Value of electric heat boilers and heat pumps for wind power integration

The paper analyses the economic value of using electric heat boilers and heat pumps as wind power integration measures relieving the link between the heat and power production in combined heat and power plants. Both measures have different technical and economic characteristics, making a comparison of the value of these measures relevant. A stochastic, fundamental bottom‐up model, taking the stochastic nature of wind power production explicitly into account when making dispatch decisions, is used to analyse the technical and economical performance of these measures in a North European power system covering Denmark, Finland, Germany, Norway and Sweden. Introduction of heat pumps or electric boilers is beneficial for the integration of wind power, because the curtailment of wind power production is reduced, the price of regulating power is reduced and the number of hours with very low power prices is reduced, making the wind power production more valuable. The system benefits of heat pumps and electric boilers are connected to replacing heat production on fuel oil heat boilers and combined heat and power (CHP) plants using various fuels with heat production using electricity and thereby saving fuel. The benefits of the measures depend highly on the underlying structure of heat production. The integration measures are economical, especially in systems where the marginal heat production costs before the introduction of the heat measures are high, e.g. heat production on heat boilers using fuel oil. Copyright © 2007 John Wiley & Sons, Ltd.     

The market value of variable renewables: The effect of solar wind power variability on their relative price

This paper provides a comprehensive discussion of the market value of variable renewable energy (VRE). The inherent variability of wind speeds and solar radiation affects the price that VRE generators receive on the market (market value). During windy and sunny times the additional electricity supply reduces the prices. Because the drop is larger with more installed capacity, the market value of VRE falls with higher penetration rate. This study aims to develop a better understanding on how the market value with penetration, and how policies and prices affect the market value. Quantitative evidence is derived from a review of published studies, regression analysis of market data, and the calibrated model of the European electricity market EMMA. We find the value of wind power to fall from 110% of the average power price to 50–80% as wind penetration increases from zero to 30% of total electricity consumption. For solar power, similarly low value levels are reached already at 15% penetration. Hence, competitive large-scale renewable deployment will be more difficult to accomplish than as many anticipate.     

System-level power-to-gas energy storage for high penetrations of variable renewables

According to outlooks by the IEA and the U.S. EIA, renewables will become the largest source of electricity by 2050 if global temperature rise is to be limited to 2 °C. However, at penetrations greater than 30%, curtailment of wind and solar can be significant in even the most flexible systems. Energy storage can reduce curtailment and increase utilisation of variable renewables. Power-to-gas is a form of long-term storage based on electrolytic production of hydrogen. This research models the co-sizing of wind and solar PV capacity and electrolyser capacity in a jurisdiction targeting 80% penetration of variable renewable electricity. Results indicate that power-to-gas can reduce required wind and solar capacity by as much as 23% and curtailment by as much as 87%. While the majority of charging events last less than 12 h, the majority of the total annual stored energy comes from longer-term events. Additional scenarios reveal that geographic diversity of wind farms reduces capacity requirements, but the same benefit is not found for distributing solar PV.     

Global wind power development: Economics and policies

Existing literature indicates that theoretically, the earth's wind energy supply potential significantly exceeds global energy demand. Yet, only 2–3% of global electricity demand is currently derived from wind power despite 27% annual growth in wind generating capacity over the last 17 years. More than 95% of total current wind power capacity is installed in the developed countries plus China and India. Our analysis shows that the economic competitiveness of wind power varies at wider range across countries or locations. A climate change damage cost of US$20/tCO₂ imposed to fossil fuels would make onshore wind competitive to all fossil fuels for power generation; however, the same would not happen to offshore wind, with few exceptions, even if the damage cost is increased to US$100/tCO₂. To overcome a large number of technical, financial, institutional, market and other barriers to wind power, many countries have employed various policy instruments, including capital subsidies, tax incentives, tradable energy certificates, feed-in tariffs, grid access guarantees and mandatory standards. Besides, climate change mitigation policies, such as the Clean Development Mechanism, have played a pivotal role in promoting wind power. Despite these policies, intermittency, the main technical constraint, could remain as the major challenge to the future growth of wind power.     

Mass and heat transfer enhancement of chemical heat pumps

An inert additive, expanded graphite (EG), has been prepared and used to enhance the heat and mass transfer process of chemical heat pumps. The effects of mixing ratio and mixing method on the chemical reaction time are investigated.     

Optimised design and dimensioning of low-technology wind pumps

This article describes the currently operational version of the low-technology wind pump of high efficiency, as presented in [Valdès L-C, Raniriharinosy K. Low technical wind pumping of high efficiency. Renewable Energy 24 (2001) 275–301]. The pump, made entirely of wood and using roller bearings for the rotating links and a rubber membrane for water tightness, is of a more modular conception. Its manufacture is slightly more complicated, but its dimensioning has been greatly simplified, its reliability significantly improved and the use of wind energy optimised.     

Performance of ejector heat pumps

An ejector-compression heat pump can use low-grade thermal energy in the neighbourhood of 93.3°C (200°F) to provide space cooling and heating. This paper applies the existing ejector theory to estimate the performance of an ejector heat pump system at various operating conditions. The study includes parametric, sensitivity and off-design analyses of the heat pump performance. The performance enhancement options and desired ejector geometry are also examined. Refrigerants 11, 113 and 114 are three of the halocarbons most suitable for the ejector heat pump system. The estimated coefficients of performance for a simple ejector heat pump are 0.3 for the cooling mode and 1.3 for the heating mode at a sample operating condition in which the refrigerant (R-11) boiling temperature is 93.3°C (200°F), condensing temperature 43.3°C (110°F) and evaporating temperature 10°C (50°F). A 24 per cent performance improvement is predicted for a heat pump with two-stage ejectors and regenerative heat exchangers. The off-design performance is relatively insensitive to the evaporator temperature variations.     

