Off-grid system review

[mschulz]

Thanks, appreciate the input and clarifications. Will provide an update when the project is done.

I am glad to hear that you have not purchased anything yet. I really think you should read some of the stickies here http://www.solarpaneltalk.com/forumd...ectric-systems as it will help you understand what everyone is talking about. It really helped me a lot and saved me a lot of money. Getting your designed wrong the first time is expensive as most of the things you are going to buy will not play nice in and upgrade and you will have to buy all new stuff. 35KW is a "**** Ton" of power to try and take off the grid. Amy@altE last post about trying to take some of your loads to gas/propane, etc. is the very first step and think of this way. With this system, running a generator, you are going to need to have diesel, propane or gasoline delivered to your home. Why not put in a big propane tank, use it to run a generator, stove, clothes dryer, and refrigerator with it. Put a solar hot water heater on the roof. All these things will help get your usage down to a manageable amount to use solar.

Secondly, I recommend talking to your neighbors that have been doing this for a while. I am sure at least 50% of them have made all the mistakes you are about to and they might be able save you from them.

[Amy@altE]

Again, much of our energy use will be during the day, in one of the sunniest/dryest parts of Hawaii (350 days of sun). Probably 20-25Kwh during the day, if I'd have to throw a figure out there (including the 3hp water pump, appliances, etc.). At night, we won't use more than 5-10Kwh (led lights, tv, possibly one load of dishes).

Generators are not my specialty, so I can't help you there, but I can show you the math for the solar and batteries, which does in fact line up with the numbers SunKing gave you.

If you are thinking 35kwh a day, I'm guessing 5 sun hours for worst case in Dec, then for the array, 35,000Wh / 5 sun hours / .67 system inefficiencies = 10,447W of solar / 280W SolarWorlds = 38 panels.

35,000Wh / .92 inverter inefficiencies /.5 (50% DoD) x 2 days autonomy x 1.11 (temp compensation for 60F) = 169kWh / 48V = 3519ah 48V battery bank. I know you said it's always sunny, so you may not think you need the 2 days autonomy, but what that also does for you is most days you'll only use 25% of your battery, which will make them much happier than 50% every day.

It's worth it to think of other ways to fuel your heat needs. You can drop this down dramatically, and make it more practical and affordable.

[Amy@altE]

Is propane an option?

Would it be possible to use propane instead of electric for the stove, dryer, and oven? Even better, a clothes line instead of a dryer? As I'm sure you know, anything that makes heat or cold use the most amount of power. The fact that you are using most of the power during the day doesn't help with an off grid system, you still have to put all of the power into the battery bank before you can use it, so you'll be beating up your batteries during the day.

I have tons of clients in the islands who have successfully gone off-grid, but you have to make concessions, you can't have it all without spending a large fortune.

[Cult of Dionysus]

That is because I made a mistake. To supply you with 35 Kwh/day at 48 volts requires a 3600 AH battery or 175 Kwh capacity. Lead Acid batteries weigh in at 60 to 65-Lbs/Kwh and a good 5 to 7 year battery cost $ 200 to $240 per Kwh. So do the math for quick calculations 175 x 60 pounds weighs 10,500 pounds and cost $200 x 175 = $35000

No go find the actual product and the real numbers are 48 units of Rolls 2 OS 33 PS, 2 volt 1800 AH for a total of 3600 AH at 48 volts. Mainland cost are roughly $770 per unit x 48 = $36,960 and weigh 285 pounds wet x 48 = 13,680 pound. Sorry I was wrong, I was working on another project and transposed numbers. To generate 35 Kwh per day in your locations still requires 11,000 watt panel system and a 15 to 20 Kw generator.

Point here is you have no idea what you need. What you stated will not work. Once you have learned what it really takes, you may change course. I could care less what you do because I am not making or loosing a dime on you. What i do know is if you go forward is going to make someone a lot of money. If it were me designing would be cost plus 15%, or about $10 to $15K shuffling papers and numbers around. You contractors and suppliers will make quite a bit more.

Thanks, appreciate the input and clarifications. Will provide an update when the project is done.

[Sunking]

The site is nearly ten miles from the nearest utilities.

Not sure I believe you on the 11k $35k battery... Twenty-four Rolls 2YS31PS 2400Ah weigh about half that and cost 2/3rds, and they are twice as powerful as the "minimum" you mentioned earlier, but what do I know I'm just a pigeon.

