Electrifying Ivanpah solar tower


Electrifying Ivanpah means actually electrifying the Ivanpah Solar Electric Generating System, which is a concentrated solar thermal power project currently under construction in the California Mojave Desert. It consists of three solar power towers, Ivanpah 1 (126 MW), Ivanpah 2 and 3 (each 133 MW). Their combined power output is 392 MW (gross) / 377 MW (net).

View of the 3 solar power towers at Ivanpah Picture 1

The three solar towers of the Ivanpah solar project.

How does the solar version of Ivanpah work

Diagram showing how Ivanpah concentrated solar power project works Picture 2

As picture 2 shows, sunlight is concentrated and reflected by mirrors at the wall of the SRSG (solar receiver steam generator), heating it to 1000 Celsius.

The SRSG consists of pipes through which water is pumped. Concentrated sun light heats the water, turning it into over 500 Celsius superheated steam.

This superheated steam is used to drive the turbine of a generator, producing electricity.


How to electrify Ivanpah solar tower


The electric emulation of the Ivanpah SRSG (solar receiver steam generator), the ESG (electric steam generator), is made by stacking electric furnaces, through which tubes for the water run. See picture 3 and 4. The electric furnaces are based on the one in picture 5.

Picture 3 Picture 4 Picture 5
Wall of eelctric furnaces functioning as SRSG Cross section view of wall made of electric furnaces Electric furnace 300 kW 1280 Celsius by Thermconcept
The Thermconcept  WK10000
Inside dimensions: 125 cm wide, 125 cm high, 700 cm deep, volume 10940 liters.
Power 300 kW. Maximum temperature 1280 Celsius.
Source: go here for brochure

According to this file (pdf), a letter in which one of the contractors answers to a supplemental data request by the California Energy Commission, the Ivanpah SRSG is 20 meters high, and its width is 17 meters.

In order to create the same heating surface for the ESG as the Ivanpah 2 SRSG, three WK10000 electric furnaces are needed to create the same width (actually two and half furnaces will do, since a furnace is 7 meters deep), and 20 electric furnaces have to be stacked in order to reach the same height (see picture 3). Resulting in a total of 60 (3 x 20) electric furnaces. Their combined energy consumption would be 18.000 kW (3 x 20 x 300 kW) or 18 MW.

Energy potential


One ESG wall has the same heating surface as the Ivanpah 2 SRSG wall, and the temperature inside the ESG is the same as the temperature inside the Ivanpah 2 SRSG (1000 Celsius).

Ergo, one ESG wall should be able to heat the same quantity of water, produce the same quantity of superheated steam and consequently generate the same amount of energy as one wall of the Ivanpah 2 SRSG.

Efficiency of the ESG


Again, according to this pdf file, quote: "While in operation, the energy from the sun concentrated on the SRSG can be up to 600 suns total (typically 100 to 200 for half of the surfaces and 200 to 400 for the other half)." This implies that at any time, two of the surfaces are fully heated (100%) and the other two surfaces are partially heated (50%) and consequently very likely operating at lower temperatures. Please compare the two pictures below.
Comparing the surfaces of the Ivanpah boiler (SRSG)
If correct, it seems the Ivanpah 2 SRSG can generate 133 MW while operating at ± 75% of its capacity. Thus, if all the four surfaces of the Ivanpah 2 SRSG were to receive a solar flux of 200 to 400 Suns, Ivanpah 2 SRSG should be able to generate 177 MW (133 MW / 75 x 100).

Net output


Now unlike the walls of the Ivanpah 2 SRSG, all the four walls of the ESG can operate at 1000 Celsius, so they should be able to generate 177 MW. Combined energy consumption of the ESG: 72 MW (4 x 18 MW)

Besides the energy for the electric furnaces, there is also energy needed to operate pumps etc. The combined gross output of the Ivanpah Solar Electric Generating System (consisting of three solar towers, each with one SRSG) is 392 MW, its net output is 377 MW. This means each solar tower / SRSG needs about 5 MW (392 MW - 377 MW / 3) to operate pumps etc.

This sets the total power requirements of the ESG at 77 MW (4 x 18 MW for the furnaces + 5 MW for pumps etc.). Net output: 100 MW (177 MW - 77 MW). Even if it would only generate 133 MW, its net output still be 56 MW.

Reasons the net output of the ESG might even be higher


1) The tubes of the Ivanpah SRSG are only heated from one side (see picture 2), the tubes in the ESG are heated from two sides (see picture 4). This means the surface of the tubes that is heated in the ESG is twice at large compared to the heated surface of the Ivanpah 2 SRSG tubes, and water can be heated faster. Compare picture 6 and 7. This could result in more power being generated by the ESG.

For instance:
A) Fewer loops are needed to pump water around, so the total volume of water being pumped around can be increased, resulting in a higher volume of steam.
B) If the same number of loops are maintained, the steam temperature will increase.

Picture 6 - cross section tube Ivanpah 2 SRSG Picture 7 - cross section tube ESG
Temperature profile of tube in Ivanpah SRSG Profile of tube in electric furnace heated from both sides
2) As picture 8 shows the heat distribution on the Ivanpah 2 SRSG is not homogeneous, also due to clouding there can be significant drops in temperature. Heat distribution in electric furnaces is more homogeneous because a fan is used to circulate the hot air, keeping it within the 5 Celsius range. Temperature fluctuations of are mainly due to hot swapping of electric heating elements during maintenance.

Picture 8  - temperature distribution on the Ivanpah SRSG

Temperature distribution on a Ivanpah 2 SRSG boiler

3) The example uses an off the shelf electric furnace. If the electric furnace and the boiler and piping would be designed as a unit, a higher efficiency rate would be possible.

4) The efficiency and potential calculations are conservative, this was done to be "on the safe side". If the exact measurements of the electric furnace are used, efficiency should be higher.

To give an indication:
The inner side is 125 cm high, to cover a height of 20 meters, 16 electric furnaces are needed  (20 / 1,25 = 16). So instead of 60, only 48 electric furnaces are needed to reach the same height as the Ivanpah 2 SRSG.

Power requirement = 48 x 300 kW = 14400 kW = 14,4 MW. Previous power requirement was calculated at 18 MW. A difference in power requirement of 3,6 MW (for one wall!). Its total energy consumption could be closer to 114,4 MW (177 - (4 x 14,4 + 5)).

It seems the net output of the ESG is a number between 56 MW and 114 MW, but even if the net output to the grid would only be 1 MW, it would still be something the people at US NIF and ITER can only dream of.

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