Off Grid Solar Power Systems for Small Homes – The Best Budget-Friendly Options
Every year an increasing number of people are turning to environmentally-friendly solar energy to offset some of the cost of their monthly electricity bills. While some believe that you need to spend a significant amount of money and own a large property to set up a practical solar power system, the truth is there are plenty of affordable solar power products that are appropriate for smaller spaces.
Modern solar power systems have become more affordable and efficient than ever before, which means you can generate a significant amount of clean solar energy, without having to spend a fortune on equipment. This explains why boat owners, RV enthusiasts, and even tent campers are all beginning to invest in small-scale solar power systems.
The declining costs of solar equipment and improving efficiency of that equipment is great news for those that are on a budget and have a limited amount of space to work with. Whether you own a tiny home, a remote cabin, or just a small residential home, there is no reason why you should miss out on the many benefits that come from setting up your own solar power system.
How Can We Help?
To help you understand your options, we are going to explain everything you will need to know about choosing a budget-friendly solar power system for your small home. We will go over some of the components you will need, as well as highlight some of the many benefits of installing an off-grid solar power system.
From there, we will recommend some high-quality products and complete solar kits that will help you harness solar power, without breaking the bank. If you are looking to reduce your monthly electricity bills, end your reliance on the utility companies, or just make your home a more environmentally-friendly space, we can help!
Why Should You Go Solar?
Before we get started, we are going to take a look at some of the reasons why off-grid solar power systems are so beneficial.
- Drastically reduce or fully eliminate your electricity bills – Going completely off-grid will save you a significant amount of money over the lifespan of your solar power system. With a relatively inexpensive investment, you can begin using solar energy to offset some or all of your electricity costs.
- Increase the value of your property – Homes that are equipped with solar power systems tend to have a higher value than those that do not. Not only that, they tend to sell much faster.
- Protect the environment – Embracing solar power is one of the easiest ways to reduce your carbon footprint. Rather than contribute to carbon emissions by relying on local utility companies for your electricity needs, you can start turning an endless supply of sunlight into usable electricity.
- Protect yourself from rising energy costs – In the United States, electricity have increased by an average of three percent per year. By investing in a solar power system now, you can immediately cut your monthly energy costs and protect yourself against unpredictable increases in energy in the future.
What are the Main Components of an Off-Grid Solar Power System?
To build a basic off-grid solar power system, you will essentially need to purchase four main components – solar panels, a charge controller, an inverter, and a solar battery bank.
Solar panels are the most obvious and important component you will need when building an off-grid solar power system. Solar panels are made up of a series of solar cells, which work by absorbing sunlight and converting it into useable DC electricity. The number of solar panels you require will depend on your particular power needs. To get the most out of your solar panels, it is important to position them in a way that that they will receive the optimal amount of sunlight. It is also worth noting that different types and sizes of solar panels will differ in terms of their power and efficiency. The number of panels, their quality, energy rating, and the way they are positioned will determine the amount of electricity they can generate.
If space is limited and you have a smaller property, we recommend taking a looking at folding solar panels. They are a practical solution for those with limited space, as they can easily be folded for storage and tend to weigh less than the more rigid options. In some cases, property owners with limited space will choose foldable solar panels because they can be moved throughout the year to make sure they are positioned in the best possible location for sunlight absorption.
If you value portability, take a look at our collection of Foldable Solar Panels and Solar Suitcases!
The charge controller is the device that will manage the flow of energy from your solar panels to your battery bank. They protect your battery by preventing overcharging and also reduce battery drain issues after the sun has set. There are two main types of charge controller to choose from– PWM charge controllers and MPPT charge controllers. PWM controllers are less advanced and act almost like a switch, which is activated at pre-set parameters to prevent overcharging issues.
MPPT charge controller act like ‘Smart’ device that contains an integrated computer system. They are programable and adaptable to changing voltages and currents. This means they measure the voltage of the panels and make sure it matches the battery bank’s voltage limits. This means you can use a higher voltage solar array than the voltage of the battery, which allows you to create a more efficient solar power system. If you are running an off-grid solar power system, you might be better off choosing an MPPT controller, as protecting the health of your battery is of critical importance.
