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Old 09-08-12, 04:20 PM   #1
creeky
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Default P-p-p-ower shed: part two

Here are a few pics and a general update on the "power shed" I built last year. (For those who missed it, the original "power shed" post is on page two or page three now).

As a quick refresh: the power shed holds 4 250 watt panels attached to 6 400 amp hour 6v batteries configured in a 12v system with 3000 watt pure sine inverter.

First, here I am, back on the farm Spring 2012 (this is a 3 season recreational property). I plug in the travel trailer and have power!



Note that the shed and the panels made it through the winter in excellent condition. My hinges were strong enough to hold up to the fiercest winter blast.

So: triumphs
* The shed is still standing.
* The mounting system is sturdy enough.
* The dock hinges allow multiple angles!

Now: tragedies
* The pwm controller was replaced with a MPPT controller (MS-MPPT 60).
I didn't realize that pwm was turning my 48v panels into 12v panels (I did sell the old pwm for what I paid for it).



I connect the new mppt controller to the wireless network and discover:
* highest power production is just over 6 kw
* given an average sunny day, easily produces 4 kw

Triumphs:
* I have run all my lights, kettle, blender, tv, microwave, water pump, battery powered devices, high speed internet via satellite and a 46" tv (I may watch too many netflix movies) strictly off of solar for the past 5 months.
* A 12v system is robust. In August I typically find my batteries in the a.m. at 12.55 or better (15% discharge). I have never had a morning with my batteries discharged more than 12.5. I do turn off the internet modem when I go to bed. It saves 30-35 watts/hr.

Tragedies:
* A 24v system with two more batteries and two more panels would have run an electric fridge and an air conditioner. So close!

Note: on occasion the 1000kw system ran an 8000 btu seer 9.9 air conditioner, usually from 3 to 7 p.m. Cooling the "house" during the hottest part of the day. This did draw down my batteries a bit. With a 1500 watt system the a/c would run completely off the panels. I could get another controller, mate it to the current one, and run two additional panels or; go 24v (still requires two more solar panels).
I turn the a/c on only after the batteries have gone to "float." This means they are fully charged. I turn the a/c off once the panels are out of the sun. The "house" is also out of the sun.

In summation:
Anyone looking to go offgrid with modest electrical needs will be well served by a 12 volt system with 1200 amp hours of battery storage and 750-1000 watts of solar panels.
A solar shed is a good idea.

Recommendations:
* Go 24 volt and up your solar to 1500 watts. Now you can have a modern electric fridge/freezer. My propane fridge accounts for the best part of my propane consumption (aprox. 40 lbs/mo.)
* add too many solar panel watts. Haze, clouds, dirt on the panels all conspire to limit output power. So more panels is better.

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Last edited by creeky; 09-20-12 at 07:00 PM..
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Old 09-08-12, 07:24 PM   #2
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I'm really inspired to start a solar project for my house after reading your thread. Great job on saving yourself a bunch of money and saving the earth a little bit.

I would like to put up about 6 panels or more on the roof and stay on-grid to earn a little cash back when we aren't using the power.

What kind of money are we talking about that you spent on your system? If you went to the 24 volt system, how much extra would you plan on spending?
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Old 09-09-12, 08:03 AM   #3
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Geo, call it 4.6k for the 4 panel 1000 watt, 1200 amp hour battery, 3000 pure sine inverter, 60 amp mppt controller, wire/combiner etc. system. And probably a grand for the "shed."

Your system should be much less expensive. Panel prices have gone way down. I note that the controllers etc also seem to be dropping in price, but not as radically. By example: my ms-mppt 60 had dropped in price by the cost of the pwm controller I bought in error (I took the wrong advice!).

To go to 24v. (my original intention) would have cost an extra 100 for the inverter (from 550 to 650) and two extra batteries, about 550 (275 ea). So for 11% more I could have increased my storage capacity by 20-25%. . Another $1k (update: today 500 watts would cost more like $600) to add two more panels would increase my solar gathering capacity by 33%.

The reason I went to 12v is it matched with my "house" the travel trailer. It was only once the system was set up that I discovered that you invert the 12v to 110 ac and then convert it back to 12v at the trailer. I'm a slow learner, what can I say?

I like 24v as it will handle a fridge (in my configuration) and there are lots of accessories for a 24v system. Pumps, led lights, etc, all come in 24v. 48 volt, which a large number of people recommend, requires the use of a dc-dc converter: which can be expensive (250-300). Though some of the converters are 95% efficient, so there aren't any real "loss" issues. However, why bother with a 12/24 volt lighting/pumping system. Just convert to AC and be done with it!

That'll get a rise outta some people!

Last edited by creeky; 09-20-12 at 07:05 PM..
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Old 09-09-12, 10:19 AM   #4
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" Just convert to AC and be done with it! " That's a good point, since there are
a lot of devices that really like 120vac..

I'm using 48v in my little backup unit and just going to 120vac, using a cheapo MSW inverter.
I do have a sinewave inverter for our 'fine' electronics, but it's a low power unit.

