Alternative technologies for US residential water heating : Energy savings and economic benefits

This article evaluates the energy savings and direct economic benefits of introducing heat pump and solar water heaters to the US residential market and the effects of a tax credit for solar installations. Energy savings are estimated for ten regions of the USA, as well as for the country as a whole, over the period 1977–2000. Changes in annual fuel bills and capital costs for water heaters are also computed. The results suggest that heat pump water heaters are likely to offer much larger benefits than solar heaters, even with tax credits. This is because heat pumps provide the same electricity savings (about 50%), but at a much lower capital cost.     

A total fuel cycle approach to reducing greenhouse gas emissions: Solar generation technologies as greenhouse gas offsets in U.S. utility systems

Greenhouse gas emissions in the electric utility sector occur not only at generation facilities, but also during upstream processes that support the construction and operation of energy facilities. A total fuel cycle approach is used to evaluate the potential greenhouse gas savings that could result from the deployment of solar generation technologies in utility systems in the United States. Total fuel cycle analyses were completed for several renewable and conventional generation technologies to estimate the total greenhouse gas emission contribution from each generation technology. These results are used to develop total fuel cycle emission rates for planned electric capacity additions in the U.S., and these rates are compared with the emission rates that would occur if solar technologies were substituted for fossil generation capacity additions. Current projections for solar technology deployment are low relative to total capacity additions. Hence, even doubling the planned additions of solar technologies produces less than a 1% reduction in annual CO₂ and CH₄ emissions from new generation. However, the total lifetime greenhouse gas savings from increased deployment of solar technologies can be substantial. Increasing planned solar deployment by only 25% up to the year 2010 can create up to six million tons of CO₂ savings over the lifetime of the solar installations.     

The marginal cost of electricity used as backup for solar hot water systems: A case study

In this study, a method is developed for estimating the long run marginal cost to electric utilities of providing backup service for solar residential heating and hot water (HHW) systems. This method accounts for all investment, fuel, and operating costs required to provide the added electric service for HHW. From the information produced using this method, the impacts of various rate design philosophies and of government tax and regulatory policies on annual homeowner costs, fuel consumption patterns, environmental pollutants, and the net social cost of providing HHW service can be computed. Also, the differences in these parameters among solar, electric, and conventional HHW systems can be compared.In an initial study, it was found that for one Northeastern utility the estimated marginal cost of electricity for backup to solar hot water (HW) systems was less than that for comparable electric HW systems for the period of the mid to late 1990s. Load management (shifting all electricity use to off-peak periods) substantially reduced marginal costs for both electric and solar systems and essentially eliminated any difference between them. In all cases, the marginal cost was lower than the average cost of all electricity generated for market penetration rates that can realistically be expected to be experienced. The impact on total annual costs to homeowners of various electricity rate schemes and the impacts of Federal tax credits and property tax exemptions were computed. Net changes in resource consumption patterns due to the use of solar systems were estimated.     

Feed-in tariff for solar photovoltaic: The rise of Japan

Japan started implementing a national Feed-In Tariff (FiT) mechanism on the 1st July 2012, which included specific payment tariffs for solar photovoltaic (PV) installations. This marks a new era in the renewable energy landscape in Japan. This paper aims at analysing the solar PV prospect in Japan, particularly in both residential and non-residential sectors. The paper presents, first, an overview of energy trends in Japan prior to the Fukushima event. This is followed by a short review of solar PV progress in the country, highlighting the major policies and programmes that have been implemented as well as the installations that have been carried out over the past two decades. Next, the financial impact of the new FiT scheme on consumers is evaluated. The financial analysis investigates the total profit, the average annual return on investment and the payback period. For a comparison purposes, a similar financial analysis is also conducted with selected countries around the world – namely Germany, Italy and the United Kingdom. The results from this analysis indicate that the new Japanese FiT rate generates a good profit, a moderate annual return on investment and an acceptable payback period, suggesting an increasing trend of solar PV uptake over the next years.     

