Journal of Energy Engineering

Offshore wind energy is developing rapidly in Europe and the trend is towards large wind farms with arrays containing in excess of 80 wind turbines. Considering the capital investment required to develop an offshore wind farm, accurate assessment of the wind resource/power output from the wind farm is a necessity. Accurately predicting the power output requires an estimate of the wind resource over the lifetime of the wind farm $(20–50\text{years})$ at the turbine hub height. The lack of climatologically representative in situ measurements at typical turbine hub heights and potential nonstationarities in flow regimes introduce uncertainties in the resource assessment which are described herein along with methods that may be used to reduce or quantify these uncertainties.

Preliminary data from controlled experiments indicate that in plasma electrolysis, metallic electrodes do not have to be immersed in water to produce hydrogen and oxygen as in the case of traditional electrolysis. Instead, the electrodes can interact with water through atmospheric pressure plasmas located between the electrode tips and the water surface. Experiments and spectral analysis of the light emitted by the plasmas as well as mass spectroscopic testing of gases from a region near the negative electrode, clearly indicate that the plasma associated with the negative electrode evolves hydrogen from the water. When a single plasma electrode was used in conjunction with a conventional immersed metal electrode, vigorous bubbling was observed at the immersed electrode. In very broad but fundamental terms, the advantage of this method is that high velocity transport of hydrogen through gas phase plasma-bounding regions (i.e., plasma sheaths) might replace low-speed diffusion through liquid phase that is currently used in conventional electrolysis. This process is likely to increase the rate of generation and collection of hydrogen over those of current electrolysis methods with high potential for integration into fuel cell systems and modular units for augmentation of small-scale power systems for distributed electricity generation.

The advanced high-temperature reactor is a new reactor concept that combines four technologies in a new way: coated-particle nuclear fuels traditionally used for helium-cooled reactors, Brayton power cycles, passive safety systems and plant designs from liquid-cooled fast reactors, and low-pressure liquid-salt coolants. The new combination of technologies may enable the development of a large high-efficiency, lower-cost high-temperature $(700\text{to}\mathrm{1,000}°\mathrm{C})$ reactor for electricity and hydrogen production. As the peak reactor coolant temperatures approach $700°\mathrm{C}$ , several technologies (Brayton cycles, passive reactor safety systems, available materials, etc.) work together to improve total system performance while significantly reducing costs relative to those for other reactors. A window of performance and lower capital costs exists between these temperatures and the practical temperature limits of materials. The higher temperatures and efficiency of the Brayton power cycle greatly reduce the total heat rejection compared with that achieved in current light-water reactors and may allow economic heat rejection with dry cooling towers, thus radically reducing the water consumption used in energy production. The option for dry cooling is facilitated by the characteristics of Brayton cycles, which reject heat over a temperature range of $40\text{to}50°\mathrm{C}$ and thus match the requirements of dry cooling systems.

A solar energy heat collector was combined with photovoltaic cells to form one single hybrid energy generating unit. This system produces both thermal and electrical energies simultaneously. An experimental setup of a double-pass photovoltaic-thermal solar air collector with a compound parabolic concentrator (CPC) and fins was designed and fabricated to study the performance over a range of operating conditions. The collector is designed in such a way that the absorber surface is partially covered by solar cells. A CPC is used to enhance more electrical and thermal energy output from the collector. However, solar cells perform poorly at high operating temperatures. Therefore, fins are attached at the back side of the absorber surface to improve this situation. A circulating air stream passes through an upper channel and then under the absorber plate or lower channel of the collector carrying away the excess heat and thus maintaining the cells at the optimum operating conditions. The performance of the system has been measured. The thermal, electrical, and combined electrical thermal efficiencies of the collector are presented and discussed.

A hybrid photovoltaic-thermal (PV/T) solar air heater system which generates both electricity and heat energy simultaneously was studied. This hybrid system consists of monocrystalline silicon cells pasted to an absorber plate with fins attached at the other side of the absorber surface. Air as heat removing fluid is made to flow through an upper channel and then under the absorber plate or lower channel of the collector. Only a small part of the absorbed solar radiation is converted to electricity, while the rest increases the temperature of the cells. Improvements to the total efficiency of the system can be achieved by the use of a double-pass collector system and fins. This paper presents the experimental and theoretical studies on a finned double-pass PV/T solar air heater suitable for low temperature applications. A steady-state closed-form solution to determine the outlet and mean photovoltaic temperature has been obtained. An experimental setup has been developed. Comparisons are made between the experimental and theoretical results and close agreement, is obtained.