Thoughts on my 48v Off-Grid Setup

googdot · November 2014

Hi all,

First post here, and after researching my upcoming off-grid setup for the past few months I’m ready to take the plunge

I’m looking for advice or critiques on my 48v setup for a very basic small off-grid cabin. I'm thinking of setting it up in two stages:

Stage 1 – Caravan living (while cabin is being built) 
Stage 2 – Cabin living

Here is what I'm looking at:

- Rec 260W panels x 3 in a a string at 48v (add 1-2 more panels for stage 2)

- Midnite Classic 200 Controller

- Trojan T-105 6v 225ah OR Generic AGM 6v (C100 286ah, C10 220ah) x 8 (add 8 more batteries in parallel for stage 2)

- Outback GFX1448E Inverter (1400W, 2000W 30min, surge 4600W)

- Generator (added for stage 2)

I've gone through a few of the calculators online, and it looks like our basic cabin will require about 2kWh-3kWh per day on average.* I know that's very low but it is a very simple living setup - no high power appliances or anything like that. The fridge is the only major appliance, and its energy saving. Here is a basic list:

Appliances would only include:
- Low-Energy Fridge (300W/day)
- Stereo (50W) 2 hrs/day
- Laptop (85W) avg 1hr/day for charging

Also included are 4-6 LED lights, and occasional use of AA charger (24W), fan (50w), phone charger (10W), Powertool Charger (50W), hand blender (200W) and washing machine (500W).

All cooking/heating is done via wood or LPG. Water is gravity based so no pump required. Kitchen and bathroom are partially outside so no extractor fans are needed.

Do you guys think I’m on the right track? Would you go with the flooded batteries or the AGM's? Any recommendations for other/different components?

Cariboocoot · November 2014

Re: Thoughts on my 48v Off-Grid Setup

Welcome to the forum.

Are you on the right track? Nope.

Okay, let's start with the lack of a target for daily Watt hours. You've got some guesses, probably based on calculations. I say this because of a refrigerator @ 300 Watt hours per day (low) and a laptop using 85 Watts (high). Do not trust the information supplied by makers as for Watts or Amps anything uses. 2-3 kW hours per day is not unreasonable for an off-grid system.

Why did you pick the Classic 200? Unless you are planning an array with very high Voltage (not a good idea) the Classic 150 is fine.

Now about that array: three 260 Watt panels is 780 Watts. On a 48 Volt system that's about 12 Amps peak current, which is not enough for a 225 Amp hour 48 Volt battery bank (eight T105's).

You've also selected a GVFX1448E. Why? Planning on running gen support? What is your largest load going to be?

Were it me I would not pick a 48 Volt system here as you probably don't need that storage capacity (around 4.8 kW hours at 50% DOD). I definitely would not go with AGM's for the first battery set either: too easy to ruin them. I would increase the array size.

Note that my own system supplies about as much power as you are looking for. It's 24 Volt, has four 232 Amp hour batteries, and 1200 watts of array. Gen support isn't necessary, but then I have a 3.5 kW inverter which will start and run just about anything I throw at it. The tare loss is the same on this as it was for smaller batteries, and even at maximum output the current @ 24 Volts is not unreasonable (<150 Amps). You don't have any heavy loads like my water pumps either. I even run the big air compressor for my power nailers off the inverter - no problem. The washing machine you list may be much worse than 500 Watts, or much better (wide range in washer power consumption).

So I think we should be looking at the end result here and what sort of maximums you expect when all is done.

If at all possible get a Kill-A-Watt and measure the usage of items you want to have or at least similar ones under real conditions. You may find it changes the design quite a bit.

googdot · November 2014

Re: Thoughts on my 48v Off-Grid Setup

Cariboocoot wrote: »

Welcome to the forum.
Are you on the right track? Nope.

Thanks for the quick reply. I'm fairly certain on the final usage being in the 2-3kWh range. I understand what you mean about actual daily watt hours, but I've tried to gather as much information as possible given that we are moving to a new country and I don't really have access to any of the appliances at the moment. My wife and I are used to simple living, and think this figure will easily cover things for us.

