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What does the wattage of a solar farm represent? The article says it's expected to produce 55 million kwh per year, but doesn't that imply 6.3MW ((55 000 000 /

What does the wattage of a solar farm represent? The article says it's expected to produce 55 million kwh per year, but doesn't that imply 6.3MW ((55 000 000 / (365 * 24)) / 1000) of constant production?

dredmorbius 9y ago
The capacity and total generation numbers do strike me as odd. OK, the reporting is wrong, and I made an error in my initial response. Capacity: 1.3 MW Output: 55 GWh over 25 years, or 2.2 GWh/yr, or 0.25 MW sustained. 19% capacity factor. Thanks, dennyabraham. ________________________________ The rated output is the nameplate capacity of a facility. That is the maximum power it's capable of delivering under ideal conditions. This applies to any generating plant: coal, oil, natural gas, nuclear, solar, wind, tidal. https://energymag.net/nameplate-capacity-or-rated-output/ https://energymag.net/nameplate-capacity-or-rated-output/ That's reduced by the capacity factor of an installation. A key difference between different generating modes is what their capacity factor is. Nuclear may run as high as 95%, whilst solar is typically rated as 20-30%. This means that the mean output, over a year, is, say, 20% of the nameplate rating. The US EIA (Energy Information Administration) publishes data on actual achieved capacity factor for different modes: https://www.eia.gov/todayinenergy/detail.php?id=14611 https://www.eia.gov/todayinenergy/detail.php?id=14611 There are other aspects of generating which also vary by source: Dispatchability: can the source be turned off, or better, on? Response time: Nuclear and coal generation take hours to adjust output to capacity. Natural gas turbines, diesel generators, and hydroelectric turbines can respond in minutes or seconds. Total energy delivery. A high-output, fast-reacting mode may only be able to deliver energy in short bursts, or for a short period before recharging. This is the case for virtually all energy storage modes: hydroelectric, batteries, flywheel kinetic storage. It also applies to some fuel-based methods: diesel generators and gas turbines used for peaking power may not be able to run for more than a few hours before fuel reserves are exhausted. Maintenance and downtime: How long to scheduled (or unsheduled) maintanance tasks take? How much capacity is involved in such tasks? Regular vs. irregular variability. Solar tends not to produce high output at night. Wind power is variable, but may provide energy at any hour. Tidal power is governed by tide tables. Any or all of these might be moderated by storage mechanisms (e.g., solar thermal energy storage, which can bank heat for hours, possibly days, and hence, "deliver solar power at night").
- maxerickson 9y ago
  55 million kwh is 55 GWh, not 55 MWh. Hence the GPs implied question about a 500% capacity factor. The answer lies in the press release, the 55 GWh is over the 25 year PPA: http://www.solamericaenergy.com/news/carter-farms/ http://www.solamericaenergy.com/news/carter-farms/ Implying a 25% capacity factor. edit: more like a 19% capacity factor. Whatever, something sensible, the reporter screwed up calling the output annual.
  - dredmorbius 9y ago
    Thank you. My error on million kW (I should have caught that), and very poor reporting.
    - dennyabraham 9y ago
      This makes so much more sense now, thanks!
      - dredmorbius 9y ago
        Team effort :)

dredmorbius 9y ago

The capacity and total generation numbers do strike me as odd. OK, the reporting is wrong, and I made an error in my initial response. Capacity: 1.3 MW Output: 55 GWh over 25 years, or 2.2 GWh/yr, or 0.25 MW sustained. 19% capacity factor. Thanks, dennyabraham. ________________________________ The rated output is the nameplate capacity of a facility. That is the maximum power it's capable of delivering under ideal conditions. This applies to any generating plant: coal, oil, natural gas, nuclear, solar, wind, tidal. https://energymag.net/nameplate-capacity-or-rated-output/ https://energymag.net/nameplate-capacity-or-rated-output/ That's reduced by the capacity factor of an installation. A key difference between different generating modes is what their capacity factor is. Nuclear may run as high as 95%, whilst solar is typically rated as 20-30%. This means that the mean output, over a year, is, say, 20% of the nameplate rating. The US EIA (Energy Information Administration) publishes data on actual achieved capacity factor for different modes: https://www.eia.gov/todayinenergy/detail.php?id=14611 https://www.eia.gov/todayinenergy/detail.php?id=14611 There are other aspects of generating which also vary by source: Dispatchability: can the source be turned off, or better, on? Response time: Nuclear and coal generation take hours to adjust output to capacity. Natural gas turbines, diesel generators, and hydroelectric turbines can respond in minutes or seconds. Total energy delivery. A high-output, fast-reacting mode may only be able to deliver energy in short bursts, or for a short period before recharging. This is the case for virtually all energy storage modes: hydroelectric, batteries, flywheel kinetic storage. It also applies to some fuel-based methods: diesel generators and gas turbines used for peaking power may not be able to run for more than a few hours before fuel reserves are exhausted. Maintenance and downtime: How long to scheduled (or unsheduled) maintanance tasks take? How much capacity is involved in such tasks? Regular vs. irregular variability. Solar tends not to produce high output at night. Wind power is variable, but may provide energy at any hour. Tidal power is governed by tide tables. Any or all of these might be moderated by storage mechanisms (e.g., solar thermal energy storage, which can bank heat for hours, possibly days, and hence, "deliver solar power at night").

maxerickson 9y ago
55 million kwh is 55 GWh, not 55 MWh. Hence the GPs implied question about a 500% capacity factor. The answer lies in the press release, the 55 GWh is over the 25 year PPA: http://www.solamericaenergy.com/news/carter-farms/ http://www.solamericaenergy.com/news/carter-farms/ Implying a 25% capacity factor. edit: more like a 19% capacity factor. Whatever, something sensible, the reporter screwed up calling the output annual.
- dredmorbius 9y ago
  Thank you. My error on million kW (I should have caught that), and very poor reporting.
  - dennyabraham 9y ago
    This makes so much more sense now, thanks!
    - dredmorbius 9y ago
      Team effort :)