Solar Generator vs DIY Solar: What the Box Trades Away

There are two shapes of off-grid system, and the choice between them is usually made before anyone understands it.

One is a box. Battery, inverter and solar charge controller live in a single case with outlets on the front, and you plug things in. The other is a set of components: panels, a controller, a battery bank and an inverter, wired together as a system that lives where you put it.

This page is about that fork. It is not about which brand to buy, which is the job of the portable power station guide.

What is actually in the box

The same four parts the rest of this section explains one at a time, with three of them inside one case.

The panels stay outside. That matters more than it sounds, because a solar generator’s relationship with panels is the specification people check last and regret first.

“Solar generator” and “portable power station” name the same product. Manufacturers use both for the same hardware, and neither generates anything: they store what a panel, a wall socket or a vehicle put in.

“All-in-one” means something else to people who build systems. In the DIY solar world an all-in-one is an inverter that has the solar charge controller and the battery charger built into it, with the batteries outside, on the floor or on a rack. It is the middle path between the two shapes on this page, and it is a different product from the box with the battery inside. If you meet the phrase on a forum, that is almost always what it means.

What the box buys you

Nobody has to design it. The parts inside were matched at the factory. No conductor sizing, no fuse selection, no controller that has to suit both the array and the bank.

Nobody has to wire it. A box with a plug on it is the one off-grid arrangement that touches no building wiring at all, which is also why it sidesteps the permit and inspection questions that a fixed installation raises.

It works the day it arrives, and it keeps working somewhere else. The three units I read run from 25 lb to 58 lb, so one person can move the small ones and two people can move the rest.

It carries its own transfer switch. Units sold for backup take over when the power fails, fast enough that a router, a desktop computer or a CPAP does not notice. The three current models I read publish 10 ms, 15 ms and 10 ms, and that figure is in the manual, not on the product page.

What the box trades away

A ceiling on the array. Every unit has a solar input window, quoted as an open-circuit voltage range, and a maximum wattage. All three of the current portable models I read accept 12V to 60V and 1,000 W to 1,200 W. Two 100 W panels in series sit at about 44V and fit. Three sit at about 66V and do not, and open-circuit voltage climbs as the temperature falls, so an array that fits in July can step outside the window on a cold bright morning. In a built system the controller is a part you choose for the array you want.

Expansion on the maker’s terms, if at all. Some units take expansion batteries, and only the maker’s own. Others take none: the 2 kWh unit I read answers it in one word on its own specification tab, under Scalability. A built bank grows by adding cells that meet its specification, from whoever sells them.

One case, one failure. The battery, the inverter and the controller share a chassis. When one of them fails, the unit goes away for repair and takes the other two with it. In a built system, a dead inverter is a dead inverter, and the bank keeps its charge while you swap it.

120V, in almost every case. The portable units are 120V. Anything on 240V, a well pump or a deep water pump among them, is outside what they do. That capability appears on the big stationary units, which are a different class again.

The number on the box is not what you get. Rated capacity is cell capacity. Between the reserve the battery management system holds back and the losses on the way out, one maker’s own runtime figures work out at about three quarters of the rating reaching a mid-size load, and about half on a very small one. The power station guide works through that in detail.

Which one fits, in numbers

The four worked systems on this site compute their own daily energy from a load list, so they make a useful ruler. The largest of the three units I read holds 3,014.4 Wh, and about three quarters of that reaches the outlets.

The pattern is not about size alone. A box suits intermittent use and modest loads: a weekend cabin, a workshop, a site hut, a van, a few days of outage. A built system suits daily use at household scale, where the array has to grow with the season and the bank has to carry a week of bad weather.

Work your own number first with the appliance power budget, then size the alternative with system sizing. If what you actually want is to ride out grid outages, start at choosing your backup type, because that is a different question with its own rules.

In a van or an RV, the box gains a second source

This is where a solar generator is at its strongest, because the vehicle brings something a cabin does not: an engine that charges the battery whenever you drive.

The cigarette socket is not the way to use it. The unit I read accepts 96 W through that port at 12V, so filling a 2 kWh box from the socket takes about 22 hours of driving.

An alternator charger is. The same maker sells one rated at 800 W from the alternator, and up to 1,200 W with solar at the same time, which turns those 22 hours into under three. It states that it works with smart alternators, which is the tell that this is not a job for a heavy cable and a pair of clamps.

That current is the part to respect. 800 W at 12V is about 62 amps, continuously, through cable you install in a vehicle.

One more detail worth knowing if the vehicle is an RV rather than a van: the 3 kWh unit I read carries a NEMA TT-30 outlet, which is the 30 amp shore power plug an RV already has an inlet for, along with a 12V, 30 A DC port for the vehicle side. That combination is what makes a stationary box behave like a campground pedestal you brought with you.

Where to go next

If the box is the answer, the portable power station guide covers the four specifications that decide which one. If the built system is the answer, start with how an off-grid system fits together, then the battery guide and the inverter guide for the parts that cost the most to get wrong.