As global demand for cars and energy continues to grow, the need for cleaner and greener paintshops has never been more vital. AMS looks at an exciting new solar thermal initiative in plant design

Life cycle assessments, soaring energy prices, growing global demand for resources and stricter environmental legislation are powerful drivers that are compelling the automotive industry to implement more sustainable and carbon-friendly production. There is a special focus on coating processes, since they account for as much as 70 percent of the total amount of energy required to manufacture a car. A partnership between paint plant and process experts Eisenmann and solar thermal systems supplier Ritter XL Solar offers an attractive way to significantly cut costs and carbon emissions: solar thermal installations that provide heating and cooling for paint shops.

For OEMs and suppliers, sustainability is not just about making vehicles more environment-friendly and resource-efficient; it is also about applying green principles to production. That is why so many OEMs have defined emissions reduction, energy conservation and the use of renewable energy as key corporate goals. Large-scale solar thermal plants can make a major contribution to achieving these goals – by dramatically reducing fossil fuel consumption and associated CO2 emissions in energy-intensive processes, such as painting.

Highly efficient evacuated tube collectors

The CPC evacuated tube collectors developed by Ritter XL Solar enable the efficient utilization of solar thermal power for process heating and cooling. Unlike conventional flat collectors, the medium in the CP tubes is not antifreeze, but water. As a result, and with the help of sophisticated control technology, the solar plant can more easily be connected to the painting system’s heating network. Moreover, collectors in installations that use water are practically maintenance free.

The high-performance tube collectors also differ from conventional technology in terms of their structure. Each module consists of a double-walled, shockproof and hail resistant evacuated tube with a special plasma coating that acts as an absorber. Inside the tube is a heat-exchanger pipe that is heated by the sun’s rays. A critical component of this system is a vacuum that acts as an insulator, minimizing heat loss.

In addition, a Compound Parabolic Concentrator (CPC) concentrates the sun’s rays onto the tube. The result is an operating temperature of between 60 and 120 °C, even in weak or diffuse sunlight.

Low-cost pollution-free process heating and cooling

The paint system consumes up to 70 percent of the energy needed to manufacture a car. That energy is mainly used to heat the pre-treatment facilities, the ovens and the shop area, to air-condition the spray booths, and keep the paint at the correct temperature in the mixing room. A solar thermal plant is an ideal option for paint shops because of their huge demand for heat and because tube collectors can easily achieve the high operating temperatures required.

The “free” heat from the sun captured by the eco-friendly collectors is transferred to a hot-water tank and supplied to the various parts of the paint shop that require it. Solar energy can also be deployed for process cooling, for example in the cooling zones. The average annual yield of a solar installation in central Europe is about 500 kWh per m2. So a plant with a collector area of 3,000 m2 can generate at least 1,500 MWh. That is enough to deliver almost one-third of the energy consumed by an 800 kW pre-treatment facility operated in three shifts, i.e. 4,800 MWh per annum.

Both energy costs and carbon emissions are significantly lower. Assuming the facility produces 300,000 vehicles per year and the solar plant is in service for 20 years, the manufacturer can save 18,000 tons of CO2. This is equivalent to the amount produced by 1,000 vehicles with an emissions rating of 120 g/ km over a distance of 150,000 km per vehicle.

And the closer the solar installation is to the equator, the higher the yield: in Pune, India, for example, at least 2,400 MWh can be generated annually by the same configuration.

Guaranteed energy enables precise planning

When it comes to designing a solar thermal plant, the key parameters include the location, the average outdoor temperature and the load profile, the type of process, the nominal temperature and the proportion of conventionally generated heat to be substituted. And although these factors do not allow an accurate prediction of energy generation on a given day, it is possible to estimate the average annual yield.

Eisenmann guarantees customers a large proportion of the estimated yield, for example 1,500 MWh per annum, providing them with an accurate basis for cost calculations. Should a plant generate less than the guaranteed yield, the customer is compensated for the difference.

High return on investment

However, quite apart from issues such as life cycle assessments, energy and resource efficiency, and the carbon footprint, solar thermal plants are an attractive investment for OEMs and suppliers because they deliver a high return. If all debitside factors – costs, rising fossil-fuel prices, emissions trading certificates and the capital invested in the solar plant – are set against the savings achievable over the entire 20-year operating period, the annual return on investment of the project is between 10 and 20 percent, depending on plant configuration and location. In addition, many countries promote the use of solar thermal energy through lucrative incentives such as subsidized loans.

The partners

The partnership between the two global players; Eisenmann and Ritter XL Solar, delivers reliable, high-performance solar thermal plants that can be integrated with new or existing paint systems. Eisenmann is responsible for project planning, sales, integration of the plant and piping, while Ritter XL Solar – a specialist in large-scale solar thermal plants – designs and engineers the collector field and manufactures the modules.