We carry a wide variety of both PWM and MPPT charge controllers, so you will be able to find exactly what you need by browsing our Solar Charge Controller Collection.
Solar panels generate DC power, which means current that flows in one direction. This means that you will likely need a power inverter, especially if you are planning to build an off-grid system and rely on solar power for all of your electricity needs.
The wall outlets you find in a typical home provide alternating current, or AC power, which is why most electronic devices and appliances run on AC power. In simple terms, a solar inverter will convert the DC power your solar panels generate into more practical AC power.
Power inverters are also extremely valuable for those that plan to run a grid-tied system in the future, as they allow you to feed AC power into your local grid for utility credits and rebates. This is really useful once your solar panels have fully charged your battery bank, as it prevents excess electricity from going to waste.
Whether you are building an off-grid or a hybrid solar power system, you will find exactly what you need by taking a look at our Solar Power Inverter Collection.
The final piece you will need for your solar power system in the battery bank. The battery will allow you to store the electricity generated by your solar panels, so you can use it at your convenience and in the event of emergencies, like grid failures.
Again, the particular type and size of battery you will need will depend on your specific power needs. Ideally, you would find a battery that could hold enough electricity to get you through the day. You can always stack multiple batteries, which will allow you to expand the storage capacity of your solar power system.
For owners of smaller homes that are limited on space, we recommend choosing a lithium battery bank, as they tend to take up much less space than the less sophisticated lead acid batteries. They also tend to be around 75% lighter than lead acid batteries, which is helpful for those that plan on moving their battery bank, rather than permanently installing it in one location.
Shop our Solar Battery Collection and choose from some of the best deep cycle batteries on the market today.
Complete Solar Kits
While you can certainly build your own solar power system by purchasing the necessary parts separately, one of the most convenient and cost-effective ways to build your own off-grid solar power system is to purchase a ready-made kit.
We offer a wide variety of solar kits that come with everything you need to get started. Whether you are looking for a compact and portable solar power system for your RV or boat, or you are in the market for a more permanent setup for your home, you will be able to find what you need by browsing through our collection of complete RV, Van, Boat DIY Solar Panel Kits
For those with small homes, we recommend the Lion Energy. 400W Beginner Solar Panel Kit. This complete kit comes with a foldable solar panel, a Savanna charge controller, a 400W power inverter, and a lithium battery bank, which is available in your choice of size. You also get solar panel cables and all of the necessary mounting brackets you need to build your first off-grid solar power system. As your power needs grow, you can always upgrade and expand this kit.
For those that are just starting out, we almost always recommend taking a look at Renogy products. Renogy offers high-quality solar components at affordable prices. They are one of the most well-known brands in the solar industry and their products have won numerous awards for efficiency, accessibility, and affordability.
We carry a wide collection of Renogy solar panels, batteries, charge controllers, and power inverters. Whether you are looking to purchase a complete kit, or prefer to assemble your own solar power system one component at a time, we carry all of the Renogy products you need.
Remember, everybody has to start out somewhere, so you should not feel overwhelmed if you are just getting into solar power. You can always start with a basic kit and upgrade the components as your experience level and electricity needs grow.
As always, if you have more questions about off-grid solar systems for small homes, feel free to reach out to us!
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Collection: Solar Battery Backup Systems
Solar battery backup guarantees a power source — even during a grid service failure or natural disaster. When the grid goes down, a solar battery backup system automatically detects and transitions your solar system from grid power to backup power. Protect your home from outages with our solar battery backup kits.
Add solar battery backup to protect against outages
These solar battery backup kits give you everything you need to power your home and keep the household running during a grid outage.
When utility power is available, the panels will generate electricity, and roll back your energy bill. If the power goes out, the system draws power from the backup battery bank to keep your most important electrical loads running.
If you live in a harsh climate, or your local power grid is unreliable, grid-tie solar battery backup can provide peace of mind and help you live life uninterrupted by power outages.
