How do I size the solar panels and battery?
Documented on the Successfully running an old UPS off solar! build
Published July 29, 2026
Estimate your AC load (watts) and desired runtime to determine battery capacity (Ah at the UPS battery voltage).
Full Answer
Estimate your AC load (watts) and desired runtime to determine battery capacity (Ah at the UPS battery voltage). Size solar panels and the MPPT controller to provide adequate charging current given your location's sun hours — panels should replenish what you consume daily plus losses.
Documented In This Build
Related Knowledge
Can any UPS be run off solar?What safety steps should I take before starting?How should I protect and organize the new wiring?Can I tap the reverse light power instead of running a dedicated trigger wire?What size fuse should I use for the amp power wire?How do I route wires through the tailgate hinge without chafing?Do I need to replace the entire wiring harness?How long does a basic dash rewire typically take?
Related Parts
Solar panel (100 W, 12 V nominal)
Generic$120
Used/Old UPS (existing)
$0
12 V 100 Ah Deep-Cycle Battery (AGM or Flooded)
Generic$250
DC Fuse / Battery Isolator (appropriate amperage)
Generic$25
PV Cables and MC4 Connectors
Generic$30
Battery Monitor / Voltmeter (optional)
Generic$50
Panel Mounting Hardware / Roof Rack Clips
Generic$20
MPPT Charge Controller (30 A)
Generic/MPPT$80
Related Tools
Multimeter
Wrench / socket set
Wire stripper / crimper
Screwdrivers (flat & Phillips)
Safety gear (gloves, safety glasses)
Insulating tape / heat shrink
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