Isolation also produces an incremental generation cost due to the impossibility of conducting a joint system optimisation in order to ensure the quality of service
The challenge of supplying a large area with renewable energy and in a standalone way is a technical, human and decision-making one
The development of efficient storage is of vital importance to the stability, security and efficiency of an isolated electrical system
The nature and size of the islands’ electrical systems, and all isolated systems in general, reflect different factors compared to interconnected systems, especially in the demands of the generating sets, which require a special process. However, establishing a general strategy for the integration of renewable energy sources for them is a complicated task since resources, needs and characteristics vary greatly from one location to another. Obviously, the process of supplying renewable energy sources to a community with 10,000 inhabitants is completely different from one with half a million.
If we take the Canary Islands as an example, which have six electrical systems (one for each island with the exceptions of Lanzarote and Fuerteventura which are connected by an underwater cable), only 7% of demand (almost 9000GWh in 2012) is supplied by special treatment facilities, while the rest is mainly generated by steam plants and gas and diesel generators. The fact that the electrical system in the Canary Islands is comprised of six isolated subsystems means it cannot take advantage of the synergies provided by electrical interconnections which result in greater system stability.This isolation also produces an incremental increase in generation costs because of the impossibility of carrying out an optimisation together with the system to ensure the quality of service. That is the reason that in isolated communities such as the islands there is the peculiarity that the cost of generating electricity from fossil fuels and derivatives is usually much more expensive for the system than doing it with renewables. This cost is derived from the higher level of reserves that must be maintained in isolated systems and the extra cost of the specific technologies used, as well as higher fuel costs. Following on with the example of the Canary Islands, and according to the National Energy Commission, the cost of conventional generation amounts to €165 per MWh, while the figure is reduced to €145 and €89 for solar photovoltaics and wind energy respectively. What follows is that what negatively affects the price deficit in the case of the archipelago is not promoting the use of renewable energies
For an appropriate integration scheme for renewables, strategies should be developed regionally taking into account local characteristics. These should specifically reflect the needs and behaviour of the of daily and seasonal consumption curve, taking into account economic and human needs, which have a major impact on energy consumption. Also, the challenge of supplying a large area with renewable energy and in a standalone way is a technical, human and decision-making one.
The most important technical challenge is the analysis of solutions for regulation, integration and storage, which represent the main obstacles to the widespread implementation of technologies based on sources of renewable energy. Several aspects must be considered, including for example the use of fuel cells, hydrogen storage, batteries, storage through hydraulic energy, thermal storage, etc. For an island to be 100% supplied by renewable energy sources, transport solutions such as the gradual replacement of traditional vehicles with electric vehicles, hybrids with batteries or natural gas, etc should also be studied.
A comprehensive approach should include the application of a regulation regarding the rational use of energy to reduce consumption.
The main difficulty for the large-scale integration of renewable energy sources with variable output (resource dependent, such as wind and fotovoltaics) in this case, is that energy storage is essential, and should be able to supply peak demand during periods in which the resource is scarce. The development of efficient storage systems is of vital importance to the stability, security and efficiency of an isolated power system. The most appropriate alternative in case of the Canary Islands is using reversible hydroelectric power stations that provide stability to the system.
With respect to storage, it should be borne in mind that this should be dimensioned so that the energy requirements can be achieved and can peak in adverse weather conditions.
The island of Tenerife for example, with about one million inhabitants, has a south-eastern coast with excellent wind resources (equivalent to 3,000 hours). This means that, in absolute terms, the island could be supplied with about 800 MW of wind. However, this figure only takes into account the energy needs during the year. But wind resources depend on the weather, which means they are not adaptable to energy demands.
However, peak demand must be taken into account. So far, we have considered only energy demand in large numbers, but peak energy demand (582 MW for Tenerife) is an important issue. Assuming that this peak demand coincides with a time of scarce resources, our storage system must be capable of providing amount of power. This means that the power from the storage systems must be equal to power consumption. In order to avoid excessive costs, turbines fuelled by diesel or biofuels, can be used during peak consumption.
Therefore a process is required for measuring pored storage, balancing the power supply with the needs of peak demand. Also, the cost of each system must be taken into account to justify the total investment. In some cases it will be necessary to increase the installed wind capacity, whilst losing energy, but significantly reducing the cost of the storage system.
The evolution to an eventual 100% renewable supply is not linear; it should be done in progressive steps, with each stage incurring a higher cost. The last stage in achieving a 100% renewable supply is extremely expensive, because you need to guarantee that a small percentage of energy will be consumed only during certain days throughout the year.
This development has to be accompanied by a process of managing intelligent electrical networks – a smart grid (Smart Grid), with the aim of providing intelligence to the electricity distribution networks to provide better use and greater efficiency in electricity distribution, and avoiding the negative impacts of sudden changes in consumption or specific deficiencies in generation.
By Guillermo Galván García
Head of the Wind Energy Department Instituto Tecnológico y de Energías Renovables (ITER) Technological and Renewable Energies Institute