Real BOS and system costs of off-grid PV installations in the US: 1987-2004

We obtained cost data on 47 off-grid and 11 grid-connected systems from Home Power magazine and Solar Energy International, ranging from 100 to 6600 W installed from 1987 to 2004. This allowed accurate analysis of installed costs ($/W, corrected to 2004$) without rebates or discounts for PV modules and balance of systems (BOS). The BOS was separated into categories of batteries, power conditioning electronics (PCE), and "other". When normalized by system size, relative off-grid BOS costs are approximately independent of system size and comparable to PV module costs, especially for systems over 1000 W. Thus the off-grid system cost is approximately twice the module cost. Off-grid BOS and PV prices have been falling at about 0.5 $/W per year since 1990. System prices have therefore been failing at similar to 1 $/W per year. Grid connected systems have much lower BOS costs. Some off-grid systems with 2 axis trackers were not cost effective for maximizing the Dec-Jan output.