CONCENTRATED SOLAR POWER

Concentrated solar power (also called concentrating solar power, concentrated solar thermal, and CSP) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight, or solar thermal energy, onto a small area. This is a scalable technology, however, the larger production appears to be the most efficient use of the related technology.

Concentrating Solar Power (CSP) Basics

Many power plants today use fossil fuels as a heat source to boil water. The steam from the boiling water spins a large turbine, which drives a generator to produce electricity. However, a new generation of power plants with concentrating solar power systems uses the sun as a heat source. The three main types of concentrating solar power systems are: linear concentrator, dish/engine, and power tower systems.

Linear concentrator systems collect the sun’s energy using long rectangular, curved (U-shaped) mirrors. The mirrors are tilted toward the sun, focusing sunlight on tubes (or receivers) that run the length of the mirrors. The reflected sunlight heats a fluid flowing through the tubes. The hot fluid then is used to boil water in a conventional steam-turbine generator to produce electricity. There are two major types of linear concentrator systems: parabolic trough systems, where receiver tubes are positioned along the focal line of each parabolic mirror; and linear Fresnel reflector systems, where one receiver tube is positioned above several mirrors to allow the mirrors greater mobility in tracking the sun.

A dish/engine system uses a mirrored dish similar to a very large satellite dish, although to minimize costs, the mirrored dish is usually composed of many smaller flat mirrors formed into a dish shape. The dish-shaped surface directs and concentrates sunlight onto a thermal receiver, which absorbs and collects the heat and transfers it to the engine generator. The most common type of heat engine used today in dish/engine systems is the Stirling engine. This system uses the fluid heated by the receiver to move pistons and create mechanical power. The mechanical power is then used to run a generator or alternator to produce electricity.

A power tower system uses a large field of flat, sun-tracking mirrors known as heliostats to focus and concentrate sunlight onto a receiver on the top of a tower. A heat-transfer fluid heated in the receiver is used to generate steam, which, in turn, is used in a conventional turbine generator to produce electricity. Some power towers use water/steam as the heat-transfer fluid. Other advanced designs are experimenting with molten nitrate salt because of its superior heat-transfer and energy-storage capabilities. The energy-storage capability, or thermal storage, allows the system to continue to dispatch electricity during cloudy weather or at night.

There’s more than one way to make good use of the Stirling cycle. Just ask the engineers at Infinia, Kennewick, Wash. They use it in both their PowerDish, a device already on the market that turns sunshine into electricity, and StAC, an innovative air conditioner that has earned development grants from the government. Both exemplify energy efficiency and sustainability.

PowerDish

In the PowerDish, heat from the Sun drives a free-piston Stirling power generator, an external combustion engine. A 161.5-ft2 parabolic dish made of mirrors bonded to curved sheet-molding compound reflects incoming sunlight onto a concentrator at the dish’s focal point. The mirrors are currently made of un-coated high-reflectivity glass and Infinia engineers see no need to add costly coatings at this time. Sunlight gets concentrated in an 800-to-1 ratio, which would raise the temperature at the heat-resistant nickel-alloy concentrator to 2,000°C if the Stirling generator didn’t extract heat from it and keep it at about 650°C, says Tim Talda, Infinia’s director for system electronics and controls.

You can learn more about this technology at: http://machinedesign.com/energy/infinia-uses-stirling-cycle-solar-power-and-air-conditioning. The company was bankrupted but the technology is still viable.

Solar Trough

A parabolic trough is a type of solar thermal collector that is straight in one dimension and curved as a parabola in the other two, lined with a polished metal mirror

Concentrating Solar Power (CSP) technologies use mirrors to concentrate (focus) the sun’s light energy and convert it into heat to create steam to drive a turbine that generates electrical power.

CSP technology utilizes focused sunlight. CSP plants generate electric power by using mirrors to concentrate (focus) the sun’s energy and convert it into high-temperature heat. That heat is then channeled through a conventional generator. The plants consist of two parts: one that collects solar energy and converts it to heat, and another that converts the heat energy to electricity. A brief video showing how concentrating solar power works (using a parabolic trough system as an example) is available from the Department of Energy Solar Energy Technologies Web site.

Within the United States, CSP plants have been operating reliably for more than 15 years. All CSP technological approaches require large areas for solar radiation collection when used to produce electricity at commercial scale.

CSP technology utilizes three alternative technological approaches: trough systems, power tower systems, and dish/engine systems.

Trough Systems

Trough systems use large, U-shaped (parabolic) reflectors (focusing mirrors) that have oil-filled pipes running along their center, or focal point, as shown in Figure 1. The mirrored reflectors are tilted toward the sun, and focus sunlight on the pipes to heat the oil inside to as much as 750°F. The hot oil is then used to boil water, which makes steam to run conventional steam turbines and generators.

