# Small Heat Source Used for Combustion of Wheat-Straw Pellets
## 1 Introduction  
The use of alternative energy resources has risen in recent years due to many European Union initiatives. Fossil fuels are being replaced by electric energy, generated from various renewable energy sources, for example wind energy or solar energy. Electricity is also generated in biogas facilities, where waste, or secondary resources, are utilized in biogas reactors. Renewable resources also play a significant role in heat production where solar energy is also used. Waste has some potential, as a secondary resource as well. Advanced waste recycling and the use of waste as an energy commodity is accepted across many countries. Many countries have already used use household waste to produce heat and electricity using waste interaction plants. Agricultural products are used as well; for example on fast growing plants. Waste or secondary products in agriculture have been used for many years, and they are considered possible energy resources, not only for biogas plants, but also as a direct resource for heat generation. One of such resources is straw and similar by-products in agriculture. Scheme of straw production is shown in Figure 1.  
There are many initiatives that handle straw as energy resource. One of the most important was the IEA initiative in the early 1990s [1]. In this study, authors compared potential and real use of straw in energy generation across five European countries: United Kingdom, Denmark, Sweden, Netherlands and Austria. The main goal of this activity was to study straw and agricultural by-products utilization for heat or electricity generation. This study identified some barriers which make the use of straw difficult; for example, the difficult organization of straw deliveries, the very light economic impact, and also some skepticism against straw and other similar resources. Straw was extensively used for heating and combined heat power production only in Denmark. Approximately 1 million tons of straw was documented by the initiative for use of heat or electricity productionin Denmark. Straw was also used for co-firing with coal in some power plants. Other countries used straw on limited scale. The initiative also identified some key aspects for influencing future use of straw:  
* The time required to collect the straw is very limited, therefore sufficient harvesting capacity is needed;
* Straw bales with specific properties, for example density and shape, are required;
* Straw storage methods are important to reduce total costs;
* Using straw briquettes or pellets is not economic;
* A decentralized use of straw might be interesting. A few years later, in another study [2], the authors focused on two countries from previous research, Sweden and Denmark. The authors analyzed, in their study, biomass energy systems with 13 examples where straw was used as main fuel, or as secondary fuel in combination with another biomass. The examined power levels ranged from small local heat production up to a large combined heat and power plants. Small heat sources using straw were mainly utilized by local farms with their own production. The authors visited all processed sites and interviewed key persons in these facilities. They also classified farm entrepreneurs according to study of [PERSON] et al. [3]. In this study, the authors also examined the reasons for the engagement or motivation of farmers to use new technologies as a use of straw for heat or electricity production. In their article, [PERSON] et al. [3] also identified three categories of farmers: (1) pluriactive farmers, those who seek new ways to increase income on the farm; (2) resource-exploiting farmers, who want to utilize material resources; and (3) portfolio farmers, who desire to exploit business opportunities and are not attached to any farming traditions. Local contexts of straw as an energy resource have been also examined in a study [2] of Sweden and Denmark. In Sweden, the market was incipient and many projects for straw use started due to the introduction of a carbon tax on fossil fuels.