Thursday May 23, 2024

The facts of going solar

By Omar S Cheema
April 29, 2017

Part - I

Information is the most valuable resource in any economy and, by the same token, misinformation can be most damaging. This article is a riposte to a recent column titled ‘The perks of going solar’ (published in these pages on March 15) and aims to clarify crucial facts about solar technology, its business economics as well as to correct any public misconceptions.

Post-truth spin, fake news and alternative facts are deeply harmful when they encroach upon scientific and technical topics of public importance. Solar power is a topic of global importance. It is key to the future of human life on the planet and vital to the energy security of countries like Pakistan. Therefore, it is necessary to set the record straight.

Before I highlight the omissions and inaccuracies in the article, let me briefly summarise why solar electricity is vital for Pakistan. First, the high levels of insolation and the vast tracts of unused barren land in every province are an ideal combination. Second, there is no need to import any fuel feedstock. Third, the production cost is fixed for a period of 25 years, since there is no volatility of fuel import prices. Fourth, the lifecycle production cost can compete with, if not beat, other sources, especially in a full economic costing.

Fifth, there are no health hazards from pollutants. Sixth, unlike thermal power plants, it does not need the withdrawal and consumption of enormous amounts of freshwater to drive the steam turbine – a dangerously scarce resource for Pakistan. Seventh, the electronics interface can be used to provide better grid stability services than fuel-based power plants. Eighth, it involves a negligible technical risk, relatively simple operational maintenance and a highly predictable long-term output. Ninth, the daily output profile closely matches the daytime consumer demand pattern in the country. Tenth, large utility-scale plants can be commissioned in a matter of months rather than years.

Now for the riposte. First, the article fails to recognise a basic difference between solar cells and modules when it talks about the efficiencies of mainstream silicon photovoltaic (PV) technology. Modules, not cells, are quoted in price to project developers and delivered for deployment in the arrays of commercial power plants. Module efficiencies are shown on the datasheets for standard testing and normal operating conditions. The cells are constituents of the modules, with higher efficiencies than the latter.

Commercially available silicon PV modules have crossed power conversion efficiencies of 20 percent – well beyond cell efficiencies “between 14 percent and 18 percent”. This includes the Sunpower X-series, the Panasonic HIT heterojunctions and the JA Solar JAC MP6PA-4.

Second, multi-junction cells may use a variety of materials, including the silicon and the III-V semiconductor family. To rank efficiencies, the irradiation condition of 1-Sun (1000 W per square metre) or concentrated sunlight (multiples of 1-Sun) must be specified to ensure like-for-like comparisons. The SpectroLab of Boeing holds the 1-Sun record for a multi-junction solar cell with a certified efficiency of 38.8 percent. The highest attained cell efficiency, with concentrated sunlight, is 46 percent by a Fraunhofer ISE-Soltec consortium.

Third, and most importantly, there is no single cost figure – the “2.3 cents/kWh” repeatedly referred to – for PV electricity generation that can be universally applied as a site-independent benchmark at any time. The PV production cost figure-of-merit is bound to vary with the insolation, ambient temperature and other meteorological conditions for the project site, as well as the cost of financing capital.

Let’s move on to rectify other misleading discourse. Cadmium telluride (used in the top tier modules of First Solar), amorphous silicon and micromorph silicon solar cells are not printed. Any such attempt has failed, at least for all practical commercial purposes. As for CIS/CIGS, a start-up called Nanosolar raised hundreds of millions of dollars to try and manufacture these thin-film solar cells in a roll-to-roll (R2R) printing process, but failed, went bankrupt. Ascent Solar has managed R2R for CIS/CIGS, but its impact has been mostly limited to the much smaller market of solar-charged consumer goods. Solar Frontier is the industry champion of the CIS/CIGS modules. Solar modules on flexible substrates have now been manufactured for both thin-film materials and mono/poly-crystalline silicon. It doesn’t have to be through R2R printing.

The idea of ‘solar paints’ is essentially the same as that of printed solar cells, ie R2R module manufacturing from solution-processed materials. The leading semiconductor hope for this possibility is a subset of materials called perovskites, a direction pioneered by the prolific Prof Michael Graetzel at the EPFL, supported by Professor Mohammad Nazeeruddin and a host of global collaborators. The Pervoskite PV is distinct in several ways from the liquid-state dye-sensitised solar cells, which were earlier invented by Michael and Brian O’Regan. Perovskites are being combined in two-junction cells (aka tandems) with silicon or CIGS/CIS. The common idea is to capture a greater share of the incident solar spectrum without compromising power output. In a single junction cell, there is an inherent trade-off between voltage and current because of the single bandgap constraint.

The recommended reading to understand the fundamentals of PV is Jenny Nelson’s Physics of Solar Cells, For information on CIS/CIGS, search the publications of Professor Tiwari or the projects of Solar Frontier. For crystalline silicon, read the works of Martin Green at University of New South Wales.

Let’s fast-forward to the mention of solar thermal – also known as concentrated solar power (CSP) – in the context of large power plants, because it concentrates sunlight using a vast array of mirrors or lenses onto a thermal receiver. Concentrated light is first converted to heat and then electricity, so unlike PV it’s an indirect process. To say that CSP is “economically unviable” is again grossly misleading and seems oblivious of what is going on in the field. Last month, Chile ordered an additional 450 MW of CSP (a price of only 6.3 US cents/kWh) – hardly a sign of being “economically unviable” per se.

PV is much more prevalent than CSP because the latter relies on direct normal irradiation (DNI), while the former uses both diffuse and direct sunlight. Apart from a high threshold DNI, CSP also has a greater water consumption requirement and lacks the simpler modular planning and faster deployment time of PV.

The electricity produced by CSP is not as cheap as PV, but it can store energy (in the form of heat) to deliver power as an around-the-clock “dispatchable” source, ie an exact amount on demand. Not only are PV and CSP financially feasible on their own – with the respective advantages of low cost and energy storage – but they can also be merged in hybrid PV-CSP projects for a more potent economic contribution.

To be continued


The writer is based in London and provides advisory services for
renewable energy and energy
efficiency ventures and projects