Technical and economic performance of residential solar water heating in the United States

This paper examines the regional, technical, and economic performance of residential rooftop solar water heating (SWH) technology in the U.S. It focuses on the application of SWH to consumers in the U.S. currently using electricity for water heating, which currently uses over 120 billion kWh per year. The variation in electrical energy savings due to water heating use, inlet water temperature and solar resource is estimated and applied to determine the regional “break-even” cost of SWH where the life-cycle cost of SWH is equal the life-cycle energy savings. For a typical residential consumer, a SWH system will reduce water heating energy demand by 50–85%, or a savings of 1600–2600 kWh per year. For the largest 1000 electric utilities serving residential customers in the United States as of 2008, this corresponds to an annual electric bill savings range of about $100 to over $300, reflecting the large range in residential electricity prices. This range in electricity prices, along with a variety of incentives programs corresponds to a break-even cost of SWH in the United States varying by more than a factor of five (from less than $2250/system to over $10,000/system excluding Hawaii and Alaska), despite a much smaller variation in the amount of energy saved by the systems (a factor of approximately one and a half). We also consider the relationships between collector area and technical performance, SWH price and solar fraction (percent of daily energy requirements supplied by the SWH system) and examine the key drivers behind break-even costs.     

On the potential trade-offs between energy supply and end-use technologies for residential heating

In Sweden, where district heating accounts for a significant share of residential heating, it has been argued that improvements in end-use energy efficiency may be counter-productive since such measures reduce the potential of energy efficient combined heat and power production. In this paper we model how the potential trade-offs between energy supply and end-use technologies depend on climate policy and energy prices. The model optimizes a combination of energy efficiency measures, technologies and fuels for heat supply and district heating extensions over a 50 year period. We ask under what circumstances improved end-use efficiency may be cost-effective in buildings connected to district heating? The answer hinges on the available technologies for electricity production. In a scenario with no alternatives to basic condensing electricity production, high CO₂ prices result in very high electricity prices, high profitability of combined heat and power production, and little incentive to reduce heat demand in buildings with district heating. In contrast, in a scenario where electricity production alternatives with low CO₂ emissions are available, the electricity price will level out at high CO₂ prices. This gives heat prices that increase with the CO₂ price and make end-use efficiency cost-effective also in buildings with district heating.     

Potential of building-scale alternative energy to alleviate risk from the future price of energy

The energy used for building operations, the associated greenhouse gas emissions, and the uncertainties in future price of natural gas and electricity can be a cause of concern for building owners and policy makers. In this work we explore the potential of building-scale alternative energy technologies to reduce demand and emissions while also shielding building owners from the risks associated with fluctuations in the price of natural gas and grid electricity. We analyze the monetary costs and benefits over the life cycle of five technologies (photovoltaic and wind electricity generation, solar air and water heating, and ground source heat pumps) over three audience or building types (homeowners, small businesses, large commercial and institutional entities). The analysis includes a Monte Carlo analysis to measure risk that can be compared to other investment opportunities. The results indicate that under government incentives and climate of Toronto, Canada, the returns are relatively high for small degrees of risks for a number of technologies. Ground source heat pumps prove to be exceptionally good investments in terms of their energy savings, emission, reductions, and economics, while the bigger buildings tend also to be better economic choices for the use of these technologies.     

Solar water heating potential in South Africa in dynamic energy market conditions

This paper is an attempt to determine the potential for solar water heating (SWH) in South Africa and the prospects for its implementation between 2010 and 2030. It outlines the energy market conditions, the energy requirements related to residential and commercial water heating in the country and the solar water heating market dynamics and challenges. It was estimated that 98% of the potential is in the residential sector and the rest in the commercial sector. The total thermal demand for 20 years for water heating was estimated to 2.2 EJ. A ‘Moderate SWH implementation’ will provide 0.83 EJ of clean energy until 2030 and estimated cost savings of 231 billion rand. For an ‘Accelerated SWH implementation’ these figures are 1.3 EJ and 369 billion rand. The estimated accumulated reduction of CO₂ emissions due to SWH can be as high as 297 Mt. The increased affordability of residential hot water due to SWH is an important social factor and solar water heating has a strong social effect.     

