Energy Analysis Of Wave Energy Concepts: Final Report, Section 1 Final Report

Abstract

Energy analysis is the study of the energy required to provide a product or service. In the case of the wave energy systems being developed in the U.K., the product is electrical energy, delivered to the electricity supply network at Skye. The energy necessary to supply this electricity comes in two forms. The first is the energy in the sea waves which is converted by the wave energy device to electricity by means of intermediate mechanical, hydraulic or pneumatic mechanisms. This route is studied carefully by the engineers of device teams in order to arrive at an efficiency for the device. The remainder of the energy necessary to supply the output electricity does not appear in the direct conversion process noted above. It is embodied in the structure and equipment of the wave energy devices, and is also used up in the installation and maintenance of the devices during their operating lifetime. Every product of the industrialised world uses energy in its production. Most of this energy is supplied by the fossil fuels such as coal, oil and gas, the remainder being supplied as nuclear or hydro-electricity. So every wave energy system will be subsidised to a certain extent by previously supplied, mainly fossil fuels. The job of the energy analyst is to find out the quantity of this external energy necessary to build and maintain a wave energy system. This energy input can then be compared with the energy output of the wave energy system, using a measure known as the net energy requirement (N). This expresses the amount of external energy subsidy per unit of energy output. If this number is very small (N < < 1) the system uses very little external subsidy compared to its energy output and the system is energetically viable. If the net energy requirement is larger than unity (N > 1) it will mean that the system is a net energy sink, as it has used up more externally supplied energy in its construction than it produces during its lifetime and thus the system is energetically futile. Most of the wave energy system studied here lie somewhere between these two extremes. To calculate the energy input to a wave energy system, a large amount of information is necessary. A detailed weight breakdown of each component of the wave energy system is needed, along with a data base of the energy requirement of all the products and processes which go in to manufacturing a complete wave energy system. This data base has been assembled at Sunderland Polytechnic, and has been greatly enlarged since first started in 1975. Information concerning device design has been obtained from device teams, their consultants, published and other sources. Energy outputs for each system are based on the productivities agreed by the programmes assessors, Rendel, Palmer and Tritten.