This week’s article features Ed, a full time RV’er. Ed is a retired commercial industrial HVAC service technician that worked in Denver providing service to everything related to heating and cooling. After leaving the workforce, Ed started living in his RV fulltime in June 2017. He sold his 29’ travel trailer and purchased a brand new 39’ fifth wheel as his home in January 2018.
Our solar project this week features customer Jason E., a full time RVer. Jason is a father and husband in a nomadic family of five that travels in their fifth wheel RV full time. His family has been living the nomadic lifestyle for 5+ years but most recently is in the process of putting down some roots, though they maintain traveling is still in their future.
Our solar project this week features customer David G. of Northern Arizona. David and his family purchased property in the high desert of Northern Arizona to be closer to extended family. Their intention wasn’t necessarily to go off-grid with their power needs, however, the location where they purchased their property dictated solar to be their only power option. That’s when David researched solar power and ultimately contacted our team at Northern Arizona Wind & Sun.
When looking at what is an ideal full system configuration for an RV, typically one would want to consider the expectations of a system and limitations of the RV, and then build the system around these expectations and limitations. In most cases you want to start from the roof and work your way down.
Solar for Roof
Roof space is usually the biggest limitation when considering solar power for an RV. Being that solar panels are one of the least expensive aspects of a complete system, maximizing production value for a given space is the most advantageous plan. In most cases putting as many panels on the roof as will fit is the best idea. Measure or use pieces of cardboard, targeting a sixty-cell panel format (~67”x40”). These are technically the best panels and the cheapest, due to the volume of sales these panels enjoy. Other panel sizes are available. Mixing sizes and shapes is complicated so plan wisely. We’ve never had a customer complain about having too much power (because this isn’t possible) but having too little power can result in too little energy production which may not meet your expectations. This can be frustrating and could lead to premature battery failure or other system wide issues.
Next you need to plan for an inverter if you need to run AC appliances and devices. The inverter converts power from the batteries to your basic household outlet AC power, 120VAC or 120/240VAC. You need to decide whether you want a fully integrated inverter system or a simple stand-alone inverter. In most cases, this decision will be dictated by what you want to power from the inverter. If you simply want to plug in a laptop or charge a phone from time to time, then a stand-alone inverter should work fine. Most of these smaller inverters will have an outlet on the front allowing low power devices to be connected. Anything more demanding than this requires a fully integrated inverter/charger. These inverter/chargers have a built-in transfer switch and the ability to charge the batteries at a much higher current than a typical converter. These are advanced inverter/chargers with powerful features and thus are usually the best solution for medium to large installations. The inverter/charger is typically placed between the shore power input and the main electric panel, the output from this inverter would go to the main electric panel. This essentially will power up all or most of the electrical circuits within the RV, depending on the configuration of the electrical panel. When AC input power is present from either shore power or generator, the inverter/charger will qualify the input (making sure it’s acceptable) and transfer that power through. It will pull from the AC input dynamically depending on certain limitations to charge the batteries. When shore power or the generator are not present the inverter uses energy from the batteries to power the AC loads. There are many more advanced features available from this type of inverter/charger, but in general if you power to all the outlets and appliances like the micro wave or the air conditioner then an inverter/charger is the way to go. Special care needs to be taken if you wish the inverter/charger to power air conditioners. Air conditioners consume large amounts of energy and need careful planning.
The final step in a design is sizing the battery bank. An RV is a terribly abusive environment for batteries. It’s common to have significant deficit cycling (infrequent full charges), over discharge is very likely, and temperature can vary significantly. There are two types of batteries that work for an RV system; lead acid and lithium-ion. Lead-acid batteries include flooded batteries (AGM), or Gel. However, gel lead acid batteries are not designed for the demands present in a typical RV system.
Can be placed inside the living space
Battery bank can be added to over time
Low chance of damage if left uncharged
Higher level of efficiency
Cost- Lithium batteries are more expensive, however, over the life of the system Lithium is cheaper.
