The article presents the part of PhD studies of the energy wood harvesting technologies in thinning, and its development possibilities. A possibility for energy wood procurement and use in Latvia as a good amount of not used energy, including estimation of how much wood for energy purposes could be available in Latvia is analyzed. Research has been made in two parts using forest stands cutting area in three different ages to get an average volume of energy wood per ha. First part of the research has been done in a 60 years old forest stand cutting area in the way that total chips volume is measured and then recalculated to the thinning area. The average volume from studied forest stand was 20.32 m**3 haE-1. The second part of the study shows that from 30 till 45 years old forest stands cutting area by the measuring possible removal tress, the energy wood volume could be 23.74 – 33.5 m**3 haE-1. Including the slash from this forest stands cutting area the possible volume of wood for energy purposes could be ~ 33 – 47 m**3 haE-1. The calculations also have been done to study available energy wood resources from whole forest stands thinning area. Totally the available energy wood volume in Latvian conditions is 0.85 million m3 yrE-1.

The study was accomplished in 2010. The applied research methods are based on the analysis of the studies by other authors, industry experts, statistic data and the (unpublished) information provided by the Latvian district heating merchant “xxx”. Spearman’s rank correlation coefficient was used for evaluating data regularity. In 2020 the energy produced from renewable sources (Directive 2009/28/EC) in total energy consumption in Latvia has to reach 40%. Such an objective can be achieved by promoting the use of biomass at cogeneration (CHP) plants, the potential of which is the district heat supply system. Wood as an energy resource in its structure accounts for only 25-30%; therefore, the primary condition is the introduction of modern technology which would provide the possibility to diversify energy resources. The calculations confirm that the realised amount of thermal energy indirectly affects profit; directly it is affected by the rate of thermal energy, so the structure of use of energy in heat supply enterprises is associated with lowering the cost of (restrictive) factors - the energy cost, specific production technologies, energy efficiency. Currently, the primary condition of heating companies is to find such energy resource(s) to ensure the approved schedule of temperature and thermal load. The next determining factor is the energy price. In assessing the factors that will affect energy usage in the future, the main strategic principle of energy consumption will be linked to limiting the growth or even reducing heat tariff, by realising optimal efficiency and minimal environmental pollution during energy transmission.

The purpose of this article has been to present a range of products which can be obtained from agricultural production and used for energy purposes. The domestic demand for plant material to be converted to biocomponents was assessed, including the demand for oilseed rape seeds and other grain used to make bioethanol in Poland. One of the ways to limit the adverse effect of fossil fuels on the environment is by using renewable resources. Agriculture is the producer of biomass used to make biocomponents for liquid fuels and raw materials for substitution of solid fuels. The EU, wishing to stimulate production of biomass for energy purposes, has brought to life several legal acts which force the use of biofuels in the European Community. Farmers who produce substrate for bio-fuel production were offered subsidies to energy crop plantations, at first paid from the state budget, and in 2007 – 2009 provided under the Common Agricultural Policy (CAP), which increased the farmers’ revenues from farming. The decisions approved of while reviewing the CAP are to improve – via the market mechanism – the production and export potential of the whole EU. This is to be achieved, for example, by abolishing the subsidies to energy crops, which ceased to be paid in 2010. Such subsidies improved (artificially) the profitability of energy crop plantations, while causing a relative decrease in food production in Europe. By participating in the CAP, Poland is obliged to undertake certain measures in the domestic policy that will comply with the decisions made on the EU level.

The research paper discusses simulation of the loading process of the vertical axis wind turbine with the permanent magnet synchronous generator. Experimental and analytical studies were done in the year 2013. The research results show that electrical load on the wind turbine generator is important for the wind turbine performance. If the load is above or below the power gained from the wind energy, the turbine operation cannot be considered efficient and its dynamic parameters fail to achieve the efficiency level at the proper operation load when the load is built up strictly in accordance with the wind energy input. In the research, 3 separate virtual electrical loading models with static, discrete, dynamic electrical load were established. MATLAB SIMULINK simulated virtual model shows the importance of usage of the right amount of electrical load in the vertical axis wind turbine with the permanent magnet synchronous generator. Final research results showed that the most effective loading process of wind turbine generator is a dynamic load.

One can reasonably argue that issues related to the increased use of renewable energy resources in the energy production processes in Latvia, are at the forefront and will remain there in the future. This relates to the aspect that Latvia is not rich in non-renewable energy resources (around 70% of total primary energy consumption in Latvia is ensured by import, which can lead to undesired effects in many areas), but at the same time, there are available renewable energy resources in Latvia, with an untapped potential to be recognized. In particular this applies to fuel wood, which is already (year 2012) the most important domestic fuel in Latvia. In this context it is important to emphasize that, according to the particular study results, if unexpected socio-economic developments do not take place, raw wood material resources required for different types of fuel wood production in Latvia should be available in the same amount as it is now if not more. As for increasing the amount of fuel wood use in Latvia, an enormous ‘potential’ can be seen in general use boiler houses, where there are currently no technological limitations to utilize this ‘potential’. General use cogeneration plants can be recognized as an even greater ‘potential’ for greater use of fuel wood in Latvia, but given the circumstances of energy supply in Latvia, the ‘potential’ is currently available on a very limited basis. At the same time it is important to note that both of these ‘potentials’ could be significantly reduced in the next few years.

