A solar generator is two products sold as one: a battery with an inverter, and a panel array that refills it. People size those two halves independently, and they get it wrong in both directions at once. They buy far more battery than they need and far less panel than they need, then wonder why the system never gets back to full. I spent a decade running a business from Bali on grid power that failed constantly, and I have made this mistake myself. This guide from E-Commerce Paradise sizes both halves together, with every figure traceable to a named source.
There are five steps. Daily load, then battery, then realistic peak sun hours, then the derating stack, then panel wattage. Then one constraint that overrides all of it, which almost nobody checks before buying.
Solar that actually refills the battery
BLUETTI publishes the solar input ceiling, the voltage window and the current limit for every unit, so you can check before you buy whether your panels will even connect. The AC200L accepts 12V to 145V at 15A up to 1,200 W.
Step 1: Compute the daily load in watt hours
Everything downstream depends on this number, so do it properly. List the devices, use published energy figures rather than the sticker on the back, and multiply by the hours you actually need each one.
Here is a realistic van or cabin day built entirely from manufacturer published figures.
| Load | Published figure and source | Hours or count | Watt hours per day |
|---|---|---|---|
| CPAP with humidifier | 22 watt hours per running hour, ResMed Air10 power consumption sheet | 8 hours | 176 |
| 12V compressor cooler | About 7.5 W average, implied by EcoFlow GLACIER running up to 40 hours on a 298 Wh battery | 24 hours | 179 |
| Fan | 40 W, BLUETTI Elite 100 V2 runtime table | 5 hours | 200 |
| Laptop charges | 60 Wh battery assumed, BLUETTI Elite 100 V2 runtime table | 2 charges | 120 |
| Phone charges | 15 Wh battery assumed, BLUETTI Elite 100 V2 runtime table | 3 charges | 45 |
| Total delivered at the socket | 720 |
That is 720 watt hours delivered. It is not 720 watt hours out of the battery, because the inverter loses energy turning direct current into alternating current. Across this cluster I plan on 85 percent of nameplate reaching an alternating current socket, and I state that assumption every time. So the battery must give up 720 divided by 0.85, which is 847 watt hours per day.
If a refrigerator is on your list, use the annual kilowatt hour figure from its EnergyGuide label rather than its plate wattage, for reasons I work through in the refrigerator runtime guide.
Step 2: Derive the battery size from days of autonomy
Days of autonomy is how long the system carries you with no meaningful solar input at all. Two overcast days in a row is a normal event almost everywhere. Three is common in winter in the north.
The arithmetic is daily draw from the battery, times days of autonomy, divided by the fraction of the pack you are willing to use. Take our 847 watt hours per day, two days of autonomy, and a decision to leave 20 percent in reserve rather than routinely running the pack flat:
847 times 2 is 1,694 watt hours. Divided by 0.8 that is 2,118 watt hours of nameplate capacity. So this system wants a machine in the 2,000 Wh class as a minimum, with the 3,000 Wh class giving genuine margin. The BLUETTI AC200L at 2,048 Wh and the Elite 200 V2 at 2,073.6 Wh both sit right on the line. The Elite 300 at 3,014 Wh gives you the third day.
Two notes on the reserve. Lithium iron phosphate packs in these units will happily discharge to zero, so the reserve is not a chemistry requirement. It is a planning requirement, because the day you actually need the last 20 percent is the day you did not plan for. And shallower cycles are gentler on cycle life, which is rated to a stated remaining capacity: the AC180 is rated “3,500+ Cycles to 80% Original Capacity” and the Elite 100 V2 is rated “4,000+ Cycles to 80% Original Capacity”.
Step 3: Peak sun hours, not the panel’s nameplate rating
Here is where the second big error lives. A 400 W panel does not produce 400 watts for every hour of daylight. It produces 400 watts under standard test conditions, which is 1,000 watts per square metre of irradiance at a cell temperature of 25 degrees Celsius. Real sunlight delivers far less than that for most of the day.
