Concept Note on Solar Thermal
Technology Description
CONCENTRATING SOLAR THERMAL POWER (CSP)
CSP is used to produce electricity (sometimes called solar thermoelectricity, usually generated through steam). Concentrated-solar technology systems use mirrors or lenses with tracking systems to focus a large area of sunlight onto a small area. The concentrated light is then used as heat or as a heat source for a conventional power plant (solar thermoelectricity). The solar concentrators used in CSP systems can often also be used to provide industrial process heating or cooling, such as in solar air conditioning.
Concentrating technologies exist in four optical types, namely parabolic trough, dish, concentrating linear Fresnel reflector, and solar power tower. Parabolic trough and concentrating linear Fresnel reflectors are classified as linear focus collector types. Dish and solar tower as of the point focus type. Linear focus collectors achieve medium concentration (50 suns and over), and point focus collectors achieve high concentration (over 500 suns) factors. Although simple, these solar concentrators are quite far from the theoretical maximum concentration. For example, the parabolic-trough concentration gives about 1⁄3 of the theoretical maximum for the design acceptance angle, that is, for the same overall tolerances for the system. Approaching the theoretical maximum may be achieved by using more elaborate concentrators based on nonimaging optics.
Different types of concentrators produce different peak temperatures and correspondingly varying thermodynamic efficiencies, due to differences in the way that they track the sun and focus light. New innovations in CSP technology are leading systems to become more and more cost-effective
Solar Heat for Industrial Processes
Solar thermal can fulfill a substantial amount of heat demand in industrial and agricultural food processes within any given country and irrespective of the geographical location. In developed economies, solar thermal can provide technically about half of this energy consumption by supplying hot water and steam in a temperature range of up to 400°C. In developing countries, especially in those where agriculture, the textile, brick and food processing industries are important sub-sectors, solar thermal energy can provide hot air and hot water needed for curing, drying, dyeing, washing, boiling, pasteurisation and sterilisation.
In general, there are three groups of solar thermal technologies that are useful for industrial process heat: solar air collectors, solar water systems, and solar concentrators.
Solar Concentrators for Medium Heat (150°C- 400°C)
For medium temperature process heat applications, some advanced FPC designs with ultra-high vacuums are available to provide temperatures up to 200°C. However, the main technology used for medium temperature heat are solar concentrator technologies. In the simplest case, compound parabolic concentrators (CPCs) are fitted behind the vacuum tubes of the ETC, reflecting both direct and diffuse sunlight onto the absorber (also called CPC vacuum tubes). Similar concentrators can be used for FPC. Depending on the configuration of the mirror, concentration factors of up to 4:1 can be achieved, although typically CPC concentration is around 1.5 or lower. Combined with ultra-high vacuum technology, these ETC can provide nominal temperatures up to 200°C. Other solar concentrators for process heat are similar to technologies used to produce concentrated solar power (CSP), except that in most cases, they are smaller in size (from 10 kW to 2 MW). Instead of using the heat to produce power however, the heat is directly used in industrial processes. Examples of solar concentrators are parabolic dishes (with flat or curved glas, fixed or moving focus), parabolic trough concentrators and Linear Fresnel collectors. The concentrators can use various shapes (e.g. troughs, cylindrical discs,mirror-strips) to concentrate the sunlight onto the absorber.
Parabolic dishes:
Parabolic dishes were already used in antiquity, and consist of a parabolic reflector dish focusing sunlight onto the focal point in front of the dish. The dish can consist of flat mirrors attached to wooden, steel or aluminium frames. Some dishes are static and need to be manually adjusted (2-3 times a day) to follow the sun, while others track the sun automatically. One particular design is the Scheffler dish, which was popularised in India. Another example is the ARUN-160 dish, a two-way tracking parabolic dish with an aperture area of 160 m2, weighing around 20 tonnes and generating 100-120 kg of steam per hour (between 80-100 kW of thermal output) (Clique Solar, n.d.).
Parabolic trough collectors use curved glass to focus the sunlight on heat receivers (i.e. steel tubes or evacuated glass tubes) placed on a focal line.
