HOW TO DIY OFF-GRID SOLAR
SPEND THE TIME UP FRONT AND PLAN IT CAREFULLY TO AVOID DISAPPOINTMENT
BY BRADLEY FORD Popular Mechanics Jan 2025
PHOTOGRAPHY BY TREVOR RAAB
THERE WAS A TIME WHEN THE TERM “OFF-GRID” conjured images of doomsday preppers or Ted Kaczynski. Today, off-grid is going mainstream, with numerous manufacturers offering equipment to provide the comfort and connectedness we’re accustomed to. Solar in particular has become more accessible, with robust system components available to DIYers.
Some reasons to choose off-grid energy include spiraling utility costs and the increased frequency in grid disruptions by natural disasters. But with remote work becoming more common, many people are choosing to build, and live, in areas where it can be costly to connect to the grid—if it is even available. This is where I found myself when my wife and I bought property to build a seasonal cabin. The location isn’t too remote, with utility poles about 1,500 feet away through the woods. But it would cost roughly $10,000 to clear trees, set poles, and run overhead lines, so we considered other options. With some basic calculations, it seemed we could install a solar system ourselves for a little less money, with no future utility bills.
As I started researching and planning, I inevitably had questions about the equipment we would need. While there are many companies offering some or all of the components, in many cases they seemed nearly identical from brand to brand. In fact, much of the equipment is manufactured overseas, so it wouldn’t be a surprise if at least some of it is made in the same factory. This became more apparent as I reached out to various companies with questions. Some never responded; some replied overnight, their responses peppered with translation issues. One brand, EG4 Electronics, had an address and phone number in Texas and real people that answered the phone.
Through the course of my conversations with EG4, they connected me with design and tech-support specialists who advised me that the details in the planning stage were critical to building a system that would meet my expectations and needs. So, I followed their planning advice—for the most part—and ended up with a system that will suit our needs, with room for expansion.
EG4’s willingness to answer questions, ease of contact, and informative online resources led me to purchase their inverter, batteries, battery enclosure, and super-efficient mini-split heat pump. Following is the process they recommended for planning and designing our system.
 Energy for the cabin is stored in four EG4 LL-S 48-volt 100AH lithium iron phosphate batteries. The batteries’ charge and discharge levels, as well as balancing between them, are managed by the inverter via communication cables.
1 PLANNING: ENERGY AUDITIf you go online to solar DIY forums or groups, you’ll see that many folks who are looking for advice start by asking a question along the lines of “What do I need to get started? I just want to run a refrigerator and an air conditioner, and charge my phone.” And then they get responses with suggestions of what they’ll need. This is a hopelessly simplified way to start your planning and will likely leave you with more questions than answers. In short, it’s not how to get started, for numerous reasons. Your physical location has everything to do with how much sun you have available—folks in Maine will have systems spec’d differently than those in Texas. Additionally, appliances of the same type can vary greatly in their energy consumption. And, once you have outlets available, people are going to start plugging more and more things into them. For these reasons, you really need to start with an energy usage audit and a solar site survey.
To perform an energy usage audit, you’ll need a spreadsheet listing everything that uses electricity in your off-grid cabin, home, or structure—down to the number of lightbulbs and their wattage. You can find spreadsheets set up for this purpose online, or you can create your own. You’ll need column headings for:
? Appliances/devices/fixtures
? Voltage (AC), 120 or 240
? Amperage
? Watts, rated or measured
? Surge, or starting watts (if applicable)
? Hours used per day
? Energy consumption, in kWh
? Energy consumption, in kWh per day
? Percent of total kWh
Start by listing the devices, including model numbers so you can look up voltage, amperage, watts, etc. Energy Star–rated products list annual energy consumption figures, which you can use to calculate daily usage. When possible, measure how much energy a device uses. Do this with a power or watt meter, plugged into an outlet which you then plug your device into. Record the kWh for each and multiply by the hours used. Refrigerators and heating/cooling equipment cycle on and off, so it’s important to record usage for a full day. Use this information to determine your total kWh per day per device, your total kWh per day, and the percentage of that total for each device.
Knowing the percentage of total energy each device uses is important—it will help identify your biggest energy users and can help guide appliance usage and selection. As a general rule, take your total daily usage and increase that number by 20 percent. The increase will help to allow for future growth—as well as losses that come from the system components, as they will not be 100 percent efficient. Your daily usage number—just under 10kWh, in our case—times the number of days you want to be able to run off your stored energy (batteries) will dictate the size of your battery bank. You have to assume there will be days with minimal sun due to storms or snow blocking your panels. We’ll mostly use our cabin on the week-ends, so we need two days’ worth of storage.
9.679kWh/day x 2 days = 19,358kWh Using 48-volt, 100Ah batteries, you can calculate:
(100Ah x 48V) / 1,000 = 4.8kWh per battery 19.358kWh / 4.8 kWh per battery = 4.03 batteries
These calculations show our system will need four 48V, 100Ah batteries to get through two days.