The correct unit is peak sun hours, which is the number of hours per day that would deliver the same total energy at that full 1,000 watts per square metre. Conveniently, peak sun hours are numerically equal to daily solar irradiance expressed in kilowatt hours per square metre per day, which is a figure you can look up.
The table below comes from the NASA POWER climatology dataset, parameter ALLSKY_SFC_SW_DWN, in kilowatt hours per square metre per day on a horizontal surface. I retrieved these values this session. Use the December column for any system that has to work year round, because the annual average will lie to you about January.
| Location | Annual average peak sun hours | December | June |
|---|---|---|---|
| Phoenix, Arizona | 5.85 | 3.08 | 8.50 |
| Los Angeles, California | 5.65 | 2.86 | 8.10 |
| Miami, Florida | 5.01 | 3.44 | 5.68 |
| Denver, Colorado | 4.85 | 2.29 | 7.22 |
| Austin, Texas | 4.81 | 2.74 | 6.70 |
| Atlanta, Georgia | 4.51 | 2.37 | 6.19 |
| New York, New York | 3.92 | 1.62 | 5.95 |
| Minneapolis, Minnesota | 3.86 | 1.31 | 6.04 |
| Chicago, Illinois | 3.84 | 1.41 | 6.10 |
| Seattle, Washington | 3.42 | 0.85 | 5.73 |
Look at Seattle. The annual average of 3.42 suggests a workable system. The December figure of 0.85 says that for one month a year, that system is a decoration. Look at Miami, which has a lower annual figure than Denver but a much better December. Seasonality matters more than the headline number for anyone planning backup power.
These are horizontal surface figures. Tilting a panel toward the low winter sun improves the December number meaningfully, which is an argument for portable folding panels you can aim rather than a flat roof mount, and it is one of the few places where portable beats permanent.
Step 4: The derating stack, or why 400 W of panel is not 400 W
Between the panel’s rating and the energy that lands in your battery sit a series of losses. NREL publishes the standard set in the PVWatts Version 5 manual, and its default total is the anchor everyone in the industry uses.
| Loss category | NREL PVWatts default | What it is |
|---|---|---|
| Soiling | 2 percent | Dust, pollen, salt, bird droppings on the glass |
| Shading | 3 percent | Partial shade from trees, vents, the van itself |
| Snow | 0 percent | Zero by default, not zero in Minnesota |
| Mismatch | 2 percent | Panels in a string never perform identically |
| Wiring | 2 percent | Resistance in the cable run |
| Connections | 0.5 percent | Every MC4 pair costs something |
| Light induced degradation | 1.5 percent | Cells lose output in their first hours of exposure |
| Nameplate rating | 1 percent | The panel may not meet its own label |
| Age | 0 percent | Zero for a new array only |
| Availability | 3 percent | Downtime for maintenance and faults |
| Total system losses | 14 percent | Compounded, not summed |
Temperature is the loss that is missing from that list and it is often the largest one. NREL lists a module power temperature coefficient of “-0.47 %/℃” for standard modules. A panel in full sun typically runs well above ambient, and a cell temperature 25 degrees above the 25 degree reference costs you close to 12 percent of rated output on its own.
Multiply the NREL default of 0.86 by a temperature factor of about 0.88 and you land at roughly 0.76. I plan on 0.75, and I state it every time I use it. Harvest equals rated panel watts times peak sun hours times 0.75.
Is 0.75 pessimistic? The manufacturers say no. BLUETTI rates the AC180, which holds 1,152 Wh, at a solar charging time of about 2.8 to 3.3 hours from a 500 W input, and adds the qualifier “With prime sunshine, ideal orientation and low temperature”. At 500 watts, 1,152 watt hours would take 2.3 hours if panels delivered their rating. BLUETTI’s own best case is 2.8 to 3.3 hours, which implies 70 to 82 percent of nameplate under ideal conditions. My 0.75 planning figure sits inside their own ideal case band, and real conditions are worse than ideal.
Step 5: Derive the panel wattage
You need to put back into the battery what you took out, plus the losses on the charging side. The battery gives up 847 watt hours per day in our example. Charge controller and charge acceptance losses take some of what the panel produces, so assume 90 percent gets in, and the panel must produce 847 divided by 0.9, which is 941 watt hours of direct current per day.
