**Designing a Waterless Toilet Prototype for Reusable Energy Using a User-Centered Approach and Interviews**

#### **Hyun-Kyung Lee**

Division of General Studies, UNIST, Ulsan 44919, Korea; hlee@unist.ac.kr

Received: 24 January 2019; Accepted: 25 February 2019; Published: 4 March 2019

**Abstract:** User-oriented community engagement can reveal insights into ways of improving a community and solving complex public issues, such as natural resource scarcity. This study describes the early process of co-designing a novel, waterless toilet to respond to the water scarcity problem in the Republic of Korea. It presents how we designed a toilet focusing on three factors—a sanitization function, an ergonomic posture, and clean aesthetics—by conducting focus group interviews as part of a user engagement approach to understand what community users want from a toilet and ways of improving their toilet experiences. The results not only supported the development of an experiential service design project to raise community awareness of water scarcity but also supported scientists and engineers in experimenting with and developing new technologies by collaborating closely with designers.

**Keywords:** design prototype; toilet design; collaboration with scientists; interdisciplinary convergence; natural resource; feces

#### **1. Introduction**

Community engagement is a suitable approach for solving complex public issues, such as natural resource scarcity. It may also reveal what people already know about an issue and provide insights that could support the creation of a better natural resource community. This study describes the fuzzy front end (FFE) stage of designing a novel, waterless toilet prototype, the first collaborative research project between designers and scientists to respond to the water scarcity problem in South Korea. The aim of this collaboration was not only to raise community awareness of water scarcity, but also to save water. The co-design of the waterless toilet at the FFE followed a community-engaged research approach that influenced the technology push and supported "silent design": that is, design decisions made by non-designers [1]. This collaboration project sought to understand what users want in a toilet and to improve the toilet experience. Unpredictably, the approach led to the creation of an experiential service design project to raise community awareness of water scarcity.

#### **2. Background: Water Scarcity**

Water is one of the most vital resources for human viability. However, there is not enough for the needs of everyone in the globe. Due to population growth, many countries face water shortages; thus, they need to prepare for future problems [2]. Water scarcity also results in low economic growth. In 2012, the Organisation for Economic Co-operation and Development (OECD) recommended that both OECD and non-OECD countries reduce water risks, such as water shortages (including droughts), inadequate water quality, non-accessible water, and anything that undermines the resilience of freshwater. Yet, all countries face different water scarcity problems.

According to the United Nations Environment Programme [3], the rapid economic growth and high population density of the Republic of Korea have caused water shortages and freshwater scarcity. This has long been—and still remains—a critical challenge. Reports indicate that current aqua-ecosystem protection mechanisms are insufficient [3]. The Ministry of Land, Transport and Maritime Affairs (2011) reported that only 26% of water in Korea is fit for use and that each Korean person uses only one-sixth of the global average for individual water consumption. Hence, the nation is considered a water-stressed nation.

Water in the Republic of Korea is contaminated for three reasons: (1) damage to the nation's hydro-ecology caused by construction near rivers, which has decreased limnobios, animals, and freshwater plants; (2) soil runoff; and (3) the eutrophication of rivers due to an increasing inflow of phosphorus into rivers [4]. According to the previous literature, people consider treated wastewater from sewage treatment plants to be clean; however, attached algae are widely visible, largely due to phosphorus discharged from farmlands during the summer flood season. More critically, the shallow depth and slow current speed of the river increase detention time, increasing nutrient salts during annual drought seasons. Since phosphorus is not filtered from sewage, it grows too much. It originally comes from toilets, and some toilets are installed in areas that lack sewage. Thus, it is important to remove phosphorus from toilets. This can be accomplished by a sewage treatment plant.

In 2015, the Ministry of Science, ICT (Information and Communications Technologies), Future Planning (MSIP), initiated the Convergence Research Centre (CRC) project, a cross-disciplinary research project that connects the arts, design, and science to prepare for future sustainable energy. Solving the water scarcity problem is one of several seven-year research projects. The collaboration team comprised two design researchers, one philosopher, seven different disciplinary scientists (e.g., water, climate change, and urban environment), and industry partners (e.g., different groups of natural artists, digital artists, graphic designers, and engineers). The team is planning to build a temporary research lab to research these issues at the UNIST (Ulsan National Institute of Science and Technology) in the Republic of Korea. The research lab building will be two stories high and approximately 99 m2.

#### **3. Waterless Toilet**

A family of four uses an average of 225 L of water per day. This represents 27% of household water consumption [5]. Domestic houses use 65.9% of total water [6] and represent one of the main causes of contaminated water in Korea. To remove phosphorus, water scientists from the Department of Urban and Environmental Science initiated a waterless toilet project.

The conventional sanitation system, the flush toilet, has improved public health and protected humans from waterborne diseases. The "drop-and-discharge" approach is a convenient and comfortable solution for disposing human excreta because it rapidly removes hazardous and unpleasant matter from households [7]. However, the complete disconnect between people and their excreta causes environmental problems. People discharge their excreta unconsciously, meaning that our environment has been forced to receive the massive flow of contaminants. In particular, algal blooming and red-tide problems occur in many countries, even developed countries with well-established wastewater treatment systems. Waterless toilets that dispose of excreta in a sanitary way could reduce the high level of clean water usage. Returning sanitized dried feces to the land may also improve the soil environment. Thus, a waterless toilet team—one of the CRC project teams—has begun to investigate alternative toilet systems. The team has explored ways to develop a prototype to examine the effectiveness of eliminating phosphorus from the fuzzy front end (FFE) stage, which is considered the earliest stage of the new product development process [8].

A prototype can be a tool for solution generation or evaluation, as well as a vehicle for team collaboration [9,10]. Supporting explorations that allow users to innovate new patterns of use in the field and over lengthy periods may provide designers insights into the domestication of radically new concepts [11].

