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With all [[solar thermal collector]] systems there is a potential risk that the solar collector may reach an  equilibrium or [[stagnation temperature]] higher than the maximum [[safe operating temperature]]. Various measures are taken for '''optical overheating protection'''.


Stagnation temperatures are encountered under conditions of high radiation while no heat transfer fluid is flowing through the collector, for example during power failures, component failures, servicing, energy storage capacity limitations, or periods when little hot water is extracted from the system.<ref name="Harrison2004" /> More generally, stagnation conditions can be considered to be any situation under which the solar collector cannot adequately dispatch the absorbed solar heat to the heat transfer fluid.


Besides any damaging effects to the system, high stagnation temperatures also place constraints on collector materials. These materials must retain their important properties during and after exposure to the high stagnation temperatures. This implies that solar collectors are generally built from high temperature resistant materials. These materials are usually expensive, heavy, and have an overall high environmental impact.<ref name="Köhl2005" />  
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[[Polymeric]] materials offer a significant cost-reduction and environmental improvement potential for solar thermal collectors and may thus benefit a broader utilization of solar energy for various heating purposes. However, the long-term service temperature of plastics is limited. Thus, for potential applications of plastics in solar absorbers an appropriate design including overheating protection is essential.<ref name="Wallner2008" /> Feasible ways would be a reduction in optical gain (for example, using [[thermotropic]] layers, or [[electrochromic]] devices) or an increase in system losses, by dumping of the hot water excess.
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In this article an alternative method to decrease the optical gain is presented. The method is based on the geometry of prisms and the phenomenon of [[Total Internal Reflection]].
 
== Working principle ==
 
[[File:Prismatic Optical Switch.jpg|thumb|right|upright=1.4|Working Principle of the Prismatic Optical Switch. When liquid is present in the switch, the switch behaves as if transparent. When there is no liquid present, the switch becomes reflective]]
 
According to [[Snell's law]], light cannot escape from a medium when it strikes the medium boundary at an angle of incidence (θ) that is larger than the [[critical angle]] (θ<sub>c</sub>), an optical phenomenon called Total Internal Reflection. The critical angle can be calculated using;
 
<math>\theta _{c}=Sin^{-1}(\frac{n_{1}}{n_{2}}),\; \frac{n_{1}}{n_{2}}\leq 1</math>
 
For a [[polycarbonate]] medium, with a [[refraction index]] of n=1.59, placed in an atmosphere of air with a refraction index close to 1, Total Internal Reflection occurs when θ > θ<sub>(c,air)</sub>=39°.
 
Consider a polycarbonate prismatic structure with an apex angle α<sub>1,2</sub>=45° placed in an atmosphere of air. A ray of light that strikes the medium boundary at normal incidence is total internal reflected, as θ<sub>in</sub>=45°> θ<sub>(c,air)</sub>=39°. In presence of water, θ<sub>(c,water)</sub>=56.8° and θ<sub>in</sub>=45°< θ<sub>(c,water)</sub>, the incoming light is merely refracted and traverses the polycarbonate medium. As such, water acts as a switching fluid. In theory, water can be replaced by any other liquid, with an index of refraction close to that of the prismatic structure, to act as the switching fluid.
 
The optical switch consists of a self-regulating mechanism. In its ''passive'' state the switch is filled with liquid and light is allowed to pass through the switch and heat the system behind it. As the system heats up, the switching fluid evaporates out of the optical switch and the prismatic structure starts to behave as a reflective surface. No more light passes through the switch, limiting the maximum temperature of the system to the evaporation temperature of the liquid.<ref name="Slaman2009" />
 
== Angular Dependence ==
[[File:Transmittance Prismatic Array.jpg|thumb|right|upright=1.4|Transmittance of a prismatic array against day rotation(δ) (δ=0 stands for 12.00h, 15° equals 1 hour). The prisms are aligned such that the angle of incidence (θ) in mid-summer at noon. (A); Vertical alignment of the prismatic array for a mid-summer day (a) for a mid-autumn & mid-spring day (b), and for a mid-winter day (c). B; Horizontal alignment of the prismatic array for a mid-summer day (d), a mid-autumn & mid-spring day (e), and for a mid-winter day (f).]]
 
Resulting from its geometry, the optical switch is sensitive to the angle of the incident beam. Depending on the shape of the prisms, the transmittance of the switch in its reflective state during a typical day shows characteristic angular dependence. This dependence can be used to find specific [[transmission curve]]s for different applications, where the geometry of the prisms serves as the input variable.
 
== Applications ==
 
The main application for which the optical switch was developed is overheating protection for solar thermal collectors.<ref name="Slaman2009" /> The prismatic geometry can be integrated within the cover plate of the collectors to prevent them from overheating, either by self-regulation through evaporation, or by draining the water out of the switch at a specified maximum temperature. Temperature limitation would allow for the use of polymeric materials within solar collectors, dramatically reducing cost-price and increasing market penetration.
 
Another application of the switch is in windows for both housing and office buildings. The amount of sunlight entering the building can be controlled by the switching liquid. Preventing the amount of sunlight entering a building will reduce the temperature inside the building on sunny days.
 
Finally, the switch can be used within roofs of [[greenhouse]]s. The plants in the greenhouse can be protected from damage on sunny days by putting the switch in the reflective state. Currently greenhouses are covered with a [[chalk]] layer to protect the plants during summer from excessive sunlight. Applying the chalk layer is time consuming and bad for the environment. Once the chalk is applied, it also blocks sunlight during less sunny days. The optical switch could potentially resolve this issue using the switching mechanism described above.
 
