Managing Volatility – Integrating Renewables into the Energy System
Figure 2: Negative Electricity Prices in Times of High Wind Power Production and Low Demand
€/MWh
100 150 200 250
50
-100 -50 0
1.1 2.1 3.1
Prices spot market (€/MWh) Network load, Germany (MW) Wind feed-in, Germany (MW)
4.1 5.1 6.1
High wind production and a simultaneous low electricity demand lead to negative prices
consumption, which signals a flaw in the functioning of the electricity market. Figure 2 shows a constellation on the EEX for the first days of January 2012, in which negative prices occurred. Even the newly introduced market premium was not able to avoid this effect.
A special characteristic of PV is peak production during noon. Power generation peaks twice a day for just a few minutes around 12:00 and 18:00, when households demand most of their electricity. Due to natural conditions, PV also feeds in most electricity at 12:00, the time of day with the strongest solar radiation. The bell curve-shaped generation graph only increases in its scale. Consequently the energy supply increases and, according to economic principles, the electricity price decreases. This phenomenon has a negative impact on the conventional power plant fleet. The merit order shifts to the right. Peak-load plants, such as gas or hard coal plants, run below full capacity, reduce their hours or are switched off completely. This effect due to PV brings down the wholesale price and also decreases the attractiveness of pumped-storage new builds, as they benefit from large base–peak spreads at the same time.
This is in total contradiction to the need for new builds, as both generation technologies – gas and pump storage – are always named as the two perfect complements to intermittent renewables, but the rebound effects from renewables in the existing system have to be considered carefully.
What options are available to integrate and deliver an increasing share of mainly intermittent renewable energies?
Option 1 – Grid Extension
The existing German distribution and transport grid guarantees the transport of every kWh of electricity produced to the end consumer, to cover the demand in time and to ensure security of supply. Currently, as the main generation centres move away from the existing load centres, a new grid infrastructure is needed. This is the most important measure to integrate renewable generation, if it is possible to transport and deliver the electricity in time. As the expansion and new build of transmission lines takes a long time and has started too late compared with the increase in
12
Independently of the share of renewables, there will be times, even in the future, where generation capacity must bridge periods with less wind or sun.
transport the above mentioned production from pumped-storage capacities. Germany is also dependent on energy transfer to and from the Netherlands, Switzerland, the Czech Republic and Poland.
In the long run, only an integrated European energy market will help overcome the challenges of rebuilding the electricity system. Therefore the measures suggested by Commissioner Oettinger to support and accelerate grid extensions and interconnectors are crucial.
But to realise concepts such as an offshore grid or stable power generated in the desert of North Africa, we need a European approach to grid regulation to gain trust from investors for such projects. Having support schemes in place does not fulfil the need for future regulation of grid infrastructure.
Option 2 – Flexible Conventional Plants
As already mentioned, a higher share of renewables will have a further impact on the operation of the conventional power plant fleet. To ensure electricity supply during downtimes of wind and solar plants, we will need conventional back-up generation to balance electricity supply and demand at any one time. Due to their high utilisation period, lignite and nuclear plants, as well as run-of-river plants, operate mainly as base-load plants. Gas and hard coal plants operate as peak-load plants. However, even these are highly dispatchable. Therefore the decision by the German government to phase out nuclear energy in Germany by 2022 will increase the need for new balancing and back-up power plants.
Beside technical challenges, such as shorter start-up and shut-down periods or general enhancement, the main problem relates to the financial aspect. The market has to pay for the needed flexibility. Investments in new
MODERN ENERGY REVIEW – VOLUME 4 ISSUE 1 MW
10 20 30 40 50
0 -10 -20
renewable generation capacity, the grid will be a critical bottleneck in the coming years. Having a massive increase in wind energy capacities (on- and offshore) in the northern part of Germany, and PV capacities – on the distribution network level – in the southern part, running a stable grid will be a challenge. As a direct result, constraint measures by one exemplary German grid operator (TenneT) increased from two in 2003 to 156 in 2009. In a short time period of only approximately 45 days in 2011 (half of March plus April), 523 constraint measures took place.
The necessary grid extension, at least for Germany, has been investigated in the German Energy Agency’s (dena) Grid Study. According to this study, Germany will need up to 4,500 km of new high-voltage transmission lines by 2020. So far, only 214 km have been realised.
Looking beyond the German border, it is obvious that, next to the national grid capacities, interconnector capacities between countries also need to be enhanced. The link to Norway is especially important to, for example,
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84