# Economic efficiency

The comparison of investment and running costs with revenue from energy generation serves to assess economic efficiency. This economic efficiency calculation was based on the net present value method.

## Investment costs

Investment costs (gross prices including assembly in €/m²) of the

types of façade examined were assumed as follows:

##### Figure 1: Façade prices (€/m²) of the simulated types of façade

## Running costs

The running costs are due mainly to the energy costs for heating and cooling the building. The following parameters were assumed:

Price per kWh for cooling: 0.07 €/kWh

Price per kWh for heating: 0.08 €/kWh

Annual energy price increase: 6%

## Electricity yield and investment subsidy

In order to calculate revenue, the photovoltaic feed-in tariff was taken from the Ökostromgesetz. The price of 0.46 €/kWh currently applies for the first ten years as of commissioning. 75% of this tariff subsidy is granted in the 11th year of feed-in, 50% in the 12th. After that, the current market price of E-Control GmbH applies.

The location of the simulated façades is Graz, which is why the current investment subsidies for PV systems in Styria were applied. (See

Subsidies and revenue).

## Comparison of net present value difference

An imputed interest rate of 6% was assumed in order to calculate the net present value difference. The net present values of the façades were compared with that of a natural stone façade. The natural stone façade is thus depicted on the x axis.

The graph of dynamic progression of net present values shows that the photovoltaic façades analysed make more sense economically than a conventional natural stone façade. One exception is the PV double façade, that only pays back after around 26 years due to the high investment costs involved. Economically, the sunshading façade (PV on brise soleil) gives the best results. The façade with polycrystalline PV modules installed at an angle of 75° comes second.

##### Figure 2: Net present value difference with Baseline natural stone façade