Charging The RV Battery With Solar Panels
The battery in your RV is there for when you don’t have access to electricity from shore power. It will let you use your 12V lights, run a tv if it’s a 12V model, and run your bathroom fan, etc. The RV battery charges in several ways. As soon as you plug your RV in at the campground, it will start charging your battery and keep it charged. If you’re out boondocking, gas generators and solar panels are popular ways to generate power for the batteries.
Today we’re talking about portable solar panels. Portable panels are an excellent option for people just getting started with solar that want to try it out without having to mount something to their RV roofs. By being portable, often with built-in stands, you can bring the panel out when you want to and connect it directly to your RV battery or a quick connect port. They’re also nice to have if you’re camping in the shade since you can place it in the sun and still generate energy.
Maybe you have a trailer with a port that says “Solar Ready” next to it. What this is, is a direct connection to your battery that the manufacturer has put there. Since they’re often made for specific brands, I won’t be listing that kind of panels in today’s comparison, but the panels we’re looking at can be plugged into that kind of plug with the right cable. Let me know in the comments if you have questions about a specific plug.
In the frequently asked questions-section, I have answered the most frequent questions about solar and accessories surrounding them. I have done my best to explain how they work and how you can monitor your batteries to make sure they stay alive. If you have a question that hasn’t been answered, please leave a question in the comment section, and I will do my best to help you.
See Also: Best Foldable Solar Panels
Now, let’s get to today’s comparison of portable solar panels.
All Portable Solar Panels On The Table
Note: Scroll left/right on tablets and phones
A Closer Look At Each Panel
We’ll start with a panel that is so portable that you can put it in a backpack. Most of the panels we’re looking at today are much bigger than this one, both in size and wattage. It’s on the list due to the capabilities, features, and accessories included with it. It was one of my top picks in my article about the best foldable portable solar panels.
Suaoki’s portable solar panel is made with nine monocrystalline panels totaling 60 watts. It’s a very versatile product that comes with several cables so you can charge phones, tablets, laptops, an RV battery, and even a car battery.
The charger has a built-in pocket where you can store your device while it’s charging. It has a waterproof layer on the pocket, so you don’t have to worry about moisture getting to your device. On top, you’ll find a big handle for easier transport. You can hang the panel on a tent or a tree with the handle or by using the two holes on the bottom of the panel when it’s folded open.
It has a DC port rated at 18V/3.4A and a USB port rated at 5V/2.1A. The USB port is fast enough to charge a phone or smaller tablet quickly. The DC output will charge bigger devices like laptops and solar generators.
In the box, you will get a cigarette plug charger, a 10-in-1 connector for different brands of laptops, one SAE-to-clamp cable to use with 12V batteries, one DC-to-SAE cable that you also can use to charge your RV battery if you have a quick connect on the RV, and two DC-to-DC cables.
My only complaint I have about the Suaoki 60W panel is the way it unfolds. I would prefer if the panels folded out both horizontally and vertically so you could put it on a table easier. Whether it matters to you or not depends on where you’re planning on using it.
I recommend Suaoki’s panel if you’re looking for an all-around solar panel to use not only to charge your RV battery but also other devices directly from the solar panel like phones and laptops. It’s small and lightweight enough even to bring on a hike, and for a 60W panel, that’s impressive.
Is it the solar panel you should buy to keep connected to the RV battery most of the time? No, there are better options below for that use. It’s the most versatile panel on today’s list though.
- Foldable and portable
- Lots of cables included
- Most versatile option
- USB port
- Monocrystalline panels
- Long when Unfolded (64.57 inches)
HQST has made this portable 100 watt solar panel that folds for easy storage and handling. A handle makes it easy to carry, and at almost 22 pounds it won’t be too heavy for one person to deal with.
Behind the panels, HQST has put a 20A PWM charge controller. If you’re interested in what the charge controller does you can click on the Frequently Asked Question section in the quick navigation on the right and go to the question about charge controllers. Basically, it makes sure the right voltage is sent to the batteries. There are also different kinds of solar charge controllers, and I have explained the benefits of both in the faq.
What’s neat with the charge controller used on this kit is that it has a USB output which you usually don’t see on charge controllers preinstalled with panels.
To charge the RV battery, you connect the 10 feet long wiring directly to the positive and negative terminals with the preinstalled clamps. The charge controller is compatible with both 12V and 24V systems and will show the current battery voltage on the screen.
The charge controller is not waterproof so if you camp in places where it occasionally rains, be aware of the damage that may occur if it’s left outside and gets wet. All corners are protected with pieces of plastic to prevent damages to the solar panel.
