Sun and ice07 / 2012, Storage & smart grids | By: Simon Rolland
Off-grid solar: The Alliance for Rural Electrification reports on a rural micro-grid project that powers a 60 home village on Santo Antão, the largest of the islands of Cape Verde, an archipelago off the coast of Western Africa. The most important application of the solar PV micro-grid, which includes an individual energy allowance scheme, is the production of ice to preserve fish.
Monte Trigo is a village in Santo Antão, Cape Verde’s westernmost island. The 60 family community is only reachable by boat and is completely dependent on fishing and trade with nearby villages. Ice is a matter of survival for the inhabitants of Monte Trigo. They need it for preserving the fish, hence the constant and frequent five hour boat trip (each way) to São Vicente, the nearest main island, for ice purchase. It is a process far from efficient, wasting precious time that could be used in other activities. A reliable and clean source of energy, which would allow a long term sustainable and affordable electricity service, would not only address basic needs like lighting, communication and community services, but also other economically productive activities like ice production.
It was because of this need that local entities came together to develop an off-grid solar energy project. It was financed under the ACP-EU Energy Facility program and lead by the local private water company Aguas de Ponta Preta (APP), in consortium with the municipality (Câmara Municipal de Porto Novo, CMPN) and other entities.
The facility installed in Monte Trigo is a multi-user solar micro-grid (MSG) based on a photovoltaic generator, a storage battery, electricity monitoring, control and power conversion equipment, and a low voltage distribution grid. The 27.3 kilowatt peak PV generator is mounted on a wooden pergola that provides shade to the village’s schoolyard, thus adding value to the community.
The PV power plant is based on a DC-bus configuration and a maximum power point tracking charge controller, while the storage comprises two 48 volt batteries with a total capacity of about 370 kWh. Two dual inverters, with a rated power of 7,000 kVA each, convert the DC electricity into 230 V 50 Hz AC, which is finally delivered through an 800 meter aerial distribution line to the 60 final end-users. Among them is a school, a church, a kindergarten, a health center, a satellite DVB TV system, three general stores, and 22 streetlights of 70 watts each (high-pressure sodium lights). The old 20 kVA generator will now be used as a backup supply and, if needed, to also charge the batteries, with the bidirectional dual inverters operating in parallel with it.
Controlling energy demand
The implications of the different charging levels of the batteries as well as concepts of a sustainable and rational use of solar energy must be understood by the end-users and introduced into their daily habits. Therefore, the concept of an Energy Daily Allowance (EDA) was established in the Monte Trigo project.
The EDA makes the demand control more intelligent and flexible by introducing the concept that the energy available to each user is capped at an agreed maximum. This ensures that the plant operates within its rated design and there will be no blackouts or unforeseen increases in operating costs. Also, higher back-up diesel fuel consumption and components like batteries and inverters will operate within their specified range, to increase efficiency and lifetime. Nevertheless, this limit is flexible according to the plant’s condition and on very sunny days users are encouraged to make use of the surplus generation at no extra cost.
In the initial phase of the project, the designers of the system interviewed users to assess their energy needs and their willingness to pay for the 24 hour service. This ensured that the community felt involved, as each family chose to contract the monthly EDA fee that better fit them. It also allowed technicians to understand in detail what would be the best technical solution for the village.
Trama TecnoAmbiental (TTA), the company that designed and implemented the Monte Trigo project, had used the EDA concept in other rural electrification projects in different cultures and parts of the world and it has been well accepted because it responds to users’ needs accurately, guides them through the management of energy use, and also establishes a fixed monthly energy budget.
The implementation is done through a special type of meter (called an electricity dispenser) that permanently shows the user the available energy allowance and includes a signal to encourage or restrict consumption, according to the plant’s condition.
The EDA is a vital design feature, as it is the element from which the PV generator and all the other major system components is sized. So it is essential to determine in a detailed and accurate way each user’s energy demand. It also estimates any future increases, according to the community’s specific social and economic environment.