Required panel watts equals 941 divided by peak sun hours divided by 0.75. Run that for three places:
| Location and season | Peak sun hours | Panel watts needed for 941 Wh per day | Verdict |
|---|---|---|---|
| Denver, annual average | 4.85 | 259 W | A 300 W array is comfortable |
| Denver, December | 2.29 | 548 W | A 300 W array falls short by half |
| Phoenix, December | 3.08 | 407 W | A 400 W array just about holds |
| Seattle, December | 0.85 | 1,476 W | Not practical with portable panels |
That single table is the whole argument. The same load in the same country needs 259 W of panel or 1,476 W of panel depending on where and when you are. Any guide that tells you a 400 W kit is “enough for off grid living” without asking where you live is guessing.
Size the panel to your December, not your June
BLUETTI sells matched panel and station kits with published input ceilings, so you can verify the array will connect and charge before you spend anything. The Elite 300 holds 3,014 Wh with a 10 ms UPS switchover.
The charge controller input limit, which overrides everything above
You can own a thousand watts of panel and be unable to connect it. Every power station has a built in charge controller with three separate ceilings: a maximum wattage, a voltage window, and a maximum current. You must satisfy all three simultaneously, and the binding one is almost never the wattage.
| Model | Solar input ceiling as published | Practical consequence |
|---|---|---|
| BLUETTI AC60 | 200 W max, VOC 12V to 28V, 8A | A 33V open circuit panel cannot be connected at all |
| BLUETTI AC70 | 500 W max, 12V to 58VDC, 10A | One panel only. Two in series exceeds the voltage ceiling |
| BLUETTI AC180 | 500 W max, VOC 12V to 60VDC, 10A | One panel only, and the current limit binds first |
| BLUETTI Elite 100 V2 | 1,000 W max, 12V to 60V, 20A max | The 60V ceiling forces parallel wiring, so current binds |
| BLUETTI Elite 200 V2 | 1,000 W max, 12V to 60V at 20A | Same constraint. Needs high voltage panels to reach 1,000 W |
| BLUETTI AC200L | 1,200 W max, 12V to 145V at 15A | The wide window allows long series strings at low current |
| BLUETTI AC240 | 1,200 W, 11V to 60V, 21A | Parallel only, current binds before wattage |
Work an example with a real panel. BLUETTI’s own 350W Solar Panel is described on its product page as having “a 33V open-circuit voltage (Voc)” with industry standard MC4 connectors. BLUETTI does not publish the panel’s maximum power voltage or maximum power current on that page, so I estimate operating current as rated watts divided by operating voltage, which lands somewhere between 10.6 A and 11.7 A depending on the assumption.
Now check that panel against the units. On an AC60, 33 volts open circuit is above the published 28 volt ceiling, so the panel cannot legally be connected regardless of its wattage. On an AC70 or an AC180, one panel fits the voltage window but its current is already at or above the published 10 A limit, and a second panel in series would put you at 66 volts, above both the 58 and 60 volt ceilings. So both of those machines are one panel machines with this panel, no matter how many you own.
On an Elite 200 V2 the 60 volt ceiling again rules out a series pair, so you go parallel, and two panels in parallel put roughly 21 to 23 amps into a 20 amp limit. At an operating voltage around 30 volts, a 20 amp ceiling caps you near 600 watts, not the 1,000 watts on the specification sheet. Reaching that 1,000 watt figure requires panels with an operating voltage nearer 50 volts, which portable folding panels usually are not.
The AC200L is the outlier and the reason it is the sensible choice for a serious solar build. Its 145 volt window lets you put four 33 volt panels in series at low current, which stays under the 15 amp limit and gets you to the full 1,200 watts. That single specification difference matters more to a real off grid system than a hundred watt hours of extra capacity.
