It is often claimed that marine renewable energy alone could meet the electricity demand of
current and future human societies. However, such claims are based on highly uncertain estimations
of the global potentials of marine renewable energy sources (including tidal, ocean currents, wave,
offshore wind and salinity and thermal gradients), and do not take into account the embedded energy
of current technologies. To better understand the effective potential of marine energy, we conducted
a literature review of its gross, technical, economic and sustainable potentials, as well as the energy
return on investment (EROI), and estimated the net energy potential. We found that all marine
technologies could provide a maximum energy surplus of 57,000 TWh/yr. This figure goes down to
5000TWh/yr when excluding offshore wind. The previous figures do not include the contribution
from ocean currents, for which no reliable estimates of global potentials and EROIs could be obtained.
Due to its high upfront costs and environmental impacts and low social acceptance, no additional
tidal range capacity expansion is envisioned. Similarly, the combination of a low sustainable potential
and the low EROI makes the large-scale exploitation of salinity gradients unlikely with current
technologies. Including all technologies, the average EROI of marine energy is 20, but excluding
offshore wind reduces the average EROI to 8. While we did consider sustainability constraints
for some marine energy sources, our estimation of marine net energy potential primarily relied
on technical factors and did not account for economic and legal constraints. Therefore, the results
presented here should be interpreted as an upper bound for the actual net energy contribution of
marine energy sources to the global energy mix.
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