Larger and heavier than Lithium
It’s not recommended to add to a lead acid battery bank after it’s installed
Life is significantly reduced if they are left uncharged for any length of time
Cheapest battery option
Must be placed in a vented enclosure designed to handle the gas fumes they create
Extremely heavy - it’s important to make sure that the location can handle the weight
Poorly suited to handle the abuse present in an RV system
Not recommended to add to their battery bank.
It’s important to have an accurate battery monitor installed in the system, one that uses a shunt. This will allow for accurate tracking of the battery state of charge. Regardless of the type of battery bank, this accessory can really help prevent excessive discharge and confirm regular recharging.
You can do all the research you want but some of the best recommendations you’ll get are going to come from experts in the industry. Northern Arizona Wind & Sun has several engineers on site happy to consult and design a system to suit your application, no matter how unique or complicated. Feel free to give us a call to discuss your project today.
A lot of people assume they need a transfer switch for an off-grid system when they are using a generator to charge the batteries or power loads. If you are using an inverter/charger there is an internal transfer switch to select between the inverter’s output and an incoming AC source. Most inverter/chargers will remain in “Invert” mode unless they see an acceptable AC source coming through (Shore / Grid Power or Generator Power). Once the inverter/charger accepts the AC voltage, it transfers over to supply power to loads and dump excess power into the batteries. Once this AC source is disconnected, the inverter will transfer back to “invert” mode and use battery power to run the loads. Some inverter/chargers will accept two AC sources and transfer between either of those and the inverter’s output. So if this is how your system would be set up, then there is no need for an external transfer switch.
You may need an external transfer switch if you have an inverter/charger with only one AC input and you want to switch between two AC sources like a generator and shore/grid power. This is the case in most mobile/RV applications. Another scenario is when you have a generator that can deliver more power than the inverter/charger can pass through and you want to power some heavy loads. The inverter charger is limited by the rating of the internal transfer switch. For example: Let’s say we have a Schneider 3.8kW inverter/charger with an internal 30A transfer switch with a split phase 120/240VAC output. The max load we can run by passing the generator power through is 7.2kW (30A x 240VAC = 7200 W). If we had a load that exceeded this 7.2 kW, and we had a generator that was able to satisfy this load, we would want the inverter/charger to be bypassed, allowing the generator to power the load directly. In this event we could use an external transfer switch to select between the inverter’s output and the generator’s output. If the inverter/charger is properly sized, this scenario does not occur often.
For more info on this call Northern Arizona Wind and Sun 1-800-383-0195 or email email@example.com.
Lithium batteries cost more up front, but in the long run they are superior to lead acid batteries for
several reasons. They are maintenance free, extremely efficient, safe, can be recharged very quickly,
and offer an expandable battery solution. Lithium batteries are cheaper long-term and are more
tolerant to infrequent full recharging and excessive discharging than their lead acid counterparts. They
make the best battery solution for high demand applications, where lead acid batteries do not and will
On the surface, lithium batteries can appear too expensive, but we believe they are one of the best
investments one can make for their system. While the upfront costs for lithium may be higher than
other battery types, the associated benefits like longer service life, superior reliability and excellent
efficiency, will far outweigh the high initial cost. In just about all cases lithium batteries have a lower
cost per KWH per cycle. This means throughout their life cycle they will cost much less than other
batteries and thus will be the most economical solution in the long run, especially when compared to
that of high-quality lead acid batteries.
Many customers contemplating the switch to lithium will be replacing an existing lead acid battery bank
of some type. A flooded lead acid battery bank will require a significant amount of maintenance
throughout its life to stay healthy. Poor maintenance is a leading cause of premature failure for flooded
lead acid batteries. The electrolyte level should be checked regularly to prevent the battery from
running dry, and the battery must be filled with distilled water when electrolyte levels are low. Checking
the specific gravity from time to time is needed to guarantee the batteries are fully charging.
Additionally, the battery must be equalized when the electrolyte starts to stratify to maintain efficiency.