Add solar battery backup to reduce your utility bill
Solar battery backup can significantly lower your utility bills. Since solar battery systems store excess energy generated from your panels, you can use this energy during peak hours when the rates are highest, making backup systems financially beneficial for any solar owner.
For California residents, starting April 14, 2023, NEM (net metering) 3.0 will go into effect, reducing the export rate for residential solar electricity from an average of 30 cents per kWh to 8 cents per kWh. Act now to lock in greater savings under NEM 2.0.
What’s in our solar battery backup kits?
Solar panels convert sunlight into electricity. Your solar panel system should be sized to offset 100% of your monthly energy bill.
Our grid-tie solar kits are packaged with high-efficiency solar panels backed by a 25-year performance warranty.
An inverter converts DC power from your solar panels into AC power, the format used by most household appliances.
These solar battery backup kits feature inverters that are designed to work in both grid-tie and battery-based applications:
- Sol-Ark is a universal string inverter that works equally well with or without batteries
- Enphase’s IQ series microinverters can be paired to a battery bank with all-native Enphase components: the IQ Batteries and IQ System Controller
Batteries store the energy you produce. You can draw power from your battery bank to run your appliances when grid power isn’t available.
The size of your backup battery bank determines which appliances you’ll be able to run from backup power. A smaller storage system can keep select loads like your fridge and phone charger running overnight. A much larger battery bank is required for whole home battery backup.
For help sizing a custom system that meets your backup power needs, reach out to our design team for a free solar consultation.
Our grid-tie solar kits come with IronRidge XR roof mount or ground mount racking materials. IronRidge racking materials are tested and proven to perform in extreme environments. Plus, their products are fully certified, code compliant and backed by a 20-year warranty.
IronRidge racking rails feature mounting holes that provide a quick and easy way to mount your solar panels. We have found their products to be intuitive for DIY solar installations, which is why they feature in all of our kits.
If you are installing rooftop solar panels, your kit will contain roof flashings to secure the racking rails to the roof.
Some parts not included: Ground mount kits will require the construction of a metal support structure to provide a strong foundation for the array. The heavy metal pipes needed to build this support structure are expensive to ship, so they are better sourced at the local pipe/tube supplier. Don’t worry, we’ll provide a shopping list with everything you need for a complete installation.
FAQs About Solar Battery Backup
How does solar battery backup work?
When utility power is available, your system works like a normal grid-tie solar kit. Your solar panels feed electricity into the utility grid to roll back your energy bill. When the grid goes down, your system automatically detects the outage and switches over to the battery bank to power your home.
Your battery bank capacity limits the amount of backup power available to you. Components like the Enphase IQ Load Controller can shed non-essential loads during outages, meaning you can shut the A/C down while keeping the lights and refrigerator running.
How big should my solar battery bank be?
Your solar battery bank should be sized to meet your needs. Ask yourself, “if the power goes out, what appliances do I want to keep running?” Then, figure out how much energy those appliances consume and size your battery bank appropriately. (We offer custom kit design services to help with this process.)
While every home is different, here are some generic examples to help you benchmark your backup power needs.
Partial backup: 10 kWh-20 kWh storage
10 kWh storage is enough to provide partial home backup for typical homeowners. You can power the essentials, along with electronics that you use every day, like your internet, computer and TV. Partial backup systems take care of most of life’s conveniences, but non-essential loads like a hot tub or EV charger are still shed during outages.
Whole home backup: 20-40 kWh storage
In addition to the above, a 20-40 kWh storage system would account for major energy-intensive loads, like your well pump, air conditioning, laundry, and dishwasher. Look for a battery bank in this size range if you need whole home backup for a single-family home.
How much do solar backup batteries cost?
Solar system batteries can be costly, which is why we recommend figuring out which appliances are necessary to run during an outage, and which you can live without.
Feel free to browse our solar battery bank kits to get a general sense of standalone battery bank pricing. Once you’re ready to go solar, our design team can provide you with a custom quote for your project.
How much do solar panels cost? Use our easy solar panel calculator to get a quick estimate of how many solar panels you’ll need for your home.
