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If you want to learn How to Build an Off Grid Solar System that’s designed to power common AC loads. This post will explain the four key components that make up an Off Grid Solar System and how they interface with one another.
Solar Modules:
Batteries:
Charge Controller:
Inverters:
Tying the Key Component together.
Each of these components has a specific job and each component is required. Learning the function of the key components better prepares you for purchasing your own DIY Off Grid Solar System and is the first step in learning How to Build an Off Grid Solar System. Most Mail Order or Online Solar companies don’t necessarily have the time to take you through the learning process. It’s better to sound like you’ve done your research to the Sales Person. It lets them know if you’re an actual potential customer or kicking tires. Believe it or not that alone can save you thousands of dollars on components by preventing you from purchasing components that are over sized for your actual needs.
The video below will show the location of the four key components that make up a working Off Grid Solar System. The system in the video was designed with a Pre Wired Magnum Dual PAE Inverter Power Center which is a great choice for folks embarking of a DIY Off Grid Solar Project. The video gives reference to the size, potential scope of electrical work, and nomenclature to prepare you for the coming design, build, and service of your DIY Off Grid Solar System.
How to build an Off Grid Solar System, Understanding Modules:
The module is where the magic happens. This is where the photons from the Sun’s light are turned into electricity. Let’s take a step back and compare an Off Grid Solar System to a machine that most of us use daily, the automobile. Even if car mechanics is foreign language to you, one thing everyone knows is that an automobile will not run on an empty tank. You must put gas in the tank to make your vehicle run. Using this analogy think of your Solar Modules as the gas station, it’s the place we fill up our tank. If the sun is shining and you have the Solar Module pointed at the sun you can fill up your tank for free!
Most modules manufactured today are what we call Grid Tie Modules. These modules range from 280 to 360 Watts and are designed to be connected in a series string that feeds a Grid Tie Inverter. Smaller modules are now considered Specialty Modules, which is funny because these are the modules that pioneered the solar industry. You’ve most likely seen both in passing. Typically the modules you see on homes or businesses are the large Grid Tie Modules. The smaller Specialty Modules are commonly seen powering roadway signs, gate openers, or on RVs and campers. These modules have a lower voltage output and are ideal for charging 12, 24, and 48 volt battery banks. Making these modules a good option for solar direct projects such as well pumps, gate opens, remote traffic lights and other battery powered devices that run off of Direct Current (DC) power. There’s a time and place for both types of modules, it all depends on what you want to power.
Let’s explore the solar cell for a minute. This is the basic building block of a poly or mono crystalline module. The solar cell is where the photons from the Sun’s light are turned into electricity. But how does it work? A solar cell is made by sandwiching two thin layers (or wafers) of silicon together. One of the wafers is doped with phosphorous, giving this layer extra electrons. This side is called the N layer and has a negative charge. The other layer of silicon is doped with Boron, this layer has missing electrons or holes. This side is called the P layer and has a positive charge. When you put these two layers together an energy field is created in the middle. This is known as the PN Junction (Positive Negative Junction). When the Sun’s light strikes the solar cell it knocks the extra negatively charged electrons off of the N layer. Theses free floating electrons are attracted to the side with the holes . There is now potential for electricity.
Metal strips are embedded into the solar cell. These metal strips are referred to as tabbing. The tabbing collects the free floating electrons and provides a roadway for those electrons to travel to the P layer. With a roadway in place these electrons can now create a complete circuit and presto we have electricity. The photons from the Sun’s light keep knocking the extra electrons free and push the electrons down the roadway. When the roadway is routed through a load or connected to a battery it will power the device or charge the battery!
A solar module can easily last 20 plus years. There are no moving parts or internal mechanics to break down. As long as the Sun is shining the electrons will keep flowing. That’s what is awesome about solar modules. The sun is free fuel. Into today’s world of wild fires, hurricanes, and pandemics having a reliable source a power provides your family security. Even if it’s as simple as a 1 module,1 battery charging station, having a source of power that doesn’t require gas or propane in a grid down event could prove to be a real life saver. Remember if the sun is shining you have an endless fuel source!