Linear Fresnel collectors:
Linear Fresnel collectors are similar to parabolic trough collectors, except for mirrors that are placed on a horizontal surface at different angles to a fixed receiver located several meters above the mirror field. Furthermore, for industrial process heat production, Linear Fresnels often need to be adapted to available rooftop and land areas around the industrial site, resulting in different lengths of collector rows and different orientations. These high-concentration collectors can produce temperatures up to 400°C and are extremely interesting for industrial process heat applications. Renewed interest in these technologies has led to new prototype development in several research institutes around the world and they are becoming more popular, especially for district heating and cooling.
The choice of heat transfer fluid becomes important for medium temperature requirements in solar process heat technologies. Direct systems (or open-loop systems) can use water or air as the heat transfer fluid directly in their processes. However, air has a low heat capacity and water a low boiling point and may be corrosive or deposit minerals in the collector. In indirect systems (or closed-loop systems), some alternative heat transfer fluids are glycol and hydrocarbons (with lower freezing points suitable for cold climates), refrigerants (with high thermal capacity but with low boiling points), molten salt (with typical melting point above 140°C and high thermal capacity), or advanced heat transfer fuels (enhanced performance but also more costly). Other considerations are the costs of the heat transfer fluid, degradation (due to higher temperatures) and the viscosity (higher viscosity means more energy required for pumping).
The selection of an appropriate solar collector basically depends on five factors: 1) operating temperatures; 2) thermal efficiency; 3) energy yield; 4) cost; and 5) the space occupied. Other aspects, such as the possibility of roof integration or system size, also have to be considered. Furthermore, the choice depends on the technology used to provide the heating or cooling services.
Global scenario of adoption or demonstration of the technology
The cumulated solar thermal capacity in operation by end of 2017 was 472 GW (675 million square meters). Compared to the year 2000 the installed capacity grew by the factor 7.6. The corresponding annual solar thermal energy yield in 2017 amounted to 388 TWh, which correlates to savings of 41.7 million tons of oil and 134.7 million tons of CO2.
Despite these achievements, the global solar thermal market has faced challenging times in recent years. This is especially evident in the large markets in China and Europe where the traditional mass markets for small-scale solar water heating systems for single family houses and apartment buildings are under market pressure from heat pumps and photovoltaic systems. In total, the global market declined by 4.2 % in 2017. Positive market developments were recorded in India (26 %), Mexico (7 %),and in Turkey (4 %). In contrast to the small-scale solar water heating systems, the megawatt-scale solar supported district heating systems and industrial applications have gained increasing interest all over the world in recent years and several ambitious projects have been success fully implemented.
By the end of 2017 about 300 large-scale solar thermal systems (>350 kW; 500 m²) connected to district heating networks and in residential buildings were in operation. The total installed capacity of these systems equaled 1,140 MW (1,630,415 m²), excluding concentrating systems that add 110,929 m².
In 2017, nine large-scale solar thermal systems with about 35,000 m² (24.5 MW) were installed in Europe. Outside Europe, 5.9 MW (8,444 m²) were installed and one concentrating system in Tibet with a collector area of 9,000 m². About 75 % of the new collector area installed in Europe is from two new large systems in Den mark and three extensions added to Danish systems. About 92 % of the installed capacity in stalled outside Europe has been installed in China.
The world’s largest plant for solar district heating is located in Silkeborg, Denmark and has an installed capacity of 110 MW (156,694 m² flat plate col lec tors). The start of operation of this plant was in December 2016.
Important to note is that in 2016 and 2017 three parabolic trough collector fields were installed for feeding into district heating networks in Denmark and China. The concentrating collector area of these three systems installed adds up to 110,929 m².
Solar Heat for Industrial Processes (SHIP) continues to be a growing market. A number of promising projects have been implemented in the last couple of years ranging from small-scale demonstration plants to very large systems with 100 MW capacity. At least 624 SHIP systems, totalling 608,994 m² collector area, were in operation at the end of the year 2017.
2017 was a record year for SHIP installations – 124 new larger systems, total ling 192,580 m² collector area, started operating. With this, the documented world total grew in 2017 by 25 % in number of installed plants and by 46 % by installed collector area. The world’s largest solar process heat application began operation in February 2018 at the Amal oil field located in the south of the Sultan ate of Oman. The Miraah parabolic trough plant with a total capacity of over 100 MW delivers 660 tons of steam per day for the extraction of viscous or heavy oil as an alternative to steam generated from natural gas.
