Loss coefficients are derived from consideration of total head loss across the junction box for straight-through flow, for flow from a 90° lateral, and for combining flow from both directions, using various combinations of pipe sizes and flow rates. The paper outlines results of model studies of a junction box designed primarily for urban highway storm drains. Only full-flowing pipes arc included. We find the total junction box losses to be small (< 1 W) compared to the power of common photovoltaic modules. Electrical losses in cabling are the dominant loss. Empirical models effectively represent loss coefficients for three-pipe junction configurations under varying conditions. Several folks have recommended "Mays, 2001" which I take to mean "Water Resources Engineering" by Larry W Mays, pub. The results from this configuration also indicate that substantial reductions in head losses at the box.