Sanity Check for new Off-grid installation

2twisty · July 2014

Wife and I are moving to the desert east of El Paso, TX in about a month. Moving into a 12x20 cabin. Not a lot of loads.

I can't build the "ultimate" system right away due to financial reasons, and I realize that this means that in the end it will cost more, but it is what it is.

So, here is what I have planned initially (see farther in for where I want to go with it as soon as I can)

8x US 1800 (6v 208AH) wired at 12VDC (I know....see "later")
Classic 150 CC
4x 230w 24v panels wired in 2 strings of 2 (http://store.mwands.com/solar-panels/230-watt-24-volt-solar-panel/) (we are driving right past there on the way out and are picking them up to save shipping costs)
12v 2000/4000w Harbor Fright inverter (I know....see "later")
3500w Genset w 100A 12v charger

I used SOLARSIZER.xls to calculate what I needed. I've attached it to this message. According to the sheet, I've got enough battery and panel for 1.7 days of storage. (Very few cloudy days out in the West TX desert)

LATER:

I know that using 12V battery banks for this size load is a "bad" idea. But it's what I've got for now. As soon as I can get the $1600 together for an Outback Inverter/Charger, I plan to go to 24 or 48V by rewiring my batteries. I also would like to add some more PV, maybe as many as 4 more panels, but I can't really see needing more than that regularly. For the odd large load, I can fire up the generator.

So, here are my questions:

Am I at least in the ballpark here?
When I get to upgrading the inverter and charger, should I go 24V (2 strings of 4 batteries) or 48V (one string of 8 )?
What gotchas can I expect with this plan? It's really too late to change it, so I need to make the best of what I've got.

I have about 987,234 more questions, but I will ask them as we move forward.

vtmaps · July 2014

Re: Sanity Check for new Off-grid installation

2twisty wrote: »

3500w Genset w 100A 12v charger

What generator? Is that 12 volt charger built into the generator? If not, what stand-alone charger are you planning to use?

--vtMaps

2twisty · July 2014

Re: Sanity Check for new Off-grid installation

The generator is a generic 3500w electric start generator that I got from Rural King. Outputs 120/240VAC.

Charger is standalone. It's a PowerMax 100A 3-stage charger. http://www.rvpartscenter.com/ProductDetail.asp?PID=54669&DID=&CID=&SID=

Cariboocoot · July 2014

Re: Sanity Check for new Off-grid installation

What I see:

1). You don't have a power demand figure to work from so there's no telling if the capacity is adequate or not. If not that monster gen will be roaring in your ear more often than you'd like.

2). Four battery strings in parallel, especially on a 12 Volt system, is asking for current-sharing problems.

3). The array size is a tad small for the amount of battery bank, regardless of configuration.

4). #1 comes up again because without that number you can't plan expansion including whether to pick 24 or 48 Volts.

5). The HF inverter is likely MSW type and may be a problem for some of the things you want to run.

What you could expect:

From 832 Amp hours @ 12 Volts (or equivalent) at 25% DOD about 2kW hours AC per day. That's not a bad start. The 920 Watt array should make about 59 Amps peak current which is a 7% charge rate - a bit low especially with loads running at the same time. End-to-end typical efficiency works out about right at 1.9 kW hours per day, a bit more with longer than 4 hours equivalent good sun.

I would strongly urge flogging the HF inverter and replacing it even with a Samlex SA 2kW 24 Volt sine wave inverter to begin with. About $850.

2twisty · July 2014

Re: Sanity Check for new Off-grid installation

There is a loads sheet in solarsizer. It's on the first tab and lists all the loads I plan to run regularly.

I plan to grow the array by at least 2 more of those panels, and my location gets between 5 and 7 hours of good sun daily according to the solar insolation chart I used when I looked up El Paso, TX.

The inverter is just one I had. I know that the 4 parallel strings are a bad idea and that I should go to 24 or 48V ASAP. However, I am waiting until I can get the cash together to buy an OutBack 24 or 48 volt inverter-charger. They run about $1600.

