Energy Return On Investment Research Articles

Life cycle energy demand and carbon emissions of scalable single‐junction and tandem perovskite PV

AbstractPerovskite photovoltaics reached record efficiencies in the laboratory, and if sustainably commercialized, they would accelerate a green energy transition. This article presents the development of life cycle inventory material and energy databases of four most promising single‐junction and three tandem scalable perovskite systems with assumptions regarding scalable production validated by industry experts. We conducted comprehensive “ex ante” life cycle analysis (LCA) and net energy analysis, analyzing their cumulative energy demand, global warming potential profiles, energy payback times, and energy return on investment (EROI). LCA contribution analysis elucidates the most impactful material and process choices. It shows that solution‐based perovskite manufacturing would have lower environmental impact than vapor‐based methods, and that roll‐to‐roll (RtR) printing offers the lowest impact. Among material choices, MoOx/Al has lower impact than Ag, and fluorine‐tin‐oxide lower than indium‐tin‐oxide. Furthermore, we compare perovskites with commercial crystalline‐silicon and thin‐film PV, accounting for the most recent developments in crystalline‐Si wafer production and differences in life expectancies and efficiencies. It is shown that perovskite systems produced with RtR manufacturing could reach in only 12 years of life, the same EROI as that of single‐crystalline‐Si PV lasting 30 years. This work lays a foundation for sustainability investigations of perovskite large‐scale deployment.

Process simulation development of a clean waste-to-energy conversion power plant: Thermodynamic and environmental assessment

Waste-to-energy (WTE) conversion technologies for generating renewable energy and solving the environmental problems have an important role in the development of sustainable circular economy. This paper presents a novel high-efficiency WTE power plant using refuse-derived fuel (RDF) as feedstock by integrating torrefaction (T) pretreatment with plasma gasifier (PG), solid oxide fuel cell (SOFC), and combined heat and power (CHP) system. The combined impacts of torrefaction conditions (i.e. temperature and residence time) and steam-to-fuel (S/F) ratio on the energy and environmental performances of the proposed T-PG-SOFC-CHP power plant without CO2 capture (System I) is first evaluated. Results show that torrefaction of RDF prior to plasma gasification provides better syngas quality and therefore the system electrical efficiency (SEE) and CHP efficiency (CHPE) of System I can be markedly boosted compared to that of untreated RDF. However, the integration of torrefaction unit shows a negative effect on the energy return on investment (EROI) due to high energy demands for torrefaction and plasma gasification. Overall, the values of CHPE of System I range from 47.25% to 55.39% when the torrefaction temperatures of 200 and 250 °C are adopted. In contrast, the torrefaction of RDF at 300 °C is not a recommended condition for operation in the T-PG-SOFC-CHP power plant because of noticeably negative energy and environmental impacts. Moreover, to prevent the risk of carbon deposition on the SOFC anode, a recirculation ratio (RR) of the anode off-gas of 30% is required. Finally, the introduction of oxy-fuel combustion technology into the T-PG-SOFC-CHP system for CO2 capture (System II) allows to achieve a zero direct CO2 emission WTE power plant. However, this results in an energy penalty of about 5.40–6.77% associated with the CO2 capture and compression process.

Treatment of Rose Oil Processing Effluent with Chlorella sp. Using Photobioreactor and Raceway

The integration of treatment of wastewater from agro-based industries with microalgae cultivation can reduce costs associated with cultivation while treating wastewater to meet the discharge limits for chemical quality of irrigation in agriculture and to obtain biofertilizers. Rose Oil Processing Effluent (ROPE) can be utilized as a growth medium for Chlorella sp. and thus can be used for biofertilizer production. The present study is aimed at determining the feasibility of the cultivation of Chlorella sp. in ROPE using a tubular photobioreactor with a capacity of 50 L and a raceway to treat ROPE while consuming less energy. The optimum mixing ratio ([ROPE/(ROPE + Bold Basal Medium (BBM)] × 100) was determined as 50% using 2-L Erlenmeyer flasks based on the COD removal efficiency. Better removal efficiencies with regard to COD, BOD5, NH4+−N, and NO3−−N were obtained from the raceway compared to the tubular photobioreactor. The effluents from both systems met the chemical quality of irrigation water. The results of the biomasses harvested from both systems in macro and microelements revealed that they have a potential as a biofertilizer in agriculture. The energetic analysis of the ROPE treatment using the tubular photobioreactor and raceway showed that the raceway system had a better net energy ratio while consuming less energy and producing more energy during cultivation. Overall, the raceway appeared to be a better option to treat ROPE with production of biofertilizer and irrigation water quality while consuming less energy.

