In order to power your appliances with Solar Panels and Batteries in your RV, you need to know how many total watts they use, then you’ll know how many Solar Panels and what size Battery Bank you will need to accommodate them. Always add some extra, as I do here with 25% or 1.25 for future needs. Most appliances list Watts, Volts & Amps on their electrical tags attached to the device but some don’t. It’s not as hard as it seems, folks. If I can do it, anyone can. How Do You calculate Solar Panels Watts needed for an RV?
- List RV devices
- Convert to watts-Amps x Volts=Watts
- Estimate use of devices in hrs. per/day
- Watts x hrs.= Watt-hours per/day
- Convert Watt hrs.to Amps hrs
- Battery Capacity=Total Watt hrs./ by 12 Volts-Add extra 25%
- # of Solar Panels
- Total Watt hrs. x 1.25=Watt hr./5 hrs.of Sun=Watts of Solar Energy
In the Basics of Solar Power Systems there are 2 types of Set-ups:
- Off-Grid System-the Solar Panels which are the source of power will be charging Batteries
- Grid-Tie System-the Solar Panels use the power derived from the Solar Panel on Demand
In this article, I will explain to you the very basics Off-Grid System along with the language and mathematical formulas that you’ll need to touch on the understanding of a Solar Power System. It’s easy to grasp once you start at the beginning with each part of the System and how we can add the proper component to the next one using a formula that converts Volts and Amps to Watts and back again.
Solar Power Calculation Formula
What are Volts
A great way of looking at electrical voltage is to compare voltage to pressure in a garden hose with water running through it. Voltage would be the pressure of the water running through the garden hose or the potential of pressure that can be used from the garden hose. The voltage can tell you what appliances you can hook up to this system a 12-volt appliance can hook up to a 12-volt battery. A 110 AC electrical appliance will be able to be plugged into a 110-volt outlet. In both cases, there is enough force to power each appliance to each system.
What are Amps
Another part of this equation is Amperage. Amps are how much electricity is going through the wire. Compared to the garden water hose Amps would be how thick the hose is. Because the thicker the water hose, the more pressure you can run through the hose.
The thicker the wire is in an Electrical system, the more electrical power you can send through to an appliance and that is why wire comes in different sizes. Simply put the larger the device or appliance you are trying to power up the more electricity it needs, the thicker the wire you’ll use.
In a Solar System, if you have a 12-volt Solar Panel System (which is the same size as a car battery) then you will be able to power 12-volt devices or components to that system. You will need the correct size wire that is required for a 12-volt battery feeding the device.
What are Watts-the formula is the Voltage x Amperage=Watts.
With Solar Power Systems the size of the systems is based on Watts. Watts is a combination of Volts and Amps. The formula is the Voltage x Amperage=Watts. Using Wattage gives you a better overall idea of the power that you are consuming.
In the world of Solar Power say for an RV you’ll get a better idea of the power consumed or needed to run the RV just by converting the Watts to time which is called Watt-hours. On your electric bill, the Electric Company lists kW/h. This formula is Watts x Hours=kW/h.
- So if you consumed 200 watts in one hour then 200 x 1 hour=2oo Watt-hours.
- If you used 1000 Watts x 1 hour=1 kWh or 1 kilowatt per hour.
The power consumption of appliances is generally always given in watts. So, for example, a small portable TV is around 20w. This information can be found on the data sticker that most electrical items have. To calculate the energy you will use over time, just multiply the power consumption by the hours of intended use.
Solar Battery Bank Calculator
Watt-hours are very important in determining what appliance draws the most power over time. Some appliances are used more and some less breaking this down points you in the right direction and ensure you buy the right components for your Solar System.
You can also use it to determine how much power a battery can store which you need as a component in your Solar system. Figuring out your Battery size is not rocket science but an important part of operating the devices in your RV or Camper, and how much electricity a battery can store. The amount of battery storage you need is based on your energy usage. Energy usage is measured in kilowatt-hours over a period of time.
A 12 Volt Battery that is rated at 100 Amps-hours means that the battery can produce 100 amps for 1 hour at 12 volts. The formula looks like this: 12 Volts x 100 Amp Hours = 1200 Watts. Knowing this information will allow you to figure out exactly how long it can power your devices or appliances and how long it will take to charge from your Solar Panels or an AC charger.
