## 2 Blockchain Technology and Energy Consumption
### Hybrid Blockchain Networks  
Hybrid blockchain networks are a combination of private blockchain networks and public blockchain networks. They blend essential blockchain components and protocols of both private and public blockchain networks. Any blockchain user can access the blockchain network, but only certain users can access all security features and services [11]. Hybrid blockchains are owned by a private user who can grant access to the public via smart contracts. The structures of hybrid blockchain networks are highly customisable, and users can choose their desired type of transactions. Figure 3 shows the architecture of a hybrid blockchain network [12]. As Figure 3 indicates, the green-coloured dots indicate users who have access to the blockchain network and services. The red-coloured dots show the users who do not have access to the blockchain network and its services. Figure 3 shows that every user has access to the blockchain network, but only certain users have access to blockchain network services.  
Figure 1: Public blockchain network.  
Figure 2: Private blockchain network.  
Blockchain technology has primarily been designed for computers with high processing power. However, with the development of the IoT industry, some researchers have begun to focus on energy-efficient blockchain solutions for low-powered IoT devices [13]. In particular, the aged care sector has started using IoT sensor-based devices to develop ambient assisted living systems [14]. As the aged care sector uses low-powered microcontroller devices to implement ambient assisted living systems and health sensor networks, blockchain algorithms must be energy-efficient [14]. The development of blockchain algorithms for IoT low-powered devices is an increasingly active research area [15].  
However, very little research has been conducted to identify blockchain energy consumption variations in low-powered microcontroller devices. Blockchain energy consumption in microcontroller devices is a significant factor that needs to be evaluated, as IoT end nodes are expected to run for long periods without battery replacement. We will use this work to help develop energy-efficient blockchain sensor networks [16]. Figure 4 shows which blockchain research areas are most popular in the IoT industry. As Figure 4 shows, most of the research that has been conducted targets blockchain security and privacy. There has been very little research conducted to evaluate blockchain energy consumption.  
Modern, IoT solutions also focus on renewable energy solutions. As a result of this, low-power IoT devices and energy solutions have been significantly improved by researchers [17]. Understanding the energy requirements of blockchain technologies will contribute to the use of suitable renewable energy sources for low-powered sensor networks. Different blockchain algorithms may consume different amounts of energy, and energy consumption is an important consideration when choosing which blockchain algorithm to use on low-powered microcontroller devices. Low-powered IoT device performance  
Figure 4: Popular blockchain IoT research sectors [7].  
Figure 3: Hybrid blockchain network.  
and energy consumption may also be correlated. If the energy consumption of a particular blockchain algorithm is high, the performance of the microcontroller device may be negatively affected [18].  
To establish maximum blockchain functionality in a microcontroller device, the utilisation of energy may be necessary. Understanding the energy consumption of low-powered microcontrollers and different blockchain algorithms is important, because it affects battery life and microcontroller performance. This work contributes to our collective understanding of the energy consumption of battery-operated IoT devices. In this paper, we evaluate the correlation between blockchain temperature variations and blockchain energy consumption in IoT low-powered microcontroller devices. We discuss related works in the next section.