Make sure you are including the full citation for your documents in your lit. review with a link.

Summary

• To stack up the case of solar photo-voltaic against the energy derived from biofuels.

Goals

• Exergetic comparison of PV cells and Biofuel energy.
• Examining the prime and most efficient biofuel crop.
• Understanding the agronomic involved.
• Maximizing the exergetic output of PV cells.
• Investigating different techniques of making PV cells more affordable.

A Review on Biofuels

Net energy from cellulose ethanol from switchgrass

Source: Schmer, Marty R.."Net energy from cellulose ethanol from switchgrass" Proceedings of the National Academy of Sciences 105.2 (2008): 464-469.^[1]

• Evaluation of switchgrass as a biofuel.

• Concerns –

1)energy efficiency and economic feasibility
2)Investigated agricultural input cost
3)biomass yield
4)estimated ethanol output
5)greenhouse gas emission
6)net energy results

• Findings

1)Switchgrass produces 540% more renewable energy than nonrenewable energy consumed.
2)94% lower greenhouse emission than gasoline.

• They considered fields on 10 farms for net energy economic evaluation so that they can eradicated the discrepancies that occur when small with similar agricultural inputs are under consideration.

• Study considers various agronomic practices

• States that biofuel from switchgrass produces 13.1MJ of energy for every MJ of petroleum input.

TAKE AWAYS

1)This paper will not only build the case for switchgrass to be used as a biofuel but will also help us what kind of location and what suitable agronomic practices must be followed to get the maximum yield. 
2)Location of the farm was found out to be one of the deciding factor for the amount of ethanol yield ye can extract.

Energy cost of rapeseed based biodiesel as alternative energy in china

Source: Chen, H., and G. Q. Chen."Energy cost of rapeseed based biodiesel as alternative energy in china" Renewable Energy 36.5 (2011): 1374-1378.^[2]

• Evaluating energy cost of rapeseed as biofuel.

• Cost can be divided into 4 categories

1)Crop production
2)Transportation
3)Industrial conversion
4)Wastewater management

• This paper stated that 1ha of land produces 1.5 ton of biofuel. This comes to around 20 GJ of energy left after taking into factor the energy used in the production.

• It focuses on an in-depth analysis of rapeseed as a biofuel.

• It gives insights on how biofuel is processed from the crop harvest.

• Detailed classification of energy cost of each and every element that goes into making the final usable biofuel.

• Findings

1)Agricultural produce contributes to the lion share of total energy cost.
2)Rapeseed biofuel has a negative energy return owing to the low production of crop.

TAKE AWAYS

1)Considering the areas where the average yield of crop is more.
2)Less nitrogen based fertilizers as they account for the highest share of cost for the agricultural production.
3)We should consider locations where the crop is abundantly available or there is some scope for increasing production and the energy input for agricultural produce is minimum.

Energy balances for biogas and solid biofuel production from industrial hemp

Source: Prade, Thomas, Sven-Erik Svensson, and Jan Erik Mattsson. "Energy balances for biogas and solid biofuel production from industrial hemp" Biomass and bioenergy 40 (2012): 36-52.^[3]

• Paper states that hemp has higher energy yield than any other crop to obtain biofuel.

• It is less susceptible to pest infection which in turn reduces the overall input cost.

• 4 cases were considered

1)Combined heat and power from spring harvested baled hemp: Combustion heat is used for generating electricity and residential heating.
2)Heat from spring harvested briquetted hemp: Combustion heat is used for small scale residential heating.
3)CHP
4)Vehicle fuel autumn harvested chopped and ensiled hemp: Depicts biofuel used in vehicles.

• The first case was found out to be most efficient.

• The study found out that the maximum chunk of input energy that goes into producing the final hemp biofuel is for processing the biofuel.

• Advantages are less pesticide requirement, weed resistant, crop rotation is possible.

TAKE AWAYS

1)Areas where probability of pest infection is more, hemp cultivation is desirable and economic than other crops.
2)Net energy yield of hemp is also more than most of the crops.
3)Less maintenance.

Improvements in Life Cycle Energy Efficiency and Greenhouse Gas Emissions of Corn-Ethanol

Source: Liska, Adam J.."Improvements in Life Cycle Energy Efficiency and Greenhouse Gas Emissions of Corn-Ethanol" Journal of Industrial Ecology 13.1 (2009): 58-74.^[4]

• This paper focuses on the greenhouse gas emission from the corn based biofuel.

• It also discusses how in recent times the net corn production has increased and new ways have been found out to produce more energy efficient biofuel.

• They performed energy life cycle simulation and greenhouse gases assessments.

• The net energy ratio was found out to be ranging from a minimum of 1.29 to a maximum of 2.23.

TAKE AWAYS

1)In the pursuit of finding the best crop for biofuel, an improved life cycle energy efficiency is essential.
2)New technological advancements help us to reduce the energy we put into “seed-to-fuel” cycle hence improving the net energy ratio.
3)Improved version of biofuel indicates towards less greenhouse gas emission.

Camelina Derived jet fuel and diesel: Sustainable advanced biofuels

Source: Shonnard, David R., Larry Williams, and Tom N. Kalnes. "Camelina Derived jet fuel and diesel: Sustainable advanced biofuels" Environmental Progress & Sustainable Energy 29.3 (2010): 382-392.^[5]

• Builds the case for camelina.

