FAQs FOR SOLAR POWER

Why use solar power at your home?

Many homeowners are installing solar power systems to reduce their reliance on Eskom, lower their electricity bills, and make their homes more environmentally friendly.  The steps that can be taken are replacing your conventional geyser with a Solar Water Heater and generating your own electricity.

Your conventional Electric Geyser can consume up to 40% of your household electricity. Solar water heaters are a set of pipes that are placed on the roof of your home. Heat from the sun warms water that can then be used throughout your home for all your hot water needs.

Solar PV technology converts energy from the sun to electricity, which can be used in buildings of all sizes. Investing in solar PV can help reduce the amount of electricity that is bought from the City.  Solar PV is one form of Small-Scale Embedded Generation. Solar PV is suitable for any place where there is a good solar resource and electricity is already used including residential, commercial and industrial areas.

Most electricity in a home is used in the early mornings and evenings and not during the day when solar power production is at it’s maximum.  For this reason we recommend using an off grid system with a battery storage system to store solar power generated during the day and make use of all this stored energy to power your household lighting and appliances at night.

The battery storage system in an off-grid system provides backup power in the event of load shedding or power failures.

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Solar Panels

Types of Solar Panels

There are 3 types of Solar Panels available, namely:

3.1 Monocrystalline Solar Panels

These solar panels are made of a large crystal of silicon. Monocrystalline solar panels are the most efficient with regard to absorbing sunlight and converting it into electricity; and thus do better in lower light conditions than other solar panels.

3.2 Polycrystalline Solar Panels

These are the most common solar panels on the market today. They look a lot like shattered glass as consist of multiple amounts of small silicon crystals. Polycrystalline solar panels are slightly less efficient than Monocrystalline solar panels but are less expensive to produce.

3.3. Amorphous Solar Panels

These panels consist of a thin film made from molten silicon that is spread directly across large plates of stainless steel or similar material. Amorphous solar panels are less efficient than the other two types of solar panels but are also the cheapest to produce. One advantage of amorphous solar panels over the other two is that they are shadow protected, meaning that the solar panel continues to charge while part of its cells are in a shadow. These work great on boats and other types of transportation.

How do you choose Solar Panels?

Determine solar panel efficiency and compare to industry average of 16-18%

  1. Check solar panel manufacturer warranties against industry average of 10-25 years

  2. Compare cost to relative efficiency – efficiency is important, but the most efficient panels aren’t always the best value

  3. Finally, and most importantly, refer to the Bloomberg rating.  Bloomberg is a ratings agencies that rates Manufacturers of Solar Panels. A Tier 1 solar panel is a panel that is made by a manufacturer that has been rated as Tier 1 by a reputable independent PV industry analyst.

Tier 1 is the highest (best) tier, and means that the analyst who ranked it believes that the module manufacturer scores well on lots of criteria including:

    1. Experience

    2. Financial position

    3. Manufacturing scale

    4. Deployment scale

    5. Durability & quality

    6. Technical Performance

    7. Vertical integration

    8. Insurance and backing

    9. Service and support

I always recommend that non-solar experts buy Tier 1 panels - as it is a simple way to filter out the junk being sold as "Top Quality".

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Solar Systems

How does a Solar Photovoltaic (PV) System Work?

Solar panels collect energy from the sun and convert it into DC electricity which is then sent to an Inverter.  The Inverter is one of the most important components of a solar power system and has two very important functions. It takes the DC electricity from the solar panels and charges the batteries as well as convert the DC from the batteries and solar panels into 240V AC. The AC electricity is then fed into your home to power your lighting and household appliances. There is no need to change any of your lighting or appliances.

Any excess solar power that is not used during the day is used to charge your battery storage system. The battery storage system supplies power to your inverter at night or when there is insufficient solar power available to satisfy your power needs. Lastly, an automatic change over switch is fitted to the system to ensure you still have power from Eskom on the occasion that there is not enough solar and battery power available. This way you are almost certain to have power available at all times, day and night.

