How to Choose the Right Generator

Having a generator is essential for construction sites or when you need a backup power supply. A generator converts mechanical energy from an engine into electrical power to keep everything going as normal. If you're asking yourself how to choose the right generator, this article is for you. 

To choose the right size of generator, start by deciding which level of watts is required for all applications, types of generators to match your needs. Consider further factors such as noise levels, portability, legal requirements, and running costs. Keep reading our blog to find out what experts recommend for your needs. 

Types of Generators  

Generators work by converting movement into electricity. Inside a generator, a magnet moves around a coil or wire, which creates an electric current. This movement is powered by external energy sources such as diesel, petrol, natural gas, or solar power.   

Fuel Types 

The choice of fuel type should depend on running costs, performance, and usage conditions. 

LPG generators run on bottled gas or a bulk LPG supply. The advantages of LPG generators are lower emissions compared to other types, along with more silent operation. However, you need to check and replace LPG bottles frequently, and models often have slightly lower output than diesel-powered units.  

Diesel generators are the most common generators for hire, especially if you need a medium to large power size. They provide a stable, strong and reliable electricity supply for long run times, suitable for industrial use. However, diesel generators have a relatively louder noise level and higher emission rates.  

Petrol generators are often smaller and more portable units for DIY projects and household tools. However, they require higher fuel consumption and aren't ideal for long running periods.  

Battery generators store electricity in battery packs, which can be recharged. They are usually smaller and portable compared to other kinds of generators. This type is suitable if you want to have a small generator for home backup or have a low power demand. 

Solar-powered generators are the most eco-friendly generator units for outdoor projects and events. The battery storage is charged by solar panels to achieve zero emissions and silent operations. With this model, you can reduce fuel and running costs. As a result, power output is more limited, and the usage may depend on sunlight. 

Power Size  

Thinking about the size of the generator you need is important since your equipment won't start if the wattage is too small. The size of a generator is determined by the kVA-rated power. The higher the wattage (kVA), the more items a generator can supply power to at the same time.  

What Does kVA Mean on a Generator?  

In simple terms, kVA (kilovolt-amperes) on a generator is the total sum of electric power the generator can produce. This kVA rating can be converted into kW (kilowatts) by the power factor.  

kW = kVA × PF 

The power factor of a generator will be stated clearly with the model. For example, a 10 kVA generator with PF 0.8 provides about 8 kW of usable active power. Note that the choice of fuel won't affect the generator size you need. 

Small Generators (1kVA – 5kVA) 

Small generators are normally portable units with convenience and flexibility. They are often used in home and DIY projects to supply electricity for basic power tools or lighting.  

Medium Generators (6kVA – 20 kVA) 

You'll see medium generators more often at construction sites or events. They are powerful enough to supply the main power to bigger equipment, such as cement mixers, heaters, or multiple power tools at the same time.  

Large Generators (20kVA+) 

If you're hiring generators for construction sites, consider generators with 20kVA or above. This size of generator can provide backup power for buildings or in remote locations. Large generators can be used for heavy machinery, large lighting systems, or high-power tools.  

Single Phase vs Three Phase 

Single-phase generators use one electrical wave, meaning the power will rise and fall as it’s delivered to the equipment. We recommend single-phase generators if you only want to use generators for small devices such as lights, TVs, basic tools, or kitchen appliances.  

Three-phase, on the other hand, operates with three electrical waves to ensure a smooth and consistent flow of electricity through the appliances. Contractors and construction sites use this type of generator more often to run industrial plants, machinery, lifts, and large tools.  

How to Choose the Right Size of Generator for Your Project 

Here is a step-by-step guide to help you decide what size generator you need, with examples and best models recommended by Speedy. 

Step 1: Make a List of Equipment 

First, write down all the tools, appliances, or equipment you plan to use. These can be any electrical tools, depending on where you want to use them. Here are some examples: 

• Household appliances: lighting, heaters, household appliances, fridges, Wi-fi router, sockets, boilers. 
• Construction equipment: drills, saws, compressors, lighting, transformers, tools, machinery. 
• Event appliances: speakers, lighting, stage appliances, mixers, sockets, plugs. 

Step 2: Calculate Suitable Generator Wattage 

After that, check the power ratings on the equipment, often written in kW and convert this into kVA. Some tools with a motor need extra power for starting (or called starting wattage), different from the running wattage (which is the power used to run the machine). The starting wattage is often 2,5 – 3 times higher than the running wattage. 

Here is the list of kW of some common equipment. For the exact calculations, check the specifications of your tools and equipment. 

Appliances	Running Wattage	Starting Wattage
Fridge	120-200	300-600
Phone charger	75
TVs	120
Microwave	1500
Oven	3000
SDS drill	200-400	600-900
Circular Saw	1200-1800	2400-3600
Compressor	800-1500	2000-3000
Rotary hammer	600-900	900-1500
Angle Grinder	700-1100	1200-2000
Submersible pump	400-900	1000-2000
Dehumidifier	500-1000	1000-2000
Tower Light	200-600	300-900

Listing out all the scenarios in which you'll use your appliances. If you need to run multiple tools at the same time, calculate the required wattage to avoid damage. In case of blackouts at home, you only need to keep the essential equipment running, such as phone chargers, boilers or lighting.  