#### **4. User-Centered Research Approach**

#### *4.1. The FFE Process*

This project is characterized by a radical technology push, such that engineers in the field develop a set of research routines based on their beliefs about what is feasible or worth trying [12–14]. However, according to NESTA [15], so-called "front-end" research into technological development, market trends, and consumer needs are now staples in design industry operations. Numerous studies identify communication as critically important because this phase allows for modifications, reorientations, and radical changes in new product planning [16]. FFE is the least expensive stage of a project [16]. This collaboration team, therefore, communicated once every two or three weeks regarding how a prototype, by developing technology to remove phosphorous from a waterless toilet, should be designed. In order to clarify the product's concept during the FFE stage, which is known to be complicated (most companies fail to have clear product definitions [17]), we reviewed the literature on new product development (NPD) during the FFE stage. Based on a theory of marketing, operation management, and engineering design, Krishnan and Ulrich define product development as "the transformation of a market opportunity and a set of assumptions about product technology into a product available for sale" [18]. Similarly, Ulrich and Eppinger define product development as "the set of activities beginning with the perception of a market opportunity and ending in the production, sales, and delivery of a product" [19]. A successful product may be viewed as a solution to customers' demands [20]. In order to design elegant and efficient solutions to customers' needs, two different types of information must be combined: "need information" (what users need) and "solution information" (how products are built) [20]. The National Endowment for Science and Technology and the Arts (NESTA) has proposed that researching people's needs, tastes, and preferences is critical for shaping new products and services [15]. However, though consumer needs should be the focal point of any design process, many organizations neglect them [21]. As a result, many design processes fail to reach their target consumers or end users [22,23]. In addition, due to the rapidity of modern technological development, many users find it difficult to directly specify their needs regarding a particular product, service, or experience [24,25]. For this reason, Borja de Mozota recommends employing user-centered and informed design research methods to support the development of products and services from the beginning so not to fail to find out what users need [26].

To design something that is meaningful for users, it is important to understand users' experiences, perceptions, and ways of making sense of things [27]. Having a thorough understanding of one's target users and their needs is necessary to be successful. Mossberg found that the growth of industry through customer experience is reflected in new patterns of consumption, new demands, and new technology [28]. He insisted that a customer's experience is a blend of many elements that have come together to involve consumers emotionally, physically, intellectually, and spiritually in an ethnographic approach. Similarly, Pine and Gilmore propose that combining NPD with customer experience creates more profit than applying NPD on its own because, in the combined approach, every touch point with the customer serves as a market opportunity [29]. Several successful organizations that regard customer experience as an aspect of economic value have been evaluated [30]. These companies position experience as a planned journey with multiple touch points, such that the packaged experience defines the characteristics of a product, service, or brand [31]. Taking the above into consideration, we aimed to identify and learn about community members who would be potential future users of our waterless toilet. Specifically, we followed a reflective problem-solving approach [32] to design prototyping. Figure 1 presents how user-centered research influenced the design of our waterless toilet.

**Figure 1.** Co-designing a waterless toilet using the fuzzy front end (FFE) process.

#### 4.1.1. Phase 1: Focus Group Interviews

We conducted focus group interviews to investigate user perceptions and understandings of the water scarcity problem and a waterless prototype.

#### Sampling Criteria

The study aimed to understand the people in the UNIST campus community where the test-bed research lab will be built. A total of 54 participants (15 females and 39 males)—all of whom had used public toilets and toilets in their homes and who would be potential users of the waterless toilet prototype—were involved in the focus group interviews. There were nine groups, each of which comprised six UNIST undergraduate students majoring in different areas of engineering (e.g., life science, chemical engineering, physics, computer engineering, electronic engineering, mechanical engineering, and engineering management).

#### Process

To ensure that all of the key issues were covered, semi-structured interview questions were used. The participants were asked about (1) their awareness of water scarcity in Korea, (2) their previous experiences attempting to save water, (3) how they could be motivated to save water, (4) their perceptions of a waterless toilet, and (5) their dream toilet. They were also asked to share their thoughts and ideas about how to save water. All interviews were audio-recorded and recorded via memo form that I used in collecting and writing about my observations, which were later analyzed using thematic analysis.

#### Results

Though the participants in each group had different majors, all shared common ideas and perceptions about each question. The thematic analysis revealed three themes: a disbelief about water scarcity, a motivation to save water, and an experience requirement for the waterless toilet.


used each day. They were from a demographic that was less likely to experience shortage or poor quality of water. As possible motivators to save water, the participants recommended water usage indicators or visual indicators of water consumption. They also suggested that more media exposure would be helpful in raising awareness of water scarcity. Lastly, they commented that financial losses would motivate them to save water. Some participants wanted tax deductions for saving water.

(3) Experience requirement for the waterless toilet: This theme emerged from the two questions about the participants' perceptions about a waterless toilet and their dream toilets. None of the participants had previously thought about their dream toilet. However, they said that they wanted a new toilet based on their public and private toilet experiences: visual cleanness, sanitariness (including automatic cleaning around the inside of the bowl), automatic flushing after usage, no bad odor, soundproofing within a public toilet, and a comfortably warm seat cover. Since the participants had not previously considered the water scarcity problem, they explained ways in which they would improve the current style of toilet. They also said that they would try a waterless toilet if they came across it in a public restroom. Most asked for simple visual guidance on how to use a waterless toilet, which is designed to suck up feces like a "vacuum cleaner" and send it directly to the energy production system. It requires about half liters of water, which is significantly less than what a regular toilet consumes.