Stand-alone micro-trigeneration system coupling electrolyzer,fuel cell,and heat pump with renewables

A micro hydrogen system in conjunction with renewable energy, namely a wind turbine, a photovoltaic array, and an air-source heat pump, is designed to satisfy the power, heating, and cooling needs of a stand-alone household in a Mediterranean climate. An hourly-based model is used to simulate its operation throughout the year. A unique power management strategy is applied to achieve optimum configuration and size of the components without shortage or excess energy. Unlike previous practices, there is no release of excess heat into the environment. An innovative combination of a fuel cell and a heat pump followed the household's electrical and thermal (domestic hot water/heating and space cooling) profile. Almost 80% of the energy for preparing hot water and household cooling/heating was obtained from waste heat from these devices. The system is compared to the most commonly used stand-alone hybrid renewable energy system with battery storage. The hydrogen system needs four time less batteries and it does not need a back-up diesel generator. Although the energy storage in batteries is more efficient than in hydrogen, the hydrogen system requires only 10% larger primary energy input than the system with only battery storage.     

Economic evaluation of heat pumps

An economic evaluation of heat pumps is presented which compares the running costs and discounted capital costs of central-heating systems based on oil-fired boilers and heat pumps. Conclusions regarding the break-even coefficients of performance are drawn for a range of fuel-price possibilities.     

Influence of debonding in ground heat exchangers used with geothermal heat pumps

Debonding in ground heat exchangers used with geothermal heat pumps may occur for a variety of reasons, such as shrinkage of the backfill materials or surrounding formation, improper grouting and thermal mismatch. The effect of thermal contact resistance on the heat conduction due to debonding in ground heat exchangers was investigated using a set of one-dimensional simplified analytical models as well as two-dimensional finite element models. From the cases studied, debonding at the backfill/pipe interface was found to be of greater significance than debonding between grout and surrounding formation.     

地源热泵的优越性及前景展望

介绍了地源热泵的工作原理，并通过比较地源热泵与传统空调系统的运行费用，说明了地源热泵在运行费用方面具有较大优势。虽然地源热泵的应用受到一些制约因素的影响，但作为一项节能新技术，地源热泵必将拥有广阔的应用前景。     

Coupling of geothermal heat pumps with thermal solar collectors

The study discussed relates to the design and development of a process consisting of combining a reversible geothermal heat pump with thermal solar collectors for building heating and cooling and the production of domestic hot water. The proposed process, called GEOSOL, has been installed in a 180 m² private residence in 2004. This installation is the subject of long-term experimental follow-up to analyse the energy-related behavior of the installation at all times of the year. In addition, different configurations of this combined system (geothermal heat pump and thermal solar collectors) have been defined and will be simulated numerically using TRNSYS software. A comparative analysis of these different alternative versions will be conducted to determine the best configuration(s) of the GEOSOL process in terms of energy, economical and environmental performances.     

Digital control of heat pumps with minimized power consumption

The paper describes the development of a microcomputer based control system for a heat pump containing an electrical variable speed compressor drive and a motorized expansion valve. It is designed to operate under very much varying load conditions with minimum power consumption. Difficulties that were encountered during engineering tests could finally be overcome by a relatively simple, practical regulator configuration. It operates near optimum efficiency by regulating a temperature difference in the evaporator.     

Steady-state simulation of vapour-compression heat pumps

A vapour compression simulation model was developed. Simple mathematical models were employed for each component of the cycle. They resulted in a set of nonlinear equations, which was solved numerically. Heat losses from condenser to ambient were included. The model is capable of predicting the operating point of the system (including condensing and evaporating pressures) as a function of equipment characteristics (for example, compressor swept volume, speed and clearance ratio, and heat exchanger overall conductances) and prevailing thermodynamic conditions (such as heat source and heat sink temperatures with the mass flow rates of their fluids). The predicted performance was compared to that of an existing R-12 unit, showing good agreement. As an application, a comparative analysis is made on the thermodynamic performance of a domestic heat pump running on two different refrigerants: R-12 and R-134a.     

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.     

Optimum arrangement and use of heat pumps in recovering waste heat

Relations are derived for the coefficient of performance of heat pump systems used to transfer heat from a low temperature heat source stream to a high temperature heat sink stream. The manner of use and operation of a number of heat pumps in such a system has been determined for the thermodynamic optimum for reversible and irreversible heat pumps.     

Ice detection in heat pumps and coolers

Some methods are discussed for detecting the formation of ice on the evaporators of air-source heat pumps and air coolers by electronic means. the sensing of thermal resistance caused by ice build-up can be done by measuring temperature differences between the evaporator and the air, and analyses are presented of the effect of using both linear and non-linear temperature sensors for this purpose. the direct detection of the presence of ice can be done by measuring the capacitance of a suitably-placed pair of plates, and the performance of such a system is analysed. Preliminary reports are presented of the use of both of these methods of ice detection in the defrosting of an experimental heat pump.     

污水源热泵技术及其应用

介绍了污水源热泵的特点。通过对空气源热泵、地源热泵和污水源热泵等不同采暖系统的经济性和环保效果分析显示，污水源热泵系统的初投资为地源热泵的70％左右。综合考虑初投资和运行费用等因素，污水源热泵系统的经济效果和环保效果最为显著。     

地源热泵及其应用分析

介绍了地源热泵的类型、原理及特点，并对水平埋管和竖直埋管的地源热泵与空气源热泵的经济性进行了比较。结果表明，对小型住宅，采用水平埋管的地源热泵经济性最好。