A method for technical-economic analysis of solar heating systems

The necessity for technical-economic analysis of solar energy systems is obvious when assessing their feasibility vis-á-vis conventional alternative systems. Optimum magnitudes of the installation parameters should be defined under the required economic conditions. In this study, the optimization procedure was chosen so as to maximize the total accumulated saving throughout the economic lifetime of the system. The annual solar heating fraction of the system is assessed using the f-chart method which can be used for both domestic hot water and space heating. The saving produced by investing in a solar installation is obtained by taking the difference between the total discounted expenditures of the conventional and the solar systems, accumulated during their foreseen lifetimes. To this end, the present value method is applied, taking into account the initial investment costs, fuel costs, operation costs and the maintenance costs for both the solar system and its conventional alternative. Based on this technical-economic analysis, a computer program is developed. This accepts three types of input data: technical design, economic parameters and meteorological conditions, and calculates the optimum magnitudes of the design parameters. It is concluded that economic parameters are much more influential on the system economics than the technical parameters. The most significant are the payback period and the internal rate of return.     

Solar power generation in the US: Too expensive,or a bargain?

This article identifies the combined value that solar electric power plants deliver to utilities' rate payers and society's tax payers. Benefits that are relevant to utilities and their rate payers include traditional, measures of energy and capacity. Benefits that are tangible to tax payers include environmental, fuel price mitigation, outage risk protection, and long-term economic growth components. Results for the state of New York suggest that solar electric installations deliver between 15 and 40 ¢/kWh to ratepayers and tax payers. These results provide economic justification for the existence of payment structures (often referred to as incentives) that transfer value from those who benefit from solar electric generation to those who invest in solar electric generation.     

A feasibility study of solar heating in Iran

A single-glass, flat-plate solar collector for air heating is analyzed for an optimum tilt angle of 45° for Shiraz (29° 36′ N latitude, 52° 32′ E longitude, and elevation of 4500 ft). The absorbed and utilized solar energy, as well as the collector outlet air temperature, the glazing, and the blackened plate temperatures, are determined with respect to the incident solar energy, parametric with collector inlet air temperatures and flow rates and outside air temperature.A 10 ft² collector and an 8 ft³ rock storage are built to experimentally verify the analysis and obtain cost estimates. A 5000 ft² single-story building is considered for solar heating and economic evaluations. Based on an annual interest rate of 8 per cent amortization of the solar heating equipment over 15 yr, electrical energy costs of 3c/kWh, and fuel costs of $1·10 per 10⁶ B.t.u., the optimum collector area which results in minimum annual operating costs (of the solar heating system and the auxiliary heating unit) is determined. A net saving results because solar heating is employed. The feasibility study is extended to eleven other Iranian cities. It is found profitable to employ solar heating in cities with low annual rainfall and relatively cold winters. An effective evaporative cooling is obtained by spraying water over the rock storage during the summer.     

Long-term perspective on the development of solar energy

We use dynamic optimization methods to analyze the development of solar technologies in light of the increasing scarcity and environmental pollution associated with fossil fuel combustion. Learning from solar R&D efforts accumulates in the form of knowledge to gradually reduce the cost of solar energy, while the scarcity and pollution externalities associated with fossil fuel combustion come into effect through shadow prices that must be included in the effective cost of fossil energy. Accounting for these processes, we characterize the optimal time profiles of fossil and solar energy supply rates and the optimal investment in solar R&D. We find that the optimal rate of fossil energy supply should decrease over time and vanish continuously upon depletion of the fossil fuel reserves, while the optimal supply of solar energy should gradually increase and eventually take over the entire energy demand. The optimal solar R&D investment should initially be set at the highest feasible rate, calling for early engagement in solar R&D programs, long before large scale solar energy production becomes competitive.     

