Solar WILL take over all other energy sources

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  • Tue, Oct 22, 2013 - 03:06am

    #11

    Mots

    Status Bronze Member (Offline)

    Joined: Jun 18 2012

    Posts: 65

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    using PV for solar hot water

thanks for 12 volt LED reference.  I notice that lowes and home depot just started selling 12 volt LEDs 2.5 watts (small bulbs) but the nicest looking best performance may be the  LED fixtures that home depot/lowes sells for 30-45$ and which are indistinguishable from  regular old fashioned single 3-5 inch diameter big lens light fixture.

The goal for using many cheap panels is simply to load them JUST ENOUGH to drop the output voltage to the maximum output voltage.  A good PWM circuit will do this with only a single MOSFET junction standing in the way between the solar panels and the heater.  THe problem with electric water heaters is that the AC voltage thermostat switches cannot handle DC and will melt -self destruct if you use plain DC instead of AC. The reference I gave uses a simple MPPT maximum voltage circuit (loads just enough to extract maximum power from panels) AND also converts DC to pulsing DC at a high frequency that DOES NOT melt the contacts.  You need to mount his circuit near the water heater or else suffer high power RF noise from the line to the water heater. I run up to 2000 watts through mine and it seems to generate only about 25 watts of heat (I dont recommend using his device for more than 500 watts- I happen to have mounted mine on a gigantic  heat sink which works because he uses a gigantic (very high  voltage and current IGBT (he calls it a MOSFET) that is only limited by heating up

hope this helps

  • Tue, Oct 22, 2013 - 03:06am

    #12

    Mots

    Status Bronze Member (Offline)

    Joined: Jun 18 2012

    Posts: 65

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    using PV for solar hot water

thanks for 12 volt LED reference.  I notice that lowes and home depot just started selling 12 volt LEDs 2.5 watts (small bulbs) but the nicest looking best performance may be the  LED fixtures that home depot/lowes sells for 30-45$ and which are indistinguishable from  regular old fashioned single 3-5 inch diameter big lens light fixture.

The goal for using many cheap panels is simply to load them JUST ENOUGH to drop the output voltage to the maximum output voltage.  A good PWM circuit will do this with only a single MOSFET junction standing in the way between the solar panels and the heater.  THe problem with electric water heaters is that the AC voltage thermostat switches cannot handle DC and will melt -self destruct if you use plain DC instead of AC. The reference I gave uses a simple MPPT maximum voltage circuit (loads just enough to extract maximum power from panels) AND also converts DC to pulsing DC at a high frequency that DOES NOT melt the contacts.  You need to mount his circuit near the water heater or else suffer high power RF noise from the line to the water heater. I run up to 2000 watts through mine and it seems to generate only about 25 watts of heat (I dont recommend using his device for more than 500 watts- I happen to have mounted mine on a gigantic  heat sink which works because he uses a gigantic (very high  voltage and current IGBT (he calls it a MOSFET) that is only limited by heating up

hope this helps

  • Tue, Oct 22, 2013 - 04:36am

    #13

    sand_puppy

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    Solar Hot Water: Thermal or Photovoltaic panels?

Hi again Mots,

My solar engineer neighbor (who has been out of the business for about 6 years) did a bit of research this evening based on your post and concluded that with the low cost of the new solar panels ($1/watt) and the newer heat pump type of electric water heaters that the PV type of hot water heater now seems to make sense to him, too.  He forwarded a recent summary article of this debate to me.

 

Solar Hot Water: Which Is Better PV or Thermal?

 

Hal Slater, Contributor
September 11, 2013

Solar thermal water heating is a temperamental thing. Water weighs a lot, it expands when it freezes, and it can cause scaling damage to pipes when it boils. Solar thermal systems are wonderfully efficient [extracting about 50% of the energy in sunlight], and some systems work just fine for decades, but even these need regular inspection. When a solar thermal system fails, however, it sets about destroying itself, and it has been clear for some time that solar thermal water heating is not the way of the future except for very low-end heat usage, like swimming pools.

Recently, however, reductions in solar electric (PV) costs and maturation of air-to-water heat pump technology have provided a new model: solar-electric assisted heat pump water heating (HPWH). HPWH comes with fewer drawbacks than solar thermal, with a smaller price tag for residential applications. 

PV Advantages

Lower upfront cost

Easier to install.

 

Uses less space.

Needs no maintenance

 

Cannot freeze.

Cannot overheat.

 

No scale build up.

No CO2 emissions.

 

  • Tue, Oct 22, 2013 - 11:35am

    #14

    davefairtex

    Status Diamond Member (Offline)

    Joined: Sep 03 2008

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    emergency use of grid-tie solar panels; how to do?

Mots –

I have always been irritated at the concept of having 2 kw of generating power on the roof and yet, if grid power vanishes, somehow I'm not able to flip a switch and make use of all those electrons.  I'd love to have some mechanism for providing the grid-tie when its available, but then isolating the house from the grid and just receiving power from the panels when the grid goes down.  And of course if its dark, no power is produced.  Your description of the current offerings: "only grid-tie solar" and "solar off-grid with batteries" is quite accurate, and it definitely has never really satistfied me.  There should be something in between.

