Will your solar panels actually keep up?
Real solar harvest is far below the number printed on the panel. Set your load and array, and we show the honest daily balance — harvest vs draw, the recharge deficit, and how many watts you’d truly need to run indefinitely. This is the input-reality math a spec sheet never shows.
A 200 W array does not make 200 Wh a day. On a typical 4 peak-sun-hour day, after real-world losses it harvests about 560 Wh — roughly 2.8 Wh per watt of panel. Everything below uses that honest figure.
- Daily draw
- 2,593 Wh
- Daily harvest
- 560 Wh
- Daily deficit
- −2,033 Wh
- Runs for
- ~6 days
☀️ Your 200 W array only slows the drain — you still lose 2,033 Wh a day. To break even you’d need about 950 W of panels.
This is the smallest station that covers your load; a bigger battery lasts more days before the deficit empties it, but only more panels (up to the input cap) or a lighter load removes the deficit. Size both in the full sizing tool.
Harvest, not nameplate
The single biggest mistake in off-grid power planning is treating a panel’s watt rating as its daily output. Between sun angle, heat, clouds, cabling, and the handful of genuinely strong hours in a day, a real array delivers roughly 2.8 Wh per watt of panel per day — under our published assumption of 4 peak-sun hours and a 0.7 combined derate, the same figure the BatteryRank scores use. Every number here is that honest harvest, never the lab nameplate. See the methodology for the full derivation.
Solar questions, straight answers
- Why is my solar harvest so much lower than the panel's rating?
- A panel's nameplate wattage is measured in lab conditions — perfect sun, perpendicular angle, cool cells. In the real world you lose to sun angle, heat, clouds, cable and MPPT conversion, and the few genuinely peak hours in a day. We assume about 4 peak-sun hours and a combined 0.7 derate, so each watt of panel harvests roughly 2.8 Wh a day — a '200 W' array yields around 560 Wh, not 4,800. That gap is the whole reason people run out of power on day two.
- How many watts of solar do I need to run indefinitely?
- Enough that daily harvest matches your daily draw. Divide your battery-side consumption by about 2.8 Wh per panel watt: a fridge kit that consumes ~1,400 Wh a day needs roughly 500 W of panels to break even — and the station has to physically accept that much input, which is a separate hard cap. This tool shows both the required wattage and whether your chosen unit can take it.
- What is a recharge deficit?
- It's the gap between what your loads consume in a day and what your panels put back. If you consume 1,400 Wh and harvest 560 Wh, you run a 840 Wh daily deficit — the battery drains that much every day until it's empty. The tool converts that deficit into days-to-empty so you know whether a trip is survivable or you need more panels or capacity.
- Does a bigger battery fix a solar deficit?
- It buys time, not a solution. A larger battery holds more, so it takes more days to hit the deficit-driven empty point, but if harvest is below consumption you're still on a countdown. The durable fix is more panel wattage (up to the station's input limit) or trimming the daily load. Capacity and solar input are different levers — size both.