1. General Description
Biomass microgrids are designed to operate autonomously, utilizing locally available agricultural residues (e.g., straw, grape marc, olive pits) and forestry by‑products (e.g., wood chips, branches). Through specialized gasification units or anaerobic digesters, the organic material is first converted into biogas (a mixture of CO₂ and CH₄), which is then burned in suitably adapted engines or turbines to generate electricity. At the same time, the heat released in the process is recovered via heat exchangers for domestic hot water or space heating. The result is a closed‑loop energy system that minimizes the use of imported fossil fuels and significantly enhances the local energy self‑sufficiency of the islands.
2. Introduction: The Challenge of Island Systems
To date, many Greek islands in the Aegean Sea meet a large portion of their energy needs with diesel fuel or liquefied petroleum gas, which must be shipped in by tanker—a process that adds 20–30% to the fuel’s final cost and carries its own CO₂ emissions from maritime transport. Moreover, international fossil fuel prices are highly volatile, with sudden spikes immediately reflected in consumers’ electricity bills. In this context, decentralizing energy production and tapping renewable resources locally becomes not only economically imperative but also environmentally necessary.
3. What Are Biomass Microgrids?
These systems typically include:
Gasification units: Dry biomass is fed into a high‑temperature (above 700 °C) combustor with controlled oxygen supply. The process produces a synthesis gas (CO, H₂, CH₄) which, after cleaning through filters, is routed to internal‑combustion engines.
Anaerobic digestion: Liquid or semi‑liquid wastes (olive mill wastewater, animal manure) are placed in sealed tanks where microorganisms produce biogas at 35–55 °C. The biogas is burned in generators, while the nutrient‑rich digestate can be returned to the soil as a biofertilizer.
Combined heat and power (CHP) modules: These co‑generate electricity and useful heat—typically achieving 25–35% electrical efficiency and 50–60% thermal efficiency—thereby maximizing overall energy utilization.
Often, the microgrid also incorporates battery storage or diesel backup generators to ensure a stable supply when biomass feedstock is insufficient.
4. Advantages for Island Communities
Energy Autonomy: Local generation reduces dependence on fuel shipments and on‑site storage; even if supply lines are disrupted, the community retains power. Case studies show that autonomy can cover up to 100% of peak demand.
Environmental Benefits: Biomass combustion is considered carbon‑neutral—any CO₂ released was recently absorbed by the feedstock plants—yielding up to a 90% reduction in emissions compared to diesel. Furthermore, it prevents open dumping of organic residues.
Economic Development: Collection, transport, processing, and disposal of biomass create local jobs (technicians, operators, administrators), while service businesses support ongoing operations. Capital costs typically range from €3,000 to €4,000 per kW installed, with payback periods of 7–12 years.
5. Social Cohesion
Biomass microgrids often develop under cooperative or community‑owned models, in which residents participate in governance, revenue management, and benefit sharing. This fosters greater awareness of energy issues, transparency around costs and benefits, and a collective commitment to environmental stewardship.
6. Application Examples
Tilos Island: The S4S Tilos project combines 800 kW of wind, 300 kW of photovoltaics, 100 kW of biomass, and 2 MWh of battery storage. The hybrid setup achieves over 95% annual coverage of the island’s electricity needs, dramatically cutting diesel use.
Agios Efstratios: The “Green Island” scheme integrates 200 kW of wind, 150 kW of solar, and a 50 kW biomass unit supplying heat via a local district network. It meets nearly 100% of municipal building heating demand and a large share of residential needs, reducing heating costs by 60%.
7. Challenges and Prospects
Technical Issues: Specialized biotechnology and engineering expertise are required; prompt access to spare parts and technical support is critical, especially in remote locations.
Financing: High upfront capital expenditure calls for a mix of European grants (e.g., LIFE program, Just Transition Fund), national incentives, and private investments.
Regulatory Framework: Greece currently lacks a unified legal regime for community energy projects; permitting can take up to two years, deterring smaller investors.
Future Outlook: With the implementation of the National Energy and Climate Plan (NECP 2030) and strengthened EU funding instruments, biomass microgrids are expected to proliferate—gradually covering the smaller Cycladic and northeastern Aegean islands.