Small Solar Office

[Abandonhope16]

Hi all - I looking to run my desk off solar. The daily load is about 400 watts during the work day, then off at night and on the weekend. I was going to use a regular inverter but it seems I should use a pure sine. I am looking at the Samlex PST-300. Does that seem adequate? I wasnt planning on spending $150 there so maybe there is a lower/reasonable alternative?
I have a 100watt panel.
4 UB12350 35ah batteries SLA
30A PWM

The panel is directly outside my bedroom, but my desk is downstairs, so I would have to run 30+ feet of cable and have the batteries/equipment in the garage. Temps in Northern Va range from 20s to 90s. The alternative would be to have my desk in my room with the batteries, which I should be able to vent out the window as a precaution. Temp would be stable and there is a much shorter distance to the panel but the the potential risk associated with the batteries in my room.
Just looking for some thoughts/insight. Thanks.

[Logan5]

My work bench is solar powered, I have 4 T-105's for 24volts and 2 X 250 watt panels and OBFlex80 CC. I do not use an inverter. I converted my benchtop computer power supply to one that runs directly from my battery bank. I also power a 19v 40" TV with a 24v to 19v step down converter. My router and other electronic equipment from 24v to 12 and 5v step down converters. Most of today's electronics run from 5v 12v and 19v native. There are few good reasons to step 12v up to 120v to power a wall wart only to supply 12v to the actual device.

[PNPmacnab]

You have a great job if you only expect to work1- 2 hours a day. Every one comes and thinks a single 100W panel will work and they want to spend all their money on batteries. To me that is backwards. I run a whole house on a single car battery and have a lot of panels. Most wall warts work when the voltage gets above 50V DC. I would be running everything with about 80V DC directly from panels, 5 in series, and supplement that with grid power from a DC power supply. When panel voltage drops the power switches over seamlessly. That is the general idea. Batteries are a LOOOOOOOOOOOOSER. Probably best if you give up on this idea.

[dennis461]

What are your loads. If you plan on using a PC or laptop, I do not think you need a pure sine wave inverter. The PC internal power supply and/or laptop AC power adapter should work properly with a crappy inverter. I've run both from an automobile with a MSW inverter.

You also need to account for two days of rain.
I would go with a 250+ watt panel, 24 volt battery (I use two lawn mower batteries in series). And find a 24 VDC desk lamp. Good luck.

[Abandonhope16]

I was thinking of adding a second 100watt panel, but how would this setup give 1-2 hours a day? I figure it will draw 35ah/day and I will have 70ah (assuming 50%) discharge. I believe I will have 2 days available with no sun. A sunny day should give 250-350 watts/day with a 100 watt panel (I think).
Basically I plan to run a monitor, laptop charger, 5watt lamp, and cell charger. Without the phone charger, its about 40 watts total at 120v.

[Mike90250]

...
I would go with a 250+ watt panel, 24 volt battery (I use two lawn mower batteries in series). And find a 24 VDC desk lamp. Good luck.

I'd say 2 lawnmower batteries (50ah ea) could easily be cooked with a 250W panel. 250W @ 25V = 10A charging, about 2x what small batteries are rated for,

[dennis461]

I'd say 2 lawnmower batteries (50ah ea) could easily be cooked with a 250W panel. 250W @ 25V = 10A charging, about 2x what small batteries are rated for,

Almost two years now and no smoke, someday I'll enclose the rig to keep snow off.
The OP already learned that his panel(s) needs to go to a controller first.
My setup has a single 285 watt panel (it was a spare from someplace), a charge controller, two batteries, and a 24 VDC inverter, making 120VAC. This goes to a laptop and portable telephone.

To the OP,

I think you can expect 300 watt-hours from a 100 watt panel on a good day on the east coast this time of year, the battery will have that capacity at 24 VDC (not 120vac).
If your loads are 40 watts @120 volts, that's 120 watt-hours for three hours of working.
The panels can provide 300 watt-hours, with some margin to charge the battery(s), don't forget the laptop battery is also drawing a charge..
Your losses due to controller, inverter wiring may eat up the margin.
I would keep all dangerous parts outside the house unless you can do a safe/professional installation (don't emulate my setup!).
This would also reduce length of the DC wiring, which is better (more amps than the 120VAC wiring)

[Abandonhope16]

Thanks all. Even with the batteries being sealed agm, would indoors still be a no-go? Running them to my garage is an option, but it puts the greatest distance between the panel and the batteries. I guess they wouldnt be exposed to the full harshness of the outside conditions, but my garage isnt temp controlled.
I'm not opposed to a second 100w panel, especially if I dont have to drop $150 on a pure sine inverter. so that would give me 200w and 4 35ah (140ah) batteries.
I have eveything on a killawatt meter, which is where I got the 400watts a day, which is over a 10hr day, Mon-Fri.

[Sunking]

I would keep all dangerous parts outside the house unless you can do a safe/professional installation (don't emulate my setup!).
This would also reduce length of the DC wiring, which is better (more amps than the 120VAC wiring)

You can say that again. I would not show anyone that abortion. SLI car batteries, no fuses, undersized wiring. What a bomb. Looks like a 3rd grade science fair project that went terrible wrong. I do not think you should be answering any questions or encouraging anyone.

