I have always been a supporter of taxpayer money being used for R and D when it benefits the US as a nation.
For example: NASA, military or medical research that has a spill over to providing a benefit, service or convenience to the American public. Everything from vaccines to mircowave ovens came from this model.
For US taxpayers to get into the venture capital game is wrong.
I say, provide the R and D money for the small solar company to develop its product because of the benefits that might be had providing improved solar power on government buildings, but the capital required to ramp up production and bring the product to market should be fronted by, and the risk assumed by, the private sector.
Unless the production of an item has an immediate impact on the greater nation, for example uranium processing in WWII, there is no need for the government to get involved in the creation or expansion of production environments.
That is crossing a line into a soviet style planned economy. And we all know how that turned out for them.