PHOTON International The Photovoltaic Magazine

10 MW for rooftops of tire maker Michelin

German Voltwerk AG is building four PV systems with a total of 10 MW on tire manufacturer Michelin's production hall and warehouse. The PV company sees the move as part of a trend away from systems on undeveloped areas and onto roofs.

	© Wilhelm Mierendorf for photon.pictures.com
Roof protection: Protective mats are used to keep the roof watertight; aluminum trays are weighted down with gravel to prevent modules from blowing away due to heavy winds.

»The largest PV project in the world,"« proclaimed Hamburg-based Voltwerk AG and Michelin Reifenwerke KGaA in a joint press release– but that's a matter of interpretation, since there are actually other larger individual systems. But the truly remarkable aspect of this cooperative project is not the sheer size of the system, but its potential to serve as a role model: in Germany, there is a seemingly limitless number of industrial buildings like the Michelin facilities .

The Michelin PV project consists of a total power of 10 MW distributed over four locations. Two systems have already been installed: a 2.6 MW on a tire factory in Homburg and a 1.4 MW system on the roof of Michelin's regional distribution center in Landau. By mid-2005, a 1.5 MW system will be installed on the Michelin factory in Hallstadt near Bamberg, while the factory in Bad Kreuznach will be adorned with a 4 MW system. For comparison: the world's largest rooftop system in Bürstadt has a 5 MW power rating (see PI 7/2004, p. 8).

In contrast to the 5 MW system of project team »Sonnenfleck Bürstadt«– conceived as a community project, a »PV system for the people,« with broad local participation– the PV power plants on Michelin's roofs are a rather exclusive venture. The Michelin systems are financed with credits and via two closed funds that are offered as private placement to a select group of investors by an unnamed financial institution. The first fund for the systems in Homburg and Landau has already been issued with a volume of almost €5.4 million ($7.2 million). Hence 28 percent will be raised through this fund out of a total required investment of €19.3 million ($25.7 million) for both of the locations. Another €13.8 million ($18.4 million) will be covered by a long-term European Recovery Program credit. The financing for the systems in Bamberg and Bad Kreuznach will be raised in a similar way. In total, investment for all four locations will come to €50 million ($66.5 million).

A secure rate of return

A new limited company (GmbH & Co. KG) was founded to serve as the principal as well as the operator of the first two systems. The new company will be managed by Voltwerk AG, which itself sells the systems at a previously agreed upon fixed price to the operating company. SunTechnics GmbH, which like Voltwerk is a 100-percent subsidiary of Conergy AG, takes care of the installation. Hamburg-based Conergy Group, which also has a factory for mounting systems, in turn was contracted by its subsidiary SunTechics to deliver modules, inverters– and even mounting systems. To ensure that the interest of the investors is served in light of all this »nepotism,« SRE Service Company for Renewable Energy Projects GmbH will serve as a relatively unbiased third party to manage the commercial business transactions as well as provide system maintenance and technical support.

Michelin is only involved in as much as it leases its roofs. Whether or not Michelin actually has shares in the operating company is just as much a secret as the identity of the remaining backers. Yet one thing is clear: the project will definitely pay off for investors. As a result of the Renewable Energy Law's (EEG) guaranteed feed-in tariffs for rooftop systems, the projects in Landau and Homburg will yield an average of 54.4 euro cents (72.3¢) per kWh: 57.4 euro cents (76.3¢) for the sections of the system up to 30 kW; 54.6 euro cents (72.6¢) from 30 kW to 100 kW; and anything over 100 kW will yield 54 euro cents (71.8¢). The electricity is then fed into the grid of local utilities.

Three expert opinions– one from SunTechnics, another from the German Weather Service (DWD), and a third from Lübeck University of Applied Sciences– provide yield estimates of between 934 and 948 kWh per kW of installed power at the system in Landau, and 919 to 939 kWh per kW for the system in Homburg. The result is an average of 935 kWh per kW, which in the overall calculations was rounded down for safety's sake to 907 kWh per kW.

At first sight, these values seem too conservative, especially if one considers the high quality of the technology being used: in addition to the new WZA central inverters, which were developed by Conergy itself (see PI 12/2004, p. 44), the system employs monocrystalline modules from Sharp. Yet, first of all (with a 22° deviation to the east) the roofs in Homburg are not optimally positioned towards the south. Second, at both locations the horizontal module angle is just 15°, which is a significant deviation from the ideal position (around 30°). Finally, to avoid penetrating the roofing, the mounting structure is attached to trays that are weighted down with gravel, but only small amounts, because of the industrial hall's low bearing capacity. Hence it's impossible to position the modules at a steeper angle, since heavy winds could blow the system off the roof.

These types of problems aren't new, and prior to the increase in feed-in tariffs as part of the EEG revision, which went to effect in Jan. 2004, they put a stop to many large flat-roof projects. But now many of these problems seem surmountable. Thorsten Vespermann, spokesperson for Conergy AG, is not the only one who sees signs that »the trend in planning is increasingly moving towards large-scale roof systems.«