“Solar” Air Conditioners

In Uncategorized by African Energy

It seems like a lot of people have questions about DC or “solar” air conditioners lately – the name seems to imply that these air conditioners could run easily from a solar system whereas the conventional AC air conditioners seem to draw too much power.  Sorry to say that in our experience, the laws of physics have not yet been suspended, and it still takes the same amount of power to cool a given mass of air, whether you do it with AC or DC power.  We don’t see much advantage in buying a DC air conditioner in most cases and either a DC or AC unit can be run from solar, if you are prepared to pay the cost.

Here is our reasoning:  Yes, there should be some efficiency gain from running a DC motor direct from a battery bank vs. running an AC motor through an inverter.  But with good motors and inverters, that efficiency gap should not be more than about 15%.  If the area to be cooled (BTU load) is very small and an inverter would not otherwise be required, then it may make sense to use a DC air conditioner.  A telecom cabinet or control room would be a good example of this application.

But, if the requirement were for an office or a home (as we suspect most are) then the client is very likely to require a good inverter anyway, and very likely to have a significant cooling load.  It would be difficult to justify the purchase of a DC air conditioner with the 15% theoretic efficiency gain that it would provide.  As a practical matter, AC air conditioners are mass produced, are available with the same efficiencies as the DC units, and are much cheaper to purchase.  We don’t normally recommend DC air conditioners for the same reason we don’t recommend DC TV or DC hair dryers or DC blenders…good inverters have changed the world – and they will run all of those devices on AC with only a very small efficiency loss.