Solar Panel Size Calculator for Medical Devices
How many watts of solar do you actually need to keep your CPAP, oxygen concentrator, or insulin fridge running through a multi-day outage? Enter your battery size and device — this calculator gives you a real number, not a marketing estimate.
Quick answer:
For most CPAP users with a 1,024Wh power station, one 200W panel in a 5-peak-sun-hour location will recharge enough in a day to cover the next night. For home oxygen concentrators, you need significantly more — the calculator shows exactly how much.
A power station is a bucket. A solar panel is the tap that refills it.
If you only need one night of backup, you can get by with a full battery and no panels. But for outages that run two, three, or four days — hurricane recovery, ice storm damage, rural grid instability — a battery alone is not a plan. You need to replace what you use every day before the next night starts.
That is what solar panels do. The question this calculator answers is a specific one: how many watts of solar input do you need to recharge your specific battery fast enough to guarantee uninterrupted medical device use the following night?
The answer depends on three things: your battery size, how much power your device uses per day, and how many hours of usable sunlight your location gets. This tool calculates all three together. It tells you the minimum panel wattage that keeps your battery ahead of your device’s daily consumption — and flags where a single panel is not enough.
Who this tool is for
This calculator is for patients and caregivers who already have — or are planning to buy — a portable power station and want to add solar panels to create a self-sustaining backup system.
It is specifically built for:
- CPAP and BiPAP users preparing for multi-night outages in storm-prone regions
- Portable oxygen concentrator patients who cannot afford a gap in therapy during extended grid failures
- Insulin-dependent patients running a 12V cooling fridge who need indefinite refrigeration coverage
- Home oxygen concentrator users building a layered backup plan
- Anyone who has a power station and wants to know whether one panel, two panels, or more is the right call
This is not a rooftop solar calculator. It does not calculate system payback, roof orientation, or grid-tie setups. It is built specifically for portable foldable solar panels paired with portable power stations in a medical backup context.
About the data in this tool
The calculation behind this tool uses published solar irradiance data, real-world panel efficiency losses, and typical medical device power consumption figures.
What the tool uses
Peak sun hours: The tool uses a location-based estimate of daily peak sun hours (PSH) — the number of hours per day when sunlight intensity is strong enough for meaningful solar panel output. This varies from about 3.5 PSH in cloudy northern states like Washington and Maine to 6.5 PSH in the desert Southwest. The tool defaults to 4.5 PSH as a conservative national average; you can adjust it for your location.
System efficiency: Real-world solar panel output is typically 75–80% of the rated wattage after accounting for heat losses, angle imperfection, partial shading, dust, and cable losses. The tool applies an 80% derate factor by default, which is realistic for a well-positioned portable panel in typical conditions.
Daily energy budget: The tool calculates how many watt-hours your medical device uses per day based on its wattage and your estimated usage hours, then adds a 10% buffer for inverter losses and conservative margin.
Required solar wattage: Minimum panel watts = daily watt-hours needed ÷ (peak sun hours × system efficiency). This is the smallest solar input that can fully replace your daily device consumption before the next night begins.
What the tool does not assume
It does not assume you will get 6 hours of peak sun every day. Realistic planning means sizing for your average, not your best day.
It does not assume you are starting each day at 100% battery. A conservative sizing plan treats each day as independent.
It does not assume one panel configuration works for all use cases. CPAP, portable oxygen, and home oxygen are very different loads. The tool sizes for your actual device.
It does not assume portable panels can always match their rated output. Temperature, angle, shading, and panel age all reduce real output. That is why the 80% derate is built in.
How to use the result responsibly
Use the result as a minimum target, not an exact specification.
Before buying panels, confirm:
- The maximum solar input wattage your power station accepts — this is listed in the station's spec sheet as "max solar input" or "PV input." Do not buy more panel wattage than your station can accept, or the excess is wasted.
- Whether your power station uses MC4, XT60, Anderson, or proprietary connectors — and whether the panel you're buying includes the right cable or requires an adapter.
- Whether you can realistically position the panel in direct, unshaded sunlight for 4–6 hours during an outage. A panel in partial shade performs 30–60% below rated output.
- That your peak sun hours match your location and season. A 4.5 PSH estimate is accurate for summer in the mid-Atlantic states, but drops to 3.0–3.5 PSH in winter or in consistently overcast climates.
For home oxygen concentrator patients: the required solar wattage often exceeds what a single foldable portable panel can supply. Two or three panels, or one rigid high-wattage panel, is typically required. The calculator will flag this when your device load exceeds what a single-panel setup can realistically handle.
Why solar sizing matters differently for medical patients
For recreational users, running short on solar recharge is an inconvenience. For a CPAP patient in day three of a storm outage, it means going without therapy by evening — or worse.
The standard advice in solar generator marketing is to pair a 200W panel with a 1,000Wh station and call it a system. That advice is based on recreational use assumptions. A camper who uses a station for phone charging, lights, and a fan draws far less daily energy than a CPAP patient running humidifier plus pump for 8 hours.
Here is a concrete example of why those recreational sizing guides fail medical patients.
A CPAP user with a heated humidifier running at 90W for 8 hours per night uses approximately 900Wh per night. After inverter losses, they need the battery to supply about 1,000Wh. A 1,024Wh station running this setup needs a near-complete recharge every day.
A 200W panel in 4.5 peak sun hours delivers approximately 200 × 4.5 × 0.80 = 720Wh per day. That replaces 72% of what was used — not enough for a complete recovery. By day two, the battery is running at partial capacity. By day three, it may not make it through the night.
The correct sizing for this patient is closer to 280W of solar input — either a single 300W panel or two 160W panels in parallel. That is a meaningfully different purchasing decision.
This tool gives you the honest number before you buy.