A tailored energy service
The Monte Trigo project’s service was set up using a mixed private/public-utility concept, in which the municipality and the water company APP are directly responsible for the service management and operation and maintenance (O&M) activities of the facility.
Tariff collection is based on fixed monthly rates related to the EDA and was established within the population’s payment capacity. This not only sustains O&M but also partially pays back the capital costs. An example of the adopted tariff options in Monte Trigo is shown in table 1.
The O&M activities are organized in order to involve local users and are structured around a concept of three levels of involvement: the end users, the fist-level O&M up-keeper/user, and the second-level O&M technicians.
Energy demand type
Energy Daily Allowance (Wh/day)
Power limit (kW)
Table 1: Example of tariff options for Monte Trigo.
The first level includes the users themselves, as they are the first component of a successful and durable service. The objective is not only to support them in maintaining their home installation, but also to make their electricity consumption behavior and habits more efficient.
The second level includes a team of trained users, responsible for the basic daily operation, maintenance and, in case of specific alarm or issues, reporting.
Finally, the operator’s technical personnel are the focal point for problem-solving, ensuring substitution when end-of-life is reached, as well as for specific maintenance and overall activities.
To ensure the successful implementation of this approach, training and capacity-building sessions were performed by Trama TecnoAmbiental previous to and during commissioning activities on all three levels. They included theory and practical demonstrations to levels two and three, and also to the project developers’ (the municipality’s and the water company’s) personnel.
In the same way, the final users were trained to understand the dispenser/meter operation and to know how to deal with a PV-based electricity service. Practical demonstrations were also performed, directly involving the users, who responded very enthusiastically. The Monte Trigans seemed to be well prepared to accept the basic concepts introduced to them and in a few days started to efficiently manage their energy allowances.
As with any successful rural electrification project, Monte Trigo involved many partners from different parts of the world. In isolated communities such as this one, the quality of the different components of the system gains new importance, so it is essential to involve experienced companies for each job.
In this case, the project mainly involved three companies: Trama TecnoAmbiental, Atersa and Studer Innotec.
The design and implementation of the Monte Trigo project was managed by Trama TecnoAmbiental S.L. on behalf of the developers. Founded in 1986, TTA is an international consulting and engineering firm working in the field of renewable energies, environmental projects and technology development in many developing countries.
The A-130P modules of mid-power range, which are chiefly used for off-grid projects, were supplied by Atersa (Aplicaciones Técnicas de la Energía S.L.). Each of the 210 modules installed contains 36 polycrystalline cells. Atersa also designed the special pergola to aid the installation of these modules at the local school and supplied the batteries and all the structures required for the installation.
Due to the engineering design, concept and size of the micro-grid, Studer Innotec’s Xtender inverter-charger, the XTH 8000-48, was chosen to supply a flexible management of the energy production and consumption. This facility is composed of two partially independent micro-grids with separate solar photovoltaic generators and batteries. However, both grids are able to share excess energy with the other, thus ensuring an optimal use of the produced solar energy. The flexibility of the Xtender dual inverter-chargers enables client-specific configurations for optimal management of the available energy.
From the first days of operation, the local authorities showed their satisfaction with the new 24 hour electricity service, as demonstrated by the visit of the President of the Republic of Cape Verde, Jorge Carlos Fonseca, and the European Union Ambassador in Cape Verde, Josep Coll, shortly after the project was commissioned.
But most of all it is the enthusiasm of the Monte Trigo population which demonstrates the success of the project. The villagers’ habits adapted very easily to their new electricity source. Major changes are already shaping the life of this community: one user already bought his first refrigerator (with an A+ energy rating) and local workers brought in a welding machine from the nearby village to fix a structure with a defect. It was the first time they were able to use something like this in the village.
It is expected that with the two ice machines capable of up to 500 kg/day production using the insolation peak of the day, solar surplus generation will improve the commercial activities on which the village economy relies.
Simon Rolland, Secretary General, Alliance for Rural Electrification