Introduction

Solar technology has advanced significantly during the past couple of years. Today’s smart solar systems are significantly more sophisticated than systems installed only a few years ago. Differences are as pronounced as between today’s smart phones and the first-generation mobile phones of the late 1980s. Elements of smart solar systems are:

  • Smart design involving both battery and grid-tie inverters.
  • Smart bi-directional programmable inverters that can communicate digitally with advanced batteries.
  • Smart load control.
  • Smart Lithium or Supercapacitor batteries that can communicate with inverters.
  • Online performance monitoring.

All these lead to higher efficiency, higher reliability and lower cost per kWh produced.

The main reasons why people consider installing solar systems for their homes or businesses are (1) to save on their electricity bills and (2) to shield them from loadshedding.  For users without access to the national grid solar power offers them a convenient and cost-effective way to generate their own power.

Before installing a solar system it is important to access the energy consumption of the house (or facility) and to consider ways of reducing energy consumption. Typically, one can replace incandescent lights with LED lights, replace old fridges with new energy efficient ones and replace electric stoves with gas stoves. The cost of such measures usually outweighs the cost of installing a bigger solar system.

There are two main types of solar systems – systems without batteries and systems with battery storage.

Systems without Battery Storage

The cheapest type of solar system consists of only a solar array and a grid-tie inverter. Such systems do not include batteries and are only geared towards energy saving. Grid-tie battery-less systems can only produce energy when connected to a live grid. If the grid falls away the system stops producing energy.  In areas with reliable grid connection, this can lead to a significant reduction in energy cost.

Systems with Battery Storage

Adding a battery inverter with battery storage gives solar systems the ability to store solar energy that is captured during daytime for usage during the night or during times of load shedding/blackouts. Battery storage is essential for off-grid systems.

Layout of Different Types of Solar Systems

1.     Simple backup system

A simple backup system consists of only an inverter/charger and a battery bank as depicted below.  The inverter incorporates an automatic transfer switch (ATS). When utility power is available it is passed directly to the load but in the event of a power cut the ATS, in a split second, connects the load to the output of the inverter, which draws DC power from the batteries and inverts it to AC power.  These types of inverters usually incorporate a battery charger which charges the battery when utility power is available.

 

2.     Simple solar system with battery backup.

By adding solar panels with a charge controller to a backup system, as shown below, it can be upgraded to a full solar system.

With many types of modern solar inverters/chargers the solar charge controller is built into the unit as shown below.  Such inverters are called hybrid inverters.

Figure: Battery Inverter/Charger

Figure: Hybrid Inverter/Charger

3.     Grid-tie System

This is the simplest and cheapest type of solar system. However, it will only be able to generate power when connected to a live grid. These types of inverters are also able to feed power back into the grid, if allowed by the grid operator.

Figure: Grid-tie System

4.     Grid-tie system with battery storage

The advantage of this type of system is improved efficiency, since power from the grid-tie inverter is fed directly into the high voltage AC supply line without the need to step the power up from the low battery voltage (12-48V DC) to the AC supply voltage (240V AC), which is not very efficient.

Figure: Grid-tie system with battery storage

5.     Smart integrated solar systems

Advanced smart systems usually integrate the grid-tie inverter, battery inverter and charge controller into a single unit.  The system manages four sources of power (utility, generator, solar & batteries) and three types of loads: essential, non-essential and smart loads. Essential loads are those that will always be powered, even if the grid is off and the generator fails. Smart loads are non-essential loads (e.g. hot water tank) that will be powered from the grid or from redundant solar power if the grid is off. The smart inverter controls the flow of energy to ensure optimum efficiency and availability of power.

Figure: Smart integrated solar systems

Modularity of Solar Systems

One of the big advantages of solar technology is that it is modular. This means that one can start with a small basic system and then incrementally grow it over time as one’s needs increase. Such an approach may involve the following steps.

  • Start by implementing energy savings measures such as replacing all lights with LED lights, replacing older inefficient fridges with energy efficient models and replacing electrical stoves with gas stoves.
  • Install a hybrid inverter with batteries to power the most important loads such as lights, computer, fridge, TV & computer. Such a system will operate as a UPS (Uninterruptible Power Supply).
  • Add a solar array to the system. This will extend the UPS time of the system during the daytime and also reduce your energy bill.
  • Increase the size of the battery bank.  This will increase the UPS capability of the system during the night-time.
  • Install more (typically up to 6) hybrid inverters in parallel to increase the power output of the system.