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Solar power for extreme cheapskates

Discussion in 'General Electronics Discussion' started by wingnut, May 8, 2017.

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  1. wingnut


    Aug 9, 2012
    As an extreme cheapskate I was naturally attracted to the idea of free power from the sun, forever.

    But equally, I was repulsed by the high costs associated with installing (photovoltaic) PV panels. Youngsters are good with technology, so I asked my son how I could lessen the costs. His immediate opinion was that if one got rid of the batteries, solar power might be viable. So I bought four 100Watt PV panels rated at 12V but which actually push out 18V. I bought one new 48 amp-hour car battery, a charge controller, and a cheap 150W inverter. The idea was to use the suns energy during the day, but not try to store it for night use. The night was made for sleep, and that is exactly what I do.

    Then I became a collector of 12V appliances which I could drive straight from the car battery (which is kept fully charged by the panels and charge controller). My 12V collection to date includes a 12V TV/monitor (8W), a satellite decoder (34W), coffee maker, vacuum cleaner, immersion heater, radio, amplifier, 12V WiFi, 12V motors, cellphone charger, bicycle tyre pump, LED strips, etc.

    I also drive small 220V appliances from the inverter, such as two aquarium pumps and a mains WiFi.

    The beauty of 12V appliances is their compatibility with 12V car batteries. You just clip them to the terminals of the battery with a crocodile clip or using a cigarette lighter socket. One has to use the appliances close to the battery because DC voltage drops quickly across long conductors.

    I do not have a grid-tied inverter, because these are hellishly expensive, but nice. Did I mention I am a cheapskate? A grid-tied inverter will feed solar power straight into your mains so that your appliances run from the normal house electrical sockets, which is very convenient and efficient. It gets old having to plug appliances into an inverter in the morning, and unplug and plug these into mains at night.

    There is a cheapskate fix for electronic appliances which run off mains, but transform down to 12V through a wall-wart. One runs a double wire from the battery to the transformed input of the device. This means the device is now running off 12V from the wall-wart and the battery (sun). The appliance will of itself automatically swap between solar and mains 12V all by itself. During the day when the battery is fully charged by the sun it outputs 13.4V which is more than the wall-wart is outputting, viz. 12.4V. The bigger voltage wins, and feeds into the appliance. At night, the battery voltage drops below 12.4V and the wall-wart now takes over providing power. Seamless transition from solar to mains. I put a blocking diode on the positive lead from the battery, to stop the wall-wart charging the battery at night. One can feel the wall-wart getting warm at night and cold in the day when it is not being used.

    I use a DPDT relay and a light-detecting circuit to automatically swap from inverter to mains 220V. At sunrise and sunset, the relay can be heard clicking once, as the WiFi and two aquarium pumps change from solar 220V to mains 220V. This is another cheapskate way of grid-tying one’s inverter to mains. I have had no problems with either of the above two means of seamlessly transitioning from solar to mains power. I acquired a second car battery which I connected in parallel with the first one. But essentially, the cheap way to do solar is to do it in the day, and not to try to store solar energy.

    When Elon Musk invents his battery pack which can cheaply store energy, then I will be the first one to include batteries. Until then, batteries are not included. Or should I say, I use one car battery which is the least one can get away with. I researched the idea of connecting 12V PV panels directly to 12V appliances, but you cannot do this as PV voltage varies, and will fry a 12V appliance with its 18V.

    If any of you have suggestions, or if you have done likewise, I would like to hear from you.
    Last edited: May 8, 2017
  2. Audioguru


    Sep 24, 2016
    Doesn't the weather produce cloudy days where you live? Then your solar power will be very low. Few daylight hours in winter?
  3. wingnut


    Aug 9, 2012
    I live on the southernmost tip of Africa which is sunny five days out of six.

    I also have a cheapskate system for heating solar hot water.
    On my flat roof I placed a 12m/yard long 15cm/6" black PVC pipe covered with bubblewrap. This is filled with low pressure water from a toilet float valve. So long as one showers between noon and sunset, the water is warm. Cost of eternal hot water less than $15.
    hevans1944 likes this.
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