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March/April edition preview: Spotlight on ‘Solar Fuel Savers’

Dr Daniel Davies

Dr Daniel Davies, Solarcentury’s director for East Africa, discusses the pros (and challenges) of hybrid PV systems — those plants that use the sun to reduce electricity costs for diesel generator applications.

In many parts of the world diesel generators are commonly used to generate electricity often as a back-up when the grid fails, or when there is no grid power available. Diesel is the usual choice of power generation when there are no other alternatives available. However, diesel generated power is expensive and increasing oil prices are hitting the bottom line for many businesses who are struggling to afford to keep their lights on. Blackouts are already a common occurrence in many parts of the world and this is set to continue unless other energy sources are developed.

Solar photovoltaic power is being deployed as a cost competitive alternative to diesel power. New control strategies enable large PV systems to be operated in parallel with diesel generators, which act as a back-up power source for when the sun isn’t shining. This kind of system is called a Solar Fuel Saver, or “SFS.”

Operating solar PV plants alongside diesel generators presents a number of challenges, including how to determine the best way to finance the investment and how to operate the PV system. Utilising SFS technology means that PV systems can run alongside diesel generators without the need for expensive batteries. The SFS control system manages the output from the PV system to ensure that the diesel generator operates at a minimum, and also so that the diesel generator can be deployed if loads rapidly increase or if clouds momentarily reduce the solar output.

One of the most common SFS applications is where PV is being used to reduce the off-take from the public grid in places with expensive and intermittent power, and then to use the same solar PV system with SFS control to work in parallel with the standby generators. This reduces fuel consumption without removing the essential back-up of the diesel generator for night time operation or when the sun is not shining. Where local utilities do not allow reverse power flow into the distribution network, the SFS can be used to switch off the inverters when reverse power flow is about to happen.

Costs. For many countries, the cost of diesel is typically US $1-1.5 per litre (fuel costs per kWh of diesel-generated power can exceed US $0.30 per kWh.) The cost of power from solar PV systems is generally 10-15USc/kWh, depending on finance coasts and radiation.

Adding a solar PV system to a network to offset diesel consumption can significantly reduce overall energy bills. In remote areas the cost of energy is often the most significant business cost so there is significant potential to boost profits and competitive advantage. Like all renewable energy technologies the up-front investment is the major cost item. However, once a PV system is installed there are no on-going costs besides cleaning and inspection. (There are definitely no fuel costs!) 

Sizing and unknown interfaces. Using solar PV in parallel with an intermittent grid and/or standby or bulk diesel generators presents additional challenges when compared to a standard grid tied PV system. The initial design challenge relates to the sizing of the system components which links back to the need to gather as much operational information as possible.

The more complex challenge covers interfaces. Linking an inverter-based PV system to an existing electricity system for which there are no drawings where equipment is old requires careful design and installation.

Logistics. Many of the sites using diesel generators are remote. To that end, getting solar PV to these sites may require many truck loads over rough roads with uncertain off-loading facilities. However, once the panels are installed on the ground the fuel is cost-free whereas a generator needs a constant supply of expensive fuel.

Look for the forthcoming March/April edition of Renewable Energy Focus magazine to read this article in its entirety. Subscribe online to receive your free issues.


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Energy efficiency  •  Energy infrastructure  •  Photovoltaics (PV)  •  Policy, investment and markets