Free Solar Roof Layout
Our engineers use state-of-the-art software to conduct a PV analysis and draft a free layout of solar on your roof, included with our complimentary quote.
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We’ll help you figure out your solar needs!
Fill out the form for a complimentary solar panel quote that includes a custom solar panel layout using satellite technology and a breakdown of solar energy production, federal tax credit and energy offset.
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Solar batteries: Are they worth the cost?
If you’ve been looking to install a solar panel system recently, you’ve probably come across the topic of solar batteries. Although battery systems are becoming increasingly popular, many homeowners still don’t know much about them.
Solar batteries let you store the energy your solar panels produce for later use. Pairing your solar panels with solar batteries to create what is known as a ‘hybrid solar system’ comes with a number of advantages, including access to reliable backup power and independence from your utility.
But how exactly do solar batteries work? And more importantly, how much do they cost? Keep reading to find out.
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Calculate how much it will cost to install solar-plus-battery-storage for your specific home
How solar batteries work
Solar batteries store the extra solar energy your panels produce that you don’t immediately use so that you can draw from it later.
See, solar panels produce the most electricity during the middle of the day, which also happens to be the time when your home uses the least amount of electricity. A standard grid-tied solar system sends that excess solar energy back to the utility grid.
However, when solar panels are paired with a home battery, excess electricity goes into the battery instead of the grid. Then, when the sun goes down and your panels aren’t producing electricity anymore, you can use the energy you have stored in your battery. instead of paying for electricity from the utility.
This means you get to power your home with all of the clean, renewable solar power your solar panels produce, no matter what time of day it is.
How much do solar batteries cost in 2023?
Depending on the battery’s chemistry, a solar battery can cost anywhere from 200 to over 15,000 to install.
Most residential grid-tied solar panels are paired with lithium-ion batteries, which cost anywhere from 7,000 to 15,000 to install. Some small-capacity lead-acid batteries can cost as little as 200, but they won’t be able to power much in your home and are typically used as emergency backup power for RVs.
The following table lists some of the most popular solar batteries available on the market:
Estimated cost before installation
The cost of solar batteries has decreased over the past few years, but they still cost a pretty penny. and most people don’t have that kind of money just lying around. Luckily, solar batteries are eligible for the 30% federal solar tax credit, and some states even have additional solar battery incentives to help cut down on upfront battery prices.
Find out if battery storage is worth it where you live
Factors that determine solar battery cost
Solar battery manufacturer
Just like everything else you buy, the brand that you choose will impact the pricing of the battery. This is because different brands offer different services and have different manufacturing processes.
For instance, German battery manufacturer sonnen offers a luxury line of solar batteries, some of which cost upwards of 30,000. The Tesla Powerwall on the other hand, costs closer to 13,000, including installation costs!
There are many different types of batteries on the market, but most residential systems use lithium-ion batteries.
Two main lithium-ion chemistries are used for solar batteries: nickel manganese cobalt (NMC) and lithium iron phosphate (LFP). NMC batteries, like the LG Chem Prime, have been around a bit longer, making them slightly cheaper than LFP batteries, like the Enphase IQ.
While some homeowners choose to use lead-acid batteries instead of lithium-ion batteries because they are cheaper, they tend to have a shorter lifespan, lower capacity, and require regular maintenance.
Number of batteries installed
This seems like a no-brainer, but the more batteries installed, the higher the solar energy storage system costs. The number of solar batteries you’ll need depends on:
- How many kilowatt-hours of energy you use
- The storage capacity of the battery
- How many appliances you want to power
- How long you want to power your appliances
In most cases, in the event of a power outage, one to two solar batteries will hold enough stored energy to cover your energy needs and provide backup power to a few key circuits.
Backup load panel
In most cases, solar batteries can’t power everything in your home.
The important things will stay on, like your lights and your fridge, but you’ll need to install multiple batteries to have the amount of energy needed to power something like your air conditioner during an outage or if you’re off-grid.
Because a battery can’t power your entire home, you might need to install a sub-panel so that the battery will back up only the most important things in your home during a power outage. Installing a sub-panel, sometimes called a backup load panel or a critical load panel, will add 1,000 to 2,000 to the installation costs.
