Solar office

[dave g]

Hello! I've been lurking in your fine forum off & on for maybe a year. I *think* this is my first post. I'm finally getting around to my first modest little PV project: Running all the stuff in my home office. This is primarily a "hobby" project, although the power goes off here with some regularity so the promise of uninterrupted power is appealing too.

I have a tiny little south-facing roof surface over the back door of my house, almost exactly the right size for the 3 panel, 45 watt set of panels that Harbor Freight sells. So I've ordered those, and went out and bought a battery today as well.

Here's what I've got / going to have:

- The HF solar "kit": http://www.harborfreight.com/cpi/cta...emnumber=90599

- From Wal-Mart today, an "Everstart Marine" battery #27DC-6. Says "Trolling, Deepcycle, RV" on it. 115 Amp Hours, 720 Marine cranking amps, 600 cold cranking amps.

- An "Aims Power" #PWRINV400W modified sine wave inverter, 400W constant, 800W surge.

And, while waiting for the panels to arrive, I'm using a Harbor Freight "Automatic Battery Charger" with an output of 1.1 amp. Supposedly this charger will stop charging when the battery is fully charged; it seem to work as advertised with car batteries, not sure if it's good for this purpose...

I've been measuring the power consumption of the stuff in the office to be operated and it totals about 150 watts. I've got everything connected and running off the battery right now, in fact. I'll fully change it tonight and see if everything will run all day tomorrow.

A few basic questions:

Will I hurt anything if I have the charger connected (and running) at the same time the inverter is running?

Is there any danger in having the battery in the room with me?

I've read (here, I think) that the HF controller that comes in the kit is not a "real" charge controller; what's up with that? Will it work to keep the battery changed properly from the panels?

Thanks! I'm really looking forward to all this .

[Dapdan]

Hey dave,

I dont want to be-little or discourage your efforts since any in terms of RE is good even though sometime they maybe not the most prudent (applies to everyone IMHO). I believe your money may have been better spent if you bought a good Si panel (you can get a 200w panel for $500 now). If you do the cal you will realise that the 45w panels from HF will only give you 135wh of energy on a good solar day (45w*6hr*50% eff). Given your loads of 150w you will only be able to carry them for 54mins and then start to deplete the battery and invariablely end up charging it back up with grid juice (which i think defies your original intent)

If you check the charging percentage of the panel it is also below the 5% min and you will not be able to equalize this battery either(this maybe not as critical for you). I believe if you added a couple more $100s you would be able to get a much better panel with much better warranty and be able to run your office strickly off that single panel. One 200w panel would give you 600wh under the same conditions of the above cal and run your loads for 3hr.


Cheers...
Damani

[icarus]

As as been said quite often,,,do your math. Calculate your loads,,, using a kill-a-watt or some similar device. Then calculate your potential from any give set of PV hardware. A simple calculation is (not perfect,, but simple) take the name plate rating of a PV panel, multiply that by the number of hours of GOOD sun, (usually ~4 in most cases over the course of a year,, maybe as much as 6 if you are in a really good location) and divide that number by 2. This will give you the useable 120volt watt hours (wh) you can expect in an average day. The number two factors in all the system (in) efficiencies, panel, wiring charge controller, inverter losses etc.

For example,, your 45 watt panel, 45X4hours/2=90 watt hours,, enough to light 15 watt cfl for 5 hours.

Now a couple of other things to consider. Modified sine wave inverters CAN destroy some electronic devices right away. They can also burn out 120 vac motors quite quickly. Also most cheap MSW inverters have terrible efficiency curves,,,so the above example only gets worse.

If I could give two pieces of advice to newbies, the first would be avoid the "ready, fire , aim" syndrome by doing your math,, and doing your homework. The second would be buy from experienced, dedicated solar retailers rather than Harbor Freight, Northern Tool, or much of E-bay. There are good reasons that people like this site sponsor have good reps to go along with the products they sell. They have been tried and tested by some very smart people,,, such that newbies don't have to reinvent the wheel.

One other piece of advice I would give newbies is battery based solar is, on average, twice the price per watt hour as grid tie. If you are looking to do any solar to "save money" you are twice as far behind using a battery. Even grid tie is not going to save you money,,, unless you have done EVERTHING you can do to conserve,,, and then you have to build a real system,,,, and even then the payoff comes in multiple number of years,, at best.

Tony

[dwh]

A few basic questions:

Will I hurt anything if I have the charger connected (and running) at the same time the inverter is running?

Is there any danger in having the battery in the room with me?

I've read (here, I think) that the HF controller that comes in the kit is not a "real" charge controller; what's up with that? Will it work to keep the battery changed properly from the panels?

Thanks! I'm really looking forward to all this .

Probably won't hurt anything to have the charger connected at the same time the inverter is running.

If that is not a SEALED battery - then YES THERE IS DANGER in having it in the room with you. The battery will vent hydrogen into the room when it's charging, and if you've never seen hydrogen burn...well it burns extremely fast. In fact it burns so fast that, like black powder, it doesn't seem to burn at all - it seems to explode. And letting hydrogen build up inside a room at night while you are sleeping...that is a BAD idea.

Don't know anything about the controller that comes with that kit. Search here for 2manytoyz, he's got that same kit and has pages on his web site about it.

