NOVELTY - A photovoltaic cell comprises a substrate (600); and two silicon germanium subcells.    USE - Photovoltaic cell for modular photovoltaic power conversion system (claimed).    ADVANTAGE - The photovoltaic cell has improved cell conversion efficiency and reduced lattice stress and crystal defects, and can be manufactured at low cost.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) manufacture of photovoltaic cell comprising providing a substrate, and depositing two silicon germanium subcells;    (2) a photovoltaic panel assembly comprising photovoltaic receiver assemblies including a photovoltaic cell; optical concentrating element(s); and support structure(s), where the photovoltaic receiver assemblies are mounted onto the support structures at a location corresponding to the focal point of the optical concentrating elements;    (3) a lens element comprising facets, where facet(s) is perpendicular to the plane of the lens in region(s) and other facets are non-opposing;    (4) a composite lens structure associated with the assembly, the lens element, and composite lens element comprising two lens element;    (5) a method of manufacturing a lens structure comprising injecting a polymer into a mold having two portions, causing the polymer to solidify, and separating the portions of the mold at the parting line in a direction such that the portion of the mold in contact with the facets of the lens is moved in a direction which separates it from all lens facets simultaneously;    (6) a cell interconnection module comprising input ports and single output port;    (7) a modular photovoltaic power conversion system comprising cell module(s) having photovoltaic cell(s), and cell interconnection module(s), which do not contain photovoltaic cells;    (8) a method of coupling together a modular photovoltaic power conversion system;    (9) a method of monitoring a modular photovoltaic power conversion system;    (10) a user access interface for a processor device, comprising a control program adapted to communicate with a cell interconnection module coupled to photovoltaic cell(s) for receiving data indicative of voltage and/or current associated with each photovoltaic cell from an interconnection module; and    (11) a computer program product stored on a computer usable medium, and adapted to monitor photovoltaic cell(s), where monitoring step includes receiving data indicative of voltage and/or current associated with each photovoltaic cell(s) from an interconnection module.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a multijunction cell.    Substrate (600)    Transition layers (601, 603, 605)    Silicon germanium layers (602, 604, 606)    Buffer layer (607)    Semiconductor subcells (608)