Heh-- this thread reminds me of buying our first 1100 watts.
In late 2004 spouse saw what we geezers refer to as a "classified ad" in the "newspaper". The seller was a retired engineer in his 80s who told me he'd broken a hip and could no longer keep up with the maintenance. "Maintenance"?!?
It turned out that he'd had his system designed from scratch and custom-built in the mid-1990s for top dollar. The panel racks are high-quality brick-outhouse galvanized steel angle iron and he'd built a shed for his inverters, charge controller, and battery. One of his five-panel racks probably weighs more than today's 40-panel aluminum rack systems. We got his panels & racks for $2500-- mainly because we were willing to go up on his roof and remove them.
He was using 12v batteries with 20 Siemens 55W 17-volt panels. I couldn't tell that they were deep-cycle lead-acid marine batteries-- I'm not familiar with boat equipment-- but he was beating the crap out of them. In the morning when the array voltage was high enough, he'd go outside to his circuit breaker box and throw SamClem's DPDT switch from "HECO" to "solar". He'd have the panels charging the batteries all day (while he also ran his 1950s small house's electrical load off the inverter output). Then he'd run off battery power as late into the night as he could, until the voltage alarm started going off and his fridge sounded weird. He'd throw the DPDT switch back to "HECO" and go to bed.
The shed was an acid-splashed high-humidity hellhole that would eat your nasal linings and erode your dental fillings if you stayed too long. EPA and OSHA would be fighting each other for jurisdiction. It was well-designed and solidly built but I swear I could feel my arm hairs standing up when I got too close to the batteries. He said he had to refill their cells every day because they were regularly steaming down far enough to expose the plates. He was tired of hobbling around doing his Gunga Din act for $25-$35/month and was wiling to give up his project.
We took the panels/racks, politely declined the electronics & batteries, and ran away fast.
I assume that solar panels are designed for a specific voltage output, and only the current would vary with solar input, though this might be horribly inaccurate...
Panel output voltage vs insolation tends to be a fairly prompt jump from "0v" to "max rated". However most panels' voltages start to roll off as their temperature gets above 125 degrees F.
It's apparently not too difficult or expensive to design a grid-tie inverter to work off a reference voltage, like the local utility's rock-solid 240v 60Hz AC. A grid-tie inverter might work off a gas-powered generator, too, although its output voltage droops a few volts as it gets up to full load. When you start up the refrigerator or a vacuum cleaner on the electric utility then its bus voltage doesn't budge. On a gas-powered generator... you'll hear it. On a smaller PV/battery system, the electric motor's starting surge would bounce around the grid-tied inverter's output voltage like a rubber ball and probably cause it to trip off.
An off-the-grid inverter needs a beefier design to set its own output and handle the wider variation in output voltages caused by demand. A separate charge controller handles the batteries (and the current flow, depending on whether the system demand is charging or discharging). Those designs seem pretty established for central inverters, but even they have their limits. I've read of off-grid systems where the house's air-conditioning thermostat triggers a gas-fired generator to come up to voltage before it starts the air-conditioning motor to run the compressor. Once the A/C is running steady then the gas generator shuts off and the PV system handles the load. It just can't easily handle the starting surge.
I don't know if there are off-the-grid microinverter designs yet (I haven't researched it). Even 2010 grid-tie microinverter technology was limited to about 225 watts, while PV panel capacity has risen to over 300 watts. So the micro tech is very encouraging but still catching up.
In the next 3-5 years we're planning to buy a (cheap used) plug-in hybrid. We'd need another 3000 watts recharging capacity above our current 3300 watts. We'd originally planned to build a pergola along the house's south wall (for more passive shading) and roof it with PV panels. However our current cheap array has paid for itself already and panel power density has more than doubled since our 1990s hardware. It might be cheaper to not build a pergola, scrap the old array, strip the south roof and properly insulate it before reshingling, and put up 6000 watts on the same square footage. The house will be cooler in summer and we'll save $1200-$1500/year on gas in addition to having a minimal $16/mo electric bill. Hopefully 350-watt microinverters are a reality by the time we're ready to make the leap.
As for electricity after a hurricane: we'd just fire up the BBQ grill & camp stove, cook all the fridge/freezer meat as it defrosts, break out our Spam recipes, and live in the 19th century for a [-]month[/-] week or two. We wouldn't even have hot showers because our solar water heater pump is AC, not DC. (Maybe DC water pumps have a better brushless design now.) If we want to feel spoiled, though, our local solar supply company sells a 1700-watt inverter designed to work off a DC battery. It comes with a set of jumper cables to attach it to a Prius. I keep going back & forth between "Cool!" and "Don't have enough shotgun ammunition to be the only house on the block with lights after dark".