So, given this new information, it sounds like it should be decent once I get away from 12v and Harbor Fright. Which is exactly my plan.

Thanks!

zoneblue · July 2014

Re: Sanity Check for new Off-grid installation

3.6KWh/d is a lot for a cabin "without much loads". I think you have better go back over your load budget with a fine tooth comb. eg:

Fluorescent Lights 4X 20W 10hrs 7days 800.0Wh/d

Really? Here we live in 60m2, and our lighting (100% LED) looks like this:

lighting 						
	kitchen	4	5	1.5	30	
	lounge	4	5	4	80	
	bedroom	2	5	1	10	
						120Wh

The load budget is critical to get right, or else everything else will be wrong.

2twisty wrote: »

There is a loads sheet in solarsizer. It's on the first tab and lists all the loads I plan to run regularly.

I plan to grow the array by at least 2 more of those panels, and my location gets between 5 and 7 hours of good sun daily according to the solar insolation chart I used when I looked up El Paso, TX.

The inverter is just one I had. I know that the 4 parallel strings are a bad idea and that I should go to 24 or 48V ASAP. However, I am waiting until I can get the cash together to buy an OutBack 24 or 48 volt inverter-charger. They run about $1600.

So, given this new information, it sounds like it should be decent once I get away from 12v and Harbor Fright. Which is exactly my plan.

Thanks!

2twisty · July 2014

Re: Sanity Check for new Off-grid installation

What can I say. I like to overestimate loads. That just means I'll have plenty of power, or room in the calculations for things I might not have considered, right?

zoneblue · July 2014

Re: Sanity Check for new Off-grid installation

Are you also a millionairre? Solar gear is expensive and you dont want to buy it uncessirily.

The numbers in your calculator dont "feel" right to me. Is 6.5 sun hours the documented year round average? Or the summer max? You need to design for the min sun hour month (for use with no genset), or for the third to lowest month for use with a genset. Also recall that heat reduces output.

I suggest you start over, tighten up the load budget, then come back and we (read Bill and Coot) will sort your PV/bank/inverter ratio out. That there is the water trough.

Cariboocoot · July 2014

Re: Sanity Check for new Off-grid installation

2twisty wrote: »

What can I say. I like to overestimate loads. That just means I'll have plenty of power, or room in the calculations for things I might not have considered, right?

No, it means you've 'calculated' for 3.6 kW hours per day and expect to meet that demand with a system that falls short.

Those calculators are practically worthless, btw, as they are based on manufacturer's ratings of how much energy their equipment uses. This can be high or low compared to what really happens. This is why it is best to get a Kill-A-Watt and measure if not the actual items to be used at least similar ones under real-world conditions to get a more accurate estimate of power needs.

Otherwise you have a 2/3 chance of getting the system sized wrong, and those aren't very good odds. Nor is it easy to resize afterwards.

2twisty · July 2014

Re: Sanity Check for new Off-grid installation

OK. I can't change the details of the system at this time -- those things are set in stone for now.

Yes, I realize that it's always best to buy the whole system once, but not everyone has that kind of money available all at once. So, knowing that I will pay more in the long run because I will have to resize the system, I'm ready for that.

It's kinda like buying a house. Sure, it's best to pay 100% of the price and not finance it, but most people don't have that kind of money laying around, so they finance over 30 years and pay 3x as much as the price of the house in interest.

Thanks for the input -- It sounds as though, while not ideal, my system is not woefully under- or over- sized. For many of my loads, I did use a kill-a-watt, and then rounded them up. I'd rather build a system that's a little too big than waaay too small.

So, I never got a weigh-in on whether to go 24 or 48V when I upgrade later. If I've got the battery bank to do 48V, is there a reason to NOT do 48? WIll running 48V use more energy in standby or something?

solar_dave · July 2014

Re: Sanity Check for new Off-grid installation

2twisty wrote: »

OK. I can't change the details of the system at this time -- those things are set in stone for now.