These common maintenance procedures can become mundane and are often forgotten, which can
cause a flooded lead acid battery to fail early. A lithium battery is completely maintenance free,
eliminating the need to add water, check specific gravity, or equalize charge.
Another significant contributor to premature failure of lead acid batteries is excessive discharge and
deficit cycling. Regardless of whether you have a flooded, AGM, or Gel type battery, a 50% depth of
discharge (DOD) limit should be observed in order to prolong their life cycle. Deficit cycling is also very
harsh on lead acid batteries. This happens when a battery is discharged before having the chance to fully
recharge. Plate swelling, loss of active material, and sulfation of the plates can be caused by excessive
discharge and/or lack of full recharge. To achieve the longest life possible, it’s very important not to
over discharge lead acid batteries and to make sure they get completely recharged every cycle.
Unfortunately, this can be difficult to manage, and you may find yourself constantly worrying about your
battery health. Lithium batteries are a worry-free alternative. It’s not necessary to fully recharge lithium
batteries every cycle and most have internal protections within the battery that will never allow you to
discharge down to the point of permanent damage. Generally, you can discharge most lithium batteries
to about 20% remaining capacity every day without shortening cycle life. Lithium batteries can also be
fully discharged periodically without significant adverse effects. You can use them, abuse them, and they
will suck up the energy you give them and spit it right back.
In several applications (especially off-grid solar), energy efficiency is of crucial importance. The typical
round-trip energy efficiency (discharge from 100% to 0%, then back to 100% charge) of a brand-new
lead acid battery is around 80%. The round-trip energy efficiency of a lithium battery is 92-98%
throughout the entire life of the battery. The charging process of lead acid batteries becomes
particularly inefficient once the absorption state of charge has been reached. This can result in
efficiencies of 50% or even less in systems with oversized battery banks or failing batteries. As a lead
acid battery ages, internal resistance builds up and the battery bank becomes even less efficient, causing
more and more energy to be converted into heat rather than stored within the battery bank. As lithium
batteries age, usable capacity is reduced but the efficiency is still maintained.
In most cases lithium batteries can take on more power than can be delivered to them. Charge and
discharge current limits for lithium batteries are often portrayed as capacity scalars. For example, most
lithium batteries can be discharged and recharged at a continuous rate of .5C or half the overall
capacity. Some manufacturers rate their batteries with a discharge and recharge limit of 1C. In this case,
a lithium battery can be completely charged in just one to two hours from 0%. It’s also important to
note that a lithium battery is usually between 95%-99% full charge after the completion of the bulk
charge stage. In contrast, most lead acid batteries shouldn’t be charged at a rate greater than .2C, and
the battery will achieve a maximum of only 75%-80% full charge once the bulk charge stage is finished.
After this, an additional 3-4 hours of absorption charge is necessary to fully recharge most lead acid
The safety and reliability of lithium batteries is a big concern, so nearly all lithium battery solutions will
use an integrated Battery Management System (BMS). The BMS is a system that monitors, evaluates,
balances, and protects cells from operating outside the "Safe Operating Area". The BMS is an essential
safety component of a lithium battery system, monitoring and protecting the cells within the battery
against over current, under/over voltage, under/over temperature, and more. Another essential
responsibility of the BMS is to balance the pack during charging, guaranteeing all cells receive a full
charge without overcharging.
One of the most significant advantages of lithium batteries over that of a lead acid alternative is that
lithium battery banks can be expanded throughout the life of the battery. This is not an acceptable
practice for lead acid batteries as the result usually ends in significant premature failure of the whole
battery bank. Being that lithium batteries don’t suffer from lack of full recharge or deficit cycling
amongst other things; the addition of new batteries simply increases the storage capacity and reduces
the load on the rest of the batteries. In most cases, this will increase the life of the battery bank. Thus,
making for a whole lot more flexibility in the design on an off-grid system and can allow one to build up a
system as needed and as a budget allows.