPV were within 10% of those of a normal roof. The PV power with the air gap was 6% higher than with an unventilated air gap and closed roof mounting. In winter, ventilated air gap and closemount reduced peak heating load and heat loss by 5 to 10%, while unventilated air gap reduced peak heating load and heat loss by 20%. The PV generation power was within 2% for all modules in winter. Finally, the modeling of BIPV effects on urban canopy microclimate Tian et al. (2007) showed a significant reduction in BIPV roof surface temperatures compared to a conventional roof with an albedo of 0.30 and a thermal resistance of 1.33 K m2 W-1.

In this study, we examine a building partially covered by a flush and horizontal PV array and an offset and tilted PV array (Section 2). Meteorological and roof temperature measurements (including thermal imaging) were taken (Section 3). Section 4 describes a roof line model to estimate the average and maximum cooling energy differences for the roof sections with and without PV. In section 5 we present a complete roof energy balance model to calculate the annual roof heating and cooling loads with and without PV. Conclusions are presented in Section 6.

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section cutouts

building and location

The building used in this study is the Powell Structural Systems Laboratory (PoSL) at the University of California, San Diego (Fig. 1; Table 1, Table 2). It's a hollow concrete cube with no HVAC system. There are no windows except for a small semi-shaded row of windows on the east and west sides near the roof. On weekdays, the building is cooled by natural ventilation through a gate on the south side of the building (many coastal San Diego buildings do not have HVAC systems due to persistent ocean breezes

solar radiation, wind speed and outside air temperature

Only data for Sunday, April 19, 2009 will be analyzed as it was the clearest day with some clouds from 07:30 to 10:00 PST (Fig. 4a). Daily global horizontal solar irradiance was 7.72 kWh−2, which was larger than on a typical April day. Fig. 4b shows wind speed following typical sea wind patterns (compare annual average).uin Fig. 4b) with no wind up to 0800 PST, increases to 5 ms−1at 1400 PST and drops to less than 1 ms−1by 2030 PST. The air temperature cycle (Fig. 5a) has a

Simulation of the roof heat flow

The results in Section 3 have shown clear differences in the thermal response of a roof under a solar panel compared to an exposed roof. However, to determine the potential HVAC energy savings associated with solar PV panels, the most relevant variable is the roof heat flux into the conditioned space (or roof cooling load). It is difficult to quantify this heat flux independently for each surface, since heat is exchanged by convection and radiation (and to a lesser extent conduction).

heat flow of the roof

The model described in Section 4 was extended to simulate the envelope heat flow over a year, which was forced by continuous meteorological observations from the PoSL roof (in Table 3 above). Table 4 shows a list of all variables used in the annual roof heat flux model. For the exposed roof these are (in that order in Equations (3), (4)) shortwave (solar) radiation, incoming longwave radiation, outgoing longwave radiation, convection, conduction into the roof, and internal energy change (storage) . For

discussion and summary

Careful measurements of thermal conditions throughout the roof profile of a building partially covered with photovoltaic (PV) panels were made. Thermal infrared (TIR) ​​imaging showed that ceiling temperatures under the PV arrays at 1700 PST were up to 2.5 K lower than under the exposed roof, a time that is within the peak energy demand interval defined by SDG&E as 1200-1800 PST is defined. The daily variation of the roof surface temperature under the PV array was half that


Anthony Dominguez was funded by NASA's PhD research program. Kleissl acknowledges funding from an NSF CAREER Award and the Hellman Foundation. The following UCSD undergraduate students were instrumental in data collection: Avneet Singh, Kevin Chivatakarn, Thomas Minor, Jeremiah Farinella. We thank Ronnen Levinson for contributing his expertise and the staff at the Powell Structural Systems Laboratory, particularly Andrew Gunthardt, for supporting our work and


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  • DSParkeret al.

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  • H.Akbariet al.

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  • Akbari, H., Rainer, L., 2000. Measured energy savings from the application of reflective roofs in 3 AT&T regeneration...
  • ASHRAE, 2005a. Cooling Load Components, Microsoft Excel spreadsheet available through ASHRAE...

