Off-Grid Solar Energy Systems

Off-grid solar energy systems (also known as independent solar power or stand-alone solar power) are completely independent of the power grid.

This means unlike grid-tied solar energy, off-grid solar systems do not use a utility company power as a backup. You use only what your solar energy system produces and what you have stored in your battery bank.

For this reason, off-grid solar energy systems typically have much bigger battery banks than grid-tied solar systems with a battery backup.

Off-grid solar systems, (typically used to power cabins or remote locations) are often used in conjunction with other renewable and non-renewable energy sources such as windmills, hydroelectric turbines, and AC generators. When two or more sources charge the battery bank, it's known as a hybrid power system.

The Off-Grid Solar Power System Set-Up

Typical stand-alone solar power systems consist of the following:

• Solar panels (to collect the power)
• Array DC disconnect (to be able to cut the power from the PV panels)
• Charge controller (to regulate the charge to the battery)
• Battery bank (to store power)
• System meter (to monitor power usage and status)
• Main DC disconnect (to cut power to battery bank/inverter)
• Inverter (to convert from DC to AC)
• AC breaker panel (to accept and distribute power to your household loads)

A generator can also be connected to the inverter as backup power. Off-grid solar systems are usually set up to handle a good couple of days of cloudy weather and can always rely on the generator in case of emergency.

If it's sunny, these stand-alone solar power systems draw power from the solar panels, but if it's cloudy or dark, they will draw it from the battery bank. If the battery bank goes empty, the generator can be used for independent power.

Photovoltaic Components

Besides solar panels and batteries, there are some other photovoltaic components (solar power equipment) necessary for your solar system to function properly and we'll explain a little more about each one below.

All of these solar power components are available in local home improvement and solar stores (as well as online), however, not every unit listed below may be necessary for your solar system.

Solar Panels

Solar panels (also known as PV panels) are the most vital of all the solar power components. They are used to collect photovoltaic light energy from the sun, which they then turn into what's called “Direct current” (DC) electricity.

There are 3 main types of solar panels and all are made up of a collection of solar cells wired together to make a complete solar panel. A group of solar panels is called an “array”.

PV panels are rated based on the amount of watts they produce in optimal sunlight conditions and thus solar panel cost varies. Therefore, the more power you want to create, the bigger sized solar panel you'll need, or the more panels you'll need to connect together.

Batteries

Batteries are an essential component of your off-grid solar energy system. Batteries are used to store the electricity created by your solar panels for later use. The type of batteries used in photovoltaic systems are deep cycle batteries and although very useful, batteries are not 100% necessary in photovoltaic systems.

You can power your home directly from your solar panels, along with the other solar power components, but the only problem is that when the sun goes down (or if it doesn't come out at all), you won't have any solar power. By using batteries, you can store and use solar energy during the day and access it at night.

Like other solar power equipment such as PV panels, photovoltaic system batteries are rated in volts (push) and amp hours (storage capacity). By connecting batteries together in different wiring combinations you can power bigger appliances and store more power.

Although deep cycle batteries come in various power ratings, the ones we'll be using in our examples on this website are standard 12-volt deep cycle batteries with 105 Ah (amp hours). If you choose solar batteries with different power ratings, you'll have to make the necessary adjustments to the numbers in each example.

Array DC Disconnect

The DC disconnect is a photovoltaic component you add to your solar system in order to be able to disconnect the power easily. This necessary piece of solar power equipment safely interrupts the flow of electricity from the PV array.

It is typically used when performing maintenance on your system and effectively stops DC power (coming from your solar panels) from reaching the other solar power equipment in your solar system.

Charge Controller

One of the most important solar power components (if you're using batteries) is a charge controller. This piece of solar power equipment is used to control the amount of current going into your battery and thus prevent it from overcharging. Once your battery bank is full, the charge controller will stop loading it with more current and as a result, this helps to extend the overall life of your batteries.

Other useful features of charge controllers include preventing your batteries from discharging past a certain point (thus extending their life span) and blocking reverse current / discharging at night (less wasted energy).

System Meter

Of all the photovoltaic components, the system meter is probably the most telling. This is because the system meter is used to monitor your solar system's power usage and status. More specifically, it lets you know how much power you have left in your battery bank and how much power your system is currently using. This is very useful information that will help you plan and monitor your energy usage better.

Main DC Disconnect

Another one of the most necessary solar power components (if you're using batteries) is the main dc disconnect. This piece of solar power equipment is used to cut the power from the battery bank to the inverter. This allows you to safely disconnect your inverter for repair, troubleshooting, or maintenance.

