System Improvements¶
Systemic Problems¶
Many components of the MET stations are old, and undersized. However simply adding solar panels and batteries, will not reduce the chance of system failure and would easily exceed the budget. The present station design is built around production of data. However, it ignores the operation of the system that collects the data. This risks generating erroneous data and allowing the system to crash. It also means that power supply is often not where it is needed. The stations need to be designed to support the function of the system as a whole. It would be difficult to supply enough power to match current demand, but it is possible to maintain current function with a lower power requirement.
Key tenants of design are:
- Monitoring all devices
- Track system power generation and draw
- Make it easy to identify system malfunctions
- Make it easy to anticipate loss of power
- Provide redundant operations
- Multiple power sources (e.g. multiple charge controllers)
- Multiple ways to restrict components (e.g. turn radios off)
- Multiple data backups
- Protecting equipment from degradation
- e.g. proper cooling for charge controllers
- e.g. controlled phase down of power usage when power generation is low
- Intelligently allocate power
- Careful monitoring allows power to be intelligently distributed to components that need it most
- Monitoring can be used to trigger reallocation of power as conditions require
| Example: | For example, 2015 a charge control went bad at UPLO. This overdischarged the batteries, ruining them. It also cut power to the logger, which stopped data collection and allowed the rain gauge to freeze. Better monitoring of power supply would have identified that there was a problem. A secondary power source would have kept the station running while the faulty controller was fixed. Redundant programatic and manual switches would have allowed high draw components such as radios to be disconnected, conserving power. A low voltage disconnect could have further protected the batteries. Finally, if the charge controller were stored in a dry, well ventilated area away from caustic battery gases, it may not have failed at all. This clearly demonstrates the need for system upgrades to focus not just on power, but on function. |
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Nearly 80% reduction in power needs can be achieved with changes to radio and power configurations. This eases the power requirements and allows focus to be directed at system liabilities such as:
Monitoring power usage
Providing manual and programmatic controls over power use
- Improving charge controllers
- Add LVD’s
- Protect charge controllers from moisture and overheating
Improving protection of degraded wiring
Proposed Improvements¶
Each station is uniquely configured and has special problems which should be addressed. Here I discuss large scale functional changes that apply to all of the met stations, and attempt to estimate the power savings and the monetary cost.
Monitor System Current¶
All loggers will have a shunt installed to track logger current. This allows close monitoring of system operations, battery depth of discharge, and number of battery cycles. Number of battery cycles is the strongest indicator of battery lifespan and number of Ah discharged is the only way to confidently measure depth of discharge. This is key in identifying when a station may be approaching loss of power. This information creates the opportunity for the logger to take steps to protect essential components.
Shunts can also be installed on the charge controllers to track solar panel output, however some loggers do not have enough open ports to support this.
Data will be logged to an independent POWER table. To assess power levels, solar panel function, and battery health will require both onboard and server-side calculations.
Todo
This requires changes to the program logic, and the installation and purchase of a shunt.
| Cost: | Quantity: minimum of 1 shunt is needed per logger. Price: a good quality sealed shunt can cost from $7 to $35 Total: $40 - $200 |
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Combine Power Supply¶
Currently the aspirated fans are run on an isolated power supply. This has the benefit of isolating the logger from any power issues the fan has. However, this also prevents the logger from knowing whether or not the fan is turned on. Combining power supplies at the terminal strip has the benefit of providing multiple solar panels and charge controllers to the logger, so that no single failure can take down the whole system. It also has the benefit of reallocating disproportionally distributed power.
For example, here is a summary of the power supply after CENT tower is combined with CENT aspirated fan.
| Station | System Daily (Ah) | Battery Bank (Ah) | < 30% DOD for 7 days | System Daily (Wh) | Solar Panel (W) |
|---|---|---|---|---|---|
| CENT Twr | 12.06 | 624 | 281 | 144.7 | 200 |
| CENT Asp | 14.63 | 416 | 488 | 175.56 | 100 |
| CEN Comb | 26.69 | 1040 | 890 | 320.26 | 300 |
Todo
This requires time to rewire the system.
| Cost: | 0 |
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Low Voltage Disconnect¶
Low voltage disconnects provide protection for batteries to prevent overdischarge. This is important for long term budgeting and allows the stations to recover automatically, without the need for an operator to replace the batteries before the station comes back on line.
