Five percent of America's electricity is used for residential air conditioning, and it is considered now to be a necessity, not a luxury. It's usually needed most when the sun is shining, so as I have noted since 2006, Solar Powered Air Conditioning Just Makes Sense. For most of that time I have been looking at absorption units that run like a propane fridge, but I recently mused that perhaps it is time for a change in the way we think about this:
I am not alone. Jamie Edens of Charleston, South Carolina read the post and wrote, telling me about his search for a solution to what he calls "the crux of our energy problem", all that coal that is being burned to generate the electricity to run that air conditioning. He also noted that there was a big movement everywhere to get off the grid, to stop paying so much money for electricity, but the real problem in doing so was the heavy load from air conditioning, and the poor efficiency of most units on the market.
I am wondering if the solar powered air conditioner might not be in the end a small, high efficiency home with a small, high efficiency air conditioner powered by a big honking bank of photovoltaics, and be done with it.
After hearing a story of how truckers had seriously efficient air conditioners that could run on batteries while they slept, he started hanging out in truck equipment shows and discovered Kingtec Technologies, a big manufacturer of direct current air conditioners for the trucking and RV market. After building a prototype that was a minor hit on YouTube, and with the help of a local Kingtec distributor, Edens convinced the company to build a unit to his specifications.
They started with very efficient 48 volt DC unit that puts out 16,000 BTUs at 850 watts, giving it an Energy Efficiency Ratio (EER) of 18.8. (Martin Holladay explains that EER is the cooling capacity of the appliance (in Btu/h) at an outdoor temperature of 95°F divided by the current draw of the appliance in watts.)
They added a 45 amp solar charge controller and a 20 amp/hour battery as a buffer for when clouds block the sun. All you have to do is stick it in your window like a regular air conditioner, plug in a thousand watts of solar panels and it will run all day. Add more batteries or add a grid connection power supply and it will run all night. So for $2895 plus a thousand bucks worth of solar panels, you in business.
Edens has been to China and played with the prototype. Comparing it to his prototype, he writes:
The new air conditioner blow three times harder and has twice the BTU output. The efficiency are there and it is ready to change the world. It's not a toy- the beauty of this air conditioner is that all of the solar components are installed in the air conditioner and the engineering is done for you. All you need to do is plug in your solar panels and turn the unit on.... Air conditioning doesn't need to burden to the grid, our finances and contribute to global pollution. It can contribute a new start to clean things up and sustain the earth for the long run.
16,000 BTUs is not comparable to a typical home air conditioning unit; it's a big window unit that might normally condition 600 square feet. But if you combine it with an equally efficient home, you might have something here. After I mused about a photovoltaic powered AC unit earlier I wrote Martin Holladay at Green Building Advisor for his thoughts and he replied:
So, if you want to minimize your air conditioning bill, install low-solar-gain windows on your west (and perhaps east) walls, include wide roof overhangs, install deep attic insulation, minimize your air leakage, install an efficient air conditioner ... and then install PV, as much as you can afford. In other words, I agree with you.
Jamie Edens and Kingtec have built a neat little package that runs on a lot less than my "big honking bank of photovoltaics"; combined with a small home designed around its output (not a difficult thing to do) and you've got that holy grail I've been looking for: the effective and affordable solar powered air conditioner.