# Optimization Model for Selective Harvest Planning Performed by Humans and Robots
## 5 Numerical Studies--Harvesters with Different Capabilities to Classify Pepper Maturity Levels
### Payback Period and Rate-of-Return Analysis  
Two return-on-investment measures for the harvester robot were calculated, similar to the analysis suggested by [55] (pp. 683-687): the payback period and the internal rate of return (IRR) in five years. The payback period is the number of years required for incoming cash flows to balance cash outflows. The IRR is the annual growth rate that an investment is expected to generate [55]. The analysis required cost estimation of the investment in the robot and the savings via its use. It includes the following data based on SWEEPER project estimations [56]:  
* The cost of the robot is set at 100,000, 130,000, or 160,000 \(\epsilon\)
* The harvest season lasts 35 weeks per year
* Manual harvesting requires 3 s/pepper
* Robot harvesting requires 10 s/pepper
* Manual harvesters work five months, five days/week, 8 h/day
* A robotic harvester works 20 h/day, six days/week
* Manual harvest hourly rates of 16.5 (corresponding to rates in the Netherlands) and 9.97 \(\epsilon\) (corresponding to rates in Israel) result in 23,100 and 14,000 \(\epsilon\)/year, respectively  
In addition, the analysis estimates robot operation costs of 20,000 \(\epsilon\) for the first two years and 10,000 \(\epsilon\) for the years thereafter. The use tax rate and the depreciation were based on the United States Internal Revenue Service's Modified Accelerated Cost Recovery System (MACRS), as in ref. [55] (p. 684).  
The analysis included the following data, based on the corresponding use case (Section 5.2.1); the use case considers four harvest weeks of planning, multiplied by 8.75  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Robot Cycle Time** & **Type A Workers** & **Type B Workers** & **Type C Workers** \\ \hline
0.5 & 25.4 & 24.0 & 23.1 \\ \hline
1 & 12.7 & 12.0 & 11.6 \\ \hline
2.5 & 5.1 & 4.8 & 4.6 \\ \hline
5.5 & 2.3 & 2.2 & 2.1 \\ \hline
7.5 & 1.7 & 1.6 & 1.5 \\ \hline
10 & 1.3 & 1.2 & 1.2 \\ \hline
12.5 & 1.0 & 1.0 & 0.9 \\ \hline
15 & 0.8 & 0.8 & 0.8 \\ \hline
20 & 0.6 & 0.6 & 0.6 \\ \hline
25 & 0.5 & 0.5 & 0.5 \\ \hline \hline \end{tabular}
\end{table}
Table 5: The equivalent number of workers for different harvester robot cycle times.  
to represent the number of plannings per year. The formulation result was used to estimate the robot quality savings. Type B workers were chosen for the analysis, resulting in 23,769.4 kg/year of quality savings.  
The results in Table 6 show that, considering the highest robot cost (160,000 \(\upxi\)), for pepper prices lower than 1.25 and 1.75 \(\upxi\)/kg, it will take more than five years to recover the robot investment in both the Netherlands and Israel. The \(p\) of sweet peppers in the Netherlands varies between 1.2-1.3 \(\upxi\)/kg, resulting in 4.72 payback periods and 1.9% IRR. The \(p\) of sweet peppers in Israel varies between 1.7-2.2 \(\upxi\)/kg, resulting in 3.98 payback periods and 7.8% IRR.  
For a lower robot cost, a 100,000 \(\upxi\) return on investment will reduce to a payback of 3.21 and 2.71 years for the Netherlands and Israel, respectively. As expected, the return-on-investment measures are sensitive to both the pepper price and the robot cost.