Add up the total of wattage, and you'll know the total of kW or kVA you need from the generators. Add around 20-25% extra capacity for a safety margin. This will prevent overload and allow room for extra tools if needed. 

Step 3: Consider Other Factors 

Besides the size of generators, you should also look at other factors and specifications for your projects. 

UK Legal Requirements 

Your generator may need an environmental permit to comply with emission limits for air quality by the UK Government. All generators should be placed in well-ventilated areas to keep harmful fumes and discharges from people. Using stage V generators can help limit pollutants and emissions, aligning with EU Stage V Non-Road Emission Standards.

Any electrical connections associated with a generator installation must meet BS 7671 (IET Wiring Regulations) for safety and avoiding hazards, including fire risks and electric shocks. 

Additional safety measures needed to be taken when using generators are carbon monoxide (CO) alarms, correct earthing and grounding arrangements, and IP rating (weather protection). 

Noise Level 

It’s important to choose a suitable noise level for your working and living environment. If you're using it for home backup, it isn’t ideal to choose a diesel engine with loud operation. Instead, look at our range of silent small generators to limit the noise level. For events or dense housing, target <60–65 dB(A). For construction sites, a 70–80+ dB(A) noise level is acceptable.  

Portability 

If you need more flexibility and portability when using generators, for example, during events or in different rooms in the house, make sure to choose lightweight generators.  

How Much Do Generators Cost to Run? 

The cost of running a generator will depend on fuel types, generator sizes, power levels, and run time during the day. Take the Pramac E3200 2.9kVA portable petrol generator as an example. 

• The unit has a fuel consumption of approximately 1.17 litres/hour.  
• The average UK petrol price of around £1.35 per litre, the running cost will be roughly £1.58 per hour. 
• If used for 8 hours, the total fuel cost would be approximately £12.64.  

Best Generators UK

Speedy offers a wide range of generators to suit your needs, from domestic use to construction site requirements.  

Pramac E3200 2.9kVA Portable Petrol Honda Generators 

The Pramac E3200 is a compact petrol generator powered by a Honda engine. It has easy recoil starting systems with a tubular steel opened frame for a sturdy design. This unit is ideal for light-duty applications such as home backup power, small tools, and mobile use, with only 94 dB(A) sound level. 

• Power Source: Petrol 
• Power Output: 2.9kVA 
• Fuel consumption: 1.17l/h 

Milwaukee MXFPS-602 MX Fuel Battery Generators 

The Milwaukee Battery Generator delivers 3,600 peak watts and 1,800 continuous watts without carbon emissions. It can run high-demand 16A tools and sensitive electronics while reducing emissions, noise, vibration, and maintenance. We recommend this unit for indoor use, urban environments, and sites with strict noise or emission controls.  

• Power Source: Battery 
• Power Output: 4.5 kVA 

Solar Generator 5kVA with Hybrid Power System 

The powerful and intelligent 5kVA solar generator with a hybrid power system offers a sustainable energy solution for sites. When paired with diesel generators up to 45kVA and/or solar PV, it helps reduce fuel consumption.  

• Power Source: Solar/ Hybrid Power 
• Power Output: 5kVA 

Pramac P6000S 5.9kVA Super Silenced Generator Diesel 

The Pramac P6000S is a super silenced generator run by diesel. Pramac generator is always adored by its robust build, reliable engine and multiple protection features. You can also switch voltage between 110V and 240V for flexibility.  

• Power Source: Diesel 
• Power Output: 5.9kVA 

Large-sized Secure Generators for Construction Sites 

These large-sized secure generators are built for high-demand construction sites with extra security. They come with extra-large kVA to support heavy equipment, site offices, lighting towers, and construction sites. 

Large-sized Canopied Generators  

Canopied generators offer high power output with added protection from weather and external damage. The enclosed canopy helps reduce noise while safeguarding internal components, ideal for long-term outdoor use on industrial and construction sites. 

Why You Should Hire a Generator 

Many people choose to hire a generator rather than buy one due to many benefits: 

• Lower upfront investment: Buying medium to large-sized generators is a big investment for homeowners or businesses. Hiring helps you reduce the operating costs.  
• No maintenance: When hiring from Speedy, you don't need to worry about any maintenance tasks. All equipment handed over is serviced and tested regularly to ensure excellent performance. 
• Wide range of generators: We offer generators of all sizes and fuel types so you can easily pick the one right for you. Contact us for more expert advice. 

Speedy helps you avoid choosing the wrong size of generators with experts in the industry. Get your personalised advice on the size of generators you need, fuel types, and the most suitable models for your projects. We deliver our hire products within 4 hours or let you collect from more than 100 depots across the UK.