First Days of Mini-Split Operations

Percent from solar, last ten days.

My new SEER30+ mini-split air conditioner has been operational for a few days now.  I’ve been running it at night with my central air conditioner off.  It’s difficult to say how much impact that has had in increased efficiency, but there is no doubt it has to have contributed greatly.  Other factors to be considered are cooler temperatures and cloudless days.   Looking at the percentage of electricity from my solar panels over the last ten days, and considering that these are the shortest days of the year, I can only conclude that it seems to be a big step in efficiency for my house.

Daily usage chart for November 19, 2017. Green bars show buying from the grid, gray bars selling to the grid from my solar panels.

Mitsubishi Mini-Split A/C

Ten years ago, when we conceptualized our photovoltaic system as an emergency power source when the grid was not available. The plan included a mini-split air conditioner for the master bedroom. The idea was that during an extended grid outage, such as occurs after a hurricane, we would be able to power our house and have an air conditioned refuge powered by solar panels and battery backup.

Recently, Hurricane Irma caused a six day power outage and the system functioned wonderfully, powering the house day and night. However, the refuge room concept had not been implemented, even though planned for. Those hot sweaty days and nights motivated me to implement this final component in the system.

On Wednesday, November 14, 2017, JWair and Urban Solar installed a Mitsubishi, inverter based, SEER 30+, 9,000 btu mini-split air conditioner in my master bedroom running on a 240 volt dedicated circuit pulled from my two inverters.

In the weeks and months to come, I will be testing the system by running it on solar panels and battery backup. I will collect and publish data on its performance here. The unit will provide increases in efficiency by allowing me to turn off the central air at night and sleep with only the master bedroom cooled by the Mitsubishi. In extended outages it will provide air conditioning powered by solar and battery backup.

Lower temperatures, higher percentages from solar

Milder daytime temperatures since the hurricane have reduced consumption from air conditioning, along with a lot of cloudless days have resulted in higher percentages of energy being produced from my solar panels.  The chart on the right shows that over the last ten days, percentages generated from solar have been near seventy percent on average.

Six Days On Solar Power Emergency Backup

My emergency circuits powered by solar panels and battery backup.

We lost power at 3:30 pm on September 10, 2017, as the outer bands of hurricane Irma, impacted West Palm Beach. At that time, due to the extreme weather conditions, little if any power was being generated from the rooftop panels, but the system switched instantly to battery power (120 volts from the inverters to all emergency circuits).  We continued on battery power until  3:30 am. when battery voltages reached the low-level cutoff of 46 volts and the charge controllers switched the system off.

My 8, 240 ah, Concorde battery, emergency backup bank

The next morning after the sun came up and the panels started supplying power, energy was first directed to the batteries to bring them up to charge.  When the batteries reached a level of 50 volts, the system restored power to the house, while continuing to bring the batteries up to 52 volts.  At that point, the system switched to float to maintain the batteries at a fully charged state through the day while supplying power to the house, including two refrigerators, lights, ceiling fans, and TV.  As the sun went down, the system switched to the batteries as the source. The second night the system shut down at 6:30 am when the batteries again dropped to 46 volts.

For six more days the process continued but with no shutdowns due to reaching the lower battery voltage limit.  With a little more care in usage, I was able to have continuous, uninterrupted power for four more days.  Power from the grid returned in the afternoon of September 16, 2017.

 

Outback Power Systems charge controllers.

Early in the morning on September 16, I became over confident about how much I could run while on battery backup. While still running on the last of the battery power, I started a load of laundry, made toast and coffee, and squeezed out the last of the battery reserve. Had I waited until the sun was fully up, I would have been okay. The charge controllers shut off the house at the low voltage threshold and directed all of the energy from the rising sun into topping off the battery bank. As soon as the batteries get up to around 50 volts, the house was powered up again.

All around me during the six days the grid was down generators were running noisily with their owners refueling them every few hours.  In conversation with my neighbors, I found their noisy generators were running no more circuits in the house than I was.  There was one exception, one neighbor was able to coax his air conditioner online for a couple of hours by shutting down all other circuits in his house.