Experimental and numerical study of a directly PV-assisted domestic hot water system

The solar domestic hot water (SDHW) system is the most highly developed system for use of solar energy. The developments for the thermal regulation of buildings should reinforce this trend given the significant reduction of heating needs. Currently, the design of these SDHW installations is well controlled and the system performance is reasonably good. The annual average solar fraction is consistent with expected level (between 60% and 70%) according to a report of CSTB by evaluating 120 SDHW installations (Buscarlet and Caccavelli, 2006). However, the control mode of conventional SDHWs induces additional costs related to the consumption of auxiliaries and other risks of dysfunction of the circulation pump due to the temperature probes and controller setup which induces low annual productivity of solar collector (200 instead of 400 kW h/m² expected). From this point of view, the photovoltaic pumped system seems suitable since it eliminates the controller and temperature sensors. This paper focuses on an experimental and numerical study of the behavior of a PV-SDHW system, focusing on the start-up phase optimized through various electronic devices. A detailed model of a circulation pump was developed by considering a direct current (DC) circulation pump coupled with various electronic devices (linear current booster and maximum power point tracker). The developed models were then validated experimentally, to reveal the influence of the threshold solar radiation on the circulation pump start-up and the pump flow rate as a function of the solar radiation, and its effects on the annual energy performance of PV-SDHW systems.     

The solar water heater industry in South Florida: History and projections

Solar water heaters were a commercial success because they offered homeowners a system for heating water which was economically superior to either electric or gas units. In 1938 a solar user could recover his initial investment from fuel cost savings in less than 2 yr and anticipate a seemingly endless supply of free hot water.By the early 1950s, however, three primary forces combined to reduce the industry to a few firms whose principal solar activity was the repair or replacement of water storage tanks. (1) The rapid decline in electricity rates along with the increasing first cost of installing a solar unit reversed the economic advantage of the solar approach. (2) The widely held opinion that solar systems would last indefinitely was abruptly altered when the water storage tanks began to develop leaks. Tank failures often caused considerable damage and became increasingly costly to repair. (3) The emergence of the large scale builder-developer largely removed the choice of hot water system from the individual homeowner. In his efforts to be first-cost competitive, the developer installed the less expensive conventional hot water unit rather than the solar unit.Recent developments in energy prices and availability, however, have produced an economic environment more promising to a resurgence of solar water heating. Under certain potentially realistic first-cost estimates and projected fuel price increases, a strong economic argument in favor of solar water heaters can be made. Further, homeowner attitudes toward solar units are generally positive and receptive to considering the solar alternatives.     

Optimization of the design of polygeneration systems for the residential sector under different self-consumption regulations

Polygeneration systems enable natural resources to be exploited efficiently, decreasing CO₂ emissions and achieving economic savings relative to the conventional separate production. However, their economic feasibility depends on the legal framework. Preliminary design of polygeneration systems for the residential sector based on the last Spanish self-consumption regulations RD 900/2015 and RD 244/2019 was carried out in Zaragoza, Spain. Both regulations were applied to individual and collective installations. Several technologies, appropriate for the energy supply to residential buildings, for example, photovoltaics, wind turbines, solar thermal collectors, microcogeneration engines, heat pump, gas boiler, absorption chiller, and thermal and electric energy storage were considered candidate technologies for the polygeneration system. A mixed integer linear programming model was developed to minimize the total annual cost of polygeneration systems. Scenarios with and without electricity sale were considered. CO₂ emissions were also calculated to estimate the environmental impact. Results show that RD 900/2015 discourages the investment in self-consumption systems whereas the RD 244/2019 encourages them, especially in renewable energy technologies. Moreover, in economic terms, it is more profitable to invest in collective self-consumption installations over individual installations. However, this does not necessarily represent a significant reduction of CO₂ emissions with respect to individual installations since the natural gas consumption tends to increase as its unit price decreases because of the increase of its consumption level. Thus, more appropriate pricing of natural gas in residential sector, in which its cost would not be reduced when increasing its consumption, would be required to achieve significant CO₂ emissions reduction. In all cases, the photovoltaic panels (PV) are competitive and profitable without subsidies in self-consumption schemes and the reversible heat pump (HP) played an important role for the CO₂ emissions reduction. In a horizon to achieve zero CO₂ emissions, the net metering scheme could be an interesting and profitable alternative to be considered.     

