Planning a DIY solar system starts on paper. A clear worksheet helps you understand your energy use and match components correctly before you buy anything. This guide walks you through two practical worksheets you can build yourself: a load list to capture what you need to power, and a design record to document the system you plan to assemble.

Before you start: These worksheets are planning tools, not wiring instructions. Connecting equipment to home wiring, a main panel or the grid requires a licensed electrician, permits and approval from your utility.

Worksheet 1: Your daily load list

The first step in any solar project is knowing how much electricity you will use. The Virginia Cooperative Extension explains that you can estimate an appliance’s energy consumption with a simple formula: multiply its wattage by the hours used per day, then divide by 1,000 to get daily kilowatt-hours (kWh). The U.S. Energy Information Administration (EIA) clarifies that a Watt measures power at a specific moment, while a Watthour measures energy used over time. One Watthour is the energy of one Watt used for one hour.

Build a table with these columns and fill in every device you plan to run.

Device Watts (W) Hours per day Watt-hours per day (Wh/day) AC or DC Surge note Notes
Example: LED light 10 5 50 DC None Two fixtures
Example: Laptop 50 4 200 AC None Charged via inverter

How to fill each column

Device. List every appliance, light, pump or electronic item you intend to power. Be specific: “kitchen lights (3 LED strips)” is more useful than “lights.”

Watts (W). The Virginia Cooperative Extension advises that you can find the wattage stamped on the bottom or back of most appliances, or on its nameplate. If the wattage is not listed, you can estimate it by finding the current draw in amperes and multiplying that by the voltage the appliance uses. Many appliances in the United States use 120 volts; larger appliances such as clothes dryers and electric cooktops use 240 volts. The source also notes that many appliances continue to draw a small amount of power when they are switched off. These phantom loads can be avoided by unplugging the appliance or using a power strip with a switch.

Hours per day. Record how many hours each device actually runs in a 24-hour period. The Virginia Cooperative Extension points out that refrigerators cycle on and off, so to estimate the hours a refrigerator actually operates at its maximum wattage, divide the total time it is plugged in by three.

Watt-hours per day (Wh/day). Multiply Watts by hours per day. The EIA states that electricity use over time is measured in Watthours. For example, a 40-Watt light bulb used for five hours consumes 200 Wh. Add all the Wh/day values to get your total daily energy need.

AC or DC. Mark whether the device runs on alternating current or direct current. This tells you whether an inverter is required and helps you account for conversion losses later.

Surge note. Some devices, especially those with motors, draw extra current when they start. The Virginia Cooperative Extension explains that a meter will show about three times more current when a motor starts than when it is running smoothly. Note any device that has a motor, compressor or pump so you can size your inverter to handle the surge.

Notes. Capture anything else that matters: quantity of identical devices, seasonal use, or whether the device can run directly from a DC source.

Worksheet 2: System design record

Once you know your daily load, you can sketch the system that will meet it. This second worksheet captures the key specifications of every major component and the assumptions behind your design. The Hong Kong Electrical and Mechanical Services Department (EMSD) describes the balance-of-system as all the components beyond the photovoltaic array itself, including charge controllers, batteries, inverters, mounting structures, wiring, switchgear and fuses.

Create a design record that covers these areas.

System voltage and array voltage

Record the nominal DC system voltage you have chosen (commonly 12 V, 24 V or 48 V). Then list the open-circuit voltage (Voc) of your solar panel array. According to Victron Energy’s Wiring Unlimited book, when designing a solar array you must make sure that the array’s open circuit voltage does not exceed the voltage rating of the charge controller. The book gives an example: a 12 V solar panel has a Voc around 22 V, and a controller rated for 75 V can accept up to three such panels in series.

Charge controller type

Note whether you are using a pulse-width modulation (PWM) controller or a maximum power point tracking (MPPT) controller. The EMSD explains that an MPP charge controller incorporates a DC-to-DC converter so the photovoltaic array can operate at a voltage that delivers maximum output power at the prevailing solar irradiance.

Battery chemistry and usable capacity

Record the battery chemistry (such as lead-acid or lithium iron phosphate), the total rated capacity in amp-hours, and the usable capacity you have designed for. The EMSD states that the storage capacity of a battery in kWh equals the Ah rating times the voltage rating divided by 1,000, and that an important consideration when sizing the battery system is the days of autonomy, which is the number of days the battery system can support the electrical loads without being recharged. The EMSD also notes that deep-cycle lead-acid batteries are the most popular type for photovoltaic systems and that their lifespan varies from 3 to 8 years.