The results of the focus group interviews revealed that, although people had heard of the water scarcity problem, they had never before tried to save water because they could always access water easily and at their convenience. A design activity exposes new issues and information needs as the work progresses [33,34]. The aim of designing the waterless toilet prototype was to improve the situation water scarcity; however, if the community is not aware that there is a genuine water scarcity problem, they are less likely to accept a waterless toilet. Therefore, since the participants required a realistic experience to motivate them to save water, we chose to design not only a waterless toilet but also an experiential visual guideline that indicates the water scarcity problem. Moreover, the engineering team decided to remove all negative odors from the toilet. This decision was based on the user-centered approach and was considered a sociable design, or a design "for the benefit of the people who use it, taking into account their true needs and wants" (Norman 2010, 130). Thus, the co-design of the waterless toilet, which was led by a technology push, was divided into two projects to meet the needs of the people in the community who would become the future users of the toilet and participants in solving the water scarcity problem.

#### 4.1.2. Phase 2: Case Studies for Service Design Guideline

The aim of case studies is to study good practices of visual and experiential designs capable of leading and increasing civic engagement and awareness of the need to save energy.

#### Criteria

In order to identify case studies capable of meeting the experiential aims of civic engagement by providing realistic visual experiences, we contacted the Korea Institute of Design Promotion (KIDP), a non-profit organization for design support under the Ministry of Trade, Industry and Energy. Though there is no service design related to water scarcity, the design policy experts and staff of the KIDP recommended three service design cases for the public sector in Korea, all involving the design and management of public campaigns to reduce energy bills and raise awareness of the need to save energy. These studies explored (1) which visual elements were strategically designed to lead or motivate civic engagement to reduce energy usage and (2) which approaches and principles were applied to the design experience to increase people's engagement.

(1) Redesigning an apartment energy bill (http://www.slideshare.net/sdnight/ss-30524771). This case concerned one of the first service designs for a utility service in Korea. It was conducted

on an apartment town comprising 600 apartments in Bangbae Dong, Seoul, and its results were highly effective, reducing the total energy bills by 10%. Many redesigning projects graphically change a certain part of an energy bill; however, in this case, the designers and design researchers reduced the energy bill based on in-depth interviews with the community. This case study prompted other apartment towns to accept similar guidelines.


#### Process

Secondary data of visual campaign were collected through online case design websites (www. designdb.com) and suggested website addresses. Thematic analysis was used to identify each case's key characteristics in relation to creating civic engagement experiences, reducing energy usage, and motivating people to do things they had not done before.

#### Case Study Results

Though all three cases were different, they shared similar characteristics in that all employed a user-centered approach to encourage people to reduce their energy usage or do things in which they had not previously been involved. Two themes emerged.


#### *4.2. Influence of User Research on the Waterless Toilet Design*

These case studies made it clear that a user research approach reveals opportunities to improve civic engagement. Mayhew and Bias indicated that such an approach supports higher returns in terms of increased product value [35]. The case study participants actively participated to reduce utility bills and safety accidents. They seemed to be tuned into the effort to overcome problems caused by a lack of staff [36]. Moreover, Boyle and Harris indicated that collaborating with users could guarantee that

services meet their requirements. Thus, user research supports better outcomes and encourages active user engagement in self-help and positive behavioral change, thus avoiding possible challenges in the future.

In order to engage with people in the community (a research test bed at UNIST), we used focus group interviews to determine community members' needs for realistic experiences related to water scarcity and for vivid visual representations to notify/warn about utility usage, health insurance check-ups, and safety cautions. To raise awareness about water scarcity in the community, the collaboration teams recommended encouraging people to visit the research lab to examine the waterless toilet prototype. Ramaswamy and Gouillart indicated that the participatory approach could improve stakeholder engagement, and could lead to higher productivity, higher creativity, and lower costs and risks [37]. Thus, the researchers created a visual board as a service design, which served as a channel for experience prototyping [38]. After the prototype at the research lab was developed and designed, this visual board was used to support community members in discussing their experiences and perceptions on water scarcity. As the community members visited the lab, it was possible to monitor their different behaviors in a real context using several variations of observation-based ethnographic field methods [39]. It was also possible to involve the users in designing and delivering services to achieve the full benefits of co-creation [39].

#### **5. Prototyping: Waterless Toilet Design**

In designing the toilet, we focused on three factors: the sanitization function, an ergonomic posture, and cozy aesthetics.

#### Sanitization Function

First, from the focus group interview, we drew the conclusion that people want a clean toilet experience. Thus, we designed the prototype for sanitization (sterilization) and cleanliness. We installed ultraviolet (UV) lights on the cover so that the toilet looks sanitizable. These UV lights also disinfect and sterilize the surface of the seat and the bowl of the toilet (Figure 2). Additionally, since the word "toilette" means "dressing room" in French, the seat cover was designed to resemble a dressing room vanity chair, which was intended to make people feel warm. The toilet hip area was designed with enough space for anyone to sit comfortably. Ultimately, the toilet was designed to provide not only a clean experience, but also a restful one.

**Figure 2.** Prototype of the waterless toilet.

#### Ergonomic Posture

Second, the toilet was designed in an ergonomic manner to support proper posture for defecating. The seat can be adjusted (raised or lowered) to an appropriate angle to fully relax the muscle around the colon and support quick and easy defecation. Once a user sits down on the toilet, the back side of seat tilts slightly, raising the user's knees. This encourages users to maintain an optimal posture

for relaxing the muscle around the colon. The concept for this posture came from the Paimio Chair, designed by Alvar Aalto (Figure 3) for patients in a tuberculosis sanatorium in Finland. When the patient sits down and leans on the chair, the patient's posture changes the angle of the chair, helping the patient breathe better and comfortably arranging his or her body organs.

**Figure 3.** The Paimio Chair designed by Alvar Aalto in Finland.

The waterless toilet is also designed ergonomically with respect to the angle of the sitting posture. Although the tilted seat relaxes the muscle around the colon, it also makes it difficult for users to stand up (compared to the upright posture of a traditional toilet). Though this may not pose a significant problem for young and healthy people, it could encumber older, disabled, or injured people. Therefore, we installed a spring under the back side of the seat that users can activate by pushing back slightly when they need to stand up. Figures 4 and 5 present suboptimal and optimal posture angles defecation.

