Get More From Your Solar Panels and Power Station

What a panel's watt rating really means

A panel's watt rating is measured in a lab under "standard test conditions": 1,000 watts of sunlight per square meter hitting it straight on, with the cells at 77°F (25°C). Renogy's 100 W panel datasheet lists exactly those conditions. Outside, you rarely get all of that at once. The sun is lower than overhead most of the day, the panel heats up, and some power is lost in the cable and the charge controller.

That's why solar planning uses sun hours, the number of hours of full-strength sun your location gets in a day once the weaker morning and evening light is added up. NREL's solar maps show roughly 3 to 6 for much of the U.S., with fewer in winter.

Watts × sun hours × 0.75, the same assumption our Power Station & Solar Sizer Calculator uses. A panel aimed well beats these numbers. A shaded or badly aimed one falls short.

Aim it at the sun

A panel makes the most power when sunlight hits it straight on, at a right angle. The further it points away from the sun, the less light it catches. The loss is small at first and grows quickly:

Direct sunlight only. The loss follows the cosine of the angle between the sun and the direction the panel faces.

The sun crosses the sky at 15° an hour. Set a portable panel up at noon and walk away, and by mid-afternoon it's pointing 30° or more behind the sun. That's why re-aiming pays off.

• Use the shadow trick. When a panel faces the sun squarely, its shadow sits directly behind it and is as small as it gets. Turn and tilt the panel until the shadow shrinks to its smallest.
• Re-aim every hour or two. Each time you walk past, turn it to follow the sun. Pick a spot with a clear view to the southwest so the afternoon sun stays on it.
• Don't lay it flat. A flat panel loses about 13% over a year at 40° north compared with a well-tilted one, and much more in the morning, evening and winter, when the sun is low.
• Morning setup: face it east-southeast. Midday: south. Late afternoon: west-southwest.

Tilt and direction for a panel you can't move

A panel on a van or trailer roof, or a cabin rack, stays put. In the U.S., face it true south and tilt it to about your latitude. Penn State's solar course and Renogy both give that rule of thumb.

• Summer: latitude minus 15°. At 40° north, that's 25°.
• Winter: latitude plus 15°. At 40° north, that's 55°.
• Spring and fall: about your latitude.

Getting it close matters more than getting it exact. Penn State's figures for a site near 40° north show how forgiving it is:

Tilt and orientation factors for a site near Wilmington, Delaware (about 40° N), from Penn State's EMSC 297 course. Renogy also suggests at least 10° of tilt so rain can rinse off dust.

A flat RV roof panel gives up a little all year and a lot in winter. If you camp in the colder months, a tilting bracket or a ground panel you can aim earns its keep.

Shade is the biggest thief

The cells inside a panel are wired in a chain, one after another. Shade one cell and it chokes the current for the whole chain, so a shadow covering a small corner can cut output far more than its size suggests. Bypass diodes help by letting current skip around a shaded section. Most panels have two or three of them, each covering a section of cells. Renogy's 100 W panel has two.

• Branches, tent lines, a roof rack crossbar or a camp chair all count. Even a thin shadow line across the panel costs power.
• Check the shade for the whole day, not just now. A tree that's clear at 10 a.m. may shade the panel by 2 p.m. Watch where shadows are heading.
• Use an extension cable. It's usually better to run 20 to 30 ft of solar extension cable out to a sunny spot than to park the panel in partial shade next to the tent.
• Studies have measured big losses. One study cited by SunSave found partial shading from a nearby obstruction cut performance by as much as 80%.

Keep it cool and clean

Heat

Solar panels make less power as they get hotter. Renogy's 100 W panel loses 0.37% of its output for every degree Celsius above 77°F (25°C). In normal sun its cells run around 47°C (117°F), which already costs about 8%. A panel lying on hot sand or a dark roof with no air behind it can run hotter still. At 65°C (149°F), the loss is about 15%.

• Prop it on its kickstand so air flows behind it. Don't lay a folding panel on hot ground.
• Cold, clear days are great for solar. A cold panel actually beats its rating when the sun is strong.

Dirt, dust and pollen

NREL found that pollen cut solar farm output by as much as 15% at the peak of pollen season, and that rain didn't wash it all off. Dust, bird droppings and tree sap do the same thing on a camping panel.

• Wipe it with water and a soft cloth. Skip anything abrasive that can scratch the surface.
• Check it after dusty roads and windy days, and every morning on long trips.

Connecting more than one panel

Two panels can be connected two ways, and the difference matters for your power station.

From the RNG-100D-SS datasheet: 24.3 V open circuit, 4.91 A at maximum power, 5.21 A short circuit.

Every power station lists a solar input voltage range, a maximum current and a maximum watts. The EcoFlow DELTA 2 Max, for example, takes 11 to 60 V, up to 15 A and 500 W per solar port, and its manual warns that going over 60 V can damage it.

• Use the panel's open-circuit voltage (Voc), not its working voltage. Voc is the highest voltage the panel puts out, with nothing drawing power.
• Cold raises the voltage. Renogy's panel gains 0.28% Voc for every degree Celsius below 77°F. Two in series read 48.6 V at 77°F and about 53 V at 14°F (minus 10°C), still under a 60 V limit. Three in series is 72.9 V before the cold even starts, which is too much for that input.
• Parallel keeps the voltage low. It's the safe choice when the station's voltage limit is tight. Just keep the total current under the station's limit.
• Extra watts are wasted, not harmful. A station that accepts 200 W of solar will only take 200 W, even with 400 W of panels connected. More panel than the limit can still help on cloudy days or in the morning and evening.
• Match your panels. Mixing different panels in series lets the weakest one set the current for both.

