Rooftop solar could displace 20,000 tonnes of CO2 in Mashhad
A single dense residential block in Mashhad, Iran’s second-largest city, could generate roughly 6.4 times its own household electricity demand from rooftop photovoltaic panels, according to a new GIS-based feasibility study. The analysis, built on a high-resolution digital surface model and the ArcGIS Pro Solar Toolbox, identifies 141,150 square meters of usable rooftop area in the block, enough to deliver 36,228,262 kilowatt-hours of electricity per year after system losses. Under a full grid-displacement assumption, that output would avoid an estimated 20,451.7 tonnes of carbon dioxide emissions annually, with seasonal avoided emissions ranging from 3,421.2 tonnes in winter to 8,386.3 tonnes in summer. The study is the first in Iran or the wider Middle East to integrate obstruction-aware, seasonal solar-yield modeling with fossil-fuel displacement and pixel-level carbon accounting at the urban-block scale, producing benchmarks that the authors say can be extrapolated to comparable residential zones across the city.
The context makes the findings striking. Iran’s electricity mix remains dominated by fossil fuels, which supplied 93.9 percent of generation, while solar contributed just 0.18 percent despite the country’s geographic advantage of 280 to 300 sunny days per year. Iran ranked fifth in Middle East solar capacity at 539 megawatts in 2022, and in the 2025 Climate Change Performance Index it placed last among the 63 countries and the EU evaluated. Mashhad alone consumes about 1,500 megawatts of electricity, of which less than one percent, roughly 7.5 megawatts, is currently supplied by solar installations, meaning the city consumes nearly three times the electricity equivalent of the entire nation’s solar output while contributing a negligible fraction of that capacity. The city’s favorable climate, with approximately 2,900 hours of sunshine annually, underscores the scale of the untapped resource.
The methodological core of the study is a 0.5-meter digital surface model obtained from the Mashhad Municipality Geospatial Data Center, produced from stereo aerial imagery acquired in 2022 with a vertical accuracy of plus or minus 0.30 meters based on municipal ground-control checks. Before analysis, the DSM tiles were georeferenced using 14 ground-control points, achieving a final root-mean-square error of 0.21 meters, then mosaicked into a seamless raster, resampled to a uniform 0.5-meter cell size, and clipped to the block boundary. The ArcGIS Pro Area Solar Radiation tool was executed for two representative dates per month at 30-minute intervals, with the three-dimensional building and tree geometry in the DSM generating dynamic shadow patterns for every rooftop pixel. Atmospheric parameters were set to a transmissivity of 0.5 and a diffuse proportion of 0.3, values the authors justify as physically consistent with Mashhad’s semi-arid, predominantly clear-sky conditions, where mean summer cloud cover is about 12 percent and winter cloud cover about 45 percent.
The study block, bounded by Jalal Al-Ahmad, Seyed Razi, Amoozegar, and Imam Ali streets in District 11, covers 0.514 square kilometers and houses an estimated 5,554 residents in roughly 1,420 to 1,480 dwellings. The block was selected because its characteristics match the median profile of Mashhad’s inner-city residential zones documented in the city’s Comprehensive Plan: land use is 88.5 percent residential, rooftops are predominantly flat, average household size is 3.7 to 3.9 persons per dwelling, and building heights of three to six stories are representative of the medium-density zones that account for the largest share of the city’s built-up area. The block is therefore presented as a methodologically appropriate representative case rather than an outlier, and its per-unit-area results can serve as benchmarks for spatial extrapolation to comparable residential districts.
Rooftop filtering applied several constraints to identify suitable installation sites. Roofs needed a minimum annual solar radiation of 800 kilowatt-hours per square meter, a slope of no more than 45 degrees in line with national rooftop-PV practice, exclusion of north-facing orientations unless the slope was 10 degrees or less, and a minimum contiguous area of 20 square meters. Non-residential zones, bare land, and undersized residential structures were omitted. A 65 percent rooftop-usability factor was then applied to account for persistent shading, stair cores, parapets, HVAC units, safety setbacks, and access pathways, a range consistent with the 60 to 70 percent values commonly adopted in urban rooftop studies for high-density blocks. From a total rooftop footprint of approximately 217,150 square meters, these criteria yielded 141,150 square meters of usable area.