• The paper discusses the biofuel alternatives to jet fuel and diesel.

• It also evaluates the life cycle greenhouse gas emission and compares it with conventional jet fuel and diesel.

• It’s grown without giving much attention as it can sustain extreme temperature and doesn’t require much inputs unlike other plants.

• Biofuel proved to be very cost effective when greenhouse gases are considered as a net minimum saving of about 67% was noted when using camelina based fuel.

• It was concluded that even though camelina based fuel was cost effective and reduced emission to a great extent, its performance and energy efficiency was almost the same when compared to conventional fuels.

TAKE AWAYS

Camelina poses a strong competition to other biofuel crops as the energy requirement for its life cycle is considerably less keeping its energy output the same as the conventional fuel.

A life cycle assessment of biodiesel production from winter rape grown in southern Europe

Source: Gasol, Carles M.."A life cycle assessment of biodiesel production from winter rape grown in southern Europe" Biomass and Bioenergy 40 (2012): 71-81.^[6]

• The paper states the benefit of biodiesel over diesel in terms of

1)Abiotic Depletion
2)Photochemical oxidation
3)Global warming potential

• This is a life cycle assessment of rapeseed in terms of different climate and net crop yield.

• The highest energy consumed during the life cycle is in transesterification and oil extraction which was found to be 25.22% and 21.30% respectively.

• The study found out that biofuel has a less impact on abiotic depletion and global warming potential.

• Putting the coproducts (glycerin) to use again reduces stress on the environment.

TAKE AWAYS

The reusability of the byproducts.

Exergetic evaluation of biomass gasification

Source: Ptasinski, Krzysztof J., Mark J. Prins, and Anke Pierik. "Exergetic evaluation of biomass gasification" Energy 32.4 (2007): 568-574.^[7]

• This paper focuses on biofuel which is in gaseous form.

• It states that most of the energy is lost during the process of gasification and hence wants to make this process more efficient.

• It suggests that by drying the gas may increase the exergetic value of the gaseous biofuel.

• It states in order to reach the maximum efficiency of gas biofuel the right amount of oxygen must be added to the gasifier.

• The data suggests that the exergic value of vegetable oil is greater than other biofuel sources like straw, wood, grass, sludge, manure.

TAKE AWAYS

1)Gasification of biofuel releases some energy into thin air while the process of gasification is in process.
2)This is not at all desirable when dealing with biofuels.

Improvements in life cycle Energy Efficiency and Green House Gas Emissions of Corn Ethanol

Source: Liska, Adam J. "Improvements in life cycle Energy Efficiency and Green House Gas Emissions of Corn Ethanol " Journal of Industrial Ecology 13.1 (2009): 58-74.^[8]

• Improved technologies to increase energy efficiency and profitability, ethanol production and co-product use • Use of thermo-compressors for condensing steam ,increase reuse, thermal oxidizers for combustion of volatile organic compounds and efficient utilization of waste heat • Estimating the values of co products formed – value analysis by substitution of value of the co-product with another component that is needed in their production .This method is called substitution method. • Corn production data retrieved from national Agricultural Statistics • The various energy values considered -thermal energy, fertilizer use, seed, drying, electricity, and conversion yield, total ethanol yield, coproduct credit- to estimate the performance and greenhouse gas emissions. • The effects of climate, soil quality and access to irrigation is discussed. • The use of nitrogen fertilizer and the required inputs are discussed along with the effect of tillage and agricultural practices to improve the efficiency.

This paper helps us in understanding the different input and output factors that need to be considered when evaluating the impact of biofuel.

Improvements in life cycle Energy Efficiency and Green House Gas Emissions of Corn Ethanol

Source: Liska, Adam J.."Improvements in life cycle Energy Efficiency and Green House Gas Emissions of Corn Ethanol" Journal of Industrial Ecology 13.1 (2009): 58-74.^[9]

• Improved technologies to increase energy efficiency and profitability, ethanol production and co-product use • Use of thermo-compressors for condensing steam ,increase reuse, thermal oxidizers for combustion of volatile organic compounds and efficient utilization of waste heat • Estimating the values of co products formed – value analysis by substitution of value of the co-product with another component that is needed in their production .This method is called substitution method. • Corn production data retrieved from national Agricultural Statistics • The various energy values considered -thermal energy, fertilizer use, seed, drying, electricity, and conversion yield, total ethanol yield, coproduct credit- to estimate the performance and greenhouse gas emissions. • The effects of climate, soil quality and access to irrigation is discussed. • The use of nitrogen fertilizer and the required inputs are discussed along with the effect of tillage and agricultural practices to improve the efficiency.

This paper helps us in understanding the different input and output factors that need to be considered when evaluating the impact of biofuel.

Land usage attributed to corn ethanol production in United States: sensitivity to technological advances in corn grain yield, ethanol conversion and co-product utilization

Source: Mumm, Rita H.."Land usage attributed to corn ethanol production in United States: sensitivity to technological advances in corn grain yield, ethanol conversion and co-product utilization" Biotechnology for biofuels 7.1 (2014): 1.^[10]

• This paper identifies the key supply variables and understand long term effects and interactions involving corn grain yield, ethanol processing and livestock feeding and how these factors affect the land area attributed to ethanol production. • This papers also explores the net efficiency considering different plant configurations. A comparison study has been done to study the trends of the crops through the years.

