Block’s Indicator of Sustainable Growth

by Ray Block

Renewable energy- wind, solar, biomass, geothermal, hydropower are rarely located near major population and large manufacturing centres. In the case of wind energy, the resource is variable, it may be strongest in night time, when electricity usage is lower. For solar,, solar power can be used at night, by the expedience of storing energy during the day in a molten salt.

It is also usually the case that renewable resources are located far from the major power grid connections. Hence the need for dedicated transmission lines to where the electrical power is mainly consumed. But there is a major drawback to long distance transmission lines of say 800km (500 miles) or even longer, where on average 8 per cent of the energy is lost.

The further alternating current (AC) is transmitted, the greater the percentage of electrical loss. This has given rise to high voltage direct current (HVDC) transmission lines, where the voltages have been steadily increasing depending on the transfer capability involved. Transmission losses can be reduced to about 3 per cent.

Until recently, the highest voltage involved in the transmission lines was 765 kV. But Siemens Energy of Germany and Chinese partners will have completed a 1400 km transmission system for China Southern Power Grid Company, Guangzhou for commercial use by mid -2010. This is the world’s most powerful HVDC transmission system, at a DC voltage of +/- 800 kV, with a transmission capacity of 5GW (5000 MW). The transmission lines will carry electricity generated by several hydro power plants from Yunnan to the Pearl River mega cities of Guangzhou and Shenzhen.

Energy storage enables the electricity power suppliers to optimise returns from peak power, with the widespread use of renewable power, and to make the grid more reliable in the process. For concentrated solar power (CSP), the German company, Solar Millennium at its Andasol 1 solar power plant uses a mixture of sodium and potassium salts heated to above 224C (435 F) to store the solar energy for 7.5 hours with full capacity of 50 MW.

There are in all three Andasol 50 MW CSP parabolic trough solar plants in the one complex, the first of its kind in Europe. They are located in the Andalusia province of southern Spain.

For wind energy to be stored, you need storage batteries. Xcel Energy, the largest US wind utility, has wind farms in Minnesota, Colorado, New Mexico, North Dakota and Texas, with more than 3 GW (3,000MW) of wind generating capacity, one fifth of total Xcel electricity capacity of 15 GW. Xcel has installed a 1 MW NAS sodium-sulphur battery from NGK Insulators, Japan at its Luverne, Minnesota wind farm.

Xcel director, Frank Novachek  (April 15 2009) said that wind energy will help the system run more efficiently. “It would smooth out the ups and downs that wind has on our system….there are often times when Xcel doesn’t use all of the energy generated by a wind farm in a given day, and without a way to store it, that energy is lost. The largest barrier to the project is the high cost of the batteries.”

Testing of charge and discharge cycles has been carried out over an extensive  period, and the system is working as envisaged. A fully charged battery will release a steady megawatt of power output over seven hours. On a busy grid network, a one megawatt battery can potentially allow more wind energy megawatts online.

However, there are downsides to the battery, with 35 per cent of the stored power lost,. The cost is a high US$3 million, and it can only be energy efficient at very high temperatures to operate.

Having originally installed a 1.2 MW NAS battery for its West Virginia service, American Energy Power (AEP) has ordered three new NAS batteries totalling 6MW. The US Department of Energy regards energy storage as one of the key strategic growth areas. The ARPA-E agency recently awarded six major battery research projects totalling over $30 million.

The most interesting of the projects for renewable energy sources, such as wind and solar, along with a more stable, reliable grid involves the considerable battery research capability of MIT. The research grant is for an all liquid metal grid-scale battery for low cost, large scale storage of electrical energy. This new class of batteries could enable continuous power supply from renewables. That  is just what is urgently needed.