Green Energy for Islands

WP (IV): Selection of an energy transition plan

In WP IV renewable energy autonomy solutions for Skyros were proposed and evaluated. These scenarios referred to the electrical, thermal and transport sectors and involved central and local applications. The results were reported both at the central and the community-level of the island.

Electricity is currently used to cover part of the space and water heating needs of the island, as well as operate lighting and electrical and cooling appliances. Thermal energy is mainly required to cover the remaining space heating needs. The transport sector on Skyros is covered using conventional fuels brought to Skyros from central fuel distillation units of the country.

The simulations of the proposed power plants for the electrical sector were realized using the commercial software EbsilonProfessional, while their dynamic/transient performance was modeled using the programming language R. The proposed systems aimed to fully satisfy the electrical energy demand of Skyros with 100 % use of renewable resources. To develop such stand-alone RES plants, while at the same time minimizing the probability of operational failures, the systems were tested under extreme conditions of energy demand and climatic conditions. To achieve reliable and robust operation, the power plants were substantially oversized, combined renewable technologies with complementary character (hybrid power plants) and included energy storage systems. In all cases, the existing diesel generator was expected to be used as a back-up technology initially to ensure no power outages in the case of unpredicted events.

Scenario 1 considered the hybridization of a concentrating solar power plant (CSP) including thermal energy storage with wind turbines supported by electrical storage. Scenario 2 proposed the hybridization of a photovoltaic (PV) system with wind turbines, supported by electricity storage and a hydrogen-generation facility. Scenario 3 concerned the combination of PV and wind (same capacities as in Scenario 2) with a pumped-storage hydropower plant in place of the electric battery.

Scenario 2 that combines photovoltaic, wind and electricity storage is found to be the best solution for Skyros overall. The best exergetic and land-use efficiencies were achieved by Scenario 1. The best solution economically, on the other hand, was Scenario 2, followed by Scenario 3 and, last, Scenario 1. Although the initial total revenue requirement of Scenario 1 was very similar to that of Scenario 2, the generated less hydrogen due to its smaller power surplus and it resulted in a relatively higher cost of electricity. The environmental evaluation showed similar results for all three of the plants, with somewhat increased impacts for plants that required the replacement of units with short lifetime (batteries, electrolyzer). Given the results, the environmental impact of the renewable plants is found to be negligible compared to fossil fuel combustion.

The scenario proposed for 100 % renewable thermal demand currently based on diesel was related to solar-thermal energy generation with and without public subsidies. The analysis showed that the investment cost of the selected solar-thermal systems became smaller than the cost of diesel currently used for space heating purposes with public subsidy scenarios equal or higher than 50 %. In addition, the renewable scenario offered a significant decrease in carbon dioxide emissions on the order of 85 %.

The scenario proposed for the transport sector included electric- and hydrogen-based vehicles. Although the investment cost of the new car fleet was found to be high, the combination of fuel and maintenance costs of the fuel cell and electric vehicles was found to be 45 % that of the current fleet. In addition, the greenhouse gas emissions of the manufacture of the new cars can be balanced out through the avoided emissions of current use within only five years.

Deliverable

Report: “Scenarios for the sustainable development of energy autonomy of Skyros”