Included in the box is a carrying bag for storing the panels. The panels themselves are polycrystalline panels, so they won’t be as efficient as monocrystalline panels found on the rest of the products on today’s list.
The HQST 100 Watt is a good choice if you just need to keep your RV battery charged up enough to be able to run lights and 12V fans. If you plan on getting an inverter to charge AC electronics, I recommend getting at least 200W of solar panels although I recommend investing in a bigger battery first.
HQST has made this panel easy to use with the built-in charge controller and the clamps on the wire that makes it easy to set up. Latches will keep the panels closed when folded for easy storage, and the adjustable stand will give you full control over how much you want the panels to lean. That way you can face them toward the sun at all times and get the most energy out of them. A great plug and play system.
- 20A PWM Charge Controller with USB port
- 10 feet wiring
- 12V/24V compatible
- Carrying bag
- Adjustable stand
- Robust handle
- Polycrystalline panels
Next up is a 120W foldable solar panel from a company called Eco-Worthy. It’s two 60W monocrystalline panels next to each other, equaling 120W. Wires from each panel meet in the 15A solar charge controller where the power then is transferred through the 10 feet wire directly to your RV battery. The built-in clamps will make it easy to connect to any battery.
The frame is made out of aluminum, and a handle will make it easy to transport the panels. Latches will keep the panels closed tight while in storage. The kit weighs 26.5 pounds.
Placing it on the ground is easy with the built-in legs that fold out and let you angle the panels. Angling your solar panels towards the sun will always increase the energy you’ll be able to get out of them. Especially in the winter months when the sun is lower on the horizon. Always try to put the panels,so they’re facing the sun directly.
What I am missing the most in this kit is a carrying bag. Like on many other panels on today’s list, the panels face outward when folded. If you would throw it in the back of a truck, you are going to risk scratching the panels, and it could’ve easily been avoided by including a carrying bag.
Is the ECO-WORTHY 120 Watt the best panel for you? It’s a portable and relatively lightweight option with 120 watts worth of panels which will be enough for most weekend-campers and let you use all your 12V appliances in the RV. A plug and play system that is easy to use even for beginners.
- 15A PWM Charge Controller
- 10 feet wiring
- 12V/24V compatible
- Robust handle
- Monocrystalline panels
- No carrying bag included
There are two Renogy panels on today’s list and this is the first one, their 100 Watt Eclipse. It’s a suitcase kit with monocrystalline panels. Monocrystalline panels are more efficient than polycrystalline, you can read more about that in the faq.
A 20A built-in charge controller sits behind the panels and connects directly to your RV battery with alligator clips. The charge controller itself is waterproof so you don’t have to worry about rain damaging it. It’s a so-called 4-stage solar charge controller that will prevent your batteries from overcharging. The solar charge controller is able to operate in temperatures from -40°F to 140°F.
The solar charge controller is good to have not only to prevent batteries from overcharging but to keep track of the voltage of the battery and the current amperage the panels are generating. Having a charge controller on the panels make it easy to follow how many amps you lose or gain by tilting the panels during different times of the day as well.
The frame is made with lightweight and corrosion-resistant aluminum, just like the adjustable stands that allow you to decide at which degree you want the panels to sit. This is a great feature that makes it easy to tilt the panels directly toward the sun and suck in as much energy as possible, even during early mornings and late nights.
A premium rugged canvas carrying case is included to protect the panels during transport. The bag is easy to carry with the handle. Each edge of the solar panel kit is protected with a piece of plastic to prevent damage during transport. They will also take the biggest hit if the panel falls over.
Renogy is known for their high-quality panels. They’re also one of the best solar companies in the United States when it comes to customer support. That’s a big reason to why one of their panels is my top pick today. There are a lot of companies making solar panels right now, but not all of them use high-quality components and offer great customer support. Buying off-brand panels can become an expensive lesson when those panels have issues or don’t perform. I’m not saying that Renogy is the only good company out there, but they’re one of the good ones.
If you’re planning on using your solar panel for at least 30 days out of the year, I recommend the Renogy 100 Watt Eclipse. It’s a plug and play system that is reliable, comes with a rugged carrying bag, adjustable stand, and a waterproof charge controller. It will keep your battery charged and if you have any issues, you can be assured that Renogy will help you.
I own the older version that you can find by clicking here, and I can vouch for their high quality. Not only are the panels putting out 75W in the winter sun for me, but the case it came with is extremely rugged and heavy duty, so my panels are protected while not in use.