Life Cycle Assessment of Corn Grain and Corn Stover in the United States

Source: Kim, Seungdo, Bruce E. Dale, and Robin Jenkins. "Life Cycle Assessment of Corn Grain and Corn Stover in the United States" The International Journal of Life Cycle Assessment 14.2 (2009): 160-174.^[11]

• To study the effects of continuous corn cultivation of corn grain and corn stover considering the current practices in agriculture • The conditions affecting the performance of the corn grains. • To study the environmental effects the corn production has two cropping systems have been considered-(1) crop produced for the grain (2) corn grown for Stover. • Impact assessment was done in the fertilizer(N,P,K ) herbicides, insecticides, lime, diesel, gasoline, LPG, electricity usage . • Sensitivity assessment of the two systems were done in terms of nitrogen usage and ammonia loss. • The effect of no tillage and tilling the fields were studied and the results indicate that no tillage practices reduce the total fossil energy GHG emissions by about 50% • The results indicate that corn stover has a lower impact on the environment than the corn grain in terms of total fossil energy,greengouse gases acidification. Planting winter crops and transitioning to a no tillage farming practice are ways to reduce these nitrogen losses from the soil.

2008 Energy Balance for Corn-Ethanol Industry

Source: Shapouri, Hosein. "2008 Energy Balance for Corn-Ethanol Industry". DIANE Publishing, 2011.^[12]

This is a report by the United States department of agriculture which is based on the net energy balance of the corn ethanol producers that was done by conducting a survey of ethanol producing plants.This report goes on to investigate about how the net ethanol production has changed from an energy sink to a net energy gain in present. This paper goes on to explain about the about how the inputs and energy needs has been varying over the past two decades.The data has also been divided statewise. This data is useful to understand how the energy calculations are done and approximately what the energy needs of the system would be on an average.

Current and potential U.S Corn Stover Supplies

Source: Graham, Robin Lambert."Current and potential U.S Corn Stover Supplies" Agronomy Journal 99.1 (2007): 1-11. ^[13]

• This paper gives an idea of Stover production, collection and supply estimation methods subjects to constraints like soil moisture constraints , wind and water erosion constraints,etc. • Grain to stover mass – 1:1 • Constraints in stover collection 1. Equipment constraints:amount left in the fiels is a function of equipment used to collect the stover and condition of stover atleast 25% left in the field 2. Soil Moisture Constraints:if rainfed agriculture all stover to be left on the field to maintain soil moisture for the next crop. 3. Water and wind erosion constraints • Collectable stover = total stover- max constraints • Discusses different tilling practices

Ethanol Production Using Corn, Switchgrass, and Wood; Biodiesel Production Using Soybean and Sunflower

Source: Pimentel, David, and Tad W. Patzek. "Ethanol Production Using Corn, Switchgrass, and Wood; Biodiesel Production Using Soybean and Sunflower" Natural resources research 14.1 (2005): 65-76.^[14]

This paper talks about the average input energy required,and cost of production of switchgrass,wood and corn to create biofuels and the approximate amount of non renewable/fossil energy that needs to be expended for their generation.This paper aides in deriving data regarding input energy and output energy of the various processes.

(1)The 2001 Net Energy Balance of Corn Ethanol And (2)The energy balance of corn ethanol: An update

Source:Net Energy Balance of Corn Ethanol^[15]

This report gives an idea of the net energy balances of corn ethanol production with reference to • Production of corn • Energy to transport corn to ethanol plant • Energy used to convert corn to ethanol and by products • Energy used in ethanol distribution This also gives an idea about energy requirements of farm by considering weighted average of data gathered from the states belonging to the corn belt. It also gives an idea about the products obtained and energy used in the dry milling and wet milling.

Biomass Supply From Corn Residues: Estimates and Critical Review of Procedures

Source: Gallagher, Paul W., and Harry Baumes. "Biomass Supply From Corn Residues: Estimates and Critical Review of Procedures" USDA, Washington, DC, USA. ^[16]

• This paper gives a good picture about how the Stover output and costs are calculated. • This also gives a clearer picture of the supply- demand of corn bio-crop and related parameters used in the estimations and calculations. • The author goes on to explain about the handling costs ,farm costs,plant costs and net value of the corn stover. This paper is useful to understand the related functions, energy and money that need to be spent on the corn crop growing farms.

Agricultural Statistics

Source: Agricultural Statistics^[17]

"Agricultural Statistics is published each year to meet the diverse need for a reliable reference book on agricultural production, supplies, consumption, facilities, costs, and returns." This is a good source to study the trends in corn crop through the last decade

Exergy and CO2 Analyses as key tools for the evaluation of Bio-Ethanol Production

Source: Kang, Qian, and Tianwei Tan. "Exergy and CO2 Analyses as key tools for the evaluation of Bio-Ethanol Production" Sustainability 8.1 (2016): 76.^[18]

Energy a thermo dynamic analysis technique. Exergy is defined as “exergy is the maximum work that can be produced when a heat or material stream is brought to equilibrium in relation to ref environment” ( Dewulf.J,2010) The analysis identifies the energy and exergy loses in a system which is usually used in a poly-generation System and as for mainly thermochemical pathways The biofuel generation is considered as more successful in an integrated plant of first and second generation. The thermodynamic efficiency of a system is

                  Ƞ =(Exergy  of useful products )/(Input Energy)

For Lignocellulosic

                 Ƞ = (Exet+Pnet+Ex res)/(Exbm+ ∑Exch.+ExLT)

The corn based plants positive energy results are doubtful exergy results.

