Applications
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| Heliostat used for direct space heating and natural lighting | Heliostat array used for concentrated solar power integrated with hydronic heating system (prototype) | |
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In bright sunlight, one Practical Solar Heliostat provides more visible light than forty 60-watt incandescent light bulbs. Natural light is not only more efficient, it is gentler to the human eye, reducing eye fatigue and headaches associated with fluorescent lighting. There are over 100 lumens per watt of sunlight. Thus natural lighting produces 3-7 times more visible light per watt of energy than electrical lighting systems. Incandescent lighting systems produce about 15-18 lumens (visible light) per watt of electricity consumed. Fluorescent lighting is somewhat more efficient, producing 30-40 lumens per watt. Electrical energy not converted to light is dissipated as heat. Incremental costs of air conditioning to remove heat generated by electrical lighting systems cost industries and households billions of dollars per year. Practical Solar Heliostats can provide natural lighting by directing sunlight through the windows of the shaded side of a building. Heliostats can also dramatically increase light input into natural lighting receivers and light tubes. Another important application is to direct sunlight into an atrium via a secondary reflector positioned at a 45 degree angle facing downward over the atrium. The secondary reflector can be sized as small as a two-foot diameter circle, if the mirrors on the Heliostats are focused to reflect a smaller sun spot (easily accomplished during the routine installation process). The Sun rays "crisscross" as they leave the secondary reflector and are gently dispersed downward through a skylight into the atrium. This technique of concentrating solar power provides an opportunity for building designers: a skylight can be small in size to minimize thermal losses through the glazing, and at the same time, the skylight can receive as much sunlight as a skylight many times its size. The result is that maximum energy comes in, while minimal energy goes out. This design concept can also be applied to thermal applications. Using Heliostats during the winter months for natural lighting works as "light therapy" to offset Seasonal Affective Disorder (SAD, "winter depression"). While many therapeutic products available on the market simulate natural sunlight, Practical Solar Heliostats deliver the real thing. Symptoms of Seasonal Affective Disorder include feelings of depression, sleeping too much, craving sweets, and having low energy. Practical Solar Heliostat Systems are most easily adapted for thermal applications that require low-grade thermal energy (<232°C or 450°F). Individual Heliostats can be used for direct thermal applications, meaning that sunlight is applied directly to an area or object(s) to be heated, rather than going through a central collector or receiver. For example, Heliostats can supplement a building’s heating systems by simply directing sunlight through windows and skylights. More sophisticated thermal applications distribute heat from a central receiver or collector ("CSP receiver"), which is the target of the Heliostats’ concentrated sunlight. Oil or steam is the preferred heat transfer medium for applications in the range of 100-232°C (212-450°F). For applications requiring thermal input below 100°C (212°F), water can be used as the heat transfer medium. For applications requiring thermal input higher than 232°C, the system can be customized to increase the concentration of energy. Thermal applications include:
Heliostats with thermal engines Thermal engines convert heat to electrical power. Most thermal engines require extremely high temperature input (e.g. 600°C [1112°F] and higher). Organic Rankine Cycle (ORC) microturbines and some Stirling engines can operate with inputted temperatures below 232°C (450°F) and are more compatible for use with Heliostats. Heliostats with photovoltaic panels Photovoltaic (PV) panels are generally mounted in fixed position, facing south with an upward tilt approximately equal to the latitude of the region (where 0° is horizontal). The result is that the Sun strikes the panels at an oblique angle (the "cosine error") early and late in the day, and is almost never perfectly perpendicular to the panel. Mounting the panel on a Heliostat, so that it is constantly perpendicular to the sun, increases the daily collection efficiency by about 30%. Heliostats can also be used to augment solar collection on fixed-position PV panels that are shaded at certain hours of the day. Care must be taken not to exceed the thermal limits specified by the PV panel manufacturer. Heliostats with advanced solid-state technologies Most intriguing is the use of solid-state technology to directly convert concentrated solar energy to electricity. Such technology might be combined with Heliostats to create a distributed generation system capable of delivering 5-50 kW of electrical power. One can envisage a pretty straightforward design concept: a receiver with a front face comprised of concentrator cells or thermo-electric material bombarded by X number of Heliostats. But concentrator cells huddled closely together present major challenges for heat dissipation, and thermo-electric technologies today do not offer high levels of solar-to-electric conversion efficiency. Most solid-state options are also extremely expensive. Practical Solar continues to monitor developments in such solid-state technologies taking place around the world. Here are some additional uses of Heliostats suggested by our customers:
We welcome your additions to the list! |
E-mail info@practicalsolar.com with questions or comments about this web site. © Practical Solar, Inc. 2008. All Rights Reserved. Last modified: 11/20/08. |