Load-shedding – watching television by candlelight and how to cope (or backup power options)
by Sean Moolman
By Hannes Roets
Indeed! This brings us to the issue of load shedding.
Load shedding is when electricity supply is intentionally interrupted or reduced to avoid excessive load on the generating plants. Whilst it is very disruptive (as we all know!), it is preferable to a total collapse of the electricity supply grid, which will have disastrous consequences for the country. Should the demand be allowed to exceed the supply, it could very well happen and it would take a week or longer to get the grid online again.
When a software glitch allowed such an imbalance to develop in 2003, the entire North-eastern and Midwestern United States and the Canadian Province of Ontario were blacked out, which left 55 million people without power for more than a week. A lack of alarms left operators unaware of the need to redistribute power after overloaded transmission lines hit unpruned foliage. Even in a technologically advanced country like the United States it can happen.
To Eskom’s credit, they have avoided such a catastrophic event thus far with a national grid that is under widespread distress.
The first thing we need to realise is that load shedding will be part of our lives for several years to come. The second thing to realise is that it will get worse before it gets better. The next thing to realise is that we have no choice but to manage the situation according to our own specific needs.
Some of us could quite happily go without Sewende Laan, the Premier Soccer League and the Internet for several hours per week. For most of us though, a power failure not only spells inconvenience but a serious financial impact. Many small businesses face financial ruin. Business continuity is critical.
Backup power options for load shedding
If you cannot live with load shedding, your only alternative is to use stored energy when the lights go out and you really only have two choices, namely a generator or an inverter/ battery system.
[box] What is an inverter?
Basically it is an electronic or electrical device that changes DC (direct current) into AC (alternating current). It is required for when you want to use a battery storage system for backup power to your home or business, since the batteries deliver direct current and your devices / appliances run on alternating current.[/box]
In most cases, inverter/ battery systems offer superior performance and significant cost savings when compared to generators. Considering the efficiency of modern, solid state inverters, generators have definite drawbacks in several areas.
Most importantly, many body corporates, home owners associations, business parks and other landlords will not allow generators to be used. You can imagine the noise and smell when 200 generators start up in a complex.
The initial cost of a generator might be less expensive than an inverter system, but in the long run they are far more costly when you consider running costs and maintenance. Generators require constant attention to assure proper operation. The oil needs to be changed regularly and other maintenance performed. It is also highly recommended that if a petrol generator does not run for more than 30 days, that the fuel is drained and the carburetor run dry. Nobody wants to go outside at night and perform a fault finding ritual when the generator fails to start.
Buying a cheap unknown brand of generator is penny wise and pound foolish. Very few are supported and even a minor unobtainable spare part could leave you in the dark once again. Connecting your expensive equipment to a unit with dubious or compromised circuitry may very well be a perilous exercise. Also, if you believe everything you read, better not read the spec sheets of some of the cheap imports.
With the ever increasing price of fuel, running a generator could become prohibitively expensive. And nobody likes the noise and fumes.
Fuel storage can be a nuisance as well. Apart from the fire hazard and regulatory problems, petrol cannot be stored for more than a month or so. You need to rotate your inventory on a regular basis to avoid problems.
An important consideration is the seamless transfer of power of the inverter system, which is impossible to achieve with a generator. Even with the fastest automatic and remote start facility, there will always be a delay of several seconds before the power comes on. By that time you might have lost important data on your computer or, even worse, you might have lost the plot of the soapie you were watching!
Having said all that about generators, an inverter/battery system is not the be all and end all of standby power. There are several disadvantages, like the energy storage limitations of the batteries as well as their expected life, which is generally between 5 and 7 years. Initial cost is an important consideration but it is for the most part justified by the preceding reasons.
Even more so than with generators, the bandwagon is overcrowded with opportunists looking to make a quick buck. If you are on a limited budget, rather buy a quality inverter of the size you prefer with fewer batteries initially. You can always add batteries later on but if you buy a 1 kW inverter with 3kW written on the package, you might as well go and play the lotto. At least you will have a chance of getting value for your money.
