Getting started generating free solar power is really not as hard as it seems. In the last 5 years, I have learned the key concepts of building a low-cost off grid solar system. Now I’ve written everything down right here. Just everything you need to know without the fluff.
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 is a lot like building a house, you start with the end users, work you way from top to bottom, and then build from bottom to top. A proper design process saves you money, time, while making the process of going off the grid a pleasant one.
Designing a DIY Solar System that Meets Your Needs
The most important thing to start with is the amount of energy you will be using and when it will be used. Renewable energy systems are inherently changeable, and therefore understanding daily and yearly rhythms of your family’s energy usage is essential in planning an efficient system.
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. Taking the time 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.
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.
Building Your Solar Battery House
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 accidentally damaging the battery and releasing 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 unsealed batteries, you will have to build in some ventilation in to your battery house in order to prevent buildup of potentially explosive hydrogen gas, which thes types of batteries release during normal charging operations.
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.
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 build many ways, depending on the materials you have on hand, and the skills you have. 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.
Wiring Up for Off Grid Solar
With the panels up, now comes time for wiring of the system. This step 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. All DC systems 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 already gets utilities, you are likely 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 this 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). If you’re looking for a detailed information on how to do this, check out my died to determining the cost of a solar system.
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. I can show you a lot 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. You could leave it attached for 24 hours, and then you would know how much energy it uses during a full day. This is best for intermittent devices, like refrigerators or computers, which I don’t use the same amount of power all the time.
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 to buy us during the day.
Lastly, you could 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. And, this doesn’t take into account any power fluctuations that would happen naturally. But it is much faster.
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. This is even more important for off grid solar, because solar power production also changes throughout the year.
Determining How Much Energy Solar Panels Produce
As you might have guessed, amount of power that are solar panel produces depends on how much sun it gets. That means 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 buy one of them and then 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 particularly dark or cloudy winters or summers.
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 you up on average how much power your solar panels will produce. The number depends on the color of your area it ranges from about 2 to 8. 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 your home or the 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 has produced during the summer in most regions because of the longer days. Go to the government website and download the maps that shows your area in both summer and winter. This way you can calculate how much power you can produce in the darkest and latest time for the year. You will need to size your solar system so that your produce enough power to cover your winter and summer needs, which means most of the year you will be producing more power than is necessary.
Now that you know how many kilowatts of solar panels you would need to cover your usage all year, 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, I’ll have some power loss associated with it. Well it is possible to go through each of your components and determine how efficient they are and this 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.
Do you calculate how many solar panels you need including any efficiencies in the system, just multiply your energy production by 0.7.
Considering Battery Capacity
The more batteries you have, the more you canThe more batteries you have, the more you canThe more batteries necessary to run your solar system at night, why no energy is being produced. Batteries can 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 except a full day is 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 24 and 48 V batteries are available for renewable energy systems.
We are going to go into more depth about using the proper battery in the next section, but be aware that many types of batteries, particularly lead acid batteries which are very cheap and accessible, have a very limited discharge depth. Even ”deep cycle” batteries should only be discharged to 50%. 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
Well the go to place to put solar panels on the roof, roofs 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.
I have a whole ride up 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 do south and when they’re not angled have a proper angle. Because many homes do not have a roof lines that face directly south, it makes it expensive, difficult, or impossible to face your solar panels in the right direction when they are on the roof.
Secondarily, Solar panel suffer greatly when they are even partially shaded by trees, other homes, and any obstructions I might be present. You might think that having your panels only 10% shaded we just reduce the help of my temper set. But in most cases it will reduce the Alpine over panel by at least 1/3. And depending on how are you why are your panels could reduce the total array output by 1/3, not just the one panel. Solar shading is a big deal, which is why I wrote a whole article about it here. So, unless your home is completely free from shading, especially in the winter, it is frequently Worth it economically to put your panels a little distance away from the house where they will receive full sun all your long.
Lastly, solar panels need to be clean and cool to work a maximum efficiency, and you have a nice long life. Dust, dirt, and snow will naturally accumulate on solar panels, I need to be cleaned off periodically. Even if the sun is down, snow accumulation on your solar panels will reduce their life overtime. 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.
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 mountain rocks they 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.
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