Energy a thermo dynamic analysis technique

Exergy is defined as “exergy is the maximum work that can be produced when a heat or material stream is brought to equilibrium in relation to ref environment” ( Dewulf.J,2010) The analysis identifies the energy and exergy loses in a system which is usually used in a poly-generation System and as for mainly thermochemical pathways The biofuel generation is considered as more successful in an integrated plant of first and second generation. The thermodynamic efficiency of a system is

                  efficiency =(Exergy  of useful products )/(Input Energy)

For Lignocellulosic

                  efficiency = (Exet+Pnet+Ex res)/(Exbm+ ?Exch.+ExLT)

The corn based plants positive energy results are doubtful exergy results.

Effects of acid treatment on different parts of corn stalk for second generation of ethanol production

Source: Li, Ping."Effects of acid treatment on different parts of corn stalk for second generation of ethanol production" Bioresource Technology (2016).^[19]

The effect of acid treatment has different effects on different parts of corn stalk for second generation ethanol production. Sulfuric acid is mostly used to depolymerize the lignin and hemicellulose fractions. pretreatment - 2% (w/v),H2SO4,121°C under 10%(w/v) solid loading for 60 min Solid fractions then collected at 105°C overnight, and stored at 4°C. Enzymatic hydrolysis/fermentation -50°C,150rpm in 0.01M citrate buffer (pH 4.7) Cellulase 15FPU/g of solid Fermentation was performed 30°C/200rpm in 1L bio reactor with working volume of 600ml,pH at 6 by ammonia,Sterilization of hydrolysis was done at 121°C . Recovery rate of Solid = Wpre/Wraw*100 Glucose Yield % = (amount of glucose in enxyme hydrolysate*0.9)/(amount of cellulose in pre treatment sample*100%) The Glucose content in husk was found high, lignin content was low ,xylan content was high in cob. Pro pre-treatment enhanced the overall efficiency in ethanol production. Ethanol Energy Return on Investment A survey of the literature 1990-present (http://pubs.acs.org/doi/abs/10.1021/es052024h) Roel Hammerschlag” Ethanol Energy Return on Investment A survey of the literature 1990-present” The paper discusses the net energy return on ethanol production- a review of different studies has been taken into account. The studies considered two methods, ethanol from corn starch and cellulosic ethanol. The term RE has been considered to represent the net energy of ethanol to the non –renewable energy input in manufacturing process. Studies by pizmental & patzak implied that the net renewable energy return is zero for the invested fossil fuels .

Pretreatment technologies for efficient bioethanol production process based on enzymatic hydrolysis

Source: Alvira, Petal."Pretreatment technologies for efficient bioethanol production process based on enzymatic hydrolysis" Bioresource technology 101.13 (2010): 4851-4861.^[20]

The paper concerns the issues regarding the technologies employed in biofuel produce from   
lignocellulosic materials. The process has a lot of chemical barriers as it should lead to high yields, digestible. The amount of toxin compounds should be kept low .The energy consumption can be kept low if the dry content is high in raw material.to ensure adequate ethanol produce concentration of sugar from coupled operation should be kept above 10%.heat requirements should be kept low.

Among all the pre-treatment methods considered chemical and thermochemical found to be the best technologies available.

Biomass Electricity generation at ethanol plants –achieving maximum impact

Source: Morey, R. V., and D. G. Tiffany. "Biomass Electricity generation at ethanol plants –achieving maximum impact" Final report for XCEL energy renewable development fund project RD3–23 [internet](2011 Dec)[cited 2013 Jan 11].^[21]

The paper studies the energy and electrical needs of 50 million gallon/year ethanol plant. The system performance of superheated steam drying and conventional steam tube drying are done for syrup and corn stover, corn stover fuels. It was found that superheated steam drying had more efficiency in electrical generation and low thermal efficiency. The process heat required was also less than the steam tube dryer. System performance was same for both syrup and corn stover, corn-stover.as syrup-corn stover had a small increase in the power sent back to grid. There’s reduction in GHG gases due to increase in electricity production. The corn entering into a plant is usually converted into one-third of distilled grains, one-third of CO2.Two driers are used for syrup and corn stover. The net energy required to remove water in superheated system drier is about 1000 KJ/kg(430 btu/lb) compared to about 2070KJ/kg (1150 BTU/lb) The water condensed is reused in ethanol processing thus reducing net water intake in ethanol processing. The logistics and storage of bio raw material has been studied.

