Solar and Potential Savings in a Class B RV

 

Financial benefits of solar on a 210P

Is there a financial incentive? At the AZ resort, electricity is $13.00 basic service charge monthly + $0.07612 for the first 500kWh, then $0.09337 for each kWh in the range 501-1000. To this are added Arizona assessments, environmental compliance charges, a utility ‘power supply’ charge, a PPFAC charge and taxes.  Typical energy charges adding all of these is about $0.1495 per kWh.

I’ve monitored the AC power used to simply power the coach, keep the AGM batteries charged and a vent fan running. The cost for that amount of electricity is about $51.67 each month.  Using solar and a good battery may reduce my 120VAC power bill by about $310 each season in AZ. If the batteries run well for 7 years, that’s a possible $2,170 in electric bills I won’t pay. 

The other six months of the year, at our “lily pad” in MI the cost per kWh is currently $0.14. That’s a cost of $290.30 to charge batteries, power the 12VDC coach, etc. for six months.  

Add the possible AZ and MI savings, and I may save $600.30 each year, or $4,202 over the projected life span of the coach battery. 

These are approximate numbers taken with intermittent readings prior to replacing the AGM batteries with LiFePO4.

Of course, to this add any 120VAC consumed.  I don't have a "full-solar" installation. At present the Tripp-lite charger/inverter is "Off" and I use AC for the Cool-Cat air conditioner/heat pump, the refrigerator 120V heater and microwave/convection oven. 

If more solar were available, I could probably run the refrigerator off 12VDC during daylight hours, increasing the savings from solar. However, "full solar" existence isn't practical in my opinion.  The Cool-Cat heat pump requires 1,227 watts when the compressor is running and cooling.  To that add electricity for the refrigerator, etc. as well as battery charging current to be stored for overnight use.  I'd need a lot of batteries and a lot of solar panels.  The roof of the 210P has space for at most 200W of panels.  I can add portable panels to the capacity of the controller and more batteries but living off the grid is not my goal.

Why? I won't park a Roadtrek in full sun in Arizona when the ambient reaches 100F in the shade. That's a recipe for a human BBQ.  

This season a couple moved into the resort after a trial at boondocking in nearby Quartzite.  Their several months-long experiment occurred with peak temperatures only about 80F.  They related their experienced and told us that they made the decision to get a site in the resort. They decided the resort fees were worth it as this provided unlimited running water, sufficient power for air conditioning, easy tank dump, etc.  Oh, and a bar & grill, swimming pools and internet access, too. 

Measuring AC Power consumed

I have two methods. One is the Power Protection Device at the 30A connector.  It includes an ammeter display. It is useful for roughly monitoring the amperes being consumed @ 120VAC.

AC Amperes with Cool-Cat AC running, Tripp-lite charging, refrigerator on AC

The other device I use is a Kill-a-Watt meter.  This can be used to determine the amperes and watts consumed on 120VAC circuits, or for individual appliances.  It is accurate and precise. It allows a variety of measurements and price calculations at any entered cost per kW. It will calculate the power consumed at any entered price per KWh and it will totalize this cost.  Here's an example of an instantaneous ammeter reading:

Kill-a-Watt indicates Coach 120VAC at 10.23A. Measurement 
with Cool-Cat air conditioner running, Tripp-lite not charging and
minimal appliances powered up

Measuring the Solar Power Available

The MPPT controller has calculations and historical data available. Data is accumulated and stored monthly. Some of the statistics available:

• Power generated
• Charge Ah same day
• Max charge power
• Max battery volt
• Running days total
• Battery full charge times
• Battery charge Ah total
• Generation amount kWh

Initial Observation

How is the LiFePO4 battery and charger doing?  So far, very well. I keep the coach powered up on solar with the vent fan running. The Tripp-Lite charger/inverter not being used. This is an experiment.  Every day the coach battery is fully recharged after a few hours in the morning sun.  Of course, this is AZ with a lot of sun.  On the other hand, this is a small 50W solar panel which is showing its age. Power output has decreased and peaks at about 85% of rated. 