Yes, I realize that it's always best to buy the whole system once, but not everyone has that kind of money available all at once. So, knowing that I will pay more in the long run because I will have to resize the system, I'm ready for that.

It's kinda like buying a house. Sure, it's best to pay 100% of the price and not finance it, but most people don't have that kind of money laying around, so they finance over 30 years and pay 3x as much as the price of the house in interest.

Thanks for the input -- It sounds as though, while not ideal, my system is not woefully under- or over- sized. For many of my loads, I did use a kill-a-watt, and then rounded them up. I'd rather build a system that's a little too big than waaay too small.

So, I never got a weigh-in on whether to go 24 or 48V when I upgrade later. If I've got the battery bank to do 48V, is there a reason to NOT do 48? WIll running 48V use more energy in standby or something?

24 or 48 volt all depends on your expanded loads.

2twisty · July 2014

Re: Sanity Check for new Off-grid installation

OK.. Let's get hypothetical.

If I expanded my loads to a level that you would recommend 24 volts, would it hurt me to go to 48? If so, how?

BB. · July 2014

Re: Sanity Check for new Off-grid installation

In general, the 48 volt inverters have higher wattage ratings and generally higher "idle losses".

There is a break between 24 volt and 48 volt switches/fuses/breakers==The 48 volt being a bit more difficult to find and sometimes more expensive.

If your system stays relatively small and you can live with 24 volt system (around 2,400 watt maximum power and 80 amps or so maximum charging), then a single string of batteries is only 12 cells to check water levels on vs a 24 cell/48 volt bank.

You amost have to do a separate design for each major system (12/24/48 volt) and see what parts play well together and if you really need the large 48 volt AC inverters or inverter/chargers.

It is sort of hard to say XX volt is good and YY volt is bad without taking the system power requirements and component sizing into account.

-Bill

jcheil · July 2014

Re: Sanity Check for new Off-grid installation

Trust us. Don't even waste your time with 12v for a system. You will find that you are seriously underestimating your loads and overestimating what your system will produce.
Even if you have to buy a cheap 24v inverter right now to "get by".

2twisty · July 2014

Re: Sanity Check for new Off-grid installation

Please send a link to a "cheap" 24v inverter and charger.

If I must, I will lower my loads by eliminating them until I have the $1600 for the OutBack, which, at most, will be 4 months. I can live with lowered loads for that amount of time, I think.

jcheil · July 2014

Re: Sanity Check for new Off-grid installation

2twisty wrote: »

Please send a link to a "cheap" 24v inverter and charger.

If I must, I will lower my loads by eliminating them until I have the $1600 for the OutBack, which, at most, will be 4 months. I can live with lowered loads for that amount of time, I think.

Don't forget that you also need to buy a mate2/3 with that outback inverter/charger - which adds a couple of hundred $ to the price.

As far as cheap inverters (and stand-alone chargers) I personally would never buy a cheap inverter, but in your situation you are kinda forced to - therefore I do not have a recommendation as to one you should get. I know too many people burned by the cheap ones. But then again, you have a HF one which is just as bad so that is why in this case it is the lesser of to evils and at least you will be on a 24v system.

Could just ebay search and find a bunch for around $200-ish. And I know the excitement of wanting to get a system up and running sometimes makes people shortcut things, but just trust us in the fact that we KNOW in the long run you will be happier just waiting and doing it right the first time. Even if that means waiting a few months to save up enough money to get the proper equipment. There are hundreds of horror stories of people in your situation and the end is never pretty and they end up spending more money that they would have if they had just waited and got the right equipment from the start. I was one of those people myself, starting at 12v, then going to 24 and then 48 all within a 2 year period when I just should have done it 48v to begin with. I can't tell you the amount of $ I "threw away" in those conversions.

Solar is addicting, you WILL find that once you have it, your loads WILL grow and then soon you will find yourself painted into a corner.

2twisty · July 2014

Re: Sanity Check for new Off-grid installation

Thanks for the input.

I think my system will serve me for now. I knew going in that I didn't have an optimal setup. I'll just have to adapt until I get the resources together for the Outback.

