Natural Lighting
In bright sunlight, one Practical Solar heliostat provides more visible light than forty 100-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.
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. Heliostats can also direct sunlight into atriums 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 escapes. This design concept can also be applied to thermal applications.
Health
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.
Thermal
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.
Practical Solar is currently developing ancillary products like thermal receivers that would be paired with a heliostat system for more sophisticated thermal applications. The heliostats reflect concentrated sunlight onto the central receiver or collector ("CSP receiver"), which distributes the heat. Practical Solar Heliostat Systems are most easily adapted for thermal applications that require low-grade thermal energy (<232°C or 450°F). 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.
Direct thermal applications include:
- Interior space heating
- Swimming pool heating
- Drying paint or wood, melting ice dams on roofs, and other miscellaneous direct thermal applications
Thermal applications with ancillary products include:
- Building heating and cooling (HVAC)
- Potable hot water heating
- Air conditioning (with hot water-driven absorption chillers)
- Thermal desalinization
- Hydrogen (H2) production (for fuel cells)
- Low temperature industrial and agricultural applications (e.g. drying of wood, grain, leather)
- Powering a thermal engine (see Electrical Power below)
Electrical Power
Heliostats with thermal engines
Thermal engines convert heat to mechanical power. A generator can then convert that mechanical power to electrical power at near 100% efficiency. 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 concentrator cell technology (advanced PV)
Most intriguing is the use of concentrator cell technology or advanced photovoltaics 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. Please see the Technology page for more information.
Creative Applications
Here are some additional uses of heliostats suggested by our customers:
Creative Lighting Applications
- Growing vegetables in winter or in shaded areas
- Lighting windowless rooms (like medical and dental exam rooms) by using heliostats in conjunction with tube & mirror natural lighting systems
- Illuminating museum and art exhibits
- Sign illumination
- "Moonlighting" a patio or deck at night (software can be adapted for moon tracking)
- Casting sunlight through a large prism
Creative Thermal Applications
- Drying shaded exterior walls to reduce mildew
- Melting ice dams on roofs
- Drying paint or glue outdoors
- Drying linens on a clothesline
- Drying firewood
We welcome your additions to the list!