Hospitals consume a lot of energy for various operations compared with other buildings. They have complex energy systems and use conventional energy sources, mainly electricity, heating oil and natural gas. However various renewable energies can be used in order to cover their energy requirements resulting in low or zero CO2 emissions from them. Solar energy, solid biomass and geothermal energy can be used for that generating electricity, heat and cooling. A case study of a hospital in Crete-Greece proves that the combined use of solar thermal, solar-PV, solid biomass and low enthalpy geothermal energy with heat pumps can cover all the energy needs of it resulting in zero CO2 emissions. These renewable energy technologies are reliable, cost effective and present many environmental benefits. For a 300 beds hospital in Crete, Greece the investment cost for using solar thermal, solar PV and solid biomass in order to cover all its energy needs is estimated at 7, 434 € per bed and for using solar thermal, solar PV and low enthalpy geothermal energy with heat pumps 8, 679 € per bed. Annual CO2 emissions savings due to use of the abovementioned renewable energies are estimated at 10.9 tons per bed.

Tourism like other industries utilizes fossil fuels and emits greenhouse gases into the atmosphere. Estimation of carbon emissions due to tourism in a popular travel destination like the island of Crete, Greece would indicate the ways that emissions could be reduced in order to mitigate climate change. Carbon emissions in various sectors of tourism in Crete including international and domestic transport, accommodation and other activities have been calculated. Available data regarding tourist arrivals, modes of transport, overnight stays carbon emissions in various modes of transport, in accommodation and in other activities have been used in calculations. Annual carbon emissions have been estimated at 488.77 kgCO2 per visitor. International and domestic flights combined with arrivals by ships in Crete have the highest share to the total carbon emissions at 80.69%. Carbon emissions due to tourism including international flights have been estimated at 3.67 kgCO2 per inhabitant in Crete which are high, compared with total carbon emissions in the island at 6.2 kgCO2 per inhabitant. Results indicate that reduction of carbon emissions in international flights is the most appropriate and effective way for reducing carbon emissions due to tourism in Crete.

Heating greenhouses results in higher productivity and better quality of the produced crops mainly in Northern climates. Apart of conventional fuels already used for heating them, renewable energy sources are expected to play an important role in the near future. Among them solar energy, geothermal energy and biomass have been used in various greenhouses all over the world. A successful operation of a greenhouse cultivated with flowers during 2012-2014 in Crete-Greece heated with olive kernel wood proves that this solid fuel is a cheap energy source which can cover all the heating needs of the greenhouse lowering at the same time its CO2 emissions due to energy use. Olive kernel wood is an endogenous, renewable and CO2 neutral energy source in areas where olive trees grow. Additional installation of a Photovoltaic system in the greenhouse already heated with solid biomass in Crete will result in zeroing its CO2 emissions due to energy use in it. Since the heat demand in the greenhouse is much higher than the electricity demand, replacement of fossil fuel with a renewable fuel results in significant decrease of CO2 emissions due to energy use.

Use of renewable energies in rural areas in the island of Crete, Greece has been investigated. Crete has rich indigenous renewable energy resources which are currently utilized for covering part of its energy requirements. Various renewable energy technologies used for heat and electricity generation in the island have been examined. Solar energy, wind energy, hydro power, biomass, and low enthalpy geothermal energy are already used. The total installed electric power of renewable energies in Crete, located mostly in rural areas, is approximately at 30% of the total electric power installed. They currently generate more than 20% of the island’s annual electricity needs. More renewable energy applications are foreseen in the future in rural areas in Crete as soon as its electric grid will be interconnected with the country’s continental grid. New renewable energy technologies, which are not currently used, could generate in the future heat, cooling, electricity, and vehicle’s fuels in the island. Their use will have positive impacts including the promotion of energy investments, lower use of imported and polluting fossil fuels, de-carbonization of the island’s energy sector as well as creation of new local jobs. It is indicated that the rich renewable energy resources in Crete could provide almost all of its annual energy needs. This will result in Crete’s transformation to a low or zero carbon economy in accordance with EU targets for zero carbon emissions in the next decades complying with the global goal for climate change mitigation.