The amount of labor required to install your battery system will also impact the price of a home solar battery installation.
If the battery is being installed at the same time as the solar panels, the labor costs could be a bit lower because all of the electrical work and permitting associated with both the solar system and battery system will be completed at once.
However, if the battery is being added to the solar panel system after the fact, labor could cost more, as new permits will need to be filed, more incentive forms may be required, and some additional electrical work may need to be done to connect the battery to the existing solar panels.
Incentives and rebates
The cost to install a solar battery can also vary depending on what solar battery incentives are available in your area.
California’s solar battery incentive program, called SGIP, can cover almost a quarter of the costs of a battery installation. Other states, like Oregon, also offer solar battery programs that help lower upfront costs.
Plus, if you qualify for the federal solar tax credit, you can get an additional 30% off the cost of your battery installation, even if the battery isn’t connected to solar panels.
Are solar batteries worth the extra cost?
Although pairing solar panels with energy storage is becoming more common, it doesn’t mean it’s the right choice for everyone.
Installing a solar battery storage solution provides the greatest benefits to homeowners who live in areas that experience frequent power outages, where full-retail net metering isn’t offered, or if there are battery incentives available in their area.
Solar batteries are also great if your main reasons for going solar are environmental, as it maximizes the amount of renewable energy your home uses.
However, if you’re only looking to save extra money, a solar battery might not be worth it for you. What we mean is, if you live in a state with full-retail net metering, you’ll be saving the same amount of money with a battery as you would without one. All the battery would do is add thousands of dollars to your solar installation and provide you peace of mind in the event of a power outage.
Solar panels and solar batteries make a great pair
Installing a solar battery storage system can be a great way to get the most value out of your solar panels.
Batteries are an excellent source of backup power, they increase your energy independence and, in some cases, can even save you more money on your electric bill because you’ll be drawing power from the battery instead of the grid.
However, solar battery systems do come at a price. If you’re looking to save money on your electricity bill, installing a solar battery might not be right for you, especially if your utility offers net metering. However, if you live in an area that experiences widespread blackouts, like the ones in California and Texas, or somewhere with Time-of-Use (TOU) utility rates, having a battery backup to store energy for when you need it will be beneficial.
The upside is that the price of solar battery technology continues to fall, so much so that someday in the near future, solar batteries will come standard with all solar energy systems.
If you’re looking to pair your solar panels with storage, make sure you contact multiple reputable battery storage installers to ensure that you get the highest quality installation at the best possible price.
Installing your own small, remote off-grid solar system
A typical residential-size solar system installation will involve properly sized and installed AC and DC electrical wiring to reduce the risk of electrical fire, a proper grounding system to prevent shock and lightning damage, proper battery installation and venting to prevent gas explosions, and a properly installed solar array to maximize performance while avoiding roof damage.
In almost all of my past articles I have described many different types of solar power systems, but did not go into detail on how to install them yourself, since most systems should be sized and wired by licensed solar professionals. However, the Backwoods Home website continues to receive many e-mail questions related to smaller do-it-yourself solar projects for remote weekend or vacation cabins in areas not served by power lines. If this is your situation, and you are willing to stick to the basics, I will show you how to install a very simple battery-based off-grid solar system just to power a few lights, and possibly a DC well pump or freezer.
Otherwisedon’t try this at home.
I am staying with all 12-volt DC equipment which has a limited shock hazard and allows using many of the electrical components you can find locally. However, a word of warning. Just because everything will be the same low voltage wiring as used in your car or boat, this still does not mean there are no safety concerns.
Any deep-discharge battery contains hundreds of amps of stored energy that can easily melt heavy gauge wire or electrical components if not sized and installed properly. I have seen electrical cable the size of your thumb quickly glow red and melt due to an improperly installed battery. This glowing cable could easily ignite any nearby walls, floors, or roofs.
This means if I say to use a specific type or size component, there is a really good reason. You should not assume you can substitute anything you have lying around that is “almost the same.” If you want to really simplify the equipment selection, all of the components required are available in pre-packaged solar lighting kits of various sizes.
