Designing Microgrids for the Solomon Islands

There is a lot of interest in the idea of 100% renewable energy both from a political and technical perspective. To understand some of the issues surrounding this goal it is useful to look at smaller systems where high penetrations of renewables are starting to become more common.  It may be that 100% renewable energy is more reasonable goal for a small microgrid, rather than on a large national or regional grid. At HOMER Energy we have been analyzing the economics of integrating different penetrations of renewable power into microgrids for decades. This is often to provide energy access in remote areas that haven’t traditionally had access to reliable electricity, or any at all. We were recently tasked by the World Bank to look at power options for a small village in the Solomon Islands, and asked to compare the costs of a 100% renewable power system that had no diesel generator for backup, with a system that had a backup generator.  

It turns out there are important economic advantages to including a relatively small amount of non-renewable backup power in a renewable system that might include solar and/or wind plus battery storage. And, this result shows up frequently in HOMER Pro, in many types of system configurations. In other words, backing off from the 100% renewable goal – even just slightly – can produce dramatic cost savings. The reasons are fairly technical but easy to observe in the context of HOMERPro software.

The Solomon Islands are located in the western Pacific, east of Papua New Guinea and have a population of about 600,000 people scattered among the many islands. More than 75% of the people are engaged in subsistence and fishing. Most goods, including diesel fuel for energy generation, have to be imported at considerable expense. Eighty-seven percent (87%) of the rural population or 495,000 – are without access to electricity. As a result, renewable energy offers the promise of important cost savings to the people of the Solomon Islands.

The Solomon Islands have an excellent solar resource, but like many islands and other parts of developing countries, they have a hard time supplying reliable and affordable power.  The loads are either too small or too isolated for an extension of a larger grid to make economic sense.  Their challenge is shared by islands and developing countries around the world. In many parts of the developing world the national utility is not supplying reliable and affordable power even to the main cities, but supplying reliable, affordable power with conventional technologies to the smaller, more isolated areas is even harder.

Fortunately, due to advances in renewable power, power electronics, and storage, these smaller more isolated areas now have new options that require new ways of thinking. Instead of simply installing a diesel generator that is relatively cheap to install but very expensive to operate, a system getting the bulk of its energy from solar (or wind) is relatively expensive to install but very inexpensive to operate.  It is also a more complicated system because solar and wind do not stand on their own. They require some combination of storage, load management, and/or backup generation to provide consistent, reliable power.

One of the big advantages of these more complex systems is their ability to supply 24-hour power. All around the world there are small diesel systems that only supply part-time power because a diesel generator sized to meet a peak load is horribly inefficient for  supplying smaller loads.

The challenge for designing a 100% renewable system comes during the exceptional periods when there are multiple cloudy days in a row. A system large enough to continue delivering the same level of service during those periods would have substantial excess capacity during the other 95% of the time.  Alternatively, the level of service could be reduced during those periods.  That would require either sophisticated load management or behavior changes on the part of the end users.

We modeled these alternatives, including an all-diesel case for comparison, and given   the capital costs, operating costs, fuel consumption, and carbon emissions of these alternatives, the system with large renewable energy penetration and diesel backup – for those cloudy periods – clearly outranks the 100% renewable system for economic performance.


  1. To all of the people suggesting various biofuels as a way to get to 100% renewables. You are absolutely right that biofuels as a backup to solar and wind can get you to 100%. Most places don’t have enough potential biomass for that to provide 100% of the energy requirements, but a combination with solar (and wind, where the resource is good) is a good pathway to 100%. Now, we just need the biomass power industry to reach a level of maturity that we are seeing with solar. In the meantime, 80% renewable is a huge improvement over the status quo.

  2. We at Ocean Current Energy( have been working on modular portable axial turbines with a rotor diameter of 1-1!/2M that can be launched and serviced and nested from a riverbank that depending on the current speed could each produce a few KWs continuously.

  3. We have had a successful pilot trial in the Solomons of a biomass gasifier dual fueling a diesel genset amongst other things. Fuel was coconut shell & palm chunks. Complete transition to non fossil fuel power is readily achieved within the skills & knowledge of the local community.

    1. Have you also considered the use of pure coconut oil for Diesel engine powered generators?

  4. Islands are becoming the case studies for microgrids. Examples are Puerto Rico and Hawaii among others. In Alaska Kodiak Island is being converted to primarily renewables. One of the lessons learned is discussed in this article about keeping conventional generation available. Nonetheless the amount of renewables is quite substantial in Kodiak. It just took a combination of equipment to make it happen.

  5. This is an eminently rational and quite predictable result. 100% renewable just for its own sake is an unreasonable proposition. This is an example of diminishing returns to scale. That which is technically possible is not necessarily optimal. One must always keep in mind the reason we do what we do and that is to deploy energy to improve the quality of life for people.

  6. what about using jatropha as a biodiesel for the fuel of the genrators instead of conventional diesel wont it still be more cost effective and less polluting? given that jatropha grows in arid land

    1. … not the best solution. The only “advantage” of Jatropha oil is that it is not edible (but mor or less toxic).

  7. We in The Bahamas have the same ideas. Some smaller islands could be powered this way. We are also exploring to subdivide the main island’s twenty-some substations to sub-grids where each substation would be self sufficient with energy. We have a lot of customer owned backup generators and these could be part of the design, but to automate this would require further dividing the area with sensors and switches that would sense demand and supply and make intelligent decisions what power source to activate. This idea also requires real time load data from each segment to predict and pick resources where available. We would need to approach this scientifically and technologically.

  8. When doing the multi year analysis, how do you assume the anticipated drop of storage prices? Cost of storage will have a big impact on the generation mix you select.

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