Use of Wind and Solar Energy

Transcription

1 Faculty of Electrical Engineering University of Žilina Use of Wind and Solar Energy Conversion technologies & grid integration Marek Höger

2 Use of Wind and Solar Energy 1. Wind energy conversion 2. Impact of wind generation on grid 3. Solar energy conversion 4. Impact of solar generation on grid

3 Wind energy in the past First machines driven by wind power are known from the ancient times ( B.C.) Wind power was mainly used for driving water pumps, later also in wind mills

4 Wind energy for power generation Firs wind turbine for electricity production was built in 1887 in Scotland by prof. James Blyth Till the middle of 1990s, installed capacity of wind power plants was neglect able During the last decade, the installed capacity has grown exponentially!

5 Benefits of wind generation The increase of installed capacity in wind was driven by demand for clear, renewable energy sources. Ecological benefits: No fuel needed, renewable source Carbon free, no emissions during operation Fully automated operation

6 Basic construction variants Horizontal turbines Vertical turbines

7 Wind turbines for home use

8 Operation principle The turbine converts the kinetic energy of moving air to mechanical energy on the shaft. The kinetic energy of air flowing through a given cross section of space is: E k = 1 m v2 2 Where the mass of air m is given by: m = ρ V = ρ Q t = ρ S v t Combining these two equation we obtain: E k = 1 2 ρ S v3 t

9 Operation principle Becasuse power is energy per given time interval, we can eliminate time: P = E k t = 1 ρ S v3 2 It is not possible to convert all this power to useful energy, the maximal theoretically possible efficiency is 59.3 %. This value is called the Betz s limit. Then the power of an ideal turbine will be P = ρ S v3 2

10 Operation principle It is more common to calculate with the rotor diameter instead of it s cross section. Then the previous formula will be: P = 1 D ρ π 2 4 v3 Combining all numerical constants together, we get the well known formula: P = ρ D 2 v 3 The power of an wind turbine is given by the square of rotor diameter and the third power of wind speed. Even relative small change in wind speed results in big change of output power!

11 Typical operation curve of a wind turbine (VESTAS V90) Cut-in speed Cut-out speed

12 Localities for wind generatio As we can see from the power curve, the operation of this type of turbine is reasonable only if the average wind speed in the location of operation is higher than 4 m s -1 Typical localities for wind generation are sea sides and hills or mountains. Inland localities have in general much worse conditions for wind generation as sea sides. For example, average wind for most of Slovakia is less than 4 m s -1 Best conditions for wind generation are on the sea, where terrain doesn t inflict the wind streaming.

13 Wind turbine in operation (delivering power)

14 Wind Parks In localities with good wind conditions, multiple units are build creating so called wind parks or nests. Wind generation is often called as distributed generation. In fact, most of installations is concentrated in relative big wind parks with overall installed capacity of several tenths or hundreds of megawatts. Such a wind park behave from grid point of view as one big power plant. In countries with high installed capacity in wind power plants, generation in wind parks significantly influences the operation of national power grid (often also power grids of neighboring countries).

15 Wind Park (12xVestas V MW)

16 Typical wind power plant arrangement

17 Wind turbine generators DFIG and SM

18 Control of a wind power plant It is possible to regulate output power of a wind power plant, but only downwards! Power regulation is achieved by changing the aerodynamics of rotor blades. Blades are rotated and their profile is moved out of optimal position, so the aerodynamic force is lowered and the aerodynamic resistance is raised.

19 Control of a wind power plant Lift coefficient Resistance coefficient Angle of attack [ ]

20 Generation forecasting In a power grid, consumption and generation must be always in balance. In order to keep this balance, it is necessary to have a qualified forecast, so the TSO can reserve enough regulation capacities to eliminate the fluctuation of wind power. If the TS operator fails to keep the balance, in the interconnected network, this disturbance will spread to neighboring states. This affects scheduled power flows an potentially can cause massive outages or black-out. Large installed capacity in wind in a system with not enough regulation capacities and limited transmission capacity significantly decreases system safety!

