Solar Air Conditioning – Direct PV DC – Project Updates and Video

Note: ongoing project updates will be posted towards the end of this page.

Thinking in terms of a grid-down scenario, besides food, water and shelter, air conditioning is one of the most important modern benefits to society. There is nothing that can boost morale like a good cold AC and a place to rest after a hard days work.

However, today’s air conditioners are almost exclusively AC (Alternating Current) powered and therefore require an inverter to operate. Ductless mini-split heat pumps, while very popular, are complex pieces of engineering. Repairing them is not something the average person can do.

In an unstable world, it may no longer be possible to maintain such top-heavy and complex technology. We might need something simpler… but who will create these simpler options?

RELATED VIDEO: My first direct solar power window AC!

Learning About DIY HVAC

I lacked the skills and knowledge to work with compressors and refrigerants. Although I had been studying refrigeration on my own for about 3 years, I had very little hands on experience. For that reason, I finally took the plunge, and purchased a gauge set, refrigerants, various compressors, copper pipes, vacuum pump and more.

As part of this research, I challenged myself to build a direct solar-powered compressor-based window air conditioner. I did not think it was going to happen. Due to health problems and so many other battles and obstacles, such a project seemed out of reach and kind of crazy. However, the project was eventually successful.

Although the AC is not completely finished, I have had it in my window cooling off my shop with only 4×100 watt solar panels. It works! The evaporator coils are temporary coils of copper tubing. They get very cold and frost up which is pretty neat!

My Real Goal: PV-to-Load Solar Direct Drive Split Air Conditioner

Since 2021 I have been on a quest to investigate various direct-drive PV DC solar air conditioning options. The project goals were as follows:

1. Create an air conditioning system that can run from commodity 12-volt power, or directly from PV DC solar panels (unregulated voltage)
2. Avoid usage of complex electronics as much as possible
3. No DC-AC off electrical grid Inverter
4. No BLDC (Brushless Direct Current) or VFD (Variable Frequency Drive) circuits
5. At least somewhat “DIY friendly”
6. Keep complexity and costs to a minimum
7. Break with tradition and try something new! Why follow along and do the same things?

This is not exactly an easy goal, as HVAC (heating, ventilation & air conditioning) are not the most DIY-friendly topics out there. Nevertheless, since 2021 I’ve been chipping away at my goals…

Sorting Through The Options

My Research Into Peltier Elements for Solar Shop Air Conditioning

Peltier Elements are semiconductor heat pumps. They have no moving parts (within the element itself) and look like a slab of ceramic with wires coming out. It is a miracle of God, that a little “piece of ceramic with wires” can literally move heat from it’s cold side, to the hot side, with no moving parts. Amazing!

Despite their interesting properties, Peltiers are often overlooked by DIY solar power enthusiasts. I believe they can play a role in some appliances and devices, even if refrigerants still perform better. Each idea has its pros and cons.

By the way, if we are using Peltiers to generate power, of course they are inefficient, because that is not their ideal purpose! When moving heat, their true talent, they can be 30-45% efficient. They don’t reach the level of refrigerant and compressor-based systems. But they have many advantages. To work properly, all that’s needed are the right conditions. Peltiers have certain requirements that must be met for them to operate efficiently.

To see what they can do to cool off my workshop, I have been testing various common Peltier arrangements in my shop. All of the tests are direct-drive PV-to-Load solar powered of course.

Peltier Testing – Phase I – July 2024 – Video posted on this page

During the first round of tests I used a common device consisting of a large aluminum heat sink with 4x TEC-12705 modules. I placed it in a bath of water and pumped that water through a radiator and fan outside. Cooling with water makes a lot of sense – it’s not specialized, controlled or hard to get a hold of.

Placing a foam box on top of the cold side with a fan, a small amount of cool air came out. The device only consumed about 140w. Not much, but it was enough to encourage me to look deeper into the topic, increase wattage and improve the heat exchange.

Peltier Testing – Phase II – July 2024 – Video Posted Below

Then I doubled the number of Peltier elements to 8, doubled the size of the radiator outside, doubled the fans, and pushed 430-450 watts through. The amount of cool air coming out was actually just a little bit impressive!

During phase II tests, I could see the water cooling setup was still probably inadequate, but this did not surprise me at all.

Peltier Testing – Phase III – August 2024 – Video Posted Below

This test was with 14 direct solar drive TEC-12705 modules, pushing 622 watts. For comparison, my 5000btu window AC takes about 480 watts. An additional water pump had to be used to move more water over the radiator outside the shop. The radiator setup was able to reject the heat produced from the Peltiers, but it needs an upgrade to go any farther. I managed to get some of this testing on camera.

Direct PV-to-Load Compressors and Refrigeration

Challenges

While Peltiers are “cool”, I think compressors and refrigeration technology are awesome and I always wanted to get more into them. My interest is primarily in direct DC solar powered systems, which bypass inverters, charge controllers and battery banks in favor of directly consuming DC electrical power from the solar panel array.

But most refrigeration compressors today are actually AC (Alternating Current) powered. There are many compressors available that state “DC” (Direct Current) on the side – but in fact – they too operate from Alternating Current. Therefore, it gets difficult to drive these compressors with unregulated direct DC solar power. Typically they need some kind of complex electronic circuit to drive them. Today’s compressors may be driven by a VFD (Variable Frequency Drive) or BLDC (Brushless DC drive).

Currently I am testing various direct-drive solar compressor systems for air conditioning and refrigeration. This is a process and takes time and of course there are financial and other costs involved. So far I have tested a solar powered water chiller, and built and tested a solar powered window air conditioner (video posted at the top of this page).

Below is a picture of a direct solar powered window AC I built to learn about refrigeration. It uses R-134a refrigerant and is directly powered by 4x 100-Watt 12v solar panels. This machine will run all day with solar panels, but doesn’t mind being powered by the 12-volt LiFePo4 batteries in my workshop either.

Summary & Ongoing Updates

This page is an overview of what I am trying to accomplish. It will be updated with project notes and videos as I have time. Please check back later for news about this research. If you are interested in this type of work, please consider subscribing to my YouTube channel, which has a lot more detail on the work I am doing.

The split solar split AC project has been under way since about 2021. However. as of July 2024, I also started working on a “super mini” version of the split system as well. Hopefully this project will be shared soon if I can make enough progress on it…

Thanks for reading! -Dave, SPE

RELATED VIDEOS