Can you explain why the panels are insufficient in the initial setup? Both suppliers I have been communicating with agree that 4-6 panels in the end would work well, and that the initial three panels would work for charging the tools, batteries etc. while living in the caravan.

I chose the Classic 200 because it would allow me to add a panel at a time as I go. In the event that I hit six panels, I would then split into two series. Why the 150 instead?

The inverter was chosen based on a largest load at any given time of 1200W. The Outback has a nice high surge capability and 2000W for 30 minutes, so that would cover any overuse as well as the startup of the washing machine and fridge in case they both went on at the same time (unlikely but you never know).

I spoke to the distributor of the fridge, and they said I'd need at least a 1500W inverter to cover the surge at startup. I got the 300W figure from the government energy test (132W operating, 0.9kWh per day).

I'm trying to choose quality components from the start with the ability to expand as we go, and I'm open to changing the design to 24v as well. What changes do you recommend?

Cariboocoot · November 2014

Re: Thoughts on my 48v Off-Grid Setup

googdot wrote: »

Thanks for the quick reply. I'm fairly certain on the final usage being in the 2-3kWh range. I understand what you mean about actual daily watt hours, but I've tried to gather as much information as possible given that we are moving to a new country and I don't really have access to any of the appliances at the moment. My wife and I are used to simple living, and think this figure will easily cover things for us.

Can you explain why the panels are insufficient in the initial setup? Both suppliers I have been communicating with agree that 4-6 panels in the end would work well, and that the initial three panels would work for charging the tools, batteries etc. while living in the caravan.

Okay, panels: Three 260 Watt units on an MPPT controller and 48 Volt system; 780 Watt array @ 77% typical efficiency / 48 Volts = 12 Amps peak current. On a 225 Amp hour battery bank that is a 5.5% peak charge rate, the minimum battery makers recommend and that does not include any load allowance.

I chose the Classic 200 because it would allow me to add a panel at a time as I go. In the event that I hit six panels, I would then split into two series. Why the 150 instead?

Because it is not a good idea to run a high Voltage array unless it is absolutely necessary: the higher the difference between array Vmp and battery Voltage the lower the charge controller's efficiency is.

On the whole you'd be better off with a 24 Volt system an four of these panels configured as two parallel strings of two in series. That would be 1040 Watts supplying 33 Amps peak current; plenty for 220 Amp hours or even a bit more (like four L16's at 320 Amp hours).

The inverter was chosen based on a largest load at any given time of 1200W. The Outback has a nice high surge capability and 2000W for 30 minutes, so that would cover any overuse as well as the startup of the washing machine and fridge in case they both went on at the same time (unlikely but you never know).

Good planning. Most any Outback inverter can cover that start-up surge, btw. What you also have to know is how much power the surge plus running loads will be. That can be fairly high. Will you be on Euro standard (230 VAC 50 Hz) power there? Also consider the OB FX2024ET as a possible inverter. No gen support (which is not the most convenient thing to use anyway) but slightly higher power handling.

I spoke to the distributor of the fridge, and they said I'd need at least a 1500W inverter to cover the surge at startup. I got the 300W figure from the government energy test (132W operating, 0.9kWh per day).

Most refrigerators will pull >1kW on start-up. Running Watts is another matter. I hope that "300W" rating isn't running, but its very low for Watt hours. It's important to keep the two designations separate. Typically a refrigerator will use near 1kW hour per day. For example mine runs at around 120 Watts, cycles 1/3 of the day more or less, and so consumes 960 Watt hours per day.

I'm trying to choose quality components from the start with the ability to expand as we go, and I'm open to changing the design to 24v as well. What changes do you recommend?

The only real problem with your proposed equipment is that the amount of panel is low for the amount of battery. If you were to go with a 48 Volt system and 220 Amp hour batteries you should have (22 Amps * 48 Volts / 0.77 efficiency) around 1371 Watts of array. Nearly double what you've listed.

Be careful with array planning as most panels these days are 'GT style' and have a Vmp lower than normal for battery systems. This gets into some conundrums for array planning. For example a Vmp of 30 is not uncommon, but it is too low for a 24 Volt system. Two in series works, but only on an MPPT controller. For 48 Volts two is not enough (Vmp 60) but three in series will work (Vmp 90). Then you start to get into efficiency drop and possibly Voc problems under cold temperatures. Inevitably at some point you have to parallel panels.

