In HOMER Pro, we often see cost tables with a single row, meaning that the cost is proportional to the size. In the PV cost table below, for example, the costs for 1 kW of capacity (kWp) are $3000 capital, $2500 replacement, and $10/year O&M. For 2 kW, it would be $6000, $5000, and $20/year.
Sometimes, for larger systems, we have a lower cost per kW (economy of scale). We can add rows to the cost table to model these systems:
For search space values other than 1, 2, or 3, HOMER Pro uses the two nearest points to interpolate or extrapolate the cost (the cost for zero kW is always zero). For example, for a system size of 0.5 kW, HOMER Pro uses the first and second row in the table to extrapolate costs of $1600 capital, $1350 replacement, and $9/year O&M. For 2.5 kW, HOMER Pro interpolates on the second and third rows in the table to get $7050 capital, $5800 replacement, and $13/year O&M. Finally, for a capacity of 10 kW, HOMER Pro extrapolates on the second and third rows, which gives costs of $25800 capital, $20800 replacement, and $28/year O&M.
HOMER Pro uses this algorithm on all the cost tables in your model. With the cost table defined this way, HOMER Pro can optimize your microgrid to take advantage of the cost savings for larger systems.