For alternative energy technologies like photovoltaics (PV), the analysis of Research and Development (R&D) expenses is important to observe and understand market dynamics. This is, in turn, essential for policymakers. However, the quantitative evaluation of global corporate R&D investments is a challenging task due to unavailability or high scatter of precise data. Here we present a top-down approach to estimate the current and global historic cumulated PV R&D investments based on international PV patent applications. High growth rates of PV-related patents and R&D headcount accompany growth and development of the PV market and are an excellent indicator to analyze R&D investments. With this approach, current annual corporate PV R&D investments are found to be about 6000 m and show a rapidly increasing trend on a global scale. (C) 2013 Elsevier Ltd. All rights reserved.