A solar load list is the foundation of any DIY solar power system. Before you choose a panel, battery or inverter, you need to know exactly how much electricity you plan to use each day. A load list is simply a table that records every device you want to run, how much power it draws, how many hours a day it runs and how many watt-hours of energy it consumes daily. This article explains how to build that list step by step, using straightforward methods and publicly available guidance.
What Is a Solar Load List?
A solar load list is a planning tool that adds up all the electrical loads you intend to supply from a solar and battery system. The U.S. Energy Information Administration explains that electricity is measured in units of power called Watts, and energy use over time is measured in Watthours: one Watthour is the energy of one Watt used for one hour. A load list turns those units into a clear daily energy budget. Each row in the list represents one appliance or device, with columns for its power draw in Watts, the number of hours it runs per day and the resulting daily energy consumption in Watt-hours (Wh) or kilowatt-hours (kWh).
Why a Load List Matters
Without a load list, it is impossible to size a solar array, battery bank or inverter correctly. The list tells you how much energy you need each day, which directly determines how many solar panels and how much battery capacity you will require. It also reveals whether a load is AC or DC, which affects the choice of inverter and the wiring plan. A careful load list helps you avoid overspending on components you do not need or undersizing a system that cannot keep up. For a deeper look at how load data feeds into the rest of the design, see our DIY Solar Planning section and the pillar article How to Plan a DIY Solar System on Paper.
The Columns of a Load List
A practical load list includes at least these columns:
- Device, the name of the appliance or electronic device.
- Watts, the power the device draws while running.
- Hours per day, the number of hours the device is actually operating, not just plugged in.
- Watt-hours per day, Watts multiplied by hours per day.
- AC or DC, whether the device runs on alternating current or direct current.
- Surge, a note if the device has a motor or compressor that draws extra current at startup.
You can also add a column for notes about phantom loads or seasonal use. The goal is to capture every regular load so that nothing is forgotten.
Finding the Wattage of Each Device
The Virginia Cooperative Extension guide on estimating appliance energy use describes several ways to find a device’s wattage. The easiest is to look for the nameplate on the bottom or back of the appliance. The guide says the wattage listed is the power drawn by the appliance. If the nameplate shows only amperes (amps) and not Watts, you can multiply the amps by the voltage. Most household appliances in the United States use 120 volts, while larger appliances like clothes dryers and electric cooktops use 240 volts, according to the same Virginia Extension publication.
If the nameplate is missing or unreadable, the guide suggests using a clamp-on ammeter, a tool that clamps around one wire of the appliance to measure the current flowing while the device is running. The guide reminds users to follow the manufacturer’s safety instructions when using an ammeter. Once you have the amperage, multiply it by the voltage to get Watts.
Refrigerators and Cycling Loads
Some appliances do not run continuously even when they are plugged in. A refrigerator cycles on and off to maintain its interior temperature. The Virginia Cooperative Extension guide recommends a simple rule: to estimate the number of hours a refrigerator actually operates at its maximum wattage, divide the total time the refrigerator is plugged in by three. For example, a refrigerator that is plugged in 24 hours a day would run for about 8 hours at its rated wattage. You would then multiply the refrigerator’s wattage by 8 hours to get the daily watt-hours. Other appliances that cycle on and off need the same kind of thinking about real run time.
Phantom Loads
Many appliances continue to draw a small amount of power even when they are switched off. The Virginia Cooperative Extension calls these “phantom loads” and notes that they occur in most appliances that use electricity, such as televisions, stereos, computers and kitchen appliances. Most phantom loads add only a few watt-hours to the appliance’s daily consumption, but they can add up across many devices. The guide states that phantom loads can be avoided by unplugging the appliance or by using a power strip and switching it off to cut all power. When building a load list, you may choose to include a small allowance for phantom loads or simply plan to eliminate them with switched power strips.
Motor Start Current and Inrush
Devices with electric motors, such as refrigerators, fans, pumps and power tools, draw more current for a brief moment when they start than they do while running. The Virginia Cooperative Extension guide notes that when measuring the current drawn by a motor, a clamp-on ammeter will show about three times more current during starting than when the motor is running smoothly. This extra demand is a normal part of motor design.
Victron Energy’s 2013 book Energy Unlimited, written mainly for boats and vehicles with lead-acid batteries, discusses how to handle the inrush current of AC electric motors. Inrush current is the surge of current that flows when a motor first energizes, and it can be several times the normal running current. When you build a load list, it is wise to note which loads have motors so that you can later size the inverter and battery bank to handle these short bursts without tripping protection or causing voltage drops. The surge column in your load list is the place to mark these loads.
AC Loads and Inverter Losses
If your system will power AC appliances from a battery, you need an inverter to convert DC to AC. The Hong Kong Electrical and Mechanical Services Department states that the conversion efficiencies of inverters of different designs are generally in the range of 85% to 95%. This means that some energy is lost as heat during the conversion. When you calculate the total daily watt-hours from your load list, you must account for that loss if the loads are AC. For example, if your AC loads total 1,000 Wh per day and your inverter is 90% efficient, the battery must supply about 1,111 Wh (1,000 divided by 0.9). You can learn more about inverter selection in our Inverters guide.
Putting It Together: A Worked Example
The table below shows a simple load list with three devices, using round numbers for illustration. The wattages are taken from the typical ranges published by the Virginia Cooperative Extension. The refrigerator run time is calculated using the divide-by-three rule.
| Device | Watts | Hours per Day | Watt-Hours per Day | AC or DC | Surge |
|---|---|---|---|---|---|
| Laptop | 50 | 4 | 200 | AC | No |
| Refrigerator (frost-free, 16 cu ft) | 725 | 8 (24 h plugged in ÷ 3) | 5,800 | AC | Yes (motor) |
| Window fan | 200 | 4 | 800 | AC | Yes (motor) |
In this example, the total daily AC energy is 6,800 Wh. If the inverter efficiency is 90%, the battery would need to supply roughly 7,556 Wh per day. This daily energy figure is the starting point for sizing the battery bank and solar array. For worksheets and formulas that help with those next steps, visit our Planning Worksheets area and the Energy Needs category page.
Frequently asked questions
Do I need to list every tiny load, like a phone charger?
It is best to include every regular load, even small ones. Even a low-wattage device adds up if it runs for several hours a day. Small loads add up, and leaving them out can lead to an undersized system. The Virginia Cooperative Extension guide shows that even a clock radio at 10 Watts can matter over time.
How do I handle a device that runs on both AC and DC, like a laptop with a car charger?
List the device according to how you actually plan to power it. If you will use a DC car charger plugged into a 12 V outlet, treat it as a DC load and skip the inverter losses for that device. If you will use the standard AC power adapter, list it as an AC load and include the inverter efficiency factor. The wattage may differ slightly between the two methods, so check the label on the charger you intend to use.
What if I cannot find the wattage and do not own a clamp-on ammeter?
The Virginia Cooperative Extension guide provides a table of typical wattage ranges for many common appliances. You can use the middle of the range as a reasonable estimate, but keep in mind that your actual device may draw more or less. For a more accurate number, measure the current with a clamp-on ammeter as the guide describes, following the meter maker’s safety instructions.
Ready to turn your load list into a full system plan? Head over to the Energy Needs category for more detailed guides on sizing batteries, panels and inverters.