**Figure 4.** Working process of the seat of the waterless toilet prototype.

**Figure 5.** The proper posture and angle to relax a human's intestines.

#### Cozy Aesthetics

Thirdly, the appearance of the toilet prototype was inspired by the white porcelain of the Yi Dynasty (Korean imperial household, called the Joseon household) (Figure 6).

**Figure 6.** Korean Yi Dynasty porcelain.

Toilet shapes have not changed very much since their first development in the 16th century. However, this new type of toilet offers several improvements. First, unlike a traditional toilet, which has a tapered bowl shape to support a suction mechanism located at its bottom back side, our proposed toilet does not require centrifugal force or a vacuum system to suction the feces. Therefore, the waterless toilet can be slimmer or wider. We chose a shape that was cozy and familiar. Second, the white porcelain of the Yi Dynasty suggests familiar characteristics of interior objects that already play a role in our everyday lives. Figure 6 presents the aesthetics of the waterless toilet. Users think this is a great idea that has Korean tradition and culture embedded in it.

#### **6. Conclusion**

This article describes the FFE process of designing a waterless toilet to combat the problem of water scarcity in the Republic of Korea. The waterless toilet prototype was co-designed based on user perceptions, a technology push, and the use of a radical technology to remove phosphorus from toilets. Through focus group interviews, we identified several key factors regarding water scarcity and users' perceptions of a waterless toilet: (1) disbelief concerning the state of water scarcity in Korea, (2) a motivation to save water, and (3) experience requirements concerning the waterless toilet.

We observed that people in Korea generally do not seriously consider Korea's water scarcity problem. However, if they experience water scarcity visually and realistically, they may be more likely to try to save water. We also found that people want a toilet to be sanitary, odorless, clean, and comfortable. These findings helped to reveal what users want and need to improve their toilet experience, and they guided the direction of the prototype development to be more user-oriented and less rushed (i.e., due to the technology push).

Based on our user research, we designed our waterless toilet focusing on three main factors: a sanitization function, an ergonomic posture, and cozy aesthetics. First, based on the focus group interview, we concluded that people want a clean toilet experience. The prototype was therefore designed with UV lights on its cover for sanitization (sterilization) and cleanliness. Second, the toilet was designed in an ergonomic manner to allow people to sit in a posture appropriate for defecating. Specifically, the seat can be lowered and adjusted to the optimal angle to relax the muscle around the colon. Thirdly, the appearance of the toilet prototype was inspired by the white porcelain of the Yi Dynasty and includes familiar characteristics of interior elements and everyday objects.

The researchers' user-centered and community-focused approach helped this collaborative research project gain new information for further improvements. The approach used in this study can be employed as a guideline for researching and solving other public problems. Engaging people in the community supports the identification of both current and future public problems. Furthermore, responding to potential users' opinions, recommendations, and insights encourages positive participation and thus a better public environment. Further studies evaluating the waterless toilet prototype with the aid of community members are needed to improve the toilet experience and to increase awareness of the current situation of water scarcity in Korea.

**Author Contributions:** H.-K.L. conceived and designed the experiments and wrote the paper.

**Acknowledgments:** This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MSIP) (No. NRF-2015R1A5A7037825).

**Conflicts of Interest:** The author declares no conflict of interest.

#### **References**


© 2019 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## *Communication* **Optimal Design of a Residential Photovoltaic Renewable System in South Korea**

**Hyunkyung Shin <sup>1</sup> and Zong Woo Geem 2,\***


Received: 4 February 2019; Accepted: 14 March 2019; Published: 18 March 2019

**Abstract:** An optimal design model for residential photovoltaic (PV) systems in South Korea was proposed. In the optimization formulation, the objective function is composed of three costs, including the monthly electricity bill, the PV system construction cost (including the government's subsidy), and the PV system maintenance cost. Here, because the monthly electricity bill is not differentiable (it is a stepped piecewise linear function), it cannot be solved by using traditional gradient-based approaches. For details considering the residential electric consumption in a typical Korean household, consumption was broken down into four types (year-round electric appliances, seasonal electric appliances, lighting appliances, and stand-by power). For details considering the degree of PV generation, a monthly generation dataset with different PV tilt angles was analyzed. The optimal design model was able to obtain a global design solution (PV tilt angle and PV size) without being trapped in local optima. We hope that this kind of practical approach will be more frequently applied to real-world designs in residential PV systems in South Korea and other countries.

**Keywords:** optimal design; photovoltaic system; renewables; residential building; South Korea

#### **1. Introduction**

South Korea is in the world's top 10 energy-consuming countries, and it heavily depends on imports of fossil fuels (natural gas, coal, and oil) [1–3]. Due to recent public awareness regarding the issue of polluted air, pressure to reduce its dependency on fossil fuels has increased. In addition, the Fukushima disaster that occurred in Japan has caused the present government to support the nuclear phase-out policy.

Therefore, various renewable energies (photovoltaics (PV), wind, geothermal, hydro, biomass, fuel cells, etc.) have been currently developed, which also helps in the country's pledge at the 2015 Paris Climate Conference to cut its carbon emissions by 37% below the business-as-usual (BAU) level by 2030.

In addition, the Korean government has recently declared a national project aiming for power generation by renewable energies to account for 20% of the total generation output by 2030 (85,905 GWh (13.6%) by 2025 and 134,136 GWh (20%) by 2030) [4]. This project especially focuses on PV and wind energies (more than 75% with respect to the generation capacity, and more than 50% with respect to the generation amount). The Korean government plans to provide urban-type self-sufficient PV systems to 760,000 residential houses by 2022, and 1,560,000 houses by 2030 [5].

To this end, as one of practical efforts, Korean government already ruled that 5% of total construction cost should be invested in renewable energy system for large public buildings (total floor area is greater than or equal to 3000 m2), and it also subsidizes 60% of the construction cost if private residential buildings install PV renewable systems [6].

