Newbie set up for off grid shop?

[sock]

Hey guys, I've just recently started investigating solar as an option when the electric company told me that they were going to charge me 9,000 to set up electricity at a small shop (thats with me digging the trench and providing the PVC, wire, ETC) 800 ft off the road.

So first, the shop (40 ft by 60 ft) is going to be used primarily for doing car restoration.

So firstly I figured up what my peak and average usage would be so here are those numbers.

Peak moment output ≈ 4 to 6 KW/H (predmoninantly the air compressor)
Average per hour usage ≈ 2 KW/H (when compressor won't be running)
Average weekly usage ≈10 KW/H to 40 KW/H (approximately 10 hours total)

Since its a shop and won't be used at all when no one is there, I was thinking of going with a back up generator-esque set up and this is what I was looking at and was hoping I could get some feedback on why this is good or bad. Oh I live in Texas where the average daily sunshine is 5 hours a day.

Panels: 6 200-220 watt panels

Battery: 12 battery bank equalling to 36 KW at full power

2 power inverters rated at 4 KW, One for the 240 plug and the other for the 110, dedicating approximately 8 batteries to the 110 and the other 4 to the 240, both going to dedicated breaker boxes.

Theoretically the panels under 5 hours of light a day will produce 36 KW in a week to fill the batteries and my usage will almost universally be lower, and since we are going to be restoring old cars there, if, after 8 to 10 hours, the power goes out, it just means its time to go home for the week.

From using Amazon and google this system would run about 9,000 dollars, and after the govt rebate (if it applies to this set up) would put it at about 7500 or so.

Long story short, if my set up above is viable it would save me about 1500 bucks and remove the monthly bill. So, will something like that work?

P.S. Eventually (4 to 5 years down the road maybe?) I am planning on building a house there, so I would like to be able to eventually tie it into my home, however, this is definitely a secondary deal as by the time I would be living there and such I am fairly certain technology will have moved past the system I would have on the shop, so it would just end up being a kick ass back up generator for my house then

[Mike90250]

the rebates are only good on your house - not a garage.


Suggestion, a honda eu2000 auto-throttle inverter generator. Should run most of your tools. Much less expense than solar. Or look at my solar for my shop if you have $$$

http://www.facebook.com/album.php?aid=2030956&id=1196643274&l=56e4b57d3e

This will eventually power my home too.

[Sunking]

OK Sock it is good you did some digging for data, but unfortunately some of your data is incorrect, and some useless for a design. Also some of your terminology is wrong, but easily to correct.

OK the first thing you need is how many watt hours you require in a day. You danced around that but did not really specify. You gave some peak hourly info, Peak moment in KWh which is meaningless gibberish. The only thing you really gave is a weekly total of 10 to 40 Kwh which is not good enough as th erange is just way too wide. But let's run with 40 Kwh per week. From that I can get watt hour usage per day of 40 Kwh / 7 /days = 5.7 Kwh per day.

OK before I go any further 5 .7 Kwh per day with an OFF-GRID battery system is a huge number, and with that comes huge cost. So that $9000 the utility wants to charge you is peanuts and one heck of a bargain.

OK you said is you live in TX. Not good enough, need a city. Next you stated you looked and get an average 5 Sun Hours per day. You cannot use the average for a battery system. You have to use worse case which is December-January.

OK let's run the numbers with 5.7 Kwh per day use in Dallas TX. Dallas receives 3. 5 Sun Hours in the months of December and January..

First we need to adjust for a battery system efficiency of 66% best case. This adjusted number is used to determine the solar panel wattage and battery capacity needed. Daily Kwh / .66 = 5.7 Kwh / .66 = 8.6 Kwh. This is how the minimum energy the solar panels need to generate each and day. So note 8.6 Kwh


OK to determine the solar panel wattage all we need to do is factor out the time element. W = WH/H = 8600 wh / 3.5 h = 2388 watts. Round up to 2400 watts or 12-200 watt solar panels. Est cost = $2 per watt = $2 x 2400 = $4800..

OK for the battery amp hour capacity we need to determine the battery voltage. I can tell you from experience you are going to need to use 48 volts. Buts let's skip the battery amp hour capacity. All we need to do for cost estimation is determine the reserve watt hour capacity which = 5 x daily adjusted watt hour = 5 x 8.6 Kwh = 43 Kwh. Battery cost are $140 per Kwh so 43 Kwh x $140 = $6020.. Now here is where it gets fun and educational. The batteries will need replaced about every 5 years at even higher cost. One more note, battery weight = 60 pounds per Kwh = 60 pounds x 43 Kwh = 2580 pounds of lead.

Now for the charge controller. This is where we need to know the battery voltage. The largest a consumer can buy is 80 amps. So to determine the charge controller size = Panel Wattage / Battery Voltage. So 2400 watts / 12 volts = 200 amps. Nope that will not work. 2400/24 volts = 100 amps. Nope that will not work. So it will take at least 36 volt battery, but you will never find an inverter for that voltage, but you can find 48 volt inverters all day long. So 2400 watts / 48 volts = 50 amps. So you need a 60 amp MPPT charge controller that cost around $400

OK the inverter is going to bite. Electric motors, especially large electric motors like those used in compressors do not play well with inverters. You will need a True Sine Wave inverter. At 48 volts is going to cost about $1.25 per watt. To determine the size for a motor you have to look at the maximum Kva the motor needs to start. and double it. You mentioned 2 Kw, so if that is what your motor needs to start up then you need a 4000 watt 48 volt inverter. At 4000 watts for a true sine wave 48 inverter is going to cost you around $5000.

Total cost of this example is around $16,000, plus $6100 in 5 year increments to replace batteries.