Photowhit · November 2014

Re: Thoughts on my 48v Off-Grid Setup

I think 'Coot cover most everything, and I agree, the only caveat would be if this is weekend work while your building the cabin? Then in a sunny area, you might be able to get by with the 3 panels. If it's in an area prone to multi day fronts moving through then I'd want more array, (or if your going to be there living daily)

Generally a Classic 150 would handle 3 panels with a VMP of about 30 volts. The advantage, as coot pointed out, to the Classic 200, 250 is if your array is a long distance from your charge controller. If that is the case there are advantages to running higher voltage to the charge controller in cost of wiring and/or lower voltage drop.

I, personally, would prefer a vented inverter. I don't like the idea of trapping heat. If your not in a dusty area, you might consider going with a vented inverter.

I would go with less expensive batteries for the first time out. Not sure what is available in your area, Trojans cost 50-60% more than our basic batteries in the same range, and they do tend to last a bit longer, but not 50-60% longer IMO. And since it's your first time with a system there is always the chance a mistake could ruin them.

Photowhit · November 2014

Re: Thoughts on my 48v Off-Grid Setup

Also ambient temperature will change how much your fridge uses, Mine will run 1.2 Kwh in the spring and fall and 2+ in the summer when it's in an un air-conditioned space that runs 75-95 degrees during the day.

googdot · November 2014

Re: Thoughts on my 48v Off-Grid Setup

Cariboocoot wrote: »

On the whole you'd be better off with a 24 Volt system an four of these panels configured as two parallel strings of two in series. That would be 1040 Watts supplying 33 Amps peak current; plenty for 220 Amp hours or even a bit more (like four L16's at 320 Amp hours).

Be careful with array planning as most panels these days are 'GT style' and have a Vmp lower than normal for battery systems. This gets into some conundrums for array planning. For example a Vmp of 30 is not uncommon, but it is too low for a 24 Volt system. Two in series works, but only on an MPPT controller. For 48 Volts two is not enough (Vmp 60) but three in series will work (Vmp 90). Then you start to get into efficiency drop and possibly Voc problems under cold temperatures. Inevitably at some point you have to parallel panels.

Thanks for all the detailed advice. Originally I was looking at doing a 2x2 48v system with these panels (which are indeed 60-cell GT style). The suppliers I'm talking with said that this isn't possible as the voltage is too low. But now I'm possibly looking at 24v which would work great. (edited to remove the voltage mixup I put down)

Good planning. Most any Outback inverter can cover that start-up surge, btw. What you also have to know is how much power the surge plus running loads will be. That can be fairly high. Will you be on Euro standard (230 VAC 50 Hz) power there? Also consider the OB FX2024ET as a possible inverter. No gen support (which is not the most convenient thing to use anyway) but slightly higher power handling.

Yes, it will be 230VAC, 50Hz. Looks like the 2024 is about 35% more in cost than the 1448, but might be worth it to have the extra capacity.

Most refrigerators will pull >1kW on start-up. Running Watts is another matter. I hope that "300W" rating isn't running, but its very low for Watt hours. It's important to keep the two designations separate. Typically a refrigerator will use near 1kW hour per day. For example mine runs at around 120 Watts, cycles 1/3 of the day more or less, and so consumes 960 Watt hours per day.

Sorry, it is 300Wh. Forgot to add the h. This is based on the 132W operating, 0.9kWh/day numbers from the government energy test. On another forum, a user there also has this exact fridge, and he measured it daily over a one week period. His highest number was 322Wh/day. It is really is very energy efficient.

Photowhit · November 2014

Re: Thoughts on my 48v Off-Grid Setup

googdot wrote: »

Sorry, it is 300Wh. Forgot to add the h. This is based on the 132W operating, 0.9kWh/day numbers from the government energy test. On another forum, a user there also has this exact fridge, and he measured it daily over a one week period. His highest number was 322Wh/day. It is really is very energy efficient.

