More Efficient Solar Powered Air Conditioner Developed in Australia

© water ammonia cycle/ Paolo Corrada

The solar powered air conditioner is a holy grail, an answer to so many problems. Perhaps the most attractive solution seemed to be the absorption cooling system, the same kind that is used on propane fridges and has been used in big commercial systems for years. It seemed simple: just put a solar collector on the end instead of the propane or natural gas, but it just never seemed to happen.

That's why I was so excited to see headlines in Physorg like Queensland University of Technology engineer develops electricity-free home cooling system It goes on:

Paolo Corrada, a PhD student in QUT's Faculty of Science and Engineering said the system he has designed cuts energy consumption by 90 per cent.

In fact, Corrada has proposed a solar collector running an ammonia based absorption air conditioning system, but has made it more efficient by using the waste heat (there is a lot of it) to heat domestic hot water, a sort of co-generation system that increases efficiency. He notes in his report that there are some problems:

© It's complicated / Paolo Corrada

It it is evident that the system has some limitations that need to be addressed for a practical application of this technology. A storage tank is required to make the domestic hot water available around the clock. Also, the availability of cooling power does not match with the cooling request; after 6.30 pm and during the night, the demand for cooling could be still relevant because of the temperature and/or the humidity.
These limitations can be easily overcome installing storages, but the cost of such a system will be increased; to reduce the cost, a reduction of the cooling capacity could be considered if compensated by increasing the insulation of the walls, roofs and windows of the standard household.

This seems to be the crux of the problem; it's complicated. the Broad Corporation in China ran into many of the same issues when trying to build commercial scaled solar powered absorption units. Six years ago I thought they had the next big thing.

As the costs for all the plumbing and storage for the absorption air conditioner go up, the price of photovoltaics keep going down. Earlier this year all of my preconceived notions about hot water heating were turned upside down by Martin Holladay of Green Building Advisor, who made a strong case for heating water with electricity from photovoltaics. Besides the issue of the imbalance of supply and demand, Holladay notes:

Solar thermal systems have lots of piping, valves and pumps. I have learned from the sad experience of my interconnected hydronic heating and domestic hot water system that you don't want your basement looking like the set for Das Boot, that simplicity matters a lot.

I am wondering if the solar powered air conditioner might not be in the end a similar approach: 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. We are almost there.