Solar Education Questions
Solar Panels
What is better mono or poly?
Monocrystalline solar panels can produce about 5% more power than polycrystalline solar panels of equal size. Polycrystalline cells are square in shape with a blue color. Monocrystalline cells are black and more octagonal (squares with beveled corners). Both types of panels will work fine but we mainly sell the more efficient monocrystalline panels.
Are higher wattage panels better?
Larger panels are easy to find, but bigger isn’t better. In RV applications, the larger residential panels have several disadvantages.
-For the most part, panel wattage is proportional to panel size. If you have a higher wattage panel it is most likely a larger panel. Because the roofs of RVs are much smaller than the roofs of homes or commercial buildings, it may be very difficult to position larger solar panels on an RV roof in a way that they won’t be shaded by air conditioners, satellite dishes, etc.
-The larger surface area of residential panels can also act like a sail, and put more strain on your mounts and your RV roof when you drive at highway speeds.
-Larger residential panels are designed for stationary mounting on buildings or ground mounted arrays. They may not be able to handle the vibrations of an RV driving down the road. Sometimes conventional solar panels can develop micro fractures in their cells when they are transported by railway.
-Multiple smaller panels fit on the roof better, mount easier and have an output more suited to charging 12 volt batteries.
How many panels do I need?
You may be thinking “I have average use, how many panels do I need?” In our experience, there really is no average. When people install a couple solar panels, they usually end up wanting to install more. Everyone has different power consumption habits, roof sizes and budgets. RV solar power systems can range in size from 100 watts to 2500 watts.
How durable are solar panels?
There is very little that can go wrong with a solar panel short of physical damage. In fact, all panels pass Jet Propulsion Labs Block V tests, which are: withstanding 125 m.p.h. wind loading, surviving one inch hail at terminal velocity (52 mph), and thermal cycling at temperatures beyond what you will experience here on Earth.
How should I clean my solar panels?
You can clean solar panels like you would any piece of glass. Use a non-abrasive cleaning agent to avoid scratching the surface or removing the panel’s anti-reflective coating. If birds leave their mark on your panels it will be very important for you to remove the mess as the shaded portion can temporarily shut down the solar panel.
How long will my solar panels last?
Crystalline panels usually come with a 25 year warranty but there is no reason to assume that they wouldn’t continue operating for many years after the warranty expires. If properly taken care of, your solar panels will easily outlast your vehicle.
Do I have to penetrate my roof?
With standard fiberglass roofs, 3M double-sided tape and Dicor sealant are usually sufficient. On rubber roofs, we recommend using ¾” stainless steel sheet metal screws, along with the double sided tape and DiCor sealant, to ensure that your rubber roof stays bonded to the plywood structure beneath it.
What will I gain by using tilting mounts?
When solar panels are tilted toward the sun their cross-sectional surface area exposed to the sun increases. In other words, the panel looks bigger from the sun’s perspective and therefore it can collect more solar energy. Tilted panels also transfer more of the sun’s rays to your cells, as opposed to reflecting them off the glass.
Tilting is especially beneficial in the winter months. In Phoenix, AZ during the month of December, a panel tilted at 30 degrees off horizontal to the south, will produce about 73%* more power on an average day than a flat mounted panel. In the month of June, that same tilt angle will actually decrease production by 10%* since the sun is higher in the sky during that time of year.
With tilted panels comes responsibility. If you don’t put the panels flat before driving it will be much easier for wind to rip them off of your vehicle.
Charge Controllers
Do I have to shut off the charge controller when I connect to shore power?
You can have multiple sources charging the same battery bank at the same time. Whether it is shore power, an alternator, a generator, solar panels, etc., it doesn’t matter. Connect them all. Run them all at the same time. No additional protections or switching of any sort are necessary. Chargers of all types are protected against reverse current flows and base their output on the voltage of the battery bank they are charging. When a battery is getting charged by any source, it’s voltage will go up proportional to the amount of current being fed onto that battery. In some situations where you have a particularly strong charging source, like an alternator or shore power, the high current fed onto batteries will drive the battery voltage up to the point that the solar charge controller thinks the battery is full. When that happens, the solar charge controller will temporarily stop charging until the voltage returns to a lower level.
What charge controllers do you sell?