Korean government also plans to promote rural-area PV systems using low-interest loans and higher-weighted RECs (Renewable Energy Certificate). The REC is a market-tradable and non-tangible instrument that certifies that the owner possesses one megawatt-hour (MWh) of electricity generated from any renewable energy resource [7]. RPS (Renewable Portfolio Standard) required for large power producers (≥500 MW) also works well after FIT (Feed-In Tariff) system ends. In order to enhance the social receptivity to PV systems, the Korean government has approved private enterprisers, to gather individual private investors, to join in PV development projects.

The objective of this study is to propose an optimal model for residential PV system design. In this model, the construction and management costs will be minimized, while considering various practical design factors such as PV generation amounts with different tilt angles, the Korean progressive electric rate, the unit cost of a PV panel, the interest rate, the project period, the electrical usage of general electric appliances, and seasonal appliances, lighting appliances, and stand-by power.

The rest of this paper is organized as follows. The optimal design model for the residential PV system is proposed in Section 2. Residential electricity demand is broken down in detail, and the monthly electrical generation amounts with varying tilt angles are proposed in the form of polynomial functions in Section 3. The optimal design solution is obtained by using an evolutionary algorithm, and compared with that from previous gradient-based methods in Section 4. Finally, in Section 5, we conclude our paper with some future directions.

#### **2. Optimization Formulation**

The objective function to be minimized in this residential PV design optimization is the total cost (*CT*), which consists of the electric bill from grid (*CElectric*), the PV-related construction cost (*CCst*), and the PV-related maintenance cost (*CMtn*), as shown in Equation (1) [6]:

$$\text{Minimize}\\
\text{C}\_{T} = \text{C}\_{Electric} + \text{C}\_{\text{Csl}} + \text{C}\_{Mtn} \tag{1}$$

where the annual electric bill (*CElectric*) is the sum of the monthly bills, and each monthly bill (*C<sup>m</sup> Eelctric*) is calculated based on the monthly grid-supplied amount (*D<sup>m</sup> Electric* − *PV<sup>m</sup> Electric*) when monthly residential demand (*D<sup>m</sup> Electric*) is greater than the monthly PV generation amount (*PV<sup>m</sup> Electric*), as in Equation (2):

$$\mathcal{C}\_{Electric} = \sum\_{m=1}^{12} \mathcal{C}\_{Electric}^{m} (D\_{Electric}^{m} - PV\_{Electric}^{m}) \tag{2}$$

For the monthly bill (*C<sup>m</sup> Electric*), Korea adopts a six-stage progressive electric rate system, which charges a higher rate for higher electricity usage, as shown in Table 1.


**Table 1.** Korean progressive electric rate (US\$1 ≈ 1100 KRW).

For example, if one household consumes 50 kWh for a certain month, the monthly electric bill will be 3125 KRW (=370 + 50 × 55.1); if it consumes 150 kWh, the monthly electric bill will be 12,020 KRW (=820 + 100 × 55.1 + 50 × 113.8). Thus, if we draw a monthly electric bill from 0 to 600 kWh, we obtain a stepped piecewise linear function, as shown in Figure 1.

**Figure 1.** The six-stage progressive electric rate in Korea.

For the PV-related construction cost (*CCst*), in order to fairly consider this one-time cost alongside other annual costs (*C<sup>m</sup> Electric* and *CMtn*), a capital recovery factor [8], which is the ratio of a constant annual return amount to the initial construction cost (*CIcc*) for a given length of time, is introduced as in Equation (3):

$$\mathcal{C}\_{\text{Csf}} = \frac{r(1+r)^n}{(1+r)^n - 1} \mathcal{C}\_{\text{Icc}} \tag{3}$$

where *r* is the interest rate (6.5% in this study) and n is number of system operation years (or the number of annual returns received; 25 years in this study).

The decision variables in this residential PV design optimization are the size of the PV panel (or module; *SPV*) and the tilt angle of the PV panel (*APV*; horizontal line is 0◦). These two decision variables have value ranges as constraints:

$$0 \le S^{PV} \le \mathfrak{Z}(\mathbf{kW}) \tag{4}$$

$$15^{\circ} \le A^{PV} \le 60^{\circ} \tag{5}$$

#### **3. Application of the Residential PV System**

The above formulated PV design model is assumed to be applied to a typical Korean residential building. For a typical Korean residential building, the monthly demand (*D<sup>m</sup> Electric*) can be assessed in four groups of consumption (general electric appliances, seasonal electric appliances, lighting appliances, and stand-by power) [6].

The first group of consumption occurs in general (year-round) electric appliances such as the television, refrigerator, and washing machine, as shown in Table 2. For example, a typical Korean residential building has two TV sets, which consume 270 W (=135 W × 2) over 6.9 hr per day, and 28 days per month, based on a statistical survey. Interestingly, a Korean house also possesses a special refrigerator which preserves only Kimchi, because it is an essential dish for every meal in Korean daily life.


**Table 2.** Power consumption of general electrical appliances.

The second group of consumption occurs with seasonal electric appliances, such as the electric fan, air conditioner, humidifier, and electric blanket, as shown in Tables 3 and 4. For example, a typical Korean residential building has one air conditioner, which consumes 1725 W over 4.65 hr per day. However, this seasonal appliance is utilized only during the summer season (13 days for June, 15 days for July, and 27 days for August).

**Table 3.** Power consumption of seasonal electrical appliances.



**Table 4.** Monthly usage of seasonal electrical appliances.

The third group of consumption occurs with lighting appliances, such as fluorescent, incandescent, and halogen lights, as shown in Table 5. For example, a typical Korean residential building has one stand-alone (stabilizer-included) fluorescent lamp, which consumes 25.86 W over 7.9 hr per day.