Inverter continuous and surge ratings

Write down the inverter’s continuous output power and its surge rating. The EMSD says that inverters convert electricity from DC to AC and that conversion efficiencies are generally in the range of 85% to 95%. A Victron Energy inverter manual for one model lists a continuous output power of 750 W and a surge rating of 1400 W as an example of how these two figures appear on a specification sheet. Your own inverter’s manual will provide the numbers you need to record here.

Fuses and isolation

Document where overcurrent protection and isolation switches are placed. Victron Energy’s Wiring Unlimited states that, depending on local regulations, a fuse, circuit breaker, RCD or GFCI might need to be installed between the PV array and the solar charger. The same book says that solar panels are not allowed to be directly connected to a battery; a solar charger must be placed between the panels and the battery. Always follow the fuse and breaker guidance in your component manuals and the electrical code. A qualified electrician can confirm that your protection is correct.

Monitoring and grounding notes

Record how you will monitor battery voltage, state of charge and system performance. Note any grounding requirements from your inverter and charge controller manuals. The Victron inverter manual warns that operating an inverter without a proper ground connection may cause an electrical safety hazard.

Design assumptions

List the key numbers that drive your sizing calculations. For solar resource, the PVWatts Calculator from the National Laboratory of the Rockies provides location-based production estimates using 30 years of historical weather data. For system efficiency, the EMSD notes that the balance-of-system can account for up to half of the capital cost of a photovoltaic system and most of the maintenance cost, and that inverter conversion efficiencies are generally 85% to 95%, so conversion losses belong in your assumptions. Write down the sun-hours value you used and the overall efficiency derating you applied.

How to use the worksheets together

Start with the load list. Add up the Wh/day column to find your total daily energy requirement. Separate the AC loads from the DC loads so you can account for inverter losses later. The EIA explains that utility companies measure electricity in kilowatthours; your load list works the same way, just at a smaller scale.

Move to the design record. Use your total daily Wh figure to size the battery bank and the solar array. The solar sizing formulas article walks through the math. Enter every component specification into the design record so you have a single reference sheet when you buy parts and begin assembly.

Keep both worksheets updated. If you add a device or change a usage pattern, revise the load list and check whether your design record still works. This is a living document, not a one-time exercise.

Sanity-check list before you build

Before you purchase components or connect anything, run through these checks.

  • Confirm that no solar panel connects directly to a battery. Victron Energy’s Wiring Unlimited is explicit: a solar charger must sit between the panels and the battery, or the battery will get damaged.
  • Verify that the array Voc stays below the charge controller’s maximum voltage rating under the coldest expected conditions for your location.
  • Check that a fuse or circuit breaker is placed in the positive cable from the battery to the inverter, sized according to the inverter manual. The Victron inverter manual states that reverse polarity connection will blow the internal fuse and may damage the inverter permanently.
  • Ensure every DC connection is tight and follows the torque values in the component manuals.
  • Confirm that the inverter’s continuous rating covers your total running AC load and that its surge rating exceeds the starting surge of any motor load you noted in the load list.
  • Review your days-of-autonomy figure against your local weather patterns and your ability to reduce loads during cloudy periods.
  • If your system will connect to a building’s electrical system, stop and engage a licensed electrician. Permits and utility approval are required.

For a broader look at how these worksheets fit into a complete plan, see the system design guide. The DIY solar planning section covers energy needs, panel sizing and battery sizing in more depth. If you want to run the numbers before filling in the worksheets, the solar tools and calculators page points you to helpful resources.

Frequently asked questions

Can I skip the load list and just buy a kit?

A kit may work for very small, predictable loads, but without a load list you risk undersizing your battery or overloading your inverter. The Virginia Cooperative Extension method of multiplying wattage by hours of use gives you a real number to design around, rather than guessing. Even a rough load list is better than none.

What if I cannot find the wattage on my appliance?

The Virginia Cooperative Extension suggests checking the nameplate on the bottom or back of the appliance. If only amperes are listed, multiply the amps by the voltage the appliance uses (often 120 volts in the United States) to estimate wattage. As a last resort, the source mentions that a clamp-on ammeter can measure the actual current while the device is running, provided you follow the manufacturer’s safety recommendations.

Do these worksheets work for a vehicle or boat system?

Yes, the same principles apply. Victron Energy’s Wiring Unlimited book covers solar array wiring, cable selection and fuse placement, and the Phoenix inverter manual includes vehicle chassis grounding. The load list and design record structure remain the same; you will simply adapt the component choices to a mobile DC system.

Return to the planning worksheets category for related planning guides.

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