It is premature to call this a success, or the LiFePO4 battery superior to the AGM batteries. For one thing, this trial has been a little over a month in duration and we are stationary. For another, I did install the coach battery in the outside compartment. It is a well-known fact that the battery management system (BMS) of a LiFePO4 battery will not allow it to be charged if the battery temperature falls below 32F. G and I have trekked and camped overnight in temperatures as low as 5F. As a consequence I did install low-wattage 12VDC and 120VAC compartment heaters.  We’ll see how that works. 

There are some LiFePO4 batteries which incorporate 12VDC heaters in the battery.  I could have chosen this type.  However, I am concerned about how much energy those heaters may use when off the grid or while the Roadtrek is stored in cold weather and not plugged into shore power. I decided two 12VDC and a 120VAC heater and solar power were a better solution, in my circumstances.  I also installed an automatic low-voltage disconnect for the battery.  The BMS will disconnect and prevent the battery from completely discharging, but LiFePO4 batteries are best disconnected at a higher voltage threshold if maximum cycles and life are to be achieved. Ergo the automatic disconnect. 

Increasing the solar Available

My plans will increase the amount of solar for the Roadtrek.  There are limitations because of the available roof space.  I have no such limitations in AZ under the shelter, so I can add even more kW on my shelter roof. 

Background Information

It was time to replace the coach batteries in my 2013 210P.  I attended the FMCA Convention in Tucson in March, and I used that opportunity to visit with battery suppliers and manufacturers in the exhibit hall. There was a battery seminar scheduled, but an issue prevented the presenter from being there so that seminar was cancelled.

I had to choose:  AGMs or LiFePO4. To assist in making that choice I wanted to review the latest technology and I didn’t want to overspend on Lithium-ion if I went that route.

My Roadtrek is relatively new, but the first set of AGM batteries were ruined when the Roadtrek control panel “Inverter OFF-ON” switch failed to open when I put it in the “OFF” position.  Sitting in storage in that condition for a couple of weeks completely depleted the AGM batteries, ruining them. After that experience I turned off the inverter function when I store the Roadtrek.  I did this by changing the Tripp-lite mode switch to “Charge Only”.

When the first set of AGM batteries failed I replaced them with similar batteries and installed a 50W solar panel and 180W desulfating solar controller to keep them charged.

LiFePO4 Today

LiFePO4 technology continues to evolve. I’m currently aware of two different cell construction techniques. I investigated different constructions and manufacturers.

Prices for a 100Ah battery range from about $350 to $950 each, plus shipping and tax.  Why is that?  There are differing cell qualities.  There may also be large mark-ups by some sellers.  I determined that there is no standard for determining cell quality in China, where many or most of the “internals” in these batteries are manufactured.  As a consequence, it is important to purchase from a reputable manufacturer. It is possible to overpay, if one assumes the higher the price the better the quality.  On the other hand, there is a lower price threshold below which it would be better to avoid.

A Decision in favor of LiFePO4

I continued my research and decided upon a  LiFePO4 battery from a quality manufacturer.  Delivered and with state sales tax the price was   $624.93.  It arrived on April 1, 2022.

I'll run some of the solar numbers later in this post. However, I concluded the LiFePO4 would be more reliable and therefore more likely to achieve the solar performance I wanted.  Solar panels are only a  portion of the system.  Energy storage is also very important.

The was shipped 30% charged, which is normal for this manufacturer.  I promptly charged it using a 10A charger which was compatible with the specifications for this Lithium-ion battery.

A new MPPT solar controller

I had determined that my solar controller with a de-sulfating mode was not ideal for the Lithium-Ion battery. It was ideal for AGM batteries.  I replaced the solar controller with an MPPT type; it had a user mode with custom settings which were ideal per the battery manufacturer’s specification.  I installed that, entered the proper settings and have since allowed it to charge the coach battery and run basic appliances off the grid (lights, fan, etc.).  I’m satisfied with the initial performance.

I’m currently in southwest Arizona with the Roadtrek on my winter site. It is parked under a shelter, which is why I used a portable solar panel. The panel is currently on the shelter roof. The ambient may be 60F at night but can reach 90F during the day. We do get some morning sun loading in the front of the Roadtrek. I run the vent fan most of the day unless I am using the Cool-Cat heat pump/AC.

(c) N. Retzke 2022