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The Basics

The situation

Load-shedding...sounds much better than "power failures" or "blackouts" right? Initially you thought you could make it a romantic evening, wine and candles with the wife (or husband)? Or maybe teach the kids how life was a century ago? A little bit of an inconvenience, you think. In reality, you come home from a hard day's work, and you just want to have a cold beer and watch your favorite TV show. The kids need to do their homework and everyone needs Wifi. Your better-half is just sitting there, staring at you, judging...or not, as it's too dark to see. This "load shedding" non-sense is really getting on your nerves now.

Your neighbour recently installed some backup system and they have lights. They invite you over and you find yourself looking at his mouth babbling on and on about kW, Ah, VA, KWh, VDC, PV Array...etc. You're nodding in approval but in reality you have no clue what the #*%@ he's talking about let alone what to get, or which system is most suitable for you. You want to take the plunge, and want to ask more, but everyone is around, you don't want to look stupid. Fear not, here's a cheat sheet to get you going.

Learn the basics

Learn the basics here and the many electrical terminology that you wish you paid more attention to during physics classes in high school. If you're interested, do click into the different sections for a more in-depth discussion. Once you know the basics and have a better understanding of each component, you will be better equipped to choose the right system that suits your needs. But before we continue, you'll need to know a few basic terms:

  • W (Watts) - Unit of Power (also denoted by "P")
  • V (Volts) - Voltage (car battery is +-12V, South African wall plug is 230V)
  • A (Amps) - Current (also denoted by "I")
  • W = V x A (Watts = Volts x Amps)

There's another one - R (Resistance) measured in Ohms (Ω), but let's leave that one out for now as it is less mentioned in this industry. If you're completely new to this, don't worry too much, from learning what inverters, batteries and solar panels actually do, you will have a better idea and get used to this terminology.

Inverters 

The inverter is the heart of the system. Unless you live in your car or on a farm using car batteries, you will definitely require an inverter. There are 2 types of currents, DC (Direct Current) and AC (Alternating Current). The modern home is equipped with AC and you cannot plug a house appliance into DC current (and vice versa), it will either NOT work and worse, you'll damage something. Without the inverter, you won't be able to convert one to the other, which is essential to any solar / power backup system. Let's start with the single most important word / concept associated with inverters:

  • W (Watts) or kW (kilowatts) - This is the unit for output power. Think of it as the maximum load that the inverter can power up. A typical system for a small-medium home is 3KW-5KW (1KW = 1000W). You may remember donkey-years ago buying light-bulbs that becomes really hot to touch? They were 30W for bedside lamps, 60W, 100W for brighter needs. Nowadays with energy saving LED bulbs, they are only 3W, 6W or 8W. A laptop is around 70W, a LED TV is 75W, WiFi & Modem  20W and a phone charger 10W. If you have everything plugged in and switched on, the total W (Watts) shouldn't be over the maximum output of your inverter.
  • I'm sure you're already thinking "hey, 3KW (3000W) should be more than enough for me". Well, think twice, a kettle is 2000W, a stove is 2000W, a PC & monitor is 400W, and a fridge around 250W.

...and of course, that's not all to it. Apart from kW output vs Price, there are  many other factors to decide. Click here to get the full details on inverters.

Batteries

Somehow, you'll need to store energy for when there is none available. It's like having food (energy) to sustain you until your next meal. Or filling up your car with petrol (energy) to take you around until your next visit to the petrol station. Batteries are needed to store the generated power from the grid (Eskom) or the sun (Solar panels). Electricity can only be stored in a battery in DC form. The inverter converts the AC power from the grid to DC power and charges the battery. When there's load-shedding, the inverter converts DC power to AC power and supplies the home with power. There are a few things to consider when buying a battery:

  • Wh (Watt-hour) or kWh (kilowatt-hour) - This is the capacity of the battery or simply put, how long you can run your appliance (at a certain power draw). Say you have a 5kWh-rated battery for your home, it means you can run a 1000W appliance for 5 hours. Or boil a 2000W kettle for half the time - 2.5 hours. (**)
  • Ah (Amp-hour) or mAh (milliamp-hour) - This is also a measure of the capacity of the battery. Remember the formulae W = V x A ? If you have a 100Ah car battery at 12V, the power generated will be 1.2kWh. (**)
  • V (Volts) - The voltage the battery produces, Examples are: AA batteries 1.5V, car batteries 12V, backup batteries typically don't exceed 48V for safety reasons. (**)
  • Lead-acid (car) or Lithium batteries - the material and technology used to build the battery. This greatly affects the Cycle life, Depth of Discharge, Efficiency, Charge / Discharge rate & Energy Density and ultimately the Price(**)

One can write a whole encyclopedia on batteries, but Click here for more details on batteries and how to choose the one for you.

(** it's more complicated than that, but for our purposes, let's keep it at that for now).

Solar Panels

Sunny South Africa has 2500 hours of Sun per year! There's no better place to harvest all that abundant clean energy and save our beautiful planet. Solar panels used to be expensive, but in recent years prices has dropped tremendously making it affordable for households to install, save money on electricity AND even make a return on the long run. The first thing you have to consider is whether you CAN install solar panels on your roof or not. If you live in a complex, you may not necessarily be allowed to install them due to body corporate rules. If your place has too much shade, it may also affect the performance of your panels. The quality, size and technology involved in the production of Solar panels affects performance and its price. Here are the most important terms related to this topic:

  • PV Array -  Photovoltaic array. There are two different types of solar energy, thermal and photovoltaic. With thermal solar, the solar panels act more as mirrors to direct sunlight to a specific location to generate heat. The more common type of solar energy is Photovoltaic (or PV), the process of converting sunlight into electricity to power homes or charge batteries. This is the type of solar panels you see on rooftops.
  • Monocrystalline or Polycrystalline silicone. Silicone is a highly durable chemical element that converts the energy from the Sun into electricity. Although both types of silicon solar panels are used to produce power, there are pros and cons to both.
  • Half-cut cells - Half-cell modules have solar cells that are halved. The resistive losses are lowered and the cells can produce a little more power. Smaller cells experience reduced mechanical stresses and there is a decreased opportunity for cracking. This essentially means higher output ratings and improved performance and durability.
  • W (Watts) - Unit for output power. This will be the maximum power that the panel can possibly produce under optimal conditions (clear sunny day, no shade, angle to the sun, cool temperature). 
  • A (Amps) - the maximum current (Amp) that the panel can produce.
  • V (Volts) - the maximum volts that the panel can produce.

When it comes to solar panels, it is absolutely imperative to understand the difference between a parallel vs. a serial connection and how they affect the A (Amps) and V (Volts). Get this wrong and it will be an expensive mistake damaging your inverter.

  • Serial connection - This is when you connect the positive (+) of the first panel to the negative (-) of the second panel. Then you continue to connect the positive (+) of the second panel to the negative (-) of the third panel... and so on. In this case, You increase the volts but the amps stays the same. Example, you bought 6 solar 400W panels (40 Volt, 10 Amps); on a serial connection, that will be 240 Volts (40 Volts x 6 panels), 10 Amps.
  • Parallel connection - This is when you connect all the positives (+) together and separately all the negatives (-) together. You increase the amps but the voltage stays the same. Example, you bought 6 solar 400W panels (40 Volt, 10 Amps); on a parallel connectionthat will be 40 Volts, 60 Amps (10 Amps x 6 panels). 
Generally, you will need to do a combination of series-parallel connection, with many factors to consider. Click here for more details on solar panels and how to calculate the size of the PV array you will need.

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