Home Solar Energy

Notes on Solar Panels

Initial Trials

2 x 15 W solar panels bought at Rona on sale at $27. Included a 6A battery charger regulator.

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These 15W rated solar panels were $27 at Rona.

For one panel, Typical performance in direct sunlight : 0.75 to 1.0 A into 12 V SLA battery when pointing directly at Sun. If the panel is inside, behind glass window in direct sunlight the current drops to 0.4 to 0.5 amperes. Under cloudy conditions: 0.15 to 0.20 A. In cloudy condition, the best orientation seems to be pointing straight up.

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The short circuit current from one panel is 0.88 A.

According to blogs, a 12 V nominal SLA (Sealed Lead Acid) battery reaches 12 V, open circuit, when about 1/2 charge is left. A full charge seems to take the voltage to 13 V. This value is probably determined by the charger controller. Immediately after charging the open-circuit voltage may be over 13 V but after a few minutes drops to around 12.6 V.

It’s possible to charge a 7 A⋅h SLA battery within a single sunny day if it starts at  12 V.

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The open circuit voltage is almost 24 V without the regulator.

Note than an 1800 kW installation  typically only reaches 1200 W maximum power in Vancouer BC. about 8000 kW.h per day on sunny days.  (Enphase energy log) In Nov, Dec, Jan and Feb the output is quite low. In Mar through Oct performance is useful. Over all there’s about 4000 kW.h/day yearly avg

Charging a Sealed Lead Acid battery with regulator. Small voltmeter reads 12.9V.
Charging a Sealed Lead Acid battery with regulator. Small voltmeter reads 12.9V.

Double Panel Mount

Here’s a simple mount for both panels, connected in parallel. The azimuthal direction is always -180 degrees (due south). The elevation can be adjusted by moving the base farther or closer to the building wall. The sage will need to be trimmed in the near future to avoid cover the panels. The wires go into the garage where the charging station is.

Double panels mounted on a pair of 2x4s.
Double panels mounted on a pair of 2x4s.

The optimum elevation angle can be calculated using an on-line tool such as at Solar Calculator.  The picture was taken on May 11 at about 16:00.  You can see from the graph that the correct elevation angle should have been 40 degrees.

Solar elevation on May 11 at Vancouver, BC.
Solar elevation on May 11 at Vancouver, BC.

The “charging station” keeps the same crude motif as all other installations.  I’ve rigged up a cheap ($10.80) digital voltmeter and a 1Ω resistor to provide a current monitor.

SLA battery being charged. The regulator was provided with the solar panels and the voltmeter provides a current reading by measuring the voltage across a 1Ω resistor.
SLA battery being charged. The regulator was provided with the solar panels and the voltmeter provides a current reading by measuring the voltage across a 1Ω resistor.

The following circuits can be used to monitor the current during charge and discharge using a simple digital panel meter. The author’s uniquely designed Battery Box combines both charging and discharging circuits as well as providing a watertight container for the battery.

The voltmeter measures the current through a 1Ω resistor by displaying the voltage. Thus 0.8 A will display as 0.8. A 1 watt resistor should be sufficient.

Next: The Battery Box

One thought on “Home Solar Energy”

  1. Wow, I had no idea you were interested in all this- I am too.
    I hope to live in an off-grid house one day.
    It’s great that someone with a scientific background is posting this; much of the stuff I’ve seen online is made by people who don’t really know what they’re doing, and just want free power.

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