MSc RESE University of Strathclyde

Once the required data for each technology had been collected, it was necessary to define a demand profile for the village for energy matching. This allowed the proposed system to be tailored to the village’s demand.

From the discussions with the community member, it was known that the majority of households in the village do not have electricity. Most hotels/hostels did have solar PV systems, but expressed desire for greater electricity supply.

Lighting and small appliances (especially phone chargers) were identified by the community as desired. This was supplemented with the Sustainable Energy for All Tier System to account for the likely change in demand once the community has seen the benefits of electricity first-hand. A table showing the Sustainable Energy for All Tier System for electrical demand is shown below.[3]

Per household, it was estimated that three 5W LEDs would be required, running an average of 6 hours per day (33 kWh a year). Additionally, phone charging and a small number of mixed appliances (radios, televisions, food processors, computers and small fridges) spread across the community would bring the total consumption to 45kWh per household per year.

From the discussions with a local from the village, it is known that some of the village population leave the village during winter for Kathmandu (the capital of Nepal). This peaks at approximately half of the population in January. This was reflected in the demand profile.

Demand profile for modelling

Daily profile of village electrical demand

To input a demand profile for matching, HOMER required the daily load for every month of year. The national grid was used to attain the total annual trend of total consumption. It was assumed that the electrical energy consumption of Pangboche would follow the same trend (which peaks in winter).

The daily national grid demand profiles for summer and winter were used as a basis for daily profiles of village demand. Winter and summer profiles were sinusoidally varied between to create daily profiles across the year. This was further adapted to Pangboche by increasing spiking. This was achieved by reducing base load, as most of the electrical load will be during times when lighting will be required (morning and evening). Alteration of the national grid profile was performed to account for the lack of diversity of both appliances and customers (i.e. mostly residential consumers and few businesses) in the community.

Once the profile for each household was generated, the values for demand were then multiplied with population of village across year to get village demand profile. This was then put through HOMER to add day to day variability as to improve the estimations of demand.

The following graph shows the seasonal demand profile for the whole village (116 households).

Map showing grid of Nepal in 2008 [1]

The current grid situation was initially investigated to evaluate whether a grid connection would be more viable than implementing a new energy system. The current grid in Nepal is underdeveloped and, as a result, does not extend to the eastern and mountainous parts of Nepal. [1]

Considering the landscape of the valley, it would be very costly as the grid infrastructure would have to be laid over rough terrain with no road access.

Dudhkoshi is the closest point of access to the grid from Pangboche at about 150km away (although Up-Tamakoshi is closer, see the above diagram, the geography of the land make this connection less likely). To simplify appraisal of grid connection, grid extension from Lukla to Pangboche is considered. Lukla is a major village which lies between Pangboche and Dudhkoshi. Therefore, Lukla will undoubtedly be grid-connected before Pangboche is.

If the grid was to be extended to Lukla, a generous and approximate cost estimate of half a million USD would be incurred across the 60km path to reach Pangboche (assuming it would cost $8000 per km [2]). A grid connection would most likely cost much more than the estimate as the estimate assumes a relatively flat terrain.

Since a grid connection was deemed unfeasible, during the energy system modelling stage it was not considered as a potential grid architecture for Pangboche. Microgrid, nanogrid, and battery charging stations were considered. Further hybrid architectures, comprising of both a microgrid and a charging station were also considered as there were a few households that could be powered in a nearby village (Shomare) if there is enough generation.

A group of porters carrying large loads on their backs

During the project definition stage, the potential uses for electricity was discussed with village contact. It was clear that the potential use for electricity would be for lighting and powering small appliances, such as a radio and charging phones. As the system was not intended to run large appliances such as dishwashers or refrigerators that would require AC current, it was decided that the network would be entirely DC. This would save the cost of buying an inverter for the village. The network would also have to use wiring with additional sheathing due to the extremely cold climate.

The transportation of the energy system would have to be carried out via yak and porters. It is possible to use a helicopter to fly in any required materials or parts of the energy system if they are too heavy or too large to be carried.

Energy system modelling software, HOMER, was used to match the demand of the village the energy produced via different combinations of technologies.

Screenshot of HOMER showing an example of an energy system

The climate data that was collected and the demand profiles generated were used as input for HOMER. The technologies considered are presented in the table below along with approximate costs.

