With increasing industrialization of Australia and the world at large, utility electricity has become expensive. Factories, schools, medical facilities, construction work and other sectors all need a share of this electricity. This has forced people to look for cheaper yet reliable source of power. Solar system is your solution to huge electricity bills.

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You will need to buy solar panels and inverter to access solar energy. Solar system emits Direct current which is not compatible with today’s devices and appliances. Therefore, you need an inverter to convert Direct current to Alternating current. Most of electrical appliances and devices like fridges, heaters, lighting and Television require Alternating current.

There are factors to consider before you buy your solar system. Look at the size of your house, its location and number of people in your house. The bigger the number of people, the more electricity you’ll need. Then, consider your budget. Some solar and inverter brands are more costly than others. Come with me as we delve deeper on how to calculate the solar panel battery and inverter for your home.

Inverter Size

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To determine what inverter to use, you have to first ascertain the peak load of your home. This means the maximum amount of electricity you use at any given time. You’ll get maximum wattage of your house by adding up the wattage of devices and electrical appliances. Right from fridges, Television and Lighting to clocks and computers. Anything in your house that uses electricity should be included. The total sum should guide you on the inverter that you need.

Remember some appliances at start-up use more than their rated power. It will be covered by the inverter’s surge rating. Let’s look at an example below.

Example:  Assuming you have a one roomed apartment with three 60 watt bulbs and a 400 watt computer. Your inverter size will be 60x3+400=580 watts.

Daily Energy Consumption

Next thing, you’ll need to calculate your daily energy consumption. Get a single appliance’s wattage and multiply it by its run-time. This will give you the daily wattage-hour for that device. Do the same for all the appliances to get the total watt-hour value for your house. The total value you get will have efficiency loses and hence is low. Multiply it by 1.5 to get a rough estimate.

Example:  Light bulbs light for 4 hours daily. The desktop computer works 3 hours daily. 180x4+400x3=1,920watt-hours.  1920x1.5=2880 watt-hours.

Days of autonomy

This is the number of days’ worth of energy that you need to store in the battery. Usually it ranges between two to five days. But for some countries, it can even go to seven days and more.

Battery Bank

To calculate the battery bank capacity, you’ll get the watt-hour and multiply it with the days of autonomy. The answer you get represents 50% discharge depth on your batteries. Therefore, you need to multiply it by 2. Then change Kwh into amp hours (AH). You convert it by dividing the result by battery voltage.

Example: You want the battery to last 1 day without recharging and your daily consumption is 2.88kwh. 2.88x1x2=5.76kwh. This value is the capacity required from batteries. To convert it into AH, you’ll need to divide by your system voltage.  For commercial applications, in Australia, these systems are 12, 24 or 48V. Let’s consider 48V. 5760/48=120AH.

*To get the number of batteries to use, get the above value and divide it by your battery’s rating.

If you need your battery to last for 5 days,

2.88x5x2=28.8kwh. To convert it into AH considering 48V, 28800/48=600AH. To get the number of batteries you’ll need, divide 600AH by the battery’s rating.

Do the same for a battery life of 6, 7 and more days without charging it.

Calculating Inverter Sizes

String/ Central Inverter

From the inverter size calculation above, you’ll need a string inverter of size similar to your solar panel rating. For example, if you are mounting an 8 kilowatt (kW) solar array, you’ll need a string inverter of 8000w. You’ll have to subtract or add a small percentage to cater for any errors.  However, with string inverter, in case a solar panel is shaded or faulty, the amount of electricity produced will reduce.

Remember that a string/ central inverter produces electricity from an array of solar panels arranged to form a ‘string’. It will give you an amount of power equivalent to its least productive panel. Don’t hold your installer by the neck in case the electricity you get at any given time is less than you expect. Also, find out if your string inverter is battery-ready. Most of them are not.

Micro/hybrid Inverter

This is an inverter that manages power both from the battery bank and the solar panels. It is battery compatible. They are economic power solutions because they first use solar energy, if it gets finished, or is not enough, it gets more from the grid. In cases when solar power surpasses demand, the excess is used to charge batteries.

From the inverter calculation above, you need to know your daily energy use. Then, consider autonomy days and know the lowest temperature which your battery bank will experience. Usually the battery has some ratings. For example, additional further load expansion (Af), battery operating temperature, battery efficiency, inverter efficiency (le), required battery backup etc.

To calculate the size of hybrid inverter, Total electricity load+ (1+Af)/le VA. You’ll get these readings from the battery and inverter. Remember the inverter is to convert DC electricity produced by your solar system. It must have the capacity to convert the DC produced by the array. Therefore, the size of inverter you choose must be similar to the size of your solar system.

Can Solar Work Without an Inverter?

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To answer this question, you have to know why you are installing a solar system. Is it for home consumption or luxury like camping? There are some incidences where you’ll need low DC electricity to power some appliances. For instance, in the world of campers, they use low-powered freezers, fridges and lighting. These will use DC electricity and hence don’t need an inverter.  Usually they are directly powered by a 12V and 24V battery. Others use specific solar panels to power their boats or use in pocket calculators.

