In this insight we continue our discussion of the market and operational impacts of high-penetration renewable energy systems by focusing on Uruguay, a market that has already achieved RE100. What lessons are to be learned from the Uruguayan experience over the past five years? Are there practical limits to renewable penetration? What enablers can allow higher levels of penetration? What inhibitors can slow or limit it? The headlines will say that Uruguay achieved a 100% net clean energy mix in 2018, but the reality is a far more complex balancing act of wind, solar, hydro, and even small amounts of fossil generation against power demand. Uruguay proves that RE100 can be achieved with current technology, but under a more narrowly constrained set of conditions, which are not necessarily ubiquitous across the globe.