How the calculator works
The tool uses a three-step calculation:
Step 1 — Daily energy used: Daily Wh = Device wattage × Hours of use per day × (1 ÷ AC inverter efficiency) This calculates how many watt-hours are pulled from the battery each day, including inverter losses.
Step 2 — Minimum solar output needed: Required daily solar output (Wh) = Daily Wh used + 10% buffer The buffer accounts for cloudy periods, brief shading, and conservative safety margin.
Step 3 — Minimum panel wattage: Panel watts needed = Required solar output ÷ (Peak sun hours × Derate factor) The derate factor (default 0.80) reflects real-world losses from heat, angle, and cable resistance.
The "Show the math" toggle inside the tool breaks this down with your exact inputs, so you can verify the logic yourself or share it with your DME supplier or caregiver.
Solar sizing by device: what to expect
CPAP without humidifier (~30–40W, 8 hours per night) Daily use: approximately 320Wh. One 100–160W panel in a good-sun location (5+ PSH) covers this comfortably. One 100W panel in a marginal-sun location (3.5 PSH) may fall slightly short — size up to 160W for reliability.
CPAP with heated humidifier (~80–100W, 8 hours per night) Daily use: approximately 720–900Wh. This requires 200–280W of solar input. A single 200W panel in 4.5 PSH covers it in most cases; a 160W panel does not. For overcast climates, two 160W panels or one 220W+ panel is the safer specification.
BiPAP / ASV (~100W, 8 hours per night) Similar to CPAP with humidifier. 200–250W of solar input is the practical minimum for reliable daily recharging.
Portable oxygen concentrator (~45–60W, 12–16 hours per day) Daily use: 540–960Wh depending on continuous vs. pulse-dose and flow rate. One 200W panel handles pulse-dose use in good sun. Continuous-flow at higher settings may require 250–300W.
Home oxygen concentrator (~300W, 12–18 hours per day) Daily use: 3,600–5,400Wh. A single portable panel cannot address this. Even three 200W panels (600W rated, ~480W real) provide only 2,160Wh per day in 4.5 PSH — still below the minimum. Home oxygen concentrator patients require a layered backup plan that includes oxygen cylinder reserves, generator recharging, or large-scale battery plus roof-mounted panel systems. The tool will flag this scenario and redirect to appropriate guidance.
12V insulin fridge (~35–50W, 24 hours per day) Daily use: approximately 840–1,200Wh. One 200W panel with a 1,024Wh battery covers this well in most sun conditions, with enough surplus to charge a CPAP or keep phones and pumps running.
Peak sun hours by region: a practical reference
Peak sun hours (PSH) is the number of equivalent full-sun hours per day your location receives, averaged across seasons.
This is not the same as daylight hours. A partly cloudy 10-hour day might deliver only 3.5 PSH of effective charging. Using realistic PSH figures — not the best-day number — is what separates a plan that works from one that fails on day two of an outage.
Practical regional averages (annual, not summer peak):
- Pacific Northwest (Seattle, Portland): 3.5–4.0 PSH
- Northeast (Boston, New York, Philadelphia): 4.0–4.5 PSH
- Southeast (Atlanta, Charlotte, Tampa): 4.5–5.5 PSH
- Gulf Coast / Florida: 5.0–5.5 PSH
- Midwest (Chicago, Columbus, Minneapolis): 4.0–4.5 PSH
- Great Plains (Denver, Dallas, Oklahoma City): 5.0–6.0 PSH
- Desert Southwest (Phoenix, Las Vegas, Albuquerque): 6.0–6.5 PSH
- Mountain West (Salt Lake City, Boise): 5.0–5.5 PSH
For outage planning purposes, use the annual average, not the summer figure. Hurricanes and ice storms — the most common long-outage triggers — often arrive in seasons with lower solar output.
Common questions
Frequently asked questions
The questions our readers ask most — answered clearly and Without jargon.
Yes, within limits. Each power station has a maximum solar input wattage and voltage it will accept. Connecting panels in parallel increases current (amps) without increasing voltage — a safe approach for most stations. Connecting panels in series increases voltage — check your station's maximum input voltage first. Exceeding it can damage the MPPT controller. Your station's manual lists both limits.
No. All of the panels listed above use industry-standard MC4 connectors or include adapters. Most power stations accept solar input via MC4 or a proprietary connector (XT60i for EcoFlow, DC8020 for Jackery, MC4 for Bluetti and most others). Adapter cables are widely available on Amazon for under $10 and allow cross-brand pairing.
Shade is the biggest killer of real solar output. Even 20% shading of one panel can reduce total output by 30–50% on some systems. For outage use, position the panel in the clearest, most unobstructed location available — a south-facing front yard, a driveway, or a balcony railing. Foldable panels are easy to reposition as the sun moves.
Yes, if it is properly weighted or staked. All four panels recommended above are rated IP65 or IP68, meaning they are waterproof in rain. However, portable foldable panels are not designed to withstand sustained high winds. In storm conditions, bring the panel inside and switch to battery-only mode.
It means your daily device load exceeds what one or two standard portable panels can reliably replace. This is common for home oxygen concentrator patients and patients running multiple devices simultaneously. Your options are to use a larger battery (more days of reserve between solar recharges), add more panels (if your station accepts the combined wattage), or build a layered plan that includes other recharge sources — generator, car alternator, utility restoration. The Medical Power Outage Preparedness Checklist covers multi-layer planning in detail.
Solar panels generate power in any daylight, including overcast conditions — just less of it. On a heavily overcast day, output typically drops to 10–30% of the rated wattage. During a storm with full cloud cover, meaningful solar recharge is unlikely. Size your battery reserve to cover 1–2 days without any solar input as a baseline buffer.