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The New Independent Home
by Michael Potts
from chapter 10 :
Thinking Like an Island |
When the power fails in your independent home, for whom does the bell ring? That's right: you! You are the power company.
It is a well-documented fact that grid power fails more often than independent power; agencies such as the Federal Aeronautics Administration and the power companies themselves use reliable independent systems for backup, for equipment that cannot be allowed to fail. Many who are designing their remote homes so that essential systems such as wells and communications are immune to the vagaries of grid power are doing so because they expect a crash. Outages are increasingly common around the globe, because growth and urbanization are out of control, reservoirs are silting up, aging distribution systems are getting knocked down more often in storms, and competitive cost-cutting among utilities has thinned out emergency response as reserves of equipment and workers are cut ever thinner in pursuit of immediate profit. Underscored by the experiences of city-dwellers in Florida, California, and Hawaii, and under the threat of Y2K and the larger notion that our far-flung utilities are fragile and subject to unforeseeable natural and man-made disasters, many homeowners and institutions are planning for autonomy. The path of least resistance still leads through the gasoline generator, but many people are seeking hardier, more self-reliant earth- and human-friendly solutions.
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sidebar: Islanding
Utilities, especially those in New England, the upper midwest, and the far west, where alternative energy production systems are concentrated, are beginning to direct some thought toward what their systems will look like when their ratepayers are also their principal suppliers. One analogy they use to analyze this phenomenon is "islanding." This is their scenario: Residents of a small town like Caspar make the solar commitment and cover their south-facing roofs with energy-harvesting equipment until the village finally attains the point where its community energy production from PVs and other sources equals its base load (minimum) domestic consumption. Caspar's energy customers would then be producing something like 50% of the power they are using. California is one of a dozen net-metering states, which means that a customer may generate electricity and send any excess back into the grid, spinning the meter backwards; at the end of the metering cycle, the customer pays for the net amount of electricity consumed. The sun shines in Caspar by day, so it is likely that Caspar would be a net exporter of energy by day, "storing" energy in the grid for nighttime use. Of course, the grid stores little or no energy; urban, industrial, and agricultural users would gobble up the excess power during the day while Caspar's producers watch their electric meters spin backwards. The utility would be able to reduce its reliance on expensive thermo-electric peak-load generators. At night, when the sun goes down and big users retire, the meters on Caspar's homes would spin in the conventional direction, powered by the utility's base-load generators.
Natural "islands" of self-sufficiency may exist
at the ends of the grid's tendrils
But what happens when a winter storm, a squirrel, or a drunk driver takes out the tenuous powerlines that connect Caspar to the greater grid? Caspar could become an energy island. By day, Caspar's small individual systems would still be able to power essential equipment even for neighbors without energy-harvesting roofs. Even today, by carefully conserving battery-stored energy, most of the essential services for my home and my immediate neighbors can be maintained for days. The whole little village could easily provide the generation and storage required to maintain essential electrical service in times when grid power is unavailable, if we can all agree to be conservative. Our utility would have to install automatic local equipment which would allow Caspar to "cast off" its ties to the failed grid and steer its own course until grid service is restored.
Utility safety officers envision another scenario: What happens when the powerlines serving Caspar require maintenance? Workers could easily cut the main connections to the grid, but to the independent systems of Caspar this would look like another grid failure, and they would automatically go into "island" mode, keeping the local grid energized. To make islanding practical, all constituent power producers must be able to be told, "go local," whereupon they would discontinue pumping excess power into the community's distribution lines so workers can do their work safely. As more and more independent power producers come online in net-metering states and good renewable energy regions, this becomes a serious management challenge to utility planners, and no final solution has been determined.
The implications for future power sourcing are apparent. As centralized, fossil-produced power becomes scarcer and dearer, local independent systems powered by cogeneration, photovoltaics, wind, and hydro will proliferate. The grid serves distributed and centralized sources equally well: It is an instantaneous power broker. The production end is already well developed, and convenient domestic-scale power-management equipment can be purchased for less than most homes pay for electricity in two years. In the next decade, the problems and possibilities of islanding will be widely explored and developed.
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Independent home systems seldom fail, but their power production often dwindles. This can be the result of reduced sun, rain, or wind, or worse: If periodic maintenance is skipped, and users are inattentive to their meters, the system's capacity may be affected. The first time or two this happens, we are surprised, but then we usually learn to pay attention, and head off trouble before it happens. Since our expensive flooded lead-acid batteries are damaged by being seriously drained, this is something we are wise to avoid.
Over the life of a house, mechanical features -- anything involving wires, pipes, or motors -- will require periodic maintenance. The practical rule, a corollary of Murphy's Law, is that the probability of failure is directly proportional to the difficulties involved in correcting the problem. Cascading failures encountered or created while repairing other problems can complicate our lives in spectacular ways if major reconstruction becomes necessary. I have spent enough time standing on my head working with my arms twisted uncomfortably to learn to plumb and wire for accessibility. Distribution panels and other equipment requiring maintenance and troubleshooting should be placed as comfortably as possible; the code is very specific about leaving room for the electrician. I have learned (the hard way) to cover mechanical, plumbing, and electrical connections with removable panels, so that systems may be revealed and repaired and the undamaged panel replaced as neatly as when new. Screws are much less expensive than nails when they must be removed.
