Getting started generating free solar power is really not as hard as it seems. Here, I’ve distilled down everything I’ve learned about off grid solar energy over the last 5 years, in to this easy to follow but comprehensive guide.
How to build an off grid solar system:
- Determine your power needs
- Pick the right site
- Choose your components
- Build the battery house
- Install the panels
- Wire up the system
- Enjoy your free power!
Going off grid with solar power doesn’t have to be hard. While there is a lot of terminology to wade through, in this guide I’ll cut through the jargon and simplify the process of building an solar system. And, I’ll save you money at the same time.
Overview of Building An Off Grid Solar System
Designing your own self-sufficient solar power system must start with your end user’s needs in mind. Making the effort to follow a proper design process saves you money, time, and makes the process of going off the grid a pleasant one.
Here is an overiew of the steps I’ll take you through over the course of this three part guide.
Step 1 — Designing a DIY Solar System that Meets Your Needs
The most important thing to know, when getting ready to build an off grid solar system, is how much energy you need, as well as how you energy usage changes throughout the day and year. Renewable energy systems are inherently variable, and therefore understanding daily and yearly rhythms of your family’s energy usage is essential in planning an efficient system.
Getting this right will be a big portion of part one of this guide.
Step 2 – Choosing the Right Place for Your Panels Is Essential
Next, we take care to find and plan for the right site. Often, the top of the house is not the most efficient place for an off grid solar array. Choosing the right spot to prevent excessive shading and to ensure proper access and passive cooling for your solar panel can more than double the efficiency of your solar panels over their lifetime.
Step 3 — Ordering the Right Solar System Components
Once you have chosen the placement of the solar panels, you will have an idea of the power power potential of you site, and will be able to choose and order the proper components for your system. There are many choices to make at this point including:
- The number and size of your solar cells
- The type and size of your charge controller (MPPT vs PWM, etc)
- Your battery bank capacity, while considering battery type
- Choosing the overall voltage of each leg, as well as which loads should be AC vs DC
- The rating of your inverter, if any
We talk about this in part 2 of this series.
Step 4 — Building Your Solar Battery House or Compartment
Once you have the components ordered, you would be ready to build your battery house, which may be a room in your existing home, part of the garage, or a separate shed. Batteries take up a fair amount of room, they need to be protected from kids or critters that might hurt themselves by touching the contacts or might accidentally damage the battery and release the acids inside.
Additionally, most types of batteries need some amount of temperature control, and don’t do well with freezing weather. However, if you go with less expensive unsealed batteries, you will have to build in some ventilation in to your battery house in order to prevent buildup of explosive hydrogen gas, which these types of batteries release in small amounts when charging.
In order to reduce costs, most solar setups have their main power electronics — the charge controller(s) and inverter(s) — as well as safety shutoffs, fuses, and breakers in the battery room as well.
We talk about this in part 3 of this series.
Step 5 — Installing Solar Panels
Finally, it’s time to build the panel support and install the solar array. Solar panels are far more efficient when they directly face the Sun, and they last longer when they are rigid and well cooled. A proper solar support structure can be built in many ways, depending on the materials you have on hand, and the skills you posses. I recommend, at the least, building a south facing A-frame type structure out of wood, or metal, with the ability to manually adjust the tilt of your panels during the summer and winter, which can increase your power output by up to 40% with almost no addition cost.
You could also go all out, and build your own one-axis or two-axis tracking system. Check out the panel installation guide below for more ideas on how to make this work.
We talk about this in part 3 of this series.
Step 6 — Wiring Up for Off Grid Solar
With the panels up, now comes time for wiring of the system. This step doesn’t need to be complex. Going off grid, with a boondocking RV, country cabin, or permaculture homestead, means that your electrical system can be much simpler than gird tie systems.
Going off grid means you have the option to install an all DC system, which can be quite simple and efficient. But even whole home replacement AC systems are possible for the DIYer.
However, if you intend to use your solar system and connect it to a home that is already connected to grid power, you are likely to be legally required to hire a licensed electrician to wire in your system, and you will need additional hardware from your utilities company to make your own energy system work with line power.
We talk about wiring your system in part 3 of this series.
How Many kW of Solar Panels Do I Need?
In order to accurately determine how big of a solar system you need, the first thing you need to do is determine how much energy you are using. Energy is measured in kilowatt hours (kWh), and by the end of this section you should be able to determine exactly how many kWh you use in a day.
How to Measure Your Power Usage
The best and most accurate way to determine your power usage is to measure it yourself. I recommend that you purchased this inexpensive “kill-a-watt” power measuring device for your plug in appliances.
Using the kill-a-watt is simple just plug it into the wall, and your appliance into it. It can provide you with a wide variety of measurements, but the one we really need is watts, or kilowatts.
The simplest way to measure energy is to just set the kill-a-watt to measure kilowatt hours. This measurement takes time to get an accurate reading. Ideally, you would leave it attached for 24 hours, and then you would know how much energy it uses during a full day.
You could also just measure the energy usage for one hour. Then just multiply that number by the number of hours you will use that item during the day.
A third, less accurate but faster option, you is to just measure the watts that the device is using, which shows up instantaneously. No need to wait. But then you have to multiply the watts by the number of hours you would use it per day. But, this doesn’t take into account any fluctuations in power usage that happen naturally happen in most appliances except entirely passive devices such as lights and heaters.
Calculating Your Daily Usage
Now, add up all of the energy measurements that you took all of the devices that you plan to use in a given day. This is your daily energy usage.
It’s important to realize I your energy usage fluctuate throughout the year. You may use lights much longer in the winter when it’s darker, yet the refrigerators will run less. I recommend you take a power measurement both in the winter and the summer, or at least attempt to adjust number of hours used by each device to account for the differences.