Inverter

The solar inverter is one of the most important photovoltaic components in a PV system. Without it, you couldn't power any of your household appliances, only DC appliances commonly used in RVs. The most expensive and best quality inverters output voltage in sine wave.

A solar inverter's function is to take the DC (direct current) electricity coming from the solar panels and turn it into AC (alternating current) which is the type of electricity needed and used by your household appliances and electronics.

Generator

A generator is not typically considered a photovoltaic component and is not one of the most necessary solar power components. However, it is needed and useful as a backup source of power, and usually only if you are going to be using an off-grid solar system.

Although not 100% necessary, it can provide emergency power in times of no sunlight or during maintenance of the solar system. Generators used in solar power systems are usually gas or diesel-powered.

AC Breaker Panel

The AC breaker panel is one of the photovoltaic components already found in your home. It is where all of your home's electrical wires end up. From here they neatly and safely connect to the power source, like the utility grid or a solar power system, for example.

The AC breaker panel can be found in your home's basement, utility room, or some kind of other designated electrical room in your house. Each municipality has its own standards, rules, and regulations regarding hooking your solar energy system up to the AC breaker. This is why we recommend consulting the appropriate local authorities such as your power company and having a professional qualified electrician do the final connection for you.

If you don't want to go through your AC breaker panel, you can power your appliances by plugging them directly into one of your solar power inverters.

Kilowatt per hour meter

The kilowatt per hour meter is another one of the photovoltaic system components already found in your home. A kilowatt per hour meter is used in any grid-tied house that gets its electricity from the city. The meter is usually found either right outside your house or somewhere inside your home – usually in the basement or utility room.

Its main functions are to measure and monitor how much power your home uses from the power company's supply or in cases where your solar system feeds power back into the meter – how much power your home adds to the supply.

If you build a big enough solar system (that produces more energy than your home uses), your meter will actually begin to spin in reverse.

Utility Grid

The utility grid is the biggest of the photovoltaic components as it is where the power supplied to your home from the city comes from. Unless you are living off-grid, you are getting your energy from the utility grid.

Household Power Loads

And finally the last of the photovoltaic system components is your household power loads. Household power loads refer to all the appliances, electronics, or any equipment that uses or requires electricity. This could be anything from your fridge to your water heater, to a lamp you plug into your wall's power outlet.

Now that you know what each of the photovoltaic components in a solar system does, it's time to show you how these solar power components are arranged together in the various solar system types.

Charge Controller Sizing

How to choose the right size charge controller for your solar energy system.

Charge controller sizing is best understood when you grasp what a charge controller does.

Solar Charge Controller Functions

The function of a charge controller is to regulate the charge going into your battery bank from your solar panel array and prevent overcharging and reverse current flow at night.

It does this by using a transistor to shunt the PV charging circuit. This means, that if your battery is full, it stops the charging and if your battery is reaching an unhealthy discharge point, it stops the discharging.

By using a PV charge controller you minimize the use of utility power and maximize the chances of your batteries and other photovoltaic components lasting longer, thus increasing the life expectancy and efficiency of your entire solar system.

More sophisticated solar charge controllers make sure the battery is charged by utilizing pulse width modulation (PWM) or maximum power point tracking (MPPT).

Charge Controller Sizing

Sizing charge controllers is a fairly simple process. PV charge controllers are rated and sized depending on your solar array's current (amps) and the solar system's voltage (push).

Therefore, solar charge controller sizing involves “getting a charge controller big enough to handle the amount of power and current produced by your solar energy system.”

The most common PV charge controllers come in 12, 24, and 48 volts. Amperage ratings can be between 1-60 amps and voltage ratings from 6-60 volts.

So if your solar system's volts were 12 and your amps were 14, you would need a solar charge controller that had at least 14 amps.

However, due to factors such as light reflection, sporadic increased current levels can occur, so you need to factor in an additional 25% bringing the minimum amps that our PV charger controller must have to 17.5 amps.

So we'll need a 12 volt, 20 amp charge controller (rounded up).

It won't hurt anything if your charge controller's amps are higher, in fact, it's a good idea just in case you increase the size of your solar energy system in the future.

MPPT Charge Controllers

MPPT stands for Maximum Power Point Tracking. An MPPT charge controller is used in the very common case where your solar array's voltage is higher than your battery bank's voltage.

This is the case with the example solar arrangement diagrams we use in our Solar Panel Wiring Diagrams section, so pay attention to this if you choose to copy any of those arrangements. MPPT charge controllers also work great with systems that have panels with odd voltage ratings, for instance: 56V.

