Calculating Solar Power Needs
Lets say you settled on one 13,500 BTU air conditioning unit for your motorhome. This unit will have 2,750 starting watts and 1,250 running watts. Running this A/C unit for 4 hours a day will draw:
- First hour: 2,750 + 1,250 watts = 4,000 watts
- Second to fourth hour: 1,250 watts x 3 hours = 3,750
- Total watts for 4 hours: 7,750 watts
You also need to take into account the power needs of other electrical appliances on a daily basis.
Lets take a ballpark figure of another 3,600 watts for running everything electrical in the RV in a day. But of course, not all appliances are going to be used 24 hours a day. Realistically, you might be using only half of that on a daily average.
Total daily power need = 7,750 + 1,800 watts = 9,550 watts
If you are using a Renogy 800-watt solar panel , this is how many panels you would need to run all the electrical items:
9,550 watts ÷ 800 watts = 12 solar panels
Dont forget the solar panels cant generate electricity at night, so for the other half of the day, you will rely on your battery bank capacity. There are other ways to shave down dependence on solar panels.
The last essential piece of your solar installation is the solar inverter. Its size should address the startup surge of the solar air conditioner. The safest way is to choose an inverter that is rated 700 to 1200 watts higher than the starting wattage of your RV air conditioning unit.
Some Advantages To Rv Solar Energy:
- Its a renewable energy source. Solar energy is 100% renewable. As long as the sun is present, solar energy is possible and can be used throughout all parts of the world.
- Reduces the cost of electricity. Energy needs are taken care of with solar energy and therefore, you are not required to pay for electricity.
- Diverse applications. Solar energy can be used for a variety of things. It is possible to use it for any electric purpose. It is also capable of heating.
- Low costs for maintenance. Solar panels do not require you to maintain them very much. If you clean them off a couple of times a year, you will be set.
What Type Of Rv Air Conditioner Do You Want
There are 3 types: mobile vertical ones, window installations and roof-mounted A/Cs. Each type has its pros and cons, and different power consumption. Since cool air is heavy, it makes more sense to install the roof-mounted type.
Of these, there are models which run on either AC or DC. Those that use DC power can be powered directly by solar panels or the battery bank without the need for a solar inverter.
The most recent type of solar air conditioner even has an integrated window. It is ideal for those who want a skylight as well as an air conditioner.
The built-in air conditioning units in RVs have 2 kinds of systems: evaporation system and compressor system. The former has lower power consumption but increases the humidity. The latter can dehumidify room air and integrate heating.
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Choosing The Right Solar Power Inverter
A solar power inverter is the last piece of the puzzle in your RV air conditioning setup. Its used to convert the DC power produced by the solar panel to AC power required to run an RV air conditioner.
There are various sizes and types of solar inverters, but if you want to run an RV AC with solar panels, youll need an inverter with a wattage higher than the starting wattage of the AC. This means if your ACs starting wattage is 3,000 watts, youd require an inverter capable of outputting around 4,000 watts so that you dont max out your inverter. We always recommend leaving as much room as possible for running other AC-powered appliances.
Since the running wattage of an AC is lower than the starting wattage, you could also consider using a Soft Starter with a smaller inverter to supply power to your AC .
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You Will Need An A/c Soft Starter
At times, the only way you will get one or more of your RV air conditioners started while on RV solar is by using an RV soft starter. An A/C soft starter helps provide that initial power surge needed to start the air conditioner on your RV. Very often, your RV solar system is perfectly capable of running the A/C. It just cant start it. Thats where SoftStartRV comes in. By self-installing a soft starter for each A/C unit on your RV, youll find much greater success keeping cool while boondocking or on limited power.
SoftStartRV is an excellent investment that helps run your AC off solar, a gas generator, or campground hookup. Its also easy to install. Check out the video below to learn more.
How To Be More Cost
You can do the following to help you better run your RV air conditioner on solar power:
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Choosing Your Battery Banks Capacity
As a rule of thumb, the larger the bank capacity, the longer youll be able to run your RVs AC, during cloudy days or overnight.
If youre working with an AC that pulls 150 amps, youre going to need an extra 150 Ah of capacity for every hour that your AC unit is running in the absence of direct sunlight.
