<p>This article investigates the characteristics, operation and challenges of zero carbon microgrids, including size, generation from renewable sources, energy balance, and costs. An isolated zero-carbon microgrid is powered exclusively by renewable energy sources. It utilizes energy storage technologies, such as long-duration batteries or hydrogen storage, to mitigate intermittency and ensure a reliable power supply, allowing it to meet demand even under conditions of low production or high variability. The temporal variability between generation and load has technical and economic implications for microgrid sizing. This mismatch can be mitigated by combining renewable sources with diverse intermittency profiles, affecting both the storage system and the size of the generating units to be installed. This article formulates the sizing problem of an isolated microgrid designed to meet all load requirements solely through renewable sources and storage. The implications of this objective are analyzed and discussed, and sensitivity analysis studies are conducted to explore potential load shedding agreements and their impact on the solution. Solar, wind, and tidal energy exhibit a good degree of complementarity and help reduce storage requirements. However, the high cost of storage makes the oversizing of renewable sources even more attractive to ensure 100% load supply. On the other side, it was observed that allowing a load shedding of only 2.5% results in an approximate 46% reduction in the total system cost. Although the studies are carried out on a small microgrid, the conclusions can be expanded to systems of any size.</p>