irrelevant if what you need the energy for is making methanol to run your tanks and missiles on
somewhat relevant, but not overwhelmingly, if what you need the energy for is running the tank and missile factories; solar intermittency just means you can only run the factories for one shift instead of three, so your capacity is three times as expensive
but historically many factories have only run one shift most of the time anyway so clearly this is not an overwhelming factor
being able to use processes that your competition would find outrageously inefficient because you can afford orders of magnitude more energy is a bigger advantage
think of victorian-era industrial-revolution britain against the zulus
The energy costs of solar at night are infinite, unless you add plenty of storage, whereas the energy costs of nat gas stay roughly the same at night