Suppose you like to run the AC an hour before going to bed. This requires an additional 150 Ah of battery capacity that your original setup may not have accounted for.
To solve this issue, if the current capacity is, say, 600 Ah, youll need to boost it up to 750 Ah or more.
In order to properly calculate the minimum Ah capacity your solar power system requires, youll need to consider the following:
- Your average electrical usage per day
- The number of days you want to have your backup capacity available in case of an emergency, or simply, if youre planning on living off-grid
- The average depth of discharge for your current battery bank
- The average temperature that your batteries will be subjected to while youre on the road
Does All This Hassle Worth It
Everyone has different priorities and can access these pros and cons in various manners.
Solar energy is a costly investment upfront, but you will break even reasonably quickly due to the savings that it has to offer. If you already own a small RV, you might not have enough space to install more panels.
So, it wont be a sensible thing to do. But for remote RVing, you will find solar panels a better option than burning all your fuels when youre off-grid.
Frequent RVing will also enable you to get the ROI, but its not going to be there if you take a few trips throughout the year. You will break even in the long run, but you will feel that it is more of an expense than anything else.
It also works great for other ways of alternate housing.
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Buy An Efficient Ac Unit
Many factors contribute to the efficiency of your RV air conditioner.
Of them, the most important is the age and how worn out the AC unit is.
Most RV rooftop units that are in the market today are built with efficiency in mind. They use advanced technology that reduces the total power consumption and the initial power surge.
Alternatively, you can also size down your air conditioner to reduce the overall power consumption.
How Does A Solar Ac Work
A solar air conditioner combines solar electricity and air conditioning. In simple words, it takes energy from the Sun and uses it to power your AC to cool your space!
A solar panel is a device that captures the power of the Sun. It converts the Sun rays into electrical energy. This energy can then be used directly or stored in a battery. This is known as DC power. A solar-powered air conditioner then uses this DC power, either directly as DC or after conversion into AC , and heats or cools your home.
Furthermore, instead of using grid energy, a solar-powered air conditioner uses the energy of the Sun. It can use the grid energy, though, if needed. That can be done by making a few modifications to the air conditioner.
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Inverter And Charge Controller Requirements For An Rv Air Conditioner
The inverter youll need to power your air conditioner and other appliances will need to be a minimum of 3,000 watts but can be as much as 5,000 watts.
A quality 3,000 to 5,000-watt RV inverter starts at around $2,000.
The charge controller that can handle such an extensive solar power system will cost on average $600.
You need to understand the difference in power output readings from your inverter or battery charge controller. Amperage draws are different between AC and DC power.
For example, if your air conditioner label says it draws 15 amps when running off 120-volt AC power, the amperage when running it off 12-volt DC power will be ten-fold or 150 amps.
Youll need a good grasp of the differentials of power between 12-volt and 120-volt electrical systems to install, operate, and troubleshoot any RV solar power system.
How Many Solar Panels In A Solar Array
Its not just about determining the amperage of your RV AC. You must also find out how many hours per day you will be running your AC. Running it for 4 hours per day will draw around 600 ampere-hours daily from those batteries.
For instance, if you have parked around a hill where the daily sunlight you receive is around 5 hours throughout the day, your solar array needs to produce at least 120 amperes for those five hours daily to make sure the battery recharges properly.
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What Size Rv Battery Do You Need To Run Your Ac
The battery size you will need will depend on the type of battery you intend to use.
Going by the previous scenario:
Your battery should be able to store at least 6250 wh of energy a day.
To calculate the Amp-hour capacity of your battery, divide the total energy expenditure of your AC by the voltage of your battery which usually is 12 V.
6250 W / 12 V = 520.833 Amp-hour 521 Ah
In this case, you may get either of the following to run the AC in your RV:
This size of battery will only account for the usage of your AC.
Obviously, a bigger battery bank is needed to accommodate the other appliances you will be using inside your RV.
You can find out how many solar modules you will need to run appliances in your RV here.
Can I Run My Fridge On Solar Power
Yes, but check your fridge carefully to see how. Remember that an RV fridge that runs on propane still needs some electricity to power the pump and control board but ours is only around 3W, so easily achieved with solar power.