Effect of pyrolysis temperature and biomass particle size on the heating value of biocoal and optimization using response surface methodology

The effect of pyrolysis temperature (T) and biomass particle size (z) on the biocoal's heating value of Oak acorn shell (OA), deseeded carob pods (CP) and olive mill solid waste (OMSW) were investigated. The higher heating value (HHV) increased with T. The effect of the particle size differed according to the biomass. Response surface methodology (RSM) was used to optimise the biocoal production system from technical, end-user and socio-environmental perspectives. The maximum HHV, representing the technical objective, is achieved at maximum T and minimum z for OA biocoal; at maximum T and minimum z for OMSW and at maximum T and maximum z for CP. The highest lower heating value (LHV), corresponding to end-user, for OA biocoal is achieved when T is greater than 450 °C and z < 1000 μm. For OMSW, particle size was the most important factor with the best LHV achieved when z > 1750 μm. The maximum net energy return per kg of biomass processed and maximum GHG offset (socio-economic) is realised at the lowest T for all biomass and particle sizes. This study is relevant to policy makers as it highlights potential conflict between the optimal conditions to produce high quality biocoal characterised by its high LHV and the optimal conditions to achieve the maximum utility from the resource and in turn potentially higher socio-environmental return.

An Explanation of Energy Return on Investment From an Entropy Perspective

Low-carbon energy transformation is a major trend in world energy development, and measures to mitigate carbon emissions can vary substantially in terms of the energy they require. A common method of evaluating energy use in energy resource exploitation is energy return on investment (EROI). One of the criticisms of EROI concerns uncertainty regarding the input and output factors for the calculation. To make the issue clear, we interpret EROI in terms of entropy, which is the most basic concept in physics. We consider an energy resource exploitation system to be a kind of dissipative structure and construct a basic entropy analysis framework for an energy resource exploitation system. We then derive the relationship between EROI and entropy change. The theory of EROI is consistent with the basic requirement for a dissipative structure, which is that the total entropy change must be negative. EROI is a method of using entropy theory to evaluate energy resource exploitation. It is inappropriate and unnecessary to quantify all factors as energy units as the input and output factors are multidimensional while energy is a one-dimensional standard. Future development of the EROI method should be guided by entropy theory. A series of EROI related indicators will increase its application and policy significance.

The environmental life cycle assessment of different electricity options in Kuwait

In Kuwait, electricity is generated from two primary sources, heavy fuel combustion and natural gas combustion. As Kuwait relies mainly on petroleum-based products for electricity generation, identifying and understanding the environmental and energy trade-off of such operations should be carefully investigated. The life cycle assessment (LCA) tool is applied to identify the potential environmental impacts and energy performance of electricity generation under three scenarios, by considering the material flow in various stages involved such as raw-material extraction, transportation, and operations. The three scenarios investigated represent current and futuristic electricity grid mixes. The analysis of four indicators consists of two environmental and two energy indicators per one kWh of the electricity generated. The environmental indicators examined are global warming potential (GWP) and water consumption (WC), whereas the energy indicators target cumulative energy demand (CED) and net energy ratio (NER). Results indicate that one kWh of electricity generated would have a GWP (0.63-0.77) kg CO2-eq, mainly from the fuel combustion process, WC (0.0013-0.0015) m3 of water, about 68% from cooling processes, CED (9.9-10.7) MJ, and NER (0.34-0.39). The variation in results depends on the scenario investigated. It can be observed from the analysis that introducing solar photovoltaic and wind to the electricity grid mix improves the environmental and energy performance of Scenarios 3, where 15% of the electricity generated from renewables (10% solar PV and 5% wind) corresponds to a further decrease in LCA results.

