12 solar panel

12 solar panel

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How to Design Your Own Solar Panel Electrical System

I know, because that is the first thing that comes to my mind when I think of going green.

I put some effort into researching various alternative green energy sources and have come to the conclusion it might not be as expensive as we first think.

From the various options, solar panels seemed to be our best option. It might not be for you though.

Reasons I prefer a solar panel system:

 

• Not as noisy as wind turbines
• Easily expendable
• Easily movable which is a bonus if you're on a farm
• Our climate is perfect for it

 

A few downsides:

 

• The initial outlay of costs
• The space it will occupy (mainly the batteries)

 

First of all, let's look what a solar panel system consists off.

It can basically be split into 4 parts, namely:

1) the solar panels 
2) solar regulators 
3) batteries - storage 
4) inverter - DC to AC

Solar Panels

Simply put, these are the panels that will take the sunlight and convert it into power. They are rated in output in Watts, which means the amount of power the solar panel is expected to produce at a sunlight intensity of 1000w/meter at 25 degrees centigrade. You might be asking, "What?!" at this stage.

Throughout the different areas of South Africa, the average amount of sun per day varies. The average in South Africa is 8.5 hours per day. (Interesting side fact, in London it's 3.8, Rome it's 6.4 and New York it's 6.9). South Africa has the of the highest average amount of sunshine per day in the world. This makes it perfect for solar panel usage.

If you take a 80 Watt panel, it means it will generate an average 680 Watt Hours (Wh) per day throughout the year.

Solar panels can be wired to increase voltage or current. A normal panel's terminal voltage is rated between 17 and 22 Volts, but making use of a regulator regulates it to 13 Volts. The reason for this is that the safe voltage for charging a battery is between 13 and 14 Volts.

Solar Regulators

As mentioned, the solar panels can produce between 17 and 22 Volts. This is however a lot more than the safe range of between 13 and 14 Volts that you can charge a battery. To regulate this we make use of a solar regulators which drops the current causing a stable voltage.

The batteries you'll be using are sensitive to over charging and dropping below a certain voltage. The regulators helps to not over charge the battery or have the batter run too flat.

Solar regulators are rated by the amount of current they can receive from the solar panels.

The regulator must be able to handle the maximum current that a solar panel may produce. This can be as much as 25% more than the rated output current of the panel. So if you have a 100W solar panel with 5.8 A current rating you'd want to use a 7.54 A regulator. I'm using 30% to be on the safe side.

Batteries

Once the sun light has been converted to electrical power, we need to store it somehow. For this purpose we'll be using deep cycle batteries. These are the same as normal car batteries, but with a few differences. They are designed to be discharged over a long period of time and can be recharged over and over and over and over. Car batteries are designed to provide a large amount of current in a short amount of time.

In order to get the most out of your deep cycle battery, you must not let it discharge to below 50% of it's capacity. By letting it go below 50% it reduces the life span of the battery.

These batteries are rated in Ampere Hours (Ah) and it includes a discharge rate in Hours. This is the amount of current that it can provide over a certain number of hours.

A 100 Ah batter with a 100 hour rate will supply 100 Ah over 100 hours. This is 1A per hour for 100 hours. This can also equate to 5A per hour for 20 hours.

Power Inverters

Now that we've got the power stored in the batteries, we need a way to use it in our every day lives. Batteries can provide stored electricity as Direct Current (DC). Our every day appliances in the house make use of Alternating Current (AC). Thus we need a way to convert it from DC to AC so that we can use it.

That is where Inverters come into play. The one that is recommended is the True Sine Wave Inverter, which provides AC power that is basically identical to the power we receive from Eskom.

Inverters are rated by the amount of AC power they can supply continuously.

Now that I've explained all the above, you might have a better understanding of what a solar power system is. Let's have a look at how you would go about sizing your installation requirements.

Appliances and Power Usage

The first thing you need to do, is also is most cumbersome. You need to determine how much electricity you will be using and for how long. This is easy, you write down how much Watts (W) an appliance uses, and how many hours per day on average you run it. That will give you a certain amount of W per day.

Let's look at an example:

5x 60W globes = 300W working 8 hours a day every day = 2400 Wh

1x 300W TV = 300W working 2 hours a day every day = 600 Wh

1x 250W Fridge = 250W working 24 hours a day every day = 6000 Wh

1x 800W Washing Machine = 800W working once a week for 2 hours = 228 Wh

That means we use a total of 9228 Wh a day

Power Inverter Size

To determine the size of the inverter you are going to require you'll need to determine the total Wattage (W) of the appliances.

From the above example it will just be:

Light Globes - 5x 60W = 300W

TV = 300W

Fridge = 250W

Washing Machine = 800W

Total power draw require = 1650W. This means that when all those appliances are on at the same time, it will draw 1650W. You will also add in about a 50% buffer. That way if you ever run your hair dryer at the same time the system will have power in reserve to run it. So a 2500W inverter will be perfect for this and will leave you with ample buffer. Remember this calculation is about appliances that will run at the same time. By planning right (i.e. use either the kettle, hair dryer or iron at a time, but not all at once) you can bring down the amount of power you require, thus bringing down the cost of this solar panel system.

The number of Solar Panels and their ratings

The total power usage daily is 9228 Wh. Now you will need to know on average how many sunlight hours your region has. I've found many websites that detail this, so that shouldn't be a problem. Let's work on about 7 hours. That means 9228Wh / 7h = 1318.30W. Add about 20% for a buffer and for any inefficiencies with the panels, and you'll end up with a requirement to generate 1576W of power per day.

You'll need to get enough panels to have all their outing ratings add to 1576W. So if you wanted to get 140W panels, you'll get 12 of them, because 12 x 140W = 1680W or 24 x 70W = 1680W.

How many Batteries?

This depends on the panels that you use. The 140W panels produce a current of 7.7A. So if you have 12 of them, the total current would be 92.4 A. The current also also be there for about 7 hours a day (the amount of sunlight per day). That means there will be 646.8 Ah per day that needs to be stored.

If we look at the 102Ah batteries, they shouldn't be allowed to discharge more than 50%. That leaves us with about 50Ah. Therefore, to make up 646.8 Ah per day we'll need at least 13 batteries.

What size regulator?

The last thing to consider is the solar regulator. A 140W panel produces 7.7A of current. There will be a total of 92.4 A of current. That means at least 4x 30A regulators.

Now the complete system:

12x 140W Solar Panels 
4x 30A Solar Regulators 
13x 102Ah Batteries 
1x 1500W Invertor

Chris Meistre
Solar Panel System

 

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How To Build A Solar Panel - Part 12