Assessing SA-US renewable energy projects

July 14th, 2016, Published in Articles: Energize

 

A solar park under construction in the heart of the Northern Cape sheds light on a combined solar photovoltaic (PV) and concentrated solar power (CSP) model which sets out to create renewable energy for baseload power. The US Embassy recently invited EE Publisher’s assistant editor Pierre Potgieter on a tour of US funded renewable energy projects in South Africa.

Travelling the roads of the Northern Cape beyond Sishen, one soon encounters pools of light which look like farm dams in the semi-desert landscapes. However, on closer inspection these turn out to be utility-scale solar farms.

Jasper solar farm.

Jasper solar farm.

One such installation, about 30 km from Postmasburg, is the 96 MW-DC Jasper solar farm. Developed by US company SolarReserve, Jasper consists of 325 360 modules of fixed polycrystalline solar photovoltaic (PV) panels on a 145 ha plot of land.

The plant’s 96 MW-DC to 75 MW-AC ratio, higher than the usual 85 MW-DC to 75 MW-AC ratio, compensates for the natural degradation of solar PV modules to extend the plant’s lifespan by being able to produce 75 MW AC power to the grid for longer.

Jasper is located adjacent to another of the company’s solar PV plants, the 75 MW-DC Lesedi Power Project, and takes its name from the vermeil red rock which occurs in the area. Taking its name from the same rock, and a gem the company is currently focusing on, is the proposed Redstone Solar Thermal Power Project, a 100 MW tower-type concentrated solar power (CSP) plant with up to 12 hours of heat energy storage by means of a molten salt system. Baseload capacity and its scale have been two of renewable energy’s biggest drawbacks so far. Solar PV is limited to daylight hours, and its shortfalls are highlighted at peak energy demand periods in the mornings and afternoons, limiting it to supplementary power generation rather than baseload power generation. Storage capacity could change all this, and if it could be scaled, which the company believes it can, renewable energy could become a source of baseload generation.

Although CSP’s generation cost is decreasing and becoming more competitive with coal generation, it is still expensive. The company’s two solar PV projects (Lesedi and Jasper) are substantially cheaper than the proposed Redstone CSP plant. Jasper, the larger of the two PV projects, cost around R2-billion to build, compared to Redstone’s anticipated cost of R10-billion. Combining the two technologies into one big project, however, could see solar PV generation offsetting CSP’s cost while retaining its potential baseload benefit.

The company intends to combine Redstone, as a baseload project, with its two adjunct solar PV plants on the same site to run them collectively as one large solar park. If this implementation proves successful, it could pave the way to more and larger such implementations, potentially opening the way for solar energy to become part of baseload power generation.

Finding the ideal energy mix

Generating renewable energy at utility scale and making it baseload-ready is a technical feat which is only achievable on a project level. Making renewable energy viable as a baseload option and finding an optimal mix is another feat altogether.
One of the aspects of the US’s partnerships in South Africa is research and development work, among others in the field of energy research. (Energy investment makes up roughly 5% of US AID’s investment in South Africa.) Research developments, policies and best practices can be exported and adopted in other parts of the world too.

The Council for Scientific and Industrial Research (CSIR) is one facility which has adopted a strong energy research focus. Dr. Tobias Bischof-Niemz, the head of the CSIR’s energy centre, explains that an earlier study found wind energy to be more promising than initially thought and that this, when combined with solar PV’s rapid growth and low price, makes renewable energy a viable baseload option.

Optimising the energy mix for renewables

To realise renewable energy’s impact as a potential baseload power source means taking a holistic view at how it offsets the use or need for other (usually more expensive) baseload and peak generation, rather than only looking at renewables’ performance during peak demand periods. Using high resolution wind energy data (5 km2 at 15-minute interval resolution) and energy costing estimations, allowed the CSIR to create a simulated scenario to demonstrate renewables’ viability (specifically that of solar and wind) for baseload generation.

Bischof-Niemz says wind generation on a large scale, with strategic placement throughout the country, could ease currently observed intermittency variations. It is however the cost benefit and the great advantage of cost and output predictability which other generation options lack which make renewable energy so attractive for baseload power, he says. Having storage capabilities in the form of hydro is especially useful to realising renewable energy optimised grids and baseload power.

Another area of the energy centre’s many research topics is embedded (or distributed) generation, and it is also currently working on creating a micro-grid for the CSIR campus. The CSIR’s micro-grid will connect a mix of energy sources for research purposes, and with some of its environmental impact assessments still underway, its scale has not yet been determined. There is however one section of single-axis tracking solar PV panels already operational, with a dual-tracking system about to be built.

The research facility is in a unique position to experiment with different energy technologies, and with a 5 to 6 MW demand – similar to a small town – can do so effectively. The variety of operations also allow it to focus on optimisations, such as heat production being fed to heat sinks.

Mixing it up with micro-grids

Micro-grids connected to the national grid can form part of the generation mix, and comprises a mix of generation technologies. It can also be a standalone, grid-independent solution. ABB’s Tony Duarte recently implemented ABB South Africa’s own micro-grid at the company’s head office near Johannesburg.

The company’s 1 MW micro-grid runs in parallel with the national power grid, and connects to solar PV and diesel generation. Generation behaviour is programmed into the flash memory of controllers which optimise the energy mix on cost criteria, favouring renewable generation. “Penetration” – or intermittency introduced to the grid – makes frequency stabilisation essential, and in this micro-grid’s case a battery system is used to achieve this.

Battery technology, although decreasing in cost, is still very expensive. For this reason, the battery in ABB’s micro-grid has not been scaled to full amount, but is instead scaled to economic viability to serve as a backup system until the diesel generation starts up in the event of a power outage.

Micro-grids offer many other benefits too. Since they are modular and scalable, they are easy to implement for short periods, and can be interconnected to run in parallel with or independent of national grids. This makes a micro-grid useful for remote industries such as mining which look to move away from, or decrease, diesel generation reliance, as well as for industries like the food and beverage producers which need an uninterrupted power supply.

Although micro-grids are generation agnostic understanding the generation technology’s behaviour and generation profile is essential in a micro-grid’s design.

Related Articles

  • Hybrid energy storage systems boost hybrid renewable energy systems performance
  • What would South Africa be like if totally powered by renewable energy?
  • The business case for microgrids
  • Energy for green buildings: Options and opportunities
  • Plug-and-play controller for high-pressure grinding mills