In line with policies to boost renewable energy capacity, German investors have built four solar power plants in Hamedan, 330 kilometers west of Tehran, and the fifth one is under construction, director general of Hamedan Province's economic affairs said.

"Athos Solar GmbH has already completed four photovoltaic power projects with a total capacity of 28 megawatts in different parts of the province," Nasser Mahmoudi was also quoted as saying by IRNA on Monday.

Pointing to the fifth venture, Mahmoudi added that operations to build a new 7-MW solar station have started and the much-needed equipment are being installed.

"Each photovoltaic plant is completed at an estimated cost of 3.68 trillion rials (€8.5 million)," Mahmoudi said, adding that the German firm has made the lion's share of investments with a limited contribution from Aftab Mad Rahe Abrisham Company as its Iranian business partner.

According to the official, the solar panels have already been synchronized with the national grid.

"The renewable industry in Iran is among the slowest-growing sectors," he said, stressing that barely 240 MW in renewable power has come on stream over the past two decades.

Based in Heidelberg, Athos builds plants throughout Germany, Britain and Iran. The company is a manufacturer-independent project developer of large-scale photovoltaic plants. As a sustainable company in a sustainable industry, Athos plays an active role in implementing the turnaround in energy policy and in preventing global warming.

Recalling the policy to expand electricity production from renewable sources to 7,500 MW by 2030, Mahmoudi said the renewable sector is still risky for investment because it demands costly and thorough research before building the infrastructure "that may or may not prove to be economically viable".

Iran's power industry is mainly based on fossil fuels, which explains why senior decision and policy makers in the energy sector have paid little attention to renewable technologies over the past four decades.

According to IRNA, the Renewable Energy Organization of Iran, known as SUNA, has also completed two 7 MW solar power plants in Hamedan Province.

The plants were developed at an estimated cost of $17 million and became operational in early 2017.

Mahmoudi said the much-needed equipment to develop the solar plants, such as low voltage panels, were manufactured domestically.

According to Energy Ministry's data, plans are in place to invest $3 billion in renewable power projects in the near future. Since the lifting of international sanctions a year ago, Tehran has held talks with European companies, including from Germany and Britain, to develop its nascent renewable industry.

Energy experts believe that there is no bigger and more sustainable energy source than the sun. This is why a large number of countries have been planning, building and investing in large-scale solar plants.

With more than 300 sunny days throughout a year, well above the likes of the UK with 150 days of sunlight per year on average and with far less intensity in radiation, Iran has huge potential to expand solar energy infrastructure.