The temperature inside the greenhouse can be regulated by switching a certain amount of roof sections in the reflective state. Also the switching fluid inside the roof can be circulated to extract heat from the greenhouse. These cooling methods allow that the (roof) windows remain closed and that the climate ([[relative humidity]] and raised [[CO2]] levels) remain optimal and constant.
 
The Switching fluid in the greenhouse roof can be used as a filter for a certain part of the [[solar spectrum]]. Water allows so-called "PAR" light ([[Photosynthetically active radiation]], the light that plants use to grow) to pass, while "NIR" (Near [[Infra Red]]) light is absorbed. The amount of NIR light to absorb can be tuned by solving micro-particles of Copper Sulphate or clay in the switching fluid. In that way  optimum growth conditions can be selected.
 
Some greenhouse products, like flowers, are grown by using artificial light during the night. This artificial light causes so-called [[light pollution]] in the environment of the greenhouse. When a greenhouse roof consists of a well designed optical switch the greenhouse roof becomes reflective during the night, which keeps the artificial light inside the greenhouse. As a side effect there are less number of lights needed since the roof acts as an efficient mirror.
 
== References ==
{{Reflist|refs=
<ref name="Harrison2004">S.J. Harrison, Q. Lin and L.C.S. Mesquita. Integral Stagnation Temperature Control for Solar Collectors, SESCI 2004 Conference
University of Waterloo Waterloo, Ontario, Canada August 21st–25th, 2004</ref>
<ref name="Köhl2005">M. Köhl et al. Durability of Polymeric Glazing Materials for Solar Applications, Solar Energy 79 (2005) 618–623.</ref>
<ref name="Wallner2008">G.M. Wallner, K. Resch and R. Hausner. Property and performance requirements for thermotropic layers to prevent overheating in an all polymeric flat-plate collector, Solar Energy Materials & Solar Cells 92 (2008) 614–620</ref>
<ref name="Slaman2009">M. Slaman, R. Griessen. Solar Collector Overheating Protection, Solar Energy 83 (2009) 982–987</ref>
}}
 
== External links ==
* http://www.nat.vu.nl/~slaman/Optical%20switch/SolSwitch.php
 
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[[Category:Solar power]]

Revision as of 12:39, 9 February 2014


Most small businesses pick an cpa - either hiring a "numbers man" on staff or hiring bookkeeping services on a contract basis - when a business' financial challenges are becoming too great to handle without expert help. Private tax preparation - Often, private tax problems are closely related to and affected by company tax issues. If you and your partner are saving for your first home, for example, you probably shouldn't hire a planner whose typical client is worth millions.

Generally the tax is levied on net profits from business, net gains, and other income. The kind of federal return filed is based upon the citizen's personal scenario and IRS rules and regulations. It does not provide for reimbursement of any taxes, fees, or interest levied by taxing authorities and doesn't contain legal representation. Many jurisdictions tax the income of individuals and business entities, including corporations.

However, you should ask your accountant for some sample business plans that he is written so you comprehend what the deliverable is that you'll be getting for your cash. As a pretty successful small business proprietor, that is great advice. I have had awful experience with accountants - it's really difficult to find one who's willing to clarify matters.

Starting your company away with the greatest tax elections for your company are amongst the most significant business decisions you will ever accomplish. This section will offer you a fundamental understanding of each, therefore providing a great reference point for selecting the level of service that is best for your company. You also want your would-be accountant in order to ask you the correct questions.

There are many different designations for accountants, from the common "certified public accountant" to a certified management accountant or an accredited business accountant. (other appellations are used in other nations). Both Dub row and Brundidge proposes finding a dependable CPA by asking for recommendations from people whom you trust. It's most likely that you're looking for a CPA if you are usually seeking an accountant in the U.

nA customs union has a common external tariff, and the participating nations share the revenues from tariffs on goods entering the customs union. The side effects of taxation and theories about how best to tax are an important issue in microeconomics Taxation is nearly never a simple transfer of riches. Economic theories of tax approach the question of the way to maximize economic welfare through taxation

The tax type should appear in the upper left corner of your bill. Business advice, UCC filings, trade names, Resident agents, business personal property appraisal and perspective recently filed records.

This section of our Web site provides you with information on state income taxes, sales and fuel taxes, taxes on retirement income, property taxes and inheritance and estate taxes, along with sales and fuel taxes

While it is sensible for many business owners to manage their day-to-day records, an accountant can help set up bookkeeping and accounting systems and demonstrate you how you can use them. This makes sure that you and your accountant have the same expectations.

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The carbon tax coupled with renewable energy research earns bulk support across all political categories, including a narrow majority of Republicans. A majority of respondents support a revenue-neutral carbon tax, and an even larger majority supports a carbon tax with revenues used to finance research and development for renewable energy programs.

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In economic terms, tax transfers wealth from homes or companies to the government of a country. Consumption tax refers to any tax on non-investment spending, and may be implemented through a sales tax, consumer value added tax, or by changing an income tax to allow for unlimited deductions for investment or savings.

When issues occur, you may realize which you lose important time in addition to cash. Bookkeeping Help supplies a list of CPA firms together with information on each CPA. If not I am receptive to ideas for a good CPA that understands nexus and all that stuff.

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