Results

Solar Field [m2]

Figure 4: Average annual earnings (beyond the required 8%) as a function of the solar field size.

Provided that the bonus tariffs in Spain will be valid for hybrid operation, it is economically very attractive to integrate a solar field into a biomass plant. The solar field should ideally have a mirror surface of 68’000 m2 for a 20 MW biomass plant. The additional earnings between 0 and 120’000 m2 (see figure 4) indicate, that the solar field in a hybrid plant is profitable with the assumed bonus. If the bonus will decrease, the additional earnings will decrease until the additional solar costs equal the additional bonus. If the bonus increases above the assumed value of 12.02 ct/kWh — as being discussed these days by political decision makers in Spain — the maximum will shift to higher surface areas.

The resulting levelised electricity costs depending on the solar field size are given in Figure 3:

Solar field size [m2]

Figure 3: Levelised electricity costs of a 20 MW biomass solar hybrid plant, as a function of the solar field size [m2]

Due to high costs of the solar field, the levelised electricity costs of a biomass plant can apparently not be reduced by coupling it with a solar field.

In Spain the legal framework for renewable energies is defined in the so called »Real Decreto 2818/1998«. For biomass and solar thermal electricity a bonus on top of the market price is being paid to cover the additional electricity generating costs. The bonus as well as the average electricity price of the Spanish electricity exchange market (March 03 — February 04) are given in table 1. For the calculations it was assumed that the corresponding tariffs could be applied according to the solar and the biomass share. The criteria for evaluating the plant investment is the annuity method, that is: In case the realised cash flow leads to an internal rate of return higher than the required 8% (see table 1), the annuity is positive, otherwise negative.