This makes no sense, is this a freezer conversion? If it's from the government numbers the government is saying it will require "...0.9kWh/day..."

googdot · November 2014

Re: Thoughts on my 48v Off-Grid Setup

Photowhit wrote: »

I think 'Coot cover most everything, and I agree, the only caveat would be if this is weekend work while your building the cabin? Then in a sunny area, you might be able to get by with the 3 panels. If it's in an area prone to multi day fronts moving through then I'd want more array, (or if your going to be there living daily)

Generally a Classic 150 would handle 3 panels with a VMP of about 30 volts. The advantage, as coot pointed out, to the Classic 200, 250 is if your array is a long distance from your charge controller. If that is the case there are advantages to running higher voltage to the charge controller in cost of wiring and/or lower voltage drop.

The cabin building won't be weekend work. We hope to do it over a 1-2 month period in peak summer. Happy to take days off when the weather doesn't cooperate.

The panels will only be about 10m away at most so not too far.

I would go with less expensive batteries for the first time out. Not sure what is available in your area, Trojans cost 50-60% more than our basic batteries in the same range, and they do tend to last a bit longer, but not 50-60% longer IMO. And since it's your first time with a system there is always the chance a mistake could ruin them.

Based on my research (considering we're not physically there), Trojans are 10% more than Crowns, and only 15% more than generic brand equivalents.

Photowhit wrote: »

Also ambient temperature will change how much your fridge uses, Mine will run 1.2 Kwh in the spring and fall and 2+ in the summer when it's in an un air-conditioned space that runs 75-95 degrees during the day.

Ambient temperature range is quite comfortable. Not too humid, around 20-25c in summer and 10c in winter (a few times a year it hits 5c).

googdot · November 2014

Re: Thoughts on my 48v Off-Grid Setup

Photowhit wrote: »

This makes no sense, is this a freezer conversion? If it's from the government numbers the government is saying it will require "...0.9kWh/day..."

The government test number of 0.9kWh/day is based on a 24hr, always running 'worst-case' scenario. So if a typical fridge normally has the compressor on say 8 hours/day, that's where the 300Wh figure comes from. This is confirmed by the other fridge owner I mentioned who did actual measurements that were right in that range.

zoneblue · November 2014

Re: Thoughts on my 48v Off-Grid Setup

Nah mate youre slicing and dicing in away that isnt right. The govt number will be based on some "standardised" ambient. Hence 900Wh/day is what you can expect it to use. Thats what we expect the average fridge to use. The only fridges that use less than that are super insulated, usually top loading. Fridges are tough taskmasters in small systems.

What you want is a 0.1C charge rate with no parallel batterys. Generally you need 2-3kWp to justify going up to 48V system voltage.

googdot · November 2014

Re: Thoughts on my 48v Off-Grid Setup

zoneblue wrote: »

Nah mate youre slicing and dicing in away that isnt right. The govt number will be based on some "standardised" ambient. Hence 900Wh/day is what you can expect it to use. Thats what we expect the average fridge to use. The only fridges that use less than that are super insulated, usually top loading. Fridges are tough taskmasters in small systems.

Thanks for the info. I think I'll budget in 900Wh/day to be safe.

The fridge is a Gram model, which are made in Denmark to be highly efficient compared to a conventional fridge. Here are a couple of quotes from the user on the other forum who measured its actual draw:

"The 286 litre gram fridge claimed 389wh/day @25 degrees. As it is about 20 degrees here in or hydronically heated abode, the actual usage has been approx. 300-350wh/day."

"It has zero standby current and the external condenser so extra insulation may well improve this figure a bit more. It has 45mm of the highest rated insulation, not 100mm as originally thought. Our 286 litre fridge and 130litre freezer total power for a 24 hr period is a just over 500 watt hrs, amazing, and the temp never varies more than a degree or so. I find the freezer particularly impressive with that thick insulation."

So the Gram fridge unit and the Elcold freezer unit together came in at 500-600Wh/day. If true, amazing.

What you want is a 0.1C charge rate with no parallel batterys. Generally you need 2-3kWp to justify going up to 48V system voltage.