Net energy balance of ethanol production

Source:Net energy balance of ethanol production^[22]

The paper review about the net energy balance of ethanol produce. The net value of energy is considered positive as the net intake of energy and non-renewable resources has decreased over years Average yield of 2.76 gallons of ethanol/bushel of corn was reported .with approx. 2.74% -wetmill,2.81% -dry mill. BTU per gallon of ethanol produced is around 20545. The large portion of energy consumed is in drying co-product distillers grain. 42 gallons of water per gallon of ethanol is consumed. The corn produced in US is mostly not irrigated co-products from plants are distiller grains for livestock feed and CO2 in food and beverage industry. The paper makes a strong point on considering the net energy credits to by-products obtained

Ethanol can contribute to energy and environmental goals

Source: Farrell, Alexander E.."Ethanol can contribute to energy and environmental goals " Science 311.5760 (2006): 506-508.^[23]

The study reviews 6 paper related to the study of ethanol energy balance. It focuses mainly on the calculation of net energy produce of ethanol as it confirms that most studies ignore the byproducts in ethanol production.one ml of gasoline needs more petroleum than one ml of ethanol. The cellulosic ethanol is being considered far more advanced technology. Energy and Resource group Biofuel analysis meta model has been used to compare data across different studies. The study reported that ethanol and co-products yielded a positive net energy 4MJ/L to 9 MJ/L

Ethanol Industry and process descriptions

Source: Ethanol Industry and process descriptions^[24]

The process involved in ethanol produce has been studied.

Integrated bio refineries are envisioned as key model for future, Bio refineries which use fuels, chemicals animal fuels as they increase profitability. Corn is the most used ethanol product in USA

The main process of ethanol production . Corn dry milling- cleaning, milling, liquefaction, addition of alpha amylase to break down starch.

Saccharification, Distillation, Dehydration, Distillation, dehydration, rectifying columns, molecular sieve.

Co-products – silage of distillation columns, centrifuge-solids.

Wet milling- Similar process but corn kernel is separated into its components Cleaning, steeping, germ fiber starch separation, saccharification, Fermentation, Distillation,dehydration Co-product processing-corn gluten meal, corn gluten feed

Biomass-to-bioenergy and biofuel supply chain optimization: overview, key issues and challenges

Source: Yue, Dajun, Fengqi You, and Seth W. Snyder. "Biomass-to-bioenergy and biofuel supply chain optimization: overview, key issues and challenges" Computers & Chemical Engineering 66 (2014): 36-56.^[25]

The paper focuses on optimization and planning of biomass and biofuel generation. The planning strategy from Bio feed stock supply to biomass energy storage and the technicalities of different biofuel procedures have been considered. Biomass pathways-terrestrial, aquatic biomass feedstocks Cellulosic ethanol is being considered due to the adverse effect on food crops Biodiesel, Intermediates corn, pretreatment, hydrolysis, Lipids, syngas, Bio oil, Feed stock supply needs to be regular. Thermochemical technologies-gasification, pyrolysis, algae harvesting and conversion. Distribution over long distance is very difficult. It reviews that cellulosic procedure is best.

Exergy Based Energy efficiency and renewability Assessment of Bio Fuel Production

Source: Dewulf, Jo, Herman Van Langenhove, and B. Van De Velde. "Exergy Based Energy efficiency and renewability Assessment of Bio Fuel Production" Environmental science & technology 39.10 (2005): 3878-3882.^[26]

The article provides comparative exergy based efficiency analysis of three crops mainly corn,soy bean, Rapeseeds in the produce of bio fuel. Exergy Based analysis to assess the net Renewable energy from non-renewable resources Highest amount of exergy 220 GJ ha-1 yr-1 is obtained from corn produce. Solar energy is the major input for all the three crops rather than the seeding material The net efficiency of solar energy input is negligible. Corn proves to be the best on the overall process and major part of energy produce has a low non renewable energy part.

Resource use efficiency and environmental performance of nine major biofuel crops,processed by first generation conversion techniques

Source: de Vries, Sander C.."Resource use efficiency and environmental performance of nine major biofuel crops,processed by first generation conversion techniques " Biomass and Bioenergy 34.5 (2010): 588-601.^[27]

In this article nine main crops like maize, wheat, sugar beet, cassava, sweet sorghum, sugarcane, winter oil seed rape, soy bean, oil palm have been considered. GHG emissions have not been considered as CO2 has already been absorbed from atmosphere Net energy yield has been calculated taking into account non-renewable inputs. Land use and soil erosion have been considered basis on the crop conditions, it was found that cassava and sugarcane have most soil erosion . It was found that crop with favorable energy ratios don’t necessarily produce Net yield per unit of water has been considered, but water usage in industrial conversion stage has not been considered. A crop with more usage of pesticide has been considered less sustainable. The study states that corn has the highest energy conversion efficiency. Sweet sorghum, sugar cane and palm oil seed found to deliver more energy than the energy input.

Variation in corn stover composition and energy content with crop maturity

Source: de Vries, Sander C.."Variation in corn stover composition and energy content with crop maturity" Biomass and Bioenergy 34.5 (2010): 588-601.^[28]

In this article corn stover over crop maturity has been considered. Total Exp was conducted for 213 days by harvesting corn (32K61,32K64) and they found that the crop which is harvested at a maturity state has given 54% of stover and 64% of grain The crops which have harvested a 213 days lost 74% of dry matter which is due to respiration of microbes. The end of experiment it was found that the amount of dry matter in stover found to be 11.7 ton ha-1 ,the dry matter and the green is same as 11.7 ton ha-1 The gross energy of corn stover is 17.65 KJ gm-1 by calerometric analysis. It can be clearly stated that the stover with dry content has given better result.

