In this work, a life cycle analysis is accomplished for flat plate solar collectors. The purpose of this investigation is to predict the energy consumption during the manufacturing processes that results in carbon dioxide emissions. Energy consumption and system efficiency enhancement will be studied and predicted. CES EduPack software is used to perform the analysis of the currently commercial system, and the suggested changes are implemented to increase the efficiency and make the comparison. Even though cost analysis is done, the priority of selection is given to the most energy conserving and environmentally friendly alternative. However, if the compared alternatives result in the same energy consumption and CO2 emissions, the cost analysis would be a better approach. It can be stated that flat plate solar collectors are sustainable and renewable energy systems that do not produce CO2 emissions during their active usage, but the manufacturing processes they undergo during the design contribute to the greenhouse gasses emission.
As world energy consumption is dramatically increasing and the scarcity of the existing energy sources are happening simultaneously in a problem known as supply/demand problem [
However, the judgment that Sustainable and Renewable Energy systems (RESs) systems do not produce any pollution is not technically true. In fact the processes that RESs undergo before and after their usage and even during their lifetime contribute in pollutants emission [
In this work, the LCA for the current properties of solar flat plate collectors is considered to investigate and then a consequential LCA is done for a proposed change in the current system that enhances the system efficiency. The main objective of this work is to investigate which parts of the flat plate solar collector system materials consume more energy and produces more greenhouse gases during their manufacturing phase.
The materials properties and environmental output/input data, which are needed in this work, can be easily accessed in the CES EduPack software database. Transportation is another important aspect in the analysis of this work. Factories that produce and manufacture each one of the materials needed in constructing the flat plate solar collector (
A life cycle analysis is done by using the CES EduPack software which includes all the information needed. It includes how much energy is used, the CO2 emissions and also the cost for each process of designing the device. Each process that consumes highest amount of energy and results in toxic gasses emissions will be investigated. After that, alternatives will be suggested and will be compared with the commercial materials that are used, and based on that select the best option. The alternatives will be advised in a way that they lower the energy use and the CO2 emissions without any alteration in the system overall efficiency or, what would be ideal, increasing it.
Part of the system | Material |
---|---|
Riser and header (tubes) | Stainless steel/Zn alloyed |
Absorber | Cast copper |
Selective coating | Bronze |
Transparent cover | Glass |
Storage tank | Stainless steel/Zn alloyed |
Collector frame | Aluminum/Zn alloyed |
Collector support | Aluminum |
Part of the system | Primary process | Secondary process |
---|---|---|
Riser and header (tubes) | Casting | Coarse machining |
Absorber | Casting | Cutting and trimming |
Selective coating | Casting | Cutting and trimming |
Transparent cover | Fabric production | Cutting and trimming |
Storage tank | Casting | Coarse machining |
Collector frame | Forging | Coarse machining |
Collector support | Rough rolling | Coarse machining |
It is noteworthy to mention that the maintenance of the solar collector is considered to be 3 hours per year (only for cleaning & electroplating the frames, which include repair, inspection and planned preventive maintenance.
The LCA of the solar collectors was analyzed using the CES EduPack software, employing the mentioned above materials. The following assumptions are taken into account: All Zn alloyed materials were considered of high corrosion resistance for this reason a high Zn percentage material have been chosen. Accordingly, no electroplating (galvanizing) is needed. Except for the collector frame which has to be both Zn alloyed and galvanized. The back-insulation material (melamine foam) will be neglected from analysis since it has to be shipped from factory in china. However, this assumption is accepted in our case because the mass fraction of the foam is (1/200) kg/kg (kg of foam per kg of solar collector). Note that for commercial projects, it has to be implemented in the life cycle analysis. The maintenance power rating was assumed to be 1000 W which is as low as power consumed by 10 electric bulbs because the system consists of static parts which dramatically decrease failure probabilities.