The energy-yield modeling adopted a nominal module efficiency of 20 percent, representative of commercially available monocrystalline silicon panels, and a 13 percent system-loss envelope covering temperature derating, inverter efficiency, soiling, mismatch, wiring, and aging. Seasonal average daily irradiance on usable rooftops ranged from 6.22 kilowatt-hours per square meter in summer to 1.73 in winter, with spring at 4.91 and autumn at 3.26. Gross annual rooftop PV potential reached 41,641,681 kilowatt-hours, corresponding to a delivered annual yield of 36,228,262 kilowatt-hours after derating, equivalent to 256.7 kilowatt-hours per square meter of usable rooftop area per year. Summer contributed the largest seasonal share at 14,042,954 kilowatt-hours delivered, reaching approximately 5.5 times seasonal household demand, a generation-to-demand ratio of 549 percent, while the annual ratio stood at 638 percent under the full grid-displacement assumption.
The carbon model derives season-specific effective grid emission intensities by combining IPCC 2019 fuel emission factors with documented seasonal fuel mixes and thermal plant efficiencies: 464.5 grams of CO2 per kilowatt-hour in spring, 597.2 in summer, 480.2 in autumn, and 895.3 in winter. The elevated winter intensity reflects gas-priority heating periods, when natural gas is redirected to residential use and diesel and mazut supply roughly 90 percent of generation at reduced plant efficiency. Multiplying each season’s delivered PV electricity by its intensity yields avoided emissions of 5,148 tonnes in spring, 8,386.3 in summer, 3,496.1 in autumn, and 3,421.2 in winter. The authors stress that the full 20,451.7-tonne annual figure assumes all delivered PV electricity, including exportable surplus, displaces fossil generation at the applicable intensity, an explicit modelling assumption rather than an empirically verified outcome. Under a conservative demand-capped scenario, annual avoided CO2 falls to 3,603.7 tonnes, bounding the plausible range pending grid-injection and curtailment analysis.
A one-at-a-time sensitivity analysis shows module efficiency has the largest influence on annual yield, with a plus or minus 2 percentage-point variation around 20 percent producing a plus or minus 10 percent change in delivered output. The rooftop usability factor produces a plus or minus 7.7 percent change for a plus or minus 5-point variation around 65 percent, and system derating losses a plus or minus 2.3 percent change. The worst-case parameter combination yields 29,405,433 kilowatt-hours annually, and the best case 43,903,145, bracketing the baseline. Because no ground-based irradiance or inverter-meter time series was accessible for the block, direct measured validation was not performed. Model credibility instead rests on published calibration of the Fu and Rich radiation model against meteorological stations, internal consistency of the seasonal totals, and agreement of the modelled summer irradiance with the 5.5 to 6.5 kilowatt-hours per square meter per day reported for climatically comparable Cairo, and with the 1,700 to 2,100 kilowatt-hours per square meter per year global horizontal irradiance documented for Iranian cities at similar latitudes.
Compared with prior GIS-solar studies, the results stand out for their seasonal resolution and integrated carbon chain. A Lisbon suburb study reported a 48 percent annual demand offset, while a Santa Isabel, Ecuador analysis found rooftop PV supplying 4.97 times neighborhood demand; the present study’s higher ratio reflects Mashhad’s stronger solar resource, high residential density, and substantial per-capita cooling loads. The delivered annual output represents an indicative avoided electricity cost of roughly 362,283 to 1,811,413 US dollars per year for the block, depending on whether Iran’s subsidized or cost-reflective residential tariffs apply, though only locally consumed electricity is directly monetizable. The authors propose prioritizing rooftop retrofits in high-solar-access blocks during summer peak months, integrating DSM-based irradiance outputs into retrofit zoning for flat roofs with contiguous areas of at least 20 square meters, embedding a seasonal carbon-accounting GIS layer to target incentives, and progressively calibrating deployment plans with meteorological and inverter telemetry. Future work should replicate the pipeline across Mashhad’s 12 districts to produce a city-wide solar cadastre, validate modelled yields against measured records, and extend the framework to techno-economic and grid-integration dimensions essential for deployment planning.
Subject of Research: GIS-based rooftop photovoltaic potential and seasonal carbon displacement modeling in Mashhad, Iran
Article Title: GIS-based feasibility study of photovoltaic potential and carbon reduction in Mashhad city
Article References: Hashemi, M., Ahmadi, A., Gheibi, M., Mahmood, A., Yeganeh Khaksar, R., Annuk, A., & Moezzi, R. (2026). GIS-based feasibility study of photovoltaic potential and carbon reduction in Mashhad city. Results in Engineering, 32, Article 113436. https://doi.org/10.1016/j.rineng.2026.113436
Image Credits: AI Generated
DOI: 10.1016/j.rineng.2026.113436
Keywords: rooftop solar, photovoltaics, Mashhad, GIS, digital surface model, carbon displacement, CO2 emissions, Solar Toolbox, Iran, urban energy, seasonal irradiance, renewable energy
News Source: Faith Mcneil. (October 24, 2026). Rooftop solar could displace 20,000 tonnes of CO2 in Mashhad. Scienmag.
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