Wednesday, October 14, 2015

Energy Aspects

In the following I want to sketch some important aspects when it comes down to power (real scale) podcars.

Basic considerations looking at the power consumption side:
  • First, max. energy consumption of fully loaded podcar per defined distance should be estimated (I assume that there is not much valuable empiric data existent so far)
  • Operating hours per day and time of operation should be considered (in terms of matching consumption with solar PV generation onsite)
  • Additional power loads for the guideway and stations (control electronics, electric lighting, ticketing system etc.) have to be put into the equation
Basic considerations looking at the power generation side:
  • If possible, 100% energy generation from renewable energy sources: Power can and should be produced from versatile renewable energy sources in a hybrid generation approach, e.g. solar and wind, to optimize energy supply and to minimize disruptions or dependency on backup systems (grid or battery storage). Ideally, the energy is generated locally where it will be consumed. This saves overhead costs for distribution.
  • Centralized or decentralized energy production: It has to be decided in the design phase, if energy should be generated locally or remotely or both. 
Two scenarios: 
1) Energy is produced in a decentralized way by mounting solar PV modules locally on top of the guideway. In this case, shortages in the power supply (evening and night times, cloudy sky) must be compensated reliably by power from the grid or from battery storage. Ideally, the then purchased grid power should come from renewable sources only. In a potential power surplus case (full sunshine at noon, no or few podcars used), a (REFIT-) scheme should be in place to repay the surplus power fed to the grid. Otherwise, it can be stored in batteries.
2) Energy is produced centrally at a (remote) solar and/or wind farm and then distributed to the podcar system. A question here would be, if power can be distributed locally or via the grid. A power purchase agreement would be an option. 

Example calculation:
Let's assume in scenario (1) that we can build 300 Wp solar PV per 1 m length of guideway, then this would equal to the theoretical value of 300 kWp per km or approx. 480 kWp per mile. This is nearly half a mega watt per mile under optimal (test) conditions.

Next steps:
When we have the value for the energy consumption of a fully loaded podcar, we can then calculate how many podcars we can power on a certain distance (minus additional loads). We can also determine how big the battery storage must be, depending on operational hours, solar climate and grid-connection or not.

Example calculation using PVWatts Calculator
Example calculation for 300 kWp solar PV system (installed along 1 km Podcar track) for location Mountain View, California, assuming solar PV modules facing South, fixed installation with 20 degrees tilt angle, and 14% total system losses. Initial Cost and CoE to be verified. Further assumed PV incentive of $0.09/kWh.

These values can be compared to get an idea of the cost-effectiveness of this system. However, system costs, system financing options (including 3rd party ownership) and complex utility rates can significantly change the relative value of the PV system.

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