In the developed world energy abundance is achieved through the consumption of cheap, high-energy fossil fuels such as coal, oil and gas. These sources provided the energy required to drive the Industrial Revolution and improve the living standards of millions of people. However, rapid exploitation of such non-renewable energy sources has had adverse effects on the environment, including climate change, air and water pollution, and ocean acidification. There exists an inequitable access to global energy resources, and increasing political and social stresses have resulted from an economic dependence on oil-producing regions.  

Future energy systems need to provide energy abundance while being sustainable and non-polluting. Energy production should be distributed, diverse, intelligent and highly integrated into technological, industrial and domestic systems. Energy technologies for RBE communities need to be evaluated on their ability to efficiently and cleanly provide abundant energy. Open-source designs are preferred in order to provide equitable access.

Energy in the broadest sense is intrinsically linked to all systems and will be the common thread connecting housing, agriculture, water and waste treatment, industry, and transport. Hence, energy production, monitoring, efficiency and use need to be carefully considered during the design stage of a community. The ideal scenario for a self-sufficient community is to produce as much energy as possible from waste products (human waste, food waste, waste heat), i.e. “energy recycling” and the renewable sources available at the location (e.g. solar, wind, hydro).

It is likely that there exists no single energy production technology that will meet all the requirements of a community and hence various sustainable technologies will need to be implemented. It is also advantageous to have a range of different energy supply technologies in order to minimise the risk of complete electricity loss if one system fails or requires maintenance. Initially the choice of technologies will be limited by the budget of the project and availability (level of development, patents/licensing). Well-developed and benchmarked technology (e.g. solar and wind) could be used in conjunction with emerging technologies (e.g. fuel cells, combined heat and power). All energy technologies are evaluated with respect to; the type of generation (base-load or variable), reliability, lifetime, cost per kWh of energy generated, ongoing costs of maintenance and consumables (e.g. hydrogen for fuel cells), whether open-source designs are available, and the impact of the manufacture (energy use, environmental problems).

For the Kadagaya pilot project, the technologies chosen for producing renewable energy are solar (photovoltaic), hydropower, and biogas (methane production from organic waste). Wind energy may be viable at a later stage, but small installations are expensive for the amount of power they produce. For the initial stage of the project we are using a small photovoltaic system (for household use) and a petrol generator for running power tools in the workshop. Solar was an easy and economical option for quickly providing some power, however it required purchasing the entire system externally, and a large amount of storage (via batteries) is required as energy generation is only during the day. The cost of photovoltaic panels continues to rapidly decrease and now the major cost over the lifetime of the system is the batteries (which have a much shorter life than the panels). We have selected a “vortex” hydroelectric system for our long-term energy. Such a system has a much higher initial investment compared to solar, but can supply high amounts of energy continuously with little maintenance. The photovoltaic, vortex hydroelectric and biogas systems are described in more detail following.

In later stages of the production of liquid fuels such as bioethanol and biodiesel will be investigated as these are important for becoming self-sufficient with respect to transport. Continued upgrade and optimisation of the energy systems could be achieved via monitoring and “intelligent integration” with other systems (e.g. waste heat, heating, lighting, telecommunications), and allow automation of various components.

Solar photovoltaic

An independent photovoltaic system that operates outside the normal electricity grid is known as “off-grid”. A schematic of such a system is shown below and consists of the following:

·         solar panels to capture the energy from the sun

·         a battery system to store the solar energy

·         a charge controller to optimally charge the batteries

·         an inverter to convert the direct current (DC) from the batteries to alternating current (AC) for use in the house

·         an (optional) generator to provide power in extended periods of low sun


In order to calculate the size of the system required by a given household the power requirements (in Watts, W) of the appliances used need to be analysed. Approximate power values for common household devices can be found here & here. See the table below for an example. By adding all powers for the required devices and multiplying by the hours of use per day a total power consumption can be found, in this case 2.5 kWh.