- A 1000 Watt-hour Battery/100 Watt Load= 10 hours- This means that if you have a 1000 Watt-hour Battery and you need to power a 100 Watt load all you need to do is divide 1000 Watts by the load which is 100 Watts and you get 10 hours.
- Another example: We have a 100 Watt-hour Battery and we want to power a 50 Watt load that formula would look like this-100 Watt-hour Battery/50 Watt load=2 Hours
Everything involved in Solar Systems needs to be figured out in Watts. So use Volts and Amps to figure out the Wattage and then use Watts and Time to figure out Watt-hours then use Watt-hours to determine how big a battery is, how long it takes to recharge that Battery, How long you can use that battery to charge your Loads, appliances and devices.
Don’t use Amp rating always, convert to Watts then find the Watt rating, or find the Watt-hour rating then use easy arithmetic to compare.
Parallel and Series Connection
By changing Parallel and Series connect components you can change the voltage and amperage ratings of Batteries and Solar Panels just by connecting them in different ways.
- If you connect components in Parallel-you are connecting all the positive and all the negatives together. If you have 4 Solar Panels and you connect them in Parrell which means you are connecting all the positives into one common wire and all the Negatives into one common wire this is what call Parallel Connectors.
- If you connect components in Series-you are connecting the Positive of one Panel to the Negative of the next Panel and the Positive of the next one to the Negative following that Panel that is called Series Connection.
In a Parallel Connection, the voltage won’t change. Amperage does. So if you connect 4 Panels together in a Parallel connection and each one
produces 10 Amps you add them together for a total of 40 Amps of power. The Amps will increase but the voltage won’t change. In a Series Connection, the Voltages will change and increase but the Amps stay the same.
So if the Solar Panels are rated at 10 volts per Panel and you connect all 4 Panels together in a Series Connection that means you can add each Panel for a total of 40 Volts but the Amperage will still be rated a 10 Amps.
The point is you can change the Amps or Voltage on Solar Panels or Batteries by wiring the components differently.
Wiring Batteries in Series and Parallel
How to Calculate Solar Panel, Battery, and Inverter
Getting to this point you have a basic understanding of what basic electrical terms like Volt or Amps mean and they can be changed by the way components like Solar Panels and Batteries are wired together even if you won’t be doing any of it yourself. Understanding the basics will give you a general idea of how Solar Energy is working and why converting the voltage to Watts is the most important formula you’ll be using some of these formulas, especially at the beginning before you buy your Solar System and install it on your RV, Van or Camper.
In this example of calculating the total amount of power you will use in your Camping vehicle in this case we’ll say RV, you calculate each appliance to determine the expected load on your Batteries.
So you need to make a list of the appliances that you will be using and how many hours they will be operating. These devices (Electronic GPS) or appliances (refrigerator) whatever you want to call them.
They are listed and converted to Watts from Voltage. Watts is the total amount of overall power needed to operate your RV to based on the number of days you can dry camp without plugging into shore power or using a generator, or if you run into bad weather without sun not enough to recharge a battery.
Start a list of appliances that you will definitely need to run and convert to Watts. Like this one (to the left) As an example, we will start with an appliance that will be running for most of the day like a Fridge. The Wattage will determine the size and amount of Solar Panels, batteries, and the size of your Inverter that will be needed. Most if not all electrical devices have a label located on the outside that gives the number of Volts, Amperage, and in a lot of cases Watts that it demands to power the appliance.
Look for Out Wattage of the electrical appliance. Some will only give you the Volts or Amps of the Output. Using this formula Watts = Voltage x Amps this formula will help convert the overall power to Watts as we talked about in the first part of the article. If they just give you milliamps then use this formula Milliamps/ 1000 = Amps then use the formula to figure out the Wattage. Watts = Voltage x Amps = Watts
Solar panels are typically rated and sold in Watts. Electrical loads are also typically rated in Watts (you can usually find the wattage stamped into any electrical appliance). But RV batteries are typically rated in amp-hours. Since we’re trying to figure out things from a perspective of energy in = energy out perspective, we need to be able to convert things easily. Fortunately, the equation is pretty easy:
Watts = Amps * Volts
Once you figure out all your appliance power usage in Watts the next step is to figure out an average daily use for the appliance. Most Appliances or devices don’t run 24 hours a day. They may only run 1 hour or maybe 12 hours per/day. On this chart, the Coffee Maker is rated at 1200 Watts and will say it runs for 1/2 hours per/day. You can get the load from the Battery. 1200 x .30= 360 Watts. This to me kind of seems to be overkill but maybe it doesn’t to you.
