Sunset at Placid Lake

Air Conditioning on Batteries and Solar

My goal is to be (electric) energy independent, this includes air conditioning on batteries and solar. I have not yet installed solar. I can now run air conditioning from my batteries.

The process was easy enough, and I started with a huge advantage over less equipped RVs. I already had a very capable Magnum Inverter/ Charger and I just installed a massive battery bank. I have plenty of battery power and maybe I can run one of my air conditioners from my batteries, starting with a full charge, for at least eight hours.

Here is a link to the description of my battery bank. Massive Electric Bucket

The next step is to install a solar panel system. I want it to be capable of creating enough electricity to run the air conditioner and recharge the batteries (slowly) at the same time. When I am not running the air conditioning my goal is to dump about 100 amp-hours of electricity into my battery as fast as possible. I would love to hit 500 amp-hours per sunny day of charging.

It is not my design goal to run my air conditioner indefinitely, in the south, in the summer on solar power alone. Simply stated, I don’t have enough roof space to accomplish such a feat. But rather, I can easily achieve my goal of occasional use.

Air Conditioning from Solar

Air Conditioning from Solar, this is a holy grail for RVs. The statement is incomplete. You don’t run air conditioners from solar. Instead, the solar charges the batteries. The batteries deliver the energy to the inverter, which in turn runs the air conditioner. Running the air conditioner directly from the solar is a non-starter because you don’t only want to run the air conditioners just when the sun is shining. Rather you want to run the air conditioners when it is most important for you to have a more comfortable RV.

Lion Energy UT1300 Lithium Battery
Lion Energy UT1300 Lithium Battery

When?

When do we want to use air conditioning from our batteries? Sometimes when we are boondocking it is quite warm at bedtime — air conditioning would be great. In this case, air conditioning would be a direct drain on the battery. When we were camping in Death Valley, we got caught by the “generator police” at 7 pm because our generator was still on (we were standing outside). It would have been so nice to have air conditioning that night. Obviously this situation has repeated many times.

Here is a link to that story. Death Valley National Park

The second time air conditioning from our battery would be great is when we are driving.  We typically drive about one or two hours in the middle of the day. While we are driving, we would be able to run our air conditioners, to keep the house cool and make the RV more comfortable during our travel days. Assuming we are traveling during the day time (we always travel during the day time) and assuming it is sunny (not always the case) The solar would still be charging the battery while we are driving.

The third time we could run the air conditioner is in the afternoon. The afternoon is exactly when the air conditioning would be most appreciated. If the battery is full or nearly full then the air conditioning could be run while charging from the solar. If the battery needs a charge, then starting the generator would both run the air conditioners and charge the battery at the same time.

Air conditioning and heat

My air conditioning units are heat pumps. This means that since I can run the air conditioners, I can, if I desired, also use them to create heat. Heat pumps are far more energy-efficient than my room space heater. So I could create heat from the batteries. I don’t have any reason to do this in that I also have two propane furnaces that are way more energy-efficient than any electrical heat source.

So how much does an air conditioner consume?

Answer = it depends on how hot it is and whether or not I am sitting in the sun or in the shade.

Edit: Here are the real numbers from my test results while running my air conditioner from my batteries. The numbers below are not accurate. Air Conditioner from Solar and Batteries

My air conditioners consume about 900 watts each per hour to run. This is based on actual use, while parked in some shade with the sun hitting at least part of the roof of the RV. The same conditions, with a big solar panel array, would actually be a lower consumption because the solar panels would shade my roof.

(Our air conditioners used to pull much more than 3000 watts during start-up. Here is a link on how I tamed the amperage spike. Micro-Air EasyStart)

So, since each battery holds about 1200-1350 watts of energy when full, and assuming the battery is full when I start, each battery is able to run one air conditioner for 1.5 hours.

In the same conditions, assuming I had the solar running at full tilt, I would be producing around 1200 watts per hour. (This assumes no shading and ideal conditions, including clean solar panels.) So easy math says if I am consuming 900 per hour and making 1200 per hour, I can charge the batteries at the same time as running the air conditioner.