There is no substitute for an intimate, up-to-date knowledge of a home's systems. Experienced homesteaders catch and correct problems before they turn into outages or equipment is damaged. To avoid the "it only fails when I'm gone" syndrome, routine inspection responsibilities should be shared by everyone in the family tall enough to read the meter, evaluate the water flow, or note any other signals that may reveal changes in the health of energy systems. In many independent homes, an amp-hour meter, the instantaneous indicator of battery-bank balance, is mounted in the kitchen where all may see it.
By refining our sense of what should be happening at any given moment in the operation of a system, and comparing this with what is actually happening, troubles can be seen coming before they bring the system to its knees. Experienced users have a finely tuned sixth sense of how much sun fell on their panels, and how much energy should have been accumulated in storage, either as hot water or battery amp-hours. For example, if the actual battery state is less than expected, then a short, seasonally adjusted litany of causes is checked. In the fall, as the sun's apogee falls lower in the sky, new growth in trees may shade the photovoltaic array where half a year previously the array stood in full sun. A failing module, loose connections, a faulty charge controller, a power-hungry task performed earlier, or a small energy-pilfering load left connected: All these can affect the battery's state of charge. A single variation is worthy of note, not concern, but if the system continues to perform below expectations, the causes must be found and corrected before equipment is damaged. This implies vigilant attention on an almost-daily basis. Since this reckoning is complicated by season, climatic variations over many years, and changing supply and demand, new operators should not be despair; the intuitive sixth sense of the system may take years to develop, but it surely will come.
[[photo: an E-meter and a battery monitor
The amp-hour meter has revolutionized the way we track our power systems by showing us the balance between incoming and outgoing power, letting us know exactly what energy we have made and spent. Modern meters reset the zero point when they deem the batteries to be full, usually at the end of a charging day. As we use power, the meter counts down; when power is generated, the meter climbs back up from whatever low figure it reached during the current cycle. Experienced operators set limits on various activities, since it is unwise to operate batteries "on credit" by pushing them into new low territory. With my system, during the winter, an outage brings an immediate halt to vacuuming, ironing, and use of the washer and dryer. If we anticipate a prolonged outage, we bring use of major elective loads -- the big desktop computer and its printer, for example -- to an orderly conclusion. When reserves fall below -400, we go into emergency conservation mode, quickly consuming any sorbet remaining in the freezer before disconnecting the refrigerator, and using only essential lights and the pump. Once self-sufficient homesteaders learn how much electricity a task requires, they can easily decide if there is enough energy in the bank, and if the task is worth the loss of other functions later on. Intelligent management of demand minimizes surprises.
When installing an electrical system, experienced homesteaders are unanimous: It is a mistake to economize on metering, switching, and lighting in areas that must often be repaired. This applies to plumbed systems, too: Careful use of valves and unions allow for repair rather than major reconstruction. During initial installation and under budget pressure, we may think it wise to leave these inessential parts out, but we are invariably wrong. If it can fail, it will fail. Time and money spent in making systems easier to understand, operate, and repair pays itself back quickly, often the first time the system has problems. Good systems are designed to work well, to be maintained and repaired easily, to recover quickly from failure, and to be as cost-effective as possible over their whole installed life.
In addition, well-organized systems are controlled, metered, labeled, and documented so that it will be easy to localize a failure. Once the failed device is found, we should know, or be able to find in the system manual, what procedures to follow. Before the system really fails, supervised "lifeboat drills" will help us know what to do. It is easy enough to separate essential circuits -- minimal lighting, water pumping, telephones -- and make sure everyone in a household who must operate the system knows how to shut off all of the inessential loads speedily and safely.
Critical components -- computers, water systems, telecommunications -- should have their own backup power or be on separate circuits so that we have a few minutes to collect ourselves, make an orderly retreat, and call for help after the lights fail. A delicate balance must be found between too many redundant systems (each of which requires separate, time-consuming maintenance) and too few self-sufficient systems. My priority is to let water pumping go at first so I can maintain computer power while I save my work -- pressure in the big tank keeps us wet for a few hours if we are conservative.
Water systems have similar failure modes, and designing for maintenance is equally important. In a gravity system or a system with a big pressure tank like mine, when the source has failed, pressure decreases slightly for awhile, then reduces to a trickle. In pumped systems, pressure decreases from normal to a dribble as water is used. In either case, hours may pass between a failure event and its recognition, and so some means for monitoring performance of the remote source may be wise. Salamanders periodically stop Frank Dolan's system, and earwigs in the pressure switch accounted for 80 percent of our water outages until our resident plumber -- that would not be me -- placed a little neon lamp in the pressure switch housing to keep the photophobic little creeps away. By using each failure as an instruction on how to make a system more robust, we may expect failures to become rarer and more interesting.
When a home utility outage occurs, low-voltage dc lights cast a useful, reliable glow in places where troubleshooting may be required -- the metering station, the distribution center, the battery enclosure. Batteries are seldom so weak that they cannot make a halogen bulb glow. Independent homes should also be well endowed with functional flashlights, easily found, near places where people spend time or where darkness would be disconcerting. As above, so below: Solar-rechargeable flashlights are especially gratifying.
Since emergency-only systems are found to be inoperative only when we have an emergency, I like such systems to be in everyday use.
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