When an MPPT solar charge controller notices a difference in voltage, it will automatically and efficiently convert the higher voltage to the lower voltage so your panels, battery bank, and PV charge controller can all be equal in voltage.

If you had a 900-watt solar array with 48 volts, and your battery bank's voltage was 24 volts, you can determine the amps your PV charge controller needs to have by dividing the watts by the lower of the two volts.

Watts / Volts = Amps

900W / 24V = 37.5 Amps

Plus, you still have to add an extra 25% for unexpected current increases due to factors such as light reflection… and you get 46.87 amps.

So, you'll need a 24 volt, 50 Amp MPPT charge controller (rounded up).

PV Charge Controller – Upper Voltage Limit

All charge controllers have an upper voltage limit. This refers to the maximum amount of voltage they can handle from the solar array. Make sure you know what the upper voltage limit is and that you don't exceed it or you may end up burning out your solar charge controller.

Wire For Solar Panels

Solar wire (also known as solar panel wire and PV wire) refers to the type of wires used to connect your solar panels with the rest of your photovoltaic system.

Choosing the right wire for your solar energy system is critical to its functioning properly and remaining undamaged. If you get this wrong and choose a PV wire too small for your PV system, your battery bank may not charge fully and as a result, your appliances might not work as well or at full power.

Solar Wire Types

Electrical wire (which is the same thing as solar panel wire) is categorized mainly based on its conductor type. If it has a single metal wire core, it's a single-stranded conductor and if it has a multiple wire core, it's a multi-stranded conductor. These are the two basic wire types.

The difference between a single-stranded conductor and a multi-stranded conductor is that the multi-stranded performs better in continuous vibration environments such as mobile applications in cars, boats, planes, and trains.

The single-stranded conductor type wire is most commonly used in domestic wiring and should be okay for your solar system. However, if your area is prone to consistent and extremely high winds, you may want to consider wire types with a multi-stranded conductor as it is more flexible and durable.

PV Wire Ratings

The wires used in solar systems are rated by their Amps. This is the maximum amount of amps that can travel through that wire and this rating must not be exceeded.

The higher the current (amps) your solar system is rated at, the thicker the PV wire has to be. If your system produces 7 amps, you will need 7 amp wire (actually it's better to go a little higher like 9 or 10 amp wire, just to make sure you can handle the current).

If you mess up and use wire rated at fewer amps than your solar system produces, the voltage will drop, your solar panel wire will most likely heat up, and eventually may even catch fire causing damage to your solar energy system and your home.

Think of your electrical wire as a plumbing pipe. If there is too much water pressure (amps) flowing through it, it will burst. Therefore you would need to get a bigger pipe (wire) that can handle the pressure (amps) produced by your system.

Solar Wire Thickness

Thicker PV wire costs more than thinner PV wire because it can handle more amps. When choosing the thickness of your wire, you can go one of two ways. A little thicker for safety or just thick enough but vulnerable to a sudden power surge.

A great way to go about choosing the wire thickness for your solar system is to buy solar panel wire big enough to cope with the biggest current (amp) drawing appliance you have and use that wire for all the other runs to the AC breaker panel. Use a wire sizing calculator for solar arrays that will figure out the size of wire you need.

PV Wire Length

Along with having to use PV wire rated at the right amps, you must also take into account the length of your solar wire. If your PV wire is longer than average and connected to a high current appliance, you will need wire with more (higher) amps. Otherwise, there may be a voltage drop and a fire.

For example: If you had a 20 amp appliance and you used a 20 amp wire of considerable length, you would be at risk of a voltage drop. To prevent this from happening increase the size of the PV wire to at least a 35% margin, so for the above example, use 27-30 amp wire to be safe.

The longer your wire is, the higher the amp rating on your wire needs to be, so don't be shy to go a little thicker in the name of safety.

Also, using thicker wire can insure that potentially high current (amp) appliances bought in the future will be more likely to handle the current. There is no harm in preparing for the future now, especially if it's going to save you from having to upgrade to thicker wires later.

Here's an example to illustrate how length affects amp rating.

Let's say your solar panels/battery bank produced 7 amps and you were using a wire length of 4.6m. This is starting to get lengthy, so add a 35% safety margin which is:

7 + (35% of 7) = 9.45 amps

Therefore, you would need 10 amp wire.

If you run PV wire that's even longer, you can use the chart below to determine the necessary wire thickness based on amp rating and wire length.

PV Wire Gauge Guide

Here is a guide to choosing the right wire gauge (thickness) for your amp rating plus your wire length.