Global concentrating solar thermal power (CSP) capacity reached 4.9 GW in 2017, with South Africa being the only country to bring new CSP capacity online (100 MW). However, at year’s end about 2 GW of new plants was under construction; China (300 MW being built) and Morocco (350 MW) were particularly active. An estimated 13 gigawatt-hours of thermal energy storage (TES) was operational, and most new plants are incorporating TES. Spain remained the global leader in existing CSP capacity – followed by the United States – with Spanish CSP plants achieving record electricity generation in 2017. The year also saw record low CSP tariffs being bid and/or awarded in competitive tenders in Australia, Chile and the United Arab Emirates, where a 700 MW CSP tender was awarded. CSP with TES emerged as a viable competitor to fossil fuel thermal power plants. Price reductions were driven by competition as well as by technology cost reductions aided by ongoing research and development activity in the sector.
Indian Scenario
India added 0.9 GW (1.28 million m2) in 2016, an increase of 6% relative to 2015.The market appears to be bouncing back, following a temporary reduction in demand that resulted from the suspension of India’s national grant scheme in 2014. The share of imported vacuum tubes grew to 88% (up from 82% in 2015).This segment included an increasing number of vacuum tubes backed with aluminium mirrors (so-called compound parabolic concentrators), which are used primarily for industrial process heat applications. This trend was supported by a national 30% capital subsidy scheme for concentrating solar thermal technologies, which has reduced the payback times to three to four years for manufacturing businesses. Only 0.11 GW of flat plate collectors (down from 0.15 GW in 2015) was sold by the handful of manufacturers that remains in India
At the end of 2012,India had 7 967 m² of solar concentrator systems for solar cooling and a total of 27 972 m² of solar concentrator-based systems for industrial heating applications (REN21, 2014)
India was the lead country and 61% of its solar thermal capacity was used for industrial process (including community cooking); in total, 78 commercial applications of solar concentrators (all parabolic dish collectors) were installed (88% for solar cooking) (Sun & Wind Energy, 2014). Furthermore, there are currently around eight projects using FPC, ETC and Linear Fresnel collectors for solar process heating (AEE INTEC & PSE, 2014) in operation. As the largest milk producer in the world, India’s dairy sector is also one of the most interesting application areas where up to 13% of process heat could be supplied by solar thermal (GIZ,2011). Out of the top ten companies supplying solar process heating plants, four are parabolic dish suppliers from India. An important driver for the deployment of solar concentrators in India are the capital subsidies (up to 60%) provided by the Indian Government and a UNDP-GEF project (Sun Focus, 2014).
Highlights of Projects commissioned in India for Thermal Process Heating:-
Location: Shirdi, Maharashtra
Type of Installation: Scheffler Dishes
Configuration: 1168m2 (16 m2 x 40 No’s)
Supplier: Gadhia Solar Energy Systems Pvt. Ltd.
Application: Cooking
System Details: The total system has an area of 1168 m2 comprising of 40 concentrators with 16 m2 capacities each. The system was commissioned during 2009 by Gadhia Solar Energy Systems Pvt. Ltd. Prior to the implementation of the CST system the establishment was using LPG as a fuel for its end use consumption. The system is integrated with its existing process. The project is set up at a cost of Rs. 106.2 Lakh with grant availed from MNRE of the order of Rs. 58.40 Lakh.
Timings & System Application Details: The system operates for 3 hours for preparation of breakfast. The daily quantum of food is around 200 kg of Rice. The system is functioning well. Usage of the system is approximately 4-5 hours / day and around 300 days in a year that also depends upon the availability of sunlight.
Steam Generation: 2600 kg/d Operating Temperature & Pressure: 170°C & 8 kg/cm2
Type of Fuel Saved: LPG Quantity of Fuel Saved: 13 cylinders/day
Functionality & Key Issues of Non-Operation: Operational
* As on 31/03/2017.
Technical Specifications
Application |
Smart Kitchen for Boiling, Frying and Baking |
Energy Output |
The MWS SmartKitchen ™ system is designed to provide energy for cooking |
Fuel Firing system |
Solar + LPG hybridized based Thermic fluid heating. |
Cooking methodology |
Closed loop header-based Jacketed vessel, No-Water, No Flame Kitchen |
Application of heat |
Heat generated through Solar + LPG hybridized based Thermic Fluid (TF) System shall be used for boiling, frying & baking. |
The schematic layout is shown below. Note that this is a sample picture of equipment arranged inside the kitchen. During solar hours, the incoming return oil from the vessels at reduced temperature will input solar field to gain the heat at desired temperature and then feed into LPG heater. Solar field will add the requisite ▲T based on solar radiation availability, and any shortfall from solar shall be made up by LPG based TF heater to provide the required temperature for cooking. During non-solar hours, a 3-way control valve will by-pass the solar field to isolate solar field.
