ALL YOU NEED TO KNOW ABOUT SOLAR
solar pv panels
Solar photovoltaic (PV) panels generate power from the sun's radiation. It can only generate power if the sun shines on it. If there is shade on the panel, it reduces the power output of the panel dramatically.
A solar PV panel is rated in Watt output (W). This is the maximum power output for a panel. As the panel produces power only from sunlight, it can't be used at night except if you have a battery storage facility. In short the solar PV system can only power appliances that you use in the daytime and will protect you from loadshedding in the daytime.
There are different makes of solar PV panels and most have an efficiency of 21-25%. (see link below) PV panels are generally quite durable and dependable. It doesn't matter that much what panel you install as long as it is a reputable manufacturer. (most panels are manufactured in China and have a 10 year warranty).
The amount of power a panel produces is dependant of the sun's radiation and can be 50-70% less in winter than in summer. The design is thus determined on the amount of radiation received in winter which will make it double the size needed in summer. Other loads, such as swimming pool pumps, aircons can be added in summer to make use of the extra capacity. PV panels operate less efficient the hotter they get, so it's best if kept ventilated.
Battery storage
There are 2 types of batteries on the market. Lead acid (also Gel) batteries and Lithium iron batteries. LA batteries are the cheapest option with a range of between R4 000 and R8 000 for a 5Kwh battery. Whereas a Lith-on 5kWh battery can cost between R25000 and R40 000.
Now here is the thing! LA batteries can only use 50% of its capacity, called Death to Discharge (DOD). Lith-on batteries has 90-100% DOD. In plain English, with a Lith-on battery you can use nearly the full capacity of the battery before it is flat. With a 5kWh battery you can utilize 1000W for 5 hours and not 2.5 hours as per LA batteries.
Lith-on batteries also has more cycles (fully charged to empty) > 8000, compared to LA batteries (at 50%) < 3000. Lith-on batteries normally comes with a 10 year warranty, whereas LA batteries come with a 1 or 2 year warranty. Batteries have a 'C' rating which indicates how fast they can charge/discharge. A 1C rating indicate that the battery can charge in 1 hour. 2C 30 min. 0.5C 2 hours.
Batteries also have different Voltage (V) 12,24,48 V. Bigger voltage is better because it reduces the current needed in the wires and current to the inverter, which makes both cheaper. It also reduces the time needed to charge the battery.
So what does 200Ah or 5kWh mean. Well for a 12v battery 200Ah=200x12=2400Wh or 2.4kWh. You can thus utilize 2400W for and hour. So it is important to figure out what appliances (load) you want on during load shedding and how long do you want them on for (2,4,6 hours or a day or 2).
In conclusion: Lith-ion batteries are expensive, but won't need to be replaced every 2-3 years and can be used nearly to full capacity.
Inverter/charge controller
Inverters are an essential part of the system. It converts the power from the solar PV panels to usable power in your home. It converts the DC current to AC current. If you don't use a backup battery you only need to use an inverter to convert the current.
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If you however you use a battery for backup power you need to charge it with and inverter /charge controller. This is generally referred to as an MPPT (maximum power point tracking). A MPPT optimized the output from your PV panels to charge the batteries and supply to the household.
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So generally speaking an inverter is referred to as as a combination of an inverter and charge controller and has a display screen to show the power output of your solar PV panels, the consumption and the state of your battery. The term inverter is loosely used, so make sure of what you get. It is rated in kW which indicate how much power from the solar PV panels it can convert to AC power and have to match the up with the maximum power of the solar PV panels.
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Prices range from small inverters (3kW) R15000 to large inverters (15kW) R70 000.
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Appliances/Load
Appliances, lights, plug points and other utilities in a house hold are referred to as load. Every utility that uses electricity has a watt (W) rating. This is the amount of power it uses to work. A fridge has for instance 130W input rating and uses 130Wh energy an hour. Because a fridge is insulated it will keep its temperature and switch on occasionally to regulate its temperature. It will thus not run for 24 hours at a time. It will run for maybe 30% of the time in a day. This is called a duty cycle. The usage per day would be 130Wh x 24h x 30% which gives you 936Wh.
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Now for instance a 60W florescent light in the hallway uses 60Wh x 24 = 1440Wh a day if it is on the whole day.
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It is important to determine what utilities you want to run on solar power by day (when the sun shines) and what do you want to keep on when it is load shedding.
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Its is best to replace light bulbs with energy efficient bulbs and don't expect your battery to run a 2400W bar heater.
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Other information
The installation of a solar PV system for a residence or business is call ed a Small Scale Embedded Generation (SSEG) and can't exceed 100MW or 100 000 kW, which is a lot.
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A SSEG needs to be registered with the municipality or ESKOM if it is connected to the grid. There has to be compliance with the grid and needs to be signed of by a qualified electrician and a COC issued. Access energy can now be sold back to the City of Cape Town only. The meter is however expensive (R12000), but the City is working on an alternative.
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