Concur, the correct answer would be about 20,000 plants (within an order of magnitude).
We’ve been operating a 1MW plant sitting on about 5 to 6 acres in SoCA, and it works fairly well. You can track the output with the daily solar angle fairly well. Off at night on in the morning.
One weakness in these projects is that they tend to be quickly finances, insufficiently designed for any maintenance aspect, are installed virtually maintenance free, then simply left to deteriorate. Whomever is going to be left to foot the maintenance and demolition charges should have review input on the initial design.
Typically, such solar projects are better sized for households at about $30-$40k a pop for say a 4kW generating capacity (about 750W per square of roofing).
One weakness in installing on the roof, is that they have to be removed when the structure is reroofed or when there is a roof leak.
They work fairly well on sunshades, such as carports where occasional roof leaks are inconsequential.
IMHO, a better investment would be to build carports over large parking areas such as shopping malls, or airport parking, and install the photovoltaics on them.
Solar heating is generally more efficient and saves more money by absorbing solar heat into a water filled copper coil, painted black with reflectors behind it, in a thin sheet shell. Simply looped and can get water up to 140 deg F fairly quickly. When tied to an insulated water tank, the hot water can be kept warm for several hours and reinforced with a secondary heat source for late night winter requirements.
Steam presents other problems in corrosion which tend to favor medium temperature hot water instead of steam as a heat medium for utility use in a campus or district wide setting.
In this project, 1 sqmi at 640 acres, or 2 sq miles of solar PVs seems a bit poorly though out especially at $15,000 per acre. Desert land is only worth about $26 -$40 /acre undeveloped. It moves up to $2k-5k per acre only after two lane asphalt roads, sidewalks and fire mains are installed around areas supporting 50 occupants each, so when subdividing a 1 section (1sqmi) area into residential lots, the value goes up with the water main and traffic circulation routes installed.
At $14,000/acre, it must be irrigated and robust arable farmland.
$14k/acre is about what FL grove land is going for. The author may have this figure wrong,