  In this paper, a multivariate constrained robust M-regression (MCRM) method
is developed to estimate shaping coefficients for electricity forward prices.
An important benefit of the new method is that model arbitrage can be ruled out
at an elementary level, as all shaping coefficients are treated simultaneously.
Moreover, the new method is robust to outliers, such that the provided results
are stable and not sensitive to isolated sparks or dips in the market. An
efficient algorithm is presented to estimate all shaping coefficients at a low
computational cost. To illustrate its good performance, the method is applied
to German electricity prices.