Currently, many installations do not have LVD’s. Xantrex charge controllers can be set as either a charge controller, or a load controller. Installations with these could be repurposed to use a Sunsaver as a charge controller and a Xantrex as a load controller.
Below is a possible reconfiguration. Components that will need to be purchased are highlighted:
| Station | Current Controller | Suggested Reconfiguration |
|---|---|---|
| UPLO Shltr | Xantrex C35 | Chrg: Sunsaver 10; Load: Xantrex c35 |
| UPLO SA | Sunsaver 10 | Sunsaver 20L |
| CENT Shltr | Sunsaver 10 | Chrg: Sunsaver 10; Load: Xantrex c35 |
| CENT Twr | Xantrex C35 | MPPT |
| CENT ASP | Sunsaver 10 | MPPT |
| VAN Twr | Xantrex C35 | Chrg: Sunsaver 10; Load: Xantrex c35 |
| VARA SA | Sunsaver 10 | MPPT |
| VARA Lgr | Sunsaver 10 | MPPT |
Note
MPPT charge/load controllers have ~20-25% improvement in solar power production over currently installed PWM controllers.
Todo
Reconfigure current charge/load controllers. Purchase and install new charge/load controllers.
| Cost: | Price: $240 Sunsaver MPPT-15L Quantity: 4 New MPPT charge/load controllers Total: $960 |
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Replace/Remove Unnecessary Radios¶
Both UPLO and CENT have 2 radios, one each at the tower and the shelter. UPLO also had a 3rd radio on the tower as a relay. In both cases, empty conduit runs between the two. By connecting the two loggers via an ethernet switch, one radio can be removed at CENT and 2 have already been removed at UPLO. This would leave only 1 network access point per station, but in the event of a network failure, the data would remain securely backed up on both the logger and the card.
VARA, CENT, and VAN have high draw Tranzeo radios. These can be replaced with lower draw Nano-locos. This would significantly reduce the power demands at these stations.
| Station | System Daily Ah | Network Daily Ah | Netwrok % | Change in Ah | New Daily Ah | % Reduction |
|---|---|---|---|---|---|---|
| UPLO Twr | 10.35 | 9.0 | 79 | -3.98 | 6.37 | 38 |
| UPLO Shlt | 5.76 | 5.0 | 87 | -3.98 | 1.77 | 69 |
| CENT Shlt | 2.0 | 1.3 | 64 | -0.73 | 1.75 | 13 |
| CENT Twr | 9.43 | 8.0 | 86 | -3.05 | 6.42 | 32 |
| VARA | 8.65 | 8 | 93 | -3.05 | 5.64 | 35 |
| VAN Twr | 9.8 | 8.0 | 82 | -3.05 | 6.75 | 45 |
Todo
VAN,VARA, CENT - Replace Tranzeo radios with Nano-Loco radios
CENT, UPLO (completed) - Remove shelter radios and run ethernet cable from shelter to tower
| Cost: | 2 Nano-locos must be purchased. |
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Control Network and Fan Operation¶
Network infrastructure and aspirated fans draw more current than any other component because they are running constantly. It is important to be able to shut off their power to save critical components during low power operations. Radios and fans serve different purposes that require different control logic, but both can be controlled with the same mechanism. By powering both components from the 12 v switch on the logger (SW12V), they can be switched off to save logger function. A manual override is also needed, to cut all power regardless of program logic.
Note
The NL116 should be turned off with the loggers. The card and ethernet port combined draw 1.03 Ah per day.