The first decision we need to make is system size. If you only need to power a few lights in two or three rooms in a remote cabin, then you can get by with one or two 12-volt batteries. If you want to also power a small DC freezer or DC well pump, then you will need two to four 6-volt batteries. Do not, under any circumstances, use standard car or truck batteries, as they have very thin lead plates to reduce weight and they will not last long under daily cycling.
Normally in this application I would recommend using either 12-volt RV/marine batteries or 6-volt golf-cart batteries. These are available locally and are fairly inexpensive. However, if you purchase the sealed GEL or AGM version, this will significantly reduce any risk of vented explosive gases or the need for battery maintenance. Sealed batteries cost almost 40% more than the same size open cap batteries that require watering, and they do not last any longer. However, since you will not need to build a special battery room or vented enclosure, this will be an advantage in a smaller cabin installation with limited storage space. Regardless of battery type, the battery bank should be insulated in colder regions since battery charge drastically drops when it gets below 35 degrees.
The size and number of solar modules needed depends on the capacity of your battery bank and where your off-grid cabin will be located. If possible, you want the solar array to face south. In my geographic area, most mornings are foggy and late afternoons are blue-sky sunny, so I favor a slightly southwest orientation.
A solar module produces the best year-round performance with a tilt angle equal to your latitude. A lesser angle will improve summer output, and a steeper angle will do better in winter. For most of the United States, this is from 37 to 42 degrees. If your cabin will only be used for part of the year, you should use the tilt angle that will produce more energy during that part of the year.
Your solar array can be mounted on your cabin’s roof, on a nearby pole, ground-mounted on a raised frame, or mounted on a nearby storage shed. Solar modules are fairly lightweight so your main mounting concern is wind uplift, not caving in your roof. Any mounting system should use only stainless-steel bolts or lag screws penetrating into rafters or blocking, since a strong wind will easily pull out any screws that only penetrate sheeting plywood.
Most of the 12-volt solar modules sold today are smaller than 100 watts. The current market trend is for larger modules, which require a nominal 24 volt output. One deep-cycle 6-volt golf-cart battery or 12-volt RV battery will store approximately 1 kWh of electricity when discharged 50%. As a rough estimate, this means you will need about 200 watts of solar array to recharge one battery in one day, assuming five hours of direct sunlight.
This is typical for most summer months, but for many parts of the northern United States, you may only receive three hours of direct sun during short winter days. This means you will need to increase the solar array to battery ratio, or simply reduce your power usage during periods of cloudy weather.
There are many design problems associated with multiple “parallel” wired solar modules and batteries, so it is much easier to use larger-capacity solar modules and batteries than smaller ones. Keep this in mind when purchasing batteries and solar modules. Ordering larger unit sizes will work out better in the long run than buying the smaller and cheaper brands typically found locally.
You need to understand that the same watt size electric loads at 120 volts AC require 10 times the amp current at 12 volts DC. Watts for a given load do not change regardless of voltage, so two 100-watt light bulbs that require 1.7 amps at 120 volt AC (200 watts/120 volts), can be wired using a #14 size wire which has a 15 amp rating. However, at 12 volts DC, this same load will draw 17 amps (200 watts/12 volts), which exceeds the #14 wire’s 15 amp rating.
In addition, these two 100-watt light bulbs would only operate about five hours before draining your deep-cycle battery (5 hrs x 100 watts x 2 bulbs = 1 kWh). So right from the start you need to use only the most efficient DC lighting and DC appliances you can buy, and do not base your wire sizing on 120-volt AC loads.
Just because we are using low voltage DC power does not mean we do not need fuses or circuit breakers. Each wire supplying a load in your cabin must have a properly sized fuse or circuit breaker to prevent overload and possible fire.
Normally you will find a DC rated fuse or circuit breaker to be physically larger and more expensive than the same amp size AC device. It is also much harder to find a local supplier for DC rated circuit breakers. However, we are in luck since the Square D “QO” line of AC circuit breakers are also dual rated for up to 48 volts DC, but this only applies to the “QO” line by Square D.
