A Simple, But Valuable DIY Method People Should Know !!
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Do you know that you can cause yourself loads of problems if you buy the wrong size of electricity generator? This is exactly what happened to my friend. He wasted twelve million (₦12,000,000) to buy a 30 KVA diesel engine generator instead of a 15 KVA generator that should cost about five million (₦5,000,000) Naira. This is absolutely financial recklessness.
His problem started when he hired a contractor to install a generator for him. The contractor turned out to be dubious; he recommended a 30 KVA generator for his selfish motives. The commission for any purchase was 10%, meaning, the higher the price of the product purchased, the higher his commission. So, the contractor recommended a 30 KVA generator instead of 15 KVA.
Apart from financial loss due to the high cost of purchase, three more embarrassing issues occurred:- Firstly, the generator was underutilised because after switching on the essential loads, it wasn't up to 20% of the rated capacity. This is not good for the engine as it results in incomplete combustion of the fuel (diesel). Running a diesel generator continuously below about 30% load can also lead to wet stacking, carbon deposits, smoky exhaust and reduced engine life. Secondly, it leads to high cost of maintenance; more money is needed to service a 30 KVA generator than a 15 KVA (considering the cost of filters, lubricants, etcetera). Thirdly, A 30 KVA generator generally consumes significantly more diesel than a 15 KVA, especially when operating under very light load, where fuel efficiency drops considerably.
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ANYBODY CAN SIZE A GENERATOR: For a non-Engineer, the easiest way to determine required fossil-fuel generator or solar system size is to set aside technical terms like watts, amps, and electrical formulae. What should be considered is, "what appliances will be 'ON' at the same time". The secret is, a generator (fossil-fuel or solar inverter) only needs to carry the appliances you are using simultaneously.
Let me use the appliances in my friend's home to demonstrate how anybody can size a generator easily; below is a simple method anyone can use, step-by-step. I prefer to call it “a DIY" action.
STEP 1: WRITE DOWN THE APPLIANCES: (1) LED bulbs (10) (2) Ceiling fans (4) (3) Standing fans (1) (4) Fridge (1) (5) Washing machine (1) (6) Borehole pump (1) (7) Electric cooker (1) (8) Split AC (2)
STEP 2: GET ESTIMATED VALUES FOR VARIOUS APPLIANCES (1) LED bulbs:10 Watts (2) Ceiling fans: 70 Watts (3) Standing fans: 70 Watts (4) Fridge: 250 Watts (5) Washing machine: 800 Watts (6) Borehole pump: 1000 Watts (7) Electric cooker: 2000 Watts (8) Split AC: 1500 Watts
STEP 3: CALCULATE TOTAL LOAD IN WATTS
(1) LED bulbs: (10×10)=100 Watts (2) Ceiling fans: (4×70)=280 Watts (3) Standing fans: (1×70)=70 Watts (4) Fridge: (1×250)=250 Watts (5) Washing machine: (1×800)= 800 Watts (6) Borehole pump: (1×1000)=1000 Watts (7) Electric cooker: (1×2000)=2000 Watts (8) Split AC: (2×1500)=3000 Watts Total: 7500 Watts
The wattages used here are average household estimates intended for quick planning. Actual appliance ratings should always be checked on the manufacturer's nameplate before making a final purchase.
STEP 3: ADD 25–30% EXTRA: Best practice is to buy a generator or solar inverter larger than total estimated load; this enables the generator to handle starting surge current of inductive loads like fridges, pumps and air conditioners, which ranges between 2 to 3 times the running current. It also takes care of future additions. In this case, 30% of 7500 is 2250 and total load is (7500+2250)=9750 Watts.
Alternating current (AC) generators are rated in Kilovolt-Amperes (not Kilowatts); to get Kilovolt-Amperes, Kilowatts is divided by power factor (usually 0.8). Hence, generator size needed is (9750÷0.8)=12188 Volt-Ampere (approximately 12 KVA).
The calculation shows that my friend needed about 10 KW of usable power. A standard 15 KVA generator provides adequate reserve capacity, which proves that installing a 30 KVA generator was unnecessary.
Based on the sizing outcome, my friend contacted the generator dealers and exchanged the 30 KVA for 15 KVA. He paid some charges for the swap and got a refund too, recovering about 50% of initial cost. Now, the generator is performing well, his maintenance and running costs have also reduced drastically. The generator will also have a longer lifespan because there's higher efficiency due to complete combustion of the fuel and adequate load carried.
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If you want to size a solar generator, you use a similar method to determine the right capacity of the inverter. However, special attention is given to the arrangement of solar panels to ensure the battery bank is properly charged; the battery bank is also professionally designed to ensure that the system performs efficiently when the sun isn't shining.
DISCLAIMER: The calculations presented in this article are intended to help homeowners estimate generator size. They are not a substitute for a detailed engineering design, especially for commercial buildings or complex electrical installations. Thanks for reading my article; your response or opinion will be highly appreciated.
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Author's note:- As a retired engineering technologist with years of experience in electrical systems, I enjoy simplifying technical concepts so that ordinary homeowners can make informed decisions and avoid costly mistakes.