I'm definitely looking at a 24V system now. I'm going to reconfigure things and post back for some further comments.

zoneblue · November 2014

Re: Thoughts on my 48v Off-Grid Setup

Gram and Elcold are the kinds of well insulated fridge/freezers that have a shot for sure.

Theres some numbers on gram nz site, but they arent that low:
http://www.lowenergyrefrigeration.co.nz/gram-fridges.html

Interestingly they are at 30 deg C. Which is kinda worst case. I thought consumer testing was usually more like 20 deg C.

And on EECA
http://www.energywise.govt.nz/energy-star/fridge-freezer

Somewhat lower and dont say what ambeint.

When i did a comparison of such appliances around 2000, the one trap i found, is that the combined fridge freezer units that had two compressors, had a consequently increased power draw, almost cancelling out the extra insulation.

Also note the timely comment further down in your reference:

http://www.ata.org.au/forums/topic/9079/page/2#position-2

"PVs being so cheap 80cents per watt, get an AC 4 star fridge freezer for $1200 (Eletrolux ETM4200 800WHr per day) and spend extra $400 on PVs"

And going the other way:

http://mtbest.net/chest_fridge.html

100Wh/day.

googdot · November 2014

Re: Thoughts on my 48v Off-Grid Setup

zoneblue wrote: »

Gram and Elcold are the kinds of well insulated fridge/freezers that have a shot for sure.
When i did a comparison of such appliances around 2000, the one trap i found, is that the combined fridge freezer units that had two compressors, had a consequently increased power draw, almost cancelling out the extra insulation.

Thanks for all the extra info. I just had a look at your setup - very nice and pretty similar to what we are going for.

What do you guys use for fridge/freezer? And what Outback VFX do you have?

Also note the timely comment further down in your reference:

http://www.ata.org.au/forums/topic/9...e/2#position-2

"PVs being so cheap 80cents per watt, get an AC 4 star fridge freezer for $1200 (Eletrolux ETM4200 800WHr per day) and spend extra $400 on PVs"

This is a very interesting comment and really makes heaps of sense. Get a decently energy efficient fridge, and put any savings back into your overall system.

googdot · November 2014

Re: Thoughts on my Off-Grid Setup

I've redone my system based on the all the great advice I've received here. Many thanks to @Cariboocoot and @zoneblue

I'm now looking at a 24v setup with the following equipment:

- 4x 260W panels in a 2x2 setup (Vmp 30.7, Imp 8.5, Voc 37.8, Isc 9.01)

- Midnite Classic 150 Controller

- 4x Trojan T-105 6v 225ah

- Outback GFX1424E or FX2024ET or VFX3024E

Once I've used the system for a while and evaluated things, I'll look into adding panels or expanding the battery bank in the future if needed.

Any thoughts or advice for this setup? What about the OB sealed vs vented inverters?

zoneblue · November 2014

Re: Thoughts on my Off-Grid Setup

Its a VFX3024E, and i actually put it on the wall last weekend. Man, that thing is heavy. Just gota wire it up.

Our existing inverter is an 1100W european unit. Weve managed to adapt most of our live to living within its means. However, theres three general areas where the vfx will improve things. a) the vacuum. 18 months with just a broom, is getting us down.( sure theres alternatives, battery powered etc) b) power saw (the 1100W unit runs 900W power tools just fine, its a toroid), c) hot water. (i had planned on doing the hot water diversion using 24V, but theres very little to choose from in the element department.

The main two things to watch there are a) tare, and b) peak amps. Inverters are notorios for their idle draw, and they have been known to consume a quarter of some systems daily production if you are not mindful. VFX at 20W i can live with, the stecca is 10W, and i may yet end up using both. Some people can make the standby feature work, but all it takes is an electric toothbrush or a walk about phone to defeat that.

The other thing is peak amps. A flooded bank shouldnt be asked to give much more than 0.2C for any period. So that means at 24v you want about 200Ah per kW of inverter. That way you avoid voltage sag, and whatnot. Here the VFX will be a little over that, but thats offset by the AGMs lower internal resistance.