There are also really good online Calculators like this one at Go Power Resources.com that you can use that will size your Solar System Kit. Watch this video from the AltE Store that explains very well Load Calculations for RV, Camper, or Off-Grid cabin.
In the 2nd example, we will test the overall load on the Batteries by Just Go Camping. *Always remember never to drain your Batteries below 50%
- Don’t use your Generator
- Don’t try and conserve energy
- Unplug Solar Panels
- Only draw from your Fully Charged Batteries
- If you don’t make it through the night then you have Battery issues.
- You’ll want to drain the Battery down to
You have a 200 amp-hour battery bank. They’re lead-acid batteries, so you don’t want to discharge them any more than 50%. At day zero, you start at nightfall with a full battery bank. At the end of 24 hours, your voltage is down to 12.4 volts.
That’s still about 80% according to the state of charge chart, so you continue on. At the end of the second day, your voltage is down to 12.2 volts. 60% according to the state of charge chart, so you keep going. At the end of the third day, you’re down to 11.9 volts. That’s 40% on the state of charge chart, so you stop the test and turn on the generator.
So with a result in three days, you used 60% of your battery capacity. Your battery bank is 200 amp-hours. 60% of that is 120 amp hours over three days. Dividing that by three, you used approximately 40 amp-hours per day. The math with this is easy but a little tedious.
Types of Solar Batteries
There a few types of Batteries used in Solar Systems but the main 2 are Lead-Acid and Lithium-Ion. A typical rule of thumb that needs to be taken into consideration in Lead Acid Batteries is 50% DOD which is the depth of discharge and that only means the manufacturers recommend that you should not train more than 50% of the battery’s capacity. Lithium-Ion Batteries can use for whatever they are rated for so a Lithium-ion 1000 wh Battery can be used up to 80-100% and a Lead Acid Battery rated 1000 watt-hours should only be used down to 50% of its charge, which takes it down to 500-watt hours.
Lithium Batteries are more expensive but they are lighter they have a longer charge cycle than Lead Acid Batteries and as your need for Solar Panels and more power will be created, you’ll be able to complement them using these smaller more powerful types the Lithium-Ion in your Battery Bank.
A Lithium Battery is most recommended but the price is higher than the rest, so the next one that is a little cheaper is the AGM Battery that is enclosed so you won’t have to maintain it adding distilled water and they will charge 5x faster and higher Amp reading than the cheapest Lead Acid model. The Battery Bank is the Solar System Foundation so start with the most and best type of Battery that your budget can allow.
How Does an RV Inverter Work
An inverter’s basic function is to “invert” the direct current (DC) output from Batteries into alternating current (AC). AC is the standard used by all commercial appliances, which is why many view inverters as the “gateway” between the photovoltaic (PV) system and the energy off-taker.
In addition to converting DC to AC, they provide a number of other capabilities and services to ensure that the inverter can operate at an optimal performance level, such as data monitoring, advanced utility controls, applications, and system design engineering.
Using your highest demand for Watts whether it’s a fridge at 1500 Watts or a Hair Dryer at 1100. The Inverter would have to be at least 1500 watts to match the watts of the fridge. By adding a buffer of another 500 watts the right size would be around 2000 Watts. There are 2 Types of Inverters used in the RV Solar System.
Sine Wave Inverter
The most common type of motorhome, RV, or Camper Inverter is called a Sine Wave also called a true sine or pure sine inverter. The best RV inverters use this modern technology because it is the strongest and most advanced design. Sine wave inverters work with almost all appliances, making them ideal for mobile home use. While these Sine Inverters are great for their maximum power capabilities, they are also the most expensive. Like this one from Renogy 1000W 12V Pure Sine Wave Inverter Charger DC AC Battery Power Converter, black with bells and whistles like an Auto generator start
Modified Sine Wave Inverter
Modified sine wave inverters have grown in popularity. These devices can effectively power most of your devices and appliances, and modified sine wave inverters are much less expensive than pure sine wave power inverters. The problem is that these converters use more battery power and don’t put out nearly as much power as the Sine Wave.
Your inverter needs to have enough power that is above the number of watts you constant output to expect to use but isn’t producing so much extra power that it ends up being a waste of money. The Benefit of an Inverter is that RV power inverters give you regular AC plugs that enable you to enjoy appliances you would normally use at home and sometimes even USB ports to keep your smaller devices charged.
