Solar panel sizing
100W vs 200W Solar Panels
One big panel or two small ones? It sounds like a question about watts, but it is really a question about your roof. A single 200W panel wins on cost and simplicity when you have open space, while two 100W panels win on shade tolerance, fit, and redundancy when your roof is cluttered. Here is how to tell which situation you are in.
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| What matters | One 200W panel | Two 100W panels |
|---|---|---|
| Total footprint | ~11.9 sq ft, ~26.5 lb | ~12 sq ft, ~29 lb |
| Cost per watt | Lowest | A bit higher |
| Connections and brackets | Fewest | Double the fittings |
| Shade tolerance | One shadow hits everything | Lose one, keep the other |
| Fit on a cluttered roof | Awkward, one big piece | Slots between obstacles |
| Redundancy | Single point of failure | Half a system beats none |
| Controller | MPPT required | MPPT strongly advised |
Where each one wins
One 200W wins on open roofs
If your roof has a clear run of space, a single 200W panel is the smart buy. It is almost always the lowest cost per watt, and it needs just one set of brackets and one pair of connectors, so there is less to install and fewer points that can work loose over years of washboard roads. Cleaner roof, simpler wiring, more watts per dollar.
Two 100W win on real roofs
Most RV and van roofs are not open, they are full of vents, fans, and an AC shroud that throw shade and chop up the space. Two 100W panels fit between those obstacles, and wired in parallel they shrug off partial shade because losing one small panel costs you less than dimming one big one. If a panel fails, you still have half a system, not zero.
The footprint is almost identical
People assume two 100W panels eat far more roof than one 200W. They do not. A 200W panel runs about 58 by 27 inches, near 11.9 square feet and roughly 26.5 pounds. Two 100W panels come to about 12 square feet together and around 29 pounds. So the total area is a wash and the weight difference is minor. What changes is the shape of that area. The single panel is one rigid rectangle that has to find one open spot. The two panels are two smaller rectangles you can scatter around the roof, which is exactly why they fit rigs where the big panel never could.
The electrical difference, in plain numbers
Using typical Renogy-class figures, two 100W panels in parallel put out about 20.4 volts at roughly 9.82 amps, while one 200W panel runs about 22.6 volts at 8.85 amps. That higher voltage on the 200W is why an MPPT controller is effectively required to convert it down to charge a 12V battery. The two parallel 100W panels sit at a low enough voltage that they can technically run on a PWM controller, but you should still use MPPT to claw back the 15 to 30 percent more power it captures. Either way, MPPT is the safe default.
Wiring shapes the rest. More panels means more MC4 connectors and a slightly higher chance of one working loose, but it buys you that shade resilience in parallel. Fewer panels means simpler wiring and a cleaner roof, at the cost of a single point of shade or failure. For sizing the controller, take total array watts divided by battery voltage and add headroom: a 200W array on 12V is around 17 amps, so a 20A MPPT works, while a 400W array is about 33 amps and wants a 40A controller. Series wiring lowers the current the controller sees, which lets you run thinner wire, while parallel raises it.
Which should you buy?
For an open roof and the best value, buy one 200W panel. It is the lowest cost per watt, the simplest wiring, and the fewest things that can fail. When you have the space, it is the obvious choice.
For a cluttered or shaded roof, buy two 100W panels. They fit between the obstacles, tolerate partial shade far better in parallel, and leave you with half a system if one ever fails. Pay a little more per watt to buy that flexibility. If you are kitting out an RV specifically, our best RV solar panels page picks the exact panels and mounts to use.
Keep going
- Pick the exact panels: Best RV Solar Panels.
- See it in a full setup: The Classic 400W RV Build.
- Run your own numbers with the solar calculator.
- Start from the solar panels hub.
Frequently Asked Questions
Is one 200W panel better than two 100W panels?
For most open roofs, yes. A single 200W panel is almost always the lowest cost per watt, and it needs one set of brackets and one pair of connectors instead of two, so there is less to install and less to fail. The catch is shade and roof clutter. If your roof is broken up by vents and fans, or if part of it spends the day in shadow, two 100W panels can actually deliver more usable power because losing one small panel hurts less than dragging down one big one. On a clear, open roof, buy the 200W.
Do two 100W panels take up more space than one 200W?
Not really, the total area is almost identical. One 200W panel is roughly 58 by 27 inches, about 11.9 square feet, while two 100W panels come to about 12 square feet together. The two-panel setup is slightly heavier, around 29 pounds against roughly 26.5 for the single 200W, but the real difference is shape. Two smaller panels split that area into pieces you can place around obstacles, which is the whole reason they fit roofs a single big panel never could.
When should I choose two 100W panels instead?
Choose two 100W panels in three situations. First, shade: if anything casts a shadow on your roof during the day, especially wired in parallel, partial shade on one small panel costs you far less total output than shade on one big panel. Second, an odd or cluttered roof: two smaller panels slot between vents, fans, and the AC unit where a single 200W simply will not fit. Third, redundancy: if one panel fails, you still have half a system instead of nothing, which matters a lot when you live on your solar.
Do I need an MPPT controller for either choice?
You effectively need MPPT for a 200W panel because its higher operating voltage, around 22.6 volts, has to be converted down to charge a 12V battery efficiently. Two 12V 100W panels in parallel run closer to 20.4 volts and can barely get by on a PWM controller, but you should still use MPPT to recover the extra 15 to 30 percent it captures. In short, plan on MPPT either way unless you are running a single small 100W panel on the tightest possible budget.
What size charge controller do I need?
Size the MPPT for total array watts divided by battery voltage, plus headroom. A 200W array on a 12V battery pulls roughly 17 amps, so a 20A or larger MPPT covers it. A 400W array on 12V is about 33 amps, which wants a 40A controller. Wiring matters too: series wiring lowers the current the controller sees for a given wattage, which lets you use a smaller controller and thinner wire, while parallel raises the current. Always leave a little headroom rather than buying right at the limit.