The reason for that is that these investments are expected to create a reliable long-term income. In contrast, stocks can swing wildly and bonds are not attractive because of very low interest rates (one might add stronger default risks as a consequence of the euro crisis).
2.5 billion Euro would still be only about 1.18% of the total Munich Re investments (212 billion).
Munich Re is also involved in the Desertec Industrial Initiative. Maybe some of that 2.5 billion will flow into some project in North Africa or the Middle East.