Direct-Current Voltage in Households

Peter Vaessen - KEMA TDC

September 2005

Energy sector liberalization and the pursuit of a sustainable energy supply are stimulating many changes in the electricity sector. Small-scale durable technologies are available and the share of decentralized generation is increasing. On the other hand, the increased vulnerability of the present and future electricity distribution system is an important issue. Certainly considering our society's growing dependence, and particularly that of European senior citizens, on electrical powered devices and information services.

DC is currently a hot topic in the industry. This is in part due to the better utilization of existing transmission corridors with High Voltage DC connections and the availability of efficient AC-to-DC, DC-to-AC and DC-to-DC conversion technology. Direct Current has also come into the spotlight due to the tremendously increased use of variable-speed motors of all sizes, local DC generation from systems including solar cells and fuel cells, and the explosive numbers of appliances in households, offices and industries that run on low voltage direct current. Examples include 12-volt halogen lighting, energy saver lamps, telecommunication and computer equipment and cordless/rechargeable devices and tools.

The introduction of a local means for generating and storing electricity will dramatically change the electricity supply system. Consider, for instance, the fuel savings at the generating stations if it is no longer necessary to increase production during the morning hours. Or consider the reduced dependence of industry, offices and households; a power supply interruption of up to 2 hours per day would no longer be a problem for critical processes and equipment. This will change the character of the electricity network, which will function more as a backup system and a provider of "extras" (in the sense of reliability and comfort), and this will be reflected in the prices that are charged for these services. Assuming local storage and electricity generation at the end-user level, from sources such as solar cells arrays, the question is whether a complete DC voltage distribution system is technically and economically feasible. This would make the untold numbers of small transformers with rectifiers (only 60 to 70% efficient) obsolete. Small variable-speed motors could be connected directly to this DC network.

This article examines whether it is technically, economically and socially possible to achieve significant savings through the distribution of DC voltage in homes and offices. The reasoning is based upon a potential future situation that is achievable for Europe in approximately 30 years. In this scenario 50% of the required electrical energy and all required heat are generated locally, in the neighborhood or at the household or office itself, and there are sufficient (inexpensive) local storage facilities for electricity and heat available.