The Practical Solar Heliostat System
What it includes
What it does
What it's for
What it costs
FAQ
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Making Solar Practical
What it includes
A Practical Solar Heliostat System consists of any number of heliostats and one control system. Click here for details and specs on heliostats, or click here for details and specs on the control system. There also are a handful of materials that customers typically provide themselves, including the reflectors. These are common products that can be purchased locally for less money than shipping alone would cost if ordered through Practical Solar. Click here for more information about these miscellaneous materials. If customers have trouble finding any of these items, they should contact Practical Solar.
What it does
Practical Solar heliostats calculate the position of the sun and move its mirror frame (up, down, left, right) to reflect the sunlight onto a fixed target chosen by the user. Each heliostat reflects about as much visible light as forty 100-watt light bulbs, as well as 600 watts of thermal energy (heat). Heliostat are individually programmed and controlled by the software, which runs as a background program on the user’s computer. This means that an array of multiple heliostats can direct sunlight to different targets simultaneously, or to a common target for concentrating solar power (CSP). Users can save multiple targets for a single heliostat and switch between the targets at will, or use the software’s timer function to switch between targets automatically.
The user also has the option of individually focusing the 8 mirrors in a heliostat’s mirror frame to customize the size and shape of the reflected sun spot. Unconcentrated sunlight is suitable for many natural lighting and space heating applications, but users have the option of achieving a 4X concentration per heliostat. Heliostat arrays can achieve concentrations of up to 250 suns. See the Technology page for more detailed information about the amount of energy heliostats deliver.
What it's for
The Practical Solar Heliostat System can be used for anything that requires light or thermal energy (heat). Used on its own, the heliostat system can be used for natural lighting, “direct” thermal applications like space heating, and a wide array of creative heating, lighting and drying applications. Because each heliostat operates independently and can have multiple targets, the heliostats can perform different tasks at different times of day or during different seasons of the year. Please see the Applications page of this web site for more information and ideas. For more advanced thermal applications, Practical Solar is currently developing ancillary products like a concentrating solar power (CSP) receiver that could be paired with the heliostat system.
What it costs
- Control system (software, driver box, & accessories) = $345
- Each heliostat (heliostat housing + mirror frame ) = $995
Quantity discounts available.
Customers in the U.S. who use the Practical Solar Heliostat System for thermal applications (e.g. direct space heating or concentrating solar power [CSP]), may be eligible for various federal and state tax credits and sales tax exemptions. For more information, please visit www.dsireusa.org (the Database of State Incentives for Renewables & Efficiency).
After installing the system (which handy homeowners can do themselves), the cost of running the system is minimal. A night light running all night consumes more power than 100 heliostats running all day. Each heliostat delivers 3,000 times more power than it consumes. Practical Solar encourages its customers to control their heliostats with a computer that would normally be on during the day anyway, and to shut off the screen or monitor when not using it for anything else. Heliostats are already more cost-effective than electricity for space heating and they will soon become competitive with home heating oil as ancillary products become more widely available.
Frequently Asked Questions
How many heliostats do I need?
Can I heat a building with heliostats?
If I direct sunlight through a window, aren’t the people inside going to get sun in their eyes?
If I direct sunlight through a window, will it feel like I’m being “blasted” by sunlight?
How can I use heliostats to warm my house at night or when the sun isn’t out?
Won’t properly insulated windows keep out heat from the sun?
Do I need a large land area to have a heliostat system?
Can this system set my house on fire?
Will I have to deal with the zoning board or historical preservation board in my city/town?
Will snowfall prevent a heliostat from reflecting sunlight?
Will deep snow prevent a heliostat from operating?
Is the size of the reflected sun spot dependant on the distance the heliostat is from the target?
Is bigger better when it comes to heliostats?
- How many heliostats do I need?
The number of heliostats you need will depend on your application.
Natural lighting: Each heliostat reflects about as much visible light as forty 100-watt light bulbs, so one heliostat is very effective for natural lighting in a single room, and the heliostat can illuminate different rooms at different times of day. If you want to illuminate more than one room simultaneously or a very large room like a lobby, you would need additional heliostats.