How to Build an Off Grid Solar System, Understanding Batteries.
Discover Dry Cell AGM with Traction Valve Technology
Storage is a hot topic these days. With rolling blackouts, severe weather storms and natural disasters it makes since people are looking for energy storage solutions. Energy storage is the primary function of your batteries. The extra electricity produced by your solar modules during the day gets stored in the battery bank for future use. The energy stored in the battery bank can be used at night or during cloudy days. Batteries are the like the gas tank in your car. It’s a big tank that stores fuel for future use.
We will briefly discuss the three most common types of batteries used in Off Grid Solar Systems, Flooded Lead Acid Batteries (FLA), Sealed Lead Acid (SLA), and Lithium Ion.
Flooded Lead Acid (FLA) Batteries are the most used battery for Off Grid Solar Systems. You will hear these referred to as “Wet Cell, deep cycle batteries”.
Pros:
Most cost effective option. Lowest cost per Amp Hour.
Thick lead plates allowing for daily discharge and recharge.
Proven technology. (150 + years)
Cons:
Requires regular maintenance.
The battery cells must be submerged in water to function. The water level of the battery will need to be checked once a month. How often you have to fill the batteries with water depends on how much the batteries are used and the temperature of their location.
Required maintenance: Fill battery with distilled water as needed.
FLA batteries produce a hydrogen gas.
Battery bank is required to be vented to the outside.
Equalization charge (EQ) – High voltage charge which is essentially a power wash for your batteries. The high voltage charge knocks away sulfate build up; bringing all the cells within your batteries back to a uniform capacity.
EQ Charge required every three months.
Batteries must be mounted in an upright position.
Recommended daily depth of discharge (DOD) is 50%
Pro Tip: *Most maintenance can be automated with Tier One Charge Controllers and Power Centers.
Trojan L16 (FLA)
Sealed Lead Acid (SLA) Batteries are a great option for people who want a maintenance free solution. As the name suggests these batteries are sealed, nothing can be added or removed from the battery. There are two types of sealed lead acid batteries. AGM (absorbent glass mat) and gel.
Pros:
No maintenance requirements.
Thick plates for daily discharge and recharge.
No hydrogen off gassing.
Cons:
Higher cost per amp hour. Trading money for time.
Recommend daily depth of discharge (DOD) is 30%. “Although the technology is getting better with traction cell technology”.
Properly maintained Flooded Lead Acid Batteries usually have twice the lifespan.
Deka Unigy Batteries, Sealed AMG (absorbent glass mat)
Lithium Iron Phosphate (LFP or LiFePO4)
In a future post we are going to have a head to head cage match comparison with two industry experts in the field of Lithium Ion Batteries. To be object and fair we are going to mention these as a viable option for battery storage.
Pros:
Longer Life Span
Deeper daily depth of discharge. Per our conversation with industry expects the recommended daily depth of discharge is 80-100%
No maintenance requirements.
No hydrogen off gas.
Cons:
High up front cost.
Longevity yet to be proven.
How to Build an Off Grid Solar System, Understanding Charge Controllers.
Outback Power FlexMax FM60 MPPT Charge Controller on right
The next key component in an Off Grid Solar System is the Charge Controller. A charge controller regulates the amount of electricity entering the battery bank. It prevents your battery bank from being over charged. Just like the automatic cut off switch at the gas pump prevents you from over filling you gas tank. The charge controller reads the needs of your batteries and gives your batteries the right amount of energy at the right time.
Think of a garden hose with an adjustable spray nozzle. You can open the nozzle full throttle to power wash the dirt off of your car or you can reduce the blast to a small trickle to water a delicate plant. The charge controller works the same way. If the batteries are empty we’ve got that garden house nozzle open full throttle blasting the batteries with electricity, but as soon as the batteries start to fill up the charge controller automatically slows down the flow of electricity allowing the batteries to be fully topped off.
Think about trying to fill up a cup of water using a garden hose. You might start out with a full blast, but you’ll soon need to reduce the flow of off water in order to fill up the cup. If you keep the spray at full blast, you’ll blast the water right out of the cup and it will never fill up. If you want to fill the cup up to the very tip top you will need to slow the flow of water down to a trickle.