Life cycle assessment of various cropping systems utilized for producing biofuels :Bioethanol and biodiesel

Source: Kim, Seungdo, and Bruce E. Dale. "Life cycle assessment of various cropping systems utilized for producing biofuels :Bioethanol and biodiesel " Biomass and bioenergy 29.6 (2005): 426-439.^[29]

In this article life cycle assessment of crops in ethanol and biodiesel production has been considered. Corn stover which is complete upper part of crop except grain uses more energy in harvesting, and has increased ethanol production ha-1 41-65% than continuous corn grain. Cropping system scenarios of Continuous corn, corn with soy bean. Corn grain is processed into ethanol via corn wet milling with a ethanol yield of 0.3 kg ethanol per kg of dry corn grains. Corn-soy bean rotation crop had less renewable energy resources and has lowest ethanol production. The CC ,CS cropping system has negative green house gas emissions. Corn stover as raw material for ethanol saw a increase of ethanol production of 41-65% per hectare.

Engineering aspects of collecting corn stover for bioenergy

Source: Sokhansanj, Shahab."Engineering aspects of collecting corn stover for bioenergy." Biomass and Bioenergy 23.5 (2002): 347-355.^[30]

In this article Corn Stover isconsidered including the moisture content .where it is considered in 1:1 ratio for dry matter of corn grain to dry matter of dry stover . Yield of stover is calculated from the corn grain produce with an increase in mass of above ground crop The moisture content of stalks and leaves has found to be 82% and grain was about 34 % Monitoring of moisture content has been consider A field test was conducted with corn grain yield of 8.8 t ha-1 as we considered 1:1ratio stover is 8.8 t ha-1. Losses due to delayed harvesting has been observed. It is observed that timely harvest and stover handling has to be done accordingly.

Techno-Economic comparision of process technologies for biochemical ethanol production from corn stover

Source: Kazi, Feroz Kabir."Techno-Economic comparision of process technologies for biochemical ethanol production from corn stover" Fuel 89 (2010): S20-S28.'^[31]

The study has been conducted by comparing different process technologies of ethanol from lignocellulosic material. Different treatment technologies of biochemical analogies have been considered for biochemical ethanol production. Ethanol yield per mass of feed stock is lower in 2-stage dilute acid treatment and high in C5 and C6 fermentation. The advantage of cellulosic ethanol is the internal energy is supplied by the plants by-products Ethanol product value increase when feedstock value is increased. The product value can be considered based on enzyme cost . It was observed that the ethanol yield by 2-stage dilute acid being the lowest (76gal/mg)

Evaluation of Solar energy as a potential source

Annual exergy evaluation on photovoltaic-thermal hybrid collector

Source: Fujisawa, Toru, and Tatsuo Tani. "Annual exergy evaluation on photovoltaic-thermal hybrid collector" Solar energy materials and solar cells 47.1 (1997): 135-148.^[32]

• Makes a more complete use of solar energy.

• It extracts electric as well as thermal power from solar energy.

• Exergy based comparison and evaluation was done as electric and thermal energy has different units associated with them.

• The paper discusses the problem associated with thermal energy as it requires a certain temperature difference so that we can extract that energy to do some work.

• 3 cases were considered-

1)A simple PV module
2)A PV/T module (Hybrid Cover Less)
3)A PV/T module (Hybrid Single Cover)

• Monthly and annual data were obtained for daily and seasonal variations in solar radiations.

• Findings :

1)It was found out that the exergy gain for electrical energy was high although the exergy gain for thermal energy was much smaller.
2)Electrical exergy was in the order of 
   1)Coverless PV/T
   2)Simple PV
   3)Single Cover PV/T
3)Thermal exergy was in the order of 
   1)Single Cover PV/T
   2)Coverless PV/t

TAKE AWAYS

1)Formulation to find the total exergy.
2)Heat and power generation characteristics.
3)Single covered PV/T should be used as they have high exergy.

Case Studies of large-scale PV systems distributed around desert area of the world

Source: Kurokawa, Kosuke."Case Studies of large-scale PV systems distributed around desert area of the world" Solar energy materials and solar cells 47.1 (1997): 189-196.^[33]

• The author challenges the present conventional energy sources which have a lion share in the energy market with large scale PV establishments.

• Major factors governing a PV power plant design were considered.

TAKE AWAYS

1)PV power plant design
2)Size optimizations 
3)Cost estimations

Cost reduction in PV manufacturing and Impact on grid-connected and building-integrated markets

Source: Maycock, Paul D. "Cost reduction in PV manufacturing and Impact on grid-connected and building-integrated markets" Solar Energy Materials and Solar Cells 47.1 (1997): 37-45.^[34]

• This paper suggests different ways to limit the pricing of PV systems to a lower level.

• Increased size of the plant reduces the cost per watt of energy.

• It advocates the use of thin film modules and manufacturing of amorphous silicon for a better cost to efficiency ratio.

• Some of the worlds’ governments have cash subsidies of about 50% in practice.

TAKE AWAYS

1)Roll-to-roll continuous process plants should be adopted rather than batch process plants.
2)Government subsidies makes PV plant cheap.
3)Making use of thin film amorphous silicon.
4)Establishing PV plant in more than one Biofuel growing crop field.

