The economic efficiency calculation in PV*SOL® is based on the net present value method.
For the capital value of the total investment $KW_{\text{Gesamtinvestition}}$ is as follows:
$$ KW_\text{Gesamtinvestition} = \sum BW_\text{dynamisch} - i + f $$
Positive capital values mean investments that can be assessed positively from an economic point of view. The payback period is the period that the plant must run in order to generate a net present value of the total investment of zero. Amortization periods greater than 30 years are not issued by PV*SOL®.
The present value $BW_\text{dynamisch}$ of a price dynamic payment sequence $Z$ over $T$ years (lifetime) is valid according to VDI 6025:
$$ BW_\text{dynamisch} = Z_\text{dynamisch} \cdot b(T,q,r)$$
with
$$ b(T,q,r) = \left\{ \begin{aligned} \frac {1-(r/q)^T}{q-r} \quad\text{für }r\neq q \newline {} \newline \frac {T}{q} \quad\text{für }r= q\end{aligned} \right. $$
and the price dynamic payment sequence $Z_{t} = Z \cdot r^{t-1}$ as a sequence of payment sequence $Z \cdot r, Z \cdot r^{2}, \dots$ periodically increasing by the price change factor $r$ beginning with the first payment.
If the price change factor $r = 1$ the price dynamic payment sequence can be converted into a constant payment sequence $Z_\text{konstant}$.It is:
$$ BW_\text{konstant} = \frac{Z_\text{konstant}}{a(q,T)} $$ $$ a(q,T) = \frac{1}{ b(T,q,r = 1)} $$
For the electricity production costs $k$ applies:
$$ k = Z / E $$
See also