[Sunking]

Thanks all. Even with the batteries being sealed agm, would indoors still be a no-go? Running them to my garage is an option, but it puts the greatest distance between the panel and the batteries. I guess they wouldnt be exposed to the full harshness of the outside conditions, but my garage isnt temp controlled.
I'm not opposed to a second 100w panel, especially if I dont have to drop $150 on a pure sine inverter. so that would give me 200w and 4 35ah (140ah) batteries.
I have eveything on a killawatt meter, which is where I got the 400watts a day, which is over a 10hr day, Mon-Fri.

Why would you put any battery outside? That is just plain silly. Does not matter if they are AGM or FLA. Using 35 AH batteries is just plain ignorant to make a 140 AH battery. Just use a 140 AH battery. At 12 volts will only give you 350 watt hours per day of usable power.

This statement is jibber jabber

I got the 400watts a day, which is over a 10hr day, Mon-Fri.

Watts is the rate at which power is used. Say a 100 watt light bulb uses 100 watts of power. So how much energy does a 100 watt bulb consume in 10 hours. Real simple Watt Hours = Watts x Hours. So 100 watts x 10 hours = 1000 watt hours.

Now here is the fun educational part you will love. If your load is 400 watts, which is a small load, and you want to use 400 watts for 10 hours = 4000 Watt Hours. Oops. Do you have any clue what it takes to generate 4000 watt hours and store it in a battery. Well let me clue you in. You will realy like this and it will be super fun.

Panel Wattage = 1500 to 2000 watts
MPPT Charge Controller = 80 Amps @ 24 volt battery.
24 volt 800 AH battery that weighs 1200 pounds and cost you $3500 today and more in 2 or 3 years when you have to replace it.

Should not cost you a penny more than $6000 to generate 40 to 50-cents of electricity per day. Told you it was fun.

[dennis461]

You can say that again. I would not show anyone that abortion. SLI car batteries, no fuses, undersized wiring. What a bomb. Looks like a 3rd grade science fair project that went terrible wrong. I do not think you should be answering any questions or encouraging anyone.

I thought you'd like it!

[Abandonhope16]

I guess its my ignorance, but its a total of roughly 400watt hours over the course of a 10 hour day where power is being drawn. 400/10 is 40 watts. I fail to see why I would need a 1500 watt panel for some equivilent to a light bulb.
And its silly to have batteries outside? So everyone should store batteries inside? I don't feel that is necessarily true. I was simply asking for input on whether hydrogen gassing would be a concern with AGM sealed batteries indoors. I can have the batteries in the garage, which will be about 15degrees warmer than outside during the winter, so it shouldnt get below 32 while in the garage.

[dennis461]

Batteries work better when warm, which is why you may want to move them inside if you can.
I suspect building codes if followed would make this impractical, although the sealed batteries would not require room venting (of course any electrical device can pose a fire hazard).
On the other hand, the battery in your car is outside and survives. Probably could use a separate post regarding batteries inside a house.

I am still a bit confused by your load, (KW vs KWH) are you saying you monitored the actual load and it never rose above 40 watts in a 10 hour period?
I though you were going to use the office for 2 hours, not 10.
So we still need to nail down actual expectations.
40 watts makes sense, my laptop draws around 22 watts (it's power supply is rated at 75 watts), telephone is around 2 watts when talking.

So, to run the office needs 400KWH (If indeed you need 10 hours);
to charge the batteries at the same time, another 400KWH per day, which only allows one rainy day;
This is because if the panel is just large enough to power the office, it cannot charge batteries.

real world numbers, getting cloudy this month
panel rating		5.1	KW
panel maximum summer generation		4.2	KW (tilt, shade, etc.)
		KWH generated total
12/5/2016		6.2
12/6/2016		2.9
12/7/2016		3.8
12/8/2016		4.4
12/9/2016		16.3
12/10/2016		17.7
		8.55	average KWH per day
correlate to a single 100 watt panel
under similar conditions, azimuth, tilt, shading, local solar-days
168	KWH	falls short of your 400 KWH
		and additional needed to charge the batteries
falls short of your measured 400 watt-hours

You will need a 238 watt panel for the office
another 238 watt panel to charge the batteries for 1 days usage
another 238 watt panel to charge the batteries for another days usage.

Starting to creep up right?
Now, if your office will only be OPEN for 2 hours, not 10, we would redo the math.
Perhaps like this
3*238= 714 watts
714*2/10= 142 watts.

So add a second 100 watt panel and get to work in your new office!

[Abandonhope16]

Thanks Dennis - I may have confused things with the terminology I used. Yes, at any given point, I observe about 40watts +/-. If I reset the meter at the beginning of the day and by the end of the day, I tend to average about 400kwh total for the day. This is only Monday-Friday, so I assume I will recover some energy on the weekend.

[SunEagle]

I thought you'd like it!

Dennis. Is that a pile of stuff for the recycle bin or a working charging system. Because it looks thrown together and pretty dangerous to me.