Anyhow, the connected 500w PV array drives a plain old PWM charge controller,
since my original goal was only to keep the batteries charged up.
Wasn't worried about using PV power in real-time, but being able to have power
for my sump pumps at 3AM when a storm took out the grid.


My Backup system has worked out fine (& we have not had any major gird fails).

But, hindsight being 20:20, I should have gone with different hardware.
Hardware that would be more compatible to any change in goals.

The initial cost would have been a lot more, but I would have purchased:

A. higher wattage PV (using a fixed array w/ elevation),
B. a power-point-tracking controller,
C. a high KW sinewave inverter (off grid type),
D. and a larger, long life battery pack (48v).

That hardware would cost a lot more, but would have been a better investment,
in the event of changing goals or power requirements.

~~~
Lately, I've been testing the capability of my little back-up system using
the new A7 AirTap hotwater heater as a load.
Since the A7 only uses about 1 kWh per day, it just might work out.
Provided we don't get too many days like this weekend.
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Last edited by Xringer; 09-09-12 at 10:42 AM..
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Old 09-12-12, 11:03 AM   #5
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Xringer you did it right. 48 volt everything! Me, I didn't understand the losses with pwm when going from 48v panels to a 12v battery system.

Live and learn!

For my next system I want to wait until there are better batteries. The air/iron batteries look good. 75% discharge acceptable instead of 20%. 25 year lifespan vs 7. But they're still incredibly expensive. Hopefully that's a technology that will follow the panel price drop. I paid 1.70 a watt (delivered) for my last two panels and this year it would be closer to 1.20. Nice!

The mppt controller is my favorite toy this year. With "live data" tracking via the web, it's the first site I go to every morning.

It's really shown me how robust and powerful these systems are. It's noon and I'm already throwing sun power away to the tune of like 500 watts/hr ... the system looks to be fully charged by one. And I've been running extra heavy loads this a.m. cleaning up the house...

I don't think you would have any trouble running your A7. Let us know.
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Old 09-12-12, 01:23 PM   #6
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I took a shower early this morning, the A7 recovery run was 0.6 kWh.
So far the solar gain to the bank is 1.3 kWh..

I guess the cloudy days we had early this week, were pretty hard on my little battery bank.

One of the main reasons I wanted to use a 48Vdc bank, was to allow the use of higher DC volts from the PV array.
The TS-45 charger will take 125vdc from the PV array.
I think the PV is pumping out about 7 Amps at 60 to 70 volts right now.
Already pulled in over 22 Ah, with another good hour to go.
Makes me wonder if this thing can really keep up with the A7..

Air temperature in the basement has already dropped to 68F..
Gonna lower the set point on the A7 soon.
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Old 09-20-12, 07:29 PM   #7
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this brings up a few questions for me
1-I recently struggled with the propane vs solar powered fridge question. I finally realized, that at today's prices, it is far more economical to expand your solar system a small amount and buy a regular fridge. You save about a thousand bucks over a propane fridge and then you save 600+ bucks a year in propane cost.
So now you tease me with your A7. .6 kw for a shower. How long was that shower???
1a) given that the best propane on-demand water heater is 500 and you can get a cheaper one for 120 and on-demand water heaters appear to be pretty frugal with gas.
How much was that A7 again?
2)Your TS-45. How do you change the panel 60-70v to 48.x (the charging current level) with a pwm controller without throwing power away?
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Old 09-20-12, 09:51 PM   #8
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That Ebay dealer sold all 52 of her Airtap A7s (120832618149 - Price: US $437.00).

The TS-45 is good for 125 VDC (max) from the PV. It controls the power to the battery bank.
http://www.morningstarcorp.com/en/su...nual.04.EN.pdf
The system is normally fully charged up. So on almost every day, the bank isn't charging much.
It's not throwing away the power from the 500w array, it's just not using much of it.
Most days, not 1 AH gets recorded. It's a waste having a 500w array. Until things go south..

The system is not for everyday use. It's made for back-up power when the grid fails.
And, if the grid stays down for a long time, 500W of PV should allow us
to harvest a few Amp hours for the small AC devices we might want to run.
Of course, if it's overcast for days.. We are outta luck..
Have to crank up the gas generator!
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Old 09-24-12, 04:01 AM   #9
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How much does it cost and over 20 years what does it = per month
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Old 10-31-12, 11:58 AM   #10
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Your system size is very similar to mine. 6-6 volt 220ah gc2 batteries, 2300 watt inverter. My problem is I don't have solar yet so I am using a Champion 2000 watt inverter to charge up. I am going to be making a couple changes so can I ask about the 24 volts you talked about. I live in the house which is off grid. I have no problem using the generator for a couple hours a day to supplement. I do need to run an AC refrigerator so would I benefit greatly by adding a couple batteries, replacing the inverter and buying 1500 watts of solar rather than 1000 watts and using what I've got?

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