I want to figure out exactly how much power we use a month in our RV and then figure out how to reduce that amount and prepare for living off grid on a solar and wind system. That means breaking down what uses power, what can be done in other ways, what can be eliminated, and what can be changed to other, more efficient technology.
For that reason, I am ordering a Killawatt so we can monitor each individual item and find out what they all use individually and figure out ways to either reduce that power use or replace that device with something else that can operate with less electricity, but still maintain the same functionality.
DC to AC and Back Again
If at all possible, we would like to avoid the process of conversion and inversion. The benefit of AC power and why it took over from DC a century ago is simply because it can travel longer differences without as much loss of energy.
In comparison, DC power degrades tremendously over power lines, so when the competition came out between AC and DC power, AC won out.
However, most devices actually run off of DC power in the end, especially electronics. There are some things that require AC power, but for the majority of devices, they actually have a power transformer built in that changes the AC power from the outlet in the wall to DC power for the device to run properly. In electronics that have a power brick, such as a game console, a USB phone charger, or a computer, that little block is changing the power from AC to the correct DC amps and voltage that the device needs.
Each time electricity is changed from DC to AC or vice versa, there is some loss from the change not being 100% efficient. Just as there is heat built up from electronics, there is some power loss in the process. If we can avoid that, then we increase our power efficiency, reduce our power demands, save on resources, and even reduce added heat to the house.
Using the RV Electrical System
In an RV, there are two main electrical systems. A third if there is also an engine as in a Class A, B or C. The main systems are the AC system and the DC system. In engine models, there is also the vehicle components which includes the engine electronics and sometimes the radio or other devices in the dash. Not all are the same though.
Inside the living area of the RV, the DC power is used for devices that are almost always specifically designed for RVs. They are built to run on battery power and usually come in a form that fits in RVs. That means smaller, lighter, and sometimes less powerful or functional.
DC items in RVs are usually (but not always!) the lights, water pump, water heater, refrigerator, and furnace. A few of those devices can also either run on propane or even require propane to run. The water heater and refrigerator often can also run on propane. The furnace is almost always propane as well. But those three devices also require DC power to run even while on propane, so a dead battery means the fridge will not have power for its electronics and the furnace and water heater have no way to spark to produce heat. There are older RVs that do have pilot lights that need to be manually lit, but newer models usually have DC powered sparks.
Some functional items that do not really count as appliances include electric steps, slide outs, levelers, and awnings.
AC items, on the other hand, are devices that plug into a traditional home-style three prong outlet (at least in the US). Microwaves, air conditioners, televisions and electronics, are all AC devices. Basically, if it plugs into an outlet, it is running on AC power. Many RV refrigerators run on AC as well, and in fact many newer models have residential fridges that run on a dedicated inverter and run only on AC.
AC devices can run off of one of three sources: Shore power, Generator, or Inverter. If you have none of these power sources, there is no way to run any of the AC devices.
Shore Power, Generator, or Inverter
Most people are familiar with shore power. An RV almost always has (or once had if converted to something else) an outlet or power cord to connect to a pedestal at a campground. They are either 30amp or 50amp. They are also 120volt. (Some call it 110v, but 110 and 120 are actually referring to the same thing.) When plugged into shore power, it is just like running power to a house, except on a smaller scale. Devices that run in a house can be plugged into an outlet and will work, but the amount of devices is more limited. 50amp allows more devices at once.
While long term stays often have a meter and charge for electric, staying just for a few days or a week usually includes electric. For that reason, most people just plug in and run whatever they need while camping and think nothing of it.
Using a generator means having a fuel source and also monitoring the devices running at once. Some RVs have builtin generators, others do not and require you to purchase your own. Some have automatic transfer switches that can connect to the generator as soon as it is turned on. There are even models that have power monitoring systems so that if the RV is plugged in and shore power goes out, the generator will automatically start and power the RV.
The fuel source is often gasoline and in a builtin model will use fuel from the engine fuel tank. It should shut off when the tank gets low though, about one-quarter tank. That way you are not stranded without fuel to get anywhere while running the generator.
The third AC source, an inverter, is connected to the batteries and the AC breakers. The inverter takes DC power from the batteries, changes it to AC, and then can power the outlets. Depending on the size of the battery bank and how fully charged it is, it is possible to run several devices off an inverter at once. Inverters measure their output in Watts though, so exceeding that wattage can cause devices to fail from being underpowered, or trip a breaker if something demands too much.
In RVs that have a residential fridge, they usually have an inverter just for the fridge, to keep it powered at all times.
In the case of air conditioning though, it is usually only able to be used when connected to shore power. It might be possible to run it off the generator, but probably nothing else at the same time. Running an air conditioner off an inverter is likely to be a losing battle though. They use a lot more power when starting up, which often pushes the inverter over its limit. Also, since air conditioners continue to use a lot of power, it will drain the batteries very quickly.
How are they connected?
An RV has house batteries. These differ from the battery the engine uses in that they are designed for long running, also called deep cycle. There are several types of deep cycle batteries, but I’m not getting into that here.
When not plugged into shore power or running the generator, the DC devices will still function since they are being powered by the batteries. As long as the batteries are charged (keep them above 50% unless they are lithium), then those devices will function. If an inverter is installed, then AC devices will function as well since they are using AC power from the batteries through the inverter.
To keep the batteries charged, some source of power is required. This is usually a converter, especially in stock models. A converter does the opposite of an inverter. While an inverter changes DC to AC, a converter changes AC to DC. Some of that power is sent to the batteries to keep them charged while some of it is sent to the fuse panel to run the DC devices.
