What is energy and why do we need it?
According to Physics, energy is the ability to do work or generate heat. Just to state that cooling is also a form of heat. To do any work, we need energy. According to the first law of thermodynamics, energy can neither be created nor destroyed but transformed from one form to another. However, there are some losses in energy conversion.
So it is very clear from the above two statements that we need the energy to do our useful works and it may need to be converted in the form we need such as electricity for lighting. This blog would not have been possible without the application of energy and therefore it has associated carbon emissions.
Though we commonly use the term generating electricity, it doesn’t mean generating energy but it means converting thermal energy from gas or kinetic energy from wind or solar energy from the sun to electricity and all those processes have losses and conversion efficiency, known as electrical efficiency.
What are the energy units?
Energy per unit of time is known as Power. In other words, the rate of energy use is known as Power. The two common forms of energy we use are thermal (heating & cooling) and electricity. The SI or metric unit for energy and power is joule and joules/second (also known as Watt) respectively.
The common unit for electrical energy we use worldwide is Watt-hour and our electrical devices and appliances are mostly rated as watts. For example, a 3Watt LED bulb would consume 3Watt-hour of electricity if it is left ON for one hour, so if it is turned off after 30 minutes, the consumed electrical energy would be 1.5Watts-hour.
The most common unit for thermal energy is also watt-hour, however, the two forms of energy (i.e. electricity and thermal) are not the same. They interconvertible such as making hot water (thermal energy) using an electric kettle. The other units of energy you might have heard are tabulated below.
| Units | Watt equivalent conversion |
| Kilo-watts hour (kWh) | Watt-hour x 1000 |
| British Thermal Unit (BTU) | 0.293071 Watt-hour |
| Kilocalories (kCal) | 1.16222 Watt-hour |
Factbox
Did you know…
– Replacing a traditional light bulb with an LED of the same brightness will save you up to £2 per year according to energy-saving trust UK.
– On the average UK households spend £30 a year powering appliances left in standby mode which can be avoided.
The unit of combustible liquids or gases such as natural gas is not Watt or kW, but they are measured by volume (e.g. litres or cubic meter) or by weight (e.g. pounds or kilograms). To convert such fuels from either volume or weight to kW, the calorific value of (CV) is used. CV is a measure of the energy contained in fuel or food.
The common unit for natural gas used on your gas bills is m3 or ft3, and the conversion method to get kWh is indicated which is usually like below –
Gas (m3) × correction factor x CV ÷ 3600
Where:
The correction factor varies but it is fair to assume 1
CV of gas also varies by region and mix but again it’s fair to assume average CV of 39,200kJ/m3
So 1m3 of gas can release 10.89kWh of heat = 1 × 1 × 39,200 ÷ 3600.
For simplicity, multiply gas (m3) with 11 to get kWh.
How to measure Electricity and gas?
Measuring energy is complex, however, with the help of modern techniques, it has been much easier than before. Introduction of smart meters has made it much simpler and useful for household energy users.
Reading Electric Meters – Usually, there is no need to read electric meters if you have got smart meter which automatically reads your electrical power consumption units depending on a pre-set interval such as every half hour, hour, week or month. In the case of conventional meters, the difference between previously noted reading and current reading results in the net electrical power consumption. See the example below.
When reading the meter, ignore the numbers in the red box which is a fraction of kWh.
In this example, the meter reading is 11,111kWh.
Assuming a typical electrical consumption for electric hob, fridge and lighting, the meter reads the following after one hour.
The meter reading is 11,115kWh. Now that we have two-meter readings within an hour interval, the electrical consumption can be calculated as follows:
11,115 – 11,111 = 4kWh
Assuming the cost per unit of electrical power (£/kWh) is £0.1388/kWh, the incurred cost for the hour would be 4 × £0.1388 = £0.56
You can find the unit cost in your electric bill or contract document from your supplier. You would also notice standing charge per day which is fixed and does not change with increase or decrease in power consumption. In some countries, it is also known as meter rental and line charges. The other charges mostly applicable in the commercial sector such as fuel adjustment, climate change levy or carbon tax are applied per unit consumption and change with respect to change in consumption. VAT (also known as GST in some countries) is charged on the total amount at prevailing rates.
Reading Gas Meters – Like electricity meters, there is also no need to read gas meters if you have got smart meter which automatically reads your gas volume consumption units depending on a pre-set interval such as every half hour, hour, week or month. In the case of conventional meters, the difference between previously noted reading and current reading results in the net gas volume power consumption. See the example below.
When reading the meter, ignore the numbers in the red box which is a fraction of volume.
In this example, the meter reading is 11,111m3.
Assuming a typical gas consumption use for the gas boiler (or geyser) for hot water and heating, the meter reads the following after one hour.
The meter reading is 11,113m3. Now that we have two-meter readings within an hour interval, the gas volume consumption can be calculated as follows:
11,113 – 11,111 = 2m3
To convert 2m3 into kWh:
2 × 1 × 39,200 ÷ 3600 = 21.78kWh
Assuming the cost per unit of gas thermal energy (£/kWh) is £0.03224/kWh, the incurred cost for the hour would be 21.78 × £0.03224 = £0.70
It should be noted that boilers have a thermal efficiency of less than 100%, with modern condensing boilers of 90-95% thermal efficiency. This means that 21.78kWh of heat generated from the combustion of gas would generate hot water of 19.6 – 20.7kWh. The final useful heat could be even slightly less due to losses in the distribution pipework and radiators.
In contrast to the boiler, there are no losses for generating hot water using the electric kettle as all the electricity converts into heat, transferred into the water. The only losses are heat loss through the surface of the kettle. However, the operating cost of the boiler is usually less than electricity due to cheaper cost per unit of kWh.
Smart Meters – In my opinion, smart meters are brilliant as they provide real-time information and any unexpected energy use can be identified and rectified immediately. The traffic light on in-home display is very useful to identify what users are energy-intensive. The amber or red light reminds you of large appliances in-use and whether they were supposed to be ON and can they be turned off immediately after use.
I often use the Now option to monitor the large appliances and also to calculate the savings from turning-off unnecessary appliances and devices.
For example, if “Now” electrical reading is 120Watts-hour, after turning-off a 20Watt LED bulb, the “Now” reading should drop to 100Watts-hour, and if I manage to do it every day for at least an hour, my energy savings and associated cost would be:
20Watts-hour/day × 365days/year ÷ 1000 (to convert in kWh) = 7.3kWh/year and the cost savings would be 7.3kWh × £0.1388/kWh = £1.01/year
Want more information on EDF smart meters? Click here
Conclusion
It is suggested to note the meter reading prior to switching-ON large appliances and after switching-off to understand the rate of use and approximate running costs. Smart meters with budget targets are a good way to understand and reduce your energy use. It is suggested to switch to smart meters by contacting your energy supplier in the UK. I would personally prefer to allow smart meters to collect data at least every hour and review it on a monthly basis to understand the energy consumption profile. Smart meters could help in identifying significant energy users following the breakdown of energy use and also prioritisation of energy reduction measures accordingly.
Do you think smart meters would help people in reducing energy and cost?