We mainly sell Victron brand charge controllers because of their proven performance in RV applications. We offer mainly MPPT charge controllers to satisfy a wide variety of customer needs. The goal of our charge controllers is to maximize battery lifespan and improve system usability.
What is the difference between PWM and MPPT?
PWM type charge controllers are simpler and less expensive than MPPT type charge controllers. MPPT type charge controllers have the ability to convert excess panel voltage into higher charging amps, which means that they will produce about 15% more power than PWM type charge controllers.
What charge controller should I use?
Charge controller selection is based primarily on the panel wattage and corresponding charging current. For every 100 watts of solar panels, assume that there will be about 6 amps of charging current. The charge controller’s current rating needs to be greater than or equal to the total panel charging current. For example, a system with four 100 watt panels can use a 25 amp charge controller.
Beyond the current rating, you should also consider the differences between PWM and MPPT charge controllers. The MPPT charge controllers are usually more expensive, but can harness about 15% more power from the solar panels.
Can I use multiple charge controllers?
Yes, multiple charge controllers can be used on the same battery bank. Multiple charge controllers are used in situations where a single charge controller is not able to handle the entire output of a large solar array.
How should I adjust my charge controller settings for optimum performance?
It is very important that your charge controller system is properly tuned for your battery bank. An improperly set charge controller can destroy an expensive battery bank.
Tuning for lithium battery banks is the easiest because they do not require equalization nor do they need regular full charges. The BMS (Battery Management System) handles most of the thinking for you. But if your charge controller or converter are configured incorrectly, and the battery bank gets too high of a voltage, the mistake could be very costly.
Tuning for lead-acid (Flooded or AGM) batteries requires the most steps. The voltage and current limits for absorption, float and equalize have to be set. You may also have to program for automatic equalization frequency and duration.
Wiring
What is a series/parallel connection?
A series connection is when you connect the positive of one solar panel, battery, etc., to the negative of another, leaving you with one free positive and one free negative. With series connections, the voltages of the items connected in series sum [18V + 18V + 18V = 54V], while the current averages [(5A + 5A + 8A)/3 = 6A].
A parallel connection is when you combine the positive leads of solar panels, or batteries, etc. to make one lead and combine the negative leads to make another lead. With parallel connections, the current from each of the items sums, while the voltages average.
If you have two six volt batteries and want to make a 12V battery bank, you would connect the two batteries in series.
If you have four six volt batteries and want to make a 12V battery bank, you would connect the batteries in two parallel groups of two batteries in series.
When a solar panel gets shaded, its current drops and its voltage remains roughly the same. This is why we recommend parallel connections for solar panels. In a parallel connection, a drop in current without a drop in voltage from one source will not have an effect on the other sources connected to it. In other words, with solar panels connected in parallel, partial shade on one panel will not bring down the other panels in your system.
What gauge wire should I use?
All of our Premium Packages come with an appropriately sized wire harness to minimize line losses and maximize value. We use 10 gauge cable from the solar panels to the combiner box. Since the panels in our systems are always connected in parallel you can assume about 6 amps per 100 watts of solar panels. For cable run lengths typical in RV applications, we recommend 8 gauge for 10 amp systems, 6 gauge wire for 30 amp systems, 4 gauge wire for 40 amps systems and 2 gauge for 100A systems.
The cables going from the battery bank to the inverter have to be much thicker because they have much more current flowing through them (up to 250A in some situations). These cables are typically limited to 10 feet in length and a 2/0 or 4/0 cable is most commonly used.
How should I route wires from my roof?
With the majority of our installations, cables go from the solar panels to a combiner box on the RV roof. Depending on your rig, these combiner boxes may be installed near existing roof penetrations, like vents, or a new roof penetration will have to be made underneath the combiner box. The placement of these combiner boxes and cable routes is always planned very carefully before any holes are made. An installer will want to keep cables as short as possible while maintaining structural integrity and preserving the vehicle’s aesthetics.
Do I need fuses or breakers? Where?
You aren’t going to get a surge from solar panels (unless maybe there was a very unusual solar flare, in which case you have bigger issues to worry about.)
To protect the charge controller in the event of a short-circuit or some other unforeseen event, we recommend a fuse or breaker on the positive line between the charge controller and the battery bank rated at the maximum current of the charge controller.