Willow species are nowadays extensively studied. Species are being investigated to evaluate their use and role in various sectors of national economy. The use of willows in short rotation coppice (SRC) for biomass and energy production has a priority in the European Union policy. There are many countries that have grants and financial aid system for so-called ‘green energy’ production. Willow species also have other economically and ecologically important features: resistance to contaminants, strong root system, high tannin contents, decorative, etc. Willow SRC systems are used for phytoremediation and in wastewater purification, in combination with biomass production. There are several countries of Eastern Europe researching adequacy of the willow SRC for the farmland contaminated by radionuclides segregated from the Chernobyl nuclear power plant disaster. Willows are used for quarry restoration, water sludge treatment, erosion control etc, but the most important field at the moment is the biomass production.

The study represents results of theoretical evaluation of forest biomass available for solid biofuel production in pre-commercial thinning in Latvia. The study is based on the National forest inventory (NFI) data; calculations are done for each NFI plot separately. The calculation is done in three steps – selection of the NFI sample plots, which fulfils criteria for the pre-commercial thinning, development of the diameter distribution table, setting the criteria of the thinning intensity, calculation of extractable biomass. Thinning from below (removal of the smallest trees) is considered in calculation. Two types of biomass are accounted – full tree (aboveground biomass) and stem-wood (stem biomass). The study demonstrates that pre-commercial thinning could become an important source of forest biomass in Latvia (15400 GWh of primary energy according to current situation in forests); however, dimensions of trees and harvesting conditions might be challenging for production. The most of the potential biofuel resources are located in stands with average tree higher than 8 m; therefore, it is reasonably to develop and introduce technologies applicable for production of partially delimbed trees.

Renewable energy resources have been developing very fast due to negative effects and finite reserves of the fossil fuels. Biomass is ranked among the most promising renewable energy resources within the Central Europe. Corn (Zea mays L.) is currently the most widely grown crop in the Czech Republic; nevertheless, the cultivation of corn provokes soil erosion by water. Perennial energy grass called tall wheatgrass (Elymus elongatus subsp. Ponticus cv. Szarvasi-1) is supposed to be a good and environment-friendly alternative to corn. Field trials including these two crops were established in the experimental locality of South Bohemia. Their yield potential was monitored during spring harvest periods (use for combustion). Dry phytomass was fundamentally analysed (N, C, H, S) and higher heating value was determined too. Universal Soil Loss Equation was calculated for both crop species. Corn provided much higher average yield in a three-year interval; corn phytomass reached higher heating value as well. The area of Elymus elongatus should enlarge considerably, if we wanted to get the identical amount of energy from corn and Elymus elongatus. However, we found that, compared to Zea mays L., water erosion theoretical land losses would be several times less serious for Elymus elongatus.

Global scale environmental problems and economic issues are the main aspects what point out exigency to do research in the construction of renewable building materials. Renewable building materials are those materials that can be regenerated quickly enough and in theory, their production could be carbon-neutral. In order to evaluate the thermal efficiency of renewable materials in the framework systems of building envelope structures, test samples were made with the filling of renewable materials. The aim of the work is to find out the thermal conductivity coefficient of these natural composites and to compare them. Different size test samples were created for determination of thermal conductivity coefficient: 1.type as reference value: (width x height x depth) 290 x 290 x 30 mm; 2.type as experimental construction value (imitation of real wall construction): (width x height x depth) 980 x 980 x (165; 250; 345) mm. In this research as renewable insulating materials were used: maple leaves, legume (Galega orientalis), the composition of hemp shives (Bialobrzeskie) and sapropel with lime. A renewable insulating materials (also known as eco-thermal insulating) as alternative building materials discussed in this research work meets the requirements of the normative documents of the Republic of Latvia on sustainable construction principles. The analysis of results indicates significant difference among investigated materials – 0.040 W mE−1KE−1 lowest obtained value of thermal conductivity coefficient.

Due to the ever increasing demand for energy resources, more and more attention is being paid to renewable energy resources. One such potential resource is lignocellulosic biomass that can be treated to acquire a carbohydrate rich substrate for further use in producing biofuels such as bioethanol or biobutanol. In this study, birch (Betula pendula) chips were used in fast pyrolysis to acquire bio-oil. This bio-oil was further hydrolyzed in pressurized reactor Parr 4554 to produce a carbohydrate rich feedstock. Hydrolysis conditions were optimized. Several conditions − three different temperatures (111, 121, 131 °C) and four different sulfuric acid concentrations (0.05, 0.1, 0.2, 0.5 M) were tested. The optimal conditions were 121 °C with 0.2 M sulfuric acid as a catalyst that allowed to acquire a solution with the total glucose concentration being 6.6% that can be further used as a feedstock for biofuel acquiring.