Power station basics

Watt-hours are the size of the tank

Power stations are rated in watt-hours (Wh). Not all of it reaches your gear. Jackery's manuals estimate run time as capacity × 0.85 ÷ the device's watts, to allow for conversion losses. A 1,000 Wh station running a 60 W CPAP gives about 1,000 × 0.85 ÷ 60 = 14 hours.

Watts are the size of the pipe

The AC output rating is the most the station can supply at once. Add up everything you'll run at the same time and stay under it. The surge rating covers the short start-up kick of motors and compressors. The DELTA 2 Max, for example, is rated 2,400 W continuous and 4,800 W surge. A fridge that runs at 400 W can pull over 2,000 W for a moment as it starts, per Champion's wattage chart.

Use DC outlets when you can

Every AC outlet runs through the station's inverter, which loses some energy as heat and draws power just being switched on. Charging phones from USB and running a 12 V cooler from the 12 V socket skips that step. Turn the AC output off when nothing is plugged into it.

Pass-through charging

Many stations can power your gear while they charge. On the DELTA 2 Max, when it's plugged into the wall with AC on, your devices run straight from the wall and the battery just charges. Check your model's manual. Not every station handles this the same way.

Lithium iron phosphate lasts longer

Most newer stations use lithium iron phosphate (LiFePO4 or LFP) cells. EcoFlow rates the DELTA 2 Max's LFP battery for 3,000 cycles before it drops to 80% of its original capacity. That's years of weekend trips. Check the spec sheet for "LFP" or "LiFePO4" when you shop.

Not sure what size you need? Our Power Station & Solar Sizer Calculator adds up your gear and sizes the station and panel. Running gear from a separate battery and inverter? Use the Inverter Run Time Calculator.

Temperature, storage and battery life

From the EcoFlow DELTA 2 Max user manual. Other models are similar, but check yours.

• Don't charge below freezing. Charging cold lithium cells damages them. Most stations block charging when they're too cold. Bring the station into a warm tent or vehicle overnight and let it warm up before solar charging in the morning.
• Keep it out of a hot car. A closed vehicle in summer sun easily passes 113°F. Shade the station at camp too, and keep its vents clear.
• Store it partly charged. Anker recommends 50 to 80% for storage and a check every three months, topping up if it has dropped below 50%. EcoFlow's manual asks for a full charge-and-discharge cycle every three months, ending at 60%.
• Avoid leaving it at 0% or 100% for weeks. Both ages the battery faster.

A day at camp, start to finish

1. Before you leave. Charge the station to 100% at home. Test the panel with the station in the yard so you know the cables and connectors work.
2. Pick your site with the sun in mind. Look for a clear view from southeast to southwest. Note which trees will shade the area in the afternoon.
3. Morning. Set the panel up facing east-southeast as soon as the sun clears the trees. Wipe off dew and dust. Keep the station in the shade with the cable run out to the panel.
4. Through the day. Re-aim every hour or two using the shadow trick. Watch the station's input watts. A sudden drop usually means shade has crept onto the panel.
5. Run big loads in the sun. Make the coffee or charge tool batteries while solar is pouring in, not at night.
6. Evening. Turn off the AC output if nothing needs it. Bring the panel in if wind or rain is coming.
7. Overnight in the cold. Keep the station inside the tent or vehicle so it's warm enough to charge in the morning.

Mistakes to avoid

• Buying panels before checking the station's solar input. Match the connector, voltage range and watts.
• Charging through a window. Glass and tinting cut the light reaching the panel. Put the panel outside.
• Setting it up once and forgetting it. A panel aimed at the morning sun is pointed well away from the afternoon sun.
• Expecting the label wattage. 70 to 80% of rated watts in good sun is normal.
• Leaving AC on all night for one small device. Use USB or 12 V outlets where you can.
• Running a fuel-burning heater in a tent. A power station makes no exhaust, but a gas or propane heater can produce deadly carbon monoxide.

Questions people ask

How big a panel do I need?

Enough to replace what you use each day. If your gear uses 600 Wh a day and you get 5 sun hours, you need about 600 ÷ (5 × 0.75) = 160 W of panel. Round up to 200 W. The Power Station & Solar Sizer Calculator does this for your own gear and location.

Will solar work on a cloudy day?

Yes, but less. How much less depends on how thick the clouds are, and heavy overcast can cut output to a small fraction of a sunny day. Plan your battery for the cloudiest day you expect, or bring more panel than you need.

Can I use panels from a different brand?

Usually, as long as the voltage, current and watts are within the station's solar input limits and you have the right adapter cable. Many stations use an Anderson, XT60 or 8 mm connector, while most panels use MC4 plugs.

Can I charge the station while I use it?

Most stations allow it from solar. Some, like the DELTA 2 Max on wall power, run your gear straight from the source while the battery charges. Check your manual.

Is a power station safe to use inside a tent?

It makes no fumes, so yes, with the usual care: keep its vents clear, keep it dry, and don't cover it with sleeping bags.