The goal of this article is to help you deeply understand about solar system components and know how to choose the best solar panel kits before buying.
Solar Panels & Batteries
We re-going to go over some of main components in a solar panels kit:
- The solar panel modules
Keep in mind that technology is moving forward at an incredible rate. I’m going to make some generalities that are true today, but there are likely to be exceptions to most rules discussed.
Wiring Solar Panels (Series vs Parallel)
Before we go further, I want to go over a quick reminder on wiring in series vs parallel.
Wiring solar panels in series, where the negative of one is wire to the positive of the other, results in the current staying the same, but the voltage increases.
Two solar panels in parallel, where the two positives are wired together and the two negatives are wired together, results in the voltage staying the same and current increasing.
W = V x A
It’s important to note that regardless of the way it is wired, the power, or watts, remains the same. It doesn’t matter if it is series or parallel.
Likewise, when batteries are wired in series, their voltage increases, and when wired in parallel, amp hours are increased. You’ll often see multiple rows of panels or batteries wired in series, each row is a string. You can then wire multiple strings in parallel. This allows you to get both higher voltage (with series strings) and higher amps or amp hours (with parallel).
In this example of 2 parallel rows of 4 batteries wired in series is called 2 strings of 4.
You can see that wiring (4) 12V batteries in series equals 48V, and wiring those 2 strings in parallel doubles the amp hours to 160ah. The power of this array is 7680 watt hours.
1. Solar Panels (PV Modules)
Solar panels are the first thing we need to consider in our solar panel kit.
How do solar panel Make electricity from Sun?
Solar panels generate DC electricity when exposed to sunlight via the Photovoltaic Effect, first observed by a French physicist in 1839.
A simple explanation is that the photons from sunlight are absorbed by a semiconductor material, generally silicon. The negatively charged electrons are knocked loose from their atoms, and flow from the negative side to the positive side to recombine with available holes. This creates a direct current flow.
This flow of electrons can then be used to either directly power a DC device, like a pump or a fan, it can be used to charge a battery bank, or it can be inverted to AC power to use in your home.
Combining cells to make a PV modules
Each solar cell generates about 1/2V. That’s not much for practical use. Multiple cells are wired together in series to create higher voltage, creating a solar module, commonly referred to as a solar panel. A typical 12V solar panel has 36 cells in series.
The larger a solar cell is, the higher the current. The cells of a 200W panel are generally bigger than a 100W solar panel. Multiple solar modules wired together then creates a solar array.
You can see the difference in the look of a 12V module compared to a 24V module.
As with anything, there are exceptions. We do have some 12V modules that have 72 cells, but the cells are wired in 2 parallel strings of 36 in series, creating the 12V.
Each module has a label on the back, stating their specs. Here’s an example of a Kyocera 140W 12V module.
It lists the rated outputs for the panel, as well as any certification it has. The ratings are actual outputs under standard test conditions, the numbers you measure in the real world may be slightly different.
- Open Circuit Voltage is the voltage you will measure when nothing but a voltmeter is connected to the solar panel. This is the highest voltage the module will output at 77 degrees Fahrenheit with the sunlight intensity at 1000 watts per square meter, which are just a few of the details of standard test conditions, or STC. The voltage will be higher when it is colder out, and lower when it is hotter.
- Short Circuit Current is the amps output with no load on the panel. It is the highest current possible at STC. There are times when the output could be higher, for instance when the sun is coming out from behind a cloud, you can see the silver lining, where the edge of the cloud is magnifying the sunlight, causing the intensity to be brighter than STC. This brings us to the two specs which are when the module is connected to a load, more real world conditions. But still at the temperature and brightness listed under STC.
- Maximum Power Voltage is the actual voltage the module will output when connected
- Maximum Power Current is the amps output while under load.
PV modules were originally designed to solar charge battery systems, it is typical to see panels listed for what voltage battery bank it is able to charge.
Nominal voltage is a shorthand grouping term, originally based on battery voltages (for example, 12V, 24V, 48V). To charge a 48V battery bank, you simply wire four 12V modules or 2 24V modules in series to add up to 48V.
