Roger, I'd say that the issue may not be quite as simple as Pielke suggests. Most things involving energy tend to be complicated.
However, the gist of his point seems reasonable. By pursuing multiple, conflicting objectives, government actions often lead to suboptimal results
If the goal of US policy is to help Africa develop economically, and reduce poverty, there's no reason to focus aid exclusively on renewable energy options.
As for natural gas, this Ernst & Young report suggests that the potential for natural gas development in Africa is substantial:
It may well be that in particular places in particular countries in Africa, investments in gas, oil, maybe even coal ('clean' or cleaner at least) could yield greater overall benefits per dollar than investments in wind farms, solar panels, and such.
Of course, as you and I both have noted, there certainly can be local circumstances where renewable/distributed energy solutions may be the most cost-effective.
This is where geopolitical considerations get more complex. One might posit that it could burnish the US image as a 'climate protection' advocate to cherry pick the productive renewable projects on which to target its investments. That might not handicap Africa's ascent from poverty if there were abundant other sources of investment available to support natural gas and other types of projects the USG spurns. But even if that were so, it still may not serve US strategic interests to indulge such a bias.
For one thing, China has the capacity and ambition to use investment as a strategic tool to further its influence in Africa (and elsewhere) in ways that often are contrary to US interests. Nor does the USG ceding potentially productive investments to other countries seem consistent with promoting US businesses, achieving positive trade balances, and so on.
President Obama's ethnic background notwithstanding, the Power Africa initiative seems another increment of the patronizing, failed "White Man's Burden" development strategy that William Easterly (among others) has criticized:
"Poverty never has been ended and never will be ended by foreign experts or foreign aid. Poverty will end as it has ended everywhere else, by homegrown political, economic, and social reformers and entrepreneurs that unleash the power of democracy and free markets."