VFX v FX. Dunno really. I think FX is for marine, or salt air areas. The VFX is the best screened vent system ive ever come across, with mesh on all the openings, and even a dust filter on the fan intake.

gww1 · November 2014

Re: Thoughts on my 48v Off-Grid Setup

Zoneblue
The outback is heavy, I do find with my opertunity load (2000 watt hot water heater) I get a little osculating of my house lighting until the 2000 watt element gets to 100 percent draw. This usually takes about 30 min. I almost find it a comfort cause I know where I am in my charging with out looking at the mate. It also dims my lights when my well pump kicks on. Other then that, these inverters are monsters and will run amazingly large loads with out a hitch. I have no experiance with anything else but outback has impressed me. Also the mate is never correct and should be used only as a general guide of what is really going on.

Cheers
gww

googdot · November 2014

Re: Thoughts on my Off-Grid Setup

zoneblue wrote: »

The other thing is peak amps. A flooded bank shouldnt be asked to give much more than 0.2C for any period. So that means at 24v you want about 200Ah per kW of inverter. That way you avoid voltage sag, and whatnot. Here the VFX will be a little over that, but thats offset by the AGMs lower internal resistance.

Thanks for all the info. Can you explain this a bit more? I just want to make sure I have everything sized correctly.

VFX v FX. Dunno really. I think FX is for marine, or salt air areas. The VFX is the best screened vent system ive ever come across, with mesh on all the openings, and even a dust filter on the fan intake.

I'd prefer to get the vented unit, as I'd imagine trapping heat cannot be a good thing for the inverter. My only concern is that it's bigger than my needs. My peak draw will be under 1400W, with the occasional surge when the fridge or washing machine kicks in.

Cariboocoot · November 2014

Re: Thoughts on my Off-Grid Setup

The difference between the sealed and vented version is some programming and the vented's ability to dissipate more heat allowing it to manage higher current levels. The self-consumption is identical, so there is no penalty for going with the vented version.

In other words an FX2024E is essentially the same as a VFX3024E, the latter can simply handle another 42 Amps DC/8.5 Amps AC. Both use 20 Watts running, 6 Watts standby. Both are 92% efficient. They have identical surge ratings for short-term loading, with the VFX having slightly higher rating for 30 minutes. Chargers are identical.

To prevent severe Voltage sag on the DC (especially at lower battery Voltage levels) current should be limited to 25% of capacity on FLA's. Thus 200 Amp hours gives you 50 Amps @ 24 Volts or a sustainable 1200 Watt drain. The duration of the load maximum varies with the size of the battery bank, type of batteries, and SOC at the time of loading.

googdot · November 2014

Re: Thoughts on my Off-Grid Setup

Cariboocoot wrote: »

The difference between the sealed and vented version is some programming and the vented's ability to dissipate more heat allowing it to manage higher current levels. The self-consumption is identical, so there is no penalty for going with the vented version.

In other words an FX2024E is essentially the same as a VFX3024E, the latter can simply handle another 42 Amps DC/8.5 Amps AC. Both use 20 Watts running, 6 Watts standby. Both are 92% efficient. They have identical surge ratings for short-term loading, with the VFX having slightly higher rating for 30 minutes. Chargers are identical.

To prevent severe Voltage sag on the DC (especially at lower battery Voltage levels) current should be limited to 25% of capacity on FLA's. Thus 200 Amp hours gives you 50 Amps @ 24 Volts or a sustainable 1200 Watt drain. The duration of the load maximum varies with the size of the battery bank, type of batteries, and SOC at the time of loading.

That makes heaps of sense - thanks for all your help and advice.

So what do you think - Am I on the right track now with the 24V setup I posted? (with one of the two OB inverters plus the T-105 battery bank)

I think you mentioned I could go up a bit in battery size if my panels are supplying 33A peak with the 24v system - do you think I should consider a larger battery bank for more days of backup, or will that stress the system too much?

Cariboocoot · November 2014

Re: Thoughts on my Off-Grid Setup

In theory 33 Amps of peak current could handle 320 Amp hours of capacity.
The question is: do you need the greater capacity? Are you likely to use an average amount of 2kW hours per day? That would be around 25% of 320 Amp hours, all from the battery.

