Question 11.AE.2: The appliances, e.g., LED (light emitting diode) lights [26]......
The appliances, e.g., LED (light emitting diode) lights [26], refrigerator, induction-type stove in a dwelling consume very little energy as compared to heating of the house. As for the induction-type stove, one must be aware that the induced energy in the bottom of pots is based on a frequency in the range of 20to 50 kHz [27]. For control of the induction heat either burst-current (Figure E11.2.1) or phase-angle current (Figures E11.2.2a, b) control schemes are applied. Both methods cause power quality problems due to the generation of integer and non-integer current (sub) harmonics. Also, persons with heart pacemakers should keep some distance from the induction-type stove [28]. LED lights are equipped with peak rectifiers [29] generating all odd current harmonics when connected to a single-phase voltage including a dominant 3^{rd} current harmonic. The high efficient residence exhibits a greater current harmonic total distortion THD_i than low efficient houses equipped with incandescent light bulbs and resistive electric stoves representing linear loads.
Calculation of the output power P as a function of the duty ratio/cycle T_{on}/T and rated power P_{rat}:
P=P_{\text {nit }} \frac{T_{\text {ont }}}{T} . (E11.2-1)
Calculation of the root-mean-squared (rms) voltage V_{t\_rms} as a function of the duty ratio T_{on}/T and the rated voltage V_{t\_rms\_rat}:
V_{t\_rms}=V_{t\_nms\_rat}\sqrt{\frac{T_{o n}}{T}} (E11.2-2)
Figure E11.2.2a represents a simple circuit for phase-current control. The firing angle α can be generated by implementing the gating circuits of the thyristors which are modelled by self-commutating switches (MOSFETs) and diodes (D) in series, as described in [1, Chapter 5].
Calculation of the root-mean-squared (rms) voltage V_{t\_rms} as a function of the ratio t_{delay}/T and the rated voltage V_{t\_rms\_rat} for phase-angle voltage control:
V_{t\_rms} = V_{t\_rms\_rat}\sqrt{1-\frac{t_{\text {delay }}}{T / 2}+\frac{1}{2 \pi} \sin \left(2 \pi \frac{t_{\text {delay }}}{T / 2}\right)} (E11.2-3)
The 7.64 kW groundwater (at about 10°C ground-water temperature during the entire year) heat pump provides the floor-heating system with warm water between 24°C and 30°C, and the hot water tank with 45-50°C, whereby the cold season outside temperatures varied mostly between -10°C and +15°C. Air heat pumps appear not to be very efficient during very cold spells (less than 0°C outdoor temperature [30]). To further increase the heating efficiency of the house, heat exchangers can be employed where ventilated warm air heats the incoming fresh air [31]. This is especially important to avoid mold [32] in houses due to humidity generated by humans. During the warm season when the outside temperature varies between 25°C and 40°C the groundwater is circulated via heat exchangers through the piping within the floor and used for cooling, maintaining the room/house temperature below 24°C. The increase of the thermal efficiency of a house is important because about 20% of the total energy consumption in Germany is used for residences, and 40% of the total consumed energy is used for heating and cooling of all buildings – residential, commercial, and industrial [33]. This is the reason why the German Renewable Energy Act [34] (Erneuerbare-Energien-Gesetz, EEG) was designed to encourage cost reductions based on improved energy efficiency from economies of scale over time. The EU and German Requirements on Energy Efficiency of Residential Buildings – the Energy Conservation Act (Energieeinspargesetz, EnEG) complement the EEG providing Energy Savings Regulations (Energieeinsparverordnung, EnEV) [34]. To date residential consumers in Germany pay about additional 0.0624 Euro/kWh for the switch from conventional electric energy generation based on coal, gas and nuclear plants to renewable sources, the so-called energy turnaround (“Energiewende”) amounting to an electricity price of about 0.33 Euro/kWh including value-added tax. In 2013 renewable energy generation represents 24.5%, and it is anticipated that by 2025 renewable generation will be 45%.
Lesser sources of energy are the geothermal sources, which have water temperatures of about 93°C [35] and are mainly used for district heating. Co-generation (either electricity and heat or electricity and cooling) as well as tri-generation (electricity, heat, and cooling) [36] are part of the generation portfolio. Environmentally sound approaches are biomass [37] and non-recyclable trash power plants [38] in the range of 10 MW.
The deployment of PV and WP plants entails the use of rectifiers and inverters generating harmonics and unwanted electrical noise such as reverse-recovery currents [1]. The magnitude of the DC input voltage of inverters determines the displacement (power) factor angle of the output current: the larger the DC voltage the greater a leading (consumer system) displacement (power) factor angle is possible. To keep the DC voltage of an inverter as low as possible, a power factor of cos φ≈1 is generally preferred. The distributed nature of the renewable sources makes harmonic compensation and elimination more difficult than in a conventional power system with central power stations, where fewer harmonic sources make voltage control through optimal placement of capacitors easier. The large conventional sources such as natural gas, coal and nuclear plants serve as frequency leaders, even in systems employing renewable distributed sources.
ources. Recent publications [39–41] address the issue of supplying residences with DC power directly from PV and WP systems without DC/AC conversion, therefore avoiding the losses in transformers and rectifier/inverter systems. These losses can amount to about 8% at rated operation.
