Solar Load Calculator: The First Step to Off-Grid Freedom
Solar Load Calculator: The First Step to Off-Grid Freedom
You cannot build a house without a blueprint, and you cannot build a solar system without a Load Calculation. Most beginners buy a “solar kit” and realize too late that it can’t run their coffee maker.
This tool by ShockTrail allows you to list every item you own and calculate your exact Total Daily Watt-Hours.
The Energy Audit Tool
Add your devices below (e.g., “MacBook”, “LED Lights”) to see your total energy budget.
System Energy Audit
Add your devices to size your solar systemWhy “Watt-Hours” Rule Your Life
In the off-grid world, we don’t pay a monthly utility bill. We pay in “Battery Capacity.” To know how much battery you need, you must convert everything to Watt-Hours (Wh).
The Formula: Watts × Hours Used = Watt-Hours
Example: A 100W TV running for 4 hours consumes 400Wh. If you have a 12V battery, that equals roughly 33 Amp-Hours taken from your tank.
Common Appliance Power Ratings (Reference)
Don’t have the sticker handy? Here are typical values based on Department of Energy estimates:
| Appliance | Running Watts | Daily Use (Avg) |
|---|---|---|
| LED Light Bulb | 9W | 5 Hours |
| Starlink (Gen 2/3) | 60W – 100W | 24 Hours (Often overlooked!) |
| 12V Fridge (Compressor) | 40W (avg cycle) | 24 Hours (Cycles on/off) |
| Microwave | 1500W | 0.2 Hours (12 mins) |
Phantom Loads: The Silent Battery Killer
Even when turned “off,” many devices draw power. A TV in standby mode, a gaming console, or a USB charger plugged in with nothing attached can draw 5-10 Watts continuously. Over 24 hours, that is 240Wh—enough to drain 20% of a small battery!
We recommend using a Kill-A-Watt Meter or clamp meter to measure the actual draw of your devices.
Sizing Your System Based on Results
Once you have your “Total Daily Watt-Hours” from the calculator above, apply these rules:
- Solar Panels: You need enough panels to generate that energy in about 4-5 hours of sun. (Total Wh / 4 = Required Solar Watts).
- Batteries: You need enough storage for at least 2 days of autonomy. (Total Wh × 2 = Battery Bank Size).
- Inverter: Must handle the highest “Running Watts” sum of devices running simultaneously.
For detailed sizing, check our specific Solar Charge Time Calculator.
Frequently Asked Questions (FAQ)
How do I find the Watts of my laptop?
Check the power brick (charger). It will list Output (e.g., 19V at 3.42A). Multiply Volts x Amps = 65 Watts. Note that laptops don’t pull max power all the time, so you can estimate 50% of that for average use.
What about the inverter consumption?
Inverters are not 100% efficient. ShockTrail recommends adding 15% to your final energy calculation to account for conversion losses (DC to AC).
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