Space heating: Each heliostat also delivers 600 watts of thermal energy (heat), so when two heliostats direct sunlight into a single room, they deliver 600 + 600 = 1200 watts of heat. This is about equivalent to the heat delivered by an electric space heater on "high", so two heliostats can essentially replace an electric space heater, or allow you to turn down the heat in that room or part of the house.
Concentrating solar power (CSP) applications: More advanced applications like primary (as opposed to supplementary) building heating/cooling typically require ancillary components like a CSP receiver and/or thermal storage. Practical Solar does not provide ancillary components at this time, but is happy to offer some guidance to customers interested in building this kind of system. The number of heliostats required will vary based on the application, ancillary components, and other factors.
- Can I heat a building with heliostats?
Heliostats only reflect sunlight when the sun is shining, which means they don’t provide heat/light at night, or when it’s stormy or cloudy. This means that using heliostats to direct light through windows is a supplementary rather than primary heating method. If you want to use heliostats for a primary heating system, you will need some kind of heat storage (e.g. thermal reservoir or thermal mass) that would keep the building warm at night, as well as during cloudy weeks without sun. You will also need a thermal receiver of some kind, which would be the target for the heliostats’ concentrated solar power. Practical Solar does not provide ancillary components at this time, but is happy to offer some guidance to customers interested in building this kind of system. The number of heliostats required to heat a building depends entirely on the building’s insulation and size.
- If I direct sunlight through a window, aren’t the people inside going to get sun in their eyes?
A good strategy to use when directing sunlight through a window is to aim the sun spot high. This way, the sunlight will diffuse off the ceiling and clear the heads of most people inside. It is unlikely to be a problem if the sun spot does not clear the head of someone inside the room or walking by the window. The reflected sunlight is no more intense than regular sunlight. Even if the heliostat mirrors were focused (e.g. to squeeze the sun spot through a small window), the sun rays would diverge once beyond the window pane (focus is dependent on focal length). Another option would be to buy a diffuser, or make one out of translucent material, to help disperse the sunlight through the room.
- If I direct sunlight through a window, will it feel like I’m being “blasted” by sunlight?
For most natural lighting and direct space heating applications, the light directed by a heliostat is no more concentrated than regular sunlight. See the answer to the previous question for more detail.
- How can I use heliostats to warm my home at night or when the sun isn’t out?
Heliostats can only reflect sunlight when sunlight is hitting them. To save some of that thermal energy for later, you would need a method of heat storage (e.g. thermal reservoir or thermal mass). The size and method of thermal storage would depend on your needs. Thermal storage can range from a small thermal mass (e.g. brick or concrete) that could stay warm for hours without sun, to a vast thermal reservoir (e.g. 10,000 gallons of water) that could keep a home warm for weeks without sun. A heliostat can deliver sunlight directly onto a thermal mass, or onto a thermal receiver that would charge a thermal reservoir. Practical Solar does not sell these ancillary products, but is happy to offer some guidance to customers interested in building this kind of system.
- Won’t properly insulated windows keep out heat from the sun?
Keeping warm air inside is not the same as keeping out infrared (i.e. heat) contained in sunlight. A well-insulated window uses multiple panes and air barriers to minimize thermal losses between inside and outside. Clear glass and plastic prevent most ultraviolet (UV) in sunlight from passing through the window, but they do not block most infrared. This means that heliostat systems can be used effectively for direct space heating through most windows, including very well-insulated ones. In warmer climates, some people do choose to use somewhat tinted windows that block out infrared. This window technology is also compatible with heliostats; it allows users in warm climates to use heliostats for natural lighting without also delivering 600 watts of thermal energy (heat) per heliostat.
- Do I need a large land area to have a heliostat system?
