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Solar System Sizing Tool & Calculator

Solar System Sizing Tool & Calculator

The following tool is intended to assist users to calculate a size of an entry-level solar system for home use, which includes the solar panels, inverter, batteries and user load. Products listed and its information is that of The Sun Pays solar products. The tool utilizes product information such as efficiencies in order to give a more realistic solar system design.

Disclaimer: The tool is intended to be used as a guide. The Sun Pays can not be held responsible for the outcome of the results of the tool. It is still the end-user's responsibility to confirm if the selected equipment will be suitable for the user's needs or to obtain professional help from accredited installers.

Feedback: The solar sizing calculator is still a work in progress. At the current stage, the solar sizing calculator is only for 48V solar systems. For requests and feedback, please contact us.

How to use the tool:
Step 1: Fill in the user load. A list of common items is provided. Choose the number of hours the items in used in the day and night
Step 2:Choose the battery type and configuration.
Step 3 A: Choose the solar panel configuration. The panel configuration will be the panels in series and how many series arrays will there be in parallel.
Step 3 B: Choose the type of solar panels.
Step 4: Choose the inverter type.
Step 5: Review the feedback and make changes to the system setup if required.

Solar System Block Diagram

Step 1: Power and Energy usage:

The power and energy usage is very important to determine the correct battery size. For this solar sizing tool, three methods are available:
Input Power Usage in R (Rands used per month) : Input your monthly electricity bill. This method is faster, but less accurate.
Input Power Usage in kW.h (units used per month) : Input your monthly electricity consumption in kW.h. Also select how much is used during night time
Accurate Method : Input appliance information (hours used per day). This method is recommended

Input power use in Rands:
Please input your monthly electricity bill (electricity portion only, VAT included): R (City of Tshwane 2026/2027)
Does this amount include your electric geyser :

Day Time Energy Usage (i.e. will be taken directly from solar panels): kW.h

Night Time Energy Usage (i.e. what needs to be stored in a battery) : kW.h

Load Instant Power requirement
Green = Inverter Power
Red = Bypass mode

Day Time Energy Consumption
Green = Battery charge + Load on solar
Red = Battery charge + Load on bypass

Night Time Energy Consumption
Green = Battery storage
Red = Bypass mode

For steps 2 to 4, the hardware (batteries, solar panels and inverter) needs to be chosen. You can either manually choose items or click the "Help me Choose!" button below

Step 2: Batteries and configuration:





  • Anciliary items:
  • Battery Cable 35mm2 with lugs
  • 125A DC Breaker Double Pole

Step3A: Solar Panel configuration:


Total number of panels =
Solar panels mounted @ 28° angle, facing North.

Step 3B: Type of panels used:


Summer
Winter
  • Accessory items:
  • MC4 single connectors:
  • MC4 parallel connectors:
  • MC4 inline fuse:
  • Solar cable (Black + Red in meter):
  • Anti-theft Clips:
  • P2000 Rail:
  • Mounting brackets:
  • Select Roof Type:

Step 4: Inverter:


Solar Array Working Voltage
Stay in Green Zone

Solar Array Open Circuit Voltage
Stay in Green Zone
May go to Yellow Zone

Solar Array Power
Stay in Green Zone

Solar Energy Generated
Available for Day Time Load
and Battery Recharge

Step 5: Results

Result Message
Solar Array Info
Open Circuit Voltage:V
Maximum Power Voltage:V Upper Limit:
Lower Limit:
Maximum Power:W
Potential generated energy during day: kW.h
Generated energy used to charge battery for night time load: kW.h
Generated energy used to supply day load: kW.h
Remaining energy used to charge battery additionally (rainy/cloudy days): kW.h
Battery Information
Battery state of charge @ 4pm: %
Useable Capacity @ DoD: kW.h
Used Capacity : kW.h
Power required to recharge in 6 hours: W
Maximum Charge Current (set on inverter): A
Battery nominal voltage: V
Hours to drain battery at night: h
Inverter Information
Min PV voltage: V
Max PV voltage: V
Max PV oc voltage: V
Max PV array power: W
PV Charger efficiency: %
Inverter rated power output: watt
Utility supply information
Instantaneous Max. Load: watt
Utility energy required for day time load: kW.h
Utility energy required for night time load: kW.h
Monthly cost for day time load make-up: R
Monthly cost for night time load make-up: R
Monthly cost for day time load if no solar is installed: R
Monthly cost for night time load if no solar is installed: R
Monthly savings: R
Annual savings: R
Annual CO2 emission reduction: kg

Cost Estimate

  • Inverter(s) Cost:
    R
  • Solar Panels Cost:
    R
  • Batteries Cost:
    R
  • Ancillaries:
    R
  • Total:
    R

Please send me a quote!

If you would like to receive a quote on the above selected items, please fill in your details below and submit it to us:

Please note: this tool is indicative only. A formal quotation will be prepared in accordance with the latest products available.


Shop your system

Got your result? Pick the parts below, or send us your result and we'll put the system together for you.

Inverters Lithium batteries Solar panels Complete solar kits

WhatsApp messages only. To speak to us, call the office on 012 734 0915.

Frequently asked questions

What size solar system do I need?

Start with the power you use at night, because that has to come from batteries. Enter your appliances and hours in the calculator above, or your monthly bill in Rand or kWh. It then suggests a battery, solar panels and an inverter.

Which way of entering my usage is most accurate?

The appliance method, where you list each appliance and the hours it runs by day and by night. Entering your monthly bill in Rand or kWh is quicker but less accurate.

Does the calculator work for 12V or 24V systems?

Not yet. At the moment it sizes 48V solar systems only.

How does the calculator split day and night use?

It counts 10am to 4pm (6 hours) as solar time, when panels power your home directly. The other 18 hours must come from the batteries.

Can solar run my geyser, stove or aircon?

Big heating loads like a geyser or stove need a much larger system, so they are usually left on Eskom or a separate circuit. Inverter-type aircons use far less power than non-inverter ones, and the calculator lists both.

Is the calculator result final?

It is a guide. Send us your result on WhatsApp (messages only) and our technical team will check it, or ask an accredited installer to confirm.