Power (W)

Hours of use per day (h)

Daily power use (kWh) (power x hours)

Lights (5 x 20 W)








Washing machine

















A major limitation of solar is that efficient generation of power only occurs during the peak sunlight hours. In Peru the average hours of peak sunlight per day is 4 h. By dividing the daily power use by the sunlight hours (2.5 kWh/4) the size of the photovoltaic system can be estimated, i.e. 0.625 kW. The system should be 20-30% larger than the maximum power needed to account for losses, therefore around 1 kW would be suitable. Solar panels are supplied in various powers e.g. 80 W, 100 W, 250 W. In this example ten 100 W panels would be required to generate 1 kW (or similarly five 200 W panels).

The size of the battery storage will depend on the climate of the region. If there are often several days or weeks without adequate sun then a larger battery system will be needed. In general the battery storage should be able to supply the household for 2-5 days. By multiplying this number of days by the power usage per day the storage capacity is found. This value should represent the state of battery at 50% charge (to avoid discharging the batteries too low), so this value needs to be multiplied by 2. In this example: 2.5 kWh/day x 3 days x 2 = 15 kWh of storage. Battery systems are rated in Amp-hours (Ah) which equals the power (Wh) divided by the voltage (usually 12 or 24 V). Assuming a 12 V system, then 15 (kWh)/12 = 1250 Ah. A standard car battery is rated 12 V and 40 Ah (or 480 kWh), therefore in this example around 32 batteries would be required. Lead-acid (Pb-acid) “flooded cell” batteries are commonly used for solar power storage as they are inexpensive and have relatively long lifetime is well treated. The “traction” type of batteries (often used in golf-carts or forklifts) is preferable and require topping up with distilled water as the only maintenance. Dry-cell acid batteries use an acidic gel and require no maintenance. Lithium ion and other new battery technologies may offer alternatives and advantages in the future but are still prohibitively expensive for household use.

The inverter converts DC electricity to AC (or vice versa). The standard commercial electricity supply in most countries has a voltage of 110 V or 220-240 V and a frequency of 50-60 Hz, and all electrical appliances bought locally will be designed for the local supply. It is important to check that inverter systems can be operated for these conditions (it is usually possible to modify the voltage, but the frequency might be fixed). The solar cells generate DC electricity, and this needs to be converted to AC in order to run the lights, appliances etc. A battery management system (BMS) or charge controller is also important to ensure that the batteries get charged/discharged in the correct way to maximise the battery life and keep the system safe (overcharged batteries can explode). A backup generator (running on diesel or petrol) can be used to charge the batteries in times of extended cloud cover or if the solar panels become damaged. An AC generator can be used directly to power the household (without using the inverter system) and run power tools and other appliances used infrequently that require more power than can be supplied by the inverter.

It is important to install the solar panels in a place where they receive maximum sunlight for most of the day e.g. the roof of a house, where the sun will not be blocked by trees or shade from other houses and nothing can fall on the panels (tree leaves, branches etc). The ideal angle for the panels will depend on the location and the latitude. For latitudes of 0 – 20°, the ideal tilt angle is Latitude x 0.87. (e.g. for Lima Peru the latitude is 12° so the ideal angle is 12 x 0.87 = 10.44°. Close to the equator where the panels lie quite flat (or in very dry regions) the panels may collect dust and need to be cleaned occasionally.

Suggested links

·         Sizing battery system


·         Electricity standards by country


·         Optimum angle for solar cells by latitude


·         Inverter systems



Vortex hydroelectric system

This technology was selected as it is cost effective (kWh/$), generates power all year round (24 hours a day), with no storage required and can easily provide enough power for a community of forty people. Excess power generated above the needs of the community can be shared with our neighbours. 

Usually hydroelectric systems require a high head (drop in altitude) to produce sufficient electricity. For example Pelton systems use a rapidly-rotating propeller fed by water falling from a waterfall or down a mountainside. Large-scale industrial hydroelectric plants need to build enormous dams to provide this head and control the water flow (which can be very damaging to the ecosystem). The vortex system is suitable for a river such as ours with low head and high flow. The water is fed into a tank with a geometry that causes the water to rotate in a vortex (something like water spinning in a toilet bowl). A vertical axis turbine sits within this vortex to harness the kinetic energy and an attached generator converts it into electricity. This is a very simple system with comparatively low investment and low maintenance that has a positive effect on the local ecosystem (the vortex aerates the water and allows the passing of fish in both directions). All water is returned to the river where it continues with its natural flow rate.

