komuw · July 23, 2025 06:34 · komuw · Feb 24, 2025 · komuw · Jul 22, 2025
diff --git a/price_of_solar_panel.py b/price_of_solar_panel.py
 # How many units of KPLC do you use per month?
 # Go to https://www.stimatracker.com/, click on `prepaid`, then enter amount in KES you use per month.
 # Click `calculate`, it will give you your consumption in kwh. Mine is KES 5000, which give ~150kwh

 monthly_kplc_cost = 5000 # KES
 price_per_kwh = 33 # kes per unit
 consumption_per_month = int(monthly_kplc_cost/price_per_kwh) # kWh 
 assert consumption_per_month == 151 # kwh
 consumption_per_month = 150 * 1000 # watt-hours

 solar_panel_rating_in_watts = 545 # Watts.  eg; https://shop.davisandshirtliff.com/products/dayliff-545w-monocrystalline-solar-module
 price_per_panel = 10_085           # KES,  eg; https://shop.davisandshirtliff.com/products/dayliff-545w-monocrystalline-solar-module
 # Monocrystalline panels are generally more efficient than polycrystalline

 number_of_hrs_of_sunlight = 5 #hours. 
 # for number_of_hrs_of_sunlight, various meteorological orgs can give you the exact value. But you can also just approximate based on you having lived in the region.
 # It is important to use the average number of hours for a bad month(like july) in this calculation. ie, use worst case scenario.
 # It is also important to note that sio jua kali pekee. Solar panels will also generate power when there's light but no sun.
 # You can use https://footprinthero.com/peak-sun-hours-calculator to calculate number of sunlight hours.
 # For example, that website says that for `sarit center in westlands`, peak solar is 6hrs in February and lowest is 4hrs in July.


 # 15/100 # ie, 15%. Most residential panels are in between 13% to 22%. Check specification before buying.
 # Note that this efficiency is different from the solar-panel-cell efficiency. That one is about 13%-22%.
 # That one is about how well a panel can convert sunlight to electricity. 
 # However when a manufaturer rates a panel 120W, they've already factored in solar-panel-cell efficiency.
 # The efficiency here is to take into account losses due to wires connections, battery inefficiency etc.
 solar_panel_efficiency = 80/100 
 monthly_energy_production_of_solar_panel = (solar_panel_rating_in_watts * number_of_hrs_of_sunlight * solar_panel_efficiency) * 30
 assert monthly_energy_production_of_solar_panel == 65_400 # watt-hours

 number_of_solar_panels_required = int(consumption_per_month/monthly_energy_production_of_solar_panel) + 1 # plus one to roundup 
 assert number_of_solar_panels_required == 3

 total_price_of_solar_panels  = number_of_solar_panels_required * price_per_panel  
 # Remember to add price of inverter, labour, cables, etc. But the price of solar panels is the main one.
 assert total_price_of_solar_panels == 30_255 # kes

 # Assuming usage is spread evenly btwn day and night.
 consumption_per_day = consumption_per_month/30
 assert consumption_per_day == 5_000 # watt-hours
 consumption_per_night = consumption_per_day/2
 assert consumption_per_night == 2500 # watt-hours

 # Lithium-ion (LiFePO4) batteries, you can safely discharge them much deeper, often up to 80-90%.
 battery_discharge = 80/100 # percentage
 inverter_efficiency = 90/100 # percentage
 battery_capacity_wh = int(consumption_per_night / ( battery_discharge*inverter_efficiency) )
 assert battery_capacity_wh == 3_472 # watt-hours

 # If we go for a 48V battery system, the required Amp-hours (Ah) would be:
 battery_capacity_ah = int(battery_capacity_wh/48)
 assert battery_capacity_ah == 72 # Ah

 # https://shop.davisandshirtliff.com/products/dayliff-75ah-48v-lifepo4-lithium-ion-battery-c-w-bms?_pos=2&_sid=66848d22b&_ss=r
 battery_price = 140_000 # kes 


 # You need an inverter that can handle your peak instantaneous power consumption.
 # ie, maximum amount of electricity your home demands at any single moment. When all the appliances are on.
 # Sum the watt rating of those appliances. Tv(100w) + Microwave(2000w), etc = 3000W
 peak_consumption = 5_000 # watt