Economic evaluation and optimization of solar heating systems

A procedure is developed for assessing the economic viability of a solar heating system in terms of the life cycle savings of a solar heating system over a conventional heating system. The life cycle savings is expressed in a generalized formby introducing two economic parameters, P₁ and P₂, which relate all life cycle cost considerations to the first year fuel cost or the initial solar system investment cost. Using the generalized life cycle savings equation, a method is developed for calculating the solar heating system design which maximizes the life cycle savings. A similar method is developed for determining the set of economic conditions at which the optimal solar heating system design is just competitive with the conventional heating system. The results of these optimization methods can be presented in tabular or graphical form. The sensitivity of the economic evaluation and optimization calculations to uncertainties in constituent thermal and economic variables is also investigated.     

Economic feasibility of solar pumping

Two major questions concerning the economic feasibility of solar pumping are addressed. The first of these is concerned with finding a least-cost solar system by considering the alternative use of either thermal or water storage. The second involves the determination of areas where solar energy would be economically competitive with electricity or fuel as a power source for pumping installations.A linear programming solution is developed to find the optimal combination of thermal and water storage for a solar installation. The formulation is then extended to determine a least-cost system when hybrid systems are considered. A hybrid system may incorporate a combination of solar, electric and fuel power inputs. The concept of a breakeven “critical” distance from existing infastructure for solar installations is developed, and an example problem is provided to illustrate typical values of this distance and to show its sensitivity to the base energy costs and rate of inflation for those costs. It appears that electrical pumping is probably the most economical alternative provided that electric infrastructure is located nearby. Fuel power will also be more economical than solar if there is a source of fuel near the proposed pumping site. However, solar systems may be economically competitive when considered for installation at realistic distances from existing infrastructure.     

A comprehensive optimized model for on‐board solar photovoltaic system for plug‐in electric vehicles: energy and economic impacts

Environmental concerns along with high energy demand in transportation are leading to major development in sustainable transportation technologies, not the least of which is the utilization of clean energy sources. Solar energy as an auxiliary power source of on‐board fuel has not been extensively investigated. This study focuses on the energy and economic aspects of optimizing and hybridizing, the conventional energy path of plug‐in electric vehicles (EVs) using solar energy by means of on‐board photovoltaic (PV) system as an auxiliary fuel source. This study is novel in that the authors (i) modeled the comprehensive on‐board PV system for plug‐in EV; (ii) optimized various design parameters for optimum well‐to‐tank efficiency (solar energy to battery bank); (iii) estimated hybrid solar plug‐in EVs energy generation and consumption, as well as pure solar PV daily range extender; and (iv) estimated the economic return of investment (ROI) value of adding on‐board PVs for plug‐in EVs under different cost scenarios, driving locations, and vehicle specifications. For this study, two months in two US cities were selected, which represent the extremities in terms of available solar energy; June in Phoenix, Arizona and December in Boston, Massachusetts to represent the driving conditions in all the US states at any time followed by assessment of the results worldwide. The results show that, by adding on‐board PVs to cover less than 50% (around 3.2 m²) of the projected horizontal surface area of a typical passenger EV, the daily driving range could be extended from 3.0 miles to 62.5 miles by solar energy based on vehicle specifications, locations, season, and total time the EV remains at Sun. In addition, the ROI of adding PVs on‐board with EV over its lifetime shows only small negative values (larger than ?45%) when the price of electricity remains below Environmental concerns along with high energy demand in transportation are leading to major development in sustainable transportation technologies, not the least of which is the utilization of clean energy sources. Solar energy as an auxiliary power source of on‐board fuel has not been extensively investigated. This study focuses on the energy and economic aspects of optimizing and hybridizing, the conventional energy path of plug‐in electric vehicles (EVs) using solar energy by means of on‐board photovoltaic (PV) system as an auxiliary fuel source. This study is novel in that the authors (i) modeled the comprehensive on‐board PV system for plug‐in EV; (ii) optimized various design parameters for optimum well‐to‐tank efficiency (solar energy to battery bank); (iii) estimated hybrid solar plug‐in EVs energy generation and consumption, as well as pure solar PV daily range extender; and (iv) estimated the economic return of investment (ROI) value of adding on‐board PVs for plug‐in EVs under different cost scenarios, driving locations, and vehicle specifications. For this study, two months in two US cities were selected, which represent the extremities in terms of available solar energy; June in Phoenix, Arizona and December in Boston, Massachusetts to represent the driving conditions in all the US states at any time followed by assessment of the results worldwide. The results show that, by adding on‐board PVs to cover less than 50% (around 3.2 m²) of the projected horizontal surface area of a typical passenger EV, the daily driving range could be extended from 3.0 miles to 62.5 miles by solar energy based on vehicle specifications, locations, season, and total time the EV remains at Sun. In addition, the ROI of adding PVs on‐board with EV over its lifetime shows only small negative values (larger than ?45%) when the price of electricity remains below $0.18/kWh and the vehicle is driven in low‐solar energy area (e.g. Massachusetts in the US and majority of Europe countries). The ROI is more than 148% if the vehicle is driven in high‐solar energy area (e.g. Arizona in the US, most Africa countries, Middle East, and Mumbai in India), even if the electricity price remains low. For high electricity price regions ($0.35/kWh), the ROI is positive and high under all driving scenarios (above 560%). Also, the reported system has the potential to reduce electricity consumption from grid by around 4.5 to 21.0 MWh per EV lifetime. A sensitivity analysis has been carried out, in order to study the impacts of the car parked in the shade on the results. Copyright © 2016 John Wiley & Sons, Ltd.     

