10 fact about solar air conditioning you may not have known

  1. It works today since solar panels are much less expensive than they were previously.  The cost per watt of solar panels roughly follows a downward cost trend known as the 'Swanson's Law,' named after Richard Swanson of one of the founders of solar power, Sunpower Corp.  The rule states that every time the number of solar panels doubles, the cost  per watt comes down around 20%.  In 2000, around 1,000 megawatts of solar had been deployed worldwide, and the cost per watt was around $5.  Now, with over 1,000,000 megawatts deployed, the cost is around $.25/watt.  This means that you only need 2 or 3 solar panels per ton of air conitioning.  You don't need to cover your whole roof with panels for this to work.
  2. It works today since traditionally expensive and complex electronics have been simplified to allow the unit to run at variable speeds and directly using the direct-current solar power.  Before, the ability to change the frequency of the sinewave pattern of electrical pulses used to spin a motor was only available for large, expensive motors.  So, you'd need to have a separate inverter to change the DC power to AC power. Now, an $80 printed circuit board (yet with some very complex electronics) can be deployed to make an air conditioner compressor move slower or faster when fed DC solar power.  This is important, since it allow the compressor (and fan motors) to speed up and slow down based on the amount of sun power available to run a unit.  Traditional on/off air conditioning compressors require 4 to 6 times more current at startup than their run current.  Variable-speed motors need less than 1/3 of the startup current comprared to their run current.  They start slowly and build up speed.  Perfect for running them off of solar.
  3. By being variable speed, the units provide more comfort and needs less sun.  The amount of refrigerant traveling in the system varies (appropriately called ‘Variable Refrigerant Flow’) allowing more or less cooling. The refrigerant running through the system works hand-in-glove with this variable motor speed.   And, as the compressor speeds up, the electronics in the EEV attune to this increased speed and add more refrigerant.  More sun means more cooling, but the unit can run to give some cooling just using solar panels even if there's very little sunlight. The faster the compressor runs with more refrigerant, the more cooling is available.  
  4. The system’s a heat pump, meaning that it has a reversing valve, and not only cools by transferring heat out of your home in the summer, but heats by transferring the ‘heat’ outside into your home in the winter. Yes, ‘heat’ is a relative word, but even in the winter, there heat that can be captured outside when the refrigerant passing through the coil on the outside part of the heat pump is even colder than the outside.  This seems magic, to move heat from the outside when it's, say, 15 degrees Fahrenheit outside into the inside, but that's exactly what happens.
  5. Since there’s an anticipated need for 2.5x more air conditioning by 2050 than now (https://www.iea.org/news/air-conditioning-use-emerges-as-one-of-the-key-drivers-of-global-electricity-demand-growth, mostly as emerging markets start to get air conditioning), the need to run units using solar will be intensified to avoid a vicious cycle of more air conditioning using fossil fuels making the planet even warmer. It'll also be easier to deploy solar air conditioners in emerging markets, where much of this growth is anticipated, since no grid power is needed to run them.
  6. Hybrid solar air conditioners can work at nighttime even without batteries. They plug into the grid when it’s cloudy, or at nighttime, when energy cost are typically less expensive.  Solar, when it's available, is always optimized and prioritized, but when it's not available, hybrid unit work using grid power in a super-efficient way so as to lower grid power consumption. So, you can run one with all solar power, all grid power, or a combinatin of both.
  7. True off-grid systems need batteries. And, much like solar panels, the cost of battery storage is also coming down exponentially.  Lithium-ion batteries are appealing because they can be fully discharged (unlike lead acid batteries, which lose their ability to rechage if they're continuously discharged more than 50%).  And, their cost have come down around 75% from where they were 10 years ago (https://ourworldindata.org/battery-price-decline).
  8. Solar air conditioning units, in most cases at this point, don’t totally replace a whole-house cooling or heating system. So, what good are they?  Well, they can be used for spot cooling or heating if they’re placed in the location where you spend the most amount of time.  As such, you can keep your main unit set to a less-expensive setting (a bit warmer in the summer and a bit cooler in the winter) and still save a lot of money.  So, these units are often only 1 or 2 tons, but they capture the 'low-hanging fruit' of the heating or cooling load.
  9. Alternatively, solar also makes it affordable and practical to air condition and heat places and in ways that traditionally don’t warrant air conditioning. Since it’s free to run, units can be placed in garages, RVs parked in outdoor storage, or barns.  Since they run for free, it's now practical for, say, a Main St. retailer to keep his front door open all day long through the summer.
  10. Solar air conditioners are simpler to implement than whole-house solar, since their solar arrays are normally only around 1.5 kWh of plug-in solar panels and don’t require net metering (a messy process requiring permitting and local utility approval).  Net metering becomes less viable every day because utilities are often at battle with solar companies, since utilities don't like acting as the free battery to the solar industry, leaving public utility commissions to act as moderators.  So, there's an inherent future risk to net metering, since it in most communities, there's no set-in-stone long-term contract to guarantee it will be available.