Solar Roof Energy Is the Answer for Mega Cities of the Future

Seven billion people will live and work in urban areas by 2050 and the demand for energy for all these people will be huge. Local production of energy will be needed with building-integrated photovoltaics (BIPV) key to make cities at least partially self-sufficient with energy. Rapid development in thin-film solar cell efficiency strengthens the business case for BIPV with great opportunities for suppliers of roofing materials and construction companies.

The electricity produced by ‘roof solar energy’ could be used for heating, cooling, running office machinery or even fed back to the grid, earning the building owners money.

The electricity produced by ‘roof solar energy’ could be used for heating, cooling, running office machinery or even fed back to the grid, earning the building owners money.

More than half of the planet’s population lives in urban regions today. This will grow to 75 percent in the next 30 to 35 years. That would mean 7 billion people living in more or less congested areas, all needing shelter, food—and lots of energy.

There is a growing consensus that the mega cities in the future cannot rely entirely on energy produced far away. Besides supply constraints, there are energy losses in the transport of the electricity; logistical nightmares; security issues; and, of course, environmental concerns.

There is a very healthy debate about distributed energy generation, often defined as electricity generation from many small sources. This discussion must be encouraged. We simply cannot solve the energy challenges of tomorrow with energy solutions of yesterday.

The distributed energy discussion has so far mainly centered on local smaller power plants, district energy, more efficient electricity distribution, the ‘smart grid’, etc. That is good. But we must also talk about the potential for local production of renewable energy by the end users on a micro scale, the very individuals who consume all this energy.

What do the end users have in common? Well, they all need a roof over their heads, at home and at work. These roofs can produce renewable energy! So the building industry can play a major role in solving mega cities’ energy challenges.

Building-integrated photovoltaics can be incorporated into the construction of new buildings as a principal or ancillary source of electrical power, and existing buildings may be retrofitted with similar technology.

Building-integrated photovoltaics can be incorporated into the construction of new buildings as a principal or ancillary source of electrical power, and existing buildings may be retrofitted with similar technology.

Look at an aerial image of a city and you will see an area densely covered by buildings—crisscrossed by roads and the occasional recreational area. All these buildings—houses, apartments, garages, offices, factories, schools and municipal buildings of all sorts—have roofs. New development in solar energy has transformed all these roofs—and even walls—into potential giant solar energy receivers.

The electricity produced by ‘roof solar energy’ could be used for heating, cooling, running office machinery or even fed back to the grid, earning the building owners money.

What I call ‘roof energy’ is building-integrated photovoltaics (BIPV), one of the fastest-growing segments of the photovoltaic industry. Photovoltaic materials are used to replace (or are added onto) conventional building materials in not only roofs, but also skylights and facades. They can be incorporated into the construction of new buildings as a principal or ancillary source of electrical power, and existing buildings may be retrofitted with similar technology.

Traditional wafer-based silicon solar cells are efficient but rigid, thick and heavy, ideal for large solar parks in sparsely populated areas but not in dense cities. They are too heavy for most roofs. However, thin-film solar cells made out of a copper-indium-gallium-selenium metal alloy (CIGS) are thin, light and flexible. They can be made frameless, can be bent, and are ideal for buildings and other structures that are uneven, moving or weak.

The business case for thin-film solar cells is strengthening rapidly since they are becoming increasingly efficient. A Swedish supplier of thin-film solar cell manufacturing equipment has managed to increase the aperture efficiency (the area on the solar panel that collects energy) from 6 percent four years ago to 11 percent two years ago and a record breaking 17 percent today by using a revolutionary all-dry, all vacuum process where all layers are deposited by sputtering.

An office, school, storage facility or factory with a flat roof in a Mediterranean country like Italy could annually yield 1,250 kWh from every kW installed, at a production cost of 7.2 U.S. cents. The production cost would decrease if the roof is slanted by up to 20 percent for an optimal 35-degree angle. The production cost would obviously be higher in colder countries and lower in countries nearer the equator. But even in Sweden the production cost could be as low as 8 cents.

Thin-film solar cells made out of a copper-indium-gallium-selenium metal alloy (CIGS) are thin, light and flexible.

Thin-film solar cells made out of a copper-indium-gallium-selenium metal alloy (CIGS) are thin, light and flexible.

A production cost of 5 to 10 cents is well below the current—not to mention the expected future—electricity prices. There are great variations in the price of electricity today, but many users pay between 10 and 30 cents per kWh (including taxes). Commercial and residential users pay even more.

The $100bn global roofing material market is in a healthy state, growing at 3.7 percent per annum and driven by an uptick in residential building construction (especially reroofing) in developed and developing markets. Here is an excellent opportunity for architects, roofing material suppliers and construction companies to take a leading position in what is destined to be the material of choice for urban planners in the future.

Thin-film BIPV solar energy solutions can be made light and are flexible. They can be fitted or retrofitted onto roofs without perforating the roofs and can be curved or bent. Installation is easy and cost-efficient with no racks or ballast needed. There are no weight constraints and no access limitations (you can walk on the panels). And they can be integrated on bitumen and TPO membranes.

Selling roofing solutions and electricity together opens up to completely new business models: suppliers can offer a discounted roofing price in combination with a stable and independent supply of electricity. Customers can secure electricity price—and get a new roof.

Municipalities and city planners in today’s and tomorrow’s mega cities will make efforts to make their cities greener and more sustainable. It is no wild guess that green buildings with ‘roof energy’ systems will get preferential treatment in public tenders and maybe even subsidies. Building owners will like the prospect of lower energy costs.

So the question to the world’s architects, roof manufacturers and construction companies is: Do you feel lucky? Do you feel confident enough to keep doing business as usual, selling traditional roofs to consumers who might sooner than expected demand energy-producing and cost-saving roofs and buildings? Or will you grab an unparalleled opportunity to gain market share by offering state-of-the-art products that will change the world or at least the way the world’s urban population powers their daily lives?

For me, the answer is simple: If end users can produce part of the energy consumed in a sustainable fashion where they live and work, that would go a long way toward solving the energy and climate challenges of the future. Flexible, efficient, thin-film solar cells for buildings are an integral part of this solution.

About Sven Lindstrom

Sven Lindström is co-founder, chairman and CEO of Midsummer, a global supplier of production lines for cost-effective manufacturing of flexible thin film CIGS solar cells. Lindström has more than 20 years' experience from international business and development of high-tech production equipment and vacuum deposition systems. He has more than 10 years' experience in the development and management of solar cell production equipment and is a firm supporter of distributed electricity production.

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