Solar Charge Converter
In a solar energy array, a converter is an electrical device that adjusts direct current (DC) voltage output either up or down from the input level. Often called Solar charge controllers, these DC-to-DC converters can maximize the energy harvest for photovoltaic systems and help regulate the amount of DC energy running through the system.
This means that everything in the system beyond the controller — battery banks, inverters, and the like receive a more consistent current that helps the system run smoother.
Typical solar panels put out somewhere between 16 and 20 volts. RV batteries are normally 12 volts. A solar charge controller is basically a voltage and current regulator that keeps your batteries from overcharging. Every RV solar installation has one. There’s more than one way to accomplish this regulation, and so there is more than one type of solar charge controller. There were 2 types of Solar Converters:
Pulse Width Modulation (PWM) Controller-This type of device is basically a switch that connects a solar array to a battery. While functional, these devices aren’t very complex; they don’t adjust for greater efficiency during more or less sunny times of the day.
Maximum Power Point Tracking (MPPT) Controller: these controllers are much more sophisticated in function. They can adjust their energy intake, helping to increase overall output efficiency for your solar array. When deciding on a Solar Charge Controller always. Buy one with a higher Amperage Rating than you actually need. This way you can add an additional Solar Panel to your system in the future without swapping out this device later on.
Types of Solar Panels
Solar panels are sold in all kinds of sizes, but a 100-watt panel is a commonly found size, especially for RVs. That panel is rated at 100 watts at peak efficiency meaning on a 78-degree cloudless day at solar noon on the equator during the equinox or what’s called a perfect day. You get it. With Solar Systems
There are a few different types of Solar Panels to choose from these days and of course, there are Pros and Cons with both.
- Rigid Solar Panels-are the most common panel on the market and are composed of two standard types of cells called monocrystalline or polycrystalline cells with a layer of protective tempered glass and an aluminum frame. These units are very durable and are used in almost all applications with flat surfaces.
- Flexible Solar Panels– The current flexible solar panels available to homeowners on the market fall under the category of “thin-film panels.” A thin-film solar panel is made with layers that are over 300 times smaller than standard silicon solar panels, which gives them a much thinner profile and can even make some thin-film panels flexible
The main difference between the monocrystalline or polycrystalline Solar Panels is The main difference between the two Cells used on the panels is the type of silicon solar cell they use: Monocrystalline solar panels have solar cells made from a single crystal of higher grade silicon used in the production of the Panel while Polycrystalline solar panels have solar cells made from many silicon fragments melted together and laid out on the panel. This quality makes a big difference in the efficiency between the two.
Ridgid Solar Panels have been around for a while and have quality construction made from Glass and aluminum and are less expensive than the Flexible Panels but are very durable and will last up to 25 years. The Flexible Solar Thin Film type is a young product but can be added in spaces that the much bulkier Rigid Solar Panels could not be adhered to. The Flexible Solar Panels can be good if they are manufactured here in the States and can be used in locations like Camping equipment, small tools, and Backpacks.
They are young and still ironing out problems like mico-cracking and heat dissipation that don’t come with the Glass Ridgid Panel Most people believe that just are still unproven in their development but most experts also agree they are considered the Future of Solar the Industry.
Portable Solar Panels for RV Batteries
You can buy a 100-watt panel, but you won’t get 100 watts output. There are many factors that can impact the energy recovery of a solar power system. Here are just a few:
- Time of Day
- Panel Tilt
- Dirt in the air
- Dirt on your panels
- Efficiency of components
- Temperature Contrary to intuition, solar panels work best at cooler temperatures. A 100-watt panel at room temperature is an 83-watt panel at 110°. So where you are in the Country will have an effect on the output of the Panel
If your Solar panels are in a good position they normally can get around 5 hours of direct sunlight per/day. So divide the total Watt-hour number that you calculated as a normal daily load by 5 because that is how many hours of sunlight each day.
So as an example, if you need 200 Amps of Battery and we need around 400 Watts of Solar Power. It’s as simple as that. Most Solar Panels come in 100 Watts and Volt Batteries come in 12 Volts. For a more portable type of Solar Panel Take a look at these 100 Watt Solar Panel from Jackery
References: FitRV.com–How Solar in Your RV Works