I am not aware of any other low cost circuit breaker typically found in a local builder supply that is also rated for low voltage DC service. I suggest using the eight circuit Square D “QO” subpanel and single-pole 10 or 15 amp “QO” circuit breakers for all your load wiring. You may be tempted to use lower cost automotive type DC fuses, but these are not approved for residential wiring. Your local RV or boating supply store will have a great selection of 12-volt DC lighting fixtures that should easily meet all your lighting needs. These are also available in weatherproof designs for outdoor lighting applications. Purchase DC light fixtures that include an internal on/off switch, since DC rated switches are hard to find and make wiring installation more costly.
An on-demand RV or boat 12-volt DC pressure pump can provide pressurized water to a kitchen sink or shower from a storage tank. This generally simplifies plumbing costs and the high electrical demand for a deep well pump. This tank can be refilled from rain water, a nearby creek, or spring. Easily accessible drain valves should be provided at all low points for quick system draining to prevent freezing when not occupied. Obviously, this water is not suitable for drinking or food preparation without proper treatment, but you can always drink bottled water you bring during each visit and avoid the cost of drilling a well or additional solar cost to power a well pump.
For an off-grid remote cabin, having an electric refrigerator or freezer greatly increases the size and cost for the solar power system. The most obvious solution for shorter periods of cabin use is to bring along a high quality ice chest full of ice. I have found that the better insulated models can hold ice for up to four days.
The RV and boating industry offer several 12-volt DC and propane-powered refrigerators and freezers, but most have a very high daily electrical load. You may want to review my article in Issue #102, (Nov/Dec 2006) which provides much more
information about DC powered refrigerators and freezers. If you are willing to spend 900 to 1,500, there are several excellent 12-volt DC refrigerators and freezers designed specifically for off-grid solar homes which require much less solar power to operate.
SunFrost and SunDanzer offer a good selection of low energy 12-volt DC refrigerators and freezers for off-grid solar applications. Although expensive, these super-efficient models will save thousands of dollars since you can get by with a much smaller solar array and battery. If you will be using your off-grid cabin for longer periods, the solar refrigerator should be your most important appliance purchase.
Wire your lighting and DC appliances using the same wiring procedures and materials as specified by the National Electric Code (NEC). My only exception is to upsize the wire size to reduce wire resistance, since we are operating at 10 times the current required at 120 volts AC. The table in Figure 1 gives the NEC amp rating for the most common size house wiring, followed by my suggested wire size for all 12 volts DC wiring:
If your wire run is longer than 50 feet, I would go to the next larger size wire even though the load is still small. Also, use only copper wire. Aluminum wire is less expensive, but it has a lower amp rating than copper for the same wire size. All aluminum wire connections require special anti-corrosion joint compounds, so keep it simple and stay with all-copper wiring, and solid copper wiring devices and connectors.
You can keep the wiring simple by locating your circuit breaker panel near the front door, and use the circuit breakers for switching loads on and off that do not have internal switches. This is because the 120-volt AC wall switches you buy in any hardware or building supply cannot be used on DC electric service. Due to the constant flow characteristic of DC electricity, it’s not unusual for AC switch contacts to “weld” together from the arcing or even melt when used in DC wiring systems.
Since your simple DC electric system will serve only a few DC lights and DC appliances, you will not have any perimeter wall outlets since most electrical loads will be wired to terminals installed in each device. However, if you do need to “unplug” an appliance, they do make a wall receptacle and plug designed for low voltage DC service. The two prongs of DC outlets and plugs are rotated 90 degrees in reference to a standard 120-volt AC outlet to prevent accidently plugging an appliance into the wrong voltage service.
Solar and battery wiring
After mounting your solar array modules, proceed with the interconnection wiring. Larger wattage solar modules sold today come with prewired male and female connectors with several feet of wire. Smaller modules still have an electrical junction box on the back, so you can use standard flexible PVC waterproof conduit and conduit connectors between each module’s junction box.