The energy consumption versus designing process bar chart below (
To investigate which parts of the flat plate solar collector during materials production, consume more energy and produces more CO2, a detailed report from the software was extracted (
Component | Material | Recycled content* (%) | Part mass |
Qty. | Total mass processed** (kg) | Energy (J) | % |
---|---|---|---|---|---|---|---|
Risers and header | Stainless steel, martensitic, ASTM CA-6NM, cast | Virgin (0%) | 12 | 1 | 12 | 9.8 × 108 | 9.3 |
Absorber | Copper, cast (h.c. copper) | Typical % | 4.5 | 1 | 4.5 | 1.8 × 108 | 1.7 |
Selective coating | Bronze, CuSi3.5Mn1, cast (silicon bronze) | Typical % | 0.7 | 1 | 0.7 | 2.8 × 107 | 0.3 |
Transparent cover | Glass, S grade (10-micron monofilament, f) | Virgin (0%) | 7 | 1 | 7 | 3.6 × 108 | 3.5 |
Storage tank | Stainless steel, martensitic, ASTM CA-40, cast, tempered at 315°C | Typical % | 15 | 1 | 15 | 7.3 × 108 | 7.0 |
Collector frame | Aluminum, 7475, T7351 | Typical % | 16 | 1 | 16 | 2 × 109 | 19.0 |
Collector support | Aluminum, 7010, T7451 | Typical % | 50 | 1 | 50 | 6.2 × 109 | 59.3 |
Total | 7 | 110 | 1010 | 100 |
Component | Material | Recycled content* (%) | Part mass |
Qty. | Total mass processed** (kg) | CO2 footprint |
% |
---|---|---|---|---|---|---|---|
Risers and header | Stainless steel, martensitic, ASTM CA-6NM, cast | Virgin (0%) | 12 | 1 | 12 | 77 | 10.4 |
Absorber | Copper, cast (h.c. copper) | Typical % | 4.5 | 1 | 4.5 | 11 | 1.5 |
Selective coating | Bronze, CuSi3.5Mn1, cast (silicon bronze) | Typical % | 0.7 | 1 | 0.7 | 1.8 | 0.2 |
Transparent cover | Glass, S grade (10 micron monofilament, f) | Virgin (0%) | 7 | 1 | 7 | 21 | 2.8 |
Storage tank | Stainless steel, martensitic, ASTM CA-40, cast, tempered at 315°C | Typical % | 15 | 1 | 15 | 59 | 7.9 |
Collector frame | Aluminum, 7475, T7351 | Typical % | 16 | 1 | 16 | 140 | 18.6 |
Collector support | Aluminum, 7010, T7451 | Typical % | 50 | 1 | 50 | 430 | 58.5 |
Total | 7 | 110 | 740 | 100 |
Since the two parts are used to carry functional parts weight, the new material must have a high young modulus and share close mechanical properties with aluminium. The density of the new materials must be close to aluminium density in order to maintain the volume of those parts.
Zn alloyed Stainless steel was suggested as a good alternative for the two parts.
Property | Aluminium | Stainless steel |
---|---|---|
Young modulus | 1.89 × 1011–1.97 × 1011 | 7 × 1010–7.36 × 1010 |
Yield strength | 2.9 × 108–3.2 × 108 | 3.59 × 108–4.27 × 108 |
Shear modulus | 7.4 × 1010–7.8 × 1010 | 2.7 × 1010–2.34 × 1010 |
Bulk modulus | 1.34 × 1011–1.46 × 1011 | 6.9 × 1010–7.25 × 1010 |
Poissons’s ratio | 0.265–0.275 | 0.330–0.343 |
From the comparison we can see that stainless steel is a good alternative for aluminium because most of the mechanical properties of them are close.
Another suggested changes were to use copper for the risers and header (tubes) instead of stainless steel since copper has a lower embodied energy and more thermal conductivity, also laminated glass were suggested to replace fibre glass transparent cover to lower embodied energy. After these changes have been made, energy consumption by materials production was drastically decreased and also CO2 footprint. They are dropped approximately by 40% (
Note that second column represents energy consumption/CO2 footprint by materials production after materials change. Obviously, manufacturing process consumption also decreases with changing the materials. The reason of this is copper can be easily handled resulting in easier manufacturing process. However, the end of life potential (EoL) is reduced because most of the new materials recyclable content are decreased.