Knowing how your power usage varies session ally is extremely important for off grid solar, because solar power production also changes throughout the year. So, it is easy to over or under size your system if you only use a yearly average to plan for your system.
Determining How Much Energy Solar Panels Produce
As you might have guessed, the amount of power that your solar panel produces depends on how much sun they gets. That means during the shorter days of winter you will get less power. Also, cloudy days will give you much less power than sunny days.
Again, the best way to know how much power your solar panels will produce is to measure it. Buy one solar panel and measure how much energy you can produce throughout the year. Not every year is the same, so you will need to oversize your system just a little bit in order to account for usually dark or cloudy years.
However, you may just want to get a rough estimate of how much solar power your panels were produce. Luckily the US government has produced solar power availability data for the entire United States.
The map above shows on average how much power your solar panels will produce per day. The number depends on the color of your area it ranges from about two to eight. This number can be multiplied by the power rating of your solar panels to determine how much power they would produce. So if you live in an area labeled as three on the map and you bought a 1 kW Solar panel array then you would get 3 kWh of energy produced per day on average.
This assumes that you have full access to the sun so long as it is up. If location of your solar panels is partially shaded, especially during mid day, then you will get less power than the map shows.
Also, most of the average power is produced during the summer in most regions because of the longer days and more direct sun exposure. To get a more accurate analysis, go to the NREL website and download detailed maps that show your area in both summer and winter months. This way you can calculate how much power you can produce in the darkest and lightest times of the year.
Choosing the Right Size Off Grid Solar System
You will need to size your solar system so that it can produce enough power to cover your winter and summer needs, which often means most of the year you will be producing more power than you can use.
Additionally, we need to account for the fact that solar systems are not 100% efficient. The process of transferring power from the panels to the charge controller, the charge controller converting it and storing in the batteries, and then the power coming out of the batteries and being potentially transformed into AC, all have some power loss associated with them.
While it is possible to go through each of your components and determine how efficient they are and thus calculate the perfect number of solar panels for your particular system, I generally just go with a 70% efficiency figure for typical after power systems.
To calculate how many kW of solar panels you need, including any inefficiencies in the system, just divide your energy needs by 0.7, or whatever figure you come up with for total system efficiency.
Considering Battery Capacity
Batteries are necessary to run your solar system at night, when no energy is being produced. They also help level out power consumption between sunny days, when you are getting plenty of power, and cloudy days when you won’t be getting so much.
At minimum, your batteries should be large enough to store a full day of charging in the winter. So, if your system is capable of producing 1 kWh during a full day in the winter, then I would choose a battery bank that is capable of storing at least that much.
Battery capacity is measured in amp-hours (Ah) so in order to get kilowatt hours you would need to multiply that number by the voltage of the battery. For many batteries it would be 12 V, although 24V and 48V batteries are available for renewable energy systems.
We will be going into more depth on choosing the proper battery in the next section, but be aware that many types of batteries, particularly lead acid batteries, have a very limited discharge depth. Even ”deep cycle” lead acid batteries should only be discharged to 50% capacity. This means you’ll need to double the size or a number of batteries in your system over what the nominal amp-hour rating would suggest.
Where to Put Your Solar Panels
While the go to place to put solar panels on the roof, roofs are very frequently not the best place to put your solar panels. There are three reasons why I don’t recommend putting solar panels on the roof: roof direction, shading, and access.
Make Sure Your Panel Location Has The Proper Angles
I have written a whole separate article on the proper angle to place your solar panels, and what happens when you don’t put it in the right spot. But, suffice it to say, you lose a lot of the potential power you could be producing when your solar panels are not facing due south and when they’re not properly angled. Because many homes do not have a roof lines that face directly south, it can be expensive, difficult, or impossible to face your solar panels in the right direction when they are on the roof.
Avoid Solar Panel Shading At All Costs
Secondarily, solar panel suffer greatly when they are even partially shaded by trees, building, and any obstructions that might be present. You might think that having your panels only 10% shaded we just reduce the power output by 10%. Yet in most cases it will reduce the total power output by at least 1/3. And depending on how your panels are wired, it could reduce the total array output by 1/3, not just the one panel. So, unless your home is completely free from shading, especially in the winter, it is frequently cheaper overall to put your panels a little distance away from the house where they will receive full sun all your long.
Make Sure Your Solar Panels Are Accessible
Lastly, solar panels need to be clean and cool to work a maximum efficiency, and have a nice long life. Dust, dirt, and snow will naturally accumulate on solar panels, which need to be cleaned off periodically. Snow accumulation on your solar panels will reduce their life. Placing your panels closer to the ground where they are easier to access can go along way towards making routine solar panel maintenance actually get done in a timely manner.
Make Sure You Solar Panels Are As Cool As Possible
While solar panels are black, they do not like being excessively hot. Over heated panels produce less power, and they wear out much work quickly. A proper solar panel set up should have at least 6 inches behind the panels where air can flow freely and cool down the panels. Roofs are not great because they tend to be excessively hot already, and while you can buy solar panel mounting racks that do allow for ventilation on the roof, putting them down where it’s cooler may save you a lot of extra money in the long run.
In terms of overall cost of the system, it is best to put the solar panels as close as you can to your home, while keeping them in full sun.
Continue to Part 2 — Choosing Components →
How many solar panels does it take to run a house off grid?
An average size off grid solar system in the US is 5 kW, which means you would need 20 solar panels at 250 W each, or 50 smaller 100 W panels. Whether this would run your house depends on how much sun you get and how much power you use.
What is needed for an off grid solar system
Off grid solar has the following components:
- Solar panels (mono or poly)
- Charge controller (MPPT or PWM)
- Battery bank (lithium, lead acid, or other)
- Inverter (pure sine wave)
- Fuses & disconnects
- Copper wire
- Misc connectors