[Sunking]

From using Amazon and google this system would run about 9,000 dollars, and after the govt rebate (if it applies to this set up) would put it at about 7500 or so.

No rebates for this setup.

[sock]

Ok, let me respecify a bit.

Its a shop that is sitting by itself on a plot of land and will only be used on weekends, or if it is used during the week, a max of 1 to 2 hours of usage per day.

99% of the time it will be a 1 to 2 day a week. Saturday and Sunday. Saturday 4 hour maximum and Sunday 8 Hour Maximum. So for all intent and purpose, The game plan is to Charge Monday - Friday, mild usage on saturday, and more usage on Sunday. So something like this in general:

Sunday - 6 hours (approximately 15 Kilowatts used total)
Monday - 0 hours
Tuesday - 1 hour (approximately 4 kilowatts used total)
Wednesday - 0 hours
Thursday - 0 Hours
Friday - 0 hours
Saturday - 4 hours ( appx 10 Kilowatts total used)

Since it will only be used on a 1 to 2 day basis in general, that is why I figured a generator type system would be best as power does not need to be on for 4 to 5 days out of the week.

Here is a list of what I plan to run:

air compressor pulling around 2500 watts of power (220 volt)
or
Welder running at peak load around 3000 watts
small radio (200 to 300 watts)
possibly a small AC unit running around 12,000 BTU's (1200 watts i believe?)
two smaller tools running around the 12 amp range (I think that comes out to 1300 watts a piece)
Possibly a mini fridge (peaking at 700 to 800 watts)
4 80 watt bulbs.


Based off of what Sunking said (fantastic information by the way, I really appreciate it). It would seem my original estimates are way off. So my next question would be, If I went with a diesel generator or something for the welder/compressor and swapped to a constant flow system would that be more cost effective?

Using that I would be looking at: 4 KW/H max pull with a general average of 1.5 KW/H pulled making my day to day totals probably closer to:

1 week day of 1.5 KW used
Saturday 6 KW used
Sunday 12 KW used

This eliminates the bigger plug and changes my needs to an average of 3 KW per day. so let me see if my math is right based off of what Sunking provided for me (again awesome info)

$2 per watt panels = 2500 for panels
140 KW/H battery = 3150 (with an average of $50 per month for replacement not added in)
$400 for controller
Inverter for largest possible item @ 1.25 per watt = $3000

So now its back to the 8,000 for the general set up, however, I will need to get a diesel generator to run the compressor and the welder which will run appx 700 bucks + gas.

Now if I were to guess based off these modified numbers since the usage is going to be almost exclusively on weekends I will still need enough batteries to handle that kind of pull so so around 15 KW arrived at by saying:

1.5 KW/H * 12 hours * (5 / 7 days) = 15 KW used.
making my battery requirements around 6000 (with appx $100 a month for battery replacement not factored in at 5 years).

So end of the day I am looking at around 12,000 to do this stuff and having 100 dollars a month basically in upkeep.

So if I'm doing this right (probably failure again) even if I changed it up to lower the cost it would end up costing more to go solar (based off my electric bill probably being lower than the $100 per month even with random stupid fees).

[Sunking]

Sock with a welder, air compressor, and air conditioner Solar PV is out of the questions. The inveter alone to run those items is a $20,000 + list item not including any thing else. Pay the utility $9000 to install a single phase 240/120 volt @ 100 amp service and be done with it.- It is a bargain and worry free with no limitations. Otherwise you are going to spend 20 times more for electricity for the rest of your life up front in cash every 5 years.

If you ever decide to sell it, you will eliminate 90% of buyers if you have solar. It is just too much baggage and way too limited for commercial operation.

If anything have utility power and then use a grid tied solar package. But even that has no ROI with as little use as you have. One thought is use a grid tied system at your home, and extend service from your home as a detached building with a 60 amp feeder. That way your neighbors are forced to pick up a large portion of your cost to pay for your profits.

[sock]

Ok, thanks for the info, that's exactly what I was hoping to find out (although I was hoping it would be the other way around haha.)

I appreciate the time though, good information for future application for sure.

[sock]

One last thing, do those numbers (the $2 per watt on panels, $140 per KW on batteries, $1.45 per watt on an inverter) apply with much smaller systems as well, like if I were to estimate the cost of a system to just run some lights, a mini-fridge, a drill or two, and maybe a radio. Something along the lines of a system that can handle 6 KW in a single day, with the same hourly usage. (like something that can store up around 9 Kilowatts of power over the week to be used over the weekend)

[Mike90250]

One last thing, do those numbers (the $2 per watt on panels, $140 per KW on batteries, $1.45 per watt on an inverter) apply with much smaller systems as well, like if I were to estimate the cost of a system to just run some lights, a mini-fridge, a drill or two, and maybe a radio. Something along the lines of a system that can handle 6 KW in a single day, with the same hourly usage. (like something that can store up around 9 Kilowatts of power over the week to be used over the weekend)

Won't work, as the batteries will sulphate Sun, Mon, Tues, Wed, before they get back up to a full charge. Unless you are using a really huge battery bank that won't go below 75% on Sunday evening.

You could add a small genset 5KW or so, and when it's not running the welder, it can charge batteries

[sock]

Yeah thats what I'm thinking about doing, is just getting a Welder/generator and using that predominantly. I was just curious if it would be cost efficient to go with a smaller solar set up to run some lights and a radio and such so I can keep the welder/generator shut off while not using any bigger tools.

If I can hook up the generator/welder to the batteries to seep off the excess while it is running, it might be a possibility still though. I dunno, in the end its still probably gonna end up to be cheaper and easier to just run electric out there. Just throwing around options.