PV Diesel Hybrids: Spotlight Sub-Saharan Africa

For several decades in Sub-Saharan Africa and around the world, diesel generators have been the solution of choice to bring power where the grid does not reach. Even as a supplement to the grid, diesel gen-sets are heavily used to keep homes and industries powered.

Despite great progress in grid expansion and growth of renewable energy in Sub-Saharan Africa, diesel generators will continue to play a big part of power supply in the region.

In fact, in 2019, Sub-Saharan Africa had the highest share of electricity output from generators in the world, at 9% of annual electricity consumption, far higher than second-place South Asia’s 2%.

The diesel gen-sets with rating between 5KVA and 75KVA have accounted the largest part of the market share in recent years, largely because of the availability, low cost and versatility. There has also been steep growth in the larger sizes above 375kva

Manufacturing plants, retail shopping centers, commercial offices, hotels and hospitals are all reliant on diesel generators for reliable power when the grid fails.

In Sub Saharan Africa Nigeria leads the way with the most diesel generators, but East Africa is also heavily reliant on diesel gensets, and East Africa has the fastest growth in the continent. The overall GDP growth for East Africa in 2019 was 5% with Ethiopia topping the chart with a 7% growth rate and a population of over 100million. Kenya is the economic hub of East Africa and a big player in the diesel generator industry. Rwanda also relies heavily of diesel generators to power the industrial sector. Uganda and Tanzania as well rely on diesel generators to compensate for the poor grid. And Ethiopia is expected to dominate the diesel generator market this decade due to fast growth and large population

However, the use of diesel generators is not an ideal solution; there are several challenges that are presented with the use of diesel generators.

Problems with Diesel Generators

One challenge with the use of diesel generators is the pollution. Burning diesel pumps black carbon and heavy particulates into the atmosphere contributing to pollution and health risks.

Another challenge with diesel generators is the high operating cost, especially in terms of the diesel consumption.

Fuel costs for the gen-sets continue to rise. And even though in recent years there has been a dip from the high prices of early last decade, these dips are generally short lived and the trend line over a large time frame continues to go up. Whether or not the price of diesel is in a climb or a recession, the fact remains that with reliance on a diesel generator, the cost of diesel is a never ending expense.

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In addition to the fuel price, the logistics of never-ending diesel consumption is a challenge to many organizations. Often times the gen-sets are in remote locations, and fuel has to be transported to remote regions which represents an additional cost, as well as additional risk in case of weather issues, political issues, safety and violence issues, and more.

The effective costs increase even more as a result of the necessary storage.

At the same time that heavy diesel consumers have been struggling with price and logistics challenges, solar PV system costs have declined dramatically, and solar technology is rapidly advancing. The cost of solar PV equipment has dropped by more than 50 percent within the last three years. The global weighted average levelised cost of electricity (LCOE) for utility-scale solar photovoltaics (PV) fell an estimated 77% between 2010 and 2018, and recent advances have made solar power more efficient than ever before.

Solar power generation assets are typically smaller in scale, and highly modular. They also have a front-loaded cost profile characterized by no fuel costs and limited operation and maintenance (O&M) expenditure.

There is no doubt that the global energy system is in an irrevocable transition to a more sustainable future, with renewables playing a central role. Renewables have become increasingly cost competitive, representing the best option for expanding and modernizing a power system.

Compared to diesel generators, PV systems are more flexible, more inexpensive to own and operate, and more flexible allowing for modular expansion as energy demand grows, and PV systems produce no carbon emissions.

But how can PV technology help owners of diesel gensets?

How can the sun help diesel generators?

One of the more exciting and practical developments in the solar industry is the solar diesel hybrid, or PV diesel hybrid.

This application combines diesel generators with solar PV modules to create a mix of solar energy and diesel energy. In this way diesel consumption can be reduced, instead consuming the free energy from the sun during the daytime, with the diesel used as a supplement and a backup source when the solar energy is not enough.

Integrating diesel generators with photovoltaic arrays has several advantages, including reduced diesel consumption which translates to big fuel savings, reduced carbon emissions, and reduced wear on the diesel generators for reduced maintenance costs and longer useful life. Hybridizing existing generators is a great way for organizations to reduce operational costs while taking advantage of existing assets.

PV Diesel hybrid projects are quick and easy to install, however, the designs will vary from site to site. Some of the considerations are the incoming solar radiation, the availability of open land for locating the arrays, the conditions of existing diesel engine, and load profile.