However, if you are setting up solar energy to use in your home, you’ll need an inverter. Most of our home appliances and electrical devices need AC energy to work. For example Lighting, television, fridges, freezers and microwave, among others use AC electricity. Therefore, you’ll need an inverter to convert DC to AC electricity ready for home consumption.

Why do You Need an Inverter?

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An inverter’s main purpose is to change Direct current into Alternating current. However, with increased technology, inverters are being used for other purposes. There are two types of inverters; power inverter and static inverter. Power inverter may be a combination of mechanical effects like rotary apparatus or entirely electronic. This will use electricity to convert DC to Ac electricity. On the other hand, a static inverter, just like its name is static. It doesn’t use any moving parts during the conversion process.

Inverters can also be used in different industrial equipment. They include pumps, fans, printing presses, conveyor belts, construction machinery and food processing equipment. It offers variable control of the motor speed hence increasing production. This is sometimes called general purpose inverter. Isn’t faster production what most factories and industries want?

The modern inverter is more diverse in shape and design. It has extra features like Ethernet and USB interfaces. This is to make it as use-friendly and versatile as possible. The added features enable you to use a remote control. You don’t have to keep moving from whatever you are doing or in the comfort of your chair. Just make use of the remote control to turn it on/off.

An inverter is the ‘brain’ of your solar system. It is responsible for the safety and quality of electricity produced by your solar panels. Also, it optimizes electricity generation under different conditions hence maximizing total energy generated. They use a feature called MMPT (maximum power point tracking). This feature enables the inverter to look and draw from solar panels maximum power possible.

Some inverters have two MMPTs. If your inverter has twin MMPT’s, output can be separated into two. This type of inverter can draw from string of panels that are facing in different directions. It can also draw from panels on different pitches, different panel types and those with different output capacity. An inverter with twin MMPTs is versatile and hence can work in different conditions of flat and not flat roofs, North or south facing roofs etc.

Do Inverters Store Power?

No. An inverter doesn’t store power. Rather it converts the electricity received from a battery or solar panel into the consumable type compatible with your appliances and lighting. It works more or less like your phone charger that transfers power from the socket I to your phone. It translates the voltage and frequency of the incoming power so it is safe for your electrical devices and you.

What Size Battery do I need for a 3kwh System?

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The size of your battery depends on its operating hours. If you want your battery to run for 4 hours, then, get the system size multiply by the operating hours.

For example: 3000x4=12000wh.

To determine battery bank size, let’s first consider this range below in its descending order;

Above 10kw: 96v

2-10kw: 48v

0.5-2kw:24v

Up to 0.5kw:12v

The commonly used battery in Australia has 12V, 100/120Ah and maximum Depth of Discharge 70%.

Battery bank charge capacity=Energy required/system voltage

12000/48=250Ah

Therefore, we need to calculate the number of battery to generate 250Ah.

Number of parallel batteries=250/ (120x0.7) =2.976. We will take approximately 3.

Number of batteries in series= voltage of system considered/ battery voltage

=48/12=4

Therefore, this battery bank will have 4 parallel batteries and 3 batteries in series to withstand the given load.

Source: Go Solar Quotes

Are some inverters More Efficient than Others?

Yes, some inverters are more efficient than others. For instance micro inverters are more effective compared to string inverters. String inverters will produce less electricity when one of the solar panel is shaded or facing the wrong direction. This is not the case with micro inverters. They produce the same amount of electricity throughout. So if you buy a string inverter, there are times you won’t have enough electricity when a panel is shaded or facing south.

There are some brands that are more efficient than others. Since I won’t mention names here, I’ll leave you to do your due diligence on brands. This should explain to you why some manufacturers will give you longer inverter warranties than others. They trust their brands.

Also, some inverters have twin MPPT’s (Maximum Power Point Tracker). This feature allows the inverter to face and draw maximum electricity from module arrays. If your inverter has twin MPPTs, its output is independent. Meaning it can draw from panels with different output and those on different pitches. It can also draw from different panels altogether. So at any given one time, you’ll receive electricity.

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Also, inverters with a higher capacity will be more efficient than those with a low one. That means they have a capacity to work with higher solar systems hence are more effective. There are those rated at 90-95% efficiency like the high quality sine wave inverters. Their low quality sine wave counterparts are less efficient with a rate of 75-85% efficiency. Remember inverter effectiveness depends on inverter load.

Conclusion

Before you buy an inverter and solar system, you have to first consider your home. Look at its geography, number of people, size and electrical appliances that you have. This will give you an estimate of your daily power consumption. Then remember, your inverter load must be similar to your solar system. Also, don’t forget that some inverters are more effective than others. The higher the inverter load, the more effective it will be. Also, acquire a battery since inverters don’t store power.