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Solar charging control: Purchase or built? — Parallax Forums

Solar charging control: Purchase or built?

Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
edited 2010-10-23 06:31 in General Discussion
I'm doing some research in solar heating/power. My plan is to eventually purchase some undeveloped real estate and slowly build a weekend retreat which will become my eventual homestead.

I'm testing the concept of solar convection heating systems right now and starting to look at what it will take to create an inexpensive solar power station. One of the designs I've seen is to use a solar panel to charge a 12v battery like those found in a computer UPS, then power a 110v inverter. It appears I could use a couple Parallax solar panel kits to accomplish this, although I'll probably start testing the idea with a homemade panel that I have the parts for. (Thanks to Bean)

My question is charging controllers. Is it possible to build a simple circuit which will charge the battery, or is it best to purchase something? Is this something which could be done with my favorite MCU? I like the idea of a circuit which could sense when the battery is at full charge, then switch the current coming from the panel to an overflow circuit. Can someone with experience here give me an idea what I'm getting into?

Thanks
OBC

Comments

  • BeanBean Posts: 8,129
    edited 2010-10-21 07:44
    I'm not a expert by any means, but they are loads of options.

    MPPT (maximum power point tracker) controller
    Sun tracking
    etc.

    For a really basic system a simple shunt (high wattage zener) will prevent overcharging.

    Keep us informed as to your progress. I'm interested in how it works out.

    Bean
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2010-10-21 08:36
    @Bean,

    Could you expand your explanation on the simple shunt idea?

    Thanks
    OBC
  • BeanBean Posts: 8,129
    edited 2010-10-21 08:39
    Yeah, you just put a zener across the output terminals of the solar panel (remember reverse bias for zeners!!!). Say a 14 V 10Watt zener for a 10watt solar panel.

    When the battery reaches 14V the zener will not let it charge any higher.

    You can also use a low wattage zener and a power transistor. You should be able to google "shunt regulator" and get some hits.

    The nice thing about the shunt regulator is that is doesn't waste any power if the battery is charging.

    Bean
  • kwinnkwinn Posts: 8,697
    edited 2010-10-21 09:11
    Oldbitcollector wrote: »
    I'm doing some research in solar heating/power. My plan is to eventually purchase some undeveloped real estate and slowly build a weekend retreat which will become my eventual homestead.

    I have been doing pretty much the same thing for the past year or so. I have concluded the best way to proceed is to plan the building to maximize passive solar heating, have a backup heat source (wood stove, oil or propane furnace, etc.), and use solar and/or wind generated electricity only where absolutely necessary.

    The prop or props will naturally be used to control everything.
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2010-10-21 11:08
    For the moment I'm still living in a rental house in the city, so I've got access to conventional (expensive) methods of light and heating. I plan to use an external steam boiler for my backup heating. I'm figuring that I won't get a great deal of sunlight during the months of Dec/Jan, but should do fair on the Nov/Feb side of the year.

    Naturally I have to limit my research to convection heating and solar electric a little, and really can't run a steam boiler in the city without upsetting my neighbors. :)

    OBC
  • FranklinFranklin Posts: 4,747
    edited 2010-10-21 20:32
    and really can't run a steam boiler in the city without upsetting my neighbors. :)
    Just might hasten your move to the boonies.....
  • icepuckicepuck Posts: 466
    edited 2010-10-22 17:38
    Have a look at...
    http://www.otherpower.com/
    and just for fun..
    http://www.otherpower.com/hamster.html
    -dan
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2010-10-23 06:31
    As much fun as it can be to build one's own, it is hard to go past the prices here http://www.futurlec.com/Solar_Charge_Controller.shtml

    Managing lead acid batteries is complex. Have a look at the UC3906 datasheet and float vs bulk charge and overcharging.

    Then there is the issue of agitating the solution. In a car, you get that for free going over bumps, but for proper solar controllers, every now and then they go into overcharge to deliberately bubble off some H2 and O2 and use this to stir up the acid.

    I've got some 20W panels and the appropriate futurlec controllers and they work very well.

    I'm on the grid but slowly working my way through adding self sufficiency. There are government rebates in Australia that distort things towards solar electricity, but for me, the priorities are

    1) solar hot water. I picked up an evacuated tube unit, approx 3.6Kw, for $1400. I don't think anything else gets as good value in terms of $ per watt.

    2) Solar heating. I'm in the process of installing a second evacuated tube unit. I'm looking at getting some more and putting them lower than the house and doing a simple thermosyphon into the house. Use the water to heat the house in the evenings.

    3) Solar electricity with grid tie inverters. For your application, solar plus battery plus battery management plus inverter is fairly standard. Go Pure Sine if you can - I have zapped a few things using a 'modified sine wave' inverter.

    4) I think wind makes a lot of sense too. But it is hard to work through the somewhat inflated figures the alternative energy industry uses. eg, solar panels that might produce 80W at midday produce precisely 0W at midnight. Allowing for cloud, winter etc, real continuous watts for solar are about 1/5th of the quoted figure. Wind power is worse - they like to quote figures for a gale. I got some real wind figures for an old multiblade water pumping windmill, and it came out at 30W per square metre of swept area.

    5) I've got some crazy ideas on other ways to use the evacuated tube solar hot water collectors. They can easily boil water, so you could potentially run a steam engine. You could even store heat for use at night, eg with oil or glycol in the tank instead of water. But that is just a dream at the moment!

    I got some quotes once for total off grid living and it was about $80,000 for solar/wind/diesel backup.

    The prices for solar panels on ebay have come down a lot in the last couple of years.

    For solar electricity, you don't really need an 'overflow circuit' when the batteries are full. Just disconnect the panel.

    Of course, for solar hot water, you do need an 'overflow circuit'. For the ones I have, the overflow is to boil the water. Crude but effective.

    In terms of sizing the panels, batteries, will you be running a fridge?
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