Example Code¶
'Example from RV50 mannual
'SW12 Voltage Control
'Turn ON SW12 between 0900 hours and 1700 hours
'for 20 minutes every 60 minutes
If BattV >12.5
If TimeIsBetween(540,1020,1440,Min) And TimeIsBetween(0,15,60,Min) Then
SW12State=True
Else
SW12State=False
EndIf
'Always turn OFF SW12 if battery drops below 11.5 volts
If BattV<11.5 Then SW12State=False
'Set SW12-1 to the state of 'SW12State' variable
SW12(1,SW12State,0)
Example Wiring Configuration¶
Todo
- Develop control logic
- Minimal power mode where the radio and fan are shut down
- Different radio schedules for different power levels
Rewire radios and fan to 12v switch
Purchase and install manual switches
| Cost: | Quality switches cost $15 - $50. Quantity 14 (4 switches x [VAN, UPLOTwr, CENTTwr] + 2 at VARA). Minimum $210 |
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Radio Controls¶
Unlike the aspirated fan, the network infrastructure does not need to be on all of the time. The network can be cycled on and off to transmit for discrete periods of time. During periods of low power the radio could turn on for one hour every afternoon. During good weather the radio could turn on for 5 minutes each hour. Using the radio changes discussed above, here are the additional effects of reducing radio transmission time. Redux % represents the reduction in Ah as \(\frac{NewRadioDaily Ah - ReducedTransmissionTime Ah}{2015 Ah}\)
| Station | New Radio Daily Ah | Daily Ah 24 x 5 min | Daily Ah 1 x 40 min | Daily Ah 4 x 20 min | Redux % (2015 Ah) |
|---|---|---|---|---|---|
| UPLO Twr | 6.37 | 1.77 | 1.49 | 1.63 | 44 - 47 |
| UPLO Shlt | 1.77 | NL116 Power must be | timed with Twr | ||
| CENT Twr | 6.42 | 1.82 | 1.54 | 1.68 | 49 - 52 |
| CENT Shlt | 1.75 | NL116 Power must be | timed with Twr | ||
| VARA | 5.64 | 1.29 | 0.84 | 1.07 | 49 - 53 |
| VAN Twr | 6.75 | 2.15 | 1.87 | 2.01 | 41 - 43 |
Todo
Change logger programs to shut down NL116 and radios and provide power at limited intervals
| Cost: | 0 |
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Separate Housing For Charge Controllers¶
Currently charge controllers are mounted horizontally on top of the batteries in the battery boxes. This can potentially damage or destroy the charge controllers due to overheating, and the corrosive gases released as the batteries charge. As described by the Morningstar Corporation:
Warning
Equipment Damage or Risk of Explosion
Never install the SunSaver in an enclosure with vented/flooded batteries. Battery fumes are flammable and will corrode and destroy the Sunsaver circuits.
Equipment Damage
When installing the Sunsaver in an enclosure, ensure sufficient ventilation. Installation in a sealed enclosure will lead to over-heating and a decreased product lifetime.
Mounting the controller on a horizontal surface does not provide optimal airflow and could lead to overheating.
Safety Precautions
Install the Sunsaver in a location that prevents casual contact. The SunSaver heatsink can become very hot during operation
Because of the importance of convective cooling it is important that they be placed in vented enclosures. However, due to the high amount of mist and fog at the stations, an outer shelter is also needed, possibly sealed like reference stands.
Todo
- Construct outer shelters
- Mount shelters to tower
- Rewire solar panels and batteries
| Cost: | 4 vented enclosures will cost a minimum of $200 |
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Projected Power Use¶
The summary below is the projected power supply and demand after the upgrades discussed above are implemented. Aspirated fans are now included in estimates for all towers. Numbers are estimates using the methods described previously and under powered components are highlighted.
| Station | System Daily (Ah) | Battery Bank (Ah) | <30% DOD for 7 days | System Daily (Wh) | Solar Panel (W) | Winter Need (W) |
|---|---|---|---|---|---|---|
| CENT Twr | 16.45 | 1040 | 548.33 | 197.40 | 300 | 286.09 |
| CENT Shl | 1.75 | 416 | 58.33 | 21 | 50.2 | 72.75 |
| UPLO Twr | 16.40 | 1248 | 546.67 | 196.80 | 360 | 285.22 |
| UPLO Shl | 1.77 | 416 | 59.00 | 21.24 | 240 | 30.78 |
| VAN Twr | 16.78 | 1456 | 559.33 | 201.36 | 262.6 | 291.83 |
| VARA | 1.29 | 208 | 43.00 | 15.48 | 131 | 22.43 |
This projection indicates that VAN Tower and CENT shelter will be underpowered during the winter. In both cases, if the smallest solar panel were replaced with 1- 140W panel, the station should generate close to the daily power demand during winter.
The estimates used here are rough estimates, that do not include such details as: voltage drop, heat loss, temperature corrected battery Ah, temperature corrected solar output, and light intensity corrected solar output. The estimates provided are likely inaccurate, but they are precisely calculated. Their primary function is to allow improvements to be prioritized.