Blackcherry04 · July 2014

Re: Sanity Check for new Off-grid installation

I have a 12 V and a 24 V in parallel with each other. To be honest, I don't see any difference in the two. Good quality cabling of sufficient size to handle the loads are a must. If I am pulling a 1,500 watt microwave pulling 180 or so DC amps off the 12 V bank I get a .3 V voltage sag, thats to be expected. I guess after 30 years with 12 V, I won't be changing in the near future.

I like your blog, we'll be right with you out there.

zoneblue · July 2014

Re: Sanity Check for new Off-grid installation

BC4 forgets to say that his 12v bank is a top of the line Surrette heavy industrial battery. It can handle that sort of load.

Blackcherry04 · July 2014

Re: Sanity Check for new Off-grid installation

zoneblue wrote: »

BC4 forgets to say that his 12v bank is a top of the line Surrette heavy industrial battery. It can handle that sort of load.

I have over 300 customers with 6 - 10, GC-2's in parallel that get that kind of service daily. While I do have a set of Surrettes that I have had since last October, it is the worse $2,500 mistake I ever made. The Microwave I have had since since 1996. One can't be stupid with Battery power, if it's over a 1 Minute load over 100 amps, I start the generator, I'd do that with any voltage bank.

I forgot to mention that 1,500 watt microwave is on a 1,300 watt Outback GFX 1312 Inverter.

zoneblue · July 2014

Re: Sanity Check for new Off-grid installation

So your theory is what, that GC2s are cheap per Ah per year. That cables even though 4 times the size are short enough for the cost to not be a factor. Kinda makes sense, in a peculier kind of way. I shudder at the battery maintenance with all those cells, but based on this model, i guess you just run them til they drop and replace them. So maintenance free. Cool.

Blackcherry04 · July 2014

Re: Sanity Check for new Off-grid installation

zoneblue wrote: »

So your theory is what, that GC2s are cheap per Ah per year. That cables even though 4 times the size are short enough for the cost to not be a factor. Kinda makes sense, in a peculier kind of way. I shudder at the battery maintenance with all those cells, but based on this model, i guess you just run them til they drop and replace them. So maintenance free. Cool.

You got it right, GC-2's are $.76 cents a amp hr @ 12v. They go 3-5 years with water every 60 days and SG's checked. On the banks we do maintenance on get taken apart every year and battery positions in the bank shuffled, all the connections wire brushed and lubed with grease. 4/0 is all I use, it's about $4.00 a foot in 100 ft rolls, GC-2 interconnects are 9 1/2 inches and a couple lugs and heat shrink, it takes 3 per pair. In the scheme of life not that expensive.

Photowhit · July 2014

Re: Sanity Check for new Off-grid installation

Blackcherry04 wrote: »

You got it right, GC-2's are $.76 cents a amp hr @ 12v. They go 3-5 years with water every 60 days and SG's checked. On the banks we do maintenance on get taken apart every year and battery positions in the bank shuffled, all the connections wire brushed and lubed with grease. 4/0 is all I use, it's about $4.00 a foot in 100 ft rolls, GC-2 interconnects are 9 1/2 inches and a couple lugs and heat shrink, it takes 3 per pair. In the scheme of life not that expensive.

I fully agree that Golf Cart Batteries (Buy them at Sam's Club or Costco at around $80 each, liberal on cores as well) represent the best value on system amp hour delivered unless it's a forklift battery(more expensive but last longer). I'd say brave boast on the 4/0 at $4 a foot even if you needed 100 feet, as I recall a foot of 4/0 has nearly 1lb of copper in it so scrap value of 1 foot would be $2.60+ and then you need lots of lugs as well.

Blackcherry04 wrote: »

One can't be stupid with Battery power, if it's over a 1 Minute load over 100 amps, I start the generator, I'd do that with any voltage bank.

Yes, but with 24 volt you would need to be running a 2000watt load to be over 100 amps, I regularly run over 1000watts, microwave, water heater, A/C with fridge and washer running, A/c and bread machine today... Never had a genny never want a genny...