- Adjustable stand
- Waterproof 20A Charge Controller with 4-stage charging
- Temperature and voltage sensor
- 10 feet wiring
- Rugged carrying bag
- Robust handle
- Monocrystalline panels
How about a 200W portable solar panel? A company called Acopower has put together four 50W monocrystalline panels to make this 200W portable solar kit. It folds out and becomes a big solar system.
A 20A charge controller has been put on it to be able to handle the amps generated by the panels.
Acopowers 200W kit sticks out with its 15 feet long wires from the charge controller to your battery. It quickly connects to a 12V battery with the included alligator clips.
In the box you’ll get a carrying case to protect the solar panels with during transport. It’s a good idea to put the panels in the case whenever they’re not in use. Scratched panels can decrease power output.
The frame is built out of aluminum and has plastic edges to protect the panels further. When the kit is folded up, it latches closed, and a handle on top makes it easy to carry the panels. It’s a heavy kit weighing almost 50 pounds.
Adjustable stands will let you choose at what angle you want the panels to sit to get the maximum amperage out of the panels. They’re not as robust as Renogy’s Eclipse stands, but since the weight is more spread out and closer to the ground, it’s not that big of a deal.
If you happen to have a trailer with a quick-connect SAE input, Acopower sells an adapter to use with their solar panel kits that you can find by clicking here.
Take note of the size of this kit when it’s unfolded. Four 50W panels next to each other will cover a bigger area on the ground compared to two 100W panels.
The ACOPOWER 200 Watt is a very powerful plug and play system that will generate a lot of energy when the sun is out. With easy to adjust legs, a waterproof charge controller, protected corners, and a carrying bag, it would be a great kit for a full-timer.
- Monocrystalline panels
- Adjustable stand
- 20A waterproof charge controller
- Rugged carrying bag
- Robust handle
- Wide When Unfolded
Last up, the big brother to the Renogy Eclipse 100W panel kit. This is a 200W kit with two 100W monocrystalline panels. High quality and efficiency.
The charge controller called Voyager is the same waterproof model we saw on the Eclipse 100W above. It will let you know the battery voltage, how many amps you’re currently bringing in to your battery, and has temperature and battery voltage sensors for easy monitoring.
It comes with a rugged carrying case to protect the panels during transport, and the panels themselves lock with latches when folded for easy carrying and safe storage. Plastic protectors on the edges protect the panels even more during transport, and will also take the biggest hit if the panels ever were to fall over.
An aluminum frame and stand will keep the suitcase relatively light at 36 lbs. Much lighter than the Acopower above with the same wattage. The adjustable legs make it easy to follow the sun during the morning, day, and night to keep the charging efficiency high.
Connecting the charge controller to your RV battery is easy with the included alligator clips and 10 feet of wiring.
The Renogy 200 Watt Eclipse is my top pick this year for portable solar panels. It comes with everything you need in a plug and play system to keep your RV batteries at a healthy level of charge as long as the sun is up. Add a 100ah AGM battery and an inverter and you’ve got yourself a sweet solar setup. If you feel like it’s too much money, you can always do a DIY system. It’s not as hard as it might look and I will help you build one down below.
- Adjustable stand
- Waterproof 20A charge controller with 4-stage charging
- Temperature and voltage sensor
- 10 feet wiring
- Rugged carrying bag
- Robust handle
- Monocrystalline panels
- Should include extension cord for this price
Conclusion And Recommendations
If you’re not sure about how many watts and panels you need, you should read through what to consider and the frequently asked questions below. The best option for you is the one that fits your needs, no more and no less. I always recommend getting more solar than you need though, as you won’t have perfect sunny conditions every day of the year. Some days you’re going to have to use the power you generated a day or two before, and some days you might be able to generate energy for an hour before a storm comes in.
Now, my recommendations.
Most Versatile: SUAOKI Solar Charger 60W – If you’re a backpacker and don’t spend 100% of your camping-nights in an RV, I believe the Suaoki is the best choice. It’s a versatile product that lets you charge your phone, tablet, laptop, and 12V batteries all-in-one. Sure, it won’t be as powerful as the big ones, but this is the most portable solar charger on today’s list.
Best For Charging RV Batteries: Renogy 200 Watt Eclipse – I wouldn’t go any higher than 200W with portable panels. If you need more, I recommend mounting them onto your RV or van roof, for practical reasons. But if you’re looking for the best portable panel to put outside your vehicle to charge your 12V batteries within hours, this is it. With 200W monocrystalline panels, adjustable legs, a waterproof charge controller, and a great rugged carrying case, it’s the best plug-and-play system on the market in 2019.
What To Consider
When shopping for a portable solar panel there are a few things to consider. Let’s name a few.