In general, you can determine what nominal voltage the module is by the number of cells on the panel.
A 12V nominal panel usually has 36 cells, and its Open Circuit voltage is about 22 volts, and its Maximum Power voltage is around 17 volts.
However, as grid-tied solar systems that don’t use batteries have become more popular, you start to see different size nominal panels that don t logically line up with battery bank sizes. The most popular size modules used in grid-tied systems today are 60 cell, 20V modules.
The wattage of available panels has been increasing, and many manufactures are achieving that by increasing the number of cells, increasing the voltage of the panels. Increasing the volts while maintaining the same amps increases the watts. As such, there are 80 cells and higher available these days.
2. Solar charge Batteries
Solar panels have no way to store power, you use it or lose it. Solar Batteries allow you to store power to use later, by using the power generated by the module or other power source to charge the batteries, this thing is very important in solar panel kits package.
Batteries used in your solar system MUST be deep cycle batteries. These are made very differently from car batteries.
- A car battery has the internal plates designed to send a short, high current blast to start the engine. It then gets recharged quickly by the alternator to send another short blast hours later.
- A deep cycle battery is designed differently. It is designed to be gradually charged and discharged over a course of hours. If you try to use a car battery for an off-grid system, it will work for a short amount of time, but you will very quickly kill the batteries.
PV systems can have many batteries, each of them can weigh 50, 100 pounds, or much more. There are losses inherent in batteries as they convert electrical energy to chemical and back to electrical: 5-15% of energy lost to storage and extraction.
You should never use more than 50% of the rated capacity, or you will quickly reduce the battery s ability to hold a charge, and have to replace the bank. These losses need to be taken into account when calculating the size of your battery bank.
Type of Solar Battery
When selecting a battery for your solar panel kits, there are 2 primary types of batteries available, flooded or sealed.
1. A flooded lead acid battery: has removable vents that you must remove to check the specific gravity of the acid and add water on a regular schedule, usually once a month. Because it is not sealed, it is designed to output the hydrogen gas that is created during its charging process. Therefore, the battery bank MUST be properly vented to the outside.
If you are looking to have flooded batteries shipped, be aware that they are considered hazardous material by the Department of Transportation, additional precautions and expenses may be required.
The advantage of these flooded batteries is that they are less expensive than a typical sealed battery, and a well maintained flooded battery will generally last longer than a typical sealed battery. But if you neglect the battery and do not handle the maintenance, you will quickly have a dead battery bank on your hands.
2. Sealed Lead Acid batteries: are most commonly available as either AGM or Gel. This refers to the form of the electrolyte. An AGM battery has the electrolyte in a spongey mat, and the gel batteries have a thicker gel that keeps itself distributed within the battery.
There are pros and cons to each of these designs that we won’t get into, but in general, both types of sealed batteries are very similar.
The biggest pro of sealed batteries is that since they are sealed, they won’t spill or outgas. This makes it a safer option than flooded batteries. They also don t require the monthly maintenance, just occasionally inspect them to see that they look to be in good shape.
Sealed batteries are an excellent choice for battery backup solar systems that aren’t charged and discharged every day, but require a long standby period. They also do better in extreme cold. The downside to the sealed batteries is that they tend to be more expensive than a flooded battery, and have a shorter life than a well maintained flooded battery. But if you are not able or willing to maintain a flooded battery, sealed is definitely the way to go.
Solar Battery Storage Capacity
This will come in handy when we size our battery bank. Many people ask how long they can run things from a battery. This depends on how deeply you discharge the battery, known as depth of discharge, and how quickly you are drawing current out of the battery. Read about depth of discharge here.
If you are drawing 2 amps out of a battery for 4 hours, this is using 8 amp-hours. You don’t want to use more than of the stored power in a battery, the most power you want to take out of a 92A hour battery is 46ah. If you are running that same 2 amps for 23 hours, you would have drained the 92A battery to 50% depth of discharge.
The amount of power that a battery can store varies based on a number of variables, including how fast you charge and discharge the battery.
In this example, you see that if you charge and/or discharge the battery over 5 hours and a rate of 49 amps, it can store half the power than if you did the same over the course of 100 hours at 4.6A.
