ECN publication
The DC low-voltage house
Published by: Publication date:
ECN 1-9-1997
ECN report number: Document type:
ECN-C--97-058 ECN publication
Number of pages: Full text:
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The use of photovoltaic (PV) energy in buildings is usually associatedwith a connection to the public electricity grid. The grid connection requires a conversion from direct current (DC) to alternating current (AC). This conversion enables both the use of standard AC household equipment and a connection to the public electricity grid. Many household appliances, however, function internally on DC. Within the AC equipment an alternating voltage of about 230V is transformed to a (low) DC voltage, for example 12 V. Utilising PV energy in this way involves two energy conversions with inherent energy losses. It is reasonable therefore to assume that these losses could be avoided by introducing a DC (low-voltage) grid. The feasibility of 'The DC low-voltage house' set within predefined boundary conditions is the subject of this report. The first part of the research is focused on household energy consumption. It became apparent that DC supply of household appliances is possible, but does not automatically reduce energy losses. The second part of the research concentrates on the DC low-voltage distribution system. It became clear that due to voltage and power losses, it will not be possible to satisfy the present power demand in households with a very low voltage distribution system. The main problems to solve in the design of the DC low-voltage distribution system are switching of DC currents and limitation of short circuit currents. The results of the first two parts of the research lead to conclusions on the feasibility of the DC low-voltage house. Observing the boundary conditions of the project, a change from AC to DC low-voltage in houses is not very promising. A large reduction of energy losses is not expected. Taking other conditions and circumstances into consideration (e.g. a very small power demand, the presence of a public DC electricity grid and the supply of certain types of appliances), may lead to a more positive assessment of the DC low-voltage house. 35 refs.

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