The first step was to evaluate the characteristics of our river to determine how much power we could generate and how large the infrastructure needs to be. The velocity of our river is around 0.5 m/s (in the dry season and much higher in the wet season). Using a 5 m diameter tank and designing the dyke, inlet and outlet channels to achieve a head around 1 m, we are able to generate 5 – 10 kW every hour, or 120 - 240 kWh/day. An average (developed world) household uses about 10 kWh/day, so we can easily supply the needs of our community and more. 

We have prepared detailed calculations, budgets and project planning on all aspects of the construction of the vortex hydroelectric system. If you would like more information, please contact us. Photos of the progress of the vortex project can be found in the Photo Gallery.

Suggested links



      Methane digester for biogas

In addition to electricity, the other important energy source for cooking and heating is gas. This can be obtained using a biodigester system where methane (“biogas”) can be produced from organic (human, animal and agricultural) wastes. The digester mimics the natural decomposition process occurring in soils, where the waste is processed by a complex biota of bacteria and fungi. Natural composting is a slow process and requires a lot of land and the capacity of the land to process the organic material is easily depleted. This natural degradation process produces methane, which is a strongly active greenhouse gas, so it is preferable to have these reactions occurring in a controlled environment where the methane is captured and can be used.

Biodigester systems are simply tanks which are filled with the organic waste and controlled to optimise the decomposition reaction to both sanitise the waste and produce methane. The solid residues remaining after the reaction (sludge) is a nutrient-rich fertilizer. Small (household-sized) systems do not produce very much gas and their main function is to process the human waste to make it safe to use as fertilizer. In India, Nepal and other developing countries basic small-scale reactors are used to process cow dung and give gas for cooking (used unrefined). Larger (community-sized) systems produce higher yields of methane which can be used for energy (in addition to sanitising the waste). We are designing a system with an appropriate reactor size for the community (to process all the waste and produce enough gas), considering efficiency of the entire process (avoiding pumping of waste and good control of process reactions).

We plan to place the digester underground, and the natural slope of the site will be used to gravity-feed the waste from the toilets to the digester. This is more hygienic, will provide natural insulation for the heated digester tanks, and will prevent rainwater or pests accessing the tank. The tank needs to be well sealed to avoid smells and excess moisture getting in. A storage tank for the waste before digester will be included to regulate fluctuations in the feed and avoid problems if the digester needs to be opened for repairs.

The system will be operated in “co-digestion” mode, where the reactor will be fed with a mixture of different wastes. In addition to human waste residues from agriculture (plants and fish) and the gardens could be used to give better gas yields and ensure a diverse and sufficient supply of waste. Also, the concentration of pathogenic bacteria is decreased and the resulting sludge will have a higher level of nutrients.

The digester will be operated at high temperature (around 70 °C), which will require some of the generated methane to be used to heat the tank. There are several advantages to using a high-temperature process. Only “thermophilic” bacteria, which can tolerate this temperature, are active, and there are no pathogenic bacteria. All bacteria that can be dangerous to humans are happiest around our body temperature of 37 °C and will die at higher temperatures. When the sludge is cooled for removal, the thermophilic bacteria die and hence the sludge can be immediately used (no sterilisation treatment is required to kill remaining bacteria). Also, the higher temperature process has a higher reaction rate (the methane is produced faster), and better gas yields. Also, the process is easier to control as small changes to the operating conditions can be seen quickly (in a week, compared to months with lower temperature processes).

The digestion process will be well-controlled and monitored, which is quite easily done with a small amount of technology (temperature controllers, logging systems etc.). Some practise using the system is required to optimise the gas quality (e.g. the ideal mixture of the feed, and how long the waste spends in the digester). Naturally occurring biogas (i.e. produced in soil, compost heaps) is 30-40% methane. Gas from a digester is usually 60-70% methane (able to be burnt), where 99% of the rest is carbon dioxide, with small amounts of hydrogen or hydrogen sulphide (from high protein feeds). It will take some months (3-6) before gas is available from the system. 

Suggested links