# Calculation of power production for EcCM

In this page, you can find an applet which calculates the
power production with an "externally charged capacitive mixing"
device.
## Description of the model and parameters

In this calculation, we consider the following electrical model:

The model is characterized by the capacitors C_{1} and C_{2},
the internal
resistance R_{int} (equivalent series resistance) and
transfer resistance
R_{T}. The ΔI current is the leakage current, and is
proportional to the square of the base (average) voltage:
ΔI = k V_{0}^{2}.
### Electrode properties panel

The panel contains the parameters described above,
namely the capacitances C_{1} and C_{2},
the transfer and internal resistance
R_{T} and R_{int}, and the characteristic time
τ for the salinity change
phase. All those parameters are provided for low salinity and high salinity
(20 mM and 500 mM).

Moreover, the parameters include the constant k for the leakage,
the voltage increase δV which takes place after the flux of fresh
water, and the leakage charge q per salinity change cycle.
### Electrode dimensions panel

The panel contains the dimensions of the rectengular electrodes,
W and L and the gap thickness H. Those parameters are used for
extrapolating the power production per square meter, but also for
evaluating the pumping power. The flow is perpendicular to the side
W, and takes place for the length L, through the gap. The thickness
of the film is used to evaluate the volume of solution inside the film.
The factor N defines the volume which must flow through the cell: it is
N times the volume of solution inside the films.
### Cycle parameters

The panel contains the parameters of the cycle: duration of phase A and
C (charge and discharge), external resistance in salt and fresh water, and
base voltage. The duration of phases B and D are taken equal to the
salinity change characteristic time.

Selecting one of the radio-buttons allows to scan one of the above
mentioned parameters.
### Calculation

Pressing the "Calculate" button starts the calculation. The resulting
graph is shown within a few seconds.

The graph represents the total (gross) produced power (when negative,
the energy is consumed instead of produced). The vertical scale is in mW.
Only the yellow part
is actually extracted, while the other colors represent the
power losses.

Red: power loss due to leakage current

Green: power loss due to transfer resistance

Blue: power loss due to internal resistance (equivalent series resistance)

Magenta: power loss due to pumping

Yellow: (net) extracted power

The horizontal axis represents the external resistance (in Ω) or
the charge/discharge phase duration (in seconds), depending on the selection.