What can you expect to pay for your solar investment?
Here are some indicative estimates on what you can expect to pay for a fully installed off grid solar power system from us:

  • 2kW Solar with 5kW Inverter and 5kWh Lithium Ion Battery – R 62 000 
  • 3kW Solar with 5kW Inverter and 5kWh Lithium Ion Battery – R 73 000
  • 5kW Solar with 5kW Inverter and 10kWh Lithium Ion Battery – R 105 500
  • 10kW Solar with 10kW Inverter and 15kWh Lithium Ion Battery – R 183 500

These prices are for a complete and fully installed system and include electrical certificates and all labour. All prices are approximate and include VAT.

Where do I find my daily kilowatt hours?
There are three ways of obtaining this information. The first is based on your electrical bill. Generally if you are billed directly by Eskom they will reflect your monthly consumption under the title ‘Difference’ and additionally will reflect the number of billed days. Once obtained you can just divide the ‘Difference’ amount by the number of billed days.

If you are billed by Municipality, they generally do provide you with a daily average reflected at the top of your bill.

If however you are on a prepaid meter,  you can just calculate how much you are spending per month, divide that figure by your price per kilowatt and divide that figure by the number of days. Not as accurate but still works.

Why are the solar day hours so low?
The solar day is based on a fixed pitch in a perfectly northern direction. The angle of the pitch varies from place to place but is set at the best median for both summer and winter generation. We are completely aware that in summer you will generate more than what is stated here but we need to have a single hour for calculation and the listed hours are reliable as they include loss efficiency adjustments.

What Voltage should I choose?
As a rule of thumb work like this:

0-3000wh (total generation per day) – 12v

3000 – 5000wh (total generation per day) – 24v

+5000wh (total generation per day) – 48v

Important to note that these figures are rule of thumb. You can squeeze or alter slightly on either side, but bear in mind that higher power(storage and draw capacity) at lower voltage causes system wide inefficiency and increases cable costs etc.

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Inverters

How do you choose the right Inverter?
The inverter size you choose depends on the power in watts (or current in amps) of the appliance/equipment you want to run (find the power consumption by referring to the specification plate on the appliance or tool or you will find the information in the appliance manual. If this information is not available, check with the appliance supplier). You need to know both the continuous rating in watts or amps; and the peak/surge rating in watts or amps. Without this information any further calculation is not possible.

Continuous vs peak/surge watts
Inverters are rated in continuous power and peak/surge power. Continuous power is the total WATTS the inverter can support indefinitely while peak/surge power is the amount of power that the inverter can provide for a brief period, usually when the equipment/appliance starts up. Induction motors driving such devices as air conditioners, refrigerators, freezers, pumps, etc. may well have a start up peak/surge of 3 - 7 times the continuous rating.

Converting AMPS to watts
Multiply the equipment/appliance AMPS x 230 (AC voltage) = WATTS (approximate)

Working out the power
Multiply the equipment/appliance AMPS x 230 V (AC voltage) to give the approximate WATTS or AC power.

Calculate approximate startup load (peak/surge watts)
Multiply the equipment/applicance WATTS x 3 = PEAK/SURGE WATTS (approximate)

So if you want to run an appliance with a continuous load of 5 Amps and a peak load of 15 Amps :

Power : V x I = VA i.e. 230VAC x 5A = 1150 Watts continuous power

Power : V x I = VA i.e. 230VAC x 15A = 3450 Watts peak/surge (also known as start or inrush current)

You would need an inverter with a continuous rating of approximately 1500 watts and with a peak/surge rating of approximately 3500 watts. It is always advisable to build in a safety factor by overrating the continuous rating by 20 - 25% .

How does an Inverter work?
A power inverter, or inverter, is an electronic device or circuitry that changes direct current (DC) to alternating current (AC). The input voltage, output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry.

Grid Tie Inverters vs off-grid Inverters?
Basically, an inverter converts the DC (Direct Current) power source into AC (Alternating Current). Grid Tied Inverters also known as GTI are inverters that you can connect directly to the power outlet. Yes, your house will have two diffrent power sources, and it will not explode. There's a microcontroller inside that synchonizes the generated power to the grid. You cannot do that in regular or Off Grid Inverters. If you will connect the Off Grid Inverter to the grid lines, the inverter will be DAMAGED and might cause injuriies and fire because it is not designed to sync the generated power to the grid. Hybrid Off Grid Inverters (HOG) also known as Grid Tie Inverters with battery backup are simply a combination of GTI and Off-Grid Inverters.

