  This paper introduces the full Low-carbon Expansion Generation Optimization
(LEGO) model available on Github (https://github.com/wogrin/LEGO). LEGO is a
mixed-integer quadratically constrained optimization problem and has been
designed to be a multi-purpose tool, like a Swiss army knife, that can be
employed to study many different aspects of the energy sector. Ranging from
short-term unit commitment to long-term generation and transmission expansion
planning. The underlying modeling philosophies are: modularity and flexibility.
Its unique temporal structure allows LEGO to function with either chronological
hourly data, or all kinds of representative periods. LEGO is also composed of
thematic modules that can be added or removed from the model easily via data
options depending on the scope of the study. Those modules include: unit
commitment constraints; DC- or AC-OPF formulations; battery degradation; rate
of change of frequency inertia constraints; demand-side management; or the
hydrogen sector. LEGO also provides a plethora of model outputs (both primal
and dual), which is the basis for both technical but also economic analyses. To
our knowledge, there is no model that combines all of these capabilities, which
we hereby make freely available to the scientific community.