I'm not enough of a hardware guy to know the implications of that sort of setup though; how do all my devices work when in aggregate the panels aren't supplying enough power is one question.  I know computers don't like brown-outs.  Presumably there could be some sort of adapter that cuts off load when the power drops below what is required.

It seems to me these are all problems that are not all that difficult to fix if someone who knew basic electrical systems felt like doing it.  And certainly, having power during daytime with limitations (for instance, at dawn/dusk power generation will be quite faint) it is infinitely better than no power 24/7 during a prolonged blackout situation.

I'd prefer to have something like that in place prior to experiencing the emergency power situation too.  🙂

 

  • Tue, Oct 22, 2013 - 11:43am

    #15

    Mots

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    Joined: Jun 18 2012

    Posts: 65

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    off grid etc

As you guessed, this involves simple switching.  Equipment has this capability.  if you have only 500 watts, easy to do by switching yourself (plug/unplug).  Grid tie invertersfor high power (2-5 kilowatt) can have switches built into them and often will switch automatically.  Because this equipment tends to be expensive, I dont pay to attention to it but you can ask any solar equipment company and they should be happy to sell to you.

  • Tue, Oct 22, 2013 - 12:16pm

    #16

    Oliveoilguy

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    Emergency Use of GT Systems

There is a way that can be done to run a pure GT inverter off-grid–But that requires a second True Sine Wave off-grid inverter, battery bank, and AC Transfer Switch (all of which have to be rated equal or greater Wattage than the GT inverter system).

  • Tue, Oct 22, 2013 - 04:02pm

    #17

    davefairtex

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    emergency use of GT systems w/o battery bank

oog-
I don’t have a battery bank and lets assume for this discussion I never want to have one.

Let’s further assume that I can deal with only having power during daylight hours – charging up my phones, UPS units, laptops, running the washing machine, etc when the sun is shining.

But I’m not a hardware guy, and so I don’t understand the implications of what happens to my devices when they get “browned-out” as the sun starts to set and my power generators on the roof slowly stop feeding power to my house.

Assuming my devices don’t get damaged by brown-outs, I’d prefer to have uncertain device performance under a variable power situation to having zero power provided from my functioning set of solar panels on the roof in the case of a prolonged (multi-week) power outage.

  • Tue, Oct 22, 2013 - 06:14pm

    #18
    Kman

    Kman

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    PV and Solar Thermal

Sand Puppy,

    I couldn't agree more.  I have solar PV on my house and a GE hybrid hot water heater (heat pump).  The hybrid water heater was an easy decision as had to replace the old water heater anyway.  I did not want to deal with the complexity of domestic solar thermal system and it just made sense to add a few more solar PV panels for the hybrid water heater.   Have been running this for two years or so.  Costs for solar PV have come down a lot in last two years, so makes even more sense now.   I would consider this option a no brainer if you are on propane.  I am on natural gas, so ROI is a bit longer, but still worth while especially if your existing hot water heater is on the way out.

   One thing to keep in mind with the hybrid water heaters is that they are a bit noisy in heat pump mode as sounds like a small window ac unit when running (which it basically is in reverse).  So, great if you have room in garage or basement, but not so good if only place is in hallway or similar.  They also require a fair amount of space to draw air from.

Kman

  • Wed, Oct 23, 2013 - 06:20am

    #19
    Denny Johnson

    Denny Johnson

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    Joined: Aug 14 2008

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    Dave

[quote=davefairtex]

  I'd love to have some mechanism for providing the grid-tie when its available, but then isolating the house from the grid and just receiving power from the panels when the grid goes down.  And of course if its dark, no power is produced.

[/quote]

Dave …..have you seen these:

http://www.sma-america.com/en_US/products/grid-tied-inverters/sunny-boy/sunny-boy-3000tl-us-4000tl-us-5000tl-us.html

  • Wed, Oct 23, 2013 - 12:08pm

    #20

    Oliveoilguy

    Status Silver Member (Offline)

    Joined: Jun 29 2012

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    SMA 4000

[quote=Denny Johnson]

[quote=davefairtex]

  I'd love to have some mechanism for providing the grid-tie when its available, but then isolating the house from the grid and just receiving power from the panels when the grid goes down.  And of course if its dark, no power is produced.

[/quote]

Dave …..have you seen these:

http://www.sma-america.com/en_US/products/grid-tied-inverters/sunny-boy/sunny-boy-3000tl-us-4000tl-us-5000tl-us.html

[/quote]

Looks good.

Here is how it works. If the grid goes down but the sun is out you go to the Sunny boy inverter and flip a manual switch mounted below the inverter. In 45 seconds it will power up a 1500 watt plug. You can then plug in a small device like a cell phone charger or a light or whatever. If you exceed  (draw more than) 1500 watts it will shut down until you reduce the load. As long as this auxiliary switch is on, the inverter will not self-restore to normal function even if the grid comes back up. You must manually turn off the switch to allow normal function to resume.

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