The cost of the solar system must (unless you are independently rich or someone else is paying for it for you) be looked-at as money borrowed. In other words: if you had to add the cost to your mortgage (as most of us would have to), you would be paying, say, about 5% per year, so, the electricity generated by a $25,000 solar PV system is not actually free: it costs you $1,250/year in interest (maybe more in lost opportunity costs if you are a good investor, but that is an entirely different story). In addition to that, there ARE operating costs: I am told that solar inverters are typically expected to last on the order of 10-15 years, after which you must replace them, and PV solar panels have some finite life. Also, when your roof (the one made of shingles) needs to be replaced or repaired, you will incur additional costs to remove and reinstall the PV panels.

Keep in mind I have no expertise in Solar PV design and operation, was the use of a normally closed contactor at or in the solar PV Panels. It would be installed so that when closed it would short the output of the panels. My understanding is that shorting of the output would not create additional hazards as the maximum fault current is the rated output current at that moment in time (Please advise if there are risks with this option). You would have a switch or circuit breaker at the switchboard supplied by normal network supply and when the switch is on and/or there is network supply the contactor would be open and allow the panels to output to the inverter but when there is no supply the contactor would close preventing output to the inverter.

There are really tow issues here about solar PV system. The first is ignition of a PV from within. I have seen many videos of PVs that have started burning at a microcrack location (the current gets concentrated there) wherein the silicon finally melts through the backing, which might catch a home or building on fire; maybe grass filre at a utility. These are the result of hot spots or lighting strikes, for example. It has to be the EVA that caught filre, the rest being nonflammable.

I'm a certified Designer / Installer from Australia. Each state has its own regulatory body that looks after Electrical installation (including PV). There are also Australian Standards that designers and installers must adhere to that are governed by the clean energy council.
Part of those standards there are mandatory forms that are filled in by 1. the solar company 2 the designer and 3 the installer. i.e testing the system and all isolation point are just a couple of points to confirm operation. These forms are then sent into the state regulatory body for record keeping. Inspections are randomly done by trained inspectors and if a issue is found, the company will have to return and rectify or face losing its accreditation and have large fines issued.

I am not a firefighter, but I have often meet with them to discuss PV solar, and the impact that solar installations have on house fires. Around 2008, the number of installations in the US, particularly here in California, grew quickly. Installation permits are controlled at the municipal level, so it getting regional or national standards established were important. The National Electric Code (NEC) was busily improving the standards for PV, as were many of the greener organizations. Designers were getting better, and training through NABCEP and other organizations were gaining ground. So things were getting better everywhere, and it was a time when more improvements were welcomed.

In recent years, fires have been attributed to: 1. PV module defects and; 2. Incorrect installation. Both causes resulted in fires that continue to burn due to DC arcing from the PV arrays continuing to generate power in sunlight even though they were disconnected from the inverter.

Having attended a number of safety seminars that were presented by a number of fire marshals, well known national electrical experts, etc., in the US, it was disturbing to find out how many people think that a DC disconnect switch, relay, or some other switch can deactivate a PV array during a fire. Even if you turn off the switch, the array itself is still producing power, so a sure way of deactivating the array is to cover the panels and keep light from reaching the modules. Once done, the individual panels need to be individually disconnected, or at least significant numbers of each string disconnected so that lethal voltages cannot be generated.

It was also acknowledged that AC modules (integrated microinverters) are safer as the modules aren't in series and therefore generating the high voltage DC which can arc and perpetuate a fire.

Due to the significant uptake in Solar PV being installed on Residential installations one problem we have incurred is how to safely isolate supply when there is a house fire.

When supply was just via the network any electrical risk could be eliminated by disconnection from the electricity distribution network, now that premises have their own roof top generation system this action does not eliminate the risk to fire services or persons at the installations. We have already had cases where, after fires that occurred at night have been controlled by the fire services, testing has found voltages up to 110 DC on the installation roofs the next day when the sun was out, due to damage that had occurred to the Solar PV array wiring by the fire.