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Batteries

How to choose the right battery?

What is Solar Battery Sizing

Solar battery sizing (otherwise known as battery bank sizing) is one of the most important considerations when choosing the specifics of your solar electric system.

The main objective when sizing a battery bank is to get one that can handle the load coming from your PV panel array and provide enough stored power for your needs without having to regularly discharge to an unhealthy point.

By wiring multiple batteries together in different wiring arrangements you can design a battery bank that's right for your solar power system and thus correctly perform solar battery sizing.

Factors Affecting Battery Bank Sizing

The number of batteries you use in your solar system depends on the following factors:

  • The amount of money you have to spend on this solar project. Part of solar battery sizing is insuring you can buy enough solar batteries to handle your power storage needs.
  • You must also take into account the number of days you want to be able to go before needing to recharge your batteries. If you need to be able to power certain appliances for a specific number of days at a time without interruption, you'll need more batteries to carry a bigger load. This is determined by the number of batteries you use and how you wire them to affect your battery bank's total amp hours (storage capacity).
  • Another factor that affects solar battery sizing is the amount of power you will be needing for all of your appliances. If your appliances require many watts (power), you'll need enough batteries to store the power so you can use those appliances.
  • Another factor that affects the size of your battery bank is the amount of volts your solar system produces. If your system produces 48 volts, then you're going to want to have enough batteries in your battery bank to store 48 volts. Actually a little less is better - like a 36 volt system with a 24 volt battery bank, just to be sure your system can charge the battery bank even in the case of a sudden voltage drop. When sizing a battery bank, always size your solar panels bigger than your battery bank to be able to compensate for factors such as voltage drop, power fluctuations and energy loss due to wear on the system.
  • To charge a battery, a generating device must apply a higher voltage than already exists within the battery. That's why most PV modules are made for 16-18V peak power point. A voltage drop greater than 5% will reduce this necessary voltage difference, and can reduce charge current to the battery by a much greater percentage. Our general recommendation here is to size for a 2-3% voltage drop. So for a 12 volt battery bank, a 16-18V solar panel should be used to allow for unexpected voltage drop.
  • Another important consideration when sizing a battery bank is the storage capacity you will need your battery bank to have. If your area gets less hours of sunlight in the day, you're going to want more batteries so you can store more "amp hours" of power in your reservoir and last out the long night's stretch. When sizing a battery bank, the more amp hours you have the longer your total power reserve would take to deplete.
  • When doing solar battery sizing, you must also take into account the rate of discharge you want to have. Remember, the slower your batteries can discharge the more hours you'll get out of them. You can find out a battery's rate of discharge by looking at it and finding the value marked: (C-?). If you see (C-10) then this means the battery takes 10 hours to discharge fully, if it's (C-5) then the battery takes 5 hours to discharge fully.
  • Lastly, when sizing a battery bank, you must consider the depth of discharge you want to go to before recharging. (This is decided by your specific power needs / capacity and affects the battery's lifespan).

Basically, the bigger your batteries are and the more batteries you have, the more convenient it is for you and the better it is for your batteries' health. This is due to the fact that with more batteries / storage capacity you will have more power available, plus you will be discharging your battery bank in smaller (more shallow) cycles and thus increasing it's overall lifespan.

 What DOD (Depth of Depletion) is right for me?
Generally when asking for a quote from a service provider they will provide you with a 50% DOD quote, this means that you will only ever use half of your battery. The reason for this is based around the number of duty cycles available to each battery. The deeper you cycle (use) your battery the few cycles are available for use and the thus the shorter the time the batteries will last. As a minimum we use a 50% DOD but should you want longer life out of your batteries we also allow for a 30% option, meaning that you will only ever use 30% of your battery. Going with a 30% DOD costs more in terms of number of batteries but ultimately will allow more years of operation.

