Reading a Solar Module Datasheet

Power at STC is a laboratory number

Maximum power at STC is measured under standard test conditions, not on your roof. It is the right number for comparing modules with each other and the wrong number for predicting what you will actually harvest. Where a tolerance is published — ± 5 % on the BSM020M and BSM030M — that is the band the module is guaranteed within.

Vpm and Ipm describe normal running

Optimum operating voltage and current, sometimes written Vpm and Ipm, are what the module delivers at its maximum power point. On the 30 W BSM030P that is 17.2 V and 1.74 A. These are the figures to use when you are estimating daily energy.

Voc and Isc size the equipment around it

Open circuit voltage is the highest voltage the module will present, with nothing connected — 21.6 V on the BSM030P, 41.3 V on the 24 V BSM020P-N. Check it against your charge controller's maximum input voltage. Short circuit current is the worst-case current and is what you size fusing and cable against, not the operating current.

The details that only some datasheets publish

The monocrystalline modules in this range publish a series fuse rating — 10 A on the BSM020M, 12 A on the BSM030M — plus cable gauge and length, glass thickness and junction box rating. The BSM030M lists 3.2 mm tempered glass, an IP-65 junction box, 900 mm of 12 AWG cable and a 6063-T5 anodised frame. If you are specifying for a permanent installation, those are the lines that tell you what you are getting.