From
Component | Material | Recycled content* (%) | Part mass |
Qty. | Total mass processed** (kg) | Energy (J) | % |
---|---|---|---|---|---|---|---|
Risers and header | Copper, cast (h.c. copper) | Virgin (0%) | 12 | 1 | 12 | 7.1 × 108 | 12.3 |
Absorber | Copper, cast (h.c. copper) | Typical % | 4.5 | 1 | 4.5 | 1.8 × 108 | 3.1 |
Selective coating | Bronze, CuSi3.5Mn1, cast (silicon bronze) | Typical % | 0.7 | 1 | 0.7 | 2.8 × 107 | 0.5 |
Transparent cover | Laminated glass | Virgin (0%) | 7 | 1 | 7 | 2 × 108 | 3.6 |
Storage tank | Stainless steel, martensitic, ASTM CA-40, cast, tempered at 315°C | Typical % | 15 | 1 | 15 | 7.3 × 108 | 12.8 |
Collector frame | Copper, cast (h.c. copper) | Virgin (0%) | 16 | 1 | 16 | 9.4 × 108 | 16.4 |
Collector support | Copper, cast (h.c. copper) | Virgin (0%) | 50 | 1 | 50 | 2.9 × 109 | 51.3 |
Total | 7 | 110 | 5.7 × 109 | 100 |
Component | Material | Recycled content* (%) | Part mass |
Qty. | Total mass processed** (kg) | CO2 footprint |
% |
---|---|---|---|---|---|---|---|
Risers and header | Copper, cast (h.c. copper) | Virgin (0%) | 12 | 1 | 12 | 43 | 11.9 |
Absorber | Copper, cast (h.c. copper) | Typical % | 4.5 | 1 | 4.5 | 11 | 3.1 |
Selective coating | Bronze, CuSi3.5Mn1, cast (silicon bronze) | Typical % | 0.7 | 1 | 0.7 | 1.8 | 0.5 |
Transparent cover | Laminated glass | Virgin (0%) | 7 | 1 | 7 | 12 | 3.4 |
Storage tank | Stainless steel, martensitic, ASTM CA-40, cast, tempered at 315°C | Typical % | 15 | 1 | 15 | 59 | 16.0 |
Collector frame | Copper, cast (h.c. copper) | Virgin (0%) | 16 | 1 | 16 | 58 | 15.8 |
Collector support | Copper, cast (h.c. copper) | Virgin (0%) | 50 | 1 | 50 | 180 | 49.4 |
Total | 7 | 110 | 370 | 100 |
Component | End of life option | % recovered | Energy (J) | % |
---|---|---|---|---|
Risers and header | Recycle | 37.5 | –2.9 × 108 | 9.2 |
Absorber | Recycle | 43.0 | –5 × 107 | 1.6 |
Selective coating | Recycle | 43.0 | –8 × 106 | 0.3 |
Transparent cover | Re-manufacture | 0.1 | –3.4 × 105 | 0.0 |
Storage tank | Recycle | 37.5 | –1.9 × 108 | 6.1 |
Collector frame | Recycle | 42.5 | –6.2 × 108 | 19.9 |
Collector support | Recycle | 43.0 | –2 × 109 | 62.9 |
Total | –3.1 × 109 | 100 |
Component | End of life option | % recovered | Energy (J) | % |
---|---|---|---|---|
Risers and header | Recycle | 37.5 | –2 × 108 | 11.8 |
Absorber | Recycle | 43.0 | –5 × 107 | 2.9 |
Selective coating | Recycle | 43.0 | –8 × 106 | 0.5 |
Transparent cover | Re-manufacture | 0.1 | –1.8 × 105 | 0.0 |
Storage tank | Recycle | 37.5 | –1.9 × 108 | 10.9 |
Collector frame | Recycle | 42.5 | –3.1 × 108 | 17.8 |
Collector support | Recycle | 43.0 | –9.8 × 108 | 56.2 |
Total | –1.7 × 109 | 100 |
From the CO2 perspective, the total savings are 375 kg which reduce the pollution in the environment. These calculations are only applied for a single mid-sized flat plate collector. Yet, for a commercial production of collectors, the savings will be multiplied by the number of units of production.