Additional references are available in the full-text version of this article.

Cited by (80)

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  • Optimization of photovoltaic power generation and roof insulation in existing residential buildings

    2022, energy and buildings

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Do solar panels reduce heat on roof? ›

According to a study conducted by researchers at UC San Diego Jacobs School of Engineering, solar panels reduced the amount of heat reaching the roof by an incredible 38%, keeping a building's roof 5 degrees cooler than portions of a roof exposed to sunlight directly.

What effects do solar panels have on a roof? ›

Solar panels can protect your roof from the sun's harmful rays. The panels absorb sunlight that otherwise would be absorbed directly by your shingles, sun bleaching them and drying them out. Additionally, air flows between the panels and the roof, cooling the roof considerably.

Do solar panels use heat transfer? ›

In PV modules, convective heat transfer is due to wind blowing across the surface of the module. The last way in which the PV module may transfer heat to the surrounding environment is through radiation.

What mode of heat transfer is used in a solar panel construction? ›

The main energy input is solar beam in the form of shortwave radiation. The solar cell endures heat removal by conduction, convection, and radiation.

Do solar panels increase heat in house? ›

It is usually most economical to design an active system to provide 40% to 80% of the home's heating needs. Systems providing less than 40% of a home's heat are rarely cost-effective except when using solar air heater collectors that heat one or two rooms and require no heat storage.

How do I reduce the heat on my rooftop? ›

How to Beat the Summer Heat by Keeping the Roof Cool
  1. Grow a roof garden. One of the best ways to keep the roof cool is by growing your own rooftop garden with green grass and potted plants. ...
  2. Paint the terrace white. ...
  3. Add shade. ...
  4. Go for heat-resistant flooring. ...
  5. Install solar panels.

Do solar panels affect roof integrity? ›

The weight of solar panels on your roof will also not compromise the structural integrity of your roof, even with added pressures such as snow. Solar panels are typically installed at an angle, allowing any type of snow buildup to slide right off of the panel.

What are the pros and cons of solar panels on your roof? ›

Consider these five pros and five cons of solar.
  • Pro: Return on Investment. ...
  • Con: Panels Cost Major Coin. ...
  • Pro: Counteract Rising Utility Prices. ...
  • Con: Not Suitable For Everyone. ...
  • Pro: Renewable, Clean, Efficient Energy. ...
  • Con: Solar Roofing Installers. ...
  • Pro: Added Home Value and Curb Appeal. ...
  • Con: Weather Dependent.

Do solar panels stress the roof? ›

Can Solar Panels Damage Your Roof? While solar panels shouldn't damage your roof, they can in the very rare case that they're installed incorrectly. For most people experiencing solar panel problems, the issue is as simple as incorrect wiring, dirty materials, or reduced panel efficiency.

Do solar panels absorb or reflect heat? ›

It is light, not heat, that generates electricity — and too much heat can actually hinder the electricity-making process. High temperatures can reduce the efficiency of electricity production, so although the solar panel will absorb both light and heat, it is the light that it wants.

What energy transfer occurs in a solar panel? ›

Solar technologies convert sunlight into electrical energy either through photovoltaic (PV) panels or through mirrors that concentrate solar radiation. This energy can be used to generate electricity or be stored in batteries or thermal storage.

What energy transfers happen in solar panels? ›

When photons, or particles of light, hit the thin layer of silicon on the top of a solar panel, they knock electrons off the silicon atoms. This PV charge creates an electric current (specifically, direct current or DC), which is captured by the wiring in solar panels.

What is solar heat transfer? ›

Solar thermal technologies absorb the heat of the sun and transfer it to useful applications, such as heating buildings or water. There are several major types of solar thermal technologies in use: Unglazed solar collectors. Transpired solar air collectors.

What are the three types of heat transfer in buildings? ›

Heat is transferred to and from objects -- such as you and your home -- through three processes: conduction, radiation, and convection. Conduction is heat traveling through a solid material. On hot days, heat is conducted into your home through the roof, walls, and windows.