What about Solar, you may well ask. Well, the truth is that if all you are trying to do is bridge the gap between power outages, Solar is not the answer. The inverter/battery system does not generate anything. It simply stores and provides energy when needed. Significantly, mains power is still by far the cheapest energy you can buy today, in spite of the drastic Eskom price increases. If, however, you want to become less dependent on Eskom power, Solar might be an option but it is still very expensive. All the same, that is a discussion for another day.
What size inverter/battery system is appropriate for my household or small business?
1 to 3 kilowatt inverter/battery systems are the most popular for households and small businesses. Bigger systems generally require dedicated designs by competent engineers, so we will focus on the smaller systems.
Although it is technically possible to design a system that can pick up the entire electrical load of a household or business, it is totally impractical because of cost. Therefore high consumption items like geysers, washing machines, heaters and even kettles should be avoided to keep the size of the inverter down and limit the number of batteries. Since our aim is simply to survive load shedding, it is not too difficult to find alternatives for these energy guzzlers. Computers and TV sets do not do too well on candle power however!
To illustrate what is achievable, typical examples of the three most popular systems give a good idea of what is realistic. The figures in the tables below are approximate. The actual power consumption of your household appliances or office equipment may vary considerably from the figures in this table. Before you do a final load calculation, we strongly recommend using an electricity usage monitor to establish how much electricity an appliance is using. They are simple to use and cost around R750.
1 Kilowatt System
Rated at 1000 Watts, the system can typically back up the systems below. However, it does not mean that it can sustain the full load all the time. That will be like driving your car flat out all day long. A constant load of about 80% as depicted in the example is sensible.
Flat Screen TV
DStv Decoder or PVR
LCD Computer Monitor
5 Lights Total
The system now runs at 80% but a photo copier or fax machine, which operates for a limited time could be used in addition. Should you want to operate your garage door (750 Watts), some of the other loads will have to be turned off for a short time while the door operates. It will however, not accommodate boiling water in a kettle (±2000 Watts) because it is way above the system’s 1000 Watt rating.
2 Kilowatt System
Rated at 2000 Watts, the system can typically back up the systems below. Even though the total Wattage exceeds the 2000 Watt rating a maximum constant load of about 80% (i.e. 1.6 kW) is recommended. Some loads such as a microwave or printer are used for a short period only and will not put an excessive burden on the system.
Flat Screen TV
DStv Decoder or PVR
LCD Computer Monitor
10 Energy Saver Lights
Inkjet Printer Total
You will obviously not use the microwave while something is being printed and it is a good idea to turn off the computer or the TV before using the microwave.
3 Kilowatt System
Rated at 3000 Watts, the system can sustain most household appliances with the exception of high power consumption items like the geyser, stove, washing machine, dryer, air conditioner etc. It will also keep a small office with several computers, printers, copiers etc. going. Typical use is depicted below.
Flat Screen TV
DStv Decoder or PVR
LCD Computer Monitor
4 Security Lights
10 Energy Saver Lights
15 LED Downlights
2 Bedside Lamps
Cell Phone / iPad / Laptop Charger
A number of the following appliances may be used, provided some of the loads are turned off to make provision for the higher consumption. The total consumption of 3000 Watts may be exceeded within limits for a short period because the inverter system has built in safety margins and will not be damaged. However, if the safety margins are exceeded the system will automatically turn off to protect itself. PowerOptimal’s Powerguard® Peak Demand Management system could be employed to manage these tasks automatically and will ensure that limits are never exceeded.
What type of installation is appropriate for my inverter/battery system?
There are essentially three different ways of employing standby power systems. For 1 – 2 kW systems, it makes sense to use Version 1 or 2. From 3 kW and above, Version 3 with automatic switching could be a serious consideration. Systems larger than 5 kW require a site inspection and a dedicated design.