 # https://shop.davisandshirtliff.com/products/sunny-island-master-si6h-12-6kw-battery-inverter?_pos=10&_sid=9042e36a4&_ss=r
 # That inverter is rated 6000W(6kw)
 inverter_price = 177_350 # kes


 total_price = total_price_of_solar_panels + battery_price + inverter_price
 assert total_price == 347_605
 number_of_years_to_break_even = int(total_price/monthly_kplc_cost)/12
 assert number_of_years_to_break_even == 5.75
	# How many units of KPLC do you use per month?
	# Go to https://www.stimatracker.com/, click on `prepaid`, then enter amount in KES you use per month.
	# Click `calculate`, it will give you your consumption in kwh. Mine is KES 5000, which give ~150kwh

	monthly_kplc_cost = 5000 # KES
	price_per_kwh = 33 # kes per unit
	consumption_per_month = int(monthly_kplc_cost/price_per_kwh) # kWh
	assert consumption_per_month == 151 # kwh
	consumption_per_month = 150 * 1000 # watt-hours

	solar_panel_rating_in_watts = 545 # Watts. eg; https://shop.davisandshirtliff.com/products/dayliff-545w-monocrystalline-solar-module
	price_per_panel = 10_085 # KES, eg; https://shop.davisandshirtliff.com/products/dayliff-545w-monocrystalline-solar-module
	# Monocrystalline panels are generally more efficient than polycrystalline

	number_of_hrs_of_sunlight = 5 #hours.
	# for number_of_hrs_of_sunlight, various meteorological orgs can give you the exact value. But you can also just approximate based on you having lived in the region.
	# It is important to use the average number of hours for a bad month(like july) in this calculation. ie, use worst case scenario.
	# It is also important to note that sio jua kali pekee. Solar panels will also generate power when there's light but no sun.
	# You can use https://footprinthero.com/peak-sun-hours-calculator to calculate number of sunlight hours.
	# For example, that website says that for `sarit center in westlands`, peak solar is 6hrs in February and lowest is 4hrs in July.


	# 15/100 # ie, 15%. Most residential panels are in between 13% to 22%. Check specification before buying.
	# Note that this efficiency is different from the solar-panel-cell efficiency. That one is about 13%-22%.
	# That one is about how well a panel can convert sunlight to electricity.
	# However when a manufaturer rates a panel 120W, they've already factored in solar-panel-cell efficiency.
	# The efficiency here is to take into account losses due to wires connections, battery inefficiency etc.
	solar_panel_efficiency = 80/100
	monthly_energy_production_of_solar_panel = (solar_panel_rating_in_watts * number_of_hrs_of_sunlight * solar_panel_efficiency) * 30
	assert monthly_energy_production_of_solar_panel == 65_400 # watt-hours

	number_of_solar_panels_required = int(consumption_per_month/monthly_energy_production_of_solar_panel) + 1 # plus one to roundup
	assert number_of_solar_panels_required == 3

	total_price_of_solar_panels = number_of_solar_panels_required * price_per_panel
	# Remember to add price of inverter, labour, cables, etc. But the price of solar panels is the main one.
	assert total_price_of_solar_panels == 30_255 # kes

	# Assuming usage is spread evenly btwn day and night.
	consumption_per_day = consumption_per_month/30
	assert consumption_per_day == 5_000 # watt-hours
	consumption_per_night = consumption_per_day/2
	assert consumption_per_night == 2500 # watt-hours

	# Lithium-ion (LiFePO4) batteries, you can safely discharge them much deeper, often up to 80-90%.
	battery_discharge = 80/100 # percentage
	inverter_efficiency = 90/100 # percentage
	battery_capacity_wh = int(consumption_per_night / ( battery_discharge*inverter_efficiency) )
	assert battery_capacity_wh == 3_472 # watt-hours

	# If we go for a 48V battery system, the required Amp-hours (Ah) would be:
	battery_capacity_ah = int(battery_capacity_wh/48)
	assert battery_capacity_ah == 72 # Ah

	# https://shop.davisandshirtliff.com/products/dayliff-75ah-48v-lifepo4-lithium-ion-battery-c-w-bms?_pos=2&_sid=66848d22b&_ss=r
	battery_price = 140_000 # kes


	# You need an inverter that can handle your peak instantaneous power consumption.
	# ie, maximum amount of electricity your home demands at any single moment. When all the appliances are on.
	# Sum the watt rating of those appliances. Tv(100w) + Microwave(2000w), etc = 3000W
	peak_consumption = 5_000 # watt

	# https://shop.davisandshirtliff.com/products/sunny-island-master-si6h-12-6kw-battery-inverter?_pos=10&_sid=9042e36a4&_ss=r
	# That inverter is rated 6000W(6kw)
	inverter_price = 177_350 # kes


	total_price = total_price_of_solar_panels + battery_price + inverter_price
	assert total_price == 347_605
	number_of_years_to_break_even = int(total_price/monthly_kplc_cost)/12
	assert number_of_years_to_break_even == 5.75