Toast, Pancakes and Waffles: Planning Wisely for Off-Grid Living


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Categories: Energy

 

Living well on a small and finite amount of electricity is not mysterious or difficult. It starts with careful adherence to three basic principles:

  1. Shift inappropriate loads to other forms of energy.
  2. Reduce waste through efficiency, and increase conservation.
  3. Use energy in proportion to the amount available.

The average home here in New Mexico uses 600 kWh of electricity per month, or about 20 kWh per day. This works out to a bill of about $50 per month, plus base charges. By comparison, a 1 kW PV array in a modern off-grid power system produces about 5 kWh per day in summer and a bit less than 4 kWh per day in winter. This is less than 25% of the amount of electricity used by the typical home. Yet for plenty of off-grid homes in New Mexico, a 1 kW system yields more than adequate power to run all of the lights, appliances, and electronics that make a comfortable life.


A load analysis—a systematic and methodical listing of everything you expect to power in your home—has always been an essential part of off-grid power system design. For each load, the expected power consumption and hours of use are listed. (For information on completing a load analysis, see the “Assessing Loads” sidebar.) There are no one-size-fits-all solutions—each off-grid system is uniquely designed to its site, loads, budget, and the personal wishes of its owners.

Shifting Loads

All forms of energy are not created equal. Electricity is a specialized, high-quality form that is not suited to all applications but great for some: lights, electronics, and motors, plus a few other specialized uses. By matching the best form of energy to its appropriate use, electricity consumption can be greatly reduced while enhancing comfort and convenience.

Five common uses of electricity in conventional on-grid homes won’t typically show up in an off-grid home. Each consumes too much energy to be appropriate when the supply is limited by typical PV system costs. All five of these use electricity in ways best served by other forms of energy.

Space Heating. Electricity may be used to run thermostats, pumps, and boiler controls, but in an off-grid system it is not usually turned into actual heat. The sun’s heat is best used directly. Build or retrofit your home to hold in as much heat as possible by maximally insulating the structure’s walls, ceilings, and/or attic spaces, and floor. Seal gaps and cracks well. If you’re building a new home, incorporate passive solar strategies by using properly sized south glazing and plenty of thermal mass. If you have or are planning in-floor radiant heat, active solar thermal collectors (“solar heat”) can be installed to decrease or avoid boiler use. Otherwise (or in addition), plan to use wood or propane heaters to provide space heating.

Water Heating. Use the sun directly to heat your water with a solar hot water system and use a high-efficiency propane water heater as backup.

Tankless gas water heaters are an option for some homes. However, in areas where hard water predominates, the cost and hassle of the increased maintenance and repairs due to scaling buildup tend to offset potential energy savings. Tankless water heaters use multiple small tubes to heat water quickly. The minerals build up in the small passages, decreasing the unit’s efficiency.

Cooking. Plan to use a gas range and oven, not an electric one. But beware: Many gas ovens use electric “glow-bars” that can draw up to 500 W continuously when the oven is on.

Also consider a solar oven, if your lifestyle allows. Many of the common-sense solutions to living well when you’re off the grid are simply reapplying lost wisdom from days before electricity was taken for granted. For instance, a summer kitchen, often located outdoors in a screened porch on the north side of the home, allows for preparing summertime meals without overheating the home.

Clothes Drying. In most parts of the country, a solar clothes dryer (also known as a clothesline) or an indoor drying rack can be used year-round. To back up these strategies, however, your standard clothes dryer should use gas, not electricity, for heat.

Air-Conditioning. Space cooling is usually only needed during summer months—when more PV power is often available—but conventional whole-house air conditioning is still too large of a load. Good passive design—like having adequate overhangs to shade windows, having trees and shrubs shade the house, and using good ventilation strategies—can often eliminate the need for any mechanical cooling. Otherwise, fans and evaporative cooling (“swamp coolers”) work well in arid climates. Ultra-efficient DC evaporative coolers are available that work very well.

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