Effect of dietary energy composition on the energy partitioning between milk production and body fat deposition in late lactating Holstein dairy cows

Whether adjusting the dietary energy composition can prevent the excessive obesity of dairy cows remains elusive. Therefore, this study aimed to investigate the effect of isocaloric diets with different ratios of starch and fat on energy partitioning between milk production and body fat deposition in Holstein dairy cows. Fifty-two cows (days in milk, 210.21 ± 6.95) were divided into 2 groups and fed either a high-starch diet (the ratio of net energy for lactation (NEL) supply by starch: fat was 30%:10%, HS), or a high-fat diet (the ratio of NEL supply by starch: fat was 26.67%:13.33%, HF) for 63 days. The dry matter intake (DMI) and milk yield was recorded daily. Milk samples were collected on day 1, 35 and 63 for composition analysis. The subcutaneous fat thickness was measured by Renco device and the body condition score (BCS) were evaluated on day 1 and 63. The blood biochemical indexes were also measured for the samples collected on day 1 and 63. There was no significant difference in the average DMI between the two dietary treatment groups. However, cows fed with the HS diet had higher (P < 0.05) average milk yield, and the difference enlarged with the duration of the treatments. The cows fed with the HF diet had higher milk fat percentage, serum urea nitrogen concentration, BCS, and backfat thickness (P < 0.05), but lower serum glucose concentrations (P < 0.05). Cows fed the HS diet utilized more energy for lactation (54.22% ME vs. 52.79% ME) but less energy for body fat deposition (0.56% ME vs. 1.94% ME) compared with the animals fed HF diet. Overall, these results indicated that adjusting the dietary energy composition may be an alternative approach to balance the energy partitioning between the lactation and body fat deposition in late lactating Holstein dairy cows.

Assessment of Indonesia’s Future Renewable Energy Plan: A Meta-Analysis of Biofuel Energy Return on Investment (EROI)

In early 2020, Indonesia implemented the biodiesel 30 (B30) program as an initiative to reduce Indonesia’s dependency on fossil fuels and to protect Indonesia’s palm oil market. However, palm oil has received international criticism due to its association with harmful environmental externalities. This paper analysed whether an investment in palm oil-based biofuel (POBB) provides Indonesia with the ability to achieve its environmental and financial goals. In this research, we performed a meta-analysis on biofuel energy return on investment (EROI) by examining 44 biofuel projects using ten types of biofuel feedstocks from 13 countries between 1995 and 2016. Results showed an average EROI of 3.92 and 3.22 for POBB and other biomass-based biofuels (OBBB), respectively. This shows that if only energy inputs and outputs are considered, biofuels provide a positive energy return. However, biofuels, including those from palm oil, produce externalities especially during land preparation and land restoration. We also compared these EROI biofuel results with other renewable energy sources and further analysed the implications for renewable energies to meet society’s energy demands in the future. Results showed that biofuel gives the lowest EROI compared to other renewable energy sources. Its EROI of 3.92, while positive, has been categorised as “not feasible for development”. If Indonesia plans to continue with its biofuel program, some major improvements will be necessary.

