How much solar do you need?
How to Figure Out How Much Solar You Need on Your Boat
Before you ask how much solar you can fit on your boat, you’ve got to ask: how much solar do you need?
This post walks you through the needs part. Not wants, not dreams. Just the basics of what your boat actually uses day to day, and how that translates into solar and battery requirements.
Step 1: Start With a Power Audit
Grab a pen, clipboard, or spreadsheet.
Here is a spreadsheet we made - [DOWNLOAD]
Go around your boat and write down every electrical device you use:
- Fridge
- Lights
- Water pump
- Starlink
- Laptop charging
- Nav system
- Phone charger
- Fans
- Heater
- Toaster
- Inverter
- Electric stove or induction cooktop
- Autopilot
- Radar
- Air conditioning
- Bilge pump
- …you get the idea.
You're not listing batteries here — just devices that consume energy.
For each one, find:
- Voltage (V) and Current (A) — this might be on a label or manual. If not, look it up online.
- Multiply them together to get Power (Watts).
- Estimate how many hours per day you use it.
Then calculate:
Power (W) × Hours used = Watt-hours (Wh)
Do this for every device. Add it all up, and now you’ve got your daily energy consumption in watt-hours.
Example:
- Fridge: 50W × 24h = 1200Wh
- Lights: 20W × 4h = 80Wh
- Laptop: 60W × 2h = 120Wh
Total: 1400Wh per day
Step 2: Define Your Goals
Once you know your energy use, it’s time to zoom out. What kind of cruising are you doing?
Ask yourself:
- Are you a weekend warrior or planning multi-week offshore trips?
- Do you want to reduce your generator use or eliminate it entirely?
- Are you converting anything from gas/diesel to electric (e.g. stove, fridge, propulsion)?
- Do you want redundancy and safety, or are you OK running lean?
Your cruising goals and level of self-suff