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Pros and Cons of Solar-Powered Air Conditioners

Posted by Matt Power, Editor-In-Chief

Mar 1, 2017 12:11:00 AM

High efficiency makes plug-and-play DC-powered mini-splits viable, but read the fine print.Lezeti-Solar-Air-Conditioner.jpg

A company called Greenpath Technologies, Inc. is selling a Chinese-made brand of SEER 35 mini-splits called LEZETi. They're not the only players in this new category (see chart below,) but let's focus on them for the purpose of discussion.

One unit they offer is a completely off-grid solar-connected DC version. The other, more flexible version they call a "solar hybrid air conditioner." I just wrotean article about how mini-splits and solar are a great combination for heating and cooling at minimal CO2 footprint, so it's a topic I'm covering aggressively.

Should you consider going with one of these solar-centric units, instead of some other A/C-only brand of mini split? It depends on the end user's lifestyle and expectations. The DC-only version, in my view, would have a fairly narrow appeal, as it's currently designed. Because it's not grid-tied, it will only run in daylight hours, when cloud cover permits, and it does require batteries, even for daylight-only operation. This type of unit might be suited to a detached home office or studio, but unless you want to invest significantly in battery storage, would not perform during the critical bedtime hours, when a lot of people like to keep their space cool.

The same company's solar hybrid system, however, does not require batteries. Instead it's tied in to 220/240 volt grid power, but does not require a special contract with the utility because it does not backfeed. It taps into the grid only when the sun stops shining. Like the DC-only unit, it requires about 885 watts of power for peak cooling, so PV arrays can be fairly modest, if you're only running one unit, which is caple of cooling about 750 sq. ft., in a well insulated building. Sizing the PV array to supply "just enough" electricity could be what pushes these units into the mainstream. Someone who wants to dabble in solar can put up three panels and start saving on electricity right away.

Here's a little detail on the LEZETi unit:

"The ACDC12(B) can utilize the maximum amount of available solar power* drawn from the PV modules during the day and supplement the grid-tied utility power, with no need for batteries. Even when the sun is not shining at all, this ultra high-efficiency air conditioner (A SEER 21 rating without solar and SEER 35 with solar) will keep you comfortable and save you money using far less electricity than a normal air conditioner of the same capacity."

Let's break down the pros and cons:

Pro:  No Net Metering Dependency

Net metering is under seige in several states. Maine, for example just rolled back net metering incentives. Florida utilities have struggled to resist solar for years. Despite the fact that net metering has been shown to have a net positive impact on utility costs, politics often trumps common sense. In this hostile environment, many would-be solar buyers might be interested in a bare bones system that does not require grid buyback to achieve a reasonable payback.

Con: DC only Version Requires Batteries

If you read the description of the off-grid version of this product, the LEZETi DC4812VRF, you'll discover that the unit doesn't actually adjust to fluctuations in solar power output to operate. It still relies on batteries to stabilize the incoming PV power. (I have queried the company about how big a battery bank is needed and will update here later). This is disappointing. Adding batteries is a major cost factor: but perhaps an innovation that will be added in future iterations of direct-from-PV units.

Pro: DC Only Version Stays Online in Power Outage

The presence of a battery bank  with the DC-only vesion  is the ONLY way the system will continue to operate during a power outage. Most PV simply stop working when the power goes out, because an automatic safety feature prevents them from backfeeding into the grid. This product does not have that drawback.

Pro: Hybrid Grid-Connected Version: Low Entry Cost

The hybrid Solar-to-DC system, has a couple of advantages over conventional heat pump-PV pairings, such as the ones I wrote about last month. First, it requires no batteries. This not only saves about $10,000 (the going installed rate of something such as the Tesla Powerwall 2), it also negates the additional cost of an inverter.  The ability to wire the hybrid unit directly into a breaker panel saves a lot of labor. Also, the solar panels themselves plug in directly with standard MC 24 wire. No fuss, no muss.

Now what?

If you're on the DC only system, you might store some of it in the small battery bank, but it won't last long when the sun goes down. If you've installed a hybrid unit, you're not set up to backfeed to the grid. And few household appliances can handle unwashed DC current. At best, you might be clever enough to wire up a couple of RV or Boat-Ready appliances. But those are going to require an even regulated power source (translation: batteries), not sporadic and variable power from panels.

I'm sure there are engineers out there who could "work the problem," and figure out a way to peel off unused DC power and store it in a separate battery bank. But the beauty of solar-to-DC "plug-and-play" cooling loses some luster.

The Big Picture

I hope I'm not being too hard on this new technology. As an affordable way to bring net-zero HVAC to homes all over the world,it could be a real game changer. The biggest advance, of course, is in the efficiency of mini-splits. A few years ago SEER 35 seemed like an impossible benchmark. But it's the super-efficiency of the equipment that makes the case for solar power so compelling.

What's left for both the DC-only units and the hybrids is to work out the problem of solar panel power variability. Sure, the off-grid units can work around this with batteries. But  for the hybrids, if the power goes out, they stop working completely, even on a sunny day. The ability to deliver at least SOME cooling or heating directly from the sun would improve their attractiveness to buyers.

lezeti-hybrid-specs.jpg

 Specs for the LEZETi solar hybrid system show that it can provide 11,500 Btu of cooling with under 1,000 watts of solar power input.

****Addendum, Shawn Martin was kind enough to send me this table of other manufacturers of solar-to-DC air condtioning.

He writes:

Here are the Mfgs I found so far for solar-assisted AC. Some do and some do not require the use of batteries.  Some are just air conditioning and others are heat pumps.  Most appear to have no net-metering function, with the exception of the Lennox system. I imagine there are more, and some of these might be the same unit private labeled, so let me know if you have any corrections.

Name

Type

 

Battery Required (y/n)

Grid Connection (y/n)

PV Power (W)

URL LINK

Notes

SolAir World

Mini Split Heat Pump

AC-HYBRID-12-1

No

Yes

900 max

WEBSITE

 

Event Solar and Wind

Mini Split AC

DC4812VRF

Yes

No

1000 min

2500 max

WEBSITE

 

Event Solar and Wind

Mini Split AC

ACDC12b

No

Yes

900 max

WEBSITE

 

Lezeti

 

ACDC12

No

Yes

780 max

PDF info

 

GREE

Mini Split Heat Pump

GWH12TB

No

Yes

1000 max

WEBSITE

 

Hotspot Energy

Mini Split AC

ACDC12

No

Yes

900 max

WEBSITE

 

DC48

Yes

No

900-3600

WEBSITE

 

Hybrid Air

Mini Split Heat Pump

H-11

No

Yes

720

WEBSITE

 

Lennox

Central AC and Heat Pump Models

XC25

No

Yes

?

WEBSITE

Allows for net  metering?

Harvest

Mini Split AC

 

Yes

?

?

WEBSITE

 

Carisol

Mini Split Heat Pump

PVAC – 9, 12, 18, 24

Yes

No

600-

WEBSITE

 


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Intersolar 2017

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