SOLAR FIELD DESCRIPTION |
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S. No |
Details |
Sub Details |
Technical Requirement |
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General |
Solar Field |
Solar Dish |
Process Fluid |
Thermic Fluid (NSF Approved) |
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Peak Operating Temperature of Thermic Fluid |
250 0C |
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Peak Operating Pressure of Thermic Fluid |
10 kg/cm2 (g) |
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Concentrator |
Reflector Area |
Minimum for transferring 20 kW energy to Thermic fluid at peak DNI of 800 W/m2 |
Reflector Material |
Back polished, Low iron content glass reflector / Solar Grade Metallic / Non Metallic Reflector |
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Reflectivity |
≥ 90 % (bidder to provide manufacturer / test lab certification for at least one sample) |
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Material of Frame Structure |
MS (Galvanized / Painted) |
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Survival wind speed |
As per Wind zone |
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Receiver |
Receiver Material |
Carbon Steel tube |
Hot Insulation |
Mineral Wool & Aluminum Cladding |
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Tracking System |
East-West Tracking |
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North-South Tracking |
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Parking |
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De- focusing & Re- focusing |
Automatic (preferable) |
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Tracking accuracy |
+/- 0.5 degree |
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Accessories |
Solar Dish Cleaning System |
Required |
Support structure, Maintenance Platform and Ladder |
MS (Galvanized / Painted) |
THERMIC FLUID HEATER (TFH) |
Specifications |
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S. No. |
Details |
Technical Requirement |
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Thermal Capacity |
1,00,000 Kcal / Hr (minimum) |
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Fuel |
LPG |
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Duty |
Multiple Start / Stop every day |
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Process Fluid |
Thermic Fluid |
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Operating Thermic Fluid Temperature |
250 0C |
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Type |
Vertical / Horizontal |
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Number of Pass |
3 (Minimum) |
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Efficiency |
85% (Minimum) |
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Burner |
Mono block |
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Burner Control |
Automatic |
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Igniters |
High Energy Arc |
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Flame Sensing |
Required |
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Air Blower |
Centrifugal |
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Chimney |
Required (to be extended above the canopy height) |
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TFH Start / Stop |
Manual from Local Control Panel and Automatic |
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TFH Tube Material |
ASTM 106 Gr-B Seamless |
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Hot Insulation |
Mineral Wool & Aluminum Cladding |
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Electric Supply |
3Phase, 415 VAC |
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Safety Protection (Minimum) |
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THERMIC FLUID PUMP (TFP) |
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Fluid |
Thermic Fluid |
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Operating Temperature |
250 0C |
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Type |
Preferably Canned Motor Pump / Magnetic Drive Pump |
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Lubrication |
Self (Preferable) |
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Cooling |
Self (Preferable) |
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Flow & Head |
Suitable for Thermic Fluid Heater & Solar Field |
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Motor |
3Phase, 415 VAC |
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EXPANSION TANK |
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Volume |
500 Litres (Minimum) |
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Material |
MS |
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Openings & Ports (Minimum) |
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Hot Insulation |
Nano insulate paint coating (minimum 10 coats) with Mineral Wool & Aluminum Cladding OR PUF insulation with Aluminum Cladding |
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Support structure, Maintenance Platform & Ladder |
MS (Galvanized / Painted) |
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Miscellaneous |
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THERMIC FLUID |
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Operating Temperature |
250 0C |
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Operating Pressure |
Ambient |
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Boiling Temperature |
> 310 0C |
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Type |
Thermic Fluid (USFDA Approved) |
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Accessories |
Hand Pump for transfer of thermic fluid |
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Quantity of thermic fluid |
This is in Customer's scope as per the site layout |
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COOKING VESSEL |
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Boiling Vessel |
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Frying Vessel |
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Hot Plate |
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PIPE WORK |
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Pipe |
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Pipe Flange |
Raised face (Preferable Finish - RMS 125) |
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Flange Gaskets |
Spiral-wound (SS-304 & Flexible graphite filler) |
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Flange Bolt |
ASTM A-193 Grade B7 (preferable) |
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Flange Nut |
ASTM A-194 Grade 2H (preferable) |
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Flange Washer |
ASTM F-436 (preferable) |
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Valve |
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CONTROL AND INSTRUMENTATION |
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As appropriate, all the above instruments shall be provided with isolation valves, thermo well, manifold etc.