From
The economic analysis which turned to be the determining factor to choose the best alternative is summarized in
It is obvious that the current commercial used materials would result in less capital costs and accordingly they are preferred. The detailed cost analysis for the two situations are tabulated below,
Component | Material | Recycled content* (%) | Part mass |
Qty. | Total mass processed** (kg) | Cost |
% |
---|---|---|---|---|---|---|---|
Risers and header | Stainless steel, martensitic, ASTM CA-6NM, cast | Virgin (0%) | 12 | 1 | 12 | 120 | 4.9 |
Absorber | Copper, cast (h.c. copper) | Typical % | 4.5 | 1 | 4.5 | 120 | 5.1 |
Selective coating | Bronze, CuSi3.5Mn1, cast (silicon bronze) | Typical % | 0.7 | 1 | 0.7 | 19 | 0.8 |
Transparent cover | Glass, S grade (10 micron monofilament, f) | Virgin (0%) | 7 | 1 | 7 | 750 | 31.6 |
Storage tank | Stainless steel, martensitic, ASTM CA-40, cast, tempered at 315°C | Typical % | 15 | 1 | 15 | 79 | 3.3 |
Collector frame | Aluminum, 7475, T7351 | Typical % | 16 | 1 | 16 | 410 | 17.1 |
Collector support | Aluminum, 7010, T7451 | Typical % | 50 | 1 | 50 | 880 | 37.2 |
Total | 7 | 110 | 2400 | 100 |
Component | Material | Recycled content* (%) | Part mass |
Qty. | Total mass processed** (kg) | Cost |
% |
---|---|---|---|---|---|---|---|
Risers and header | Copper, cast (h.c. copper) | Virgin (0%) | 12 | 1 | 12 | 380 | 13.9 |
Absorber | Copper, cast (h.c. copper) | Typical % | 4.5 | 1 | 4.5 | 120 | 4.4 |
Selective coating | Bronze, CuSi3.5Mn1, cast (silicon bronze) | Typical % | 0.7 | 1 | 0.7 | 19 | 0.7 |
Transparent cover | Laminated glass | Virgin (0%) | 7 | 1 | 7 | 190 | 6.9 |
Storage tank | Stainless steel, martensitic, ASTM CA-40, cast, tempered at 315°C | Typical % | 15 | 1 | 15 | 79 | 2.9 |
Collector frame | Copper, cast (h.c. copper) | Virgin (0%) | 16 | 1 | 16 | 470 | 17.2 |
Collector support | Copper, cast (h.c. copper) | Virgin (0%) | 50 | 1 | 50 | 1500 | 53.9 |
Total | 7 | 110 | 2758 | 100 |
The difference in cost of collector frame using aluminium and copper is (470–410) = 60 AED, for the collector support the difference is (1500–880) = 620 AED, for the pipes the difference is (380–120) = 260 AED, for the glazing material (190–750) = –560 AED (the negative sing here represents cost saving). The total result is 380 AED. However, manufacturing process results in 20 AED savings which reduces the result to 360 AED.
In this work, the lifecycle of a flat plate collector for solar heating was analyzed using the CES-Edupack software to know total cost, carbon dioxide emission and total energy consumption. After completing the design for all steps materials, manufacturing, transport, use (maintenance) and end of lifecycle, it was found that the step that consumed most of the energy and had the largest CO2 emission was the materials production process. It was also found that the parts that consumed the most energy and produced the largest amount of CO2 in material production were the collector frame and the support. So, in order to decrease the energy production and the CO2 emissions in the material production copper was used instead of using aluminum for the collector frame and the support, because the energy used to produce 1 kg of copper was much less than the energy consumed for producing 1 kg of aluminum, and hence resulting in less CO2 emissions than the Aluminum production. The percentage decrease in the total energy consumption in the materials production was nearly 40%, but using copper would cause the cost to increase by almost 30%. However, the end of life potential to energy consumption ratio of using copper is approximately the same of the EOL potential to energy consumption ratio of aluminum frame and support.
To conclude, the equivalence of the two EOL potential to energy consumption ratio seems to be cost dependent and as it was found, the cost of using copper frame and support would be less than using aluminum frame and support. Hence, it is recommended to use the copper frame and support.
The major outcomes of this work are: Even though solar flat plate collectors are sustainable and renewable energy systems that do not produce CO2 emissions during their active usage, the processes they undergo during the design contribute to the greenhouse gasses emission. Materials production are usually the phase where most of energy consumption takes place. By looking to the direct energy or CO2 production rate savings, you cannot determine whether changing the materials would be beneficial to the system, EoL potential to energy consumption ratios should be the main factor of judgment. When changing materials of the system is desirable to achieve less energy consumption and CO2 emissions in materials production process, new materials must share the same properties. Usually, environmental-friendly materials are more expensive. For this reason, commercial firms avoid such materials in designing such systems. Taking the cost analysis as an approach is suitable for our situation since the EoL potential to energy consumption ratios were approximately equal.
The second author acknowledges Aalto University, Department of Mechanical Engineering, Energy Efficiency and Systems, Finland.