[BB.]

2manytoyz' personal Website:

http://2manytoyz.com/

-Bill

[n3qik]

About the HF charge controller. The one with the single LED's is junk. Now if you get the one with a digital voltage display. Then that will work for you. I had both, the digital display one lasted 3-4 months till I upgraded to more powerful system. Also, the HF for some reason have good resale value. Plus, if you got them directly from HF, you can return the kit with in 30 days. So I would use it for 20 days get your feet wet, then see if you like it or not.

[RandomJoe]

I also started with an HF kit. Used it about 9 months until I started buying the "serious" gear!

A few comments about the HF kit based on my experience - reinforced by reading others' comments in various places:

- Their 45W rating is VERY optimistic! I don't think anyone has actually see that. (In fact, I think they got that rating by taking the short-circuit current and open-circuit voltage to multiply together.) In my case, the very best I *ever* got was 30W, and that was the day I opened the box and very carefully pointed the panels directly at the noontime July sun. Normal daily operation is more like 18-20W with occasional forays to 25W. (And yes, all three panels are still working.)

- I have the "new" digital-display charge controller and I'm not all that impressed with it either. It's a very crude controller, just applies panel power to the battery until the terminal voltage rises above its internal setpoint then switches them off until it falls below another setpoint. With the controller I have, that switch-off setpoint was alarmingly high - I didn't want the battery going that high. (Haven't used it since last summer, so can't remember exactly but it switched off somewhere between 14.5 and 15V.) Far as I know there's no way to adjust that.

I wound up buying a small better-quality charge controller from NAWS, and been much happier. It implements the three-stage charge algorithm - bulk, absorption, then float.

- The controller and panels have no reverse-current protection, so if you leave the whole kit set up overnight current will flow backward from the battery into the panels. The kit does mention not to leave things hooked up "when unattended", but doesn't mention why. I had a Watts-Up meter inline with my panels, which is how I noticed. I eventually installed diodes in the panels - there was *just* enough room inside the junction box on the back of the panels. (You could also just put a diode at the controller.)

- Some have worried about the glass on the panels, as it's (apparently) not tempered. (Not that I would know how to tell myself...!) But others have said theirs withstood hailstorms, and mine are fine so far - although they haven't seen much if any hail.

I still have mine on the roof, they charge the various batteries I have laying around for miscellaneous projects, or keep the battery topped up in my seldom-used car. Having said all the "negatives" above, I will say one nice thing I like about them (and amorphous panels in general) - these things start producing *some* current as soon as it's barely light! And keep producing right up until the sun goes down. Might not be a whole lot, but it's still better than zero!

[RandomJoe]

A note / question about the battery issue.

I used an AGM battery with my HF set, sat right on the bench with everything else (powered part of my ham bench). I like not worrying about battery acid leaking out if I tip it over! :)

But, I do have a question for everyone regarding the hydrogen gas issue. Because in the past I've had regular wet-cell batteries (usually one of the Wal-Mart "marine" batteries such as the OP bought) in the house. Used them, charged them, everything - usually in a very rough manner, I didn't know then what I know now about batteries. Never had an issue.

I'm not saying there *isn't* a problem, by any means. However, I have to wonder - how much hydrogen gas (by volume) does a battery actually generate when charging? Certainly I can see a battery - or worse, a whole string - in a small enclosed space being able to generate sufficient gas to reach volatility. But one or two car-sized batteries in an open room?

Also, how much gas is generated from "normal" charging as opposed to equalizing? My understanding is that equalizing is where you really generate the gas, but that doesn't happen often (if at all, in a very small setup). Would normal bulk / absorption charging generate much?

One of the things that made me wonder about all this is checking my T105s after they had been set up for a few months. The water level has barely budged from where it was when I bought them, so I'd hardly think they could have generated much gas at all.

I started wondering if this was perhaps along the lines of the warnings they put on gas cans (heck, just about EVERYTHING now) that warns of hideous, dire consequences if you just look at the can wrong. When I was a kid, we had a gas can for the mower in the garage (attached, with gas water heater and furnace) and it almost never had a cap on it - for that matter the caps they provided then were nowhere close to sealing! (Of course, we also didn't store it right beside the water heater either!) Really, the only gasoline-caused garage fires I remember reading / hearing about were always because someone had actually spilled a large quantity on the floor.

Again, I am NOT saying there's no risk! I just wonder (I really, truly would like to know) what the real risk actually is. I have so far not found anything that tells me that! Something like "one T105 emits roughly X parts hydrogen gas per Y time while charging, and it (only?!) takes Z PPM to go *BOOM*!

[niel]

it all depends on how concentrated the gas gets just like lng or propane. a battery or 2 probably won't be a problem.

[mike95490]

My personal hydrogen worry level:
only when in EQ, or something goes wrong.

It's produced at a fairly low rate, even in EQ, and then, you'd have to have a way to gather it, in a room, with a person walking by every hour, the room full of air would be stirred to dilution. Any window cracks, that air exchange will pull some H out with it.

But, that's my personal feeling, in contrast to what the fire departments and insurance companies want you to do.

And when something goes wrong, you have little time/chance to get it right.

If there was a single battery, in a house, on a UL, 3 stage charger, something else is far more likely to happen: