Soiling Effect

The effect of soiling on the performance of the PV plant is modelled by reducing the irradiance reaching each module by a simple user-supplied soiling effect. All such effects are input into SolarFarmer as percentages, and a negative value indicates a loss of irradiance or energy (e.g. an input soiling effect (\(E_{\text{soil}}\)) value of -2 would indicate that 2% of light fails to reach the modules owing to soiling).

$$G_{dir,poa,soil}\left( o_{j},t \right) = G_{dir,poa,far}\left( o_{j},t \right) \bullet \left( 1 + \frac{E_{\text{soil}}(t)}{100} \right)$$

$$G_{dif,poa,soil}\left( o_{j},t \right) = G_{dif,poa,near}\left( o_{j},t \right) \bullet \left( 1 + \frac{E_{\text{soil}}(t)}{100} \right)$$

$$G_{r,poa,soil}(o_{j},t) = G_{r,poa,near}(o_{j},t) \bullet \left( 1 + \frac{E_{\text{soil}}(t)}{100} \right)$$

These are combined to give the average irradiance on submodule j after the soiling effect as follows, taking near shading into account:

$$G_{poa,soil}\left( j,t \right) = \left\lbrack G_{dif,poa,soil}\left( o_{j},t \right) + G_{r,poa,soil}\left( o_{j},t \right) \right\rbrack + \frac{G_{dir,poa,soil}\left( o_{j},t \right) \bullet A_{u}(j,t)}{A(j)}$$

Where \(A(j)\) and \(A_{\text{u}}(j,t)\) are the total and unshaded areas of submodule j at time t respectively as before.

Soiling is assumed to be constant across the Plant Array. Average irradiance on the Plant Array at time t after soiling:

$$G_{plant,soil}(t) = \frac{\sum_{j = 1}^{N_{\text{submodules}}}{G_{poa,soil}(j,t) \bullet A(j)}}{\sum_{j = 1}^{N_{\text{submodules}}}{A(j)}}$$

The annual soiling effect can be calculated by averaging \(G_{\text{plant,soil}}(t)\) and \(G_{\text{plant,near}}(t)\) over the year (or any other period of interest) and comparing the results:

$$\Delta_{soil,year} = \left( \frac{\sum_{\text{year}}^{}{G_{plant,soil}(t)}}{\sum_{\text{year}}^{}{G_{plant,near}(t)}} - 1 \right) \bullet 100%$$