Occurrence of negative prices on the German spot market for electricity and their influence on balancing power markets

In this paper, we analyse the occurrence of negative electricity prices on the German day-ahead spot market for the years 2008 and 2009. An empirical analysis shows that either a low system load combined with a moderate wind generation or a moderate system load combined with a high wind generation is a neccessary condition for the appearence of negative prices. However, the linear correlation between the negative market prices and global variables that characterise the system status (system load, wind generation, net export, residual load) is relatively low - wind generation having the highest correlation (-0.42). By elaborating the actual volumes of renewable electricity that are traded on the spot market, a marginally better correlation can be achieved. Limited transparency in this field makes this type of market-oriented analysis difficult. We also find that the negative spot market prices cause higher capacity prices in the negative minute reserve market. The influence on the secondary reserve is less definite because of the long contracting periods in this market.