116 Effect of Coated and Non-coated Steroidal Implants on Growth Performance, Dietary Net Energy Utilization and Carcass Traits of Feedlot Finishing Steers

Abstract Maine-Anjou x Angus steers (n = 156, initial BW 366 ± 37.2 kg) were used in a 132-d finishing experiment at the Ruminant Nutrition Center in Brookings, SD. Steers were weighed on two consecutive days and assigned into 5 weight blocks. Within each weight block steers were randomly assigned to two implant types (equal steroidal hormone dose; both from Zoetis, Parsippany, NJ) and two dietary treatments in a 2 × 2 factorial arrangement. Implant treatments consisted of 1) Coated implant, 200 mg trenbolone acetate (TBA), 28 mg estradiol benzoate (EB) (Synovex ONE Feedlot, ONE) or 2) Non-coated implant, 200 mg TBA, 28 mg EB (Synovex PLUS; PLUS), placed in the left ear. Dietary treatments were 1) 15% or 2) 30% corn silage (DM basis). No interaction between implant and corn silage inclusion was observed for carcass-adjusted (hot carcass weight / 0.63) growth performance, dietary net energy (NE) utilization or carcass traits (P ≥ 0.16). Bunks were managed using a slick bunk approach and all diets contained (DM basis) 33 mg/kg monensin sodium. Implant status was checked on d 28 by a single trained evaluator; steers with missing implants were immediately re-implanted. There was no difference in carcass-adjusted growth performance between implants (P ≥ 0.85). There were no differences in observed NE or the observed-to-expected ratio of NE for either growth or maintenance (P ≥ 0.90). No differences were observed for dressing percent, hot carcass weight, ribeye area, or rib fat (P ≥ 0.22). Marbling differed between implant treatments (433 to 466 ± 8.7; P = 0.01) for PLUS and ONE respectively. Implanting cattle with a coated implant had no detrimental effect on growth performance or carcass traits, but it did increase marbling scores.

Lysine requirements of finishing boars and gilts: A meta-analysis

The expected increase in boar (pig entire male) production while societal concerns for castration increase requires good estimations of their nutrient requirements. In this work, a meta-analytical approach was used to overcome the inconsistent results between studies that compared lysine requirements of boars and gilts. For this meta-analysis, data from 14 different studies analysing the effect of increasing dietary lysine on growth performance of finishing pigs, 70–100 kg average body weight, were extracted from 11 publications. Those studies represented 128 different treatments (53 for boars and 75 for gilts). Diets were reformulated based on NRC (2012) ingredient values to calculate standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and daily SID Lys intake using average daily feed intake (ADFI). As expected, no evidence for differences in ADFI (P = 0.303) was observed between boars and gilts. However, boars grew faster (P < 0.001) and had higher gain to feed (G:F; P < 0.001). The divergent effect of SID Lys:NE on average daily gain (ADG) and G:F was analysed in a quadratic polynomial model showing different parameters for each sex (P < 0.001). Although performance between sexes was similar at low SID Lys:NE, differences were greater at higher SID Lys:NE. Furthermore, broken-line linear, broken-line quadratic (BLQ) and quadratic polynomial (QP) models were fitted to each sex to determine SID Lys:NE and SID Lys daily intake requirements to maximize ADG and G:F. Overall, QP models showed the best fit, and reported that to reach maximum ADG 0.88 (95% CI:[0.82–0.94]) or 1.01 (95% CI:[0.91–1.11]) g SID Lys/MJ, NE was required for gilts and boars, respectively. However, boar ADG was best fitted by BLQ using SID Lys daily intake as independent variable, with the requirement for maximum ADG at 24.2 (95% CI:[21.3–27.2]) g SID Lys/day. The three models reported wide confidence intervals for the requirements at maximum performance, and consequently those were overlapped when comparing boars and gilts. Maximum boars’ productive performance when dietary lysine was not limiting was 116% of gilts, and at those levels the amount of SID Lys intake required per kg gain was similar between both sexes. Thus, because ADFI and Lys efficiency of gain was similar, the requirement differences were driven by the increased growth rate and gain to feed ratio between boars and gilts. In conclusion, the present study confirmed a greater productive response of boars compared to gilts when increasing dietary lysine.