Most batteries are rated at 20 hours, basically how much power you can use during a day. If you are using power faster or slower than 20 hours, you must adjust the sizing accordingly.
Solar Battery Storage Specifications
When selecting a solar battery for your solar panel kits, you must:
- Decide between flooded or sealed, what voltage battery, and how many amp hours.
- You need to keep in mind the size and weight of the batteries, will they fit in your available space?
- Note what terminals they have to connect the battery cables.
Charge Controllers & Inverters
To get more detail, read here:
- Solar Charge Controller | What is it and How it works in a Solar Power System
Solar Array Racking
Solar Array Racking is a less glamorous, yet critical component to a solar panel kits. We’ll briefly go over three of the most common types of racking:
The first place people think about installing solar is on the roof. There are options for installing on all types of roofs, including asphalt or tile shingles, metal standing seam, and flat rubber roofs.
1. Shingle Roof Mount
Any roof penetrations, including bolts for the mounting feet or the conduit going through the roof, must be flashed to prevent leaks.
When selecting a roof mount, you do have the option of using legs to tilt the angle of the panels higher or in a different direction if needed, but it is generally recommended that you just mount the panels flush on the roof, and accept that it may not produce as much power as it would if at the idea angle.
Unless you have to squeeze out every last bit of power from the array, generally, a flush mount looks better, and you don’t have to be concerned with additional wind loading by being raised off the roof.
2. Standing seam metal roofs
Standing seam metal roofs need a solution that won’t drill through the metal. Clamps are available to grab onto the standing seam, allowing you to connect the rails, or the panels themselves, right to the clamp.
3. Flat Roof
You don’t want to drill through a flat rubber roof. A ballast mount allows you to weigh down the racking with concrete blocks instead of bolting them to the roof.
Ballast mounts are generally tilted at a lower angle than a traditional roof mount, as it tries to reduce the wind loading that could potentially move the array, since it is not bolted to the roof.
There are a lot of options for mounting the array on the ground.
1. Pole Mount
Smaller arrays can be mounted on the side of the pole, larger ones, up to 18 modules or more, depending on the panel size, can be mounted on the top of a pole. Pole mounts and some ground mounts provide an adjustable option, allowing you to optimize the angle of the panels to match the seasonal angle of the sun.
2. Ground mounts
Ground mounts give you options for very large systems, provided you have the space for them.
Carports provide shelter for your vehicle, while providing you solar power.
4. An awning mount
An awning mount on the side of your house can sometimes be an option when no horizontal location is free.
There are many options available, not just on your roof.
Trackers will automatically follow the sun throughout the day from east to west, and optionally change the tilt throughout the year as well.
1. Passive Tracker
A passive tracker generally has canisters with a gas inside, which changes weight as they heat up and cool down. This causes the array to gradually move from east to west during the day, returning to east by morning. This requires no electricity to track the sun throughout the day.
2. Active Trackers
Active trackers have an electric motor that follows the sun east to west throughout the day. It can also adjust the tilt seasonally. Active trackers are usually more expensive than passive trackers.
Depending on your location, a tracker can increase your output by as much as 30%. But they also add complications to the system, adding a mechanical component that could potentially fail. It’s often less money and less work to simply add 30% more panels to your fixed system to increase the output.
Solar Array Racking Performance
To help decide which racking is right for your solar panel kits, let’s talk about performance based on the angle of the array.
For best output, you want the sun’s rays to hit the array at a 90 degree angle. To figure out the angle you should mount your system, know that generally, for a fixed mount, which is one that doesn’t get adjusted seasonally, the best tilt is equal to your latitude.
Example, we are at 42 degrees latitude, the best angle to tilt your system is 42 degrees off horizontal. If you have a system that you want to optimize for Winter output, squeezing every bit you can out of the short day, you would tilt it an additional 15 degrees, at 57 degrees here, to keep the panels pointing at the low winter sun.
The sun is higher in the summer, if you have a seasonal cabin that is only used in the summer, you would tilt the panels 15 degrees higher than latitude, or 27 degrees.
