These days, the term “solar energy” is almost always associated with photovoltaic (PV) systems that produce electricity from sunlight. Those systems range from a single small PV module used to maintain charge in a 12-volt battery, to acre upon acre of land covered with thousands of PV modules to create a “solar farm” that, by day, generates megawatts of power. Where I live in upstate New York, the latter are sprouting up in many local communities. Utility-scale solar developers are leveraging significant investment incentives provided by state and federal governments on their quest to reach 100% renewably-sourced electricity in the not-too-distant future. Landowners, who once made an “adequate” living from their acreage as dairy farmers, are comfortably retiring on leasing agreements made with these developers.

Few would have envisioned such a situation back in the 1970s. That’s when I got my first job with a company that designed and manufactured solar thermal collectors. Back then, solar photovoltaics was mostly reserved for remote mission critical or spacecraft applications, where the nominal $1,000/ watt cost (in 1970s dollars) was acceptable. Outside of this small niche, solar thermal applications were the norm, with much of the market focused on residential solar space heating. Houses were constructed as supporting structures for massive solar collector arrays in an attempt to approach 100% solar heating. One example, from 1978, is shown in Figure 1.