To determine the size of solar wire needed, just look at the AMPS in the left column and select the amp rating of your solar system. Next, follow the same row over to the approximate length of PV wire you will be using. Then, follow the column up to the yellow box at the top which will be the AWG number wire you'll need. AWG is a system of labeling wires that has been used for many years in the USA. AWG numbers get smaller, as the wire length increases.

One important thing to note is that all wire used for individual runs from the breaker panel to the appliances must be able to handle the amps of that appliance. The wire from the battery to the rest of your photovoltaic components must be able to handle the total amps of all the individual runs, plus at least 35% more.

Also, keep in mind that it's better and much more affordable to try and use solar wires that are shorter in length rather than to have to buy very thick (and expensive) wire to compensate for unnecessary length.

If you stick to these rules and basic safety precautions to choosing the right solar wire type and thickness, you will improve your effectiveness and efficiency as well as reduce your chances of causing damage to your solar energy system.

Solar Cell Tabbing

How to attach tabs or tab wire to untabbed solar cells.

Safety First

Always take all necessary precautions when connecting solar cells together.

Always wear a respirator mask and safety glasses during soldering to protect from the inhalation of fumes and flicking solder.

During solar cell tabbing, always make sure to wear gloves when handling solar cells so you don't get oil on the cells and reduce their effectiveness. Solar cells are very fragile and can break if handled roughly during solar cell tabbing.

Instructions For Tabbing Solar Cells

Solar cell tabbing involves soldering tab wire to the contact points of the untabbed solar cells.

How To Connect Solar Cells (Un-tabbed)

Step 1

Place your solar cell down on a clean work surface with the negative side (front) facing up.

Step 2

Grab your flux pen and rub it along the entire surface of both contact strips. (These are the two vertical lines you see running up and down the solar cell).

Step 3

Next, you need to cut out 36 x 2 = 72 pieces of tabbing wire (the thinner of the 2 wires in our materials list). The length of the wire pieces should be two times the height of the solar cell. So if your solar cell is 3.25 inches high, cut your pieces of tab wire 3.25 x 2 = 6.5 inches in length.

Step 4

Take one of the pieces of tab wire you just cut out and place it on one of the contact strips as shown in the diagram below.

Step 5

Heat your solder iron and apply some very light pressure with it along the surface of the tabbing wire (which is sitting on the solar cell's contact strip.) This should bond the tabbing wire to the solar cell. If not, add some solder directly to the tab wire and heat to secure the tab. Since tabbing wire comes pre-coated with solder, you shouldn't normally have to use any extra solder.

Step 6

Now take another piece of your pre-cut tabbing wire and do the exact same thing to attach it to the solar cell's other vertical contact strip.

That's it! You have now tabbed your first solar cell. I hope you had fun tabbing solar cells because you will have to tab all 36 of your solar cells this way before you can add them to your solar panel.

Testing Solar Stringers

How to test your solar stringers to make sure they're working properly.

Procedure For Testing PV Solar Stringers

Testing PV solar stringers is easy. You can test your solar stringers one at a time by placing them in direct sunlight and using your multimeter. Test the whole 9 cell stringer by setting your multimeter to “volts” and following the instructions below.

Testing Stringers For Volts

1. Touching the multimeter's (red) positive lead to the tab wire coming from the positive side of the first cell in your stringer.
2. Then touch the multimeter's (black) negative lead to the tab wire coming from the negative side of the last cell in your stringer.

The volt reading on your multimeter should be close to (or just under) 4.5 volts. If it's not, there is a problem. Go back and check all the connections of your solar cells or check for cracks in the cells themselves.

Testing Stringers For Amps

Next, test your 9 cell solar stringers' amp output by setting your multimeter to “amps.”

1. Touch the multimeter's (red) positive lead to the tab wire coming from the positive side of the first cell in your stringer.
2. Then touch the multimeter's (black) negative lead to the tab wire coming from the negative side of the last cell in your stringer.

The amp reading on your multimeter should be close to (or just under) 3.5 amps.

When Is a Stand-Alone Solar Power System a Good Idea?

Although the initial cost of an off-grid solar system is higher than a grid-tied solar system, off-grid solar systems can be a more economical choice in the long term, especially in remote places where you would have to have utility poles erected and bring power lines in for a grid-tied setup.

Without the grid, you will never get a utility bill again and this makes a big difference in your energy savings over time. The largest benefit of off-grid solar is that once it's installed, electricity will be free for the next 40 years or so. Though it costs more to set up a stand-alone solar power system, the money you save in the long run is definitely worth it.

If you do the math, it becomes clear that off-grid solar power makes a lot of sense if you have the initial bucks, want to be completely independent of the grid, and especially for remote location applications.