We also recommend a fuse on the positive line between the battery bank and the inverter. To determine the size of this fuse, take the wattage rating of the inverter, divide it by 12 and multiply it by 1.25. For example, a 2000 watt inverter would have a rating of about 200A (2000 / 12 x 1.25 ≈ 200).
Do I need grounding?
Since your RV moves down the road on rubber tires, a grounding rod obviously isn’t going to be a part of your system. Our systems are designed in such a way that a lack of grounding will not affect performance.
Batteries
How many batteries do I need?
Batteries come in a variety of types and sizes. Batteries are like gas tanks, in that some are bigger than others. A better question would be “How many Amp hours of capacity do I need?”
When dealing with lead-acid batteries you will want between 0.5 and 1.0 Amp hours for every 1.0 watts of solar panels. If you have too much battery capacity your batteries may not be able to reach a full charge frequently enough to prevent sulfation. Additionally, battery charging inefficiency will eat up an increasing amount of solar production as you add to your battery bank. But, if your battery bank is too small, you will reach a full charge early in the day while there is still plenty of sunlight. Solar panels connected to a fully charged battery bank cannot produce power and therefor become expensive roof decorations.
With lithium batteries you don’t need to worry about full charging or inefficiencies. Get as much lithium battery capacity as you can afford as long as you have enough to store a full day’s solar production.
What is better, 6V or 12V batteries?
If you are comparing similar battery types, from a chemistry perspective, there is no difference between 6V batteries and 12V batteries. The only difference is that 12V batteries have twice as many of the same type of cells as 6V batteries. In other words, aside from smaller plates, a 12V battery is just two 6V batteries in the same enclosure. People choose one type over another based on space constraints and costs. Two 100Ah 6V batteries connected in series will have the same electrical characteristics as a single 100Ah 12 battery.
Are lithium batteries worth the upfront cost?
Many customers that factor in the longer lifespan and improved performance of lithium batteries conclude that in the long term they are cheaper than AGM batteries.
What should I do to keep my AGM batteries healthy?
The challenge with AGM batteries is managing the build-up of sulfate on the internal plates. This accumulation of sulfate on the plates is a natural side effect of the battery discharging, but getting that sulfate off the plates and back into the electrolyte solution is an often-overlooked aspect of battery management. If the sulfate isn’t regularly removed from the plates it will harden and reduce the conductive area of the plates, which will reduce the capacity of the battery.
In order to remove the sulfate, the battery has to be fully charged. But, if the battery is over charged the electrolyte will boil off. A careful balance has to be maintained in order to get the most useful life out of your battery bank. A well-tuned charge controller system can automatically regulate the charging cycle of your batteries.
How long will my batteries last?
Batteries have varying lifespans depending on how they are used. AGM batteries may last up to 5 years. Lithium batteries are warrantied out to five to ten years but can last longer than ten years.
What does Bulk, Absorption, Acceptance, Float & Equalize mean?
These are all terms pertaining to the various stages of lead-acid battery charging.
Bulk: This is the stage where the battery gets about 80% of charge and where it can handle the highest current and voltage.
Absorption: This stage can be described with an analogy of pouring beer into a glass. After the main pour (bulk stage) you have a lot of bubbles in the top part of the glass and you have to slow down the pour rate to keep from overflowing the glass. The absorption stage is essentially a slower charge than the bulk stage.
Float: The float stage is a very slow charge rate and how batteries are maintained long term when they are full. Back to the beer analogy, the float stage would be like slowly replacing beer that evaporates as a glass sits full for a long time.
Equalize: A battery is composed of cells that may not always be at the same charge level. An equalization stage is a brief overcharge that brings all the cells to full (equal charge) to remove the accumulated sulfate on the battery plates. In terms of beer, it would be like having several closely spaced shot glasses with a pitcher pouring beer all over them and only stopping when the last shot glass is full. Some shot glasses will fill quickly and overflow, but in the end they will all be equally full.
Inverters
What size inverter should I get?
Inverter capacity is measured in Watts which should be higher than the total watts of all the devices that you plan on running simultaneously. For example, if you have a 1500 watt microwave oven, a 300 watt refrigerator and maybe another 200 watts of lights, cell phone charging and misc., you will need at least 2000 watts of inverter capacity. If you only have a 2000 watt inverter and you try to run all of that equipment plus a 1000 watt blender it will overload your system and your inverter will turn off.