Remember that these solar models will be wired in “parallel” since you are using a 12-volt battery system. This means your wiring may require separate wire runs for each module back to a central roof-mounted combiner box. You will also need a solar charge controller which controls the rate of battery charging and prevents overcharging. You should not connect any solar module directly to the battery without a charge controller in between.
If you are using sealed GEL or AGM batteries, it is critical to use a high-quality charge controller that includes a “GEL/AGM” switch or jumper that switches to a lower charging voltage. This will prevent damaging your new battery bank since the standard wet cell charging voltage setpoint will damage sealed batteries.
If you need more than four solar modules, this makes it harder to wire them all in parallel, so you may want to consider using a charge controller that allows using a higher-voltage solar array with a 12-volt battery.
This means you may be able to wire your solar modules in series to reduce the parallel wiring and have a 24 or 48-volt solar array, supplying a 12-volt battery bank. This will all depend on the model solar charge controller you purchase.
Most likely you will be installing two to four solar modules under 100 watts each, but on larger systems you can add a solar combiner box. This is like a fuse or circuit breaker panel, but is made for mounting outside next to the solar array. When you have multiple solar modules, you wire each separately to this nearby combiner box which has separate terminals to make this wiring easier.
Finally, be sure to include a fuse in the positive wire between the solar array and charge controller, and between the charge controller and the battery. On systems this small, you can use a two-pole Square D fused-disconnect, and use each fuse separately for each wire which allows using a single disconnect to break both connections to the charge controller.
You may be building your off-grid system where it will never have an electrical inspection and the low 12-volt wiring will not electrocute anyone, but this is no reason to not use safe wiring practices, and this includes grounding. The National Electric Code requires all professionally-installed roof-mounted solar arrays to include a ground-fault circuit breaker and separate grounding wire connecting each solar module directly to an earth-ground.
Many grid-connected solar arrays produce over 400 volts, so any electrical short to frame could actually electrocute someone, or the electrical short could arc and cause an electrical fire. Smaller 12-volt DC solar systems like this and designed for boat, RV, or camping applications do not usually include this added safety device due to the much lower voltage, and I cannot recommend leaving it out of your solar array wiring. However, if you decide your small solar array has very limited safety risk, it is still important to provide a good array ground to reduce the risk of lightning damage since you are bolting large metal objects high up on a roof in an open area.
Every solar module has a predrilled and labeled hole in the frame for a ground wire, and you should use a bare solid-copper ground wire to connect each module. Do not just connect the ground wire only to the array mounting rack and assume this will ground the entire group of modules. Aluminum quickly corrodes when bolted to other metals which makes a very poor electrical connection.
Without cutting the bare copper wire, connect to each module’s grounding point using a stainless-steel sheet-metal screw, then route down to a standard 8-foot copper-clad ½-inch steel groundrod driven next to the cabin’s foundation. You also need to add a separate bare copper wire from this same groundrod to the grounding buss bar inside the main circuit breaker panel and array fused disconnect. For a system this small, a #8 or #10 bare-copper ground wire meets code, but the code also requires ground wires smaller than #6 to be in conduit to prevent damage to the smaller wire. It’s usually easier to just use the larger #6 wire and forget the conduit.
Testing and setup
Never, never connect any wiring to a new battery until you have checked each wire separately with a volt-ohm meter to make sure there is no short, and that all positive leads are connected to only the positive battery post, and all negative (-) leads are connected to only the negative (-) battery post.
When using multiple 6-volt batteries or multiple 12-volt solar modules, it is very easy to end up with the wrong voltage output, so also check to make sure there is no mismatch of voltages. A typical 12-volt solar module will actually measure between 17 and 21 volts when in full sun and not connected to any load, so don’t let this higher voltage concern you. However, if you measure over 21 volts, then you have a problem unless you are using a solar charger designed for these higher input voltages.
I do not recommend installing a 120 VAC inverter on a system this small due to limited solar and battery capacity, and added complexity of having two separate sets of wiring. Keep it simple and buy a DC powered radio or TV if you must have entertainment.
Now you are ready to turn on each circuit breaker and start enjoying the benefits a little solar electrical power can bring to almost any remote application.