Watts: Each of us uses a different amount of energy every day. How many watts you need depend on what you plan on running on the battery and for how long. If you’re only running 12V lights and the bathroom fan for an hour a day, I can almost guarantee that 100 watts will be enough for you. If you have a 12V tv that you plan on watching every day, at least 200 watts is recommended. Those are extremely general guidelines and there are so many factors that play into whether 100 or 200 watts is enough for you. In the end, it’s about how many hours of the day the solar panel can generate energy to charge your battery. A 200W panel won’t be any more useful than a 100W panel on a completely cloudy winter day.
Weight: If you travel a lot and would have to pack the panel in and out several times a week, weight becomes important. If you leave the panel out for a week, maybe not so much. I know people often get surprised at how heavy solar panels are, so before you buy anything, check how many pounds you’re going to have to deal with on a daily or weekly basis.
Cord Length: If you often park in the shade, you’re going to need a longer cable to reach your battery. The longer the cable, the more power loss in DC power though, so try to have a short wire as possible going from the solar panel to the charge controller and onto the 12V battery.
DIY Solar Setup
If you ever go on forums to look for opinions on portable solar panels, you’ll probably run into somebody that says: “Just build your own solar panel system, much cheaper.”. And while it’s true that you sometimes can build your own system for a lower price than buying a plug-and-play system, it does take some learning and understanding of how to put the pieces together if you do it yourself. Buying a plug-and-play system is, in my opinion, a great option that might cost extra but will save you time if you’re totally new to solar.
Not only do you have to learn how to put the panels, cables, and solar charge controller together, you will have to build your own stand, corner protectors, and stitch together a carrying bag to protect your panels during transport. Not everybody has free hours or will to do this.
I went out to find the easiest DIY system to put together to save at least some of the money from a plug-and-play system, and this is what I would do:
Panels (100% Necessary): I recommend going with 100W 12V monocrystalline panels. The lighter, the better. I recommend the Renogy 100 Watt 12 Volt Monocrystalline Solar Panel (Compact Design). You can buy as many panels as you need but the charge controller I recommend below has a max of 260W input at 12V, so I recommend two panels. If you want more panels you have to buy a solar charge controller that can handle the amp input all the panels will put out together if they’re wired in parallel. To understand parallel vs series, check out the frequently asked question section.
Solar Charge Controller (100% Necessary): The solar charge controller will regulate the amount of voltage being transferred to your RV battery and is a necessary part of a safe solar system. With two panels, a 20A solar charger will do the job. Like the ACOPOWER VS20AK that includes the cables we need to connect it to the Renogy solar panels and the 12V battery. The ACOPOWER solar charge controller is a 3-stage PWM model with two USB ports on it.
It comes with an SAE connector for pre-wired 2 pin sockets found on some RV brands. But you also get alligator clamps that connect directly to a 12V battery.
Stand (Not 100% Necessary): You can use a 5-gallon bucket as a stand to lean your panel on. But if you want adjustable legs there are stands for sale. I recommend the Adjustable Solar Panel Mount by Link Solar. These fit the Renogy 100W panel I recommended and will let you adjust the angle your panels are sitting at.
Cables And Connectors (Necessary Depending On Use): There are a couple of cables and connectors we can use depending on your needs.
Renogy MC4 Y Branch Connectors – These will let you connect two panels together in parallel so if you plan on having at least two panels, this will be necessary.
Battery Charging Cables SAE TO SAE – This is a SAE to SAE 12 feet extension cable. If the cable coming from the solar charge controller isn’t long enough to reach your 12V battery, this is the kind of cable you’ll need.
WindyNation MC4 Extension Cable – If you want the solar charge controller sitting by the battery instead of behind the solar panels, you can use an MC4 extension cable like this to be able to put the solar panels further away. There are several lengths to choose from.
How to connect the parts above
- The first thing we need to do is connect the charge controller to the battery. To be able to use the charge controller we must make sure that we have a sealed, gel or flooded kind of battery. The label on the battery will let you know this. You must set what kind of battery you have on the charge controller so it can charge and protect your specific kind of battery. We connect the charge controller to the battery by using the SAE to Alligator Clips adapter that came with the ACOPOWER VS20AK. If you plan on mounting the solar charge controller to your batteries, you might need a SAE TO SAE Extension Cable. The extension cable will let you put the panels and the charge controller at least 12 feet away. Sometimes that is necessary to reach the sunlight if you’re parked in the shade. Remember that: RED is POSITIVE. BLACK is NEGATIVE. Never connect the red to negative.