The prices presented here are approximate and are used this stage aid the decision making process in the sustainability analysis stage. These prices should not be used outside of this project. Costs were determined by comparing prices of technologies on the market in Nepal (or India when unavailable). This method of pricing was used despite its unreliability due to time constraints. The cost of transportation was also estimated using the rate for transportation of goods per kilogram, which was provided by the village contact. This came to be about 330 Rs/kg ($3.15/kg).

Simulations were run by HOMER to obtain technically viable combinations of technologies that meet the communities demands via different grid structures. Systems that did not meet over 99% of the annual electric load were omitted. As there was a large amount of excess electricity being generated throughout the day, the option of powering a small village near Pangboche was considered (consisting of 20 households).
It was assumed that each of those households would have the same electrical load as those in Pangboche and they would each have a small battery to charge up.

Some of the results exported from HOMER are included in the table below:

These results obtained show that systems comprised of hydropower are very cost effective, whilst wind turbines are far more expensive. This stage only considers the technical viability of a system, which would not cover all the community’s aspirations. To assess which of these architectures and system combinations work best for the community, a sustainability analysis was performed.

The first step of thermal system design is to create a demand profile in order to see how this can be met with different thermal technologies. Information on the thermal demand for the village was collected by interviewing the community contact. The community’s primary thermal uses are cooking and space heating. Space heating is especially important during the winter months when temperatures go below freezing point.

The community primarily uses animal dung and fuel wood as the sources of thermal energy. Each household typically has at least 3 yak and other livestock that can provide the dung required. A typical household uses about 10 - 15 kg of animal dung per day for cooking and space heating [1].

Since the community is in Sagarmatha National Park, there are restrictions on wood harvesting. The village contact confirmed that each family is only allowed to collect fuel wood for only 10 days a year, and only two bundles or loads for each of the 10 days. One load translates to roughly 30kg [1]. Therefore, a typical household in Pangboche would use about 600kg of fuel wood per year for cooking and space heating.

In addition to biomass sources, kerosene is also used for cooking meals especially in the morning. A typical family uses about 0.19 litres of kerosene a day.

Determining the energy content per source was challenging since this largely depends on the composition of the organic matter and the moisture content, there is no standard value. In addition, the fuel wood and the animal dung are usually used together in the cooking and space heating process. To tackle this challenge, the energy content of the animal dung and fuel wood was determined separately by using lower heating values based on literature review. The following values were used:

The second challenge was distinguishing between thermal energy for cooking and thermal energy for space heating. In Pangboche, heat emitted from the biomass fuels during the cooking process fulfils the role of space heating. Cooking and space heating are therefore interlinked. To deal with this challenge, cooking and space heating were considered together as thermal energy.

The third challenge was quantifying energy from kerosene used specifically for cooking. This is because kerosene is used for both cooking and lighting purposes in most households in Pangboche. To deal with this challenge, it was assumed that all kerosene was used for cooking. The heating value was based on literature review [5] and was taken to be 43 MJ/litre.

Household thermal energy demand can therefore be profiled as shown in the table below. The thermal energy system can now be designed

Cook stoves are the major technology used for cooking and space heating in Pangboche. Literature suggests that a typical family in Nepal, especially in the mountain region, uses two types of cook stoves: Agenu or Chulo whose descriptions are in the table below. These stoves are usually used in small, poorly ventilated kitchens. The poor ventilation is meant to keep as much heat as possible in the room, especially during winter months when temperatures are very low.

Energy flow in cook stoves

The performance of a cook stove depends on two major factors: the conversion of fuel to heat and the transfer of this heat to the load [7]. It is therefore important to understand how heat is transferred during the fuel combustion process in order to determine methods to reduce heat loss and improve thermal efficiency, as shown in the table below.

A summary of heat losses and ways to minimise these losses in a cook stove is desribed below [9]:

In addition, unlike other thermal technologies, the improved cook stove is user-specific [7]. Therefore, it is important to not only look at the technical specifications but also look into non-technical aspects such as social aspects when designing a cook stove for use in a rural community.

