Your cited link, is also cited in the paper.
They said that with only solar, wind, and HVDC but no batteries you could get 80% renewable.
Or, with 12hr of battery but no HDVC you could get 80% renewable.
And, if you used only batteries, you could get the last 20%.
Which, is pretty good? They're not recommending you ignore other technologies, they're just trying to establish rough costs for simplified models.
They seem to think so back in 2018 anyway:
> “The fact that we could get 80 percent of our power from wind and solar alone is really encouraging,” he said. “Five years ago, many people doubted that these resources could account for more than 20 or 30 percent.”
>But beyond the 80 percent mark...Options could include nuclear and hydroelectric power generation, as well as managing demand.”
Here's where it gets cited in the current work (footnote 275):
> Critics of 100% RE systems like to contrast solar and wind with ’firm’ energy sources like nuclear and fossil fuels (often combined with CCS) that bring their own storage. This is the key point made in some already mentioned reactions, such as those by Clack et al. [225], Trainer [226], Heard et al. [227] Jenkins et al. [228], and Caldeira et al. [275], [276]. However, while it is true that keeping a system with variable sources stable is more complex, a range of strategies can be employed that are often ignored or underutilized in critical studies: oversizing solar and wind capacities; strengthening interconnections [68], [82], [132], [143], [277], [278]; demand response [279], [172], e.g. smart electric vehicles charging using delayed charging or delivering energy back to the electricity grid via vehicle-to-grid [181], [280]–[281][282]; storage [40]–[41][42][43], [46], [83], [140], [142], such as stationary batteries; sector coupling [16], [39], [90]–[91][92], [97], [132], [216], e.g. optimizing the interaction between electricity, heat, transport, and industry; power-to-X [39], [106], [134], [176], e.g. producing hydrogen at moments when there is abundant energy; et cetera. Using all these strategies effectively to mitigate variability is where much of the cutting-edge development of 100% RE scenarios takes place.
> With every iteration in the research and with every technological breakthrough in these areas, 100% RE systems become increasingly viable. Even former critics must admit that adding e-fuels through PtX makes 100% RE possible at costs similar to fossil fuels. These critics are still questioning whether 100% RE is the cheapest solution but no longer claim it would be unfeasible or prohibitively expensive.