- Connect the solar panels to the charge controller. If you only have one panel this is done quickly through the MC4 connectors. Positive to positive, negative to negative. If you have two panels, you’re going to need to connect them in parallel with Renogy MC4 Y Branch Connectors. A parallel connection means that you have all positive wires connected to each other, and all negative connected to each other. So you will take the positive connection from each solar panel, plug it into the MC4 Y Branch Connector, then plug that connector into the MC4 coming from the solar charge controller. Then do the same with the negative wires. What this does is that it keeps the voltage the same, but the amps add up. So if you have two 12V panels rated at 5 Amps in a parallel connection, they will output 12V and 10 Amps. Positive to positive, negative to negative. Red is positive. Black is negative.
- Place your solar panels in the sun and start generating power!
That is essentially the most basic setup that you could do on your own. From there, you can buy an inverter like the Power TechOn 600W Pure Sine Wave Inverter and put in your RV so you can run regular 120V AC appliances.
Frequently Asked Questions
How much solar power do I need?
To know how many solar panels we need to have to be able to use the appliances we do daily, we need to know how much energy they consume. I recommend getting something like the Poniie PN2000 Plug-in Kilowatt Electricity Usage Monitor. You can plug your appliances into this and see exactly how many watts it uses. Its max is around 1900 Watts though so don’t plug your RV into it and start the air conditioner.
When you know the watts, make a table with each item that uses electricity in the trailer. It will be easier to know how long an appliance can run on the 12V battery if we turn those watts into amps. Take the watts, divide it by 12, and that’s the amps. For example, if your microwave is rated at 900 watts, it uses 75 amps per hour to run (900/12). Let’s say you have a 12V battery with 100AH capacity. We can fit 75 in 100 at least once, so if you have a 100AH battery and want to run the microwave through an inverter, you’ll be able to run the microwave for at least an hour before the battery is dead. An inverter uses some amps when it turns DC into AC though, and it also uses energy so don’t expect the microwave to run 1.3 hours just because 75 fits in 100 1.3 times. It’s good to overestimate how many amps an appliance uses, rather than underestimating.
If you would rather look at the appliance to figure out amps instead of using an electricity usage monitor, we need to know if it’s a 12V or 120V item. If it’s 12V, like the water pump in your RV, we can write down the amps it says on the pump without changing them. If it’s 120V, like a laptop charger, we’ll take the amps and multiply it by 10. So a 120V appliance rated at 2 amps would be 2*10=20 amps. If it tells you watts it doesn’t matter if it’s a 12V or 120V, we’ll just divide it with 12 as we did with the microwave above.
The sucky part with batteries and Amp Hours is that you should never run a battery to 0%. Most deep cycle batteries should only go to 50% state of charge before being recharged, or you’ll shorten its lifetime. Lithium batteries are better in that sense and can often be run down to 20% without hurting the battery. Ask the manufacturer of the battery what they recommend to be sure. For example, if you have a 100AH Deep Cycle Battery, never use more than 50AH before charging it up again.
If you have no idea how many amp hours your battery has, we can figure it out as long as we have access to the Battery Reserve Capacity. This number is sometimes written on the label of the battery, and if it isn’t, there should be a model number. If you Google that number and find the exact battery on the manufacturer’s website or a store you might be able to find the Reserve Capacity (RC) in the specifications. If you find several Reserve Capacity numbers, look for the one that says minutes @ 25 amps. What we’re going to do with that number is divide it by 2.4. So if it says in the specifications that the battery has 120 minutes of RC (Reserve Capacity) at 25 amps, we’ll take 120/2.4=50. That means it’s a 50AH battery.
Now let’s say that we want to watch TV in the RV, and we have a TV that says on the back that it uses 60 watts. We’ll start by dividing that with 12 to know the amps, 60/12=5 amps per hour. If we know that we have a 100AH battery and can safely use 50AH of that, let’s see how many hours we can watch TV. 50 (how many amp hours we can safely use in our battery) divided by 5 (how many amps our TV uses per hour) equals 10. So 10 hours of TV-watching, right? Well, unfortunately, as I earlier stated, an inverter isn’t 100% efficient when it turns DC (our 12V battery power) into AC (household plug, what our tv uses). It’s more realistic to assume 80% efficiency. We’ll take the 10 and multiply it by 0.8 (80% efficiency) and end up with 8 hours. So what we learned by all of this is that we can watch a 60W TV for 8 hours with a 50AH battery if we’re using an inverter with 80% efficiency. Without an inverter, we can’t run the 120V TV unless we’re connected to shore power or a generator. You can use 12V TVs wired to the 12V battery without an inverter. I have written a post about the best 12v TVs for RVs that you can find by clicking here.
I recommend investing in a big battery before spending a lot of money on solar panels. The more power we can store and use for rainy days, the better.