The worked example, end to end
Pulling every step together for a van based setup in Denver that has to work in winter.
| Step | Calculation | Result |
|---|---|---|
| Daily delivered load | 176 plus 179 plus 200 plus 120 plus 45 | 720 Wh |
| Daily draw from the battery | 720 divided by 0.85 inverter efficiency | 847 Wh |
| Battery for 2 days of autonomy | 847 times 2, divided by 0.8 usable fraction | 2,118 Wh nameplate |
| Machine chosen | Elite 200 V2 at 2,073.6 Wh or Elite 300 at 3,014 Wh | Elite 300 for margin |
| Daily energy the panel must produce | 847 divided by 0.9 charge path efficiency | 941 Wh direct current |
| Denver December peak sun hours | NASA POWER climatology, horizontal surface | 2.29 |
| Derate applied | NREL default 0.86 times temperature factor 0.88 | 0.75 |
| Panel wattage required | 941 divided by 2.29 divided by 0.75 | 548 W |
| Panels needed | Two 350 W panels, giving 700 W | Comfortable margin |
| Input check | Elite 300 published solar ceiling | Verify before purchase |
Notice the last row. Two 350 W panels wired to satisfy both a voltage window and a current limit is a wiring question, not a wattage question, and it is the step that sinks builds. Confirm the unit’s published window against the panel’s open circuit voltage and estimated operating current before any money moves.
Notice also what happens if you try this on an AC180. Its published solar ceiling is 500 W. In Denver in December, 500 W times 2.29 peak sun hours times 0.75 gives 859 watt hours per day, which is short of the 941 the system needs. No quantity of panels fixes that, because the machine will not accept more input. The capacity was never the problem. The input ceiling was.
The common failure: plenty of battery, not enough panel
This is the pattern I see most often, and it is created by the way these products are marketed. Capacity is the headline number on every box, so people buy capacity, then add “a solar panel” as an accessory rather than as half the system.
Put numbers on it. Take an Elite 300 with 3,014 Wh of nameplate and pair it with a single 200 W panel. In Seattle in December, at 0.85 peak sun hours and a 0.75 derate, that panel produces 200 times 0.85 times 0.75, which is 128 watt hours per day. Refilling 3,014 watt hours at 128 watt hours per day takes about 24 days. The battery is not a battery at that point. It is a very heavy one time use power bank.
Move the same pair to Phoenix in June, where peak sun hours are 8.50, and the panel produces 1,275 watt hours per day, filling the pack in under three days. Same hardware, completely different system, and the only variable is the one nobody puts on the box.
The rule I would give anyone building one of these: fix the panel wattage first from your worst month, then buy whatever battery your autonomy requirement demands. Doing it the other way round produces the exact failure above. If a big battery is genuinely the goal because you charge from a vehicle alternator or a generator rather than the sun, that is a legitimate design, but call it what it is and stop calling it a solar generator.
For a fixed installation at a house rather than a vehicle, the tradeoffs shift again, and I go through them in the home backup solar generator guide. For the vehicle case specifically, see the RV power station guide.
Selling solar generators rather than only buying one
Solar and backup power is one of the strongest high ticket categories available right now, precisely because buyers arrive with a technical question and reward whoever answers it honestly. The category sits alongside others in our high ticket niches list. The mechanics of the model are covered in our explainer on high ticket dropshipping.
Getting approved as a dealer is the real barrier, and solar brands are stricter than most because of installation and liability concerns. Our supplier sourcing guide walks that process. Form the entity first, because approval conversations start with a business, and the business formation guide covers the structure and the filings.
I run these stores on Shopify, mostly because panel and battery freight needs good shipping rules and the app ecosystem there is the deepest. I file through Bizee and keep the registered agent with them.
Anything containing a lithium battery carries product liability exposure that I would not take on uninsured, so general liability cover from Hiscox goes in before the first sale. Books go into QuickBooks from the beginning, because dealer credits and freight adjustments are impossible to untangle later.
Frequently Asked Questions
How many watts of solar do I need for a 2,000 Wh power station?