The next thing to determine from the energy audit is the size or capacity of the inverter you will need. This is not as simple, but it will fall somewhere between 60 and 80 percent for the total of your continuous loads. Smaller installations like our cabin won’t have too many big loads—things like HVAC systems, electric dryers, ranges, or other heating appliances—so, figuring closer to 80 percent should work. For larger installations, with more loads in general, particularly things like heating/cooling or kitchen appliances, you’ll figure closer to 60 percent of the total. There are online tools to help with this, but be sure that the inverter capacity you choose will handle the largest loads you will likely run simultaneously, with room for typical smaller loads like lighting circuits, chargers, or entertainment systems.
The biggest loads in our cabin will be the mini-split and a microwave, which add up to less than 3kW, so we’re installing a 6kW split-phase inverter. This will give us the ability to run both 120V and 240V devices, with room to add things like a well pump at a later date.
2 SOLAR SITE SURVEYWith your storage requirements and inverter selection sorted, you’ll need to figure out how much solar energy, or irradiance, is available to you. Your distance from the equator, the season, your local topography, as well as surrounding buildings, trees, and vegetation all play a role in the potential energy you can collect. The folks at EG4 recommended using a Solar Pathfinder tool and Assistant PV Software to conduct an accurate solar survey that takes into account all the various shading factors at your array site. This will help determine the size (number of panels) you’ll need, as well as the orientation of your system. You can find online tools, like the PVWatts calculator (https://pvwatts.nrel.gov/), to help figure this out, but you’ll have to estimate the shading you may have at your specific location.
We followed the directions provided with the Solar Pathfinder, leveling it and then orienting it to true north, adjusted for magnetic declination. (Note: A compass will show magnetic north, which can differ by several degrees from true north.) We placed the appropriate sun-path diagram for our latitude in the base of the Pathfinder—this diagram shows the arc of the sun for each month, with intersecting lines indicating each solar hour of the day. Over the top of the diagram, we placed a transparent dome that reflects anything, down to the horizon, shading the diagram. With the tool all set up, we took photos from directly above the dome, being sure we got one that clearly showed the shading features at our site.
When we loaded this image into the Assistant PV Software, tracing the shaded areas, entering our inverter specs, and entering the solar panel specs, we were able to see how much energy we would be able to collect each day, for each month of the year, for the panel we planned on using. We planned to roof-mount our panels on a shed that was not yet built. Based on lower projected winter power generation, we chose a fixed panel angle that was optimized for better performance during those months. We used this angle to dictate the slope of the shed roof.
 The last step in installing the EG4 6000XP splitphase inverter is replacing the cover(s)—on it, on the wire trough, and on the main service panel.
3 SOLAR ARRAY SIZINGThe number of panels you’ll need for your array is dictated by many factors, the first of which is your chosen inverter’s maximum input capacity. The next factor is the output of the panels you plan to use. Note that temperatures can affect panel output—on colder days, they perform better, putting out more voltage. And bifacial panels that can collect energy from light reflected on the back of the panels can add as much as 25 percent to the rated watts. Due to the number of variables that impact a panel’s potential output, using a string calculator is the ideal way to determine your array size. By the time this publishes, EG4 should have a new version of its online calculator available.
To use a string calculator, simply enter all the specs for the inverter and panels you’re using, as well as any other data it requires. The calculator will provide the number of panels you’ll need. Sometimes it will give you a range, like 8 to 10 panels, with the potential output range.
4 INSTALLATIONThis might actually be the fastest and easiest part of the project. With all the specs and components sorted out, you just need to connect the pieces. First, check with your municipality or authority with jurisdiction to see what version of the National Electric Code (NEC) they are using. Then look up the relevant sections for solar installations to see what requirements you need to meet.
You’ll likely be required to create a system wiring diagram or schematic, as we did. Show and label every connection, conduit, wire size and type, and all system components. Refer to both the electrical code and the installation manual for the components you’re using, and record the wire sizes and types needed to connect the components. The electrical code will require that certain wire/cable for parts of the installation be specific colors, so be sure to take that into account when estimating lengths and purchasing. For example, ground wires to connect components to your structure’s main service panel will need to be green. If your system provides 240 volts to the panel, line 1 (L1) and line 2 (L2) will be black and red, respectively, and the common wire will be white.
If you need to run conduit, be sure to size it appropriately for the gauge and number of wires running through it. You can look up conduit fill charts for reference, but if you have long conduit runs, you can bump up to the next conduit size to make it easier to pull the wires through.
Note that the version of the NEC will dictate how solar panels can be shut down to isolate them from the system. In our case we simply needed DC isolator switches at the array and the inverter. Newer versions require a rapid-shutdown device. The
Pay particular attention to the grounding requirements in the NEC. The solar panel frames and mounting rails need to be bonded (connected so that they maintain electrical continuity), and the whole mounting system then needs to be grounded to earth—i.e., with an 8-foot copper rod driven into the earth. In our case, that rod also had to be connected all the way back to our main service panel.
