Justification of the structure and parameters of a micro-cogeneration unit for the electricity supply of a local facility

Abstract

Abstract

Purpose. The work aims to justify the structure and parameters of a micro-cogeneration unit intended to cover the base electric load of a local facility, taking into account realistic parameters of small generating sets with a rated electric power of 1–10 kW. Methodology. The study applies system analysis of micro-generation schemes, the fuel–electricity energy balance of the generating set with allowance for the losses in the prime mover, in the permanent-magnet generator and in the power converter, structural-parametric modelling of the elements of the electrical part, and a comparison with centralised electricity supply using the primary energy savings (PES) criterion in accordance with the EPA approaches and Directive 2012/27/EU; a scenario calculation is carried out for the electric power range of 1–10 kW with a comparison of the residential gas-fired and the pellet-fired options. Findings. An improved structure of the unit is proposed, comprising a fuel-fired energy source, a Stirling prime mover, a permanent-magnet generator, a rectifier, a DC link, an inverter, a buffer tank of 300–500 L, a controller with relay protection and a connection unit to the 0.4 kV grid; a control algorithm oriented towards the maximum self-consumption of the generated electricity is formulated. For the base pellet-fired case of 3 kW at ηel = 12 % and ηΣ = 90 %, a fuel input of 25.0 kW, PES = 14.7 % and an annual generation of about 9.0 MWh at 3000 operating hours have been obtained. Originality. A structural-parametric approach is proposed in which the rated electric power of the generating module is constrained not by the available fuel power but by the base electric load of the facility and by its ability to absorb the accompanying energy flow; a system of matching criteria Pel,r ≤ Pbase and Qth,r ≤ Qbase + Qbuffer is introduced, which replaces the intuitive selection of the unit size by a methodologically grounded choice. Practical value. The results are suitable for the preliminary design of local distributed generation sources for private houses, small agricultural and industrial facilities with a base electric load of 1–10 kW: the methodology makes it possible to choose the fuel type, the rated electric power of the generating module and the buffer capacity on a justified basis, and to estimate the annual electricity generation and the primary energy savings.