21 Real-life data (Tennet, Germany) 2500 Power generation & forecast Forecast Generation

22 Example Austria

23 Example Germany

24 Example Germany

25 Results Large installed capacity in wind in a system with not enough regulation capacities and limited transmission capacity significantly decreases system safety! More wind power is not automatically more ecological if the fluctuation of wind generation is high and regulated with fossil power plants! Generation is very effective near sea side and offshore. Inland generation is in general less effective and negative impacts on grid are stronger.

26 Solar power

27 Brief history of solar cell First PV cell created in 1839 by Edmond Becquerel During next decades, several prototypes were introduced, but the efficiency of these cells was only about 1 % First practical PV cell developed in 1954 by Bell Laboratories Until 2006, application of PV panels was limited by high prices to special applications (satellites, off grid power sources for small electronic devices) High demand for ecological energy and government subsidies have driven the research and nowadays, price of PV panels was reducet significantly, photovoltaics is applicable for general use (but still expensive).

28 Price history

29 Irradiance map

30 Technologies Photovoltaic panels

31 Technologies Thermo solar plant

32 Technologies Solar Stirling Engine

33 Technologies Effective in environment with large portion of difuse light Efficiency decreases significantly with panel temperature Simple construction, no moving parts DC output Effective in environment with large portion of direct light Storage of thermal energy is possible Suitable only for large instalations Power generation similar to conventional thermal powerplants E Photovoltaic panel Thermo solar plant

34 Installed capacity

35 Diode model of a PV cell E

36 CV & PV characteristic E

37 Thermal characteristics E

38 Cell types E Monocrystalline cell Efficiency up to 20 % Longer life Expensive Polycrystalline cell Efficiency ~ 15 % Good performance with diffuse light Cheaper Multi crystalline cell Efficiency ~ 16 % Good spectral response Higher energy production in difficult light conditions Expensive

39 Typical on-grid arrangement E

40 Typical off-grid arrangement E

41 Power generation optimal whether conditions E

42 Power generation most common weather conditions E You can see very fast power fluctuations, practically unpredictable! (Both pictures are from the same day, but different locations)

43 Generated energy E Daily production is very unstable. In case of an off grid system, large accumulation is needed! Energy production per watt of installed capacity is very low in average (when compared to other sources).

44 Electricity production in SR E Installed capacity of solar is 524 MW. Peak production is ~ 350 MW. System load ~ 3500 MW. Total share of solar on generated energy was only about 2 %. Load factor was 12.8 %.

45 Impact on daily load diagram E

46 Voltage changes in MV network Local generation decreases the voltage drop on a power line, reducing the current flowing from network to distribution transformers. Result: voltage in the network raises proportional to power line impedance and locally generated E power. Changes in power generation are causing significant changes of nodal voltages.

47 Nodal voltage [V] Voltage changes in MV network Nodal voltage in PV coupling point E Generated power [MW]

48 Conclusion PV Price for photovoltaic panels has decreased significantly and PV is available for general use (but still expensive) PV technology is suitable for home use, typical plants have installed capacity between 1 kw and 1 MW (installed capacity per generating unit is smaller than in case of wind generation) Because most of PV plants are connected to low voltage and medium voltage networks, integration E of PV plants in to grid affects primary the distribution grid The most significant problem are voltage changes, the voltage often oscillates from -10 % of nominal voltage to +10 %. Wide use of solar energy supported by state subsidies leads to significant increase of electricity prices.

49 Conclusion renewables Renewable sources are very popular, public support is usually very high, installed capacity is rising exponentialy Distributed RES (wind & solar) are unpredictable, on large scale causing several problems to control of grid operation (voltage and frequency regulation, loop flows, overloading of power lines) grid has to be adapted to these new conditions Subsidies have deformed the electricity market significantly PV panels are becoming very popular for home use E Use of RES is not just technical problem, but also economical and legal.