Connecting renewable energy to the grid
Big cities need large amounts of electricity to function. Often, this is transported from generating sites located in remote areas hundreds or even thousands of kilometers away.
The question is how to move as much electricity as possible from renewable generation sites like hydro plants and wind parks without impairing the function of the power networks that need it.
HVDC (high-voltage direct current) power transmission pioneered by ABB 50 years ago and Flexible AC Transmission devices (FACTS) are answers to these difficult technical problems.
One of the challenges of renewable power generation like wind and solar power is that it can be interrupted, and this variability affects the stability of the power produced. FACTS devices address network capacity and stability as more renewable energy is brought online.
Power grids are facing a major transformation, driven by the need to integrate renewable energy, improve energy efficiency and allow consumers more control over their energy consumption.
As it evolves, the “smart grid” will combine established power technologies with advanced analytics, smart devices and automation technologies to create a power system that is more reliable, flexible, secure and efficient, and has a lower impact on the environment.
ABB FACTS technologies such as Static Var Compensators and Series Capacitors enable more power to flow through existing power lines while improving voltage stability, and also make a power network more resilient to ‘system swings’ and disturbances.
ABB is installing SVC Light with dynamic energy storage capability based on lithium-ion batteries at an installation for UK Power Networks at a site in the UK. This system will level out load peaks and connect more renewable energy to existing electrical networks by correcting the destabilizing effect of renewable power.
In addition to voltage control, the EDF installation can also store surplus energy from wind farms, which can later be used to level out peaks in grid loading. This way wind generated power can be put to the most efficient use possible.
Another challenge is moving renewable power generated in remote places. High voltage DC bulk power transmission moves electricity across thousands of kilometers with exceptionally low losses. Transmission at higher voltages reduces the amount of electricity lost to resistance in the wire conductor, which is dissipated as heat.
Delivering renewable energy over long distances
ABB can now transmit up to 6,400 MW (megawatts) of clean, renewable hydropower across several thousand kilometers with 93 percent efficiency, at voltage levels as high as 800 kV (kilovolts) to minimize losses.
In Brazil, ABB is currently building the world’s longest power transmission link. This nearly 2,500-kilometer long power highway will send electricity generated by two new hydropower plants in Brazil’s northwest to the densely populated São Paulo area in the southeast.
To cross this vast distance, the electricity will be transmitted at a very high 600 kV in order to minimize transmission losses, ensuring as much power as possible reaches those who need it.
It is the second transmission project in Brazil using HVDC rated at a high 600 kV. The Itaipu HVDC project, with two transmission links built by ABB in 1984 and 1987, is still the world’s highest-voltage DC power transmission system currently in operation.
HVDC is also the best technology for integrating more intermittent forms of renewable energy into the local power grid, particularly over long distances. This is especially significant for large scale offshore wind projects, or large scale solar power production.
Technology of choice
Offshore wind generation – particularly far out at sea where the wind is strong and steady – is an enormous potential power resource. For distances of more than 100 km or for large power levels, HVDC Light transmission has emerged as the technology of choice to link it to the grid. FACTS is a good option for shorter distances and lower power levels.
For example, ABB has just built a 400-megawatt transmission link using HVDC Light technology for a wind park 130 kilometers off the German coast.
When commissioned in 2010, wind-generated electricity from Borkum 2 is expected to displace 1.5 million tons of CO2 emissions each year by replacing electric power generated from fossil fuel on the mainland.
With HVDC Light, high power levels generated offshore can be fed into the network without destabilizing it. Nor will intermittent offshore electricity generation disrupt the grid.
HVDC Light transmission systems are also extremely efficient, with very low transmission losses, even over long distances.
HVDC Light is also attractive for its simple-to-handle cable design and modularized, factory-assembled voltage converter, which means the network links essential to receiving power from offshore wind parks can be quickly installed and commissioned. 1