I like the idea of having a backup and have run a small place on 4 golf cart batteries, including A/C and likely running 4kwh easy during the summer months, Looks like you have no huge single loads, I'd buy 4 golf cart batteries for now, and go ahead and do a 24 volt system and buy an ExelTech 1100 watt pur2e sine 24v inverter($600 at NAWS). This would be 'the system' for a couple years of feeling out your ability of dealing with heat with just an evaporative cooler and fans.

In a couple years if you haven't messed up the batteries, look at replacing them along with getting that larger inverter and perhaps some more panels, I recall running the numbers with a guy moving to south Texas, and it's nice having such abundant sun! Good Luck dealing with the heat!

I would look at your loads , check out O2cool 10" fans run on less than 20 watts and put out a good bit of air, also look at bread machines, mine runs on 400 watts max and does a nice job. I know you've just now looked at what things use, but it looks like your on the right track, Good Luck!

2twisty · July 2014

Re: Sanity Check for new Off-grid installation

I've already got my batteries. I have 8 GC2s. The real weak points in the system that I have put together (but not yet assembled) is in my Harbor Fright 12v inverter and the fact that my solar array is a bit undersized. I have plans to rectify both of those situations. I can't do it all at once, wish I had that kinda money falling out of my pockets!

At any rate, I've ordered my 4/0 cable and will start with a 12v system at 832AH. My plan is to go to 24V@416 using the same battery bank. I plan to monitor and chart my SG monthly, and plan to rotate cells in the bank periodically. At what frequency should they be rotated? 3 months? 6?

Also, I thought that GC2s had a longer life than 3-5 years. I was hoping to get 7-8, but that's looking like it's not likely to happen, especially since I am a noob at this and noobs usually kill some batteries before they figure it out. I guess I will start setting aside money to replace the battery bank, figuring a life of 3 years. If I get longer out of them, fantastic, right?

Blackcherry04 · July 2014

Re: Sanity Check for new Off-grid installation

Photowhit wrote: »

I'd say brave boast on the 4/0 at $4 a foot even if you needed 100 feet, as I recall a foot of 4/0 has nearly 1lb of copper in it so scrap value of 1 foot would be $2.60+ and then you need lots of lugs as well.

Here is a BOAST for you !! How many feet do you want @ $3.95 a ft ? and thats one google. Do you want the lugs in Chinese or UL certified American ?

http://www.ebay.com/itm/100-4-0-EXCELENE-WELDING-CABLE-RED-MADE-USA-NEW-/350451354029?pt=LH_DefaultDomain_0&hash=item51988749ad

Photowhit wrote: »

Yes, but with 24 volt you would need to be running a 2000watt load to be over 100 amps, I regularly run over 1000watts, microwave, water heater, A/C with fridge and washer running, A/c and bread machine today... Never had a genny never want a genny...

Just think if you had a 96 Volt system what you could do. The OP is going to be a 12 v system, it doesn't matter what you have.

Amp Hrs are amp hrs, you take them out, you have to put them back in, sometime, some way.

.

Blackcherry04 · July 2014

Re: Sanity Check for new Off-grid installation

2twisty wrote: »

Also, I thought that GC2s had a longer life than 3-5 years. I was hoping to get 7-8, but that's looking like it's not likely to happen, especially since I am a noob at this and noobs usually kill some batteries before they figure it out. I guess I will start setting aside money to replace the battery bank, figuring a life of 3 years. If I get longer out of them, fantastic, right?

I doubt they will go that long. There life span all depends on how deep you pull them and their maintenance. 6 Years is about as most want to live on the reduced capacity. Once they don't have enough capacity to last to the next charge cycle, it's time to replace them.