(You may have noticed I said 900 watts per hour which is way less than 2017 watts of electricity that my air conditioner is rated at. The difference is that the compressor does not run continuously but rather cycles on and off. This was not the case in Las Vegas in August 2017, but that was an extreme condition with temperatures more than 110 degrees after sundown.)

These calculations will not be replicated in real life except during ideal conditions. There are too many variables. One tree shading part of one panel can affect the output of three panels. Shade kills the output of solar panels dramatically.

When we get the solar installed, the solar should be able to run one air conditioner at full blast with no net drain on the battery. (I hope)

Air Conditioning on batteries and solar is an achievable goal.

An electrical remodel

When Tiffin designed our RV in 2008 they never anticipated that anyone would want to run the air conditioner from the battery. It simply wasn’t on their radar. They were pushing the design when they included a residential refrigerator. To do this, Tiffin installed extra batteries, and solar to help run the refrigerator. Anytime air conditioning was needed, the answer was to start the generator, or plug into shore power. Air Conditioning on batteries and solar was not part of the design.

Ninty-nine percent of RVs coming off the assembly line today in 2020 are designed the same way or with less capable electrical systems than our RV had in 2008. This includes our previous 2013 Tiffin which is electrically inferior to our 2008.

What we needed was a re-design on inside the circuit breaker panel.

Here is a general overview. Power comes into the circuit breaker panel from three different sources. The three sources are Shore Power, Generator, or Inverter. Shore power can deliver 100 amps of power to the circuit breaker panel. The generator can deliver 55 amps of power to the circuit breaker panel. The inverter can deliver 23 amps of power.

Circuit Breaker Panel rewire for air conditioning on batteries and solar
Circuit Breaker Panel

One of the ways you could wire the RV would be to have a manual switch that would select the power source. The way nearly all RVs, with factory-installed inverters are designed is that there is an electronic transfer switch that chooses between the generator or shore power. Inverter power is delegated to a secondary role and is only used when the generator or shore power is off. This is accomplished via a sub-panel. The sub-panel is powered from either the inverter directly when operating on battery power or from either shore power/generator when that is our power source.

RV power math: 50 amp = 100 amps and 30 amps = 30 amps

Shore power or generator feeds the “50 amp main” supply to the circuit breaker panel. This supply is broken into two branches commonly named red and black, as associated with the wire color. Each red and black wire can supply 50 amps to the branch for distribution. Thus when you have 50 amp service you have two sources of 50 amp power. Thus 50 amps = 100 amps of power

When plugged into a 30 amp supply, then both branches share the 30 amp service and deliver the 30 amp to distribution. Thus 30 amps = 30 amps. The same is true for 20 amps. 20 amps = 20 amps

Electrical flow in the circuit breaker panel

This is how my RV works — it is very likely that your RV does not work the same way!!! If you don’t understand it then don’t monkey with it.

Shore power or generator power enters the circuit breaker panel via the 50 amp circuit breakers (one red, one black) and energizes the red and black bus. From the red and black bus, part of the power (30 amp red and 30 amp black) is then routed to the inverter from a circuit breaker labeled “inverter out”… The power passes through the inverter and is returned to the circuit breaker sub-panel on the “inverter in” circuit breakers. (30 amp red and 30 amp black). The sub-panel routes the electricity to the sub-panel circuits.

If electricity from shore power is not available, then the inverter will convert battery DC power into AC power and supply the sub-panel with electricity to operate sub-panel circuits. My microwave and refrigerator operate from the sub-panel and thus will run with or without shore power. (assuming the batteries are full enough to operate the inverter)

Remodeling

The circuit breakers that operate the air conditioners were on the main panel. Thus the air conditioners could not operate from the inverter (even though the inverter was big enough) because the air conditioners were not on the sub-panel powered by the inverter. Hence to achieve air conditioning from batteries, I rewired the inside of the circuit breaker panel to remove them from the main panel and put the air conditioners on the sub-panel. Now they can operate from the inverter.