Outback Power Systems, solar emergency backup system.

I would say that my grid-tie photovoltaic system with battery backup performed exactly as it was designed to do.  I was able to run two refrigerators, all lights, ceiling fans, and 60 inch Samsung TV.  All of my lights are LED lights except for one halogen light which I avoided using.  I am most appreciative of the design work by Roger Messenger and the great installation by Mike Vergona and his crew at Urban Solar.

Hurricane Irma and my photovoltaic system.

 

Hurricane Irma came through Florida the weekend before September 11, 2017 and did massive damage throughout the state.  It lost its tropical characteristics after 11 days and traveling 4,000 miles.  Half of Palm Beach County, 500,000 people are without power.

 I am running completely on my photovoltaic system and have been for two days now.  This is the first extended operation of my system in emergency mode and it has been interesting.  We, my step-daughter and her husband, sheltered in place.  We lost power at about 3:30 in the afternoon on the day the storm went up the west coast of Florida.  The system switched to battery backup which carried us into the next morning until about 3:30 am.

When the sun came up the next morning, the charge controllers directed all of the energy from the solar panels to the battery bank.  We had no power in the house while that was taking place.  That was because we lost power in the afternoon and it was cloudy and stormy.  Also, we didn’t have a good idea of how to manage our consumption.  My children have returned to their home so I will be consuming much less tonight.  It will be interesting to see how things perform.  With careful management my house is powered for about 12 hours on the battery backup.

So, what can I run on emergency power from the solar panels and/or the battery backup?  Pretty much everything in the house except for air conditioning.  With the tight envelope this house has, impact glass windows with low-e reflective glass and good insulation in the attic, the house stays around 80 – 83 in the day and cools down at night.  It’s quite comfortable sitting under a ceiling fan.  I am definitely not uncomfortable or suffering.  This, after all, is what we designed and implemented the system for.  It is basically functioning as a generator would, but with no noise or fuel.  Additionally, it runs every day all year long, generating power.  It will eventually pay for itself while a generator never would.

 

Lots of Watts

Yesterday was so clear and cool that I think the charts from my house might represent an ideal system maximum for March 17th at this location. March 16th, the day before yesterday, was almost identical.

This chart reveals that night time usage runs around .5 kWh.  That’s got to be phone chargers, DVR, and some other “phantom” loads from various small electronic devices that are plugged in.  The increase in usage just before sunrise is my irrigation system coming on.

The percentage of total electricity used from my solar panels was 108.  Yesterday and the day before the totals generated for both days were exactly 24.7 kWH. That’s why I think this is a good measure of the maximum my system can generate under ideal conditions in mid-March.  Because of differences in my usage, there is a slight difference in the percentage generated for yesterday and the day before.

 

 

 

The last ten days are shown below in both graphic and tabular form. So far, we have had three 100 percent plus days and one 90 percent plus day.

Worst Case

Yesterday, March 3, 2107, was overcast and gray all day long.  We even had some light showers.  It was probably a worst case day for solar energy generation.  Even so, we generated 28 percent of our energy from the sun.  This ends. a series of very good days up in the 80 percent range.  Our best days are ahead in the months of April and May.  My energy efficient window replacement project should be done by then so I am optimistic about how well the system will perform then.  The time-lapse for the day reveals some opportunities for generation were available in the morning.

Worst Case Scenario

January 29, 2017, was cold, cloudy, and rainy, a worse case scenario for our photovoltaic system.  I stood the chill as long as I could, but finally gave in and turned on my electric heat.  Because of the clouds, our solar panels only generated 1.9 KWH of energy while the heat used over 30 KWH.  The percentage from solar shown in the chart is the result. The chart below shows a very atypical day where all of our energy came from the grid and none from our solar panels.

The chart below shows the last ten days of percentage from solar. We were doing quite well actually until the cold front came down and stalled over us.