Energy Needs of The Home

We measure energy in joules. It is the same unit for heat energy as for electrical energy as for mechanical energy as for any form of energy. A joule is a watt-second. There are 3,600 watt-seconds in a watt-hour, and 3,600,000 watt-seconds (3.6 megajoules) in a kilowatt-hour.

My household consumes energy in two forms:
eh = thermal energy for space heating and hot water
ee = electrical energy for lighting and electrical devices

My first task in this personal project is to monitor how much thermal and electrical energy my family actually uses in our suburban home; in other words, to find out our energy needs.

Our domestic energy is currently provided by the national gas and electricity grids from the street. My quest is to see how this energy could be provided directly and sustainable from nature independently of any utility.

Sustainable Sources

Systems like anchored floats to extract energy from ocean waves are not practical for small scale use. Not everybody lives near the ocean. Hydropower - a water wheel or turbine in a fast flowing stream driving an alternator - is also not much use to the majority of people who do not have a mountain stream flowing through their back yards. Electrolytic methods - making damp ground act like a battery cell - give only a very low yield and only work where the ground is damp and acidic. Geothermal energy - natural warmth from below ground - is universally available but involves the cost, practicality and legality of drilling a deep hole in the ground. Small-scale fuel cells are being developed but are currently still way too expensive for household use and would have to be designed for sustainable fuels.

Although wind power is simple and practical, many people find wind fans irritating and unsightly. Consequently, planning permission is difficult to obtain for wind generators of a size capable of providing enough electricity for a household. However, one small wind generator capable of delivering a maximum of about 250 watts can often be erected without planning permission. This may be useful to supplement solar arrays in the depth of winter. There is however another far less obtrusive way for implementing a wind generator.

This leaves only the following sustainable sources of energy which are both universal and practical for household use:

There are of course other sources which are currently still at the stage of scientific speculation. These are based on exotic phenomena like cold fusion and the zero-point energy which is thought to be woven in to the universal fabric of space-time.

Practical Systems

Systems which convert these sources of energy into electricity usually also produce heat as a by-product. Since we need heat also, it is well to make use of this heat to warm the house or provide hot water. The process of making use of otherwise wasted heat in the generation of electricity is called co-generation. So far I have considered only the following co-generation systems:

I have also provided an interactive table for calculating the size of backup battery needed to compensate for fluctuations in electrical supply and demand.

My attempt at integrating these into a practical co-generating system is shown below. The little wind generator is an after thought which, it is hoped, will tend to compensate for the reduced performance of the PV array on overcast days and in winter.

The PV array is water-cooled in winter by a low-temperature home heating system, which is switched to a cooling pond in summer. Keeping it cool makes the PV array more efficient and co-generates heat for keeping the house warm in winter. A low-temperature home heating system provides a more efficient heat sink for the Stirling engine and the PV array. A low temperature central heating system uses much larger radiators operating at only 40 to 45°C. These radiators would normally be implemented as integral sections of wall.

My PV array does not generate quite enough electricity in the depth of winter, yet generates far more than is needed during the summer. This summer excess cannot be stored for winter use. A battery of sufficient size would be way beyond practicality. Nevertheless, this large summer excess of electricity can be put to good use in the cutting of wood for winter. There is also plenty for powering static farm machinery at the time it needs to be used most.

© January 2001 - Robert John Morton
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