Solar Panels

It is possible that most of us believe that solar energy is the way forward. Certainly there are many major manufacturers who contribute to this idea.

It is also possible that most of us just think you can get a solar panel, or more, and just plug them into the house’s electrical supply point.

Solar panels produce DC (Direct Current). This is the same current that you get from your batteries and what Edison proposed for the grid system in cities. It is not efficient to distribute DC over a large area – the losses in the system are too high.

Your house uses Tesla’s AC (Alternating Current) system. This is more appropriate for large-scale distribution. Losses still occur, of course, but it is still better than DC.

DC current is pretty much a straight line on a graph but AC follows a sine curve where the charge reverses fifty or sixty times a second depending on where you live.

Alternating Current

Somehow you will have to change DC into AC so that your household appliances and your computer will understand it.

The first thing to look at is what equipment you will need to run your house.

Major system components

Solar PV system includes different components that should be selected according to your system type, site location and applications. The major components for solar PV system are solar charge controller, inverter, battery bank, auxiliary energy sources and loads (appliances).

The solar panel is known as a ‘PV Module’. It is what converts sunlight into DC electricity.

Solar Panels in Australia

Then you need something that will control how much electricity is being produced. That is a ‘Solar Charge Controller’. The purpose to this is to regulate the current coming from the panels that is going into the battery(ies). This prevents the battery(ies) overcharging thus extending battery life.

Solar Charge Controller
(This one is about USD27 - USD30)

The battery, or batteries, will store unused electricity to supply appliances when there is a demand but limited supply, at night, for example.

Battery
You will need more than one that are connected in parallel

To convert DC into AC you will install an inverter. In the old days it was like a small alternator that spun by being driven by the DC but now we have static inverters that are solid state so they do not spin – no moving parts. The electricity can now be put back into the gridline or sent into your house to drive the TV.

Inverter
This is a solid state inverter

When we consider the ‘Load’ we are thinking about how much each appliance will consume at any given time. It will be necessary to calculate this so that the solar panels match the need in your house without spending too much on huge levels of equipment that are unnecessary - or having an inadequate supply. The ‘Load’ might be a ‘Fridge/Freezer. TV, Computer, Washing Machine, Lights, Fan, Air Conditioning, etc.

It will also be necessary to have a back-up system that might be a diesel generator or some other renewable energy source – like a wind generator*.

*Beware of wind generators. These look like a big fan that are spun by the wind and drive a generator. Many have fixed blades and so they operate with varying speed depending on wind strength. In high winds they can overproduce electricity, burn out and leave you with a hefty replacement bill. Try for a generator that has rpm (revolutions per minute) control on the blade angles so that they run at a fixed rpm.

Variable Pitch Wind Generator
This is a 5KW so is quite big = expensive

Now we need to refer to your local expert. The reason for this is that the PV (Solar Panel) has an output that will vary widely depending on its size and the location. Thailand, Malaysia and Singapore will have a different rating to Northern Europe or Canada. Thailand, Malaysia and Singapore have a Power Generation Factor of 3.43.

You will need to calculate the total peak power wattage (power requirement) at any time during the day.

This will also affect the Solar Charge Controller requirement. The Solar Charge Controller will need to have a greater capacity than the PV input. That is easily done by multiplying the PV Isc (short circuit current) output by 1.3.

The Solar Charge Controller will also need to match the battery(ies).

The battery type recommended for using in solar PV system is deep cycle battery. A deep cycle battery is specifically designed to be discharged to low energy level and rapidly recharged (or cycle charged and discharged) day after day for years. The battery(ies) should be large enough to store sufficient energy to operate the appliances at night and cloudy days. To find out the size of battery, calculate as follows:

1 Calculate total Watt-hours per day used by appliances.
2 Divide the total Watt-hours per day used by 0.85 for battery loss.
3 Divide the answer obtained in item 4.2 by 0.6 for depth of discharge.
4 Divide the answer obtained in item 4.3 by the nominal battery voltage (usually 12V).
5 Multiply the answer obtained in item 4.4 with days of autonomy (the number of days that you need the system to operate when there is no power produced by PV panels) to get the required Ampere-hour capacity of deep-cycle battery.

Battery Capacity (Ah) = Total Watt-hours per day used by appliances x Days of autonomy**
(0.85 x 0.6 x nominal battery voltage)

**Autonomy = the time when the battery(ies) is(are) running the appliances on its(their) own. 

Let’s look at the whole system piece by piece.

Example:

You have, typically, the following Appliances

1 x 18Watt (W) fluorescent lamp that has electronic ballast and you run it for 4 hours every day.

1 x 60W ceiling fan used for 2 hours every day.

1 x 75W refrigerator with compressor that runs 24 hours per day – 12 hours on and 12 hours off.

Your PV Module is 12VDC at 110Wp (Peak Watts)

In order to determine your power requirements we will need the total appliance use:

Total Usage       = (18W x 4Hrs) + (60W x 2Hrs) + (75W x 0.5Hrs)

                           = 1,092 Wh¹/Day

Total PV Panels Energy Needed

= 1,092 x 1.3 (Remember that Isc?)

=1,419.6 Wh/day 

¹Wh = Watt Hours

To size the panels you need we do this:

NB: In Malaysia the Panel Generation Factor is 3.43 (see above)

Total Wp of PV panel required   = 1,419.6 / 3.43

                                                      = 413.87

Number of Panels required        = 413.87 / 110

                                                      = 3.76 modules

Since it is hard to get 0.76 modules it is suggested that you need 4 x 110Wp PV modules.

To get the right size of inverter you will need to do this:

Total Wattage of all appliances = 18 + 60 + 75W

                                                      = 153W

You need an inverter bigger than this for reliability and safety. Multiply the need by 25% to 30%.

Inverter size required is about 190W or greater.

Battery?

Total Appliances use 

= (18W x 4 Hrs) + (60W x 2Hrs) + (75W x 12Hrs)

Nominal Battery Voltage   

= 12V

Days of autonomy (dependence on the Battery) 

=  3 days

Battery Capacity =

[(18W x 4 Hrs) + (60W x 2Hrs) + (75W x 12Hrs)] x 3

(0.85 Battery Loss x 0.6 Depth of Discharge x 12V)

Total Ampere-Hours required = 535.29 Ah

This means that the battery should be rated at: 

12V 600 Ah for 3-day autonomy.

Solar Charge Controller sizing:

PV Module specification   = Pm 110 Wp

         Module Voltage                  = Vm 16.7VDC 

         Module Current        = Im 6.6A

      Open Circuit Voltage   = Voc 20.7A

    Short Circuit Current    = Isc 7.5A

Solar Charge Controller Rating

                  = (4 x Panels (strings) x 7.5A) x 1.3

                                                                                                                                                = 39A

The Solar Charge Controller needs to be rated at:

40A at 12V or greater.

A System 

A Typical Home System
To add to the grid there are more components required.

Daunting? It is a bit. But remember that, armed with this information, you will now be better able to discuss your needs with the local installers without being intimidated or held to ransom by someone telling you to buy more than you need.

Of course, buying surplus power is fine if you want to earn money by feeding it back into the grid but, generally speaking, you are best just running your house and giving back the odd dribble.

Now you see that buying solar panels is not a simple ‘plug’n’play’ system. 

Sorry.