The energy analysis of five summer operating hotels in Crete, Greece was implemented and their average annual energy consumption has been estimated at 149 KWh/m 2 and 19.4 KWh/p.n.s. Their average annual CO2 emissions due to energy use have also been estimated at 12.1 kg CO2/p.n.s.. Hotels in Crete utilize various renewable energy technologies with solar thermal energy being the most widely used. Apart from solar thermal energy, solar cooling, passive solar, solar-PV, solid biomass burning and low enthalpy geothermal energy with heat pumps have also been used in various cases. Since some of these technologies are currently cost effective having at the same time many environmental benefits , it is expected that in the future renewable energy technologies will have more applications in providing heat , cooling and electricity in hotels in Crete. Use of various renewable energy technologies in hotels could result in zeroing their CO2 emissions due to the energy use in them. The Greek government currently subsidizes the use of energy saving and renewable energy technologies in hotels aiming in reducing their high energy consumption and the use of the polluting fossil fuels in them.

Investigation of energy consumption and carbon emissions in an Academic Institute located in Crete, Greece has been implemented. The possibility of using sustainable energy technologies for covering all its energy needs has been examined. It has been found that the main energy source used was electricity while renewable energies had a small share in the total energy mix. The specific energy consumption has been estimated at 164.96 KWh/m2 and the annual CO2 emissions at 110.64 kgCO2/m2. The combined use of solar thermal energy, solar photovoltaic energy and ground source heat pumps could cover all the annual energy requirements in the Academic Institute zeroing its net carbon emissions. These energy technologies are mature, reliable and commercially used while solar energy is abundant in Crete, Greece. Solar electricity can generate all the electricity required annually with net metering regulations. The investment cost of the required sustainable energy systems to zero the net carbon emissions has been calculated at 184.32 € per m2 of its covered surface. It is concluded that if some financial support in the energy investments will be offered then the Academic Institute would become carbon neutral.

The possibility of creating zero CO 2 emissions residential buildings due to life cycle energy use in the island of Crete, Greece has been examined. In a typical residential building located in Crete, Greece, its annual operating energy has been appraised at 170 KWh/m 2 and its embodied energy at 30 KWh/m 2 . Various locally available renewable energies including solar energy, solid biomass and low enthalpy geothermal energy with heat pumps have been considered for generating the required heat and offsetting the grid electricity used. Their technologies are mature, reliable and cost-effective. Offset of the annual grid electricity use in the building with solar-PV electricity is allowed according to the net metering regulation. For zero carbon emissions due to embodied energy of the building, generation of additional solar electricity injected into the grid is required. A mathematical model has been developed for sizing the required solar-PV system installed in the building in order to offset the grid electricity use. For a residential building in Crete, Greece with a covered area of 100 m 2 , the power of the additional solar-PV system has been estimated at 1.6 KWp and its cost at 2400 €. In the current work, it is indicated that the creation of a zero CO 2 emissions residential building due to life cycle energy use in Crete, Greece does not have major difficulties and it could be achieved relatively easily.

The role of solar energy for heat and power generation is very important during the transition to a low carbon economy. Floating solar photovoltaics consists of a novel and rapidly growing sustainable energy technology having many advantages compared to conventional ground-mounted solar photovoltaic systems. Aim of the current research is the investigation of the possibility of installing floating photovoltaics in the existing water reservoirs in the island of Crete, Greece. Data on existing water dams in Crete were used and the nominal power of floating photovoltaics as well as their potential for electricity generation were evaluated. It has been estimated that the nominal power of floating photovoltaics that can be installed in these water dams, with coverage ratio at 0.1 to 0.3, varies between 55.76 MWp to 167.3 MWp while the annual electricity generation from the floating photovoltaics varies between 78.3 GWh to 234.9 GWh. The annual electricity generation from the abovementioned floating panels corresponds at 2.57 % to 7.72 % of the annual electricity consumption in Crete in 2018. Our study indicates that floating solar photovoltaics can be installed in the existing water dams in Crete generating significant amounts of green electricity having also various environmental co-benefits. The current work could be useful to policy makers, local and regional authorities, energy companies as well as to owners of the water dams in the island.