Now that we’ve gotten a basic understanding of amp hours, let’s look at the table I have made for my needs:
The total amp hours found in the furthest right column is found by taking amps x quantity x hours per day. For example, on the first 4W light in the table, the calculation is 0.3*10*2=6.
My very rough estimate is that I need 103.3 amp hours a day to live the way I want in the RV. If I don’t have a lithium battery and want to keep my batteries at 50%+, I’m going to need a battery with at least 206.6AH of capacity (103.3*2). If I buy the NP6-225Ah 6V 225Ah AGM 2pcs and wire in series to make them 12V, I will have 112.5 usable amp hours.
Now, back to the question about how much solar power I need. A good 100W solar panel like the Newpowa 100 Watt Monocrystalline generates about 5 to 5.82 amps in good sunlight. So now we must need how many hours of sun we get, here’s a picture with the average sun hours a day for the lower 48 states.
I’m in Utah, so the average is 5 hours. If I had one solar panel pulling in 5 amps, 5 hours a day, my panel would generate 25 amps (5*5). But I need to generate at least 103 amps a day as we calculated above. So let’s say I have 4 solar panels equaling 400W. They should be able to generate 20 amps an hour to my batteries (5*4), and if they get 5 hours of sun per day, that’s 100 amps (20*5). A little bit closer to what I need. I will add a fifth panel since my solar charge controller and inverter isn’t 100% efficient. That way I will generate 25 amps per hour and 125 amps per day. There will always be cloudy days when I won’t get another 125 amps in my battery, but that’s the way it goes when you rely on solar power. By having more than I need, clouds won’t hurt me as much.
To conclude, five 100W panels will bring in 125 amps per day in perfect sun to charge my 225AH battery of which 112.5 are safe to use before my battery goes under 50%. If I use 100 amps a day I better hope I won’t get any cloudy days. If I see that the forecast says rain for the next four days, it would be smart to charge up my battery on the last sunny day and only use about 20-30 amps a day so I don’t run out of juice before the sun comes back.
How much my panels can actually generate depends on several factors, but I will talk about that in a question below about how long it takes to charge an RV battery with solar.
How long will it take to charge my RV battery with solar panels?
How long it will take to charge your RV battery with solar depends on several factors, let’s name a few:
- Battery Size – How long it takes to charge your specific 12V battery depends on how big the battery is in Amp Hours.
- Solar Panels – How many solar panels you have and how efficient they are will determine how long it takes to charge your battery.
- Charge Controller – Do you have a PWM or MPPT charge controller? MPPT is more efficient and will bring in more amps in worse conditions like early morning/late afternoon and in the winter.
- Weather – A solar panel rated at 5 amps might only generate 0.5 amps when it’s cloudy. It can be a mistake to do a calculation based on perfect conditions because you won’t have 365 sunny days every year. It also matters if it’s summer or winter. The sun is lower on the horizon in the winter, so it will be harder for the solar panels to generate their max amperage.
Remember that these factors play into how long it will take to charge your RV battery. But let’s do a rough estimate.
Let’s say that this is my setup:
100AH 12V Battery
200W 12V Solar Panels Wired In Parallel
I wake up at 8 am with my batteries at 50%, at 10 am I put my solar panels in the sun and it’s sunny all the day until 3 pm, so my panels got five hours of sun. My panels generate 5 amps each per hour, so 10 amps together each hour, equaling 50 amps after five hours. Since my 100AH battery was at 50% I needed 50 amps to recharge it, and that’s exactly what I got. So it took five hours to recharge my battery from 50% to 100%.
Do solar panels work at all when it’s cloudy?
It depends. What time of the year is it? Do you have an MPPT charge controller? Are your panels angled directly towards the sun behind the clouds? Are your panels monocrystalline and high-quality? Using an MPPT charge controller will increase the chances of generating a couple of amps when it’s cloudy. Sometimes if it’s really cloudy you won’t generate any power at all.
How do I get the most out of my solar panels?
- Keep them clean – If they’re on your roof, remember to clean them. If a storm comes through and it suddenly takes longer to charge your batteries, you might just have to clean them with some glass cleaner.
- Angle – Especially important during the winter months. Tilt your panels so they face the sun.
- Kind of charge controller – By using an MPPT charge controller you will usually generate more amperage when the sun is weaker. Like in early mornings and late afternoons, winter months, and when it’s cloudy.
- Monitor your system – By monitoring your system you will learn what generates the most amps. Tilt your panels and experiment to see which angle works the best in the winter or late afternoons.
Do solar panels work in the winter?
