So much emphasis has been put on keeping the portable systems small that significant compromises have been made. I took a fresh look at the goals of a truly reliable system that could produce meaningful AC power for days on end. End user cost is a factor, but most everything else is not. Here is what I found:
A typical solar day is limited to about 6 hours of energy-producing sunlight. The sun may seem to shine overhead for 10 or more hours, but as the light tapers off the usable result averages out to about 6 hours. Smaller systems that only collect 100-200 watts of energy will have saved maybe 1200 watt-hours* and that is only if the user does not consume any of that power during the charging time. Our FA460-260S foldable solar panel system uses four commercial (and readily available) 260 watt rooftop panels and collects around 1000 watts* per rig and you can stack two of these for 2000 solar watts.*
Most of the small systems do produce a decent sine wave like the normal electricity that comes into your home. However, to keep weight and cost down there are some compromises. The biggest one is that the output devices (FETs) send the power directly to the AC receptacle. This makes them vulnerable to spikes and overloads that can easily damage the system. A typical statement from one of them is that they will handle twice the power for a moment. That moment is extremely short. We use a low frequency inverter that has a heavy output transformer like the permanent rooftop systems. This acts as a buffer to protect and regulate the output. A LF inverter can typically take three times the load and for 10-20 seconds or more. Look for these specs when comparing systems. Look for more about that in my Application Notes.
Another way that the smaller systems keep weight down is to use Lithium-Ion or Lithium-Polymer batteries. They can hold a significant amount of power for their size but again there are drawbacks. They are very unstable. Each cell of a Li-Ion battery has to be connected to a Battery Monitoring System (BMS) to continuously adjust its charge and discharge rate or they could catch fire and even explode. We use AGM (Absorbed Glass Mat) batteries that look like the ones in your car. The difference is that these are truly sealed. Instead of plates dipped in acid (flooded batteries) there is a piece of Fiberglas in between the plates allowing for much closer placement. These are then soaked in acid for more energy storage per cubic inch than flooded car batteries.
Multi Point Power Tracking charge controllers take the best advantage of incoming solar energy. With a wide range of input voltage and current, they convert it to whatever is needed by the battery type and capacity. Unregulated systems (pocket-size systems) and PWM (Pulse Width Modulated) charge controllers cannot make the best use of available solar power from the solar panels. We found a reliable and separate MPPT controller than can be stacked for use with multiple panel systems. I have more comments in Further Expanding the System in the Application Notes.
A truly robust system as described above can be very heavy. The Compact Portable Foldable Solar Panel Support System is the core part. Awarded three patents so far, this frame system holds two or four 60- or 72-cell rooftop solar panels and allows the user to roll it out of a garage or shed and unfold the array in as little as 2 minutes for solar energy collection. Two or more folded systems can be nestled to each other to keep the footprint as small as possible during storage. Our companion inverter/battery electronics carts hold the group of indoor electronics together for a compact system that can be moved about with relative ease. I go into more detail about this in the Application Notes.
*Adjusted for typical system inefficiencies.
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