What size charge controller for a 200 watt solar panel?

Short answer

200 W of panels on a 12 V battery is about 16.7 A through an MPPT controller — 20.8 A with 25% headroom, so a 30 A controller, or a 20 A one at its limit.

How to work it out

MPPT: 200 W ÷ 12 V = 16.7 A
× (1 + 25% headroom) = 20.8 A → 30 A controller

A 200 W array — one panel or two 100 W panels — is the classic camper or boat setup, and the one size where PWM is still a reasonable choice if the panels are 12 V-class and wired in parallel.

Adjust for your project

More options: Headroom

Headroom

Your choice of margin: panels can briefly beat their rating on cold, bright days with passing clouds.

Controller size to look for30 A

Current with headroom: 20.8 A
Current with no headroom: 16.7 A
At other battery voltages (MPPT, with headroom): 24 V: 10 A · 48 V: 5 A

Also check the controller’s maximum PV input voltage against your array’s cold open-circuit voltage — that is the limit that damages controllers. Use the series and parallel calculator.

Before you wire itWire and fuse sizes come from NEC/ABYC ampacity tables and the equipment manual — have a qualified installer check them.

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MPPT solar charge controllerMatch both numbers on the box: output amps (this result) and maximum PV voltage (your array’s cold Voc).

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Controller size for other array sizes

Controller size for other array sizes
Solar array watts	Current with no headroom	Current with headroom	Controller size to look for
100	8.3 A	10.4 A	15 A
200	16.7 A	20.8 A	30 A
300	25 A	31.3 A	40 A
400	33.3 A	41.7 A	50 A
600	50 A	62.5 A	70 A
800	66.7 A	83.3 A	100 A
1000	83.3 A	104.2 A	104 A
1200	100 A	125 A	125 A

What to know about a controller for 200 W

20 A vs 30 A. Without headroom 16.7 A fits a 20 A controller; with 25% headroom it doesn’t quite. The 30 A size also leaves room for a third panel later.
PWM with two panels in parallel. Two of Victron’s example panels have a combined Isc of about 12.2 A; with headroom, about 15.3 A — a 20 A PWM controller.
Series needs MPPT. Two 100 W panels in series run at about 36 V; only an MPPT controller can use it — see two 100W solar panels in series.
Charge current vs battery. About 17 A is gentle on any 100 Ah battery.

Daily output for 200 W is on how much power a 200W solar panel produces per day. Bigger arrays: what size charge controller for a 400 watt solar panel and what size charge controller for 1000 watts of solar.

Different size? Use the full Charge Controller Size Calculator.

What you’ll need

PWM solar charge controllerBudget price
Simple and cheap for one or two 12 V panels on a 12 V battery. It ties the panel to battery voltage, so it harvests less than MPPT in cool weather.
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MPPT solar charge controllerMid-range price
Converts a higher panel voltage into charging current, so you can wire panels in series and lose less in the cables. Size it on output amps and maximum PV voltage.
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100 W solar panelMid-range price
The building block of most van, boat and RV systems. Check the data-sheet Voc and Isc before you decide how to wire several of them.
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Frequently asked questions

What size PWM charge controller for two 100 W panels in parallel?

15.3 A with headroom — a 20 A PWM controller.

What size charge controller for a 100 W solar panel?

About 10.4 A with headroom — a 15 A controller.

Other common sizes

What size charge controller for a 400 watt solar panel — 50 A MPPT on 12 V (33.3 A minimum)
What size charge controller for 1000 watts of solar — 60 A MPPT on 24 V (too much for one on 12 V)

Sources

Victron Energy — Which solar charge controller: PWM or MPPT? (2020) (opens in a new tab) — MPPT output current = panel watts ÷ battery voltage (100 W ÷ 13 V = 7.7 A); a PWM controller pulls the panel down to battery voltage (81 W from a 100 W panel at 25 °C, about the same as MPPT at 75 °C); temperature-coefficient method; example panel Voc 21.6 V, −0.35 %/°C.
Victron Energy — Energy Unlimited (book) (opens in a new tab) — Lead-acid charge efficiency 80–95% (85% suggested as a starting value); battery energy efficiency about 75% for full cycles, about 89% in partial state of charge; inverter efficiencies above 90%.