The inverter and batteries are contained in a steel cabinet, which is fitted with a standard 15Amp plug outlet. Castors make the unit easily movable, but it is not designed as truly portable because the batteries are heavy and the weight could be considerable. It is typically used in the vicinity where it is required or with an extension lead.
The inverter unit is stored remotely and its output extended with its own cable via existing electrical conduit or surface mount to dedicated plug outlets that are completely isolated from the standard wiring. Potential problems with this solution are lack of space in the existing conduit or unsightly surface mounted cables.
By employing the PowerGuard® DPM 30 – 8 Switcher, the inverter is permanently wired to the distribution board with minimal disruption during installation and present wiring remains untouched.
Unlike far too many risky installations, this perfectly legal connection complies with all regulations. Since it is impractical to use an inverter that is capable of picking up the full load, the PowerGuard® switcher ensures that high power consumption loads like the geyser and stove are turned off instantly during a power failure. With bigger units of 3kW and above, most other circuits like lights and plugs remain powered. Before installation, the client decides what should continue working during a power failure.
While we are on the topic of using existing wiring, a note of caution. Be very aware of wiring directly to your DB without a change over system that automatically and completely isolates the mains while running on the inverter. This is a serious fire hazard and while the electricity police will not come around and fine you, the insurance assessor will certainly take a keen interest in the wiring in the case of a fire damage claim.
What about battery types and sizes?
Although it is critical to use a high quality inverter capable of sustaining the design load, the batteries should also be of similar quality and of sufficient quantity. A bank of batteries with a combination of parallel and series connections provides the reservoir for the energy that has to be stored and later released when needed.
High performance lead acid batteries are usually used but they are not of the automotive type. While they are of similar construction, they are designed to withstand many more charge and discharge cycles and can also be deeply discharged. Known as a deep cycle battery, they can be cycled down to about 50% charge without incurring any damage. At that depth of discharge most of the potential energy had been extracted from the battery making them very useful for this application.
There are many varieties on the same theme ranging from the well known wet cell that requires regular maintenance to the more recently developed lead crystal with far superior performance and no maintenance whatsoever. As with all good things the superior performance naturally comes with a superior price.
The Sealed Maintenance Free Battery is reasonably priced and for that reason one of the more popular types. As the name suggests, it is to a large extent maintenance free, but the chemical reaction produces Hydrogen and Oxygen, which could form an explosive mixture. For that reason, these batteries cannot be used in a confined space and must be installed outside where it is well ventilated. They are generally about 35% cheaper than AGM batteries, which is the next step up.
In AGM (Absorbent Glass Mat) batteries, the electrolyte is mostly absorbed in glass fibre. This type of battery is entirely maintenance-free and there is no gas formation with normal use. Not requiring any ventilation, these batteries can be installed anywhere.
Batteries are rated in Amp Hour (Ah), which is a measurement of the amount of current it can supply over a certain period. They are rated over a period of 20 hours, which means a 100 Ah battery will supply 5 Amps over that period.
Simply put, the more Ah you have, the more capacity you have and the longer your system will produce power before the batteries run flat. To calculate the number of batteries required you may use the following rule of thumb. You need about one 100Ah battery per 1kW per hour. In other words if you have a 3kW system that should last for 4 hours you need 12 X 100 Ah batteries. 3 (3kW) X 4 (4 hours) = 12.
How can I contribute to reducing load shedding?
In spite of having alternatives for the times when the lights go out, all of us can contribute to limit load shedding to a minimum. We are in the middle of an energy crisis and each and every one of us needs to modify our lifestyles to accommodate this harsh reality. Here is what to do:
Switch off your geysers, electric heaters and pool pumps from 17h00 to 21h00 every day.
Switch off unnecessary appliances and lighting.
Consider alternative heating solutions (gas stoves, gas heaters, solar geysers, etc.).
Switch to CFL and LED lights.
Turn off anything that consumes standby energy (TVs, DVD players, computers, cell phone chargers).