How To Workout What Size Solar Solution I Need?

With the looming threat of national load shedding always over the horizon, you might be ready to pull the trigger for a new solar system. But how big does it need to be?

How does anyone determine the size of the solar solution you need?

The short answer to this question is a more complex journey than expected.

Here’s our step-by-step guide to help you determine your solar system requirements. Luckily, the first step is the easiest.

 

1.   Starting at Home and in your Pocket

Before picking up any pamphlets for solar systems, one of the biggest hurdles to overcome is budget, you need to determine solar size and cost.

While many solar system companies and banks offer payment plans, paying for what you can with cash is always best.

Most home installations cost between R120,000 and R150,000, so it is always best to plan far ahead of time.

The next element to consider is your space constraints. Is your home situated in a shady area? Or is the roof space limit? Either way, space constraints can affect the system size you install.

Other major factors to consider are:

• Sun exposure on your property
• Can you orientate your panels in the correct direction (north-facing)
• Will it be possible to expand your setup in the future
• And the product’s efficiency ratings

Once you know where the panels can be installed and whether they’ll have access to lots of sunlight, it’s time to determine your energy consumption rate.

 

2.   Determine Your Energy Consumption

Estimating your average daily energy usage in kilowatt-hours (kWh) can be tricky. You’ll want access to 12 months of electricity bills indicating how much power you’ve used.

This information is usually available via your monthly electricity bill. If you are using a prepaid meter, you must review your electrical usage on the voucher.

When you’ve got enough numbers for the last year, divide the monthly usage amounts by 12. This will give you the average monthly consumption. Divide it by 30, and you’ll get a rough estimate of daily power usage.

Example: If your monthly usage is 900 kWh, your daily usage is 900 kWh / 30 days = 30 kWh/day.

While this isn’t incredibly accurate, it will give you a ballpark figure for your daily electricity needs. Also, remember that power usage will change depending on the season, with some homeowners using heaters during winter.

 

3.   Consider Peak Sunlight Hours

Average peak sunlight hours can vary massively due to your home’s location, climate, and topography (landscape or surrounding mountains).

You want to know how many peak hours of sunlight you get so you can figure out how much you can determine how to harvest the most sunlight.

Luckily, nowadays, there are online tools to assist you with determining your area’s peak sunlight hours.

In addition, peak sunlight hours are different from daylight hours. Peak sunlight hours are an instantaneous measurement of solar power over a certain area and time, sometimes called solar irradiance. Solar irradiance is achieved when one kilowatt of energy is generated for an hour per square meter (kW/m²).

South Africa as a whole averages between 4.3 to 6.3 peak hours per day. We’d suggest narrowing this down and researching your specific areas.

Now that we know how many hours a day you’ll be able to harvest the peak sunlight, you’ll want to calculate what you want your solar panel output to be.

 

4.   Calculate The Solar System Size You Need

Now that you’ve crunched the numbers, you’ll need to determine the size of the solar system you need to install, bearing in mind the solar cost.

To calculate the solar system size, you’ll want to take your daily kWh energy requirements and divide them by your peak sunlight hours to get the kW.

Or use this formula:

For example, if you need 30kWh daily with an average daily peak sun hour value of 5, you’ll want a 6kW solar system.

However, as we know, no solar system works at 100% efficiency all the time. Many external factors will contribute to lowering how much solar energy you can harvest, which include:

• Shading losses of 7%
• Dust and dirt of 2%
• Reflection of energy of 2.5%
• Spectral losses of 1%
• Irradiation of 1%
• Thermal Losses of 4.6%
• Array mismatch of 1%
• Inverter losses of 1%
• And AC cable losses of 0.5%

These factors can contribute to a net loss of 23%. However, these are all estimates, so you will want to multiply your formula above by an efficiency factor of 1.25 to cover these potential losses.

This will result in a formula that looks like this:

So, the actual size of the solar system you want is around 7.5kW, which will cover all your power requirements during the day.

Now that we know what sized system you need, you’ll need to work out how many solar panels you need.

This can be done by multiplying the kW by 1,000. For our 7.5kW example system, you will need enough solar panels to produce around 7,500 watts of power.

If you’re buying Jinergy 550w solar panels that generate 550 watts of energy, you will need around 14 (rounding up from 13.6 units) to cover your needs.

For those overwhelmed by all the maths required, you can simply call us in to give you a quote, or use our online Solar Guidelines Calculator to get your solar system size calculation today.