Which brings up the question of when the power is used: if most is at night then you want larger battery capacity. If most is during the day you can have less battery and more panel. It's the trickiest bit of off-gird: balancing the load usage time with the power production time.

The basic calculations are done on a basis of all the power being put in to and taken out of the batteries. This is why the end-to-end efficiency is so low. But as the batteries charge there is potential production from the PV which goes unrealized unless loads are on at the same time. This is when we get into the issue of "opportunity loads" which are turned on when the batteries are up and the PV is still producing. It makes the system more efficient, but isn't easy to achieve.

For most systems at least some of the load will be daytime. Refrigerators run 24 hours a day, cycling on and off. But the weight of loads may be at night (lights, TV) and so you need the battery storage. Things like water pumps may come on at any time, but if you can shift them so they only come on while the batteries are Absorbing or Floating then your efficiency goes up. Storing up water can be much more economical than storing up electrical power.

As it is 33 Amps would be about 15% charge rate on T105's, about the top you would want to see. If I were you I'd start there and see how well it goes. If the capacity turns out to be too low you can increase the battery bank once the first set are worn out (you would be discharging them deeper if the load demands are off-charge time so their life would be shorter).

You might also want to consider something similar to the Trojans but less Voltage demanding such as Crown GC2's @ 220 Amp hours or East Penn/Deka/US Battery PS2200's @ 232 Amp hours or even warehouse GC2's.

googdot · November 2014

Re: Thoughts on my Off-Grid Setup

Cariboocoot wrote: »

You might also want to consider something similar to the Trojans but less Voltage demanding such as Crown GC2's @ 220 Amp hours or East Penn/Deka/US Battery PS2200's @ 232 Amp hours or even warehouse GC2's.

Thanks again for all your help. Can I ask why are these less Voltage demanding than the Trojan's?

Cariboocoot · November 2014

Re: Thoughts on my Off-Grid Setup

googdot wrote: »

Thanks again for all your help. Can I ask why are these less Voltage demanding than the Trojan's?

Trojan's recommended Absorb Voltage is higher than the others. It may not seem like much, but it's a difference of 29.6 for Trojan or 28.8 for the others. Getting to a higher Voltage takes more time and some have had trouble as a result.

googdot · November 2014

Re: Thoughts on my Off-Grid Setup

Cariboocoot wrote: »

Trojan's recommended Absorb Voltage is higher than the others. It may not seem like much, but it's a difference of 29.6 for Trojan or 28.8 for the others. Getting to a higher Voltage takes more time and some have had trouble as a result.

That's very good to know - thanks. So do you use the RE version or just the standard deep-cycle?

Cariboocoot · November 2014

Re: Thoughts on my Off-Grid Setup

googdot wrote: »

That's very good to know - thanks. So do you use the RE version or just the standard deep-cycle?

Personally I just use the standard deep cycle.
There are a few forum members who are trying the (fairly new) RE battery versions; so far, so good. Too early to say if there are any substantial differences though.

googdot · November 2014

Re: Thoughts on my Off-Grid Setup

Cariboocoot wrote: »

Personally I just use the standard deep cycle.
There are a few forum members who are trying the (fairly new) RE battery versions; so far, so good. Too early to say if there are any substantial differences though.

I think I'll stick to the standard deep cycle as they are easy to get/replace. For my first go I don't want to invest too much until I get the hang of things. I had a look at the specs of the 2200 and they look good.

Midnite recommends the following charge profile for the US2200 (start in the middle and test from there):

Flooded
Volts per cell- Equalize = 2.5v to 2.6v, Absorb = 2.35v to 2.45v, Float = 2.17v
For 12v system- Equalize = 15v to 15.6v, Absorb = 14.1v to 14.7v, Float = 13.02v
For 24v system- Equalize = 30v to 31.2v, Absorb = 28.2v to 29.4v, Float = 26.04v
For 48v system- Equalize = 60v to 62.4v, Absorb = 56.4v to 58.8v, Float = 52.08v

Is that comparable to what you've got yours set at?

