Institute of Physical Energetics

This study compares the performance of two wind farm sites located in Northern Europe: an onshore site and an offshore area in the eastern Baltic Sea region. This study investigates the optimisation of wind farm performance within a fixed project area by maximising annual energy production (AEP) and increasing energy density. Three wake-loss scenarios (≤10%, ≤15%, and ≤20%) were examined to assess the sensitivity of layout optimisation to aerodynamic interaction constraints. Several layout configurations were analysed to reduce wake losses and enhance overall energy output. Wind conditions were assessed using NORA3 reanalysis data, and wake interactions were modelled using the Jensen wake model to estimate AEP. Both wind farms were further compared across key criteria, including cost, power generation efficiency, installation and maintenance requirements, and site availability. Offshore wind farms achieve 1.5–1.7 times higher energy density under similar spatial conditions. However, offshore levelised cost of energy (LCOE) remains roughly 25% higher due to higher capital and infrastructure costs, while onshore LCOE demonstrates better economic performance, driven by lower CAPEX and O&M expenses. The findings highlight the trade-offs between cost efficiency and wake-driven energy performance for onshore and offshore wind development in the eastern Baltic Sea region.

Renewable energy communities (REC) are one of the instruments to increase uptake of renewable energy (RE) sources. The EU policy underlines the necessity of citizen wide involvement in the energy system transformation processes to meet the renewable energy (RE) targets. In the article, the energy community is understood as mostly locally-rooted form of co-operation in order to jointly use RE sources with the aim of producing RE dominantly for collective self-consumption and providing socio economic benefits for REC participants and particular local areas. The article estimates the potential of the households regarding rooftop solar photovoltaic (PV) uptake in Latvia. Evaluation is based on the cascade approach: starting with the technical solar PV potential, housing type analysis, then estimating the financial capacity of households and household investments statistics, finally the household willingness to invest in joint energy production is considered. As a result, REC potential to attract additional household investments to increase solar PV electricity production is calculated in the range from 43.69 MEUR to 87.42 MEUR. The REC potential to scale up RE in power generation is calculated for 76.6 GWh electricity in 2030, or 11.6% of the additional electricity from solar PV installations planned in the national energy-climate plan scenario. REC facilitating is understood as one of the policy wheels of municipal sustainable energy and climate action plans. By applying the regional model for climate change mitigation measure impact evaluation, the potential contribution of REC in greenhouse gas emission reduction and providing socio economic benefits for both REC participants and municipality are evaluated at the city level.

In households, solar collectors are finding ever increasing use for hot water preparation. Although the design of solar collectors is relatively simple, the authors over many years concentrate attention on modelling the cross-sectional temperature field of the solar collector’s absorber [1-7]. In solving the cross-sectional temperature field for an annular pipe [1], the periodical cross-sectional domain is divided into three sub-domains where the first sub-domain is the plate between pipes, the second – a pipe’s wall, and the third – the liquid; as a result, the temperature field expressions have been obtained for all the three sub-domains. In works [2, 3] the temperature fields obtained were simplified. To define its variations in time, the temperature field was found by solving the Laplace equation under non-stationary time-dependent conditions [4]. The obtained results evidence that the non stationary conditions might not be taken into account in long- lasting sunny weather, while such non-stationarity changes considerably the temperature field when it is short-term (e.g. in cloudy weather). The temperature has also been found for a square-pipe absorber [7] as more technological in design. In the present work, the final temperature field model is proposed for the absorber of a round-pipe collector. As distinguished from [1], in this work the temperature of liquid is assumed to be constant over the entire pipe cross-section. Such an assumption significantly simplifies the calculation while not changing the physical essence.