“Sun hours” uses a compilation of historical weather data to determine the amount of solar energy available at the solar array, based on Standard Test Conditions. Although the sun is shining for 12 hours, the intensity of the sun isn’t the same for all of those hours.
For instance, the sun is half as intense at 8:00AM as it is at 11:00AM, from 8-9 would count as half as many sun hours as from 11 – 12.
Find the number of peak sun hours of your location by insolation world map.
Following chart shows the sun hours of 2 extremes here, Anchorage Alaska and Key West Florida.
For an array that is fixed, or doesn’t move, and at different angles in relation to the latitude, vs a tracker, one that automatically follows the sun throughout the day, set at different tilt angles or one that automatically changes the tilt throughout the year. It shows the sun hours per month, as well as an annual average.
This is very useful to determine the amount of electricity output you can expect for your area, depending on how you rack the array. You can decide if it is worth the extra money and effort to change the angle of the array seasonally, or if it makes more sense to just set it and forget it, and size the array based on that angle.
You can see that in Key West, setting a fixed array at latitude gives you an annual average of 5.5 Sun hours. A single axis tracker also set at latitude would increase that by almost 30% to 7 sun hours, but going up to a dual axis tracker that also changes the tilt seasonally, only adds another 0.2 sun hours on top of that, it may not be worth it to you.
Solar System Protection
Overcurrent Protection (OCP)
One of the most important components in a solar panel kits is the Over Current Protection, the Fuses and the Breakers. The key to a safely installed system is to plan for the unexpected, and have the system automatically turn itself off if something goes wrong.
A fuse or breaker is required on every segment of the system, protecting the wire between devices.
- A breaker has several advantages over a fuse; the breaker can also be used as a disconnect to turn off that segment.
- A fuse cannot be inserted or removed under load, you need a way to turn off the current before removing or installing a fuse.
A fuse is a one time use device, once it blows, you need to replace it, whereas a breaker can just be reset once the problem has been resolved.
However, fuses are usually less expensive than breakers, and generally available in higher voltage ranges, which make them common in Grid tied systems.
But remember the fuse also needs a fuse holder, which can add to the expense.
In this battery based schematic, you see the DC breakers in the combiner box where multiple strings are being wired in parallel, the breakers at the input and output of the charge controller, and at the input of the inverter. There are AC breakers at the AC input and output of the inverter, and generator, if used.
When selecting the breakers or fuses for your solar panel kits, in addition to selecting the right amps, be sure to check the maximum voltage they are rated for, and if they are for AC, DC, or both.
Most DC breakers are rated for up to 150VDC, grid tied systems that have the DC input up to 600V, or even 1000VDC, need to use fuses, or specialty high voltage breakers.
The National Electric Code requires you oversize any OCP by 25% if it will be running for more than 3 hours, which the solar system will. Also, the breakers before the charge controller need to be oversized an additional 25% for instances when the sun is shining brighter than the standard test condition, called over-irradiance.
If your string is outputting 10 amps, you would need a breaker that can handle 15.6A, probably round up to a 20A breaker.
Ground Fault Protection (GFP)
A ground fault is when there is current flowing through the grounding wire of a system, which is a bad thing. This is usually the result of the positive wire accidentally shorting with a grounded component. This is commonly caused during
installation, when pulling the wire through the conduit and accidentally scraping off the insulation, causing the positive wire to touch the grounded metal conduit.
Believe it or not, another common cause can be from squirrels chewing on the delicious insulation on the wires on the back of the panels, causing the positive wire to touch the grounded frame or racking.
The National Electric Code requires that any PV system, with 2 exceptions, is required to have a Ground fault protection device, or GFPD. The 2 exceptions are off-grid instances where chances of fire are low.
- 1st, a ground or pole mounted system that is isolated from any building, and has up to two parallel strings, for instance a stand alone water pumping system.
- 2nd, installs for “non-dwellings”, where the grounding wire is doubled in size to handle any extra current.