Cariboocoot · November 2014

Re: Thoughts on my Off-Grid Setup

Similar.
My 24 Volt system Absorb is set to 28.8 and Float to 27.
In five years I've never had to equalize them, but if I did it would probably be at 30.8 Volts.

Do keep in mind that Voltage readings differ depending on the equipment used to measure it, so always check to see you're getting proper results with a hydrometer. Another reason to start out with inexpensive FLA's.

jcheil · November 2014

Re: Thoughts on my Off-Grid Setup

Cariboocoot wrote: »

There are a few forum members who are trying the (fairly new) RE battery versions; so far, so good. Too early to say if there are any substantial differences though.

My new Trojan L16RE-B's are doing great so far and they have been in for about 8-9 weeks now.
The L16's are way more than you need, but the RE line does have a longer warranty than the standard ones.
But as others have said, your first set is your practice set - you will likely unintentionally murder it (as most do).

googdot · November 2014

Re: Thoughts on my Off-Grid Setup

What do you guys think on my battery options?

From what I can find out (given we're not physically there yet to price things out) 4x 6V (24V total) prices are Crown CR-225 $750, US battery US2200-XC2 $835, Crown CR-350 $1250 (all USD).

I'm tempted to go for the larger Crown 350 to ensure I have ample backup and don't have a big DOD, so hopefully they will last longer. Or for my first bank should I go for the smaller and cheaper set and see how I go?

Cariboocoot · November 2014

Re: Thoughts on my Off-Grid Setup

How much capacity do you actually need? Too low a DOD is a waste of battery dollar, as they will 'age' about the same at 25% DOD or less.

The CR-350 will require a controller capable of handling more than 35 Amps and about 1090 Watts PV.

The US2200 can be used with a MidNite Kid and about 718 Watts PV (I have the East Penn equivalent of these myself).

The CR-225 can be used with a Kid and about 686 Watts PV.

Capacity difference between the biggest and smallest: about 1.5kW hours.

If you're still going with the four 260 Watt panels and Classic 150 that would handle any of these batteries, but the CR-350's would be a tad low in peak charge rate.

googdot · November 2014

Re: Thoughts on my Off-Grid Setup

Cariboocoot wrote: »

How much capacity do you actually need? Too low a DOD is a waste of battery dollar, as they will 'age' about the same at 25% DOD or less.

The CR-350 will require a controller capable of handling more than 35 Amps and about 1090 Watts PV.

The US2200 can be used with a MidNite Kid and about 718 Watts PV (I have the East Penn equivalent of these myself).

The CR-225 can be used with a Kid and about 686 Watts PV.

Capacity difference between the biggest and smallest: about 1.5kW hours.

If you're still going with the four 260 Watt panels and Classic 150 that would handle any of these batteries, but the CR-350's would be a tad low in peak charge rate.

I'm still going with the Classic 150 as it allows me room for adding panels in the future if need be.

If my calculations are correct, at 24V the 50% DOD capacities would be: CR-225 2700Wh, US2200 2784Wh, and the CR-350 4200Wh. So as you said, the CR-350 would have 1.5kWh greater capacity than the CR-225.

If my usage is 2kWh/day on average, then I would looking at be these numbers: CR-225 37% DOD, US2200 36% DOD, CR-350 24% DOD.

With the four 260 Watt panels at 77% efficiency, the peak charge rate would be about 14-15% on the CR-225 and US2200, and about 9.5% on the CR-350.

I understand what you mean about wasting battery dollars, but what happens if the peak charge rate is greater than 15% on the smaller batteries? Couldn't this happen on a nice bright day in the middle of summer when efficiency could be more than 77%? And is 9.5% on the CR-350 really too low? And what, on the odd occasion, I go over 50% DOD?

I guess the ultimate question here is do you want an average DOD of around 25%? Or is closer to a 50% average the DOD price 'sweetspot'? (as noted on the battery FAQ's)

Another thing to note: When I use the PVWatts Calculator for my area and the four 260W panels, during the lowest month the solar radiation is still 2.69kWh/m²/day or 69kWh AC, which is really good considering my usage is well below 50% of the potential harvest even in the winter months. So maybe I don't need to worry too much autonomy?

Thoughts on my 48v Off-Grid Setup

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