That is because I made a mistake. To supply you with 35 Kwh/day at 48 volts requires a 3600 AH battery or 175 Kwh capacity. Lead Acid batteries weigh in at 60 to 65-Lbs/Kwh and a good 5 to 7 year battery cost $ 200 to $240 per Kwh. So do the math for quick calculations 175 x 60 pounds weighs 10,500 pounds and cost $200 x 175 = $35000

No go find the actual product and the real numbers are 48 units of Rolls 2 OS 33 PS, 2 volt 1800 AH for a total of 3600 AH at 48 volts. Mainland cost are roughly $770 per unit x 48 = $36,960 and weigh 285 pounds wet x 48 = 13,680 pound. Sorry I was wrong, I was working on another project and transposed numbers. To generate 35 Kwh per day in your locations still requires 11,000 watt panel system and a 15 to 20 Kw generator.

Point here is you have no idea what you need. What you stated will not work. Once you have learned what it really takes, you may change course. I could care less what you do because I am not making or loosing a dime on you. What i do know is if you go forward is going to make someone a lot of money. If it were me designing would be cost plus 15%, or about $10 to $15K shuffling papers and numbers around. You contractors and suppliers will make quite a bit more.

[paulcheung]

The site is nearly ten miles from the nearest utilities.

Not sure I believe you on the 11k $35k battery... Twenty-four Rolls 2YS31PS 2400Ah weigh about half that and cost 2/3rds, and they are twice as powerful as the "minimum" you mentioned earlier, but what do I know I'm just a pigeon.

If you going to use the 2400AH Rolls batteries, then you need about 48 of those panels and three 80AMP Classic 150 charge controller and 15KVA Generator to charge those batteries properly.

[Cult of Dionysus]

You need to start over and completely rethink things. If you rely on contractors, especially those selling you something is a really bad bad idea. I am a EE who works for my clients interest, not a vendor or industry. I can tell you right now going off-grid is a HORRIBLE ideal especially for you in an All Electric Home.

I know Hawaii electric rates are high. So is everything in Hawaii. Anything you take off grid or on battery is going to cost you 5 to 7 times more than buying it from the POCO even in Hawaii. Why do you want to do that? At this point you have no idea what you need. I suspect a 2000/ft2 home is going to require about 30 to 35 Kwh per day. In your location for off grid will require 10,000 watt panel (5 Sun Hours off season), three very expensive controllers, and a 11,000 pound $35,000 battery you get to replace every 5 to 7 years at even higher cost and that is mainland prices, not Hawaii. If I were a Solar Contractor would foam at the mouth to sell you that every 5 years as it would make me very rich man lining up pigeons like that. I advise you to reconsider. I won't charge you a dime.

The site is nearly ten miles from the nearest utilities.

Not sure I believe you on the 11k $35k battery... Twenty-four Rolls 2YS31PS 2400Ah weigh about half that and cost 2/3rds, and they are twice as powerful as the "minimum" you mentioned earlier, but what do I know I'm just a pigeon.

[Sunking]

One final point that I would appreciate a little input on... Assuming I get the batteries/controllers Sunking mentioned and either the Outback GS8048 or a pair of Schneiders, what would be a smart genet solution? Would a 10kw Generac make sense, one or two Hondas EUs, or something else?

You need to start over and completely rethink things. If you rely on contractors, especially those selling you something is a really bad bad idea. I am a EE who works for my clients interest, not a vendor or industry. I can tell you right now going off-grid is a HORRIBLE ideal especially for you in an All Electric Home.

I know Hawaii electric rates are high. So is everything in Hawaii. Anything you take off grid or on battery is going to cost you 5 to 7 times more than buying it from the POCO even in Hawaii. Why do you want to do that? At this point you have no idea what you need. I suspect a 2000/ft2 home is going to require about 30 to 35 Kwh per day. In your location for off grid will require 10,000 watt panel (5 Sun Hours off season), three very expensive controllers, and a 11,000 pound $35,000 battery you get to replace every 5 to 7 years at even higher cost and that is mainland prices, not Hawaii. If I were a Solar Contractor would foam at the mouth to sell you that every 5 years as it would make me very rich man lining up pigeons like that. I advise you to reconsider. I won't charge you a dime.