How much heat is reflected from solar panels? ›

Think of it this way: the solar panel absorbs about 30% of the suns heat energy, re-emits half out toward the sky and half toward the roof, which absorbs about 30% of the heat emitted by the solar panel or only 5% of the sun's heat (30% of 50% of 30%). This concept is supported by a study by UC San Diego.

Can solar panels heat a house in winter? ›

Yes, a solar thermal system does work in winter. However it will be a lot less efficient than it is over the summer.

How do I reduce the heat on my roof in the summer? ›

7 Ways to Keep Your Roof Cool in The Summer
  1. Update Your Attic Insulation. Your attic is the space in your house directly below your roof. ...
  2. Paint Your Roof a Lighter Color. ...
  3. Increase the Shade On Your Roof. ...
  4. Start a Rooftop Garden. ...
  5. Consider Solar Reflective Shingles and Tiles. ...
  6. Install Solar Panels. ...
  7. Set Up a Roof Misting System.
Jan 20, 2022

What is the most energy efficient roof? ›

Metal roofing is by far one of the best choices you can make for your roof in general. They're the most energy-efficient roof for residential installations, can last more than 50 years, and require very little maintenance. Metal roofs are very reflective, which is why they get so hot to the touch.

Why do houses lose most of their heat through their roofs? ›

Heat Can Escape Through Your Roof

Hot air rises, which is why it's so important to ensure that your roof is properly protected against unnecessary heat loss. If you're losing heat through your roof then you may also experience draughts and cold spots, which could lead to problems with damp.

What type of roof is not good for solar panels? ›

Roofing materials that are not ideal for solar include wood and slate roofs. For one, these roofing materials are brittle, so solar panel installers can't just walk around on the roof as they normally could.

Why don't more people have solar panels on their roof? ›

The first being the cost; the initial capital cost required for installation is very high relative to other energy sources. There is a positive return on investment (ROI) in the future; however, it is slow and can take up to a few years.

Does mold grow under solar panels? ›

Solar panels are similar to your home's roof. They can slowly develop organic growth like moss, mold, mildew, algae, and lichen. Organic growth on your solar panels can reduce power outputs and create hot spots.

Is it better to put solar panels on roof or in the yard? ›

When you install ground-mounted systems you can align your panels to get as much sun as possible and the more sun you have, the more energy you'll be producing. Ground-mounted systems produce optimal performance that outmatches rooftop systems, largely because of this.

How much weight do solar panels add to a roof? ›

Most solar panels weigh about 40 pounds That means, for pitched roofs, solar panels add about 2.8 pounds per square foot. For flat roofs, they add about five pounds per square foot.

Are solar panels too heavy for my roof? ›

Rest assured, the answer is, No. You don't have to worry about the weight of solar panels on your roof. You can put any of these items up on your roof and not worry, even for a moment, that they might plunge through the roof.

Does installing solar panels void your roof warranty? ›

In most cases, solar panels will not void a roof warranty. However, you have to be cautious of some companies that may install solar panels without considering the consequences of some actions, such as drilling holes in your roof.

What is the heat island effect of solar panels? ›

For this study, the team defined the heat island effect as the difference in ambient air temperature around the solar power plant compared to that of the surrounding wild desert landscape. Findings demonstrated that temperatures around a solar power plant were 5.4-7.2 °F (3-4 °C) warmer than nearby wildlands.

At what temperature do solar panels lose efficiency? ›

Research has demonstrated that panels begin losing efficiency around 77ºF. However, this diminished efficiency is balanced out thanks to more daylight hours during the spring and summer months.

What effect do solar panels have on global warming? ›

As a renewable source of power, solar energy has an important role in reducing greenhouse gas emissions and mitigating climate change, which is critical to protecting humans, wildlife, and ecosystems. Solar energy can also improve air quality and reduce water use from energy production.