Photowhit · July 2014

Re: Sanity Check for new Off-grid installation

Blackcherry04 wrote: »

Here is a BOAST for you !! How many feet do you want @ $3.95 a ft ? and thats one google. Do you want the lugs in Chinese or UL certified American ?

http://www.ebay.com/itm/100-4-0-EXCELENE-WELDING-CABLE-RED-MADE-USA-NEW-/350451354029?pt=LH_DefaultDomain_0&hash=item51988749ad

That's a good price, if you need 100 feet, I'm Surprised, copper must be down. If your using this vendor buy now, since even with Ebay rules you'll get it at that price, they say actual shipping charges in the post.

Blackcherry04 wrote: »

Just think if you had a 96 Volt system what you could do. The OP is going to be a 12 v system, it doesn't matter what you have.

Amp Hrs are amp hrs, you take them out, you have to put them back in, sometime, some way.

Actually, no you don't, you can put in 100 amps at 12 volts or 50 amps at 24 volts! higher voltages mean you can use smaller wiring over the same distance...

The original poster has said they will switch to a higher voltage system, I was presenting a way to switch now rather than later and have a backup inverter when they made the switch at nearly no additional cost. I didn't realize they had purchased the batteries already.

Photowhit · July 2014

Re: Sanity Check for new Off-grid installation

2twisty wrote: »

At any rate, I've ordered my 4/0 cable and will start with a 12v system at 832AH. My plan is to go to 24V@416 using the same battery bank. I plan to monitor and chart my SG monthly, and plan to rotate cells in the bank periodically. At what frequency should they be rotated? 3 months? 6?

Even more important than rotating your cells is to properly wire your batteries, you want to have equal resistance through each pair of batteries. The easiest way to do this is to wire them to a buss bar with equal lengths(and gauge) of wire (including the wire between the batteries)

2twisty wrote: »

Also, I thought that GC2s had a longer life than 3-5 years. I was hoping to get 7-8, but that's looking like it's not likely to happen, especially since I am a noob at this and noobs usually kill some batteries before they figure it out. I guess I will start setting aside money to replace the battery bank, figuring a life of 3 years. If I get longer out of them, fantastic, right?

Right! 5 years is not uncommon, but if your prepared for 3 years that would be good.

Blackcherry04 · July 2014

Re: Sanity Check for new Off-grid installation

Photowhit wrote: »

That's a good price, if you need 100 feet, I'm Surprised, copper must be down. If your using this vendor buy now, since even with Ebay rules you'll get it at that price, they say actual shipping charges in the post.

You want 10 feet, that will cost you a little more. The shipping alone is 15% of the cost

http://www.ebay.com/itm/10-4-0-WELDING-CABLE-EXCELENE-5-FEET-RED-AND-5-FEET-BLACK-MADE-USA-NEW-/350708024185?pt=LH_DefaultDomain_0&hash=item51a7d3c379

Oh, the cost of wire, thats a big factor in the scheme of a solar system. Now Racking is a big factor that shouldn't be over looked.

Cariboocoot · July 2014

Re: Sanity Check for new Off-grid installation

BTW we say it's the same power regardless of system Voltage but in fact as the Voltage goes up so does the efficiency. A 24 Volt system is about 2% more efficient than a 12 Volt one. Good luck on noticing that difference, though.

Blackcherry04 · July 2014

Re: Sanity Check for new Off-grid installation

Cariboocoot wrote: »

BTW we say it's the same power regardless of system Voltage but in fact as the Voltage goes up so does the efficiency. A 24 Volt system is about 2% more efficient than a 12 Volt one. Good luck on noticing that difference, though.

I think there a is a huge difference in the Charge Factor of one battery over another based on size and plate composition. While I haven't had it long, the Outback FNdc has a default setting of 95% on the charge factor on the SOC settings, I am down to 77% on the Surrettes. That alone regulates the Charge time and requirements. I am going to switch the FNdc to a set of GC-2's in the next few weeks and see what they are. Based on what I see on a set without any data suggests they charge to 100% much faster and would have a higher factor. With the Surrettes thats 1 to .77 factor, not real good. I have seen posts that suggest they are about .85 %, but I am not there yet.

I know your talking about other efficiencies with 24 V and I totally agree.

Sanity Check for new Off-grid installation

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