All you
need to know

What is rooftop PV?

A rooftop photovoltaic (PV) system has its electricity-generating solar panels mounted on the rooftop of a building or structure. Solar panels are exposed to sunlight or solar radiation and generate electricity which is called a photovoltaic effect. This solar power flows via cable to a device called an inverter which converts the direct current (produced from the panels) to alternating current. With the inverters synchronising the solar power and the Eskom grid, that power can be fed directly into your internal electrical network and save electricity. So every KWh generated by the solar system is a kWh less required from Eskom or local municipality.

How do I plan for PV?

Planning for a PV system will require you to analyse your electricity use, implement energy efficiency measures, decide if you want to operate your system entirely off grid or use a hybrid or grid-connected solution, and then finally select, the technologies to help you meet your objectives. And because your system is going to be working for the next 20-25 years, you need to be sure about working with a supplier that has the network, financial stability, product quality and warranties in place to maximise your investment. Reputation, credibility and the expertise of your renewable energy partner are fundamental to you realising the maximum benefit from your PV investment.

Why do I need to implement energy efficiency measures beforehand?

Implementing energy efficiency measures before you buy your PV system will reduce your electricity use and allow you to buy a smaller and less expensive system. For example, converting geysers which are your biggest electricity users to solar or heat pumps, installing LED low energy lighting, using gas for cooking, installing lighting motion sensors and so on. If you’re designing a new building, consider working with the architect and builder to incorporate renewable energy solutions into your design from the outset. In fact, some measures are already legislated. SANS 10400-XA: Energy Usage in Buildings, and SANS 204: Energy Efficiency in buildings requires a focused solution for areas such as water heating, whereby 50% of all hot water in new buildings needs to be produced by methods other than electrical element heating.

What is an essential vs non-essential load?

Your essential load consists of the appliances and equipment that you want to be able to power up in an outage while non-essential is exactly that – items that are not necessary or vital during an outage. By splitting your loads, you are able to use your batteries for longer to power up the essential equipment. Secondly, you also reduce the capital outlay needed on a bigger PV system and battery capacity if you were to try and power up everything in your home/office.

Essential loads

Non-essential loads (heavy loads)

How long will my battery last?

The amount and duration of battery back-up is dependent on two factors – the size of the battery bank and the size of the load drawing power from it – in other words how many appliances you have running at the same time, and the total wattage being drawn by these appliances. It’s one of the reasons why we split essential and non-essential loads, to extend the battery capacity.

For purposes of this exercise, we used one 3.5kWh li-ion battery which allows for an 80% depth of discharge. This means that once your battery is discharged to having 20% power left, it is automatically disconnected by the inverter to protect your battery’s lifespan. You can of course add additional li-ion batteries if you require more back-up.

Estimated battery running times based on a 3.5 kWh li-ion battery:

2000W = 1.4 hours
1000W = 2.9 Hours
800W = 3.6 Hours
600W = 4.8 Hours
400W = 7.1 Hours
200W = 14.3 Hours

What is the difference between grid-tie, hybrid and Island PV Connections?

A solar PV system typically comes in three configurations:

System 1: Grid Tie
No batteries, grid connected. This system supplements your grid energy usage and is a very good option for reducing your electricity usage from the grid. In the event of a blackout or power outage, your solar system is forced to shut down and does not provide back-up as there are no batteries linked to the system.

Grid-tie systems are typically used in commercial operations where the key objective is to electricity costs by producing your daytime energy requirements, free from the sun, and where a battery storage system is economically impractical for the business needs. A grid-tie system is highly cost-effective and has a much shorter payback period, and the system most typically installed in power purchase agreements for commercial operations.

System 2: Hybrid
Inverter, batteries and solar panels along with a grid connection and is commonly referred to as a hybrid system and with the correct installation will act as a UPS (uninterrupted power supply) in the event of a power outage. Hybrid systems are the ideal system for homes and offices, especially with the fact that battery storage is far more affordable, with prices still dropping.

The PV system will charge up the batteries first and then the excess production will supplement your household/ business energy needs. Many of our clients start with system 1 with a plan to build up to a system 2 and then add battery back-up at a later stage as their budget allows to build up to a system 2 configuration. The great benefit of solar PV is that it’s entirely scalable and you can add to it as your needs grow. Clients typically opt for this when power outages are an ongoing issue. The proviso of the system being expandable later is that you start with the correct hybrid inverter and capacity that is able to take batteries and additional panels at a later stage.

System 3: Island

Inverter, solar panels and batteries and no grid connection, useful for areas where no grid exists, such as farms or remote areas. The energy produced will charge up the batteries which should allow for three days’ worth of energy needs and these batteries will feed the power requirements of the property

What is the cost to install PV?

Many people believe renewable energy is too expensive without actually doing their homework. The reality is that the cost of renewable energy solutions has come down significantly over the last few years. When we take them through the costs versus the savings and the fact that their savings can even finance their move to renewable energy, most are stunned at how absolutely affordable it is.

If we look at a typical PV system, your initial capital layout would be in the beginning when you purchase the equipment and on average takes around 5 years to offset the costs, but then for the expected 25 years of the lifespan of your panels, you will get free electricity. The initial upfront cost is the only cost involved with solar. After that, because there are no moving parts, the maintenance on the system is very low. Once fully paid, you have an incredible investment and asset for your property that keeps saving you thousands of Rands each year, for many years to come. And you’ll have a highly efficient, green home or business which is an absolute win. Another advantage of PV is that it is entirely scalable and can be ramped up as your requirements demand and, more importantly, as your budget allows.

Solar PV benefits

Systems focused primarily on savings (grid tied systems) and typically used in commercial environments immediately reduce your electricity bill pro rata to the size of the system you install.
Back-up systems, which provide during power outages, provide clean, quiet, instant and environmentally friendly electricity when your utility lets you down. Hybrid solutions provide back-up with a measure of savings.
The true benefit of Solar PV is the fact that you are protected from future Eskom price increases. Any component of your electricity requirement covered by a solar system is in effect hedged against future tariff escalations. All indications are that South African electricity users are in transition from enjoying the lowest cost of electricity in the world ten years ago to becoming one of the highest payers

All you need to know