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media ecologies :: the eco-garden, a long-term project  

Making of Stand-Alone Nodes in Meshed networks

saturday december 22, 2007
okno-rooftop, brussels
with support of Fo.am

Preparation of the Making Off Stand-Alone Nodes in Meshed networks
Scenario 1: Stand alone PhotoVoltaic-system

Step by Step description by Bartaku.
Date: 2007 12 22.

Vernacular Observation:
Setting up the system coincided with the moment the plants start growing
towards the sun again... winter solstice!

Set up location:
OKNO rooftop, center of brussels (50°50'13" North, 4°22'3")
Set up time: from 11am to 5pm, with numerous interuptions
(normally feasible with 3 persons in 2hrs max).

Step 1:
Estimate power and energy needs.
Existing Calculation has to be adapted after confirmation tech spec Asus).
In any case, max. current output of 2 panels is 6A; they are connected in parallel (Voltage stays unaltered, 12V). Charge controller's max. input = 10A.

Step 2: Rough evaluation of PhotoVoltaic-Size.
1. Autonomous or hybrid? -> autonomous.
2. Estimation of available sunlight:
Nominal power of the PhotoVoltaic system: 50.0 kW (crystalline silicon).
Estimated losses due to temperature: 7.0% (using local ambient temperature).
Estimated loss due to angular reflectance effects: 3.0%.
Other losses (cables, inverter etc.): 14.0%.
Combined Photovoltaic system losses: 24.0%.
Average for December: 36.10kWh (July=238kWh).
3. Estimate the Required Photovoltaic Array Size.
For the moment we have an experimental set -up/try out with the panels we
have at our disposal).
4. Estimate battery capacity: (12V x 75 Ah = 900 Wh (Wh = V x Ah)).

Step 3:
Mounting pv-panels.
1.Direction: South (more or less; (northern hemisphere, a deviation of 15 degrees east or west will not affect performance very much).
2.Tilt angle – More or Less 35° (to be measured).
3.PV-panels attached to metal structure with plastic straps.

Step 4: Connect to Balance of System components.
Note: unless shading is a concern, try to locate the modules as close as possible to the battery bank or to the load - if there are no batteries.
This will lower wiring distances and resultant power losses.
1.Secure the negative wire (black) to the regulator and connect it to the negative battery terminal.
Secure the positive (red) wire to the regulator and connect to the negative terminal of the battery.
The green charging LED should not be on!
2.Connect Photovoltaic panels to regulator in parallel:
start with both the negative cables to the solar terminal of the regulator and then the 2 + cables to the + solar terminal of the charge controller.
If charge current is available from the solar panel, the
green charge LED will light up.
3.Connect to the load from the regulator.

Step 4: Measuring output:
Time: 4.30pm.
Voc: 13V.
Isc: 0,02A.

Hardware List:
PV-panel Kyocera: 700€ (350€/pc)
- Peak Power: 54 Watts
- Peak Power Voltage: 17,4V
- Open Circuit Voltage: 21,7V
- Maximum Output Current: 3,11 Amps
- Short Circuit Current: 3,31A
- Dimensions (LxWxD): 639 x 652 x 54mm
- Weight: 5 kg
- Cell type: Polycrystalline Si

Balance of System (BOS)
- Charge controller: Steca Solsum 10.10c; 12V; Max.
- input 10A; 43€
- Lead Acid Battery: Norauto 22 (12V, 75Ah, 680A); 131€

Antenna: ???????
Asus Wireless Storage Router (12V; 3A); ??? €
Arduino board (connected to Asus via USB); 50€

PV moubting structure: metal structure 'objet trouvé'; €0
Plastic box, semi-transparent with sealable cover (protection electronic hardware) (dimensions: ?????)
Plastic Straps (attaching pv-panel to metal structure)
2 small screws

Set up Tools
Glue gun & Sticks

Most urgent issue at this moment: LOW TEMPERATURE EXPOSURE BATTERY
“Though a battery may be capable of operating at cold temperatures, this does not automatically allow charging under those conditions.
The charge acceptance for most batteries at very low temperatures is extremely confined. Most batteries need to be brought up to temperatures above the freezing point for charging.
Around 0°C the capacity is about 75% and at -25 °C about 50% of the capacity at 25°C. (-20°C is threshold at which the nickel-metal-hydride, some sealed lead-acid and lithium-ion batteries cease to function...)”





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