Financing solar thermal technologies under DSM programs: an innovative approach to promote renewable energy

A wide range of demand side management (DSM) options has been practiced so far in developed as well as in developing countries. However, solar thermal technologies have been left out from DSM programs considering them as supply side options. This study argues that a number of solar thermal technologies, which provide the same services as electric appliances, can be considered as DSM options and examines the possibility of promoting solar water heaters (SWH) under DSM programs in Thailand. The study found that installation of SWH in place of conventional electric water heaters (EWH) to meet hot water demand in the residential sector would be economically beneficial to the country as a whole. However, switching to SWH from EWH would be unlikely without having government interventions as there would be no incentives to individual consumers in doing so. If the government or state electric utilities provide funding to residential consumers through DSM programs for replacing their EWH by SWH, the total electricity generation in Thailand during the 2000–2015 period would decrease by 3.8 per cent. Moreover, promotion of SWH under DSM programs would cause 3.35 and 1.41 per cent reductions of total power sector CO₂‐ and NO_x‐emissions respectively, during the same period. This study also reveals that solar thermal technologies, especially the SWH, could be better options for DSM programs compared to the end‐use efficiency improvement options in Thailand. Copyright © 2000 John Wiley & Sons, Ltd.     

Estimating the potential for electricity savings in households

Improving efficiency in the use of energy is an important goal for many nations since end-use energy efficiency can help to reduce CO₂ emissions. Furthermore, since the residential sector in industrialised countries requires around one third of the end-use electricity, it is important for policy makers to estimate the scope for electricity saving in households to reduce electricity consumption by using appropriate steering mechanisms. We estimate the level of technical efficiency in the use of electricity using data from a Swiss household survey. We find an average inefficiency in electricity use by Swiss households of around 20 to 25%. Bottom-up economic-engineering models estimate the potential in Switzerland to be around 15%. In this paper we use a sub-vector input distance frontier function based on economic foundations. Our estimates lie at the upper end of the electricity saving potential estimated by the afore-mentioned economic-engineering approach.     

Energy harvesting, reuse and upgrade to reduce primary energy usage in the USA

Two-thirds of input energy for electricity generation in the USA is lost as heat during conversion processes. Additionally, 12.5% of primary fuel and 20.3% of electricity are employed for space heating, water heating, and refrigeration where low-grade heat could suffice. The potential for harnessing waste heat from power generation and thermal processes to perform such tasks is assessed. By matching power plant outlet streams with applications at corresponding temperature ranges, sufficient waste heat is identified to satisfy all USA space and water heating needs. Sufficient high temperature exhaust from power plants is identified to satisfy 27% of residential air conditioning with thermally activated refrigeration, or all industrial refrigeration and process heating from 100 to 150 °C. Engine coolant and exhaust is sufficient to satisfy all air conditioning and 68% of electrical demands in vehicles. Overall, this study demonstrates the potential to reduce USA primary energy demand by 12% and CO₂ emissions by 13% through waste heat recovery. A detailed analysis of thermal energy demand in pulp and paper manufacturing is conducted to demonstrate the methodology for improving the fidelity of this approach. These results can inform infrastructure and development to capture heat that would be lost today, substantially reducing USA energy intensity.     

Reduction of carbon dioxide emissions by solar water heating systems and passive technologies in social housing

Growing global concern regarding climate change motivates technological studies to minimize environmental impacts. In this context, solar water heating (SWH) systems are notably prominent in Brazil, primarily because of the abundance of solar energy in the country. However, SWH designs have not always been perfectly developed. In most projects, the installation option of the solar system only considers the electric power economy aspects and not the particular characteristics of each climatic zone. Thus, the primary objective of this paper is to assess the potential of carbon dioxide reduction with the use of SWH in comparison with electric showers in social housing in several Brazilian climatic zones. The Brazilian government authorities have created public policies to encourage the use of these technologies primarily among the low-income population. The results of this paper indicate that hot climactic regions demonstrate a low reduction of CO₂ emissions with SWH installations. Thus, solar radiation is not useful for water heating in those regions, but it does lead to a large fraction of household cooling loads, implying a demand for electrical energy for air conditioning or requiring the adoption of passive techniques to maintain indoor temperatures below threshold values.     