The prospects for cost competitive solar PV power

New solar Photovoltaic (PV) installations have grown globally at a rapid pace in recent years. We provide a comprehensive assessment of the cost competitiveness of this electric power source. Based on data available for the second half of 2011, we conclude that utility-scale PV installations are not yet cost competitive with fossil fuel power plants. In contrast, commercial-scale installations have already attained cost parity in the sense that the generating cost of power from solar PV is comparable to the retail electricity prices that commercial users pay, at least in certain parts of the U.S. This conclusion is shown to depend crucially on both the current federal tax subsidies for solar power and an ideal geographic location for the solar installation. Projecting recent industry trends into the future, we estimate that utility-scale solar PV facilities are on track to become cost competitive by the end of this decade. Furthermore, commercial-scale installations could reach “grid parity” in about ten years, if the current federal tax incentives for solar power were to expire at that point.     

A simple model for solar energy economics in the U.K.

A simple model is proposed which enables one to find conditions for the economic viability of solar thermal or photovoltaic energy conversion, in the presence of an average inflation rate i and an average interest rate r. It enables one to find the minimum viable conversion efficiency η(T) as a function of the life T (years) of the converter given the sensitized area a (m²), the insolation $\text{P (}\text{Wm}{}^2\text{)}$ averaged over day and night and the year, the cost c (cents or pence per kWh) of the competing fuel, and the cost C ($ or £) of one installation. By a slight extension one can also estimate the maximum economical funding for research and development. This is done by assuming u annual investments C, followed by T annual savings s, both per installation, and discounting costs and savings to the present. This yields a maximum economically viable value for $\text{c}\text{η}$ when the other parameters are given. The maximum annual investment, for example for research and development, can be obtained if the market is known in terms of the number of installations required. This is done on the principle that one must not use more money on R and D than one expects to save by using the converters.It is shown that thermal collectors on mainly domestic rooftops can contribute in the U.K. an amount of energy saving in excess of the hydro electric element, and of the same order as the nuclear element, in the 1974 U.K. inland energy consumption.The model can be applied to other problems of investment in research and development.     

Solar-fossil HYBRID system analysis: Performance and economics

This study has developed a method of accounting for the dominant energy flows within a solar fossil hybrid power plant. The method is incorporated in a computer code called HYBRID, which can be linked to a solar central receiver code such as STEAEC. STEAEC, or a similar code, must be used to calculate the power from the solar central receiver (solar power) on an hourly or quarter-hourly basis. HYBRID determines the quantity of solar power directed to thermal storage, the quantity of solar power directed to a specified load, the amount of power retrieved from thermal storage, and the mass of fuel used by the fossil portion of the hybrid power plant. HYBRID uses the calculated fuel requirements to determine the present value of required revenue for the life of the plant. Fuel consumption is shown to be a dominant variable cost in the economic evaluation of a solar-fossil hybrid system. Fuel costs and other economic parameters are normalized to the present value of the capital investment. The range of normalized parameters is established to reflect economic unknowns and system design variability. It is shown that, under the most favorable economic conditions allowed in this study, the present value of the capital investment for a solar-fossil hybrid system should not exceed 2.5 time the present value of the capital investment for a comparable fossil power system if the hybrid is to be economically competitive. Under more probable conditions, this ratio declines to 1.5–2.0.     