Caution

This re-wire creates a potential for an over-allocation of electrical power. I looked carefully at this issue, Tiffin already over-allocated the electrical circuits on the sub-panel. By adding the air conditioners, I have increased the potential of turning on too many devices and thus tripping the circuit breaker. You cannot ask for too many amps, all at the same time or the circuit breaker will trip. So even though I am over-allocated, I am unlikely to trip my circuit breaker. The reason is that the items that could be used when operating on battery only, are unlikely to be used when operating on battery only.

Where are the power hogs?

My power hogs are the inverter (when operating as a battery charger), air conditioners, water heater, engine heater, electric space heater, convection oven/microwave, clothes dryer, hairdryer, and instant pot. The refrigerator also needs to be included in this discussion. The refrigerator does not consume lots of power, all at one time, but is an essential item.

Of the above items, the only things that I cannot ever operate from the inverter are the engine heater and water heater. These items are only hooked to the main bus, not the secondary bus.

My power hogs that are able to operate when I don’t have external power are air conditioners, electric space heater, convection oven/microwave, clothes dryer, hairdryer, and instant pot.

Items that I will rarely use on battery power are the air conditioners and convection oven. Items that I am likely to never use when on battery power are the clothes dryer, and electric space heater.

If I attempt to operate too many of the power hogs at the same time, I will trip the circuit breaker.

Important Items when on battery only

Used all the time = refrigerator. Occasional use = microwave, and instant pot. Rare use = hairdryer and air conditioner. Almost never used = clothes dryer. Never used = electric space heater.

Air Conditioning on Batteries and Solar

Air Conditioning on Batteries and Solar is very possible, but you have to know the limits of the system. Just because you increase the abilities of the design, it does not mean you are operating without limits.

Critical Component

Air conditioning from batteries and solar would not be possible without adding this one critical component. This component tames the spike that happens when the compressor starts. Here is my link to installing my Micro-Air EasyStart.

Components List

This is what we used. We do not get commissions on the links and are provided only to help our friends.

Lion Energy UT1300 Lithium Iron Phosphate Batteries

Battle Born BB10012 Lithium Iron Phosphate Batteries

Magnum 2812 Inverter Converter (charger measured at 125 amps per hour)

4 thoughts on “Air Conditioning on Batteries and Solar”

  1. Another former “nasal radiator” here….mostly WestPac including a tour on the Midway after her blister mod flying Hornets. (Call sign was BUFLO)

    I’ve crossed paths with your blog on solar and lithium somewhere in the past while doing my initial research….and I’ve somehow incorporated quite a bit of your same thoughts and considerations without consciously knowing they originated with you.

    My system is just about done being field-tested now and I will be making my wiring runs and component locations more permanent soon. I went with a Magnum Energy MSH4024M and built my battery bucket @ 24VDC using two EG4-LifePower4 Lithium Battery | 24V 200AH in parallel to provide 10KWH of storage…..on the roof is 1,640 Watts of PV solar connected series / parallel to work at just under 100VDC / 22Amps down to a Victron MPPT 150/70 solar controller. My house DC is hybrid in that I retained a single “placeholder” flooded 12VDC fed from the 24VDC LiON battery bank via a Victron Orion 24V|12V-30A buck converter charger to support normal 12VDC house loads and provide a battery boost capability for the chassis battery if needed.

    As far as the rig knows, nothing has changed for any of the house wirings at this point….the 12VDC loads remain as from the factory, and the AC panel hasn’t yet been modified.

    My plan for the roof A/C is to insert a transfer switch in the source to the roof A/C that will prioritize between main panel AC and inverter AC, i’e., when on external power, the transfer switch passes power to the roof A/C unit via the original main panel CB (factory stock!!!) – if no power is being provided from the main panel, then the transfer switch passes inverter AC to the roof A/C via a CB on the inverter sub-panel.

    The “Easy Start” has been installed in the roof A/C and works REALLY well! I’m sure to find the same heat management issues as you’ve encountered, but haven’t yet decided how to best solve for heat extraction from the basement electrical utility compartment…..cross ventilation is probably in my future.

    1. Sounds like you have it well under control.

      I think perhaps the only original part of my system is the hybrid battery setup. I didn’t go with 24 volts because I didn’t want to replace my inverter.

      You didn’t mention the RV you stacked all this gear on. I assume that you are going to use it very frequently.

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