The Most Important First Step: Figuring Out Your Energy Needs
Before you buy solar panels, batteries, and other parts for your solar power system, there’s one very important thing you need to do first: figure out how much electricity you use each day.
When I built my own DIY Off-Grid Solar Setup, this was the first thing I did. If you skip this step, you might spend too much money on a system that’s too big. Or, even worse, you could build a system that’s too small and doesn’t give you enough power.
This guide will show you exactly how to calculate your energy use, using my own project as an example.
Step 1: List All Your Electronic Devices
First, walk around your home and make a list of every single thing that uses electricity. Don’t forget the small stuff, because it all adds up!
Here’s a list like the one I started with:
- LED Lights
- Ceiling Fans
- Laptop
- TV
- Phone Chargers
- Modem/Router (for internet)
- Small kitchen gadgets (like a blender)
- Water Pump
Step 2: Find Out How Much Power Each Device Uses (in Watts)
Next, you need to know how much power each device uses. This is measured in Watts (W). You can usually find this information on a sticker on the back of the device or on its power cord.
If you can’t find it, you can search online for the device’s model number and the word “watts.”
Here’s my list with the power for each device:
| Appliance | Quantity | Power (Watts) |
|---|---|---|
| LED Lights | 4 | 9 W |
| Ceiling Fan | 1 | 75 W |
| Laptop | 1 | 65 W |
| TV | 1 | 100 W |
| Phone Charger | 2 | 10 W |
| Modem/Router | 1 | 15 W |
Step 3: Guess How Many Hours You Use Each Device a Day
Now, be honest about how much you use each device on a normal day.
- Lights: How many hours are they on at night?
- Laptop: Do you use it for a full workday or just for a little while?
- Refrigerator: A fridge doesn’t run all the time, but it’s best to guess that it runs for about 8 to 12 hours a day to be safe.
Here’s my table with my best guesses for daily use:
| Appliance | Quantity | Power (Watts) | Hours/Day |
|---|---|---|---|
| LED Lights | 4 | 9 W | 5 |
| Ceiling Fan | 1 | 75 W | 8 |
| Laptop | 1 | 65 W | 6 |
| TV | 1 | 100 W | 4 |
| Phone Charger | 2 | 10 W | 3 |
| Modem/Router | 1 | 15 W | 24 |
Step 4: Calculate How Much Energy You Use Each Day (in Watt-Hours)
Now it’s time for some easy math. To find out the daily energy use for each device, multiply its power (Watts) by the number of hours you use it each day. The answer is in Watt-hours (Wh).
Formula: (Watts) x (Hours/Day) = Watt-hours (Wh) per day
Let’s fill in the rest of the table:
| Appliance | Quantity | Power (Watts) | Hours/Day | Daily Energy (Wh) |
|---|---|---|---|---|
| LED Lights | 4 | 9 W | 5 | (4 * 9) * 5 = 180 Wh |
| Ceiling Fan | 1 | 75 W | 8 | 75 * 8 = 600 Wh |
| Laptop | 1 | 65 W | 6 | 65 * 6 = 390 Wh |
| TV | 1 | 100 W | 4 | 100 * 4 = 400 Wh |
| Phone Charger | 2 | 10 W | 3 | (2 * 10) * 3 = 60 Wh |
| Modem/Router | 1 | 15 W | 24 | 15 * 24 = 360 Wh |
Finally, add up all the numbers in the “Daily Energy (Wh)” column to get your total daily energy use.
Total Daily Use = 180 + 600 + 390 + 400 + 60 + 360 = 1,990 Wh
Step 5: Add a Little Extra for Safety and Future Use
No solar power system is perfect. You lose a little bit of power when it’s changed from the batteries to your devices. So, it’s a good idea to add about 20-25% more to your total. This also gives you some extra power if you get new devices later.
Calculation: 1,990 Wh * 1.25 = 2,487.5 Wh
So, my goal is to have a system that can make about 2,500 Wh, or 2.5 kWh, of electricity every day.
This final number is the most important one. You’ll use it to choose the right size batteries and solar panels. Taking the time to do this calculation will make sure your solar power system works for you.