Future energy systems need to be more flexible. The use of cross-sector coupling in combination with thermal storage in thermal grids has been shown to provide such flexibility. The presented study reviews how short-term storage in district heating distribution networks is used or modelled for flexibility, what are the most important parameters, and where the knowledge gaps remain. The results show that the potential for flexibility from district heating has not been fully exploited. Sensible thermal storage tanks are 50-100 times cheaper than electrical storage and storage in the distribution network requires little additional investment in infrastructure. In some countries, the majority of district heating systems have sensible thermal storage tanks, with as much as 64 % of their capacity available for flexibility services. Initial results suggest that only smaller networks are prevented from using the distribution network for storage, but the impacts of this type of use on the physical components and the capacity limitations remain unclear and show a need for standardised methods for analysis. There is a growing interest, both in Europe and China, in the use of short-term storage in district heating to provide flexibility, particularly in the form of ancillary services to the electricity grid, but implementations of these techniques are rare. The presented study identifies a number of remaining knowledge gaps that should be addressed in order to harness available flexibility in district heating. © 2019 The Authors. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 - The 10th International Conference on Applied Energy.

Emissions reductions are often achieved through the increased share of renewable energy sources (RES) and China is the leader in the growth of RES in the power sector. This growth has led to high levels of curtailment of RES power due to insufficient reinforcement of the electricity grid to support such growth and due to competition with other power sources. Although the problem of curtailment has been alleviated in recent years, large amounts of power are still discarded, and it is important to consider how to address this problem in the short term and how much CO2e emissions could be avoided as a result. The use of district heating systems to reduce the curtailment of renewable power has seen increasing interest in recent years. Based on a review of potential energy storage in district heating, the current paper assesses the capability to use the national storage potential of district heating systems in China to reduce curtailment and to determine what effects that may have on avoiding CO2e emissions. The distribution networks and the thermal inertia of buildings connected to district heating are considered as two major forms of storage that can be “charged” using power that would otherwise be curtailed. The results show that there may be sufficient storage available to absorb all renewable power that is currently curtailed in those provinces using district heating during the heating season, resulting in avoided emissions of up to 14 MtCO2e/annum. This article is categorized under: Energy and Climate > Economics and Policy Wind Power > Climate and Environment Energy Infrastructure > Climate and Environment Energy and Urban Design > Climate and Environment.

Recent improvements in low-temperature heat-to-power (LTHtP) technologies have led to an increase in efficiency at lower temperatures and lower cost. LTHtP has so far not been used in district heating. The aim of the study is to establish under what conditions the use of existing LTHtP technology is technically and economically feasible using a district heating system as the heat source. The organic Rankine cycle (ORC) is identified as the most interesting LTHtP technology, due to its high relative efficiency and the commercial availability of devices operating at temperatures in the district heating operating range. The levelised cost of electricity of several ORC devices is calculated for temperatures found in district heating, assuming a zero cost of heat. A case study from Sweden is used to calculate the levelised cost of electricity, the net present value and payback period, based on income from the electricity produced, excluding taxes. Hourly spot market electricity prices from 2017 are used, as well as forecast scenarios for 2020, 2030 and 2040. A sensitivity study tests the importance of electricity price, cost of heat and capital/installation cost. Based on the case study, the best levelised cost of electricity achieved was 26.5 EUR/MWh, with a payback period greater than 30 years. Under current Swedish market conditions, the ORC does not appear to be economically feasible for use in district heating, but the net present value and payback period may be significantly more attractive under other countries’ market conditions or with reduced capital costs. For a positive net present value in the Swedish market the capital cost should be reduced to 1.7 EUR/W installed, or the average electricity price should be at least 35.2 EUR/MWh, if the cost of heat is zero. The cost of heat is an important factor in these calculations and should be developed further in future work.

Recent improvements in heat-to-power (HtP) technologies have led to an increase in efficiency at lower temperatures and lower cost. HtP is used extensively in power generation via the steam Rankine cycle, but so far has not been used in district heating (DH). The aim of the study is to analyze the economic feasibility of using HtP technologies in a DH network. This is achieved by establishing suitable technologies and calculating the levelized cost of electricity (LCOE) under conditions that may be found in DH. The result, for the vendors, temperatures and assumptions considered, is a range of 25-292 €/MWh, excluding the cost of heat. The breadth of this range in part reflects the importance of selecting appropriate products to match the heat source temperature.

Horse manure consists of feces, urine, and varying amounts of various bedding materials. The management of horse manure causes environmental problems when emissions occur during the decomposition of organic material, in addition to nutrients not being recycled. The interest in horse manure undergoing anaerobic digestion and thereby producing biogas has increased with an increasing interest in biogas as a renewable fuel. This study aims to highlight the environmental impact of different treatment options for horse manure from a system perspective. The treatment methods investigated are: (1) unmanaged composting; (2) managed composting; (3) large-scale incineration in a waste-fired combined heat and power (CHP) plant; (4) drying and small-scale combustion; and (5) liquid anaerobic digestion with thermal pre-treatment. Following significant data uncertainty in the survey, the results are only indicative. No clear conclusions can be drawn regarding any preference in treatment methods, with the exception of their climate impact, for which anaerobic digestion is preferred. The overall conclusion is that more research is needed to ensure the quality of future surveys, thus an overall research effort from horse management to waste management.