Circular economy approach of enhanced bifunctional catalytic system of CaO/CeO2 for biodiesel production from waste loquat seed oil with life cycle assessment study

Herein, we utilised Loquat seed oil as a waste resource to produce biodiesel over a novel bifunctional catalyst system based on CaO loaded on a ceria oxide support. The catalysts were characterised using XRD, SEM-EDX, SBET STEM, and TPD analyses, followed by parametric analysis to optimise the catalyst performance. The XPS analysis showed a strong synergistic effect between CaO and CeO2 support. The parametric study revealed that the most active catalyst (15 wt% CaO-CeO2) showed optimum biodiesel yield was 90.14 (±0.1) wt% at a temperature of 70 °C, methanol: oil of 9, time of 90 min and 4 wt% of catalyst. The reusability test showed that when the most active catalyst was calcined and reused, the biodiesel yield was almost the same ±0.5%; however, when biodiesel production was used without calcination, the biodiesel yield was reduced by 15%. The quality of the produced biodiesel was investigated by the American Society for Testing and Materials (ASTM) and European Union (EU) Standards. It showed that it satisfied all standards and could be used as potential alternative fuel instead of fossil diesel from novel Loquat seed oil. The Life cycle Assessment (LCA) was condcuted to assess environmental feasibility of the process with 1000 kg of biodiesel as 1 functional unit (FU). The LCA using midpoint indicators (from CML-IA baseline V3.06 method) showed the cumulative abiotic depletion of fossil resources over the entire process of biodiesel production was 26349 MJ, global warming potential was 1129 kg CO2 eq, and human health toxicity was 422 kg 1,4-DB eq (kg 1,4 dichlorobenzene equivalent) per FU. The highest damage in most environmental categories was observed during catalyst preparation and regeneration. This was confirmed in endpoint LCA findings (ReCiPe 2016 Endpoint (E) V1.04), where catalyst preparation contributed to human health (119.2 Point (Pt)), ecosystems damage (9.3 Pt) and resources depletion (0.5 Pt). Furthermore, the net energy ratio was 2.23 for the biodiesel production process (computed as output energy/input energy) by considering allocation of output energy due to biodiesel and glycerol.

Comparative life cycle energy and greenhouse gas footprints of dry and wet torrefaction processes of various biomass feedstocks

This study compares the life cycle energy consumption and greenhouse gas (GHG) emissions of electricity generation from bio-coals produced from various biomass feedstocks via dry torrefaction (DT) and wet torrefaction (WT) processes. Wheat straw, pine woodchips, grape pomace, manure and algae are the main feedstocks evaluated. The energy consumption and the associated GHG emissions at each life cycle stage were calculated. The main stages included are in-field preparation, feedstocks transportation to torrefaction plant, torrefaction process, bio-coal transportation to power plant, and power plant operations. The results show that all pathways are competitive with coal-based electricity in terms of GHG emissions except pathways with algae as feedstock and manure biochar-based electricity generation. Among the pathways, electricity generation from pine woodchips biochar appears to be the best option, with an 82% GHG emissions reduction compared to coal-derived electricity, followed by wheat starw biochar and grape pomace hydrochar with 80% and 75% emission reductions, respectively. Electricity generation from wheat straw biochar, pine woodchips biochar, and grape pomace hydrochar lead to the highest net energy ratios (NERs) of 4.19, 3.58, and 2.59, respectively. The results also show that the combustion of the biomass for supplying electricity used in the plant decreases GHG emissions in all pathways particularly in WT ones. Sensitivity analysis of using different emissions allocation methods, transportation distances to torrefaction plant and to power plant, emission factor of electricity consumed, and quantity of natural gas consumed were aslo conducted. The developed information is novel and can be used for investment decisions and policy formulation around the world.