Most installs require GFP. The good news is that all grid-tied inverters and some MPPT charge controllers, such as Midnite’s Classic and Schneider’s XW, have GFP built in. You only need to have a separate GFP device if you are using a PWM charge controller, or an MPPT that doesn’t have it built in, like Outback’s or Blue Sky’s. Check your charge controller manual to determine if a GFP Device is needed.
Note that if you have a charge controller that has it built in, when you are using multiple charge controllers in your system, you need to disable all but one of them, only 1 GFP can be used per system. Check the manual on how to disable the GFP on your device.
The GFP works by having multiple breakers combined. One is between ground and negative, and the other is in the positive line of the circuit. If more than 0.5A is detected between negative and ground, the small breaker trips and also trips the larger breaker that is in the positive line. If have multiple devices in the system that require GFP.
For instance, if have 2 solar charge controllers that do not have integrated GFP, you would use a dual GFP that has one ground/negative connection, but multiple positive connections, one for each charge controller.
PV Breaker Boxes
1. Combiner Box
The combiner box is generally installed outside, near the solar panels. They provide a way to bring each string to its own breaker or fuse, and then combine the outputs of the strings in parallel.
You can then exit the combiner box with wire in conduit, protecting the wire as it travels back to inside the building to the grid-tied inverter or charge controller.
An additional feature is available that allows you to throw a switch at the array, turning off the DC power coming out of the panels.
Also, some have the ability to have a remote switch that is installed at the service entry point of the building, allowing firefighters to turn off the power from the array at the same location that they are turning off the grid power to the house.
States enforcing NEC 2014’s Rapid Shutdown are requiring this capability to protect firefighters.
The combiner box is also a nice place to put a lightning arrestor, as it is generally at the location in the system that would be most susceptible to lightning strikes.
2. DC Load Center
The DC Load Center is generally installed in a solar battery based system inside near the batteries, charge controller, and inverter.
There are several different models available from different manufacturers, but they all usually contain the breakers from the PV array, the GFPD if needed. The breakers between the charge controller and battery bank, and the big breaker between the inverter and the battery bank.
3. AC Load Center
The AC Load Center provides a place to put your AC breakers in a battery based system.
You can’t just use your Mains breaker box for the output of a battery based inverter, as anything in the main box will be shut off when the grid is down.
Having a separate AC breaker box allows you to isolate the AC output and power your critical AC loads from the batteries through your inverter. It also provides a location to wire in an optional generator, if it is needed to supplement your solar when there is not enough sunshine.
Bypass breakers allow you to remove the inverter from your system and power your loads from an alternate AC source, like the grid or a generator. This is useful if you need to take the solar inverter out for maintenance.
If you are doing a straight solar grid-tied system, a separate AC breaker box is not usually needed, you would just add a 2-pole AC breaker for the inverter output to your Mains breaker box.
To determine the size of that breaker, divide the wattage output of the inverter by the AC voltage, generally 240V in North America, and multiply by 1.25 to oversize by 25% as required by NEC.
For instance, a 5000W 240V inverter would need at least a 26A breaker, rounded up to 30A.
4. A Critical Loads Panel
A Critical loads panel is used in a grid-tied battery backup system.
It’s just a regular AC breaker box that is separate from the mains breaker box. When the grid is up, the inverter is connected to both the mains box and the critical loads panel, power is going to both.
But when the grid goes out, the inverter disconnects from the mains box, and only powers items wired to the critical loads panel, like your fridge and well pump, getting its power from the batteries. Items not considered critical, and therefore not connected to the critical load panel, like your hot tub, will be off until the grid comes back.
ePanel or Power Distribution Panel
An ePanel or Power Distribution Panel holds both the DC and AC breakers in one box. It makes for a clean install with all of the breakers in one place, and some of the sections may be prewired from the manufacturer, saving time during the install. It is usually one ePanel per inverter.
Inverter Power Panel
A battery based Inverter Power Panel is a prewired system complete with inverter, charge controller, and breaker boxes, with all of the required breakers installed. They make installing the system a snap, just hang it on a wall and connect it to the solar input, battery bank, and AC input and output.
Hopefully this helped clear up some of the different over current protection requirements and enclosures.
Above is my knowledge of Solar Panel Kits, hopefully it’s fine with you.