Quick Guide To Solar System Sizing

Introduction

Effective solar energy designs and system sizing brings about lasting and efficient solar energy installation and energy usage of a household or business environment. Non-conformity with the standardised system designed steps and requirements will make such solar energy installation to fail, resulting in poor performance and poor enegy output that will not beneficial for the owner. This may even cause fire outbreak that can engulf the entire installation site. However, if proper design and system sizing guidelines are strictly adhered according to the owners daily enegy needs, not only the system performance would be excellent, all the important components parts - panel, battery, charge controller, inverter, and wire for example of such solar energy would be protected. In this article we will explain in details what solar system sizing is, and a project example will be brought to focus to elaborate how to size your solar energy components for that given example. Please ensure you read Solar Power Simplified: A Guide to Perfecting Your Energy Installation article before your system sizing for your installation begins.

How To Size Solar Energy Components

Solar Energy system sizing are done with carefully determine energy usage of a particular owner. When daily energy usage is determined, then comes the next step, which is component sizing, such as:

solar panel
Battery
Charge Controller
Inverter
Wire

Here’s a comprehensive overview:

1. Assessing Energy Need

Analyze Energy Consumption: Review past electricity bills to determine average monthly usage (kWh), or determine total amount of energy needed if your system would be stand-alone (off-grid) solar system.
Future Projections: Consider any future increases in energy needs, like new appliances. This means there should be an addition of certain percentage of wattage on top of your total estimated energy needed. If for example your estimated energy requirement is 1kw, you may want to add another 200 watts to make it 1.2kw. This addition of 200 watts will take care of any future increase in household appliance you may purchase.

System Sizing

There are several number of methods for sizing components for solar energy installation - solar panels, batteries, charge controllers, inverters, and wires. For effective system sizing to take place, you need to know the size which your solar project requires, first you must know the total daily energy usage for your property. This is express in watt-hour (Wh), meaning that you need to calculate daily energy consumption of all loads in your household. If your loads (TV, fan, electric bulb, radio etc) total energy consumption is 1000 watts/h per day for example, this will form the basis for your design and system sizing. Below are the guideline and steps for your solar energy design and installation

1. Solar Panel

Energy harvester in the solar energy project is the solar panel, it is this panel that gets energy from the sunlight, before it is transported to various household appliances. To know the solar panel size and number of panels required for your project, follow this steps below:

step 1. multiply the total load's watt-hour per day by factor of 1.3, hence 1000 watts x 1.3 in our example above, this gives us 1300 watts or 1.3kwh expected from the panel
step 2. divide the number you get in step 1 above (1.3kwh) by the panel generation factor for your solar energy installation location. Panel generation factor differs from geographical location to the other, in the tropical region - Africa for example, common factor generation in most places is 3.41. So, divided 1300W by 3.41 to give you the peak-watt (Wp) for the solar panel. The formular is:

Wp =

1300 watts

3.41

400

Step 3: To know the number of panels reqire is simple. Solar modules are available in 12 volts and different power ratings (100w, 200w, 300w etc), at this point, divide what you get in step 2 by the power rating of the solar module in yor local market. That gives you the number of solar panels needed for your project. In the above example, let us take 200w panel as panel available to us in the market, that means 400w/200w; that gives us 2 panels.

Note! if your division resulted in fraction, you have to round it up to the nearest whole number. For example if your answer is 4.3 panels, 5 panels would be used.

Battery sizing

To size appropiriate battery bank capacity for you system, following factors should be considered:

System voltage: The overall system voltage must first be considered. Ensure that the chosen system voltage ryme across all the components - panel, battery, caharge controller and inverter must be on te same voltage in the design system.
Battery efficiency: most batteries have about 85-90% working efficiency while some low quality have lesser.
Depth of discharge: depth of discharge is allowable maximum percentage of full rated capacity of the battery that can be withdrawn before the next charge cycle takes place. For lead acid battery, the allowable depth of discharge is put at 80% , and lifePo4 battery can be completely drained.
Days of authonomy: This refers to the number of days there would be no sunshine to charge the battery by the solar panel, typically, three days are set for this on the minimum.

