Off-grid power to remote locations: a balanced mix of renewable and fossil sources

There are articles around the web assuming that off-grid power can be supplied by 100% renewable sources coupled with storage facilities. In most actual situations that’s not the case.

When approaching the sizing of a power supply system two parameters are essential: [1] the availability rate and [2] the variations of the power source over the year and over the day.

The reason is that you cannot ensure 100% availability of a source which is itself not 100% available, unless you increase the size of the storage to a degree which makes the system either not financially sustainable or technically impossible to be operated efficiently.

The availability rate differs widely depending on the users served by the power system. Typically, the required availability is around 95-98%. In some cases (e.g. oil pumping systems, mobile telecom infrastructures) the rate must be close to 100%. When talking about solar power, data sources provide the typical reverse-bell daily irradiation diagram, but no clues are available about the variations (actually the mean square variation) around the average value.

You must then make assumptions according to historical weather data to define the number of continuous days of full clouds your system would be required to face in order to grant the users with the required availability rate.

Another point of concern is the seasonal variation of the irradiation.

If the PV generator is sized to supply enough energy during the winter (or low-sun) season, you must expect to “waste” energy during the summer – unless the user has seasonal power-loads consistent with the seasonal variations of the solar irradiation (like e.g. seasonal farming).

It won’t be even thinkable to have batteries sized to store months of energy for only a 2-cycle duty per year (unless you are capable to find other means to store the energy locally).

There is also a relationship between the size of the solar generator and the storage size. The batteries provide for two services: [1] to store the energy produced by the PV plant in excess of the energy supplied instantaneously to the user and [2] to supply the loads with energy as the PV plant is not producing. The point is that the lifespan of electrochemical batteries is affected by the number of charge-discharge cycles as well as by the completeness of each cycle. The more the cycles are complete (according to the set-point provided by manufacturers) the more the batteries last. So the number of cycles has also to be factored in the economic simulation.

What it turns out in most of the cases, is that the optimal system’s solution requires a programmable source of power – typically a diesel or LNG genset.

The genset has two functions: to recharge the batteries during low-sun periods (and/or to feed power directly to the loads) and to contribute to reach the required availability rate. The good point is that given that the batteries may supply (for short periods) a power capacity higher than the generator’s peak power, the generator’s size does not have to bear the full loads’ capacity.

Simulations with a spreadsheet help come to the optimal mix of solar power and fuel-powered generator in a proportion generally around 80/20 of the total energy supplied.

Which is indeed by far cheaper – and environmental welcoming – than a 100% diesel-fuelled power system.

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Guidelines for grid-connected energy storage systems by DNV-GL

DNV-GL-guidelines-storage-2016[18-01-206] Guidelines for grid-connected energy storage systems by DNV-GL have been issued at the end of 2015. The comprehensive document covers the safety, operation and performance of grid-connected energy storage systems. These aspects have been assessed for electricity storage systems in general, with emphasis on lead-acid, Li-ion and redox flow technologies and Li-ion capacitors.

The proposed guidelines are limited to common requirements, based on worldwide accepted regulation and best practices like IEC, ISO and IEEE standards. Any electricity storage applications at the high, medium and low voltage grid level as well as home energy storage are considered within scope of the document – which is available for free download formthe DNV-GL website here >>.




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New investment model for the off-grid-energy sector in Africa

shelter new House

A new investment model for the off-grid-energy sector in Africa that seeks to bring securitization to the off-grid sector in Africa has been developed by the Dutch investment firm Oikocredit International teams with London solar innovator BBOXX.

Backed by New York merchant bank Persistent Energy Capital LLC, the program aims to raise up to $2 billion over the next five years to turn solar in Africa into an asset class, and creating contracts for thousands of solar rooftop arrays to sell as bonds to investors.

Read more from the PV magazine >>.


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Enel Green Power, Powerhive to develop solar grids in Western Kenya

[11-01-2016] From PVTech. Enel Green Power is partnering up with mini-grid technology solutions provider and developer Powerhive to construct and operate mini-grids in 100 villages located across Kenya.

Agrialma 1

Farm-building roof-top solar PV (credit Solar Farm Srl)



The grids will require an investment of around US$12 million over the span of 2016 — 93% provided by Enel Green Power and 7% from Powerhive.

The project, which will be developed by Powerhive, will be comprised of solar mini-grids with a total installed capacity of 1MW and will be built in the Kenyan counties of Kisii and Nyamira. Once completed, the grids will provide clean energy to 20,000 homes, businesses, schools and health care centers, powering around 90,000 people in the process.

Francesco Venturini, CEO of Enel Green Power, said: Kenya’s rich and differentiated technology mix in the renewables industry offers a quite unique platform for the business development of Enel Green Power in Africa. This country couples a low electrification rate, still in the range of 30%, with one of the highest mobile phone penetration rates of the region, thus making this union ideal to implement innovative solutions able to integrate the electrification of rural areas with generation from renewables, storage facilities as well as advanced billing systems.”

