Why solar-powered air conditioners need more panel power on hot days

Here in Las Vegas in April or May, everything is hunky-dory to easily run a 1-ton variable-speed mini split heat pump with around 500 watts/hour.  But, when June rears its ugly head, and then July, look out!  Not only does the compressor consume lots more energy, but solar panels also lose efficiency based on their temperature coefficient rating (PMax).  Panels are calibrated at 25° Celsius as a starting point, and at 1000 watts/square meter of irradiance. (To check your irridiane based on seasonality, check out this handy tool: Peak Sun Hours Map & Calculator - Footprint Hero).  Most lose around .35%/°C (.194%/°F) above 25° (or above 77°F).  So, at 107°F, you'll be losing around 7% efficiency.  But, the rub may be quite different.  How much hotter are the panels on your roof than that 107°F? Maybe it's 137°F?  If so, that's 11.6% or so of loss in efficiency, or more, depending on your panel brand.  Plus there's not always (or not usually?) the perfect 1,000 w/sq. m irradiance if it's a bit cloudy or hazy. So, a good rule of thumb is that if your peak kW demand for a solar-powered air conditioner is around 1 kW (1,000w), then install around 1,500 w of solar to consistently run your Airspool solar-powered hybrid mini split when it's hot and sunny.

Oh, a bonus:  In the winter, panels actually become more efficient for each degree below 77°F.  So, if it's 50°F,  77°-50° =  27°F delta, and 27° delta x.194% = 5.24% more efficient.  So, this extra efficiency can help run your Airpsool unit in heating or cooling mode.  The only problem with this?  Well, in these cooler times of the year, the irradiance of the sun is lower, since the photons are needing to travel through more of the lower atmosphere, so, alas, you're probably not going to be able to enjoy this increased efficiency since less energy will actually be making it to the panels (due to lower irradiance).  There's always something!  Anyway, that's why it's good that Swanson's Law (https://en.wikipedia.org/wiki/Swanson%27s_law) is continuing to make solar panels cheaper so you can 'panel up' in preparing to run your Airspool unit.  As implementation of panels increases, cost/watt will continue to approach zero. 


107 degrees outside--around 1,000 watts needed to run the 1-ton unit (first below).

89 degrees outside--around 500 watts needed to run the 1-ton unit--much easier (below).  But, of course, air conditioning is needed the most on peak days like the above.  So, panel up, friends, and let the photons work their magic even in the hot hot heat.


Powered by Froala Editor