Potential application of solar thermal systems for hot water production in Hong Kong

This paper presents the evaluation results of conventional solar water heater (SWH) systems and solar assisted heat pump (SAHP) systems for hot water production in Hong Kong. An economic comparison and global warming impact analysis are conducted among the two kinds of solar thermal systems and traditional water heating systems (i.e. electric water heaters and towngas water heaters). The economic comparison results show that solar thermal systems have greater economic benefits than traditional water heating systems. In addition, conventional SWH systems are comparable with the SAHP systems when solar fractions are above 50%. Besides, analysis on the sensitivity of the total equivalent warming impact (TEWI) indicates that the towngas boosted SWH system has the greatest potential in greenhouse gas emission reduction with various solar collector areas and the electricity boosted SWH system has the comparative TEWI with the SAHP systems if its solar fraction is above 50%. As for SAHP systems, the solar assisted air source heat pump (SA-ASHP) system has the least global warming impact. Based on all investigation results, suggestions are given on the selection of solar thermal systems for applications in Hong Kong.     

The use of conservation supply curves in energy policy and economic analysis: The case study of Thai cement industry

The cement industry is one of the largest energy-consuming industries in Thailand with high carbon dioxide (CO₂) emissions. Using a bottom-up electricity Conservation Supply Curve (CSC) model, the cost effective and the total technical electricity-efficiency potential for the Thai cement industry in 2008 is estimated to be about 265 and 1697 gigawatt-hours (GWh) which account for 8% and 51% of the total electricity used in the cement industry in 2005, respectively. The fuel CSC model shows the cost-effective fuel-efficiency potential to be 17,214 terajoules (TJ) and the total technical fuel-efficiency potential equal to 21,202 TJ, accounting for 16% and 19% of the total fuel used in cement industry in 2005, respectively. The economic analysis in this paper shows how the information from the CSCs can be used to calculate the present value (PV) of net cost savings over a period of time taking into account the energy price escalation rate. The results from the policy scenario analysis show that the most effective and efficient policy scenario is the introduction of an energy-related CO₂ tax for the cement industry under a voluntary agreement program. This scenario results in 16.9% primary energy-efficiency improvement over a 5-year implementation period.     

Renewable energy resources as an alternative to modify the load curve in Northern Cyprus

The average annual increase in electricity consumption and peak demand in Northern Cyprus (N. Cyprus) during the past 20 years have been 7.1 and 5.5%, respectively. In recent years, the demand for electricity has been stretched to its limits in winter. This raised the question of whether renewable energy resources could be utilized to reduce the level of peak demand. Indeed, Cyprus being a Mediterranean island, enjoys an abundance of solar energy, and preliminary studies showed that a considerable potential of wind energy is also available. Utilization of renewable energy for space heating, water heating, pumping and power generation would increase electrical reserve margins, raise system load factor, improve load following capabilities, and reduce the need for capacity expansion. Currently, solar water heating which leads to a saving of at least 72 GWh energy per annum and a significant reduction in CO₂ emission has been extensively used in N. Cyprus. In N. Cyprus, despite the availability of renewable energy resources constructing renewable base-load, electrical power stations has not been found feasible. However, constructing such systems is recommended for two reasons: firstly, as a supplement to saving fuel and secondly, expanding capacity. In this context, the economic analysis for both solar and wind energy systems, has shown a reasonable internal rate of return (IRR). Although, the IRR is higher for wind energy systems, the availability of wind is limited to a few locations and therefore energy distribution is required.     

The potential for electricity conservation and peak load reduction in the residential sector of Brazil

This paper summarizes the methodological approach and the results of a study aimed at assessing the potential for electricity conservation and peak load reduction in the Brazilian residential sector. The study splits the residential sector into 15 subsectors, considering five different geographical regions and three household income classes. Technical, economic and market potentials are determined both for electrical energy conservation and peak load reduction in the period from 2000 to 2020. The main findings show an electricity conservation technical potential for the residential sector of 28%, an economic potential of 14% and market potentials of 12% and 8%. The corresponding results found for the peak load reduction in 2020 were a technical potential of 21%, an economic potential of 4% and market potentials of 3% and 2%, with the large reduction in percentage savings for peak demand in the economic and market scenarios explained in particular by the omission of solar water heating from those scenarios. Finally, carbon dioxide emission reductions associated with the electricity conservation potentials and peak load reductions are also estimated.     

Electricity dependency and CO2 emissions from heating in the Swedish building sector—Current trends in conflict with governmental policy?

