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Publication Title | Y2K Prescription Advice from Renewable Energy Dealers & Distributors

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Backup Power

Advice from Renewable Energy Dealers & Distributors

Allan Sindelar & Ian Woofenden

©1999 Allan Sindelar and Ian Woofenden

Renewable energy dealers and distributors are receiving lots of inquiries about standby electrical

power systems to provide power and water in the event of an extended utility outage on January 1, 2000. Some people are asking about photovoltaic (solar electric, or PV), wind, and microhydro power options. Others ask about using a portable gasoline or propane fueled generator as a backup power solution. Others want to know about battery banks and inverter/chargers.

Predictions of what will occur on January 1, 2000 range from a few minor inconveniences to the total collapse of society. Unlike a hurricane, tornado, or earthquake, we have a date circled on our calendars. But no one can accurately predict the extent of disruption, or if there will even be one.

How can you prepare for a power outage and the problems it would cause? Unfortunately, the solution is not simple. A PV system that can provide abundant electricity for a typical off-grid home will not run a conventional home.

Designed for Efficiency

Off-grid homes are designed and built with solar electricity in mind. Lighting, appliances, electronics, and wiring are all selected and installed to make each watt- hour of electricity do as much work as possible. Tasks

70 Home Power #71 • June / July 1999

such as cooking, clothes drying, water heating, and space heating are shifted to natural gas, propane, wood, or solar heat. Done well, the result is a home that is bright, warm, and comfortable, while using a tiny fraction of the electricity of a typical on-grid home.

Conventional homes are seldom designed and built to this level of efficiency. Here’s one way to look at the difference: A typical PV power system that can supply about three kilowatt-hours worth of electricity on a winter’s day might cost $15,000 or more. With a small amount of backup generator power during cloudy periods, this is ample to meet the needs of a family. Supplied by the utility company, the bill would be less than ten dollars a month, plus base charge and taxes! Few utility customers have bills this small, because few have done the load shifting and high efficiency improvements necessary to live comfortably on the amount of electricity supplied by an independent PV power system.

DC to AC

There is another key difference between homes supplied with utility power and off-grid homes. Power from PVs and small wind and hydro installations is low voltage DC power, and is stored in batteries. Inverters convert the stored DC power to conventional 120 volt AC power.

Most small appliances, lights, tools, and other electrical devices operate at 120 volts AC. Larger appliances such as electric heat, water heaters, stoves, dryers, and many well pumps operate at 240 volts AC. Heating water and cooking can be done by propane or natural gas. But a backup power system must be oversized with a step-up voltage transformer or two inverters operating together to run many well pumps. This adds to the cost and complexity of the backup power system.

Short Days & Cloudy Weather

If this isn’t enough, Y2K will occur when the nights are long and the days are short. A winter storm that brings a week of cloudy weather means that little solar electric power will be available to recharge the batteries.

People who live off-grid typically use a combination of wise use, battery storage, and a backup generator/charger to weather these seasonal periods. When the batteries are depleted and the system is without generator backup, the only option is to stop using electricity and wait until the PV array can catch up. This might take several days or weeks.

Expert Opinions

Coming up with a successful backup power system is not easy. There are many questions, and they are not always simple. Opinions within the industry vary. What’s best for the customer? What’s best for the industry?

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