May 15, 2009

As the book proceeds, I keep coming back to the question, is it possible to achieve the same level of amenities in a completely off-grid residence as in a home using utility supplied heat and electrical power. Or, if it's not possible now, will it be possible eventually?

Here I'll attempt to provide some brief answers. An extended consideration will form of the subject matter of the book.

Heat and Electricity

The question has to be approached from two perspectives, one focused upon satisfying heating needs and the other upon self-generated electrical power.

Residential Electrical Generation Capacity

The huge majority of off-grid energy self sufficient houses derive their electrical energy from solar power. Wind is a distant second. In a favorable solar regime approximately a kilowatt of power impinges continually on exposed surfaces during the hours of daylight. Only about ten percent of that can be harvested by solar panels, and further losses occur in the ancillary electronics used to store, convert, and condition the electricity produced by photovoltaic cells. Consider as well that the panels must be properly oriented toward the sun to generate much electricity, and so it's rarely possible to use the entire roof as a mounting surface. You can mount solar panels on other surfaces such as patio shades or even on the ground, but a patio will only a provide a small increment of energy retrieval, and ground level installations are difficult in many cases due to shading. Windows with photovoltaic properties are also coming on the market, but windows are nearly always suboptimally oriented for maximum electrical generation.

So if it's hard to get there with solar, what are your options?
Wind, the distant second among renewable energy sources, is not limited by the size of your roof. You can put a huge wind turbine in your back hard that takes up maybe a couple of square meters of ground and almost any property can accommodate that. The problem is the cost and the legality. Wind is an excellent resource in the classic off-grid setting, a lot in the hinterlands where the home being served is isolated and zoning laws and building restrictions probably don't exist. But in a suburban residential neighborhood you may be enjoined from erecting a sizable wind turbine.

And you're still looking at a fairly mammoth installation if you aim to replace grid power. A wind turbine capable of generating ten kilowatts on a fairly continuous basis is necessarily huge. The blades may span thirty feet or more, and the nacelle may weigh hundreds of pounds and will probably necessitate crane mounting. A massive steel tower and a concrete slab will be necessary to elevate the turbine to the requisite height of close to a hundred feet and to secure it in place. And don't be fooled by company power output specifications. Wind turbines are always rated at maximum output. Typical output is generally a fraction of that figure.

There are some promising developments underway. A Massachusetts based company calling itself FloDesign claims to have developed a turbine with a maximum output rating of 100 kilowatts and having a diameter of merely twelve feet. These guys are aircraft manufacturers specializing in jet engine design and they claim that they derive their approach from fanjet machinery. But they also claim that their turbines can operate at much higher windspeeds than can conventional turbines and I'm willing to bet that's how they arrive at the 100 kilowatt rating. I imagine it's based on 50mph wind velocities.

There are some other innovative designs of high efficiency and compact form factor and even a few that can be installed close to ground and don't require cumbersome towers, but the really innovative companies are all small and struggling. The leaders cling to traditional designs. I wish firms like FloDesign a lot of luck. They're going to need it.

You can of course combine a wind turbine of moderate dimensions with an extensive solar array and that might provide you with enough generation capacity to maintain a high energy lifestyle. Again, you're probably going to be limited in terms of what is permissible within your area regarding wind installations and how many solar panels you can deploy on your roof. So are those the only options?

Not exactly. I will present some of those options in the following entry.