Coal-condensing power is marginal production in the deregulated Nordic power market and an increase in electricity consumption will therefore result in increased CO₂ emissions. One goal of the Swedish energy policy is to reduce the amount of electricity used for heating in the building sector. This paper investigates the potential for reduction in electricity dependency and CO₂ emissions from heating, taking the energy infrastructure into account, here defined as the capital stock of the buildings and heating systems together with geographical variations in heat intensity. In order to include the energy infrastructure in the analysis the study is made on a regional level (Southern Sweden) applying a comprehensive database describing the energy infrastructure of the region. The paper compares two scenarios for converting the heating systems of the region: one employing energy savings and with the aim to phase out the oil and most of the electricity used for heating purposes and a second which illustrates the effect if the current trend in the heating market continues. Both scenarios apply commercially available technologies only.From the second scenario it is seen that the current trend—contrary to the aim of the Swedish Governmental policy—shows an increase in electricity dependency for heating, mainly due to a large diffusion of heat pumps, but also due to installations of electrical floor heating and electricity heating systems installed in newly constructed one- and two-dwelling buildings. However, the options proposed in first scenario show that it is possible to reach significant reductions in the electricity dependency due to heating and in corresponding CO₂ emissions. An analysis of the age structure of the heating systems shows that the transformation of the heating system is not completed until the year 2025, if new investments for replacement of heating systems are made only provided they have reached their economical life time, and only applying heating technologies which at present are known to be economically competitive. It can be concluded that future policies on transforming the energy system should be based on an analysis that takes the entire energy infrastructure (in this case of heating system) into account (e.g. not directed towards single technologies). More specifically for the region studied, which is considered representative for Sweden as a whole, policies should aim at installing heat pumps to replace electricity heating only in regions with low heat density where district heating is not competitive, in contrary to the present situation where heat pumps replace all types of heating systems.     

Recent estimates of energy efficiency potential in the USA

Understanding the potential for reducing energy demand through increased end-use energy efficiency can inform energy and climate policy decisions. However, if potential estimates are vastly different, they engender controversial debates, clouding the usefulness of energy efficiency in shaping a clean energy future. A substantive question thus arises: is there a general consensus on the potential estimates? To answer this question, this paper reviews recent studies of US national and regional energy efficiency potential in buildings and industry. Although these studies are based on differing assumptions, methods, and data, they suggest technically possible reductions of ~25–40 % in electricity demand and ~30 % in natural gas demand in 2020 and economic reductions of ~10–25 % in electricity demand and ~20 % in natural gas demand in 2020. These estimates imply that electricity growth from 2009 to 2020 ranges from turning US electricity demand growth negative, to reducing it to a growth rate of ~0.3 %/year (compared to ~1 % baseline growth).     

A methodology for the electrical energy system planning of Tamil Nadu state (India)

In this paper, an energy planning optimisation procedure of a selected territory is illustrated and applied using an energy flow optimisation model. The developed approach takes into account various electricity generating options to meet the energy needs of various demand sectors. Energy saving techniques and hybrid technologies are considered and various scenarios are developed by assessing the contribution of renewable energy technologies over the planning period. The procedure aims to reduce the total actualised cost of energy generation over selected time horizon and predicts the additional installations required along with the existing facilities to meet the energy demand. At the same time the role of renewable energy technologies and of energy saving measures is evaluated by imposing suitable constraints on CO₂ emissions and primary energy sources exploitation. The procedure is applied to the territory of Tamil Nadu state (India) by considering different energy planning scenarios.     

China's transition to green energy systems: The economics of home solar water heaters and their popularization in Dezhou city

Studying the popularization of solar water heaters (SWHs) is significant for understanding China's transition to green energy systems. Using Dezhou as a case study, this paper presents new angles on analyzing SWH deployment in China by addressing both the economic potential and the institutional dimensions at the local level. Using estimates from the demand-side of hot water for a typical three-person household in Dezhou, the paper evaluates the economic potential of a SWH in saving electricity and reducing carbon dioxide emissions. Then, expanding the analysis beyond economics, we take an institutionalist approach to study the institutional factors that contribute to Dezhou's success in SWH adoptions. By examining the five main actors in Dezhou's energy regime, we find that Dezhou's SWH deployment is driven by an urge to develop businesses and the local economy, and its success results from at least five unique factors, including the development of SWH industrial clusters in Dezhou, big manufacturers' market leadership in SWH innovations, a tight private enterprise-local government relation, geographic location within the SWH industrial belt, and the adaptive attitude of Dezhou's households towards natural resource scarcity.     