PV-Diesel Hybrids

A PV diesel hybrid system generally consists of a PV array, diesel gensets and an intelligent management controller to control the mix of solar energy and diesel energy.

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The basic idea is that while the sun is shining and the PV array is generating power, you can reduce or eliminate your diesel consumption. The PV inverters will be synchronized to the generators via the fuel save controller, and the PV and diesel can run simultaneously.

However, the real application is not that simple.

First, it is important to understand that diesel generators are designed to run with a load. This may seem trivial but loading a generator properly is essential for a healthy engine and a long engine life.

The ideal load range of each generator will depend on the application and the rating of the genset. Generators can run in prime application, and stand by application. Generally speaking, prime applications will use the generator between 50 and 85 percent of the nameplate value. And you must also be aware of the minimum load which is usually around 30% of the nameplate value.

Manufacturer recommended service intervals and the projected lifetime of internal components are based on operating the genset within these ranges to deliver the ideal mix of generator performance, power density, and long life.

This is why the design stage of a PV Diesel hybrid system is critical to ensure that the load is supplied continuously with the generators operating within the specified range, and also that the PV is optimized to take full advantage of the energy from the sun.

Operating a generator with less than the minimum load will impact the generator negatively. The most common consequence is that the temperature within the cylinders will decrease which allows unburned fuel and oil deposits to leak through the exhaust slip joints. Long periods of under loading will also allow a deposit buildup behind the piston rings and inside the cylinders. Ultimately this will lead to power losses, poor performance, shorter life of your components, increased maintenance costs and unplanned downtime or engine failure.

Proper design of a PV Diesel Hybrid will take into account the number of generators, and the size of each generator to make sure that the minimum number of generators will be used, and that none of them will be used below the minimum rated load.

In order to do that properly you must examine the load profile of the site. There is usually a baseload requirement that should not be left un-powered. Most often this can be assigned to the diesel generators.

Then you must observe how the load varies throughout the day, and compare to the solar irradiation pattern in the region. When you compare the solar irradiation pattern to the daytime load you can properly size the PV array to power as much of the load as possible without excessive clipping from over production.

In the sample load profile below you can see that diesel generators are powering the full load, and you can see the curve of the solar irradiation that is available during the daytime hours.

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The next image shows an example of what the PV penetration could be on such a site.

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In this example the baseload will be covered by one generator. When the load increases around 7am the solar is not yet enough to power the load so the generators will increase and power the load. As the sun starts to rise and the solar energy increases, the PV array is able to cover the entire variable load, and the generators reduce again to supplying only the base load, above the minimum rated load for the generators. In the afternoon as the sun starts to set the solar energy starts to decline and the generators again increase to cover the load. And when the loads reduce again in the evening, the generators resume powering only the baseload.

In this example the solar array is able to reduce fuel consumption by approximately 40%. There is a small amount of clipping in the daytime hours where the solar energy produced is more than the required load. This is lost power and should be kept to a minimum. When this happens the inverter must be instructed to reduce the solar power production to match the load exactly in order to prevent power flowing from the PV array into the generators.

Now you can see that in a PV Diesel hybrid system the solar array and the diesel generators must communicate with each other and work together to meet the load requirements. This is accomplished by a Fuel Save Controller.

Fuel Save Controller

The intelligent monitoring and controlling unit is called a Fuel Save Controller. This device communicates between the generators and the PV inverters. It makes sure the power from both devices is synchronized, and also matches the power supplied with the load required.

The controller has a reverse power protection to protect the gensets, against PV energy going in reverse into the gen sets. It also protects the gen sets from damage caused by operating below the minimum rated load.

The device can also allow for remote monitoring and reporting on the amount of PV energy produced and consumed, and also on the performance of the generators. There is active and reactive power control as well.

Generally speaking, when all factors are considered, a PV array can reduce fuel consumption by 40-60%, although in some cases it could be as high as 80%.

When and where does a photovoltaic diesel hybrid system make sense?

For industrial large-scale loads in remote regions, or even smaller loads, complementing diesel gensets with photovoltaics is the ideal solution under the following conditions:

  • When the effective cost of diesel exceeds one approximately $0.80 per liter.
  • When local solar irradiation is abundant
  • When generators typically operate through the daytime sunlight hours.
  • When logistics costs associated with diesel are high

In conclusion, all industrial owners of diesel gensets should look into hybridizing their operations with adding a PV array. There are financing options for hybridizing diesel gensets so the capital expenditure can be small. You can reduce your carbon emissions, reduce your operation costs, and increase your profits by pursuing a PV Diesel hybrid system.