The high volatility of electricity markets gives producers and retailers an incentive to hedge their exposure to electricity prices by buying and selling derivatives. This paper studies how welfare and investment incentives are affected when markets for derivatives are introduced, and to what extent this depends on market completeness. We develop an equilibrium model of the electricity market with riskaverse firms and a set of traded financial products, more specifically: forwards and an increasing number of options. Using this model, we first show that aggregate welfare in the market increases with the number of derivatives offered. If firms are concerned with large negative shocks to their profitability due to liquidity constraints, option markets are particularly attractive from a welfare point of view. Secondly, we demonstrate that increasing the number of derivatives improves investment decisions of small firms (especially when firms are risk-averse), because the additional financial markets signal to firms how they can reduce the overall sector risk. Also the information content of prices increases: the quality of investment decisions based on risk-free probabilities, inferred from market prices, improves as markets become more complete Finally, we show that government intervention may be needed, because private investors may not have the right incentives to create the optimal number of markets.