Prospect of China’s synthetic natural gas from coal gasification technology under consideration of economic, environmental, and security factors

Synthetic natural gas (SNG) from coal gasification technology has become an alternative method to alleviate China’s natural gas shortage. However, the Chinese SNG industry still faces a series of problems, such as low profits, high carbon emissions, and water shortages, and Chinese SNG policy is cautious and unstable. Considering economic, energy security, and environmental constraints, this study analyses the future of SNG in China by using a system dynamics model. The results are as follows. In under various circumstances, SNG production is projected to reach 20.8–44.2 bcm by 2030. SNG production could reduce the dependence on gas imports to 23–40% in 2030, which may help to reduce the risk of natural gas imports. The energy production efficiency index, EROI (Energy Return on Investment), of SNG is only approximately 1.5, and thus, economic profitability will remain very low for a long time; in general, price subsidies will be conducive to increasing SNG production. Based on these results, the study provides some suggestions for policy-makers.

Modelling energy transition risk: The impact of declining energy return on investment (EROI)

A number of papers in the field of net energy analysis have argued that declines in energy return on investment (EROI) could lead to increasing energy prices and a fall in economic growth. This paper develops a model (TranSim) which can simulate the economic and financial implications of an energy technology transition involving a reduction in EROI, by combining the stock-flow consistent (SFC) approach with an input-output (IO) model.The TranSim model has the following key features. First, it includes three firm sectors, that produce energy, capital, and other (non-energy, non-capital) goods. Second, an IO model and an Almost Ideal Demand System are integrated into the SFC model. Third, capital vintages have embedded levels of labour productivity and intermediate good requirements that depend on the economic conditions in the period the vintage was produced.Simulations are characterised by an initial increase in output (due to higher investment), followed by periods of recession and below trend growth (due to price inflation and changes to the functional income distribution). The negative effects associated with the transition – recession, stagnation, stagflation, increasing inequality and asset stranding – are positively related to the capital intensity of green energy production and reductions in EROI.

Life cycle energy–carbon–water footprints of sugar, ethanol and electricity from sugarcane

Sugarcane is an important cash crop used for producing sweeteners and also some bioproducts (alcohol and bioenergy). The current study assesses life cycle energy, carbon and water footprint of sugarcane based sugar, ethanol and electricity in India. A farm to factory gate attributional life cycle assessment (LCA) is conducted to assess the energy and carbon footprints whereas the Food and Agriculture Organization’s (FAO) CropWat model is used to estimate the water footprint (green, blue and grey). For the base case, electricity has the highest energy return on investment (EROI), lowest carbon and water footprints among the bioproducts. The choice of allocation method (economic, mass, and energy) impacts the energy and environmental outcomes of the bioproducts. The comparison among four different sugarcane seasons shows that bioproducts available from Adsali sugarcane have the highest EROI, lowest carbon and water footprints. The findings could lead to improved sustainability of sugarcane bioproducts in India.

Aqueous pretreatment of triticale straw for integrated production of hemicellulosic methane and cellulosic butanol

Despite its advantages, lignocellulosic butanol cannot become a real alternative without processes for obtaining credits from non-cellulosic fraction of lignocellulose. In this study, the process of “cellulosic butanol” was integrated with “hemicellulosic methane” process, i.e., anaerobic digestion (AD), for higher energy return on investment (EROI). Aqueous pretreatment was evaluated as a connecting chain between the processes. The alkaline (1% NaOH), acidic (1% H2SO4), and neutral (autohydrolysis) pretreatments were utilized at 140, 160, and 180 °C for bioenergy recovery from triticale straw. Enzymatic hydrolysis of the straw pretreated by alkaline (180 °C), dilute acid (140 °C), and autohydrolysis (180 °C) and fermentation of the hydrolysates by Clostridium acetobutylicum led to 13.6, 8.5, and 10.2 g/L acetone-butanol-ethanol (ABE), respectively. AD of the liquors remained after pretreatment by alkaline, dilute acid, and autohydrolysis led to 83–121, 240–247, and 380–430 mL/g VSS methane leading to more than 60% increase in EROI.

Why energy return on energy investment is not useful for policy

This paper presents a critical comparison of EROEI and Relational Analysis applied to the Mexican Oil and Gas sector. Energy return on energy investment (EROEI) is used in this paper as an example to flag the problem that arises when data are aggregated into a simple ratio, leading to the loss of a significant amount of meaningful information. In contrast to that approach, this paper shows how Relational Analysis is helpful for policy discussion and for embracing complexity by means of adopting a variety of categories of accounting across different levels and dimensions, characterizing the relationships among the different metabolic patterns of the different components, and integrating inequivalent views of the same system: a structural (bottom-up) and a functional (top-down).