[Cult of Dionysus]

OP: I sure hope you have not purchased anything yet or you can return some of that.

Nothing at all, luckily. My general contractor has fwd me the specs that his solar contractor has given (described in my initial post). Clearly he's put together something on paper which doesnt work. I'm trying to figure out what is a properly balanced system.

Based upon the input above, it seems that I need to upgrade the batteries, make sure the charge controllers are appropriate, and figure out the best inverter solution. Sunking, thanks for laying out some suggestions. That's very helpful, and my apologies for my ignorance.

One final point that I would appreciate a little input on... Assuming I get the batteries/controllers Sunking mentioned and either the Outback GS8048 or a pair of Schneiders, what would be a smart genet solution? Would a 10kw Generac make sense, one or two Hondas EUs, or something else?

Again, much of our energy use will be during the day, in one of the sunniest/dryest parts of Hawaii (350 days of sun). Probably 20-25Kwh during the day, if I'd have to throw a figure out there (including the 3hp water pump, appliances, etc.). At night, we won't use more than 5-10Kwh (led lights, tv, possibly one load of dishes).

[Amy@altE]

I'm double checking with Outback if the Radian GS8048A and Mate3 only support 2-wire gen start, like their FX series. If it hasn't changed to support 3-wire, you can use an Akinson GSCM to convert from 2-wire to 3-wire gen start. http://www.atkinsonelectronics.com/m.../gscm-mini.pdf . I'll confirm when I hear back from them.

Schneider XW+ with AGS and Magnum MS-PAE4448 with ME-AGS-N both support 2- or 3-wire generators.

Just got confirmation from Outback, you would need the Akinson GSCM to do 3-wire support. So if there are features in the Radian that you like, don't discount it because of the gen start, there's a solution for it.

[mschulz]

OP: I sure hope you have not purchased anything yet or you can return some of that.

[Amy@altE]

I'm double checking with Outback if the Radian GS8048A and Mate3 only support 2-wire gen start, like their FX series. If it hasn't changed to support 3-wire, you can use an Akinson GSCM to convert from 2-wire to 3-wire gen start. http://www.atkinsonelectronics.com/m.../gscm-mini.pdf . I'll confirm when I hear back from them.

Schneider XW+ with AGS and Magnum MS-PAE4448 with ME-AGS-N both support 2- or 3-wire generators.

[Sunking]

Thanks for the input, WWW. Forgive my ignorance, but what is the significance of having 1 string versus 2 or 3 strings?

The difference is replacing the battery every two to three years instead of every 4 to 5 years assuming it was sized correctly to the load which you have not done.

We can tell from what little information you have provided your whole system is completely out of acceptable tolerances. The most important peice of information missing is you do not mention how many watt hours you intend to use in a day. As it stands right now your batteries are sized to only support 9.2 Kwh per day, and your panels are sized to support 26 Kwh per day. Do you see any problem with that statement? It means you get to replace them in less than a year. You are going to fry your batteries with 160 amps of charge current. That is I assume you know a 8400 watt panel system requires two very expensive 80 amp MPPT charge controllers. The minimum size battery to support those panels are 1280 Amp Hours or Rolls S-1725 a 2 volt 1300 AH battery so you would need 24 of them.

Having said all that is a moot point because you failed to do the very first requires step of determining your daily watt hour usage. Everything is determined by daily Watt Hour use and Location. At this point all anyone knows is location and a huge all electric home.

[Cult of Dionysus]

Thanks for the input, WWW. Forgive my ignorance, but what is the significance of having 1 string versus 2 or 3 strings?

[Wy_White_Wolf]

I'm assuming the battery bank is wired as 2 strings of 48V. It would be better if you bought large enough batteries for a single string.

It also seems a little undersized in relation to the rest of the system. They would be @950Ah and the array can put out ~ 160A at 48V. That would give you a charge rate of C/5.9. That's on the high side and may void the warrantee. Charge rate should be between C/8 and C/12 with C/10 being about ideal.

You also have the same problem with the inverter. It's capable discharge rate is higher than what the batteries are designed to support. It'll be worse with the 2 inverter setup.

Without doing a load analysis i'd say you need to increase the battery bank size by about 50% to balance with the rest of the system and look at batteries that can be wired in a single string.

WWW