Biomass is one of the largest renewable energy sources in Latvia. Since 54,7 % of the state area is covered by forests, the firewood, wood chips and pellets play a significant role in the heat production, especially at households and municipal heating facilities. Wood chips and pellets are also important export products. Changes in the energy-producing wood export since 1997 are explained. Other kinds of biomass that can be used for heat and electricity production are various agricultural and food production residues, livestock breeding buy-products, sewage sludge, combustible (organic) part of household and industrial wastes, etc. In the present paper, a variety of biomass forms used as the energy sources are analysed. The characteristics of different types of wood biomass and the variations in their parameters are considered. The following determined parameters of biomass are presented: the calorific value, ash content, bulk density, melting point of ashes, sulphur and chlorine content, and others. The biomass energy potential calculated for different regions of Latvia (the data of 2007) is discussed. On the map of Latvia the amount and energy potential of agricultural straw and other biomass for different regions are shown. Some recommendations elaborated how to improve biomass utilization for heat and electricity production.

Renewable and local energy communities are viewed as a key component to the success of the energy transition. In this paper, we estimate wind power potential for such communities. Acquiring the most accurate weather data is important to support decision-making. We identify the most reliable publicly available wind speed data and demonstrate a case study for typical energy community scenarios such as a single commercial turbine at coastal and inland locations in Ireland. We describe our assessment methodology to evaluate the quality of the wind source data by comparing it with meteorological observations. We make recommendations on which publicly available wind data sources, such as reanalysis data sources (MERRA-2, ERA-5), PVGIS, and NEWA are best suited to support Renewable Energy Communities interested in exploring the possibilities of renewable wind energy. ERA5 is deemed to be the most suitable wind data source for these locations, while an anomaly is noted in the NEWA data.

Received: February 1st, 2021 ; Accepted: March 27th, 2021 ; Published: April 29th, 2021 ; Correspondence: janis.galins@llu.lv

Abstract An autonomous micro combined heat and power (Micro-CHP) is usually installed to increase energy efficiency and reduce energy costs in areas remote from large power systems. The main goal of autonomous Micro-CHP is to provide residential and industrial areas with electricity and heat. By designing an autonomous Micro-CHP, one of the key issues is the determination of rated power, since the energy efficiency of equipment and the costs of fossil fuels depend on the rated power. The mathematical model can better calculate the necessary rated power for an autonomous Micro-CHP in the case of operation with rechargeable batteries. Overall, the results have shown that the engine characteristics, operation process of three-phase synchronous generator and statistical information on loads are the criteria for improving energy efficiency.

Abstract The authors determined the morphological composition of refuse derived fuel (RDF) produced in Latvia and Lithuania by manually sorting. The parameters of RDF (moisture, net calorific value, ash content, carbon, nitrogen, hydrogen, sulphur, chlorine, metals) was determined using the EN standards. Comparing obtained results with data from literature, authors have found that the content of plastic is higher but paper and cardboard is lower than typical values. Results also show that the mean parameters for RDF can be classified with the class codes: Net heating value (3); chlorine (3); mercury (1), and responds to limits stated for 3rd class of solid recovered fuel. It is recommended to separate biological waste at source to lower moisture and ash content and increase heating value for potential fuel production from waste.

One of the challenges that the implementation of river or in-stream hydrokinetic technology faces is a lack of research providing tools and/or methodology for the assessment of economic potential including choice of the placement and quantity of hydrokinetic devices (HKDs). The present study proposes and applies the developed tool to estimate and compare economic benefits of placement of different kind of HKDs taking into account local restrictions. The paper describes in detail how the tool functionality and modelling results can serve as a basis for economical calculations and prognosis, under electricity market conditions. Experimental data along with in-flow measurements of the Daugava river’s different cross-sections have been used to demonstrate functionality of the proposed tool.

Abstract The paper discusses issues related to the optimisation of magnetic couplings used in bioreactors (manufactured by JSC “Biotehniskais Centrs”). The purpose of optimisation was to preserve the maximum breakaway torque of the magnetic coupling while reducing the mass of rare earth elements used in its structure. The paper presents the rationale for the selected optimisation option taking into account the economic aspect. To solve the optimisation problem, the factors affecting the maximum torque of the magnetic coupling, such as the shape and height of the internal and external magnets, the angle of the external and internal magnets, as well as the height of the internal and external yoke, were determined. The design of the existing magnetic coupling was optimised and its prototype was made based on the results of optimisation. The results obtained by means of optimisation were compared with the results obtained experimentally by testing the manufactured prototype.