Primary energy use for heating in the Swedish building sector—Current trends and proposed target

One goal of the Swedish energy policy is to reduce the amount of electricity used for heating in the building sector. This means to reduce the primary energy used for heating which in this paper is analyzed in the context of various heating technologies and CO₂ emissions. The analysis is applied to a region in Sweden (southern Sweden) for which detailed information on the energy infrastructure (the capital stock of the buildings and heating systems together with geographical variations in heat intensity) is available from a previous work [Johansson, P., Nylander, A., Johnsson, F., 2005. Electricity dependency and CO₂ emissions from heating in the Swedish building sector—current trends in conflict with governmental policy? Energy policy] and which is large enough to be assumed representative for Sweden as a whole. The detailed mapping of the energy infrastructure allows a good estimate on the rate at which the energy system can be expected to be replaced with respect to economical lifetime of the capital stock (the year 2025 in this case). Two scenarios are investigated; a target scenario for which energy savings are employed (e.g. improving climate shell in buildings) and oil and most of the electricity used for heating purposes are phased out and a second for which the current trend in the heating market continues.     

Potential of energy and water efficiency improvement in Abu Dhabi's building sector – Analysis of Estidama pearl rating system

Energy and water infrastructure in Abu Dhabi provides a strong example of the interconnection between energy and water, where the majority of its electricity and water demand is jointly produced from cogeneration plants. The total cost of fuel used for cogeneration plants are heavily depending on the efficiency level of end-use energy and water consumption. Buildings are the major electricity and water consumers with 84.6% and 92.2% respectively from the entire demand. The aim of this study is to analyze the energy and water consumption reduction by implementing Estidama pearl regulations and compare it with Business as Usual -the normal execution of things as they always do-for three sample buildings (villa, multistory residential and office building). For energy assessment, eQUEST software was used to examine the energy performance of the chosen buildings and to evaluate the energy saving potential after applying Estidama requirements. While for water assessment; Estidama and LEED calculation tools were used to do the same. The results of energy simulation and water analysis of the chosen buildings showed a potential of electricity reduction between 31% and 38% and a potential of water reduction between 22% and 36% depending on building type and other parameters. Also, a total monetary savings of 19 Billion AED can be achieved cumulatively over ten years period (2011–2020) after Estidama regulations have been applied. In addition, a reduction of 31.4 Million ton of CO₂eq cumulatively can be achieved.     

Biomass gasification opportunities in a district heating system

This paper evaluates the economic effects and the potential for reduced CO₂ emissions when biomass gasification applications are introduced in a Swedish district heating (DH) system. The gasification applications included in the study deliver heat to the DH network while producing renewable electricity or biofuels. Gasification applications included are: external superheater for steam from waste incineration (waste boost, WB), gas engine CHP (BIGGE), combined cycle CHP (BIGCC) and production of synthetic natural gas (SNG) for use as transportation fuel. Six scenarios are used, employing two time perspectives – short-term and medium-term – and differing in economic input data, investment options and technical system. To evaluate the economic performance an optimisation model is used to identify the most profitable alternatives regarding investments and plant operation while meeting the DH demand. This study shows that introducing biomass gasification in the DH system will lead to economic benefits for the DH supplier as well as reduce global CO₂ emissions. Biomass gasification significantly increases the potential for production of high value products (electricity or SNG) in the DH system. However, which form of investment that is most profitable is shown to be highly dependent on the level of policy instruments for biofuels and renewable electricity. Biomass gasification applications can thus be interesting for DH suppliers in the future, and may be a vital measure to reach the 2020 targets for greenhouse gases and renewable energy, given continued technology development and long-term policy instruments.     

Meeting residential space heating demand with wind-generated electricity

Worldwide, many electricity suppliers are faced with the challenge of trying to integrate intermittent renewables, notably wind, into their energy mix to meet the needs of those services that require a continuous supply of electricity. Solutions to intermittency include the use of rapid-response backup generation and chemical or mechanical storage of electricity. Meanwhile, in many jurisdictions with lengthy heating seasons, finding secure and preferably environmentally benign supplies of energy for space heating is also becoming a significant challenge because of volatile energy markets.Most, if not all, electricity suppliers treat these twin challenges as separate issues: supply (integrating intermittent renewables) and demand (electric space heating). However, if space heating demand can be met from an intermittent supply of electricity, then both of these issues can be addressed simultaneously. One such approach is to use off-the-shelf electric thermal storage systems.This paper examines the potential of this approach by applying the output from a 5.15 MW wind farm to the residential heating demands of detached households in the Canadian province of Prince Edward Island. The paper shows that for the heating season considered, up to 500 households could have over 95 percent of their space heating demand met from the wind farm in question. The benefits as well as the limitations of the approach are discussed in detail.