Low cost solar module manufacturing

Source: Little, Roger G.."Low cost solar module manufacturing" Solar energy materials and solar cells 47.1 (1997): 251-257.^[35]

• The burgeoning solar industry has been expanding many folds which has made the manufacturers to adopt numerous ways to make PV cells affordable.

• PV cells manufacturers have developed several cost cutting ways which will help them against the growing competition.

• This paper gives stress on high automation and a higher throughput capacity of module manufacturing and fabrication plants.

TAKE AWAYS

1)Similar output cells clubbed together to form a module with higher efficiency.
2)An assembler developed by Spire can make series cell soldering a much faster process hence saving time and money.
3)Larger area cells helps in cost reduction.

Photovoltaic systems: A cost competitive option to supply energy to off-grid agricultural communities in arid regions

Source: Qoaider, Louy, and Dieter Steinbrecht. "Photovoltaic systems: A cost competitive option to supply energy to off-grid agricultural communities in arid regions" Applied Energy 87.2 (2010): 427-435.^[36]

• In order to connect rural and remote inhabited locations to the power grid, the generating public utility needs to build a network of electrification which seems impractical as far as the cost parameters are concerned.

• The author compares

1)A diesel generator set
2)A PV system

• Procedure conducted

1)Identifying the solar energy potential and the demand.

2)Optimizing the PV cell size to accommodate the demand of entire locality.

3)Comparing the life cycle cost of both systems.

TAKE AWAYS

1)Decentralized power generation.
2)Electrification of such locations are feasible only when the generation is cheap.
3)Although the energy cost of PV electricity is lower, PV was found out to be more capital centric which puts us in a position where we need to find out ways to make the manufacturing and set up cost a couple of notches lower.
4)When set up in locations of high solar irradiations its profitability increases manifolds.

Energy and Exergy analysis of photovoltaic-thermal collector with and without glass cover

Source: Chow, Tin Tai."Energy and Exergy analysis of photovoltaic-thermal collector with and without glass cover" Applied Energy 86.3 (2009): 310-316.^[37]

• This paper gives a thermodynamics viewpoint on the PV/T collector module.

• PV/T cell with glass cover has a greater total energy absorption while it lowers the photovoltaic efficiency owing to the reduced absorption and increased reflection of irradiation.

• If the thermal energy extraction is secondary with less or little importance then the PV/T should be without cover.

TAKE AWAYS

1)The factors working in favor of  PV/T without cover are
    1)PV cell efficiency
    2)Packing factor
    3)Water mass to collector area
    4)Wind velocity
2)The factors working in favor of PV/T with cover
    1)Ambient Temperature

Low cost processing of CIGS thin film solar cells

Source: Kaelin, M., D. Rudmann, and A. N. Tiwari. "Low cost processing of CIGS thin film solar cells" Solar Energy 77.6 (2004): 749-756.^[38]

• This paper discusses the use of thin layer CIGS (Copper Indium Gallium Selenide) for low cost PV module.

• The machinery required for such kind of module manufacturing is also low as compared to conventional silicon wafer.

• The following properties of CIGS were highlighted

1)High optical absorption
2)Tunable bandgap

• The process manufacturing process of CIGS PV module is explained and it’s also stated that this process can be set up as a roll-to-roll process which in turn decreases its production cost.

TAKE AWAYS

1)CIGS PV module stacks up a very bold case for itself even though the efficiency is compromised.
2)If cost is the primary constraint then the use of CIGS would prove vital.
3)Or even a hybrid combination of silicon wafer and CIGS module would do a great job in cutting down the cost to a great extent.

Photovoltaic technology: The case for thin-film solar cells

Source: Kaelin, M., D. Rudmann, and A. N. Tiwari. "Photovoltaic technology: The case for thin-film solar cells" Solar Energy 77.6 (2004): 749-756.^[39]

• This paper is based on the argument that although the prices of PV cells have gone down with a substantial increase in the our reliability on PV cells, the cost associated with silicone wafer will eventually go up owing to the availability of limited silicon resources.

• Silicone thin film cells are made by depositing silicon which is in its gas phase on a low cost substrate.

• It builds up the case for use of amorphous silicon vs crystalline silicon.

• Amorphous silicon has low deposition temperatures which enables us to use glass (low cost substrate) as a substrate.

TAKE AWAYS

1)Use of polycrystalline wafers instead of conventional monocrystalline could prove beneficial in cutting down cost but the efficiency would be compromised.
2)The thickness of thin film cells being a few microns, this terminates the very problem which was the limited availability of silicon.
3)Amorphous silicon has a higher absorption coefficient than crystalline silicon.

Life cycle assessment and energy pay-back time of advanced photovoltaic modules: CdTe and CIS compared to poly-Si

Source: Raugei, Marco, Silvia Bargigli, and Sergio Ulgiati. "Life cycle assessment and energy pay-back time of advanced photovoltaic modules: CdTe and CIS compared to poly-Si" Energy 32.8 (2007): 1310-1318.^[40]

• This paper stacks up the case for CdTe and CIS PV module against the conventional polycrystalline silicon.

• The efficiencies were found out to be in the order of:

1)CdTe: 9%
2)CIS: 11%
3)Poly-Si: 14%

• CdTe and CIS based PV modules are found out to be toxic in nature. Hence their use and disposable must be done in a reliable manner.

