You are correct that properly installed solar PV is not a significant fire hazard in itself. The NFPA publishes many other code books dealing with manufacturing and installation of combustion appliances and systems. The NEC requirements mentioned are a resolution of firefighter life safety issues.
Visualize the home in the picture with an attic fire caused by a faulty gas furnace chimney right under the middle of the PV array. The north side is not part of the attic so firefighters must ventilate the attic through the array. The firefighter will use his axe with an insulated handle to smash several modules out of the way. Each axe blow leaves exposed live parts at the array voltage. The DC side of the system does not shut down through overcurrent or short circuit protection but perhaps only through ground fault protection. Otherwise the module conductors will stay energized posing a life safety issue to firefighters.
DC circuits can readily sustain arcing at low voltages, i.e. DC welding, raising the possibility of causing additional fires on the roof. Fires not caused by the PV system but by damage to the PV system. The changes to the 2014 NEC do not fix this problem at the module level but will standardize the local requirements for fire department rapid shutdown.
As for setbacks from roof edges. I am sure a couple of young guys in shorts and sneakers had no problem installing those modules but then they did not have to deal with smoke, flames and spraying water while they worked.
In an introductory PV segment for apprentice electricians we demonstrate how a broken PV module can have live voltages even when broken into three pieces. We have two identical modules except one has been broken. We lay them out on a table under florescent lights and usually reach nameplate voltage on the undamaged module. We isolated conductors along the broken edges and measured voltages that were a major fraction of the module nameplate voltage. The sum of the voltages from the pieces was less than the module nameplate and could be treated as low voltage presenting minimal hazard. The series-parallel connections of multiple modules develop higher and more hazardous voltages.
Nameplate voltages are present even when the module is disconnected from the array. Take it out of the box, expose it to light and it is an energized component. Break it into pieces and the pieces are still energized.
Mr McCune, your comment "amazing that an electrical product was manufactured for decades without an off switch" made me wonder if you are developing and isolation product for small storage battery systems. As storage becomes part of more PV systems the disconnection of the series-parallel connections of battery racks will be a major issue. The available fault current from even a small battery system will pose a much greater fire and life safety hazard than a PV array
There are about 5000 jet airliners aloft at any given time, 24/7. Each of those aircraft consumes about one pound of kerosene/jet fuel per second. Every day we intentionally inject more than a million TONS of high temperature CO2 and H2O, high in the atmosphere. Gosh, I hope my math is wrong.
5000 aircraft X 24 hours X 3600 seconds X ( 1#/second) = 432 million pounds or 216,000 tons of jet fuel burned per day. Jet fuel is basically C12 H24 and combusts into 12 CO2 and 12 H2O molecules for each molecule of perfectly combusted kerosene. One ton of jet fuel becomes many tons of CO2 / H2O. Plus some NOx and SOx and particulates for flavor. Once again, all this energetic jet engine exhaust is injected into the atmosphere at 35,000+ feet. If something is invisible, does it actually exist?
Sir Richard knows this very well. He also knows that his businesses are major contributors to the high altitude pollution problems, largely ignored by almost everyone.
There were no suggestions in my comment, only observations about high altitude emissions which are an insufficiently studied source of greenhouse gases.
I agree completely that humans will continue dig up and burn carbon until it is gone or it kills us.
Mr Gelbert, I am actually more optimistic than my previous curmudgeon(ish) response might indicate.
Tomorrow, NASA plans to launch OCO-2, an orbiting carbon observatory. Soon we will have real data about the atmospheric column mapped by location.
We already have precise information about the airline routes so correlation should be easy if it exists at all.
This video shows why airlines may have reason to be concerned about their specific contribution to climate change. Or maybe it is just a cool depiction of tens of thousands of humans flying much faster and higher than birds.
Human destiny or Icarus on steroids?
@ PJ Van Staten
Thanks for the clever metaphor
"Thus in short, perhaps we find ourselves at a point where we should be "capacitive" (thinking leads action) and not be "inductive" (thinking lags action)."
As a technical instructor for apprentice electricians I am sure I will use the basic idea to convey a complex concept, so thanks again.
Most small PV systems produce "single phase" AC (120-240VAC). Almost all utility distribution is "three phase". This seemingly arcane difference poses a fundamental problem for residential PV providing realtime "reactive power" with any real value.
If one neighborhood widely adopts solar PV, AND, is served served by a single phase utility extension, then it is possible that a phase imbalance will be injected into the three-phase system. Upstream motor loads can be significantly impaired. Three phase motors rely upon a very precise electro-magnetic phase shift to rotate and deliver torque. A 3% (@10 degrees of rotation) phase shift can cause a three-phase motor efficiency drop to 90% or less. Very precise control functions would be required (not yet invented) to manage single phase reactive power sources. Fifteen years from today, maybe.
Industrial and commercial facility managers:
From the article. Around 50% of all power consumed is used by electric motors.
If you have electric motor applications including pumps, fans and compressors which use modulating dampers or valves to control pressure or flow, you might realize a 40-50% drop in the power consumption by using VFDs on those motors, and modifying the dampers or valves.
Tens of millions of Variable Frequency Drives have been installed in the last decade.
Even in China, dozens of coal-fired power plants remain on the drawing boards.
Energy consumption per unit of production has been reduced in many industries.
The VFD is not magic, in fact the solar PV industry has adopted the name of its primary component, the inverter, for a major system component. A VFD typically has three functional stages. A three phase rectifier producing pulsating DC from 60Hz AC. A DC filtering section with inductors and capacitors which produces a smooth DC waveform, similar to PV output. An inverter comprised of (6) IGBTs controlled by a microprocessor. The AC source allows voltage manipulation through transformers and the DC output is both frequency and voltage controlled. Motors work better, run cooler and last longer. It is easy to ramp the starts so belts are preserved for years instead of months.
Less than three year payback without any subsidies. Permanent baseload reduction. Reduced demand charge exposure.
Almost all of your local HVAC and electrical contractors know about these devices.
Elon Musk is today's Howard Hughes, without the fingernails. Yet!
Obviously a brilliant visionary with gobs of money, like Howard Hughes.
He has already contributed to the advance of global industry, like Howard Hughes.
He may spend large amounts of his own and other people's money on boondoggles, like Howard Hughes.
I hope he does not die incredibly rich and very insane, like Howard Hughes.
Although Lithium is far lighter than lead, a "gigafactory" will probably develop as a distributed system of extraction, production and distribution facilities which meet market demands.
Transportation costs are a significant portion of battery cost, even lithium ion.
The transportation infrastructure is a nationwide distributed network of interconnected nodes, aka the interstate highway system.
Electric vehicles will rely on a local/regional network of support infrastructure; a modification of the gasoline service station model, perhaps even piggybacked on that model.
Battery pack quick change out to fully charged battery pack in less than 15 minutes.
Battery charging systems which recharge the onboard battery pack in less than 15 minutes.
Decent fast food restaurant which feeds you in less than 15 minutes.
Placed at intervals of 50% of the advertised range of the typical electric vehicle.