Our fridge is a two-way fridge, so as well as propane it can run on AC power. However, as is common for RV fridges, its an absorption fridge this means its really inefficient when running on AC and uses around 300W.
If your fridge can run on 12V DC power, then thats a great option check to see how much power it draws though so you can size your solar panels accordingly.
If your RV has a residential fridge , then youll need an inverter to run it when off-grid. Electrical consumption can vary widely on residential fridges from as little as 100w on very efficient models, to many times that on less efficient models with an ice maker and defrost mode.
Your manufacturers website or instruction manual should have the information you need to calculate how much power it draws, or better yet, use a device like a Kill-A-Watt to measure it.
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Some Disadvantages To Rv Solar Energy:
- The cost. To buy solar panels, the initial price is very high. You will also need to pay for the inverter, batteries, wiring, and installation.
- It is weather dependent. If you come from a place like me, where it is always cloudy and rainy, solar energy will not be very reliable.
- Storage is expensive. Batteries can be charged throughout the day so that the energy can be used during the night. Either the solar energy is used right away, or it is stored.
- It uses up a lot of space. With high electricity needs, you will have high solar panel needs to get the most sunlight possible. Solar panels require a lot of space.
Solar electric power systems in RVs and traditional homes are similar and the same principals apply.
Is Your Rv Solar Power System Big Enough To Run A/c
Sizing is the most important factor in how your RV solar power system will function with your RV. One size does not fit all. You need to calculate your RV solar power needs in kilowatts . Once you know, follow these steps to determine the size of your RV solar power system:
If you want your RV solar panels to power A/C, the three components that require extra sizing attention are the solar array, battery bank, and your inverter.
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You Will Need An Inverter Too
An inverter will convert battery power into 110 volt power. Air conditioning units will require 110 volt AC power. When you consider a 15,000 BTU air conditioning unit needs about 3,500 watts of power just to start up, you will need at least a 5,000 watt inverter. The reason is because inverters will convert DC to AC power with a 85% efficiency. So, a 4,000 watt inverter will realistically deliver 3,400 watts. Meanwhile, a 5,000 watt inverter will deliver about 4,250 watts.
Rv Roof Space Requirements
An RV roof is almost never an uninterrupted space. There are always AC shrouds, vent pipes, TV antennas, fan shrouds, Radio Antennas, WIFI antennas and range extenders to consider. The total self-contained roof solar must be less than or equal to the total available square footage of your RV roof. It is not ideal to cover most of these items with panels.
Each solar panel will take up certain square footage based on the amount of power they produce and the panels efficiency.
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Sizing The Battery Bank
Now its time to talk about electricity storage. There are not many calculations involved in this step here. With an AC unit that can draw 150 amperes, you will need 150 ampere-hours hourly as you plan to run the AC at night time .
Running the AC for an additional hour ahead of the sleeping time might be comfortable for you to go to sleep, but it will cost you additional 150 ampere-hours. If you have the capacity, you can undoubtedly go for it.
Your battery banks capacity will tell you how much you can operate your AC when the sun is not out. Using the above example, you will need 650 ampere-hours daily, at least in your batteries, before you go to sleep.
Its simple you need to determine your average daily use that is measured in watt-hours. And then, you will have to determine how many days you must backup in case of an emergency or when you are off-grid.
After that, you need to assess the average discharge depth for the battery bank and the average temperature your batteries will be exposed to during your trips.
Now Lets Get Straight To Calculations
The latest ACs come with a nameplate having details mentioned, e.g., power consumption, rating, size, etc. That power consumption thing comes in handy when calculating how much power your AC will use approximately annually or in your desired days. OR If you want to figure out your AC power consumption manually, use a Kill A Wattmeter. You have to plug your AC wire into the meter and connect the meter to a socket. It is recommended to study the readings for at least seven days. To calculate how many watts would be used by your AC in a day, multiply the number of hours you want to use by power consumption. To calculate the number of watts for a whole year, multiply the result by 365 days, or if you want to run for summer, four months, then multiply it by 120 days. Not to mention, less power AC starts consuming after constantly cooling for two to three hours, so calculations would be rough, not exact. For the sake of calculations, we assume your AC adds 3000kW to your bill annually, your solar panel system would have to be producing equal or more to offset additional load.
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