The exception to this is solar power. With solar panels, the power generated is DC and sent through a charge controller which monitors the battery levels and fills them. As long as there is sunlight, the panels generate power, send it to the batteries and then it goes to the fuse panel and to the DC devices.
What does this have to do with our off grid house?
Whenever power is changed from DC to AC or AC to DC, there is some loss. It is usually through heat. If we can avoid this, then we reduce our need for incoming power, reduce heat generated, and reduce the size of an inverter we need.
There are many, many devices that already run directly on DC power or can be replaced with models that do. Some are more expensive to get new models, others actually require the elimination of a component to work.
In our situation, we have computers, TVs, game consoles, smartphones, tablets, hotspot, router, servers, and hard drives that can be or already do run on DC power. There are outlets that can be hooked into a 12v system and are simply a direct USB power source. There is no need to add an AC outlet, only to have a small brick that changes it back to DC for the device attached.
For our computers, I would eventually like to be able to upgrade our laptops to newer MacBooks of some sort. All Apple laptops are now powered over USB-C, so I will have to find a way to add USB-C outlets in a few strategic locations in the house that can provide enough watts to charge a laptop battery quickly enough. Right now on Amazon, there is only one but I expect more will be available soon.
We currently have a couple Raspberry Pi’s doing different functions in our RV and they use 5v/2.5a, so I will have to find some other way to get power to those as most USB car outlets are only 2.1a. There are ways, but it will require a little more research and work. We will probably get a computer for a heavier duty server that can run on DC power as well, and there are companies out there that make devices just to put a computer in a car.
For lights, we can even just use DC powered lights for an RV and wherever we put them, we can connect them with light switches and smart controls to turn them on and off. At about $7 a fixture, even with a non-removable LED, if they do last close to the 5 years of being always on, it is well worth the investment. Besides, by the time they start to burn out, something better will likely have come along to replace them with.
There are some DC TVs, but I’ve never used any so I’ll have to research which ones will work or if that should remain AC and with what we have now. A few other devices, like a game system and the router will need to remain AC as well. I’m going to run plenty of Cat6 through out the house, probably to far more locations than actually needed. That will also require a much larger switch, which will have to be AC powered.
Our hotspot already runs on DC, so putting it on a USB outlet is simple. Depending on the LTE coverage in the area, we have to look at providers and see who has the best coverage at the most affordable price.
Our water system will also most likely be DC powered with heating help from a tankless, battery and propane powered water heater from Marey. While I’m not certain yet, we will probably have to get a well, and there are DC powered well pumps. The water system is an article all on its own though.
For other devices, it is mostly food preparation that remains. There are a couple DC-powered coffee pots, but not many and we will have to try them to find one that works or just stick with what we have. We only make one or two cups of coffee a day usually anyway, so that is an acceptable power use.
I cannot find a DC-powered slow cooker or microwave though, so those are two devices that will likely need to remain on AC power.
To keep the temperature at an acceptable level, the most important concept is removing the need to alter the temperature. If we can maintain a comfortable temperature as much as possible, then we don’t have to artificially alter it.
This means one thing: Insulation.
If the inside temperature does not change as much as the outside, then we don’t have to change it as much. If it stays cool while it gets hot outside, no need to run an air conditioner. For that reason, good insulation, closing any areas of drafts, using quality windows and doors, and eliminating as much loss of desired temperature to the outside is our goal.
We also have to build with passive solar techniques. By placing the house facing the best way, it should warm up in the morning, hold heat during the day, and release it at night from a heat sink. The easiest way to do that is with monolithic structures, which means we have tile flooring at the least and windows facing south. I don’t know if we can have something large and stone in the middle of the main room, but maybe surrounding a kitchen island/bar with stone facing will work.
Because heat rises and the house will be raised up above the ground, I am working on a system to bring in cool air from underneath the house and push hot air out the top. This should both cycle the air and keep it cooler during the hot summer months. I will tie it all together so I can simply flip a switch to turn the system on and have a method to close it all off in the winter to prevent heat loss there.
For artificial heating and cooling though, we do still need a backup system.
There are small wattage systems that can provide cooling with a split system. The main unit is outside with a blower unit inside to push cold air into the house. The only drawback to this is that it requires AC power and also will most likely need to be installed by a professional. If I can get most of the work done myself though and just need someone else to connect the parts together and to power, then it should save us some money.
I am still working on winter heating though. The location we are aiming for does get cold in the winter, down in the 20s for most of December and January, so we will need some source of heat. Since we will be using propane for the water heater and stove, then it makes sense to use it for the heater as well. Done correctly, we can run everything off of one tank or even have several tanks connected together and separate from the house so that they switch from one to the next when one empties.
I may actually just use a Suburban RV furnace and adapt it to the off grid home. If I can get one with ducts or find a way to direct the air from this model, then it would be an easy and affordable solution.
The only other item then is fans, of which there are many USB powered varieties. Since Tiffany almost always has a fan running somewhere, I can make mounts for them in key locations with a USB plug right next to it.
And anything else that may come up.
Of course, our main objective is to live off grid and on our own power. To do that, we need power and water. While I’ve gone through the power system here, I’ll be delving into the water and sanitation system in the next article. That is a whole other beast that requires a lot of insight.
And of course, this article has nothing about how we plan to generate power either, so we will have to figure out how much power we need to use every day and how to assemble that system with solar panels and a wind turbine.