**Table 5.** Power consumption of lighting appliances.


The final group of consumption occurs with stand-by power from various appliances, as shown in Table 6. Normally it accounts for approximately 10% of total household power consumption.


**Table 6.** Consumption amount of stand-by power.

If we aggregate the above-mentioned four types of consumption, we can obtain a monthly power consumption graph, as shown in Figure 2. Here, it should be noted that a consumption amount of 2.2 kWh/day for any additional appliance was added to each monthly amount.

**Figure 2.** Monthly power consumption for a typical Korean house.

So far, the monthly power consumption of a typical Korean house has been assessed based on four different types of consumption. Now let us assess the monthly power generation amount from the PV system (*PV<sup>m</sup> Electric*).

The monthly PV generation amount is affected by two major decision variables (PV angle, *APV*, and PV size, *SPV*). The first affecting factor is the tilted angle of the PV panel, as shown in Figure 3. As seen in the figure, the lowest angle (15◦) generates the highest amount in June, while the highest angle (60◦) generates the highest amount in December. The highest amounts in March and September occur in the middle.

**Figure 3.** Monthly photovoltaics (PV) generation amounts with different tilt angles.

For this study, in order to estimate the energy production of the residential PV system, the PVWatts calculator [9], which was developed by the National Renewable Energy Laboratory (NREL) in the U.S. Department of Energy, was utilized. After inputting various PV system specifications such as the DC system size (unit size (1 kW) in this study), array type (fixed in this study), array azimuth (180◦ (full south) in this study), system losses (14% in this study), inverter efficiency (96% in this study), and PV tilt angle (*APV*) into the software, we could obtain an estimation of the month-average solar radiation (kWh/m2/day), and the monthly unit-size PV generation amount (kWh) for a specific location.

For the specific location, this study selected Seoul, the capital city of South Korea. However, PVWatts provided the PV generation data of Incheon, as the nearest location from Seoul (24 miles west from the center of Seoul), whose latitude is 37.48◦ N and longitude is 126.55◦ E, as shown in Figure 4.

**Figure 4.** Location of the solar data source (Incheon) from Google Maps.

The influencing factor, PV size (*SPV*), can be multiplied by the unit-size generation amount (kWh/kW) at a certain PV angle (*APV*), to calculate the monthly PV generation amount (*PV<sup>m</sup> Electric*).

The PV-related construction cost (*CCst*) in Equation (1) is the function of PV size (*SPV*). The original PV construction cost is 7,210,000 KRW/kW in this study. However, after considering the Korean government's subsidy (60% of the original cost = 4,326,000 KRW/kW) and the building materials cost savings (\$462,500/kW), the PV-related construction cost (*CCst*) becomes 2,421,500 KRW/kW (=7,210,000 − 4,326,000 − 462,500) multiplied by the PV size (*SPV*).

The PV-related annual maintenance cost (*CMtn*) in Equation (1) is 12,105.7 KRW/kW (0.5% unit *CCst*) multiplied by the PV size (*SPV*).

#### **4. Computational Results**

The residential PV design model is optimized with various practical data, as proposed in the above sections. Figures 5 and 6 show the total PV design cost, as specified in Equation (1), with different PV sizes (0 ≤ *<sup>S</sup>PV* ≤ 3 kW, by 0.2 kW) and tilt angles (15◦ ≤ *<sup>A</sup>PV* ≤ <sup>60</sup>◦, by 2.5◦). In this resolution, 639,919 KRW, with a PV size of 1.2 kW and a PV tilt angle of 27.5◦ is the minimal design solution for the system.

When we narrowed down the PV size (0.95 ≤ *<sup>S</sup>PV* ≤ 1.3 kW) and the tilt angle (26.4◦ ≤ *<sup>A</sup>PV* ≤ 28.6◦), and then divided them into finer intervals (0.05 kW for the PV size and 0.1◦ for the tilt angle), Figures 7 and 8 were obtained. At this resolution, we obtained a better solution (639,901 KRW with PV size of 1.2 kW and PV tilt angle of 28.3◦~28.4◦) than that with coarse resolution (639,919 KRW with PV size of 1.2 kW and PV tilt angle of 27.5◦).



 cost at a

In order to find a global optimal solution, we applied a genetic algorithm [10] as a global search meta-heuristic algorithm [11] to this PV design problem. When this meta-heuristic optimization algorithm was applied, we obtained an even better solution (639,824 KRW) at different solution spot (a PV size of 1.1904 kW and a PV tilt angle of 26.7013◦) than those at the previous two resolutions. This phenomenon means that there exist local optimal solutions within the solution space.

Here, it should be noted that this PV design problem cannot be solved by using calculus-based approaches, because the monthly electric bill, as a part of the objective function, possesses stepped piecewise linearity, as shown in Figure 1. At certain stepped points such as 100, 200, 300, 400, and 500 kW, this cost function is not differentiable. Although a previous research [6] tackled this problem with a gradient-based approach, named SQP (Sequential Quadratic Programming), it had to sacrifice the accuracy of the objective function by smoothing out this step function with polynomial curve fitting.

In order to compare our approach by using a genetic algorithm with the old approach, using SQP, we first performed a polynomial regression based on the electrical rate data in Table 1, and obtained the following second-order polynomial function:

$$\mathbf{C}\_{Electric}^{\rm m} = 0.5632\mathbf{x}^2 - 76.207\mathbf{x} + 7612.3 \text{with} \mathbf{R}^2 = 0.9947\tag{6}$$

Then, based on Equation (6), the SQP optimization was performed, obtaining an optimal cost of 617,529 KRW, with a PV size of 1.3935 and a PV tilt angle of 29.7229◦. It appears that the solution (617,529 KRW) from SQP was better than that (639,824 KRW) of our approach. However, when we verified the SQP solution with a real cost table (Table 1), we obtained 644,252 KRW, which is worse than our solution.

