Solar-powered heating with high-tech heat pumps is now here
What exactly is solar heating? Unlike solar air conditioning, which seems almost magical in its ability to make use of the sun which ultimately makes a home or other space almost unbearably in the summertime, solar heating seems more logical. We've all taken advantage of solar heating in the past. I remember as a youth gravitating to the south-facing living room windows to capture the radiative heating in the late afternoon, even as some of that sunshine was bouncing off of the snow just a few feet away. And, thermal solar panels on back roofs with water pumped through them to heat swimming pools have been commonplace and effective for over 50 years.
But today, another type of solar heating has emerged with the solar-powered heat pump. This type of solar-powered heating is becoming relevant firstly because of the precipitous cost decrease in photovoltaic solar panels. Swanson's Law, coined by Richard Swanson of Sunpower, states that for every doubling of worldwide production capacity of photovoltaic solar panels, the price of the panels comes down 20%. And, in line with this curve, the cost/watt of solar is now around $.15, or around 1/8th of what it was 10 years ago. Next, the advanced electronics in variable-speed heat pumps now allow the motors to speed up and slow down based on available sun and to avoid the ability-to-use-solar-crushing inrush, or surge, current that starting up a heat pump required in the past. So, less power is needed, and these units can run without batteries because they adjust to the available sun. Many of these units are hybrid, so they can be 'plugged in' for grid power to seamlessly fill in on cloudy days or at nighttime. Finally, the dubiously-named Inflation Reduction Act is offering up 30% investment tax credits for solar power installations (on both labor and materials) and 30% on EnergyStar certified heat pumps (again, on both labor and materials). And, for those who qualify, some local jurisdictions will be offering up even additional savings via rebates on heat pumps. The money tree is raining in the solar heat pump direction!
But, setting aside the environmental benefits of heat pumps, will a heat pump, solar or not, work to save you money on a monthly basis long after these up-front rebates and tax credits have been garnered? Since heat pumps run off of electricity, and most heaters now run using natural gas, you need to put the math to it (and we'll do that in a blog post showing a real-world example based on MI electric and gas rates soon, so stay tuned). Right now, natural gas rates are higher than they've been in years. So, heat pumps have that going for them. But, unfortunately, many electrical utilities are now increasing their electrical prices, in part because many still generate most of their power from burning natural gas. In Georgia, where rates are clocking in at around $.119/kWh, a heat pump likely will save you money, especially since, yes, if it's solar hybrid, there's a good amount of sun there to further lower the use of grid power. In Connecticut, not so much sun in the winter, and electric rates average a whopping $.25/kWh. It'd be worth doing the due diligence before jumping in on a heat pump just to get the rebates. Having said that, lots of folks are going solar in CT because these enormous rates make solar cost justified.
The challenge of solar heating in the winter is that there's not only less sun (since the days are shorter), but a good chunk of the photons which shoot straight down in the summer get refracted by the atmosphere when they come in at a lower angle of trajectory in the winter. What's the good news? Solar panels gain around .2% efficiency for every degree below 77 degrees Fahrenheit. So, winter's wonderful for solar panel efficiency. And, if there's snow on the ground (but not on the panels), that snow really can help reflect light onto the panels if the panels are properly tilted (to your local latitude less 14 degrees in the winter, by the way).
Why is solar heating already working in much of the world, and why will it certainly win even in colder, less-sunny spots in the future? In addition to the technology gains allowing heat pumps to efficiently run solar and the fact that solar panels will continue to decrease in cost, the other ace is battery storage, which is following a similar pattern of cost decreases as solar panels. Integrated solar heat pump systems with battey storage will help make the analysis always favor heat pumps over fossil fuels in the near future, allowing those using them to do good for the environment while they're saving money.