Bench Degree·SOLAR POWERchapter

Before You Start

One page. The parts list for the whole volume is Appendix A, at the back of the book; Chapter 1 will tell you what it needs. This page is the part you should not find out later.

This subject has one hazard with no equivalent anywhere else in this series, and it is not the voltage. It is that the source has no off switch.

A panel in sunlight is generating. There is no breaker upstream of it and no switch on it. A string of ten modules at nine on a Sunday morning sits at 340 V with the house main off, the inverter dead and the utility disconnected, and it will still push 13 A into whatever completes the circuit. The only real isolation is a cover: a tarpaulin, a blanket, cardboard, or dusk. That is why every wiring experiment here says to work with the panels covered.

Direct current is harder to break than alternating current. Mains passes through zero a hundred times a second and an arc goes out on its own. A solar string has no zeros, so an arc is fed continuously and gets longer as you pull the contacts apart. MC4 connectors are not switches and are not rated to break current. Cover the array or open the DC isolator, then unplug. Chapter 10 Section 3 is the full argument.

Nothing in this volume asks you to get on a roof. The thermal survey is done from the ground, the inverter measurement with a clamp meter that touches no conductor. Falls kill more people in this trade than electricity does. Roof work needs an anchor, a harness and training, all three, and none of the three is in this book.

Three more, each owned by the chapter that uses it. The Chapter 11 inverter box makes mains voltage and is the most dangerous thing here; never put a bench scope directly across an inverter output. A lead-acid cell vents explosive hydrogen while charging, and any 12 V battery will put hundreds of amps into a dropped spanner, so fuse the positive lead and take off rings and watches. The Chapter 3 copper plate reaches about 600 °C (1,112 °F), and the panel in Chapter 9 must stay under about 80 °C (176 °F) or the encapsulant softens.

Four panels in series is the ceiling this book sets for a bench, about 88 V open circuit. Nothing here asks you to build, modify or rewire an installed array.

Bench Degree

Get the degree without the diploma.

Learn the material, not how to pass the exam.