Beyond Coal: What Future Lies There?

Bluntly put, 23% of our national energy consumption comes from coal. We have enough coal to meet our complete energy needs for app. 250 years. Natural gas, a byproduct or co-recoverable resource found with oil and coal deposits, supplies 24% of our energy needs, and we increase our ability to recover and store it each year. Crude oil, about which so much political ado has prevailed in the last 50 years, is still partly a domestic resource. We only import about half of our yearly consumed aliquot. And oil supplies about 37% of our national energy needs per year.

If you subtract industrial use and home heating, coal supplies, through generating plants, about half of our nation's electric power. Natural gas generation, nuclear generation, and renewables do not promise to put coal out of the picture soon. A huge portion of the nation's carbon footprint, if you care about global climate change, comes from the burning of coal.

We recently lost 29 miners in the Upper Big Branch mine explosion, and we lost 47 miners in 2006 in the Sago mining disaster. Coal mining ranks with commercial fishing and military service as the most dangerous professions in this society. We all listened and watched as prayers, opinions and excuses went up all over the country over the fate of those 29 men, and the question came up once or twice: Do we have to do this? Do we have to put men and women at risk to gouge coal from the earth profitably, burn the coal in some of the dirtiest smokestacks to generate our electricity, and deal with the effects of rapid climate change while wringing our hands and engaging in denial, while our hunger for energy as a society grows every year without respite?

Do we have to kill our miners at this rate to keep the coal plants burning? Yes, apparently we do. Until we have an alternative, and right now we don't, we have to keep drilling, mining, leasing offshore sites to the highest bidder and waiting for the accidents and spills. We have to have the energy. At any cost, human, economic and apparently military. The quiet conspiracy to secure Iraq's oil was an expensive failure. "Clean coal," at least so far, is a myth few of us can buy into. Nukes are scary, and dirty in the long run (dangerous to all life forms for 159,000 years after disposal). Yes, it seems we do have to do all that. And we're all doing it together, all of us consuming energy, and that's all of us, except for a few survivalists.

We have no alternative, so we have no choice. We will continue to put miners at risk, drill and pipe natural gas, float drilling rigs where a spill would be disastrous, humble ourselves at foreign tables, and spill American blood to secure a share of the world's oil reserves. We don't know how long we can keep this up; but we don't have a plan to free us from this dangerous and expensive cycle: the pursuit of more and more energy. God bless the miners, drillers, reactor jockeys and power plant construction workers. We need you more than we let on; and we sacrifice you at a rate that would certainly shame an enlightened society.

Photovoltaic Panels and the Deadly Enemy-- Shade

A prime parameter in the specs for photovoltaic system installation in the Connecticut Clean Energy guidelines refers to shading of the panels: to wit, no shading allowed during the normal "solar day," reckoned to be between 9 Am and 3 Pm. It's a pretty stiff requirement here in tree-covered New England, and it may seem unfair to disqualify a potential roof site because a tree shades it for part of the day. But here, in brief, is the danger of shading and the logic behind zero tolerance for it.
A solar PV array is configured in "strings," or source circuits, of two to 12 panels, according to system voltage. The string of panels is connected from one to the other via the connected module leads so that the current through the string is constant, and the voltage of each module adds up to the nominal system voltage, anywhere from 24 volts for small battery-connected systems to nearly 5oo volts for high-output grid-tie systems. And in that string, or series circuit, a little patch of shade can limit the current of the entire string to a small fraction of capacity. Diodes are installed to permit current to bypass shaded or malfunctioning modules or cells, but the effect is still significant on performance.
Shading analysis in the planning stages is critical to predictable and maximum performance. If an area selected for panel installation is shaded, the time and extent of the shading must be calculated and deducted from the expected output of the system. Sometimes module choices are affected by shading analysis; "amorphous" crystalline cells are slightly more shade tolerant than other module types.
Non-grid tie systems suffer at least as much, if not more than grid-tied arrays. If batteries are matched to the output of the array, a small shaded area alerts the Maximum Power Point Tracking device in the inverter, which senses the efficiency and total output of the system, simply shuts down and waits for the shading to pass. For the duration of the shading, the system sits idle.
Shade analysis, then, is a vital part of planning when photovoltaic arrays are being sited on rooftops or on the ground. The panel manufacturers and government agencies aren't kidding when they say that zero shading is the proper amount. And we, installing professionals, may be advising you to trim or remove trees, or purchase costly racking systems to relieve shading conflicts; we're not just upselling the job. Shade is your enemy in the solar game, whether it's for hot water or photovoltaics. And for photovoltaics, a little shade can be deadly.