They do, but fewer hours from a sun lower on the horizon will make it harder for your panels to generate energy. Tilting your panels and using an MPPT charge controller are two ways to improve the number of amps you can generate in a day.
Are solar panels better than generators?
Better for your wallet? No. Better for the environment? In the long run, yes.
Buying a solar system is something you do to leave a smaller footprint on the earth. Producing your own clean energy feels great, and it’s also more peaceful when you’re camping because you won’t have to listen to a loud generator (unless your neighbor has one).
Solar panels are an investment that will cost you, and buying a generator is much cheaper even if you have to spend money on gas or propane, that’s just a fact. Hopefully, it will change in the future to where solar systems can compete more in terms of cost.
What is a solar charge controller and do I need one?
Yes, you do need one. A charge controller will regulate the voltage to your batteries to protect them from overcharging. Even though a solar panel might be 12v, it will often put out between 16 to 20 volts when the sun is out, and if a solar charge controller isn’t there to regulate the voltage going into your battery, it could damage it.
Solar charge controllers have a neat function that prevents reverse-current flow. Without them, electricity could actually flow back from the battery to your panels and waste power. The way it works is that the charge controllers opens the circuit when it senses voltage from the solar panels, and stop it when there is nothing to gain.
There are different kinds of charge controllers, but the most popular kinds when it comes to solar are PWM and MPPT.
PWM, short for pulse width modulation) is cheaper than MPPT but less efficient at around 70-80% efficiency. PWM controllers will take the voltage coming from your panel and turn it into 12V to safely charge your battery and avoid overcharging.
MPPT, short for maximum power point tracking, costs more than PWM but are more efficient with 90-98% efficiency. MPPT controllers take the excess voltage and turn it into amperage, instead of wasting it like PWM controllers. They also allow higher voltages through the wires, resulting in reduced power loss.
So is it worth the cost for 10-20% more efficiency? I would argue that it depends on how big your solar system is. If you have 1000W worth of solar panels it can be worth it since the 20% increase would be a lot of amps per hour. PWM controllers are only available in sizes up to 60 amps, while MPPT goes up to 80 amps, so if you have a really big system it might be your only option. If you only have one 100W solar panel, then I would spend that money toward another panel or a bigger battery.
All the portable solar panel kits we looked at in this post today come with PWM charge controllers so there’s no need for any additional purchases.
A feature often found on solar charge controllers are 3 or 4 stage charging. These are different stages that charge your battery in specific ways to prolong life and protect your battery. It’s important to set the settings of these stages depending on what kind of battery you have. If your charge controller is capable of 4 stage charging you should read the manual of both the charge controller and the battery to be able to set the right values to keep your battery charged safely.
The 4 most common stages are:
Bulk – Often the first stage of charging your battery. When your battery is under 80% state of charge and the sun is hitting your panels or a generator is turned on, the bulk stage tries to put as much amperage as possible into your batteries.
Absorb – When a battery reaches around 80% state of charge, the absorb stage comes into play. Now the batteries will stay at a preprogrammed voltage and the amperage coming in from your solar panels will reduce. The absorption stage helps retain the energy the panels generated during the bulk stage. When the absorption stage is completed, the battery is fully charged.
Float – When the charge is complete, we enter the float stage. Now the voltage is dropped further to a preset value so setting the right value for your battery here is critical.
Equalization – The goal of the equalization stage is to equally charge every single cell in the battery to the exact charge, basically a controlled overcharge.
Does a charge controller charge my batteries any different from the built-in converter charger in my RV?
The converter that came with your RV is most likely a “dumb” charger with only one stage, the bulk stage. This won’t fully charge your battery to 100% and have the other stages that can make your battery last longer.
Look in the manual you received with your RV to learn how many stages your specific converter has. It might be smart to upgrade the converter if it’s a one stage and you’re spending money on big batteries. A lot of inverters nowadays come with a built-in smart converter charger with 3 or 4 stage charging.
How do I connect a solar panel to my RV battery?
Your solar panel will be connected to a solar charge controller, and the charge controller will be connected to your battery. Read above about why you need a charge controller and the purpose it has.
Connecting the charge controller to the battery can be done in different ways, both “permanent” and temporary ways. Standard ring terminals are the more permanent way since bolts will be sitting on top to hold the terminals fastened and connected. A temporary way can be alligator clips like the clamps you probably have seen on jumper cables. For portable solar panels, alligator clips are the way to go since you can connect them so easily. If you have solar panels on your RV roof and don’t have to disconnect your cables every other day, ring terminals will be the better solution.
When connecting any cables to your RV battery, remember that RED is POSITIVE. BLACK is NEGATIVE.
How do I know how charged my RV battery is? Percentage?
