Electricity production in insular environments can be distinct depending on the type of energy supply in the network:

• An electric cable connects the island to the mainland, supplying all or part of the island's electricity.
• Part or all of the island's electricity is produced locally through proper infrastructure, solar PV, wind, etc.

The following indicators can be gathered for the entire system explanation:

• Total installed capacity per technology (whether this is an engine generator, wind, or solar energy, CHP, etc.)
• Total energy produced per technology and year
• For any technology that consumes any type of fuel (like fossil fuels, biomass, etc.) the annual fuel consumption i.e. the primary energy consumption of the electricity sector in the island.

A connected island without any auto-production receives its electricity from the national grid. In this case, electricity is analyzed from the perspective of final energy consumption - the data should represent the total electricity consumed on the island by households, industry, and agriculture. It is recommended that this data be divided into categories, e.g. residential, primary (agriculture, forestry, mining, and fishing), secondary (manufacturing), tertiary (tourism), and transport (on the island and to and from the island). Additional data points that may be interesting include the consumption recorded at the island's point of interconnection with the mainland. If there is some degree of auto-production on the island, apart from final electricity consumption, it is also necessary to consider the local electricity generation.

In addition, the accurate estimation of energy supply from RES technologies is crucial for having an efficient equilibrium. More details about methods and tools for RES potential calculation are presented in the sub-section.

Figure 1 Indicative mapping of the energy produced per technology and year

Heat and/or cooling may be required on the island, depending on the weather. This category should include the consumption of boilers, heat pumps, air conditioning systems, or any other heating or cooling device or technology used on the island over the last (or most recent) year. Some appliances such as A/C systems, electric boilers or heat pumps may use electricity to produce heat or cold. In this case, their consumption could either be allocated to electricity or to heating/cooling.

Possible sources for the required information are as follows:

• Electricity companies operating on the island.
• Energy cooperatives' operation on the island.
• Transmission and Distribution System Operators.
• Statistics agency in the country/region, either through databases, annual reports, etc.
• Gas/fuel providers.
• Unless there is an industry or another sector on the island that requires a specific type of fuel, it could be assumed that the rest of the fuels are consumed for heating (unless there is electricity production on the island that requires a specific type of fuel).
• The Odyssee-Mure project provides average data on heating consumption per dwelling and per country. By estimating the island households' heating consumption with these data, we could also get an idea of the conditions on the island.