The size of an inverter system has nothing to do with how many solar panels you have or how much battery capacity you have, it is only relevant to the size of your AC loads.
What is the difference between pure and modified sine?
A pure sine inverter is universal and works with all AC appliances. A modified sine inverter is usually less expensive and does not work well on devices with moving parts. The output of a pure sine inverter is smooth and constantly changing as its output goes from negative to positive.
What kind of efficiency would I get on an inverter?
A typical inverter used in RV applications would have an efficiency of around 90%. In mathematical terms, this means Voltage out x Current out x 0.9 = Voltage in x Current in, or if an inverter is driving a 2000W load, you would see 120V x 17A x 0.9 = 13V x 141A.
In addition to power conversion inefficiency there is also an idle wattage consumption of around 7 watts, just for having your inverter turned on. A consumption of 7 watts over a 24 hour period works out to 168 watt hours, which is about half the daily production of a single 100 watt solar panel.
What extra features might I want on my inverter?
Many inverters will have an option for a built-in DC charger for your 12V system when you are plugged into shore power or running from your onboard generator. Other inverters may have an option for a pass-through AC function that enables shore power (or generator) to bypass the inverter when you’re “plugged in.” Some inverters may even have both of the options described above. Of course, the price point changes with the addition of these options.
Is my inverter a good match for my panels?
A better question would be “Is my inverter capable of supporting my load?”. The solar panels and charge controller determine how quickly the battery bank charges. The inverter determines how quickly power can be drawn off the battery bank and converted to Alternating Current. The two systems don’t have any contact or influence over each other.
What happens to the onboard converter/charger when I install an inverter/charger combination? We typically disconnect the onboard converter/charger from the circuit breaker in the AC distribution panel. We do this in order to prevent a feedback loop between the two chargers. Most often, we leave the onboard converter/charger in place, as a backup, in case the inverter/charger fails. For this contingency, you may want to leave the wiring intact, but label the circuit breaker to remain OFF at all times.
System
How will my alternator interact with my system?
Our systems are designed to work in conjunction with your vehicle’s alternator. You will not need to disconnect your solar system when charging your battery bank with an alternator. You can have both sources running at the same time.
How will a generator interact with my system?
Our systems are designed to work in conjunction with a generator. You will not need to disconnect your solar system when using a generator to power AC loads or charging your battery bank. You can have both sources running at the same the time.
When do I need to turn off my solar?
The short answer is never when outside. A well-designed RV solar power system will have a charge controller that automatically detects when your batteries are at full charge, and tapers off the charging current from your solar panels to prevent overcharging.
When stored inside a garage or covered area, you will want to turn your solar OFF at the circuit breaker (or remove fuse) to ensure the solar charge controller doesn’t become a load on your house battery bank. Your normal house disconnect switch will not turn OFF your solar.
Service
Do you do installations?
We do complete system installs, but you will want to set your appointment a few weeks to months in advance. We are a two man team and are always running at full capacity, and it isn’t unusual for us to be booked out months into the future.
What do you offer for warrantees?
Many of our components have their own warranties underwritten by the manufacturer, which range from 1-5 years with some proration; and, we do our best to ensure that all components are properly installed to the specifications. Our workmanship is 100% guaranteed, aside from normal wear and tear that transpires with RVs. Vibration and stress can cause connections to loosen over time, and we expect RVers to periodically have check-ups performed.
Misc
How much lithium battery capacity do I need to run an air conditioner?
As a rule of thumb we recommend 200Ah of lithium batteries for every hour of run time for a standard RV air conditioner. You will also need at least a 3000w Inverter and a soft start kit.
I’m living on a fixed budget and I want to get rid of my energy bill. Is solar a good option?
Most of our customers buy solar equipment because it gives them the freedom to camp without shore power or to reduce the amount of time that they have to run a generator, not because it is cheaper than the utility company. That being said, if you are a full time RVer, and the system we install dramatically reduces the number of times per year you have to pay for a full hookup, you could see a shorter payback period with your RV system than you would with a residential solar system, only because full hookup camp sites charge you for a lot more than the value of the utility power you consume. An RV power system will cost between $5,000 (really roughing it) to about $25,000 (most of the comforts of home), and that amount of money could pay for a lot of energy bills.