#### **5. Conclusions**

This study proposes a design optimization model for the residential PV systems in South Korea, where the objective function to be minimized consists of three costs, such as the monthly electric bill, the PV-related construction costs, and the PV-related maintenance cost. Here, the monthly electric bill has six ranges in the form of a stepped piecewise linear function. The PV-related construction costs also include the government's subsidy and the building-material cost savings. The initial construction costs, and the annually occurring maintenance costs are fairly compared by introducing the capital recovery factor.

Regarding residential electrical consumption, four consumption types, such as year-round electric appliances, seasonal electric appliances, lighting appliances, and stand-by power, were considered. Also, regarding residential PV generation, the monthly generation amount was calculated by considering different solar altitude angles.

While local optimal solutions, this model could find the global optimal solution by using a genetic algorithm. We hope that this optimization model will be practically used in residential PV system designs in South Korea.

For future study, we plan to construct more detailed PV design optimization models by considering discrete PV size variables [12–14], ESS (energy storage systems) [15,16], AC–DC conversion [17], and more energy-efficient lighting devices (light-emitting diodes). Normally, the size of PV is discrete, because a PV system consists of an integer number of panels. Thus, we would like to consider this discrete nature of the PV size after gathering sufficient data in the future. In order to efficiently utilize surplus energy from the PV system, we may install an ESS and optimally schedule it [15].

The climate change cast over in Korea has made its summers hotter than before, which has led to more energy consumption in the summer months, and higher energy bills. Thus, the Korean government is about to reform the multi-stage progressive electric rate, in order for lower-income groups to be able to afford to pay it. Once all-new data, including billing, panel capacity and costs, ESS capacity & costs, etc., are obtained, we will correspondingly construct a more detailed and up-to-date model design.

**Author Contributions:** H.S. and Z.W.G. wrote the paper, and Z.W.G. supervised the submission.

**Funding:** This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP), and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20163010140690). **Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## *Article* **Eco-Friendly Education Facilities: The Case of a Public Education Building in South Korea**

**Eunil Park <sup>1</sup> and Angel P. del Pobil 1,2,\***


Received: 23 August 2018; Accepted: 20 September 2018; Published: 25 September 2018

**Abstract:** Since the importance and effects of national energy policies, plans, and roadmaps were presented in South Korea, the role of renewable energy resources has received great attention. Moreover, as there is significant reasoning for reducing and minimizing nuclear and fossil fuel usage in South Korean national energy plans, several academic scholars and implementers have expended significant effort to present the potential and feasibility of renewable energy resources in South Korea. This study contributes to these efforts by presenting potential sustainable configurations of renewable energy production facilities for a public building in South Korea. Based on economic, environmental, and technical information as well as the presented simulation results, it proposes an environmentally friendly renewable energy production facility configuration that consists of photovoltaic arrays, battery units, and a converter. Subsidies for installing and renovating such facilities are also considered. The potential configuration indicates \$0.464 as the cost of energy, 100% of which is renewable. Potential limitations and future research areas are suggested based on the results of these simulations.

**Keywords:** eco-friendly; renewable energy; energy subsidies; SEMS; South Korea

#### **1. Introduction**

After the peaceful turnover of political power in 2017, the new South Korean government is attempting to reform national energy policies and plans. During this reform process, the government is aiming to phase out the usage of nuclear energy. One of the major decisions undertaken in this regard was the suspension of the construction of the fifth and sixth nuclear reactors in Kori when the construction process was 28.8% complete [1]. Although construction resumed when the government was implored to do so by a jury of 471 randomly selected citizens, the government decided that no new nuclear power plants in South Korea should be constructed [2].

Therefore, exploring, adopting, and using new energy resources is one of the most important research areas for establishing national energy policies and plans. As nuclear energy constitutes approximately 12% of South Korea's national energy supply system, alternative energy resources could be unpalatable or infeasible [3]. Moreover, because of the Paris Agreement, which requires South Korea to reduce its large greenhouse gas emissions, increasing the use of fossil fuels would also be infeasible [4].

Accordingly, the South Korean government is aiming to implement renewable energy resources. Approximately 4.6% of primary energy in South Korea was provided by renewable energy production facilities in 2015, with an annual growth rate of 15.2% [3]. Moreover, South Korea's energy dependence on foreign countries is very high, and compared with other countries, oil price fluctuations have a greater effect on the South Korean economy [5]. Thus, ensuring reliable energy production and securing stable energy resources are important.

The South Korean government has pursued the expansion and distribution of renewable energy production facilities to achieve its goal that, by 2035, 11% of primary energy in South Korea should be generated from renewable energy resources. To achieve this goal, the government established *The fourth basic plans for the technology development, usage, and distribution of new and renewable energy*, with detailed programs for promoting each energy source [6]. Based on these promotion programs, the duty ratio of the renewable portfolio standards was revised and enhanced. All public buildings with a certain total floor area that are planned to be constructed, reconstructed, or enlarged should have at least 21% of their energy supplied by renewable resources [7]. Therefore, both central and local South Korean governments urge public organizations and institutions to include electricity and energy production facilities that use renewable resources. For this reason, several studies have attempted to investigate the feasibility of implementing renewable energy production facilities in diverse public buildings, including a public university, local government office, and multi-purpose public buildings [8].

Considering this background, this paper presents a case study for the economic and environmental feasibility of renewable energy production systems in a public education building in South Korea. After careful simulation, a potential configuration of a renewable energy production system for the building is suggested.

#### *Review of Prior Feasibility Studies in South Korea*

Several studies have attempted to investigate the feasibility of renewable-oriented power generation facilities in South Korea. Table 1 summarizes the key prior studies. As presented in Table 1, the majority of prior studies have focused on specific regions such as certain islands or areas. This means that only a few studies have explored the sustainable cases of renewable energy facilities for public buildings in South Korea.


