333,606 research outputs found
Gossamer roadmap technology reference study for a solar polar mission
No full textA technology reference study for a solar polar mission is presented. The study uses novel analytical methods to quantify the mission design space including the required sail performance to achieve a given solar polar observation angle within a given timeframe and thus to derive mass allocations for the remaining spacecraft sub-systems, that is excluding the solar sail sub-system. A parametric, bottom-up, system mass budget analysis is then used to establish the required sail technology to deliver a range of science payloads, and to establish where such payloads can be delivered to within a given timeframe. It is found that a solar polar mission requires a solar sail of side-length 100 – 125 m to deliver a ‘sufficient value’ minimum science payload, and that a 2. 5μm sail film substrate is typically required, however the design is much less sensitive to the boom specific mass
The effect of colour on the thermal performance of building integrated solar collectors
No full textThe use of solar collectors with coloured absorbers for water heating is an area of particular interest when considering their integration with buildings. By matching the absorber colour with that of the roof or façade of the building, it is possible to achieve an architecturally and visually pleasing result. Despite the potential for the use of coloured absorbers, very little work has been undertaken in the field.
In this study, the thermal performance of a series of coloured (ranging from white to black), building integrated solar collectors for water heating was examined both theoretically and experimentally. Subsequently, the annual solar fraction for typical water heating systems with coloured absorbers was calculated. The results showed that coloured solar collector absorbers can make noticeable contributions to heating loads. Furthermore, although their thermal efficiency is lower than highly developed selective coating absorbers, they offer the advantage of improved aesthetic integration with buildings
Designing photovolaic/thermal solar collectors for building integration
No full textWith concern growing over the environment and resource use, there has been greater emphasis placed on sustainability, particularly in the built environment. One of the key points of sustainable urban environments is the need for an increase in the densification of the population. A by-product of increased densification however, is a reduction in the area per person that can be used for on-site renewable energy generation from the solar resource. Where previously it would have been possible to have a photovoltaic array and solar water heater side-by-side for a free-standing household, this may not be achievable in a high-density living situation.
As a counterpoint to this issue, the design of a novel combined photovoltaic/thermal for building integration (BIPVT) solar collector is analysed and discussed. The panel has a higher efficiency per unit area, than an array of photovoltaic panels in combination with solar thermal panels. In addition, by integrating electricity generation, water heating and facade elements it is possible to reduce the complexity associated with traditional solar installations while also achieving an architecturally sensitive appearance. As such the BIPVT is ideally suited to environments where facade space with suitable solar access is limited, or where large numbers of people share a single building.
In this study, the influence of key design parameters on the performance of a BIPVT collector are presented and discussed. Finally, a transient systems analysis is used to illustrate the performance benefits of BIPVT style collectors over traditional technologies
Performance of a building integrated photovoltaic/thermal (BIPVT) solar collector
No full textThe idea of combining photovoltaic and solar thermal collectors (PVT collectors) to provide electrical and heat energy is an area that has, until recently, received only limited attention. Although PVTs are not as prevalent as solar thermal systems, the integration of photovoltaic and solar thermal collectors into the walls or roofing structure of a building could provide greater opportunity for the use of renewable solar energy technologies. In this study, the design of a novel building integrated photovoltaic/thermal (BIPVT) solar collector was theoretically analysed through the use of a modified Hottel–Whillier model and was validated with experimental data from testing on a prototype BIPVT collector.
The results showed that key design parameters such as the fin efficiency, the thermal conductivity between the PV cells and their supporting structure, and the lamination method had a significant influence on both the electrical and thermal efficiency of the BIPVT. Furthermore, it was shown that the BIPVT could be made of lower cost materials, such as pre-coated colour steel, without significant decreases in efficiency.