These are utility scale solar power systems. They require land, permitting, grid management, employees, taxes, insurance and all the usual conditions for a mid-level business structure. There are many of these projects underway and ready for new investment capital and expansion and it makes perfect sense to join with existing businesses in this area.

Another very promising species of this concept is the use of concentrated solar with photovoltaic power generation. The global market for concentrated photovoltaic (CPV) systems is on the verge of explosive growth, with worldwide installations set to skyrocket 750% between 2013 and 2020, according to a report published on Tuesday by market research group IHS.

IHS is a global information company with world-class experts in the pivotal areas shaping today’s business landscape: energy, economics, geopolitical risk, sustainability and supply chain management. It employs more than 8,000 people in more than 31 countries around the world.

In the new IHS Report, Concentrated PV (CPV) Report – 2013, IHS predicts CPV installations will rise to 1,362 MW in 2020, up from 160 MW in 2013. Indeed, installations are expected to expand at double-digit percentages every year through 2020.

CPV technology employs lenses or mirrors to focus sunlight onto solar cells. While this allows for more efficient PV energy generation, the use of additional optics for focusing sunlight has also driven up the cost of CPV compared to conventional PV installations, limiting the acceptance of concentrated solar solutions.

The situation is changing rapidly, however, as advancements in CPV technology are reducing costs.

“What is happening in today’s CPV market is very similar to that of the overall PV space in 2007, beset by high costs and an uncertain outlook,” said Karl Melkonyan, photovoltaic analyst at IHS. “However, the CPV market in 2013 is on the verge of a breakthrough in growth. Costs for CPV have dropped dramatically during 2013 and are expected to continue to fall in the coming years. Furthermore, when viewed from the perspective of lifetime cost, CPV becomes more competitive with conventional PV in large ground-mount systems in some regions.”

Prices for CPV are retreating as manufacturing processes progress down the learning curve.

Average installed pricing for high-concentration PV (HCPV) systems are estimated to have decreased to $2.62 per watt in 2013, down 25.8% from $3.54 per watt in 2012. Rising volumes and improved system efficiencies are driving the decline, according to the report, which adds that prices will slide further at an annual compound rate of 15% from 2012 to 2017, falling to $1.59 by the end of 2017.

Taking lifetime costs into account

In the conventional PV market, cost analysis predominantly focuses on the module price-per-watt and the total installed cost-per-watt, IHS points out. When comparing the installed cost-per-watt of conventional PV to CPV, the cost of conventional PV is significantly lower.

“This is mainly due to the higher panel cost of CPV, given that CPV suppliers have yet to achieve the economies of scale, as well as a better balance of system and installation cost, because of the required tracker system,” IHS says.

“To be sure, conventional PV has a lower upfront cost and appears to be a more attractive option based on upfront system costs. However, this does not take into account the overall cost of the system over its lifetime, nor does it consider the energy yield of the system.”

Instead, the report adds, it is important to compare the levelized cost of electricity (LCOE). The LCOE estimates the cost of generating electricity at the point of connection, dividing the total lifetime system costs by the total energy produced over the system’s lifetime.

“Such a calculation is also necessary in order to compare the competitiveness of PV and CPV with that of conventional power generation.”

Using the LCOE, IHS predicts that system costs for HCPV will remain low enough to compete with conventional PV for large commercial, ground-mount systems in target regions. These are the areas with hot, dry climates and high daily irradiation at more than 6 kilowatt-hours per square meter of direct normal irradiation.

Power generation with solar tracking systems : CSP vs CPV vs Flat PV

Manfred Armoureux Blog

The following is a comparison of CPV (concentrated photovoltaic) to CSP (concentrated solar power), more properly called concentrated thermo-electrical solar power to flat PV with solar tracking.

CSP (concentrated solar power), more properly called concentrated thermo-electrical solar power

 

and flat PV panels with solar tracking

First, I should make clear for you that each one of those categories actually encompasses different sub-technologies. Solar tracking may be along one or two-axis. In particular, the CSP technologies show a great deal of variety between Fresnel, parabolic trough, parabolas and central receivers (there is plenty of literature available around there). CPV systems are usually not as well known but there is also very different systems : inflatable parabolas (Cool Earth Solar), Fresnel lenses (Concentrix solar), parabolic trough (Exosun), panels of small parabolas (Solfocus) and I am probably missing many other companies.

Notwithstanding these differences, I chose to distinguish only the 3 categories  mentioned above.

Flat PV vs CPV

We start with the easiest comparison.

Cons of CPV compared to Flat PV:

  • you only capture the DNI (direct normal irradiation)

Pros :

  • Price per peak watt, given that your concentrating systems costs less per unit of surface than the PV cells.
  • If your do cogeneration of heat using the (absolutely required) residual heat of cooling system, it is much easier to achieve significant temperatures (i.e. 60ºC)

So choosing CPV instead of flat PV can be summarized in two short questions :

  • How much radiation do I loose because of diffuse radiation and how much cheaper per unit of surface is my CPV compared to flat PV ?”
  • Could I use most of the residual heat ? Does it have an economic value for me ?”