**Table 1.** Summary of prior feasibility studies of renewable energy facilities conducted in South Korea (W: Wind turbines, P: photovoltaic (PV) arrays, D: Diesel generators, B: Battery units, C: Converters, K: Kerosene generators).

#### **2. Case Study: Research Background**

#### *2.1. Location and Facilities*

This study focused on an elementary school located in southeastern South Korea. To investigate the economic and environmental feasibility of potential renewable energy production facility configurations for school buildings, this study selected *Samrangjin Elementary School in Miryang* (SESM), which has smart meter facilities to record the school's hourly electricity usage. The location of this school is 35◦23 44.76 N and 128◦50 15.89 E, and it has approximately 100 students and 40 members of staff. The school has four buildings: the main education building, education support building, warehouse, and kindergarten building. Figure 1 presents the location and an overview of SESM in South Korea.

**Figure 1.** The location of SESM in South Korea.

#### *2.2. Energy Load Information*

SESM's energy system mainly uses electricity provided by the national grid. In 2016, SESM used 99,263 kWh. The SESM electricity load shows a scaled annual average electricity level of 223 kWh/d with a load factor of 0.464.

#### *2.3. Renewable Energy Resources*

This study uses the solar resource data provided by the National Aeronautics and Space Administration (NASA). Table 2 summarizes the monthly baseline data. Annual average solar daily radiation is 4.259 kWh/m2/d, with a solar clearness index of 0.514. The wind resource information of SESM is collected and provided by the Korea Meteorological Administration. Figure 2 summarizes the monthly wind speed.


**Table 2.** Monthly solar resource information for SESM.

**Figure 2.** Average wind speeds at SESM.

#### **3. Simulation Parameters**

#### *3.1. Annual Real Interest Rate*

To present precise simulation results, the actual South Korean interest rate is computed and used in the simulations [18,19]. Based on a report by the Bank of Korea, an annual interest rate of 3.51% is used.

#### *3.2. Evaluation Criteria*

To explore the results of the simulation, the suggested sustainable configurations are ordered by two economic outputs: the cost of energy (COE) and net present cost (NPC). The COE is defined as *the mean cost of generating 1 kWh electricity by the suggested configuration*, while the NPC is defined as *the total cost of installing, utilizing, replacing, and performing the functions of the suggested configuration throughout the project* [15]. In addition, the project lifespan used by this study is 25 years.

#### **4. Renewable Electricity Production Systems**

To introduce the configurations of the sustainable renewable energy production system, the economic information of each component that can be used in the configurations should be investigated. Based on detailed economic information about the components from previous studies, Table 3 summarizes the specific economic information about the components employed in the simulations presented here. In addition, the standard electricity price, which is introduced by KEPCO, is used in the grid connection.


**Table 3.** Economic information about the components (\* The supporting policies and plans by the South Korean government are applied).

#### **5. Results**

The sustainable configuration, which contains PV panels, battery units, and a converter, is proposed based on the simulation results (Table 4). Table 5 summarizes the total and annual costs of the proposed configuration. The suggested configuration for providing reliable and sustainable energy services to SESM includes 500 kW-capacity PV arrays, a 247 kW-capacity converter, and 202 battery units (Table 4).

**Table 4.** Summary of the suggested configuration from the simulation results for SEMS.




The estimated net present and annual costs are \$623,617 and \$37,837, respectively. The computed COE is \$0.464 per kWh. Table 6 provides the annual electricity production. All the energy provided by the suggested system originates from renewable sources. As shown in Table 6, approximately 14% of

the electricity produced by the suggested system fulfils the electricity demand of SEMS (AC primary load), while 86% is sold through the grid connection.


**Table 6.** Annual electricity consumption and production of the suggested configuration.

Altering the current grid connection to the suggested configuration is expected to reduce annual emissions of carbon dioxide, sulfur dioxide, and nitrogen oxide by 308,661 kg, 1338 kg, and 654 kg, respectively.

#### **6. Discussion and Conclusions**

To develop more sustainable and eco-friendly energy plans in South Korea, the government intends to distribute renewable energy generation facilities to public buildings and organizations. Considering this trend, this study introduces a potential sustainable renewable energy generation facility configuration to fulfil the electricity demand of SEMS using local, natural resources. To evaluate the suggested configurations of the simulations, both the COE and the NPC are computed and employed.

The suggested configuration achieves 100% renewable energy, with a COE of \$0.464. Although the COE of this configuration is higher than the current price of the South Korean grid connection [20], the suggested configuration can be applied to SEMS, a public education building in South Korea, as an on-site test. In addition, the simulation results also indicate that subsidies are an important issue in distributing and maintaining renewable energy production facilities [21].

As using renewable energy production facilities significantly reduces greenhouse gas emissions, the South Korean government and associated industries should distribute renewable energy production facilities [22]. According to the Paris Agreement, which introduces a mandatory level of greenhouse gas emissions for 195 nations, the South Korean government should also attempt to distribute more sustainable energy production facilities within its electricity system [23].

Although both economic and environmental information, which can be applied to the potential configuration of SEMS, was investigated considering subsidies for renewable energy production facilities in South Korea, this study has several limitations. First, the economic aspects of the certified reduction in greenhouse gas emissions were not considered. This can produce better economic results on utilizing renewable energy resources than the simulation results [24]. Second, economic theories in the renewable energy industry were not considered in the simulations. Several studies have already indicated that various economic theories can be applied and used in the renewable energy industry and market [25,26]. Therefore, future research should aim to eliminate the limitations of the current study.

**Author Contributions:** E.P. designed and wrote the majority of the manuscript. A.P.d.P. contributed to the analysis and revised the manuscript.

**Funding:** This work was supported by the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea (NRF-2018S1A5A8027730). This research was also supported by the MIST, Korea, under the National Program for Excellence in SW supervised by the IITP (2015-0-00914). Moreover, the second author's research is funded by Ministerio de Economía y Competitividad (DPI2015-69041-R) and by Universitat Jaume I.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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