A unique consideration for Pangboche is the necessity for the cook stove to provide space heating functions in addition to cooking. Since these two functions usually occur concurrently, the challenge would be to have a balance between adequate heat for cooking and reasonable heat output for space heating. In addition, the selected cook stove design must be able to burn animal dung since this is the main source of biomass fuel in the community. This presents the challenge of handling ash content from the dung as well as minimising emissions from the combustion process. The following considerations were used for determining the most suitable improved cook stove design for Pangboche.

From this criteria, two main stoves were identified as the most viable for Pangboche, the Jumla (smokeless) metallic improved cook stove and the SNV and WWF promoted metallic improved cook stove. Their specifications are detailed below:

The Jumla Cook Stove

The Jumla (Smokeless) Metallic Improved Cook Stove

The SNV and WWF Cook Stove

The SNV and WWF Promoted Metallic Improved Cook Stove

The next technology considered in the project definition stage of the methodology was biofuels, therefore the biofuel technology available in Nepal using the sources available was assessed.

Through reviewing literature it was identified that there were many organisations within Nepal promoting and encouraging the use of biogas plants mainly for cooking purposes. Some of these were as follows: ‘The Nepal Biogas Support Program’[16], Nepal Biogas Promotion Association’[17], ‘Biogas Sector Partnership’[18] and ‘Alternative Energy Promotion Centre (AEPC)’[19]. A review of the systems in place using biogas plants  and the technologies currently in use elsewhere in Nepal were identified

Due to the rural location of Pangboche it was necessary to ensure that any biogas technology considered was already developed, as brand new technology would be difficult to maintain and monitor in a rural area. Therefore, after assessing the technologies installed by ‘The Nepal Biogas Support Program’ and ‘Nepal Biogas Promotion Association’, it was identified that the process of biogas digestion was the same for all plants.  However, differences were present in the overall structure of the biogas plant [17].

The Anaerobic Biogas Process

In a biogas digester, the organic material (waste) is firstly put into a hollow chamber where it is mixed with water in order to form a slurry. Within this chamber (ensuring its airtight), anaerobic digestion takes place, forming methane which can then be used as gas for cooking.  The overall process can be seen in the diagram to the right.

Although the process is the same for the production of biogas , the structure of the technologies differ. The optimum technology for a specific community depends on the demand for cooking and supply of biomass sources.

As the energy supply and demands for cooking were identified earlier in the methodology, thermal energy design, the possible technology options could be identified using these demand requirements. 

After cook stove use,  total thermal demand left was calculated to be 217MJ/per day per household. Therefore the biogas system would need to replace the kerosene used for this. Taking into consideration the demand of each household, the design options therefore fell into two steps: size of biogas digester and structure of system.

Size of biogas system

The biogas system can be split into two main sizes.: an individual sized system or a community/ institutional sized system. The individual biogas plant allows each household to have their own system where the digester would be fitted outside in the garden with a pipe running into the kitchen, allowing the flow of the biogas. The community sized biogas plant would be in an area either within or close to the community where the dung would have to be collected from each household. The biogas supplied would then be available to each household either by pipes or by plastic canisters.

Individual Sizes [16]

The sizes mentioned above are the biogas plants which are promoted through the ‘Biogas support program’ (BSP).  The promotion is only available for individual systems, as this would help poorer households and farmers who do not have a large number of livestock [16].  It can be seen that a specific number of livestock are required for each sized digester which helps narrow down the choice for Pangboche. It was identified in the biomass supply estimate that each household owns between two to three livestock, therefore only the 4m³ digester would be applicable for the households in order to match the supply. This size of digester would also supply enough biogas to burn a stove for a cooking time of 2/3 hours which is the cooking time of a small meal [16]. The community sized plants are not promoted or installed to the same scale as the individual systems but the larger sizes would be as follows:

Community Sizes [16]

For Pangboche as the community has around 116 households the community sized plant required would be larger than those installed previously by the program. As community biogas plants are not as highly promoted or installed as much as individual plants these may result in more technical issues within the operation as it has not been tested as much, especially if the size of the plant is bigger than previous systems. 

Modifications to biogas system

The structure of the system used is specific to the needs of the community and also depends on specific aspects of the community location. For Pangboche the main challenges with system design came with the high altitude of the community at 4000m and the resulting severe cold climate during winter. This brings difficulties in keeping the digester at the optimum 37ᵒc in order for anaerobic digestion to take place during the whole year. Due to this challenge special adjustments were required to be assessed in order to reduce temperature fluctuations and maintain constant temperatures [20], these are as follows:

 The choice of dome used for the biogas system would depend on the location of the community and accessibility, as for Pangboche a steel drum would not be possible due to the materials required.  