Solar absorption cooling feasibility

The feasibility of small scale solar absorption cooling systems is dependent upon its technical and economically competitive position with respect to other cooling systems alternatives. Technical feasibility can be shown by comparisons of the thermodynamic efficiency of solar absorption cooling with conventional vapor-compression cooling equipment and by reference to numerous experimental evaluations. Economic feasibility is heavily dependent upon the financial parameters assumed (in particular the inflation rate of conventional fuel costs). In particular cases, i.e. particular assumptions of the financial parameters, economic feasibility of solar absorption cooling can be demonstrated.     

Economic comparison of solar-assisted heat pumps

A study of the economic performance of a solar system, air-to-air heat pumps, and several solar-assisted heat pump systems (SAHP) for residential heating is presented. The study is based on a computer simulation which is supported by monitoring data from an existing installation, the Terrosi-Grumman house in Quechee, Vermont. Three different SAHP configurations as well as conventional solar and air-to-air heat pump systems are evaluated for a northern New England climate. All systems are evaluated both with and without a peak/off-peak electricity price differential.

The SAHP systems are: (1) the series system in which the solar storage serves as the energy source for the heat pump, (2) the series off-peak system in which the heat pump in the series system operates only during certain periods of the day under a special electric rate structure, (3) a parallel system in which the environment is the source for both the collector and the heat pump, and (4) a peak/off-peak parallel system in which oil is operated during the period of peak electricity price. Hybrid air-to-air heat pump/oil systems are also evaluated.

For all alternatives, two different economic analyses are used: (1) the rate of return which emphasizes the return earned on the capital investment, and (2) the life cycle critical price which compares the current capital cost to the present worth of the stream of all future energy savings.

Both economic measures select the air-to-air heat pump/on-peak oil system when there is a peak/off-peak electricity price differential. (In this case the ratio of off-peak to average price is 40 per cent.) When there is no price differential, the air-to-air heat pump/oil system is still preferred, but the oil system is now operated when the ambient temperature falls below −6.7°C (20°F). When the electricity price is doubled (from 19.5 to 40$/GJ), solar/oil is the preferred system.     

Optimized Integration of Renewable Energy Technologies Into Jordan's Power Plant Portfolio

Jordan has experienced a significant increase of peak load and annual electricity demand within the last years due to economic development and population growth. The experienced growth rates are expected to continue during the next decades, making large investments in new power plant capacity necessary. Additionally, when gas supply from Egypt was interrupted several times and crude oil world market prices increased simultaneously, recent years have shown painfully that a power supply exclusively based on fossil fuel imports is subject to a very high risk and can have a strong negative impact on the national budget. Electricity-sector authorities are therefore looking for suitable solutions to keep up with the increasing electricity demand, to make Jordan more independent from fossil fuel imports, and to provide electricity at reasonable prices in the future. This paper presents a methodology for the optimized integration of renewable energy (RE) technologies into Jordan's existing power plant portfolio. The core of the methodology is the mixed integer linear optimization program REMix-CEM, developed at the German Aerospace Center (DLR), which optimizes capacity expansion and unit commitment of RE and conventional power generation technologies simultaneously. After describing Jordan's electricity sector and the available RE resources, the developed methodology and the results are presented. The paper shows that by the year 2022, Jordan could generate at least 47% of its electricity demand by a well-balanced mix of concentrating solar power, utility-scale photovoltaics, and onshore wind power. This scenario would maintain the security of electricity supply, absorb present growth rates of power generation costs, and make Jordan significantly more independent of fossil fuel imports.