How does photovoltaic effect work? ›

Photovoltaic (PV) effect is a process by which PV cell converts the absorbed sunlight energy into electricity. PV system operates with zero carbon-dioxide emissions which has benefits for environmental safety. The photon energy absorbed by nanomaterials is transferred to the electrons in the atoms.

What is the principle of conversion of solar energy into heat? ›

The thermal conversion process of solar energy is based on well-known phenomena of heat transfer (Kreith 1976). In all thermal conversion processes, solar radiation is absorbed at the surface of a receiver, which contains oris in contact with flow passages through which a working fluid passes.

Why people didn t switch to solar energy rather than fossil fuels? ›

It all comes down to cost and infrastructure. Ultimately, the biggest hindrance to the development of renewable energy is its cost and logistical barriers.

What is solar thermal vs photovoltaic? ›

Solar photovoltaic panels produce electricity, while solar thermal systems produce heat. While both of these processes are energy efficient, solar photovoltaic only works during the day when the sun is out. It can work on cloudy days, but the energy producing capacity will reduce to 10-30%.

Why do solar panels generate heat? ›

These panels are absorbing a tremendous amount of energy from the Sun, converting some of it into electricity, but then warming up because they're not able to use all of the energy. So, these PV panels tend to be rather hot surfaces in the environment.

What is the difference between photovoltaic and solar thermal technology? ›

While the science and the details may be complicated, the difference between the two is rather simple. A solar PV system is one where the light hits a solar panel and is turned into electricity. On the other hand, a Solar Thermal System absorbs sunlight and uses the energy to heat your office or water.

What materials are best for reducing heat transfer? ›

Insulation helps to prevent that transfer of heat. Many different materials are used for insulation. Engineers often use fiberglass, wool, cotton, paper (wood cellulose), straw and various types of foams to insulate buildings. A layer of trapped air can serve as insulation, too!

What are the factors affecting heat transfer in building? ›

Temperature, moisture content, and density are the most important factors. Other factors include thickness, air velocity, pressing, and aging time. The relationship between main factors with thermal conductivity is presented.

What factors affect the rate of thermal energy transfer? ›

The rate at which an object transfers energy by heating depends on: the surface area, volume and material of the object and the nature of the surface with which the object is in contact. The bigger the temperature difference between a body and its surroundings, the faster the rate at which heat is transferred.

Do solar panels reduce air temperature? ›

Solar panels change the way sunlight is reflected and absorbed by the Earth. Any radiation they take in is radiation that's not being absorbed by the Earth. This leads to a cooling effect in the region surrounding the array.

How effective are solar roof vents? ›

A solar roof vent can help you cut energy bills by as much as 30 percent. These cost-effective, environmentally-friendly fixtures are a smart way to keep the attic temperatures at optimal levels. And since they're solar-powered, they utilize free energy helping you save money all year round.

What are the negative effects of solar panels on the environment? ›

While solar is labeled as a clean and alternative energy source, there are still negative environmental implications that are not commonly discussed. Photovoltaic panel production is linked to carbon emissions, toxic waste, unsustainable mining practices, and habitat loss.

What is the most effective roof venting system? ›

Ridge vents combined with under eave venting (soffit) are the most efficient system you can install. While other forms of ventilation create hot and cold zones on the roof's surface, ridge vent provides an even distribution of temperature. This means sections of the roof are not aging faster than others.

Do solar panels affect air quality? ›

Solar technologies provide energy for heating, cooling, and lighting homes and heating water without any direct emissions; as a result, these technologies can help reduce air emissions and improve air quality.


1. Energy 101: Cool Roofs
(U.S. Department of Energy)
2. 4 Year Update - Are Solar Panels for Home Still Worth It?
(Undecided with Matt Ferrell)
3. Florida solar customers, others shocked over new charge on electric bills
(WKMG News 6 ClickOrlando)
4. Make electricity and heat with one device: hybrid solar technology
(Tyler Disney)
5. Heating Seattle backyard studio with soda cans as solar panels
(Kirsten Dirksen)
6. URGENT! Do Not Buy Solar! Do This Instead. Save $1,000's!!! Mango Power E Review
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