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Old 04-22-10, 03:39 PM   #21
jwxr7
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you've got me thinking about trying this with my pv array. Mine is capable of 280w peak (when new), so maybe I could get better use of the power this way than feeding back into the grid with my 200 watt inverter like I do now. Hmmm, I'll have to do some calculating. The only cost for me to try, is some type of heating element. Heck, I might even have something that will work for surface mount already.

I need to price propane, we only fill once a year since we burn lots of wood, but my back problems are quickly changing that .

As far as I know, My boiler doesn't try to maintain a set internal water temp when in standby. So it doesn't use the main burner unless a zone calls for it. There are times in warm weather when the gage is showing a pretty low water temp. The standing pilot probably keeps some heat in it .


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Old 04-22-10, 05:10 PM   #22
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Default 280w = 955 BTUh

It sounds like your domestic hot-water doesn't come from your boiler.
You must have a gas hot-water heater.

My original goal was to save some oil during the summer by increasing the
time between burn cycles, by adding in some PV BTUs. (Maybe 240w ~ 819 BTUh).

But, I've been thinking that a bit more-is-better with PV..
And maybe about 1200 to 1300 BTU of extra heat would provide a more substantial oil savings.

I think maybe two high performance panels providing about 400w total might be the right stuff.
And about all my tracking mount can safely carry.

I'm guessing that any more PV-BTUs might over-heat the boiler on a good day.

Going for more power would boost the cost up to the 1k range
and make it a little harder to sell to the little woman..
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Old 04-23-10, 10:42 AM   #23
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Quote:
Originally Posted by Xringer View Post
It sounds like your domestic hot-water doesn't come from your boiler.
You must have a gas hot-water heater.
Sorry, I should have noted in my last post that the Amtrol boilermate used for our domestic hot water does have a set temp range that it maintains in it's small holding tank, like a regular water heater, but it gets heat exchanged from the boiler, not a direct heat source. The Amtrol is one of the 5 zones running off the boiler and it holds heat pretty well. The boiler itself doesn't try to maintain a set temp for the water that's inside it.

I'm not even sure what point I was trying to make earlier .
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Old 04-23-10, 10:56 AM   #24
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It's somewhat clear now. I'll bet the HW holding tank temperature sensor can issue a call for a burn,
somehow.. Even if indirectly. If you use a bunch of HW, the holding tank-zone is going to end up costing you fuel.

If you could put some PV BTUs into the holding tank?? Stop it from issuing a call?
If it's a small tank, maybe it wouldn't need many watts to keep it warmed up..
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Old 05-04-13, 11:51 AM   #25
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Default Waking up this old idea

I've been doing some hot water heating with PV for a while now..

http://ecorenovator.org/forum/solar-...r-heating.html

http://ecorenovator.org/forum/geothe...html#post29717


Since the wattage required has always been the big question,
I wanted to post the above links, to give PVDHW DIYers
an idea of what's possible these days.

Keep in mind, I'm using PV to supplement our A7 ASHP water heater.
Recently, while using about 1kW of PV, the A7 isn't running at all.
(Unless it gets really over-cast, it won't come on).

From what I can tell right now, it seems that our household
could get by using about 1,000 watts of PV (or power from the grid) for hot water.
That's 3412 BTUh, or x6 hours ~ 6 kWh (20,472 BTUh per day).

That's only $1.00 USD from the grid, at today's NStar rates. (16.61 cents per kWh).
So, by running a GE water heater on 120vac using a Timex timer,
http://ecorenovator.org/forum/introd...html#post25549
A low usage family could get by on $1 day for hot water..

So, if you have an extra 1kW of PV that's not being used,
or you can afford to pay for 6kWh a day, to Mr. Grid,
and don't mind waiting for a slow recovery time..?.

It seems like using the grid at 120vac and a timer,
is the most cost effective way to cut hot water cost.
Using PV is going to cost more up front, but will be Greener..
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Old 05-06-13, 11:47 AM   #26
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Quote:
Originally Posted by Xringer View Post
I've been doing some hot water heating with PV for a while now...
Xringer,

I'm not sure how it is that you are applying your solar PV power to your electric water heater when you are in resistance mode?

Last time I tuned in, you had bolted a big power resistor to your old oil burner water reservoir.

Are you still doing that?

Reason I ask is that Elgo correctly pointed out that 'immersion resistance' heating was much more effective than 'surface contact resistance' heating.

In my experiments in measuring the actual efficiency of surface contact resistance heating, I got an efficiency of about 66%, and I would assume that a power resistor bolted to a water reservoir would be much worse.

Although I didn't test it, I would assume that immersion resistance heating would be closer to 100% efficient.

So, are you using a resistance heating element that is actually in contact with the water you are heating, or not?

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Old 05-06-13, 02:38 PM   #27
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Nope, not trying to heat the oil burner anymore..
Since 5/1/2013 we are using the 13 ohm heating elements in the new GE water tank.
It's got the A7 ASHP on top as the primary heat source.
And using the two solar PV arrays to supplement the A7 on sunny days.