TAKE AWAYS

1)Thin film operate at higher efficiencies in overcast condition.
2)Overall performance was found out ot be competitive with poly-Si based PV module.
3)The choice of CdTe or CIS type PV module will decrease the capital cost but would increase the maintenance and disposal cost.

Cumulative exergy extraction from the natural environment: A comprehensive life cycle impact assessment method for resource accounting

Source: Dewulf, Jo."Cumulative exergy extraction from the natural environment: A comprehensive life cycle impact assessment method for resource accounting" Environmental science & technology 41.24 (2007): 8477-8483.^[41]

• This article talks about the total exergy derived from nature which is used to generate power in the form we can make use of.

TAKE AWAYS

The exergy data of different resources can be of very vital use in our project. 

Energy Viability of photo-voltaic Systems

Source: Alsema, Erik A., and E. Nieuwlaar. "Energy Viability of photo-voltaic Systems" Energy policy 28.14 (2000): 999-1010.^[42]

• This paper talks about the different processes involved in manufacturing, processing and assembling of the solar panels.

• Factors included in the calculation of payback time and carbon dioxide emissions

PV Watts Calculator-NREL website

Source: PV Watts Calculator^[43]

This is a tool that has been developed by the NREL and is used to “estimate the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations” by entering the system details like climate data ,PV module information. This tool is useful for this project to estimate net solar output energy and possible losses at the chosen location of installation.

Land-Use Requirements for Solar Power Plants in the United States

Source: Ong, Sean."Land-Use Requirements for Solar Power Plants in the United States" Golden, CO: National Renewable Energy Laboratory (2013).^[44]

• This is a document report released by the National Renewable Energy Laboratory which discusses about the land requirements for the different installations. This report gives a fair idea of the total area usage, system configurations and capacity and electricity generation.

• This document also has data regarding the PV Projects within the US and gives data relating to

   1.	Total capacity in MW
   2.	Total area in acres
   3.	Direct area in acres 
   4.	Solar Tracking type and  module efficiency

This report is a good source of data for our project.

Life Cycle Assessment of photo-voltaic electricity generation

Source: Stoppato, A. "Life Cycle Assessment of photo-voltaic electricity generation" Energy 33.2 (2008): 224-232.^[45]

• Discusses about the net mass and energy flow right from production to final assembling the panel. The net electricity production by the panel is also captured to evaluate the total payback time and potential carbon dioxide mitigation.

• This paper identifies all underlying processes in the manufacturing of a solar panel and the input usage and output quantity.

• Gross energy requirement per panel was calculated and the greenhouse effect or global warming potential was also studied.

• The Energy Pay Back Time = Einput/Esaved, Where,

Einput = energy input during the module life cycle
Esaved = annual energy savings due to electricity generated by the PV module

Studies shows EPBT is estimated shorter than the panel operation life.

This paper is useful to estimate the approximate energy input to set up a plant with PV panels.

Iowa energy centre- Solar calculations

Source: Iowa energy centre- Solar calculations^[46]

This web page is hosted by Iowa energy center and has an online solar calculator that calculates the data for Iowa county based on the chosen configuration and location and irradiation levels. This data could prove useful for our project for PV modelling considering a solar farm in Iowa .

Solar Statistics- Solar Energy industries Association

Source:Solar Statistics^[47]

This site serves as a good source to collect statistics for out project .It gives us an idea of the current solar projects the locations installed and the capacity of these plants and the type of systems used.

Life cycle analysis of solar PV system

Source: Baharwani, Vishakha."Life cycle analysis of solar PV system " Int J Environ Res Dev 4.2 (2014): 183-190.^[48]

The paper reviews the life cycle analysis of different PV systems modules. The entire lifecycle of PV cell from the point manufacturing and installing of PV cells and GHG are considered It reports that crystalline modules had good conversion efficiency but high energy inputs and GHG emissions.Thin film modules have less energy inputs and GHG emissions.

Energy and exergy analysis of 36w solar photovoltaic module

Source: Sudhakar, K., and Tulika Srivastava. "Energy and exergy analysis of 36w solar photovoltaic module" International journal of ambient energy 35.1 (2014): 51-57.^[49]

The exergy and energy analysis of 36 w solar pv module has been considered with efficiency being calculated with the net energy delivered to the solar panel to the energy output. Percentage of power converted and collected is considered as the energy efficiency

                                       Ƞenergy = (Voc*Isc** FF)/(A*G)

To reduce the higher surface temperature which would probably cause efficiency reduction artificial cooling by passing air or water on the back side of the module is done. Exergy input= Exergy output + Exergy loss+ Irreversibility. The thermal energy from solar radiation dissipates as heat which is considered as exergy destruction An experimental study was conducted which found that the electrical exergy was much less than that can be obtained because of loss of exergy as result of irreversibility. The exergy efficiency has reported low and can be improved with optimization in design of solar panel The PV exergy efficiency can be improved with solar radiation intensity and decreases after reaching a maximum point.

Planning guidance for the development of large scale ground mounted solar PV systems

Source: Planning guidance for the development of large scale ground mounted solar PV systems^[50]

• Those document is impotrtant in the sense that it gives a clear idea about the planning,installing and maintainence of PV panels on a large scale .
• It also discusses about the electrical capacity of the PV system.This could be useful in understanding and planning the PV farm simulation.

References