Finally, it was shown that by integrating the BIPVT into the building rather than onto the building could result in a lower cost system. This was illustrated by the finding that insulating the rear of the BIPVT may be unnecessary when it is integrated into a roof above an enclosed air filled attic, as this air space acts as a passive insulating barrier
Solar Central Receiver with an Irising Aperture
No full textVariable sun elevation, azimuthal and declination angles with the time of day, and seasons of the year respectively, give variable projected image size defects produced by field site concave mirrors on the central cavity receiver's aperture entrance. If the aperture is small, it will be inefficient for periods when the solar isolation is inclined due to spillage. However, if the aperture is large, it will be inefficient for periods when the solar isolation is normal, due to excess heat radiation and convection losses. Thus, the fixed aperture area size is a compromise between ideal sizes for different conditions. The end result is a loss of efficiency as a function of time of day and seasons of the year. This research presents an approach to maximize the interception factor on the receiver entrance, with reducing the heat losses by radiation and convection through its aperture area. A central receiver system, having a down-looking cavity with an irises aperture is being proposed for application in rich environmental solar conditions, utilized solar flux insolation throughout the day on the city of Kuwait. Solar tower focusing collector with a cavity type receiver having a fixed area aperture at the entrance is presented for comparison with the proposed technique. This collector is proved to be less efficient than the suggested design. The isiring cavity receiver with a variable area aperture provides an approximately constant efficiency regardless of the time of day or season of the year. The end result is the proposed system shows improved performance and capability. However, over the life-time of installation these advantages of the proposed system should overweigh its disadvantages of additional cost due to extra automation
Solar Sailing: applications and technology advancement
No full textHarnessing the power of the Sun to propel a spacecraft may appear somewhat ambitious and the observation that light exerts a force contradicts everyday experiences. However, it is an accepted phenomenon that the quantum packets of energy which compose Sunlight, that is to say photons, perturb the orbit attitude of spacecraft through conservation of momentum; this perturbation is known as solar radiation pressure (SRP). To be exact, the momentum of the electromagnetic energy from the Sun pushes the spacecraft and from Newton’s second law momentum is transferred when the energy strikes and when it is reflected. The concept of solar sailing is thus the use of these quantum packets of energy, i.e. SRP, to propel a spacecraft, potentially providing a continuous acceleration limited only by the lifetime of the sail materials in the space environment. The momentum carried by individual photons is extremely small; at best a solar sail will experience 9 N of force per square kilometre of sail located in Earth orbit (McInnes, 1999), thus to provide a suitably large momentum transfer the sail is required to have a large surface area while maintaining as low a mass as possible. Adding the impulse due to incident and reflected photons it is found that the idealised thrust vector is directed normal to the surface of the sail, hence by controlling the orientation of the sail relative to the Sun orbital angular momentum can be gained or reduced. Using momentum change through reflecting such quantum packets of energy the sail slowly but continuously accelerates to accomplish a wide-range of potential missions
An oriented-design simplified model for the efficiency of a flat plate solar air collector
No full textIn systems design, suitably adapted physical models are required. Different modelling approaches for a solar air collector were studied in this paper. First, a classical model was produced, based on a linearization of the conservation of energy equations. Its resolution used traditional matrix methods. In order to improve the possibilities for use in design, the behaviour of the collector was next expressed in terms of efficiency. Lastly, simplified models constructed from the results obtained with the classical linearized model, and explicitly including the design variables of the collector, were proposed. These reduced models were then evaluated in terms of Parsimony, Exactness, Precision and Specialisation (PEPS). It was concluded that one of them (D2), using a low number of variables and of equations, is well suited for the design of solar air collector coupled with other sub-systems in more complex devices such as solar kiln with energy storag
Performance of a building integrated collector for solar heating and radiant cooling
No full textDue to their limited temperature range, unglazed solar collectors have long been relegated to providing low cost heating in applications such as swimming pool heating systems. This limited temperature range is due to heat loss: firstly by convection to the surrounding air and secondly by radiant heat transfer to the cold sky. During the day an unglazed collector can be operated as a standard solar absorber to heat water in a storage tank. However, it is possible to take advantage of radiant cooling of unglazed solar collectors by operating them at night. Under night conditions when there is no solar radiation and the sky temperature is low, the collector can radiate heat to the sky and cool a cold storage tank to provide cooling in the building the following day.
This study theoretically and experimentally examines the performance of a building integrated collector for heating and cooling and explores the contribution it can make to heating and cooling loads in typical New Zealand and Australian buildings
Solar sail capture trajectories at Mercury
No full textMercury is an ideal environment for future planetary exploration by solar sail since it has proved difficult to reach with conventional propulsion and hence remains largely unexplored. In addition, its proximity to the Sun provides a solar sail acceleration of order ten times the sail characteristic acceleration at 1 AU. Conventional capture techniques are shown to be unsuitable for solar sails and a new method is presented. It is shown that capture is bound by upper and lower limits on the orbital elements of the approach orbit and that failure to be within limits results in a catastrophic collision with the planet. These limits are presented for a range of capture inclinations and sail characteristic accelerations. It is found that sail hyperbolic excess velocity is a critical parameter during capture at Mercury, with only a narrow allowed band in order to avoid collision with the planet. The new capture methodis demonstrated for a Mercury sample return mission
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