How many solar panels do I need for 500 watt-hours a day?

About 3 panels of 100 watts, or 222 watts total, assuming 3 peak sun hours and a 0.75 system derate. Fewer, larger panels install faster but are harder to fit around roof vents and air conditioners, so the panel count usually comes down to available roof area rather than watts.

What is the difference between peak sun hours and daylight hours?

Peak sun hours is the equivalent number of hours of full rated sunlight, not the number of hours the sun is up. A location can have nine hours of winter daylight and under two peak sun hours, because low sun angle, short days and cloud all reduce the energy reaching the panel. Sizing an array on daylight hours overestimates output badly.

Why is the array bigger than the daily load divided by sun hours?

Because panels do not deliver their nameplate rating in service. Heat reduces output, dust and pollen reduce it, wiring and the charge controller lose a little, and a flat RV roof is rarely aimed at the sun. The derate factor accounts for all of that. At 0.75, a 222 watt array behaves like about 167 watts.

Can I add panels to this array later?

Usually yes, but the charge controller sets the ceiling. A 30A controller on a 12 volt bank carries roughly 360 watts of panel, so check that headroom before adding. Mixing panels of different wattage or age on one controller also reduces output, so keep an added string on its own controller where that applies.

Solar

What Size Solar Array for 500Wh a Day at 3 Peak Sun Hours?

Researched from published standards and manufacturer specifications. Updated 2026-09-17.

Quick answer

Replacing 500 watt-hours a day at 3 peak sun hours needs about 222 watts of solar once a 0.75 system derate is applied, which is roughly 3 panels of 100W. That array produces about 18.5A at 12 volts, so it needs a 30A charge controller.

Array size comes from three numbers: how much energy you use in a day, how many peak sun hours your location gets, and how much of the panel's nameplate output you actually realize. This page fixes the first two at 500Wh and 3 hours.

Peak sun hours is not hours of daylight. It is the equivalent number of hours at full rated sun, and a nine hour winter day in a cloudy region may contain under two of them. Check your own figure on the peak sun hours by region chart, then run your numbers through the solar array calculator.

How many watts of solar for 500Wh a day?

The derate factor covers panel temperature, soiling, wiring loss, controller efficiency and imperfect aim. An RV roof is flat and cannot be tilted toward the sun, which is why the conservative end of the range is the honest planning figure.

Array size for 500 watt-hours a day at 3 peak sun hours
System derate	Conditions	Array size needed	100W panels
0.8	Cool, clean, well aimed	208 W	3
0.75	Typical flat RV roof	222 W	3
0.65	Hot or partly shaded	256 W	3

Convention Source: Common derate for real-world array output against nameplate rating.

How does this change with the seasons?

The same array produces very different amounts across the year, because peak sun hours move. This is the same 500Wh daily load against a range of sun hours.

Array needed for 500Wh a day across peak sun hour figures
Peak sun hours	Array needed	100W panels	Typical case
1.5 h	444 W	5	Northern winter
2 h	333 W	4	Northern winter
3 h	222 W	3	Winter, mid latitudes
4 h	167 W	2	Spring and fall
5 h	133 W	2	Summer, most regions
6 h	111 W	2	Summer, most regions
7 h	95 W	1	Desert summer

Published standard Source: Peak sun hours derived from published NREL insolation data. Array sizes use a 0.75 derate throughout. The seasonal labels are indicative and vary considerably by location.

What charge controller does this array need?

A 222W array on a 12 volt bank produces about 18.5A at nameplate output. Controllers get sized above that because panels produce more than their rating in cold, bright conditions, which puts the buy figure at 30A.

At this array size MPPT is still the better controller, though the gain over PWM on a small array is modest. See MPPT vs PWM and size it with the charge controller calculator.

Expert

Renogy

Renogy Rover 40A MPPT Charge Controller

$194.67

User-settable charge parameters mean you can set the correct lithium absorption and float voltages rather than accepting a lead-acid default.

Best for: A lithium bank that needs its own charge profile.

Check price on Amazon

Expert

Renogy

Renogy Rover 40A MPPT with Bluetooth

$197.40

Bluetooth means you can read actual harvest against your sizing assumptions instead of guessing at them.

Best for: Verifying an array is producing what it was sized for.

Check price on Amazon

What battery bank does this array support?

An array only matters alongside somewhere to put the energy. 500Wh a day is about 42Ah a day at 12 volts, which needs roughly 105Ah of LiFePO4 for two days of autonomy. That pairing is what keeps a cloudy day from ending the trip.

Solar kits around 222W

Expert

Renogy

Renogy 400W Premium Solar Kit with 40A MPPT

$637.99

Ships with an MPPT controller sized for the array, which removes the most common sizing error in a self-specified kit.

Best for: A full roof array bought as one part number.

Check price on Amazon

Intermediate

ECO-WORTHY

ECO-WORTHY 400W Kit with 40A MPPT

$449.99

Four 100W panels rather than two 200W ones, which gives more freedom to route around roof vents and air conditioners.

Best for: A cluttered roof that cannot take large panels.

Check price on Amazon

Expert

RICH SOLAR

Rich Solar 400W Premium Kit with 40A MPPT

$649.99

Two 200W panels plus mounting brackets, so the roof work is two panels instead of four.

Best for: An open roof where fewer, larger panels install faster.

Check price on Amazon

Beginner

Mndstek

Mndstek 400W Kit with 30A MPPT

$329.99

The lowest cost route to 400W, though the 30A controller is closer to its limit than the 40A units in this group.

Best for: A 400W array on a 12V bank and nothing more.

Check price on Amazon

Frequently asked questions

How many solar panels do I need for 500 watt-hours a day?: About 3 panels of 100 watts, or 222 watts total, assuming 3 peak sun hours and a 0.75 system derate. Fewer, larger panels install faster but are harder to fit around roof vents and air conditioners, so the panel count usually comes down to available roof area rather than watts.
What is the difference between peak sun hours and daylight hours?: Peak sun hours is the equivalent number of hours of full rated sunlight, not the number of hours the sun is up. A location can have nine hours of winter daylight and under two peak sun hours, because low sun angle, short days and cloud all reduce the energy reaching the panel. Sizing an array on daylight hours overestimates output badly.
Why is the array bigger than the daily load divided by sun hours?: Because panels do not deliver their nameplate rating in service. Heat reduces output, dust and pollen reduce it, wiring and the charge controller lose a little, and a flat RV roof is rarely aimed at the sun. The derate factor accounts for all of that. At 0.75, a 222 watt array behaves like about 167 watts.
Can I add panels to this array later?: Usually yes, but the charge controller sets the ceiling. A 30A controller on a 12 volt bank carries roughly 360 watts of panel, so check that headroom before adding. Mixing panels of different wattage or age on one controller also reduces output, so keep an added string on its own controller where that applies.

Wiring safety. Never exceed a conductor's rated ampacity, and always fuse a circuit at or below what the wire can carry, because the fuse protects the wire rather than the appliance. Fuse every positive conductor as close to the battery as practical. Use proper crimped lugs and heat shrink rather than twisted joints, support cable so it cannot chafe through on a frame edge, and keep the battery compartment ventilated. Permanent AC wiring is work for a qualified RV technician or a licensed electrician.