Hammar_Modern Energy Review 01/03/2010 16:49 Page 71
Marine
Electrification Based on Small Electricity Grids in Africa –
Ocean Energy in Combination with Land-based Renewable Energy Sources
a report by
Linus Hammar
1
, Jimmy Ehnberg
2
and Sverker Molander
3
1. Doctoral Student, Energy and Environment, Chalmers University of Technology, Gothenburg; 2. Vattenfall Power Consultant AB, Gothenburg;
3. Professor, Energy and Environment, Chalmers University of Technology, Gothenburg
Development and Rural Electrification swells that provide energy with relatively high predictability. Along the
Africa requires the development of modern energy systems to release eastern coast of Africa the semi-diurnal tides are significant, with
women and men from heavy labour and to make industrial production 6.4m mean spring tidal range (MSR) in central Mozambique. In this
more efficient. While electricity – a key component of energy systems – area, the tidal range is high enough to indicate a role for tidal energy
is highly versatile, readily available and technologically well-established, impoundment technologies. Moreover, such a tide creates conditions
the vast majority of the population in sub-Saharan Africa lives in rural for very fast-flowing currents in narrow sounds and channels;
settings, making energy distribution a major challenge. unfortunately, data are limited. From other parts of Mozambique
where the tidal range is lower, currents are still reported to reach
Combining Top-down and Bottom-up Solutions 1.5–3m/s at investigated locations.
2,3
Currents exceeding 1.5m/s are
A large interconnected national electric grid must be the final goal of also reported in Tanzania.
4,5
With most potential sites remaining
all electrification strategies due to its reduced dependency on single unexplored, the hidden tidal resources in East Africa may be large,
sources, line tripping and other malfunctions. There are two different with currents well within the range of what is economically
approaches to achieving that goal: top-down or bottom-up. The top- extractable. Of less interest for small-scale ocean energy, but
down approach is the traditional extension of a central grid based on noteworthy for future ocean energy extraction, are the massive
a few power sources – in Africa typically fossil fuels or hydropower. Mozambique current and the East African coastal current, which both
This is an expensive and slow method due to very high installation pass close to land and seasonally reach surface velocities of 2m/s.
costs (especially for the high-voltage part of the grid) and low
profitability due to the low purchasing power of the population and Technology and Need for Adaptation
the resulting limited number of connections and use. To lower the Currently, ocean energy technology comprises more than 100 types of
cost, solutions such as one-phase connections and single wire earth electricity converter at different stages of development. Many converters
return (SWER) have been installed and tested. However, both of these are set for larger installations (MW-order) that are suitable for connection
technical solutions have a reduced power transfer capacity and higher to larger grids. However, several small-module systems in the range of
losses than conventional three-phase connections. The bottom-up 20–500kW are also being developed; in remote areas these smaller
approach involves the implementation of autonomous smaller grids modules are more appropriate. When technologies mature and costs are
supplying certain loads or restricted areas, to be gradually trimmed down, those ocean energy converters that are adapted to this
interconnected with each other and ultimately with the national grid. niche market may come to contribute to rural electrification in
Installations thus become more affordable, but this approach also developing coastal Africa. Many rural electrification initiatives have
implies a limited amount of power and consequently reduced failed as a result of mismatches between social and technical
generation reliability. Diesel generators running on fossil fuel have prerequisites, especially among those relying on the introduction of
been attractive due to low installation costs and high generation modern renewable technologies.
6–8
Locally working institutions and a
reliability; however, diesel fuel and its transport are expensive. productive use of the electricity are of fundamental importance;
Emissions are another disadvantage. By using renewable energy however, many other barriers can be met by employing specially
sources such as wind, solar or small-scale hydropower, autonomous adapted technology. Here, we put forward and discuss what we
power systems open up for clean so-called development financial rate as the most important technology-dependent barriers for ocean
mechanisms. Here, ocean energy such as tidal and wave power energy technologies in developing countries: generation reliability,
provides an interesting and under-utilised energy source for Africa. maintenance, transport, vandalism and the marine environment.
Ocean Energy Resources in Africa
A highly resolved resource distribution of ocean energy is generally
Linus Hammar is a doctoral student within the
Environmental Systems Analysis department of
lacking in Africa; however, global resource overviews reveal both
Chalmers University. His research focuses on the
substantial wave and tidal power resources. Measurements are few,
sustainability aspects of renewable energy technologies,
with ocean energy as a case study. This work is carried
but wave resources from 20 to 50kW/m wave front are estimated in
out under the umbrella of Socio-Technical-Ecological
the waters of southern Africa.
1
In the most promising regions of south- Evaluation of Potential Renewable Energy Sources
western Africa, the near-shore available wave power is estimated to be
(STEEP-RES), a collaborative project between Swedish
and African researchers that is sponsored by
40kW/m wave front. In central West Africa and south-eastern Africa,
Stiftelsen Futura. As a consultant, Mr Hammar has previously worked to assess the
including the eastern coasts of South Africa and Madagascar, trade
environmental impact assessments of marine technologies.
winds create prominent wave climates. Moreover, many African E: linus.hammar@chalmers.se
offshore islands have the benefits of continuously in-rolling oceanic
© TOUCH BRIEFINGS 2010
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