It’s the same concept, except we have electricity from our solar modules (water), be regulated by the charge controller (adjustable spray nozzle), filling up our batteries (cup). The charge controller allows your batteries to fill up to the very top by slowing the flow of electricity down to a trickle. (external link to Midnight Classic)
There are two types of Charge Controllers available in today’s market; the Pulse-Width Modulation (PWM) and the Maximum Power Point Tracking (MPPT). We’ll get into the technical details of these two types of charge controllers in a future post. For now I just want you to know they exist. Using our car analogy, the Charge Controller is the carburetor and controls the fuel injection process for a perfect balance of air and fuel.
How to Build an Off Grid Solar System, Understanding Inverters.
In a nut shell an inverter will take direct current (DC) battery power and turn it into usable standard household voltages, alternating current (AC). This can be done on a 12V, 24V, and most commonly now a days a 48V battery platform. We call the battery platform our system voltage. The solar modules generate DC electricity. That electricity is stored in the battery bank. The inverter takes the DC power from the batteries and converts it to AC electricity. *Note what we are describing here is for Off Grid Battery Base Inverters only. Grid Tie Inverters work differently (link to Wholesale Solar – Grid Tie)
Going back to the car analogy; an inverter acts like an engine. It takes the fuel from your gas tank (DC battery power) and converts it to usable energy for inside your home.
How to Build an Off Grid Solar System, Choosing an Inverter.
Magnum Energy MS4448PAE, 4400 Watt Sine Wave Inverter
Bestek MRZ3011HU, 300 Watt Sine Wave Inverter
What will be determined in your design is not unlike picking out a 4 cylinder verses an 8 cylinder. We will equate in this example output watts as horse power. After you determine if you want a moped verses a turbo diesel you would then select an inverter and or a group of inverters acting in concert much like a twin engine air craft.
Above we have a picture of a Magnum Energy MS4448PAE and Bestek MRZ3011HU. The Magnum is our turbo diesel and the Bestek is the moped. You can understand a lot about an inverter’s capability by dissecting the model number.
The Magnum inverter has 4,400 Watts of inverting power (this capability is captured by the first two numbers in the model number MS4448PAE). This means it can draw 4,400 watts of power from your battery bank and provide that amount of power to your loads continuously. This particular model has a 5 sec surge capability of 8,500 Watts. Meaning this inverter has the capability of providing 8,500 Watts of power for 5 seconds. This is a very useful feature because motor loads and pumps require a surge of power for a few seconds when they first turn on. The 48 at the end of the model number (MS4448PAE) tells us the required battery voltage. The Magnum Energy MS4448PAE inverter requires a 48 volt battery bank to wake up and turn on. Making the system voltage 48 volts. (link to spec sheet).
What’s a Watt anyway?
A watt is a unit of measure and that unit of measure is power. Say it with me….A watt is a unit of power. To be precise lets break it down to its algebraic formula. 1 Watt = 1 Amp X 1 Volt. In other words Volts X Amps = Watts. When you take this unit of measure over a distance, in our case electricity over time we get Watt-hours. (Insert picture on Edison old school light bulb). If we have a 50 Watt light bulb and it runs for one hour, what we have now is 50 Watt-hours (50 WH). 1000 WH = 1 Kilowatt Hour (KWH). If you get your electricity from a Utility Company you are billed for the amount of Kilowatt Hours you consume.
Now that you understand what a Watt-hour is and how an Inverter works let discuss a few additional factors that need to be considered when choosing an inverter for an Off Grid Solar System. The first thing to consider is how many watt-hours you plan to use per day. This will dictate the size of your array (amount of solar modules you need) and the size of your battery bank (i.e size of your fuel storage tank, ensuring you have enough power to power your electrical loads at night and during cloudy days). *Note other considerations apply such as location and available sun hours. This ensures you have the right amount of power for the appliances you’ve decided you need or want.
