Mini off-grid setup and configuration for a 500w draw inquiries

[Sam Lee]

I'm new to solar tech and have many questions. My objective is to reduce at least $100-150/month to the utility company. I'm using power to power Macs and PCs workstations. A 16-core Mac Pro with 4 filled eSATA hd bays will consume about 180-250 w. It depends on how much processing is used. Leaving it idling is about 180w.

Here're what I'm planning to get for a starting system to test the water:

Grape Solar GS-S-250-Fab5 250-Watt Monocrystalline Solar Panel
Vmaxtanks Vmaxslr125 AGM Deep Cycle 12v 125ah SLA rechargeable Battery
Voltec 10-00487 Pure Sine Power Inverter, 2000-Watt, Blue & Black

So my preliminary setup is as follow:

125 AH AGM -> Pure Sine Wave inverter -> Tripp Lite 2200 VA UPS -> Mac Pro, 27" LED monitor, speakers. ext hdds.
I'm estimating about 350-400 w of power draw for a short 10-12 hrs per day period. I will not be using it every day.
More like every other day. This should allows plenty of time for the panel to charge the battery on the off days

I'm still baffled is to find a 24 vdc charge controller that will charge 12 VDC panels. There are 180w 12 VDC panels, but because of
tight space, I prefer to have large wattage panels (3 max) vs. smaller ones. Is it possible to get a 12/24 VDC charge controller to put the voltage
down to 12 vdc? Is it safe during sunny day to simultaneously use the 250 w panels while also with the battery?

Future expansion will be two 250-w panels and two 125 AH SLA batteries in parallel to boost the wattage. Not planning to do any switch over to the house.
This will be installed in a 15x20' shed with its own independent off-grid power supply.

The initial investment of about $1,800 should pay itself after about 15 months of use. I do no want to exceed $3K for solar equipment to make this work. The electric bill adds up quickly for these computers. Kind of wasteful. My concern here is that I'm not sure if the SLA battery can handle continuous demands for about 500 w of power. Planning to use the computers from 9am to 9 pm.
Roughly a 12-hr continuos power period only.

[russ]

I'm using power to power Macs and PCs workstations. A 16-core Mac Pro with 4 filled eSATA hd bays will consume about 180-250 w. It depends on how much processing is used. Leaving it idling is about 180w.

How many? Only one? How many hours a day?

You have said nothing about the total load - any lighting for ezample.

[Sam Lee]

Total load will be 400 watts max with a couple of fluorescent bulbs included in the shed. It will be stripped down to only a single Mac Pro. 12 hours/day No PCs or other Macs as I realized it's eating up too much power. There may be a few occasional peak loads of 500 watt as the Mac Pro crunching all of its 16 cores. But for the most part, I'm planning to keep everything under 400 watts total for roughly 12 hrs straight. Can remove extraneous idling hard drives that consume about 10 watts each. And can shut down a 40-watt LED monitor when the Mac Pro is performing rendering or file exporting.

How many? Only one? How many hours a day?

You have said nothing about the total load - any lighting for ezample.

[russ]

Total load will be 300 watts max with a couple of fluorescent bulbs included in the shed. It will be stripped down to only a single Mac Pro. 12 hours/day No PCs or other Macs as I realized it's eating up too much power. There may be a few occasional peak loads of 400 watt as the Mac Pro crunching all of its 16 cores. But for the most part, I'm planning to keep everything under 400 watts total for roughly 12 hrs straight. Can remove extraneous idling hard drives that consume about 10 watts each. And can shut down a 40-watt LED monitor when the Mac Pro is performing rendering or file exporting.

Location - necessary for insolation numbers - when Sunking comes along this is gonna warm up!

[Sam Lee]

Location - necessary for insolation numbers - when Sunking comes along this is gonna warm up!

I just modified the post to 400 watt total. Forgot to incorporate ethernet routers, pro speakers, pro video monitor, and misc items.

I'm located in Southern CA - Los Angeles area.

[FloridaSun]

My objective is to reduce at least $100-150/month to the utility company.

I'm estimating about 350-400 w of power draw for a short 10-12 hrs per day period. I will not be using it every day.
More like every other day.

The initial investment of about $1,800 should pay itself after about 15 months of use.

Strange math you have there... You might want to check your figures again.

[Sunking]

I'm new to solar tech and have many questions. My objective is to reduce at least $100-150/month to the utility company.