Manufacturers really do a crappy job when it comes to helping you monitor your RV battery. The high-end brands are starting to get better, but most trailers come with a 0 – 25 – 50 – 100% monitoring screen. Push a button, and we will let you know. The problem is that this value isn’t accurate at all.
Some solar charge controllers have a screen with features and on some models, it will tell you the battery voltage. Unfortunately, these aren’t 100% correct either.
The best way to know the state of charge of your battery is with a battery monitoring system. It’s done with a shunt hardwired to the battery. A popular option is the Victron BMV-700 Battery Monitor. The monitor can be put in your RV and once you’ve set how big your battery bank is in total amp hours, it will give you a percentage. It will also tell you the current voltage and how many amps you’re consuming at the moment.
If you do know the voltage and believe it’s somewhat accurate, here are some general guidelines for a 12V AGM and wet cell battery based on voltages and its corresponding state of charge percentage.
As always with general info, this is a general guideline and you should always read the manual or contact your battery manufacturer to know what is best for your specific 12V battery.
How low can I safely discharge my RV battery?
The safe depth of discharge and usable amp hours depends on what battery type it is. Most RVs and trailers come with flooded cell batteries installed, and we should never bring those under 50% state of charge.
If you have gone out and bought lithium batteries, you probably know already that they’re usually safe to discharge all the way down to 20% without risk of damaging them.
Now, will you kill the batteries completely if you go to 10%? No, but if you want the batteries to last longer and not have to buy new batteries every year it’s smart to not discharge them under 50% or 20% with lithium.
Again, these are general guidelines and you should read the manual or contact the battery manufacturer to get the exact recommended safe discharge voltage and percentage for yours.
What is the best 12V battery for RVs?
I recommend watching this video (less than 10 minutes) about the different lead-acid battery types often used in RVs and what each of them does good and bad.
What is not talked about in the video is lithium batteries which are becoming more and more popular, although at a much higher cost than flooded, AGM and cell. If you plan on living fulltime in your RV it can definitely be worth the investment. I recommend purchasing 12V lithium batteries from reputable companies like Battle Born or Renogy. Click here to see Battle Borns 100AH 12V Lithium on Amazon or Click here to see Renogy 100AH 12V Lithium on Amazon. Both of these are “drop-and-replacement” which means that they’re extremely easy to install on RVs.
Parallel Vs Series?
You can wire both solar panels and batteries in parallel or series, the idea and result are the same.
The image below by parkedinparadise.com clearly shows the difference between solar panels wired in series and parallel.
As you can see in a series connection, negative is wired to positive and at the end wired to negative. In a parallel connection, each positive wire meets and is separate from each negative wire.
So what difference does it make? In series, the voltage will add up while the amps stay the same. Meaning that if you have two 12V solar panels generating 5 amps each, in series they will put out 24V at 5 amps.
In the parallel connection, the voltage stays the same while the amps add up. So our two 12V solar panels generating 5 amps each would still generate 12V, but 10 amps.
Which way should you wire your panels?
If you have a PWM charge controller and plan to charge a 12V battery, you must wire your panels in parallel. If you have an MPPT charge controller, you can decide yourself. If the distance between your solar panels and the MPPT charge controller will be longer than 20 feet, I recommend series. The reason being that longer distance will cause the voltage to drop, so we want the voltage to be as high as possible when our wire is long, which series wiring will help with.
What is the difference between solar panel types (Poly vs. Mono)?
Both monocrystalline and polycrystalline have their pros and cons.
Monocrystalline panels are more expensive than polycrystalline but have a higher efficiency rate. On average 15-20% versus poly 13-16%. Monocrystalline panels are also more space-efficient, meaning that it takes less space to generate the same amount of power as poly.
Polycrystalline panels cost less to make, which turns into a lower cost to you. They don’t handle heat as well as monocrystalline and can perform slightly worse in high temperatures.
I recommend monocrystalline panels for their efficiency and reliability.
Can I use the electrical outlets in my RV if I have solar panels?
To use the electrical outlets in your RV, the outlets must be getting power from somewhere. If you’re connected to shore power, that’s how your outlets get power. Solar panels can not directly deliver power to your outlets since they generate 12V DC power to your battery and your outlets are 120V AC power. To use the energy that the solar panels have generated into our batteries, we’re going to need an inverter. An inverter turns DC into AC, and if wired to your AC panel, it can power your AC outlets.
I have done my best to explain solar power and how it works with the products surrounding them. Please let me know if you have a question, or if there is something you feel should be corrected or added. It would be great if we could create a discussion in the comment area and help each other out. Making solar easy to understand isn’t easy, but together we can make it work.