An important measure which needs to be taken when implementing biogas digesters in Pangboche, is for a trial biogas system to be put in place first. This is mainly for testing the modifications required by the system for use at this altitude and also as the technology will be new to the community. 

The thermal energy system design options should then be put through the next stage of the methodology where they can assessed against social, economic and environmental parameters.

This section demonstrates the methodology detailed in 3. Energy System Design found HERE. Fabric improvements were identified to address the community's desire to have greater indoor temperatures, reduce fuel consumption, and improve indoor air quality (identified in 1. Project Definition).

The data used to create the model is provided in 2. Data Collection and assumptions have been stated where used. Challenges encountered in performing this step of the methodology for the case study are also presented along with the methods used by the authors to overcome them.

Following discussion with the community contact, it was determined that insulation was not commonplace in the village. This was supported with pictures (see below), by the account of our contacts and by the literature review conducted. [21][22][23]

Wall and ceiling insulation was identified as potential areas of upgrade. Wall insulation is currently nonexistent and ceiling insulation is minimal (typically less than 50mm depth, see picture below).

The ceiling of a typical house in Pangboche demonstrating the lack of insulation used is shown below.

Materials

Potential insulation materials considered are presented in the table below. These included advanced and non-conventional materials. Imported materials were also considered with material costs per m3 given in the table below. Costs were based upon Kathmandu prices and adjusted for transport costs (310 NPR from Kathmandu to Pangboche according to the contact). These costs do not include installation costs or any potential subsidies that may be available.

Thermal Comfort

Only temperatures across the day were obtained via literature review. These are presented in the table below.

Modelling

A model representing the typical housing stock of Pangboche was created using ESP-r (link). This model was based upon the gathered information from Data Collection. Simplifications were made to reduce modelling and computational time. These were:

Subsequent models were created with fabric changes to the loft space and walls. Loft space fabric depths were 100, 200, and 300mm. Wall fabric depths were set at 200mm.

The model of a typical Pangboche house, created on ESP-r

Google Street View of Pangboche

Results

Simulation results can be found in the tables below. To provide a comparable metric of impact, USD per % demand reduction is shown. Loft and wall insulation changes were separately investigated. Following this, a further investigation of wall insulation changes was conducted. This consisted of changing wall material with a constant change of loft material set (200mm straw slab was used as it was found to be the average performer of the loft materials).

As can be seen in the above results all materials produce a reduction in demand although there are great variations between materials and areas of upgrade. From the USD/% column loft upgrades offer significantly greater demand reductions for investment compared to wall upgrades at an average of 26 and 486 USD/% respectively.

The high capital cost of both wall and wall-and-loft insulation make them unlikely to be implemented in the village hence all are not considered further. Of the loft insulation materials considered both straw slabs and local wool appear to be highly effective and low in initial cost. Local wool is considered for further analysis as it is known to be locally available (straw is thought to be available but this was not confirmed by the contact or literature review). A depth of 200mm was considered as cost effectiveness is shown to drop with increasing thickness.

Heating demand across winter (the first 50 days of the year) was considered for both the base model and improved model as well as for base thermal comfort and improved thermal comfort (average increase of 4°C at all times of the day). These results are displayed in the figure below.

This further simulation shows that improved loft insulation can either reduce fuel consumption by approximately 33% or raise indoor temperatures by 4°C for the same fuel consumption.

Challenges & Considerations

Modelling: As discussed in both this section and Data Collection, simplifications and assumptions were made to create the model. These will affect the accuracy and reliability of the model and results.

Viability of installation: The proposed insulation measures are proposals only. As a site visit was not conducted it may be found that these proposals do not work in practice. Similarly, materials used may be inaccurate in cost, inaccessible or require additional materials (such as moisture barriers and flame retardants).

In addition to the above, challenges and considerations are further discussed in the Energy System Design – Methodology.

Further work: This study does not consider the effect upon other comfort factors such as humidity. Furthermore, improvements of indoor air quality are not considered. Future research should consider these factors before recommendation of fabric improvements as part of the proposed energy system.