Using solar in the winter to run a solar-hybrid heat pump may have its challenges, but there's a huge upside
We're talking solar heating using photovoltaic solar to create electricity to run a solar-hybrid heat pump here, not some radiative/conductive/convective device or thermal solar heating water for a swimming pool. Not that there's anything wrong with these, but, as an extension to solar-powered air conditioning, a solar-hybrid (air conditioning) heat pump also heats. And, so, there's this positive duality that heating devices alone lack.
And yet, all types of heating with solar have their challenges. First and foremost, the time of year when you likely need heat the most also, not coincidentally, is when the days are the shortest. And, the further north you live, the shorter the days get. Additionally, most areas in the United States are sunnier in the summer than they are in the winter (we feel you Wilmington, NC, and other outlier spots with cloudy summers). As such, capturing solar in the winter is exacerbated by cloud cover. Finally, the angle at which the photons travel to hit solar panels in the winter is lower on the horizon than in the summer. In the summer, the sun beats pretty much straight down, and as such, there's little-to-no diffraction of the rays. As such, panels can gather peak sun (as defined by 1,000 watts of energy per square meter) much of the day. But in the winter, when the sun needs to pass through a good chunk of atmosphere for much of the day, days just aren't as bright, and panels can't gather as much energy. Or, what if it snows? Egads, not much solar then. Of course, if your panels are tilted (ideally around 14 degrees more than your latitude in the winter), that helps, but only to a point.
And, this couldn't come at a worse time, since in most areas of the United States, you need more heat than cooling (as measured in BTUs). Why? Well, if your ideal set point is 75 degrees, in the winter, in most areas, you're more likely to see it be 35 degrees (or below) than you are to see it 115 degrees and above--note that these are both 40 degrees from your target set point. So, to achieve the required temperature difference in the winter is more work in the winter than in the summer.
But, the good news is that solar panels actually function better in the winter than they do in the summer. Solar panels are tested at 25 degrees Celsius (around 77 degrees Fahrenheit). For most panels, every degree Fahrenheit above 77 makes the panels around 1/3 of 1% less efficient. But in the winter, as the temperature dips well below 77 degrees, the panels get more efficient by this same 1/3 of 1%. So, that's good news. And, well, solar has huge advantages that burning fossil fuels don't have. The cost for fossil fuels vacillates, but tends to go up. The cost of solar panels has continued to come down, and, once the panels are purchased and installed, the power is free until the panels are no longer effective. And, most panels are still producing over 80% of their Day 1 output after 25 years.
So, although heating with solar has its challenges (availability, for instance), all heat is good heat, and heat that solar can provide is the best heat, since it's free heat.