Now, follow the following steps to size the battery bank for your system:

Sstep 1:calculate total watt-hour of the load needed to be powered (1kw in our example).
Sstep 2:multiply what you get in step 1 by the set days of autonomous. Usually this is set between 3 - 5 days, let's take two days for our example. That will give us 2kw
Sstep 3: Devide what you get in step 2 by 0.85 x 0.6 x 12 (loss in the battery, depth of discharge, and system voltage respectively). This will give us

battery capacity =

1000w x 2

0.85 x 0.6 x 12

This will give us 3266.79A. Remember that solar batteries do not exist in fraction, hence you need to round it up to the next whole number. That means 400A battery will surfix.

Note! If your answer in step 3 ends up in decimal fraction, it must be rounded up to the nearest whole number. This is because solar batteries amps are always in whole number eg. 50ah, 100ah, and so on.

Charge Controller Sizing

The function of the charge controller in the system is to charge the battery bank and protect the attached batteries from being over-charged, also prevents the reverse charging in the system. Reverse charging is a situation whereby the battery is trying to send stored enegy back to the panel. There are two types of solar charge controller - Pulse Width Modulation (PWM) and Maximum Power Point Tracking (MPPT), choice of solar charge controller is strictly dependent on the size of the solar project on ground. For a small solar project, PWM is suggested while a solar big project applauses MPPT carge controler.

Charge controller capacity specification depends largely on the specification of the solar panel you are using for the project. To size your charge controller, please pay attention to this! Amongst the solar specification data is the "short circuit current" (Isc), Ise rating of your panel is taken and multiply by the fraction of 1.3. The result of this calculation gives you the size of the charge controller to be used. If your panels's Isc rating is 7.5A for example, your chosen charge controller should be 7.5 x 1.3 which is 9.75A. So 10 amps solar charge controller should sufix for this project.

Note! If your panel is more than 1, you will have to multiply the number of your panel by the panel's Isc rating, then multiply the result by the fraction of 1.3 to give you the correct amperage for the charge controller capacty to be used. Note also that, this assumes that your panels are connected in parallel configuration. For example, you have two panels wired in parallel, and each of them has Isc of 7.5A, that means (7.5 x 2) x 1.3; which is 19.5A. In this case, 20A charge controller will be ok.

Inverter Sizing

Inverter is the heart of the solar power system. It inverts energy from low voltage to a much more desired high voltage according to the need in the solar energy project on the ground. The direct current (DC) of the battery, usually from 12v is converted to as much as 220 - 240 volts alternating current (AC) which most electric appliances need to operate. So sizing of the inverter is critical in any on-going solar energy design project. Now, to estimate the required inverter size, all you need do is to add up the total power of all appliances to be powered up by the solar project and multiply it by 1.3 (1.3 being the safety margin which can also takes care of the low power consumption appliances that may be plugged onto the system later on). Assuming the total power required by all appliances is 1000 watts, that means 1000w x 1.3, the inverter capacity is 1.3kw or 1625VA.

Note! You can also size your inverter just by the total wattage of all appliances to be used at once. However, this system is not recommended because it doesn't give room for future expansion in the system.

Wire Sizing

Refer to the American Wire Gauge (AWG) chart to select the appropriate wire size based on current carrying capacity, acceptable voltage drop and distance of your panels from all other components.

Note! You should provide for not more than 3% voltage drop in the sizing of the cable to be used. In fact it would be excellent if the voltage drop is less than 3%.

Conclusion

As a well-designed and installed solar energy system can significantly reduce energy costs and contribute to sustainability, carefully sizing each component ensures optimal performance, enhances the system's effectiveness and longevity of the solar energy system. Always consult with a professional solar installer for specific requirements to avail your property solar project the above aformentioned opportunity.