The size of your inverter (or inverters) is determined by the amount of power needed for the appliances deemed critical in the event all those appliances are turned on at the same time (this is your peak electrical load). Your peak electrical load must match the continuous output ability of your inverter. Or in other words your inverter’s continuous output ability must match your peak electrical load. This is what we call inverter head room and is the main reason you would choose a larger inverter.
*Note: If you have decided you are going with the truck stop inverter (aka the moped) beware there are two types of inverters available. There are Modified Sine Wave inverters and Pure Sine Wave inverters. When inverters first came out a Modified Sine Wave was the cheapest way to build an inverter. The Modified Sine Wave inverter works for some appliances, but it does not work for devices with sensitive electronics. Remember the inverter takes Direct Current (DC) power from your battery bank and converts it to Alternating Current (AC) to power your household loads. Direct Current is a straight line, it has no wave form. Alternating Current is a continuous/symmetrical wave form. The wave rises to 120 Volts, returns to O Volts and continues down to -120 Volts and then back up to 0 Volts. What I described is one cycle of Alternating Current. This cycle happens 60 times a second and what is referred to as frequency. In the USA our electrical appliances operate off of 60 HZ (this is the frequency). 60 HZ is the frequency of Alternating Current, 60 cycles of Alternating Current a second. This is the electricity that Tesla Invented.
The Modified Sine Wave tries to mimic this smooth continuous wave form but it does so by creating chunky stair steps. Check out the diagram below for a visual. Appliances like smooth clean electricity and the Modified Sine Wave inverter does not deliver that. If you’re a surfer you want a nice smooth wave to ride. You’re not going to try and catch a ride on a bunch of choppy waves. Remember when choosing an inverter spend the extra money and pick a Pure Sine Wave inverter. Now a days they aren’t that much more money. This way you don’t run the risk of damaging some of the electrical devices you want to power.
The inverter system works independently from the charge source (charge source being the solar modules regulated via charge controller), but off the same battery storage. However, inverters used for whole home off grid systems in most cases are Inverter/Chargers. Inverter/Chargers can convert DC to AC like we have been talking about, but they can also take an external source of AC electricity and use that to charge the batteries. If you have a long stretch of cloudy weather days you would then have the ability to fire up the generator and charge your batteries, allowing you to power your household loads. Both generators and power from a utility company can be used in this capacity.
Although we design systems to match your daily needs sometimes weather can be unpredictable, who would have thought right? We get cloudy days even in the desert; therefore a backup generator is most often built into the design of whole home off grid solar systems. We’ve seen customers though go three to five years without ever using their backup generator. The idea here is to make your solar system size adequate for your needs and be preventive by anticipating needing a charge by having a small generator available. The Honda EU series is one of our favorite generators. (Link the Honda EU series). These are super quiet and very fuel efficient.
How to Build an Off Grid Solar System, Tying all the Key Components together.
Custom built S.M.R.T Wedge. Array on top, batteries located inside the bottom portion of the wedge, power center (ie. inverter, charge controller, over current protection) inside the front closet. AC output is trench over to the main service panel of the Off Grid Home.
Your solar modules when pointed at the sun will output a certain amount of watts (this depends on the size of the solar module and how many you have connected together to make your array), remember a solar module can range from 5-360 watts. These watts (or in other words) this power is coming out of the solar modules in the form of direct current (DC) power. The power produced by your solar modules gets routed to the charge controller first; from there the charge controller regulates the flow of electricity entering into your battery bank (fuel storage tank). Next you connect your inverter to your battery bank. The inverter converts the direct current (DC) electricity stored in your battery bank to usable alternating current (AC) electricity, to power your household loads. The amount of house hold loads you would like the ability to power all at the same time needs to match the size of your inverter’s continuous output capabilities.
There are addition design considerations that need to be taken into account to make sure each of the key components is correctly sized to work with one another. In addition some brands are compatible with other brands, some are only compatible with their own brand, and sometimes mix and matching different brands can have warranty implications.
Stay tuned for our next blog post on How to Build an Off Grid Solar System! We are going to dive into Off Grid Solar design principles!
DIY with a Little Help, Off Grid Solar!