SOLAR - Installation - Technical

The first step is to determine how much electricity you use in a month / day. (For the next examples, let’s assume that you use 600 units a month.)

Also convert this to daily usage: 600 ÷ 30 = 20 units a day

Implement various power saving tips (solar geyser / heat pump, gas stove, LED lights etc) to reduce your electricity consumption. The re-assess your electricity usage.

Next step is to determine what your goals with your system are. Let’s assume your goal is to aim for 90% independence from Eskom (you don’t have to start there, you can build up to that goal over time)

Next, pick your inverter, then the solar panels and lastly the batteries. See the following questions for more detail.

Electricity consumption is measured in kilowatt hours (kWh), or commonly referred to as a “unit”.

If you are on a post-paid account, the invoice from your municipality / Eskom will show how much units you have used in the past month.

Alternatively, if you use pre-paid electricity, check the slip next time that you buy electricity. Pre-paid electricity currently cost around R 3.25 per unit, so for every R 100 you should receive around 31 units. You can thus calculate how much units you use in a month based on the amount that you spend on electricity every month.

Yes, we can. For the most accurate data, we can install an energy meter in your Distribution Board and measure your consumption over a week or two. This power meter can measure overall consumption but also different circuits in your house to see how much electricity the geyser or stove use. We can also install separate plugs to calculate how much electricity individual appliances consume (tumble dryer, kettle, microwave etc).

Such an energy audit will cost between R 1 500 and R 4 000 depending on your needs, however, the data obtained through such an audit can be invaluable. Please contact us should you require an energy audit.

• The geyser consumes 40% to 60% of your total electricity consumption:
  
  • Install a Solar Geyser, Heat Pump or Gas Geyser.
• Install energy efficient LED lights
• Install a gas stove
• Replace old, inefficient appliances with modern, efficient ones.

We generally do not recommend trying to go fully off-grid. To ensure that you have enough storage capacity for cloudy / rainy days means that you will need unnecessarily large batteries and too many panels. These extra items will cost a LOT more and will only be needed c 10% of the time and is thus not a good investment.

However, if you live on a small holding with direct Eskom Feed, a large part of your bill is for fixed line fees etc. In such a case it could be beneficial to go fully off-grid, but then one can rather add a generator for cloudy or rainy days.

Off-Grid Inverter

• If you stay in a town and only need a back-up solution and will NEVER add solar panels, an Off-Grid Inverter will be fine.
• If you plan to go fully Off-Grid, an Off-Grid Inverter will be fine.
• However, an Off-Grid inverter is NOT approved to be used with solar panels when you are connected to a municipal / Eskom grid.

Hybrid Inverter

• If you are connected to a municipal / Eskom grid and you want to add solar panels to your system, you will need a Hybrid Inverter.
• We only use Inverters that ARE approved for connection to a municipal / Eskom grid.

• 5 kW – If you use less than 900 – 1 000 units a month
• 8 kW – If you use less than 1 400 – 1 500 units a month
• 12 kW 3 Phase – If your house uses 3 phase power and if you use less than 2 100 – 2 300 units a month
• 16 kW – If you use less than 2 800 – 3 000 units a month
• If you are close to the upper end of the guidance as above, rather take the next size inverter to allow you to expand in future.
• PS: You can also install more than one inverter in parallel if you need a bigger system. I.e. 2 x 5 kW inverters can give you up to 2 000 units a month. You can also start with 1 inverter and add the second one at a later stage if you want to.

In our Kit Builder above you can simply select a solar panel and play around with the amount of panels until the calculator shows the desired units of production in a month.

However, you can also roughly calculate the amount of panels you need with the steps below. Let’s say you use 600 units a month:

• Convert your monthly electricity units to daily units (Example 600 ÷ 30 = 20 kWh per day)
• Divide Daily units by 5 hours* and convert to Watts (Example 20 ÷ 5 = 4 kW per hour or 4 000 W)
• Divide the Watts by the panel size (Example 4 000 ÷ 550 = 7.3 (select 8 panels))

* 5 hours of effective sunshine is a good estimate for Gauteng. 1 kW = 1 000 Watt

PS: The calculator uses the same formula to calculate how much electricity will be generated in a month. Using the above example: 8 panels x 550 W x 5 hours x 30 days = 660 kWh.

The above calculation assume that your roof is sloped around 26 to 29 degrees and is facing close to North. Also, it assumes there is nothing that will cast shadows onto the panels.

If your roof / installation deviates from these guidelines, your production will probably be lower.

For a more accurate estimate, contact us and we will use your exact location and roof orientation to give a much better estimate.

Step 1: Determine what % of your electricity is used when the sun is NOT shining.

• If, like most South Africans, you are at the office during the day and only home in the evenings and early mornings, you probably use c 60% to 70% of the electricity during the evenings until early morning. (We will use this as our example)
• However, if you work from home you could potentially use > 50% of electricity during the day.

Step 2: Determine how many units you use when the sun is not shining:

20 units per day x 65% = 13 units

Step 3: Most batteries only have an 80% useful capacity (Also referred to as Depth of Discharge “DoD”). That means if you have a 5 kWh battery, only 4 kWh can be used safely. You thus divide the units calculated above by the DoD:

13 units ÷ 80% DoD = 16.25 kWh storage capacity required

You thus need a battery bank of around 16.25 kWh to last you through the night.

Step 4: Pick your batteries:

Let’s pick the Hubble AM-2 – it is a 5.5 kWh battery:

16.25 ÷ 5.5 = 2.95 (Select 3 batteries)

The calculations as above can be used to determine where you ultimately want to end up. However, you can start smaller and expand your system over time.

• Inverter: We recommend that you select the correct size inverter on day 1 since it is not efficient to replace it with a bigger one later on (unless you know that you want 2 or more inverters – in that case you can start with one and add the other(s) later on).
• Solar Panels: All the inverters have 2 or more MPPTs (inputs for the solar panels). We suggest that you start with enough panels to fill up one of the MPPTs (i.e. select half of the maximum number of panels as calculated by the Kit Builder). You can the double up the final number of panels at a later stage.
• Batteries: Start with as many batteries as your budget allows. While you can add extra batteries later on, it is not 100% ideal. Batteries starts degrading immediately after you start using them and their available capacity thus decrease over time. When you add the new batteries, their capacity will be limited to the capacity of the older battery.

Off course!

Play around with the Kit Builder to get a feel of how it works and then contact us for a detailed need analysis / consultation.