Days of store?
Batteries are crazy expensive. They are the achilles heel of a solar system. Wherever possible, use only exactly what you need. Having an extra day or two storage is nice but costly so bear that in mind. In a nutshell should you have days of poor generation (solar) and do not have Eskom as a backup for battery charging then adding additional days of store is a worthwhile consideration.

Determining a Battery's Storage Capacity

An important part of solar battery sizing is determining the storage capacity, so you know how long you can use it for.

Sizing a Battery Bank - Watt Hours

Let's say you go out and buy a battery for your solar system that is 12 volts (push) and 105 amp hours (storage capacity).

You could find out approximately how much energy this battery will store / provide by calculating the watt hours. To do this, just multiply the volts (V) x the amp hours (AH) and divide by 100.

Volts x Amp Hours / 100 = Watt Hours

12V x 105AH = 1260 / 100 = 12.6 Watt Hours

What this means is that you can power a 100 watt appliance for 12.6 hours on a fully charged battery.

Make sure you find out what the specs on your batteries are before buying them. By knowing what to look for and what each spec means, you can insure your solar project's battery bank operates smoothly, efficiently and free of costly "battery bank sizing" mistakes.

Battery Life Expectancy

One thing you want to pay close attention to when solar battery sizing is how long the batteries you buy will last. The life expectancy of a sealed lead acid battery is rated using the number of cycles that battery can perform.

The "number of cycles" refers to the number of times the battery can be charged and discharged before it's dead.

So if your battery is a 3000 cycle battery, this means it can be charged and discharged 3000 times before it dies, that is providing it is consistently charged correctly and not discharged past acceptable levels. Batteries are considered to be at the end of their lifespan when 20% of their original capacity is gone.

Solar panel requirements and batteries?

In as far as possible, use as few panels or batteries as possible to make up the required output/storage.

Battery Chargers

What is a solar charge controller?
A charge controller or charge regulator is basically a voltage and/or current regulator to keep batteries from overcharging. It regulates the voltage and current coming from the solar panels going to the battery.

Difference between MPPT charge controller and PWM charge controller?
The most recent and best type of solar charge controller is called Maximum Power Point Tracking or MPPTMPPT controllers are basically able to convert excess voltage into amperage. ... With a PWM charge controller used with 12v batteries, the voltage from the solar panel to the charge controller typically has to be 18v.

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Solar Geyser Systems

How Exactly Do Solar Water Geysers Work?
Just like any other big purchases made for your home, it’s important when buying a solar geyser that you understand what you’re paying for, and how it will benefit you in the long run.

Did you know that solar geysers rely on more than just sunlight?

Or how its internal workings assist with producing the warm water you use for your home?

For those who are considering a solar water geyser, click here for a brief guide to how it works. Understanding how solar water geysers work can help you with decision-making. Remember, like any purchase, you got to weigh up the pros and cons before installing a solar water geyser.

What is water heating system?
The water heating system  makes use of photovoltaic technology and a unique PTC AC/DC element to heat water in the geyser. This differs from the traditional thermal hot water systems where water is cycled from a collector through pipes to the hot water cylinder by either making use of a 220V pump, 12V pump or through a natural thermo-siphoning process. By making use of PV panels that produces DC power to heat the water (instead of circulating water through pipes) a lot of the problems with traditional solar water heating systems are eliminated.

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Accessories

What Cables do you use for Solar Systems?
Aluminum or Copper: The two common conductor materials used in residential and commercial solar installations are copper and aluminum.

Solid or Stranded: The cable could be solid or stranded, where stranded wires consist of many small wires that allow wire to be flexible.

What is a solar-powered pump?
solar-powered pump is a pump running on electricity generated by Solar panels or the radiated thermal energy available from collected sunlight as opposed to grid electricity or diesel run water pumps. The operation of solar powered pumps is more economical mainly due to the lower operation and maintenance costs and has less environmental impact than pumps powered by an internal combustion engine (ICE). Solar pumps are useful where grid electricity is unavailable and alternative sources (in particular wind) do not provide sufficient energy.

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If you have any questions, or would like some additions to this information please drop us a mail at sifiso@solaretc.co.za

 

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