CPV vs CSP

CSP systems are great toys for engineers : they are complex and require a very multidisciplinary knowledge. However, that engineers enjoy working on them is not what will make them successful on the market.

The main advantage of CSP compared to CSP is its capacity to produce also during night time (using thermal storage). Unfortunately, as far as I know, there is no country giving any special incentive for this. Thus, to the investors, it is irrelevant.

The other advantage is that, at the present time, big CSP power plants are able to produce electricity at a cheaper cost than CPV. However, CPV systems are more recent and prices may go down in the future as experience is gained.

Cons of CSP compared to CPV :

  • Not very scalable (although some organizations are working on the smaller end of the power range)
  • More maintenance leading to more O&M costs for small plants.

Pros :

  • Lower costs if you can reach  a size big enough.
  • Capable of operations during night (but as stated earlier, it may not be valued economically).
  • Possibility to do co-generation with higher temperatures (above 100ºC). This has not been exploited much so far, but there has been enough research suggesting that industrial applications are possible.

PV generators are quite uninteresting for engineers : it is almost too easy. But that is exactly what makes the beauty of it. The cost PV also already decreased seriously these last years and will carry on. On the other hand, that cost decreases are possible in CSP is not yet a clearly established fact .. but many companies are betting their money on it.

You can see more images of these and related devices by searching google.com for the term “image of concentrated solar pv”.

Third attempt for Dish-Stirling, Infinia’s Tooele plant goes ahead

By CSP World on 12 June, 2013

Infinia Tooele Dish-Stirling plant

Infinia Corporation has announced it has begun commissioning the first of seven commercial-scale PowerDish™ installments currently underway at the Tooele Army Depot, a U.S. Army installation in Utah, USA.

This project is likely to be the third attempt to commercially deploy the Dish-Stirling technology. The 1.5 MW solar power plant that includes 429 PowerDish units will be the largest Concentrated Solar Power plant to use the Dish-Stirling technology, after the decommissioning of the Maricopa Solar Project, a 1.5 MW Dish-Stirling plant developed by a consortium made of Tessera Solar and Stirling Energy Systems.

The Dish-Stirling technology has always been seen as the most vulnerable of the Concentrated Solar Power technologies to falling prices of photovoltaic modules due to its similarity with it, in terms of intermittent generation and non availability of cost competitive energy storage system. Despite of this, Tessera Solar built the 1.5 MW Maricopa Solar Project as a demonstration project for further planned large-scale plants of nearly 700 MW. Unfortunately, Stirling Energy Systems filed for bankruptcy, the pilot project was decommissioned and auctioned and the planned projects were turned to photovoltaic plants or withdrawn.

Another attempt occurred in Spain, Renovalia tried to deploy this technology with a pilot plant and up to seven commercial plants announced. After the decision to change its technology provider, Infinia, to another company -a fact that was announced as ‘the 3rd generation CSP is here’-, and expected changes in the regulatory framework of Spanish CSP sector, the company withdraw the projects.

Infinia has deployed, in a small-scale so far, its PowerDish product at numerous locations around the globe and is currently involved in two NER300 projects awarded by the European Commission. The Cyprus/Helios project includes a 50 MWe transmission-scale PowerDish deployment near the city of Larnaca where each of the 16,920 dishes will supply electricity to the national grid. The Greece/MAXIMUS project in the Florina region will have a total installed capacity of 75.3 MWe. The plant includes 25,160 PowerDish units composing 37 distribution-scale power plants, each connected to the grid via a single connection point.

“We are excited to mark this milestone in providing the Tooele Army Depot with a long-term, dependable clean energy solution,” said Infinia President and CEO, Mike Ward. “Given their need for secure energy, high performance and reliability, our PowerDish is ideally suited to help them optimize their sustainable energy goals and provide them with 30% of their electricity requirements.”

PowerDish is a parabolic dish with a unique free-piston Stirling generator that converts the sun’s heat into grid-quality AC power at 34% efficiency. The PowerDish uses no water, and can be deployed faster than other concentrating solar thermal technologies.

“Infinia has been a leader in free-piston Stirling technology for more than 25 years,” said Jos van der Hyden, Infinia Chief Commercial Officer. “The maturity of this technology combined with our lean manufacturing expertise creates a compelling message that resounds with our customers and is setting the tone for our expansion in the European solar market.”

The European Commission’s strict eligibility criteria for awarding these projects is similar to the high standards Infinia is required to meet for the U.S. Army Corps of Engineers, and includes proven innovative technology, scalability, and on-time delivery. “We are confident our free-piston Stirling technology will help create a lasting impact as we move forward to help the EU meet its aggressive renewable energy goals,” added Van der Hyden.

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