The many individual wires that connect system components will need to be protected anytime they run from one component to another. This means they’ll need to be in conduit, in junction boxes, or in wire troughs or raceways. Again, be sure to check your code requirements. We used a large wire trough to collect and route all our wiring. Incoming wires from the array, cables from the batteries, and connections between the inverter and main service panel are all routed through this trough—this was a neater and more efficient solution compared to a maze of conduit.
We also chose to install a Midnite Solar lightning and surge protector. Devices like this are designed to absorb voltage spikes that come in through the wires that run from the solar array to the inverter. Since the panels are roof-mounted with metal frames, lightning strikes are a risk. Compared to the cost of the system, the device is cheap insurance.
If you’ve done all the planning and research, and drawn up the diagram, this part should go smoothly—just follow the code requirements.
 The main service panel in the cabin, with breakers for each circuit, is a standard 100-amp residential model. The only difference in being fully offgrid is that an inverter supplies the power instead of a grid doing so.
A final word of caution: You may encounter folks online who proclaim that certain elements of the code are unnecessary, or over the top, and suggest simpler or easier ways of installing certain parts of the system. They may suggest that alternative methods accomplish the same objectives from an electrical theory standpoint. If you need to pass an electrical inspection and you expect your insurance company to honor any future claims that include components of your system—or are a result of your system—just follow the code.
WHAT YOU NEED TO KNOW ABOUT VOLTS, AMPS, WATTS, AMP HOURS, AND KILOWATT HOURSThe terms used to describe the capacity, size, and power of the various components in a solar system can be confusing. Here is what you need to know—in layman’s terms.
VOLTS ? VThe strength, or pressure, pushing an electrical current.
AMPS (AMPERES) ? AThe amount, or volume, of electrons flowing in an electrical current.
AMP HOUR ? AhA measure of current flow, over time, commonly used to describe battery capacity.
WATTS ? WA measurement of power. A x V = W
KILOWATTS ? kW1,000 watts. So, 1kW = 1,000W
KILOWATT HOUR ? kWhThe number of kilowatts used over one hour.
Note that battery capacities are typically described in volts and amp hours, while power consumption is described in kWh. So when determining battery storage requirements, you need to convert battery capacity to kWh. (Ah x V)/1,000 = kWh. So a battery bank with four 48V, 100Ah batteries would store 19.2kWh of power. (400Ah x 48V)/1,000= 19.2kWh.
BATTERY VOLTAGE AND CHEMISTRYIf you start digging into energy storage for your system, you’ll find that your main battery choices are 12, 24, and 48 volts. And, in those voltages, there are different chemistry choices: lead-acid, AGM, lithium, and lithium-iron phosphate (LiFePO4).
12-volt batteries, typically lead-acid, exist as an option mainly due to their use in RVs. AGM batteries are a more advanced, sealed, maintenance-free version of lead-acid batteries. Either can be used in small, off-grid applications, but there are some limitations. They have a lower number of discharge cycles and thus shorter life spans. They can be damaged by discharging below 50 percent. And they aren’t suited to high loads and rapid discharge rates. So, these would be an option if you’re using 12-volt RV appliances.
24-volt batteries perform better at higher discharge rates than 12-volt. Plus, they are more commonly available in modern chemistry options that can last thousands of discharge cycles. Lithium-based chemistries are your main options, with LiFePO4 being the most stable and preferred option. The 24-volt batteries can be wired in series to be used in 48-volt systems.
48-volt batteries, available with LiFePO4 chemistry, are the most robust and stable option. They can withstand repeated heavy loads and discharge rates, and may be rated to last as many as 10,000 cycles. For this reason, these are a preferred basis for larger energy-storage solutions powering entire homes or structures with typical appliances and heating/cooling systems.
SOLAR SYSTEM COMPONENTSThere are four main components in an off-grid solar system: solar panels, batteries to store the energy, a charge controller, and an inverter to convert direct current (DC) from the batteries and/or panels to alternating current (AC) that you can use to power your devices. The capacity of each of those components will depend entirely on the power you need to supply to all of your devices/appliances—and for how long. Larger systems often combine the charge controller and inverter in one device—these types often have inputs for generators, or even grid power, to charge the batteries when there hasn’t been enough sunlight. ends, so we need two days’ worth of storage.
PARALLEL OR SERIES CONNECTIONSThere are two options for how both batteries and solar panels can be wired—in parallel and in series. In parallel, the positive terminals are all connected, and the negative terminals are all connected. In this configuration, the total voltage remains the same, but the amperage increases. In series, the batteries or panels are daisy-chained together, with the negative of one connecting to the positive of the next. In this configuration, the amperage remains the same, but the voltage increases.
For batteries, the way you wire them depends on the system voltage that the inverter is designed for. In many cases, systems designed to fully power a home will be 48-volt-based. So you’ll have either multiple 48-volt batteries connected in parallel, or smaller batteries wired in series, to yield 48 volts.
For solar panels, the one you choose depends on two things: the maximum PV (photovoltaic, or solar) input for your inverter, and the solar array location and shading. In theory, if you have some part of the array shaded for significant portions of the day, then parallel will be better because the shading affects only the output of the shaded panels. Shaded panels connected in series, on the other hand, can bring down the whole array’s output. ¦ |