Based on selection of the above by the user, all the following conditions can be activated:
In addition, the user will have the option to indicate "No Cooking" and "Heat to be given to water for use in kitchen", "STCS Off" and "Emergency Shut Down" conditions. |
Or
DETAILED TECHNICAL SPECIFICATIONS OF VARIOUS COMPONENTS OF SOLAR COOKING SYSTEMS (SCHEFFLER DISHES)
The solar steam/pressurized hot water/oil generating system will comprise of automatically tracked parabolic concentrators and balance of system (BOS) for conditioning and utilizing thermal energy in working fluid. The working fluid can be in the form of water, steam and organic or inorganic fluid. BOS may consist of solar thermal receivers, steam/ hot water/oil pipelines, feed water/oil pumps, tank assemblies, steel structures and civil works, instrumentation like pressure gauges and temperature indicators etc. It will be hooked up with conventional system already in use for specific applications. In case of new systems, fossil fuel based boiler, vessels for cooking/ vapour absorption machine for cooling etc may be provided as the case may be. Minimum technical specifications of various components of the system will be as per below:
Concentrators
Shape & make of each |
Of any shape made of reflecting mirror(s) fixed to a |
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concentrator |
supporting frame / structure |
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Aperture area |
10 sq. m minimum (for Scheffler dishes, it will be p/ 4 x |
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lengths of major & minor axis of the ellipse) |
Reflecting mirrors |
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i) |
Material* |
i) High quality glass mirrors for outdoor use with |
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protective layers of coating on back surface and sides |
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to protect from exterior weathering effect or any other |
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reflecting material of similar reflectivity and durability. |
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For coastal and colder regions, special protections to |
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be made. |
ii) |
Reflectivity |
ii) 90% minimum with a maximum degradation of 10% |
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over its life span. Warranty/ guaranty to be provided |
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for a period of five years. To be replaced immediately |
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by the supplier if found deteriorating during this period. |
iii) |
Mirror fixing |
iii) With positive locking or sticking by industry proven |
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outdoor-rated adhesives. Due protection of mirror |
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coatings be taken while fixing the mirrors. Tying of |
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mirrors with wires not acceptable. For high wind areas |
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special protection to be made. |
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* For newer upcoming technologies, reflectors other than |
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glass mirrors will also be acceptable subject to fulfillment |
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of all the above requirements |
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Concentration ratio |
Over 80 for single axis and 120 for double axis tracking |
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(Aperture/ Receiver areas) |
concentrators |
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Tracking Arrangement |
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· Any reliable automatic tracking mechanism with motorized reverse in evening & park at morning position including safe position in case of abnormal operating conditions.
· Made of standard components; to be protected from rain, dust & outside environment
· Tracking accuracy : +/- 0.5 degree (to be ensured using field-calibrated inclinometer)
Heat receivers, Headers and piping
Insulation
Frames & supporting structure
Instrumentation & Controls
Other requirements
Note: General
Or
TECHNICAL SPECIFICATION
For Supply, erection and commissioning of Concentrating Solar Thermal (CST) based Solar Steam system for Steam Cooking Application with Thermal Storage Facility.
PART – A SUPPLY
1.0. FUNCTIONAL REQUIREMENT
The Solar Concentrator along with thermal storage system will be used to generate steam directly at a required pressure of 6 to 8 bar from the solar radiation and used for the Steam Cooking Application at canteen kitchen. The technology is of CST based either Parabolic
This specification covers the design, fabrication, and testing the performance of Solar Dish along with its all accessories including reflector and receiver assembly, steam separator / accumulator, feed water pump, dish cleaning system and other necessary accessories. The specification comply with MNRE guidelines.
2.0 Design, Construction and Erection:-
The design, material, construction, manufacture inspection and performance testing of Solar Dish and receiver assembly shall comply with all currently applicable statutes, regulations and safety codes in the locality where the equipment will be installed. Nothing in these specifications shall be construed to relieve the vendor of this responsibility. The equipment supplied comply with the latest applicable Indian standards. Other national standards are acceptable if they are established to be equal or superior to the Indian standards.
