## UC Berkeley / Lawrence Berkeley Laboratory

#### Search spaces and algorithms for inverse material design and other renewable energy applications

**Peter Graf, National Renewable Energy Laboratory**

##### September 18th, 2013 at 3:30PM–4:30PM in 939 Evans Hall [Map]

In this talk I will describe efforts at NREL to use simulation
optimization in renewable energy research, with particular emphasis on the
search for better materials for organic and inorganic photovoltaic cells.
Depending on how we formulate the problems, the search spaces and solvers
come in a wide variety of "shapes and sizes": continuous, discrete, mixed,
large, small, hierarchical, linear, nonlinear, analytic, black box, cheap,
expensive, etc. A major theme is the idiosyncratic nature of the search
spaces, which arises primarily because the natural representations include
domain specific structure. In fact, the more canonical the
representation, the less effective the algorithm, because often
constraints can be built into the representation that can dramatically
decrease the size of the search space. Unfortunately, this sometimes
complicates the search (*e.g.*, off-the-shelf methods are hard to apply).
Another important characteristic is that due to the discrete nature of
molecular space, there is often no natural distance metric to make use of.
An additional challenge is that the simulations are often expensive, not
particularly robust, and not well validated. These points will be
illustrated via discussion of successes and failures in several domains,
especially organic and inorganic semiconductors, but also including
techno-economic analysis of wind energy, multi-scale battery simulation,
building energy optimization, systems biology parameter estimation, and
renewable energy deployment and grid modeling.