Integrating these grids with energy storage facilities will give these systems the ability to balance supply and demand, reducing concerns over offset variations in customer loads and unpredictable spikes in power generation.

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Demystifying microgrids

glob-off-grid-mapMicrogrids are multiple generation points and loads under one control system that is optimising the generation and the power distribution to the users. Microgrid refers to distributed energy resources and loads that can be operated in a controlled, coordinated way, optimizing the use of the grid resources.

The main features of microgrids are:

  • they can be connected to the main power grid, operate in “islanded” mode or be completely off-grid;
  • they can be supported by storage systems and grid-regulation systems
  • compared to centralised generation systems connected with multiple-voltage grids,  they account for more reliable and better quality power supply, grid resiliency, source independence almost no grid losses;
  • can be tailored to each customer’s requirements;
  • microgrids are scalable and there is no cap as to size; can power remote mines, industrial and commercial sites, villages, communities, clusters of farming facilities.

Microgrids can deliver energy at a lower cost compared with the energy supplied from far-away generation points, since they are optimized for the the local conditions. Microgrids work at best when exploiting local sources of fuel – typically renewable sources – and geografically concentrated loads.

The trade-off between a centralised system and a microgrid is based essentially on the assesment of transmission costs and generation costs.

An interesting post about how India is planning to develope microgrids can be found here:

A new frontier for the development of microgrids is the financial sustainability of a business model in which there is not a major off-taker signing a PPA to grant the power purchase for the time required to pay back the investment.
Marco Bonvini

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Solar-diesel hybrid and storage projects targeted by a large investment fund

2015-10-22 | According to THEnergy, a renowned investment company has established a fund between 100 and 200 M€ for hybrid diesel-electric power systems addressed to off-grid industrial sites worldwide. The equity is scheduled to be invested within a period of three years. Taking into account additional debt capital on a project level the finance company expects the total investment to be in the range of EUR 200–400 million. Read the full post here from Solarserver.

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DNV-GL Pilot projects picked focused on hybrid marine development

The shipping company Nor Lines will take the lead on the cargoferry project.

The shipping company Nor Lines will take the lead on the cargoferry project.

Global classification society DNV GL and 25 partners from the Norwegian maritime industry and the Norwegian authorities have presented the five pilot projects that will be pursued as part of Norway’s Green Coastal Shipping Programme. Four out of five include #hybrid #marine engines or infrastructures.

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New Offshore Service Vessel with hybrid diesel-electric engine

OSV-Siemens-1Innovative (and bold) Offshore Service Vessel (OSV) dedicated to off-shore wind turbines came on line recently from a concept devised by Siemens which features a hybrid diesel-electric engine to propel the ship. Read the original post here and download here an interesting infographic.

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Hybrid Marine Propulsion (Diesel-Electric Drive) – A project to assess performances.

Overall Concept

Hybrid Marine Propulsion Systems – propulsion systems coupling diesel engines with electric drive – have been around only for a few years but the industry is currently growing at a 12% rate y/y and is expected to grow at a 8% CAGR up to 2022 [1], compared with a 3% rate for standard fossil-fueled engines.


Though type-certification standards are long-established about single components – engines, generators and batteries, battery management systems – there are no standards about the hybrid systems as a whole and more specifically about performance prediction systems.

Published trials by engine and ship manufacturers claim significant results in terms of fuel saving and emissions reduction in actual installation on OSVs [2], tugs[3], ferries . Still there is no evidence of the methodology used to calculate the performances and to prove consistency in the results with different vessels.

Project outline and expected results

It is known that the performance of diesel engines at partial loads is different from the performance at full load. …. Continue reading from the original post on LinkedIn here >>

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Off-grid bivouac in high mountain | Bivacco Fanton | Italian Dolomites

An off-grid bivouac in high mountains, at 2.660 mt above the sea in the heart of the Italian Dolomites, was the ambitious challenge posted by the local authority. A new “Bivacco Fanton” bivouac was required in replacement of the old one worn out, and located close to “Forcella Marmarole“a saddle connecting two valleys frequently reached by trekkers and skitourers.

Bivacco Fanton concept

Bivacco Fanton concept by Arch. M.Calvi and G.Ferrari

The requirements were challenging: self-powered with sufficient energy storage for communication and minimal heating, equipped with TLC connection, roomy for 12 people, accessible in winter with deep snow, designed to be almost maintenance-free, less for a twice-a-year food and water resupply. The construction had to be carefully planned to allow the transportation by chopper and the assemble of the kit in a dash time.

The energy requirements and the power supply planning are here (summary table) and here (detailed sheet).

Our partners arch. Matteo Calvi and arch. Guido Ferrari did not win the contest, but they worked hard and developed a cool project we like to share it here. Specifications and detailed design available upon request for other applications -> please contact us here.

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