How to Calculate Daily RV Power Use Before Sizing Solar
Part 2 of 8 in the RV Solar Planning Series.
Two RVs parked side by side can need very different solar systems. One may use propane for cooking and heating, while the other asks a battery bank to support a residential refrigerator, work equipment and several countertop appliances. Roof size does not reveal either energy budget.
Start with the 12-volt side
List the equipment that runs directly from the house battery: lighting, water pump, vent fans, furnace blower, detectors, control boards, USB outlets, jacks, slides, stabilizers, awning motors and any 12-volt refrigerator. Not every item runs daily, but high-current intermittent equipment still affects battery and protection requirements.
Propane appliances may still need 12-volt controls, ignition and fans. “Runs on propane” does not always mean “uses no battery.” Check the manual and label for the actual appliance.
Make a separate 120-volt inverter list
Record each AC appliance you want available away from shore power: microwave, coffee maker, television, laptop charger, medical device, residential refrigerator or air conditioner. Note its running watts, likely daily run time and any starting surge the manufacturer identifies.
Do not assume everything will run together. Build a realistic simultaneous-use plan. An inverter must support continuous and surge power, while the batteries, BMS, cables and fuses must support the DC current that creates that AC output.
Convert each load into daily energy
The basic calculation is:
watts × hours used per day = watt-hours per day
A 10-watt light used for three hours is 30 watt-hours. A 1,000-watt appliance used for six minutes is about 100 watt-hours because six minutes is one-tenth of an hour. For inverter loads, divide the AC watt-hours by the inverter efficiency used in the equipment documentation so conversion loss is included.
Duty-cycled equipment requires care. A refrigerator, furnace blower or air conditioner may turn on and off, so nameplate watts multiplied by 24 hours can badly overstate use. Measurement over a representative day is better when practical.
Use reliable inputs
Begin with equipment labels and manuals. For uncertain DC loads, a qualified person can measure current with appropriate instruments. Plug-in energy meters can help with compatible AC appliances. Record conditions because weather, thermostat settings and personal habits change results.
Add reserve without hiding the assumptions
Total the expected daily watt-hours, then choose a reserve for weather, changing habits and battery aging. Keep the base estimate and reserve separate so the plan remains understandable. “Extra” is not a number until it has a reason.
The load and energy worksheets in the Gram & Pap RV Solar Planning and Setup Guide carry the same inventory from 12-volt loads to inverter loads and daily watt-hours, so later battery and panel decisions use one consistent set of assumptions.
Make the energy budget honest
Solar planning improves quickly when every desired appliance has a row, a power figure and a run-time estimate. The calculator cannot decide what matters on a trip. It can show what those choices cost in stored energy.
Safety note: This article is a planning aid. RV electrical systems and equipment requirements vary. Follow current manufacturer manuals and applicable codes, and use a qualified RV electrician when the work or requirements are uncertain.