We've only used about 1.2 kWh from the grid (in 6 days), since it's been mostly sunny.
Not able to track the amount of PV power used, but I have been taking
sample DC Amp readings. When it's nice out, we see about 1.0 kW of PV.

The 500w tracker seems to stay at around 4 to 5.5 A most of the day..
While the fixed 800w array peaks up to around 7.4A in the middle of the day,
but can drop down to 3 or 4 amps in the early afternoon..
Whilst, the 500w Tracker is maintaining a good 5 to 5.5..
The tracker is lower power, but provides that power for longer hours.

I have some DC current sensors that I can use with the CAI board,
that I may use to display real-time power..
Have no idea how to program for daily power logging..

I should be able to have the CAI send me emails when the temperature gets too high.
Right now, it seems to be peaking out around 67C max. (152.6)
Mostly it stays under 65C. (149F) Good for dish washing! Kills some germs.

If we go boating for a few days, I'll have to leave everything unplugged,
so the T&P doesn't open up and make a mess..
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Old 06-09-13, 10:06 PM   #28
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[QUOTE=Xringer;5360]This simple technology (DC heating of water using PV panels)
has been tested for a few years by the government.
BFRL: Solar Photovoltaic Hot Water System

it just might be cheaper to skip all the plumbing hardware and just wire some PV to a heating element in your HW tank.?.
-----------------------------------------------------------------------------------
On a trip this spring on the park side of Gatlinburg, Tenn. I saw a Photovoltaic Array
Ref: fire.nist.gov/bfrlpubs/build02/PDF/​b02162.pdf

That solar photovoltaic water heating system had been installed at the Great Smoky Mountains National Park (Sugarland) Visitors Center in the 90's. The solar was out behind the restroom/vending area. I had asked the Park Ranger about it and he pull out a reference info book, out of their office and told me a little about it. He said it was for hot water.

That's what got me thinking about Solar Hot Water (Electric Resistance Water Heater)

OK here's what I'm a thinking ……….

"Using electric resistance heat, it takes 0.171 kWh to raise a gallon of 50 degree water to 120 degrees".
Ref: http://http://www.greenbuildingadvis...r-thermal-deadSolar Thermal is Dead | GreenBuildingAdvisor.com

And my PV System does 320-326 kWh per panel, per year.

So I generate about 1 kWh per day per panel at this location. Lets say I build a stand alone system and use 4 panels and a inverter transfer device…

4/0.171 = 23.4 gallons of 120 degree hat water. (only two of us here)

My cost would be around est. of $1250 for all the parts (I know a guy that knows a guy and so on)

My savings would be 1460 x $0.0954 (kw rate now) = $139.28 per year (or (8.98) years for payback, but with the 30% tax credit it comes to 6.28 years)

I plan on using the bottom element (electric resistance heat) for this on my two element electric water heater.

This might be Pie in the Sky, as the costs will only go up the more I dig into this. But it's what I'm thinking for now.

So far I plan on separate either 2,3,4 panels but will start with 2 and see how that would work.

Can't tie in to the grid as that's AC (get paid base $0.10 plus $0.12 over per kw) and my contract is set, to open it up would lower the over rate to $0.09 or even lower.
http://http://tackyted.com/solar/

(I'll have to read up on the code for this DC stuff)
The new 2 panels would feed about 50 VDC down to a fused interface (working on it!) and then to the tanks lower heat element. The thermostat on the lower element on the tank would dictate the on/off.
The upper element would run on the normal AC power, but set at a lower temp. As heat rises (well really cold falls) the upper element would stay off most of the time, cause the lower is keeping it warm.

My big problem is finding a type of MPPT controler in the USA. I've seen the immerSUN & EMMA from the UK but these are for AC and I just want to do the DC.

If y'all see any problems with my line of though or know of a control link please post, Thanks
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Old 06-09-13, 11:29 PM   #29
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"my PV System does 320-326 kWh per panel, per year"..
So, you have a grid-tied system running right now?


I didn't know they were into PV hotwater in the UK..
http://www.reuk.co.uk/Water-Heating-...s-Solar-PV.htm
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Old 06-10-13, 10:20 PM   #30
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Smile Share of my Solar PV outputs

Here's my Solar PV system
TackyTed - Solar
At the bottom is a picture of what I produced my first year before I expanded.

Here's all my output since upgrade ….
Teddy-Denise 5kW Crossville,TN 4.998kW | Monthly
My enphase inverters one per solar panel
http://enlighten.enphaseenergy.com/p...tems/Wjgg11567

Here's some UK links for transfers to water heating, but AC and I need DC for a stand alone system I hope to build.

PV Water Heating, Solar Hot Water Switch and Controller Supplier in Lincolnshire, UK | immerSUN

Intelligent Solar PV Immersion Heater Switch - Use Surplus PV Power to Heat Water

EnergyMyWay

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