Microalgae to biofuels through hydrothermal liquefaction: Open-source techno-economic analysis and life cycle assessment

Hydrothermal liquefaction is a promising conversion technology in algae biofuel research due to its ability to agnostically convert proteins, carbohydrates, and lipids to biocrude. The high-temperature conditions that define this conversion process require the material to maintain a subcritical liquid state, which complicates the assessment of accurate thermochemical properties due to the required pressure. To clarify this issue, this work compares the estimated performance of algal hydrothermal liquefaction between different thermodynamic models. A process model was developed in Aspen Plus from a robust assessment of current literature. Techno-economic assessment and life-cycle assessment metrics are derived from this model and used as key performance indicators. The baseline fuel price contribution of hydrothermal liquefaction is $0.45 per liter gasoline equivalent. Independently decreasing the temperature from 350 °C to 260 °C while maintaining yield reduces the conversion cost by 19%, illustrating the importance of understanding the high-temperature thermodynamics of the system. Different thermodynamic property models can vary fuel conversion cost results by $0.07 per liter gasoline equivalent. The baseline global warming potential is +23 g CO2 eq MJ−1 and the net energy ratio is 0.30. Environmental metrics beyond global warming potential and net energy ratio are also discussed for the first time. Uncertainties in conversion performance are bounded through a scenario analysis that manipulates parameters such as product yield and nutrient recycle to produce a range of economic and environmental metrics. The work is supplemented with an open source model to support future hydrothermal liquefaction assessments and accelerate the development of commercial-scale systems.

Illumination system for growth and net energy ratio enhancement of Arthrospira (Spirulina) platensis outdoor cultivation in deep raceway pond

One major problem found in open raceway ponds for algae production is the limited light penetrability, which means that the pond depth should not exceed 25–30 cm. This study aimed to use transparent light-scattering column (LSC) to enhance the brightness in the deeper level of a deep raceway pond. A maximum of 16 LSCs were immersed vertically in the testing pond, which was compared with a control pond without LSC. The results showed that the cultivation period to the stationary phase of the LSC pond was 4 days faster than that of the control pond. The biomass productivity and net energy ratio of the LSC pond were respectively found to increase by about 48.3% and 41.7%, while the water loss from evaporation decreased by about 13.6%. The overview from the results indicated that the environment can be conserved by means of reducing the energy, time and water for cultivation.

Edible Energy Production and Energy Return on Investment—Long-Term Analysis of Global Changes

The projected increase in the world’s population requires an increase in the production of edible energy that would meet the associated increased demand for food. However, food production is strongly dependent on the use of energy, mainly from fossil fuels, the extraction of which requires increasing input due to the depletion of the most easily accessible deposits. According to numerous estimations, the world’s energy production will be dependent on fossil fuels at least to 2050. Therefore, it is vital to increase the energy efficiency of production, including food production. One method to measure energy efficiency is the energy return on investment (EROI), which is the ratio of the amount of energy produced to the amount of energy consumed in the production process. The literature lacks comparable EROI calculations concerning global food production and the existing studies only include crop production. The aim of this study was to calculate the EROI of edible crop and animal production in the long term worldwide and to indicate the relationships resulting from its changes. The research takes into account edible crop and animal production in agriculture and the direct consumption of fossil fuels and electricity. The analysis showed that although the most underdeveloped regions have the highest EROI, the production of edible energy there is usually insufficient to meet the food needs of the population. On the other hand, the lowest EROI was observed in highly developed regions, where production ensures food self-sufficiency. However, the changes that have taken place in Europe since the 1990s indicate an opportunity to simultaneously reduce the direct use of energy in agriculture and increase the production of edible energy, thus improving the EROI.