In our last posts, we have looked at efficiency factors across different power sources as well as efficiency losses through transmission and distribution. In this post we will look at efficiency losses in use-cases, such as batteries, electric heating, and home applications such as ovens, washing machines, TVs and computers and more; in other words: application efficiencies.
We know that primary energy factors (PEF) vary significantly between operational and theoretical values, and across the different power generation sources. Hydropower is the most efficient, with functional efficiency values reaching as high as 90%. By contrast solar PV has the lowest efficiency at around 6%.
In addition to efficiency losses inherent in the power generation source itself, the transmission and distribution grid does not function at the highest efficiency either. Losses range from a couple of per cent up to greater than 50% sometimes, in less technologically advanced countries. This calls for immediate support in terms of technology deployment and help.
Because end-users often are households, their energy use contributes to total emissions. Therefore, it is essential to reduce these emissions to a minimum to meet ambitious, yet necessary, carbon reduction targets.
In the US, for example, around 20% of emissions can be directly attributed to households. When looking at indirect emissions such as the energy intensity of products such as food, electronic gadgets, furniture, and so on, figures are closer to 80%. Estimates for the UK are not very promising either: indirect household emissions are estimated to be 74%.
Let’s start our look at end-use efficiency rates by looking at batteries. When charging a battery electric vehicle (BEV), the US Department of Energy says that around 16% of efficiency is lost in the process of transferring energy from the wall power source to the battery. On top of that, another 20-30% of efficiency is lost in the vehicles themselves due to the process of delivering power to the wheels. Even so around 17% can be recovered through regenerative braking, bringing the power-to-wheel efficiency ratio to roughly 80%. In contrast, a conventional car engine typically does not exceed 30% of power-to-road efficiency. (The complete picture of fuel engines vs BEV in terms of total efficiency is on another page.)
Batteries, however, are used not only in cars but in all sorts of devices. The problem of self-discharge is inevitable among batteries and is a well-known issue. This is the rate at which a battery loses a percentage of its stored energy while it is stationary and without a load. The loss is caused by chemical reactions that take place inside the battery even when there is no load applied to it. This process is very well described in the first law of thermodynamics: energy cannot be created neither destroyed nor continuously stored.
Next, let’s look at electric resistance heating, which is claimed by some sources to be 100% efficient, in the sense that the entire incoming supply of electricity is converted into heat. However, because most electricity is sourced from coal or gas, we need to consider their roughly 30% efficiency in terms of converting the fuel’s energy into electricity. On top of that, power is lost on the way from the generation site to the consumption site. As a result, claims of 100% efficiency need to be treated carefully!
Moving on to in-home applications, the International Journal of Engineering & Research says that the average electric stove is roughly 49% efficient when calculated from measured input and utilized energies. This calls for enhancements to improve efficiency.
Many households today include washing machines and fridges, raising the question of whether their efficiency is at a high enough level. Fridges, for example, have seen rapid improvement in their efficiency, as modern ones use only about 25% of the energy that models from the 1990s did. Washing machines have seen similar improvments; high-efficiency washers (laundry appliances that meet specific criteria based on water, electricity, and detergent use) use load-sensing technology that helps them optimize water and electricity use to be eco-friendlier and more efficient.
Further improvements from these levels would benefit from agreement on a worldwide energy efficiency scale of such devices. Currently, a range of scales and input factors are used for such ratings. This ultimately causes a lack of transparency in efficiency markets.
In light of the Covid-19 pandemic, the use of computers, mobile phones, TVs and screens at many homes has seen a rapid increase. We have taken a closer look at energy efficiencies of these devices and were not too impressed.
LED televisions and screens are said to be among the most efficient, saving between 30% and 70% of the electricity consumption compared to plasma TVs. Even so, they are still heavy energy consumers, as they can draw more electricity than your fridge or freezer, depending on size, display brightness and, of course, usage.
When it comes to our closest companion, the smartphone, researchers from South Korea have found, that iPhones running on iOS are more energy-efficient than smartphones running on android OS. Our intention is not to encourage everyone to buy iPhones from now on but to be aware of the differences.
Charging your smartphone correctly and effectively also contributes to its overall efficiency. Phone chargers itself are only demonstrating efficiency rates between 63% and 80%, and that is before overcharging your phone or accounting for self-discharge. Studies show that charging your phone to only 80% is better and healthier for your battery than topping it up to 100%; the same holds true for laptops and tablets.
Many systems/operating software are using the 80% charging approach already by studying your charging habits, to extend battery life and keep efficiencies higher. Nonetheless, only with your active help can this be optimized further still. It’s not only good for your battery, but also for emissions goals and energy efficiency.