You are fooling your self. While it is possible to reduce you monthly electric rate to the utility, in the process you will now pay your solar dealer $1000/month to do that. Taking anythin off-grid will cost you roughly 10 times more than you can buy it for from the POCO.

Just base don what little infor you have provided up front initial cost will be some $15,000, and $6000 of that in batteries you have to replace every few years. I am not even going to bother doing the calculations as this project will never happen.

[Sam Lee]

You are fooling your self. While it is possible to reduce you monthly electric rate to the utility, in the process you will now pay your solar dealer $1000/month to do that. Taking anythin off-grid will cost you roughly 10 times more than you can buy it for from the POCO.

Just base don what little infor you have provided up front initial cost will be some $15,000, and $6000 of that in batteries you have to replace every few years. I am not even going to bother doing the calculations as this project will never happen.

I see. This is only in the planning stage. I guess I have to be pretty heavy power user to take advantage of solar power. My electric bill probably have to be in the $300-400/month range to make it worthwhile for solar. The $6K in batteries replacement cost for every 2-3 is not what I have in mind. Ouch. That's expensive. I thought SLA or AGM batts last 8 years. But that's only for keeping it trickling and not continuous daily use.

[Naptown]

Sam
What is the goal here to reduce the electric bill or to provide a means of running without grid power.
For half of what you would spend on an off grid project you could do a grid tie and save twice as much money with almost no maintenance.

[Sunking]

There is no level that can save you money. Anything you take off grid is going to cost you 10 times more for the rest of your life. Only possible way for Solar to pay off is Grid Tied.

[SunEagle]

I see. This is only in the planning stage. I guess I have to be pretty heavy power user to take advantage of solar power. My electric bill probably have to be in the $300-400/month range to make it worthwhile for solar. The $6K in batteries replacement cost for every 2-3 is not what I have in mind. Ouch. That's expensive. I thought SLA or AGM batts last 8 years. But that's only for keeping it trickling and not continuous daily use.

There are a couple of areas that you greatly underestimated. The biggest area is the size and number of batteries needed for your 400 watts for 12 hours load (one 125ah battery is way to little). The next is the number of solar PV panels needed to charge that really big battery bank as well as the battery replacement costs every 3 to 5 years.

The third area that you misunderstand solar power is that the systems that become anywhere close to being cost effective for off-grid are the very small power users. They are more cost effective because you need much less in the way of batteries, panels, charger and inverter. The cost for all of those items can be less expensive then the cost to run a grid tie connection a long distance from the road side power grid.

Unless your electric costs are in the $5/kWh range connecting to the grid is always much less expensive.

[Sam Lee]

There are a couple of areas that you greatly underestimated. The biggest area is the size and number of batteries needed for your 400 watts for 12 hours load (one 125ah battery is way to little). The next is the number of solar PV panels needed to charge that really big battery bank as well as the battery replacement costs every 3 to 5 years.

The third area that you misunderstand solar power is that the systems that become anywhere close to being cost effective for off-grid are the very small power users. They are more cost effective because you need much less in the way of batteries, panels, charger and inverter. The cost for all of those items can be less expensive then the cost to run a grid tie connection a long distance from the road side power grid.

Unless your electric costs are in the $5/kWh range connecting to the grid is always much less expensive.

Will have to scrap this solar plan. The initial & on-going maint. costs are just way too much for so little return on investment. My cost here in Southern CA is 29 cents/kwh. It jumps up to 36 cents/kWh during peak summer months (June-Aug). But overall pretty reasonable rate. That's way under $5/kWh. Just a waste to see all of the sunlight not being utilized though. Perhaps another decade or two solar tech will be more realistic?

[Sunking]

Just a waste to see all of the sunlight not being utilized though. Perhaps another decade or two solar tech will be more realistic?

Not for a battery system.

[Naptown]

In your case you could do a grid tie system. It is a huge bang for your dollar there.
The problem is you started to look at the most expensive, least efficient way to go solar.
Southern California is a great place for grid tie considering the tiered rates. and the federal and perhaps local incentives to do so.
Research Grid tie solar or solar leasing.

[Sam Lee]

Not for a battery system.

If I invest in two 125 AH 12 VDC batteries for about $500 and it will give me at least 3-years of daily full charge and discharge usage, then is it a worthwhile investment to capture that energy for later use?