3.0 Design Requirements:-
Concentrated Solar Thermal Steam Generation System It should be envisaged for full load operation to cook for a total of 200 - 250 students per day for Breakfast, Lunch andDinner preparation along with thermal storage facility for non-solar hour operation From one or more number of concentrators as per capacity. However, the plant should facilitate for part load operation with one or more Solar Dishes based on cooking energy demand.
4.0 Technical Specifications of Various Components of Concentrated Solar Steam Generator
Capacity Required
To generate solar steam energy required to cook for 200 -250 students in a day for Breakfast, Lunch & Dinner preparation along with thermal storage facility for non-solar hour operation from one or more number of concentrators.
Suitable devices for sensing solar radiation, position of the dish, wind
speed, receiver status etc. The input of the
Devices shall be used as feedback for high accuracy tracking in
both axis (seasonal and diurnal) for positioning the dish with
± 0.2 deg accuracy. and for safe operation of the plant.
· The receiver shall directly generate steam at the required pressure.
· The receiver shall be cavity absorber type.
· The receiver shall be designed to with stand 10 bar pressure.
· The Standard should meet Std. - ANSI:B - 31.1 (or) ASME Sec 8, Div. II
b). Pressurized Hot water / Steam storage tank:
· The storage tank should comply with standards ASME Sec 8, Div II.
· The suitable storage facility to be provided to meet the STEAM requirement of non-solar hours cooking operation at each different Hostel.
· The real time energy generated is considered for preparation of Lunch and Dinner and offline/stored energy is considered for breakfast preparation ie., from the thermal storage facility.
· The pumps used in the system should comply with the following standards:-
· API: 674/5: Reciprocating pumps
· IS: 1520 - Horizontal centrifugal umps
· IS : 5659 - Pumps for process water
Steam / Hot water piping shall be of SA 106 Grade with fittings of SA 105, 3000# for sizes less than 40 NB.
It shall be a complete unit including high-pressure-jet pump, hose, pipe, nozzle, lance etc
All working fluid piping shall be insulated with mineral wool of density of 120kg/m³. All insulated components shall have Aluminum sheet cladding with 26SWG thickness as per industrial practices.
Strong enough to avoid any deformation of the dish under wind speed of 200 km per hour when parked. The structure shall be constructed of mild steel / any other strong material and shall be galvanized (min 65 µm) or epoxy coating (with 120-150 DFT). The structure shall be designed for operating life of 25 years.
Complete with all instrumentation such as pressure gauges, temperature indicators, fluid level indicators, safety valves, etc.
Complete reliable automatic dual axis tracking mechanism (Vertical & Horizontal) which will orient towards the sun at the touch of a button and with motorized reverse tracking for parking (safe position) of solar dish in evening & for parking in case of any emergency conditions. No manual intervention shall be required in normal course of operation. However, manual override for all functionality of the dish shall be provided. For seasonal movements also, no manual adjustments shall be required. The tracking shall be made of standard components.
Suitable capacity steam cooking vessels and LPG based back up boiler needs to be provided
Cost and economics of the technology
Solar Thermal technology (cooking system) cost and economics depend on many variables such as location, no of people, food items , cooking timings , site orientation, distance of installation technology ( i.e.Thermic fluid & steam based) & system configuration( i.e. Parabolic tarf type, Scheffler , Single axis tracking / double axis tracking etc).
Thus ,cost and economics can not be identified precisely before preparing feasibility report .
Benefits of the technology
Economics
Environmental
Burning wood, charcoal, fossil fuels, and other types of fuel contribute to the ever increasing global air pollution. Because there is no fire and no flames, there is no air pollution. Because there is no fire and no flame, solar cookers can be used in “no burn” areas and on “no burn” days. So it is perfect for camping in areas with fire restrictions.
Because solar cookers use the sun and you use less fuel, there is less garbage to deal with. There are fewer bottles of butane to carry to a campsite, and fewer bottles to carry out of a campsite. And, of course, fewer empty butane bottles in the landfill. Large solar ovens have been built on top of Mt. Everest for this same reason – fewer bottles of fuel to carry up and down the mountain. Solavore Sport Solar Oven benefits of solar cooking
Health
Whether it be in a village hut or on a suburban patio, open cooking fires and hot barbeque grills present a danger to everyone, but especially to children. Using a solar oven, with no open flames, prevents burns and is safe for children to play around.
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