Exam: this system fails on cold mornings
A 24 V system in Baguio: five 100 W modules in one string into a charge controller rated for 100 V input. It works every afternoon and dies, controller after controller, on cold mornings. Diagnose it with the safety check and fix it so the array still gives at least 300 W at full sun, with zero safety fails.
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How it works
Graded on:
- A1: string Voc at the record low (5 °C) under the controller’s 100 V input
- The array delivers at least 300 W at 1000 W/m² into the controller
- Zero safety fails
Build on this bench, then press Check my design on the exam card. 20 minutes is the target; attempts and time are kept in your transcript. Hints cost nothing but are noted.
Parts on the bench
- 5 × Solar panel
- DC breaker
- Solar charge controller
- Fuse
- LiFePO4 battery
- Surge protector (SPD)
- Ground symbol
More on solar pv physics
- The IV curve: Voc, Isc and the knee
- Cold mornings raise Voc; hot noons cut power
- Shading and bypass diodes: a shadow costs more than its size
- A string against the controller: the cold-morning Voc
- PWM against MPPT: the harvest, as a number
- Lead-acid against LiFePO4: usable capacity, voltage and life
- Wiring, fuses and breakers for an array: the 1.25 and 1.56 rules
- Grounding, bonding and surge protection: the two jobs of earth