No. A heliostat can be installed in nearly any area that receives direct sunlight during most of the day. Little-used and out-of-the-way areas are good choices. The ground area required is only as large as the pole – 2 3/8 inches diameter – and the clearance needed to allow the heliostat to rotate freely can be roughly imagined as a 3-foot diameter circle around the pole. Heliostats can also be installed on rooftops and other building structures. One customer’s house is on the bank of a pond, making it impossible to install the heliostat north of the home. Instead, the customer installed the heliostat on the roof, facing south. Secondary reflectors bounce the sunlight into various windows (and a skylight) at different times of day. The flat roofs of buildings in urban locations are also very conducive to heliostats. Practical Solar recommends consulting with a structural engineer before installing a heliostat on a building structure.
- Can this system set my house on fire?
Although we all know what a small magnifying glass can do to an ant, there is little risk of fire when using heliostats – even if the customer uses the mirror focusing technique (tilting the individual mirrors in the frame to control the size/shape and therefore concentration of the sun spot). Heliostats used for natural lighting and/or direct space heating generally deliver sunlight that is not more – or not much more – concentrated than regular sunlight. Even a 5X sun concentration would not catch wood on fire. When using several heliostats for concentrating solar power applications, Practical Solar recommends various safeguards to ensure there is no fire danger.
- Will I have to deal with the zoning board or historic preservation board in my city/town?
Heliostats are not very obtrusive and are relatively easy to hide, if desired. In most cases, a heliostat should not require any permission or permitting to install. Homes in historic districts will sometimes be prohibited from installing heliostats in view of the street. Practical Solar has worked with these customers to find creative ways to install the heliostats, so they are effective but hidden from view.
- Will snowfall prevent a heliostat from reflecting sunlight?
Snow rarely affects a heliostat’s performance. While it is snowing, light accumulation is unimportant, since the heliostat will not be reflecting sunlight while there is heavy cloud cover. At night, heliostats “sleep” in a vertical position that allows the snow to fall off, and keeps new snow from sticking. Since heliostats generally face the sun, any snow left on the frame usually melts away.
- Will deep snow prevent a heliostat from operating?
If the snowfall is deeper than the clearance below the heliostat’s mirror frame, the heliostat will be able to push through the snow and clear a path for itself. If the snow is too heavy for the heliostat to push through, it will stop tracking, but it will not be damaged. It will resume tracking automatically as soon as it is able to. The customer would have the option of manually clearing the snow from around the heliostat. Practical Solar recommends installing heliostats so the bottom of the mirror frame is above the expected snow line. However, customers should also bear in mind that heliostats close to the ground (e.g. 18 inches clearance below the mirror frame) are more resistant to high winds.
- How often do I have to clean the mirrors, and what other maintenance is required?
Most customers will never clean the 8 mirrors in the heliostat’s mirror frame. Even during the height of pollen season, the effect on mirror reflectivity is negligible. Rain also has a natural cleansing effect. The heliostats’ other exterior parts are all aluminum and stainless steel. Heliostats are extremely rugged against the elements and require no maintenance.
- Is the size of the reflected sun spot dependant on the distance the heliostat is from the target?
Sunlight diverges 1 foot over every 100 feet of distance, so as a general rule, the further the heliostat is from the target, the larger the reflected sun spot. However, by using Practical Solar’s mirror focusing technique during installation (tilting each mirror slightly in the mirror frame), the customer has some control over the size – and shape – of the reflected sun spot. Tilting the mirrors essentially creates a parabola that is tailored for a particular target at a particular distance away. However, the customer should be aware that the reflected sun spot may look different on a target a different distance away from the heliostat, since the focal length will have changed. The mirrors can also be de-focused during installation to diffuse sunlight. The most concentrated sun spot possible is about 15-18 inches in diameter. This is achievable from a heliostat-to-target distance of about 25-50 feet. From a distance of 100 feet, a 2-foot-diameter sun spot is possible. From a distance of 200 feet, a 3-foot-diameter sun spot is possible, and so forth.
- Is bigger better when it comes to heliostats?
Surprisingly, no. In order to be wind-resistant, small heliostats like Practical Solar’s require less structural material (e.g. steel, aluminum) per square meter of reflective surface area than larger heliostats. This means less cost per square meter of reflective area. Small heliostats are also easier to ship and require only hand tools to install. Small heliostats also have the advantage of taking up far less real estate, so they can be used effectively in suburban and even urban environments (e.g. flat rooftops).