That is the wrong question, because panel wattage follows your daily load and your location, not your battery size. For a 720 watt hour daily load in Denver, the panel needs to produce 941 watt hours of direct current per day, which is 259 W of panel on the annual average and 548 W in December. Same battery, same load, and the answer roughly doubles between the two.
What are peak sun hours and where do I look mine up?
Peak sun hours are the number of hours per day that would deliver the same energy as the actual daylight at a full 1,000 watts per square metre. They are numerically the same as daily irradiance in kilowatt hours per square metre per day. The NASA POWER climatology dataset publishes this for any latitude and longitude, and the table above lists ten United States cities with annual, December and June values.
Why does my 400 W array never produce 400 W?
Because the rating is measured under standard test conditions that almost never occur outdoors. NREL’s PVWatts manual sets default system losses at 14 percent covering soiling, shading, mismatch, wiring, connections, light induced degradation, nameplate tolerance and availability, and separately lists a module power temperature coefficient of -0.47 percent per degree Celsius for standard modules. Combine those and a planning derate near 0.75 is realistic.
Can I just add more panels to charge faster?
Only up to the unit’s published input ceiling, and usually not that far. The AC180 caps solar input at 500 W with a voltage window of 12V to 60V and a 10 A limit, so with a 33 volt open circuit panel you are limited to one panel by current, and a series pair would breach the voltage ceiling. Check the wattage, the voltage window and the current limit before buying panels, because the current limit usually binds first.
Should I buy a bigger battery or more panel?
Panel, in almost every case where the sun is your main charging source. Battery buys you days of autonomy, which is a one time buffer, while panel determines whether the buffer ever refills. Fix the panel wattage from your worst month first, then size the battery to your autonomy requirement.
Do portable folding panels beat fixed roof panels?
For seasonal performance, often yes, because you can aim them. The peak sun hour figures above are for a horizontal surface, and tilting toward the low winter sun recovers a meaningful part of the December shortfall. Fixed panels win on convenience and on never being stolen or forgotten, so many people run both.
The Bottom Line
Size both halves together or you will get both wrong. Daily load in delivered watt hours, divided by 0.85 to get the draw from the battery. Multiply by days of autonomy and divide by the fraction of the pack you will actually use, and that is your battery. Divide the daily draw by 0.9 for charge path losses, then divide by your worst month’s peak sun hours and by a 0.75 derate, and that is your panel.
Then check the one thing nobody checks. The unit’s charge controller has a wattage ceiling, a voltage window and a current limit, and the current limit usually binds long before the wattage does. A 60 volt window on a machine rated for 1,000 watts of solar means you will realistically get closer to 600 watts out of standard 33 volt folding panels. A 145 volt window on the AC200L means you can actually reach the number on the sheet.
Get all of that right and you own a system that refills itself. Get the panel half wrong and you own a heavy battery with a decorative solar accessory, which is the most common outcome in this category and the most expensive one to fix afterwards. The full buying framework for the battery half sits in how to choose a portable power station.
Build a system that actually refills
BLUETTI publishes solar input ceilings, voltage windows and current limits on every product page, and rates cycle life to a stated remaining capacity. That is what makes a real sizing calculation possible.
If you would rather build a business around this category than just a system for your own van, our done for you high ticket dropshipping build and launch service handles the store, the brand approvals and the freight setup end to end.
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Trevor Fenner is an ecommerce entrepreneur and the founder of Ecommerce Paradise, a platform focused on helping entrepreneurs build and scale profitable high-ticket ecommerce and dropshipping businesses. With over a decade of hands-on experience, Trevor specializes in high-ticket dropshipping strategy, niche and product selection, supplier recruiting and onboarding, Google & Bing Shopping ads, ecommerce SEO, and systems-driven automation and scaling. Through Ecommerce Paradise, he provides free education via in-depth guides like How to Start High-Ticket Dropshipping, advanced training through the High-Ticket Dropshipping Masterclass, and fully done-for-you turnkey ecommerce services for entrepreneurs who want a faster, more hands-off path to growth. Trevor is known for emphasizing sustainable, real-world ecommerce models over hype-driven tactics, helping store owners build scalable, sellable, and location-independent brands.
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