Unavailability of the system

What this step does

The energy lost to outages and maintenance. It acts on the grid energy, as the last row: a flat share of the exported power on every timestep, and the whole inverter output inside a shutdown period. Inside a shutdown period the other AC rows and the day auxiliaries are zero, and only the night auxiliaries are drawn.

The math

1. Running total
2. Loss at a timestep

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000\,P_{DC}}\sum_i L_i \tag{1}$$ $$L_i = \begin{cases} N_{inv}\,P_{inv,i} & \text{inside a shutdown period} \\ u\,P_{in,i} & \text{otherwise, when } P_{in,i} > 0 \end{cases} \tag{2}$$

where

Symbol	Meaning	Unit
$E_{before}$	the running total of the loss diagram before this row	kWh/kWp
$E_{after}$	the running total after this row	kWh/kWp
$E_{row}$	the row taken as a loss	kWh/kWp
$\Delta t$	the length of one timestep	hours
$P_{DC}$	the DC nameplate of the system	kWp
$L_i$	the power lost at timestep $i$ over the whole system	W
$N_{inv}$	the number of inverters	—
$P_{inv,i}$	the output of one inverter at timestep $i$, taken as 0 when it is negative	W
$u$	the flat unavailability fraction	—
$P_{in,i}$	the power after the auxiliaries at timestep $i$	W

Reading the number

A loss, negative. 1 to 2 % for a utility system, often 0 for a rooftop system. The fraction, or the season and length of the shutdown periods, set it.

API

loss.unavailability

Symbols follow the symbol registry.