Off-grid system - 960W of 12v PV goodness - now what???

[Sunking]

Just an aside - when one looks closely at the cost to produce small scale solar power, it's just nuts compared to mains. Which doesn't make solar expensive, but rather mains is unsustainably cheap and always has been.

Not quite sure what you mean here. Generating electricity is very cheap but varies depending on the fuel source, and there is a lot of it. Fuel cost for:

Coal $30/Mwh
Natural gas $25/Mwh
Uranium $75/Mwh
Thorium $35/Kwh

In Australia you have the worlds richest deposits of uranium and thorium but refuse to use it, and you have around 100 million years of it just laying around. What is mined and processed is shipped out of the country to Japan, China, France, and the USA.

The problem with subsidies is it artificially raises the price of electricity and taxes. Not a problem for the people who can afford to install the RE systems, but raises the cost on those who cannot afford it and get stuck with the bill. Free markets will decide what fuel source to use no matter what the governments try to do.

[Naptown]

haha I just looked online at the FiT (feed-in-tarriff) for my area and it is presently 0c/kWh! Other energy providers are offering as much as 6c/kWh. Industry suggests that 8 to 10c/kWh is the approx. cost to produce a kW and that is likely to become the FiT here in Oz.

FYI cost per kWh is 20.6c for the 1st 730kWh and well as 48c per day service availability charge.

Those numbers above are going to change all over the place in the next few years, but certainly my original guess of getting 20c/kWh Fit is way out, and that $1300 pa has turned into a fluffy cloud of smoke. At 6c FiT at 3500kW/pa comes to a whopping $210 for about $5k investment taking 23 years to pay off at that rate.

Suddenly no solar option is financially viable

So you don't get the feed in tariff
Say you install 3.5 KW grid tie
Here in Maryland that would produce about 4200 KWH per year At .20 per KWH (You mentioned the 730 KWH base is the rate structured tiered so that if you go over the 730 you are charged at a higher rate) That would be a savings of $840 per year. Or a little over a 6 year pay off.

[Outbackshackhack]

Well it's morning again now and my mind is changed again - I'm off mains now and back to looking at an off-grid system.

Before you all reach for your flame throwers, here's the thing - when I think about connecting the mains and going away from solar, I get sad . When I chuck that idea away and go back to solar and batteries, I get very excited . It doesn't depend on money. One way makes me feel good, the other not so good.

Now the cost to me to get the mains put on will be around $5000. Then there's a daily charge of 48c to have the power available. Plus 20c/kWh.

I'm back to installing a new off-grid solar system for around $10k. This would be 24v 1000Ah batteries ($5k) and 2000W in panels ($3k), 80A charger (or 2x 40's) ($800), new inverter ($1k). Plus accessories and panel support framing. Maybe closer to $12k by the time all is said and done.

I can still run aircon for a couple of hours a day with no trouble. My office is no bigger than 9'x9'x8' from 2" coolroom panels, so the aircon doesn't need to work on full all the time. Failing that, I am excited to dabble in evaporative cooling (in Coota, summer humidity can get below 20%).

The final straw in this whole shebang for me is that going mains stifles my creativity, there's pretty much nothing else to do but plug in anything and everything I feel like. Going off-grid solar demands that I be innovative and thoughtful and come up with creative ways to use less power. That makes me smile!

Also, $11 or $12k is about the amount I would spend in 10 years on power, including the start-up costs. So it's not that far off (I'd happily pay at least double for off-grid power).

[Naptown]

On grid off grid that is a personal choice. Sometimes it isn't about the money but the quest.
As long as you are going in with eyes wide open that's fine, it's your money to do with what you please.
So whatch gotta run and what would be nice?

[Outbackshackhack]

On grid off grid that is a personal choice. Sometimes it isn't about the money but the quest.
As long as you are going in with eyes wide open that's fine, it's your money to do with what you please.
So whatch gotta run and what would be nice?

This whole setup is intended to only run my office, as home power is adequate for the moment. In the office will be a PC (300W - a guess) 2x LED screens (25W each), peripherals like printer and speakers (10-100W) and lighting (40W). Perhaps a fan on warmer days (15-100W), and of course there's the aircon (plated as using 1200W, 1600W max). My intention is to put in 5 or 6 work hours per week day, although it could be less on many days, 2 hrs in the am, 2 in the arvo, and 2 at night. The hours in the am likely wouldn't need the aircon, but the afternoon period might - if it were sunny and 40 degrees C (say 100-ish F) I'd allow 50% on for the aircon for 2 hours (1200W), and in the night time I'd hazard that the aircon would just idle at around 25% for 2 hours (600W).

So if I total things up: 300Wx6 + 25Wx2x6 + 10Wx6 + 40Wx6 = 2400W plus aircon as required. On a hot day, we use aircon for a total of 1200W + 600W plus the inbuilt fan for 4 hours at say 100W = 2200W.

Total (Max) power usage = 4600W per day. x 2 = 9200W per day (50% efficiency) x 5 days = 36kW @ 24v = 1500Ah.

But this is not really necessary, as not every day is so hot and if it is that hot then the sun would be shining and the batteries recharging, and on several cloudy days I might not need that much aircon power anyway, so this number of 36kW is dubious to me. Only real-world usage will tell. My gut feel is that it will be fine and I have room to make more efficient cooling technology to help.

I would consider doubling the batteries up to make it 48v, but I don't have the panel space just yet, unless I ground mount them, which is on the cards.

I'm reminded of my present setup for the home, which is 480W panels and tired 525Ah 12v battery and that provides me with full-time bar fridge, 2x LCD TVs, fans, lights, charging of cordless tools, phone, camera, laptop, toothbrush, plus electric blankets in winter. Rarely is there a power issue and usually because I cocked something up! It's pretty impressive what CAN be run from solar if properly thought about.

[Outbackshackhack]

Not quite sure what you mean here. Generating electricity is very cheap but varies depending on the fuel source, and there is a lot of it. Fuel cost for:

Coal $30/Mwh
Natural gas $25/Mwh
Uranium $75/Mwh
Thorium $35/Kwh

In Australia you have the worlds richest deposits of uranium and thorium but refuse to use it, and you have around 100 million years of it just laying around. What is mined and processed is shipped out of the country to Japan, China, France, and the USA.

The problem with subsidies is it artificially raises the price of electricity and taxes. Not a problem for the people who can afford to install the RE systems, but raises the cost on those who cannot afford it and get stuck with the bill. Free markets will decide what fuel source to use no matter what the governments try to do.

I guess my point was that the estimated price of producing power from fossil fuels does not often include the cost of developing renewable energy, which IS a part of using fossil fuels, and does not include the costs to the environment nor the cost to humans in dollars from having to deal with the environmental messes caused by fossil fuels. We as a race have not yet had to face the true cost of using fossil fuels, but we will and it will be a lot higher than the estimated $30/MWh. Trillions will be spent cleaning up and we are already in the throws of this spending (a certain carbon tax comes to mind). Electricity prices have doubled in recent years and this trend will continue, all due to the costs of fossil fuels and the big clean-up that until now have not been passed on to the consumers.

I suppose that's why I'm so keen to go renewable, even though the tech is poor at the moment, encouraging its use will improve the tech and I want that. In 10 years when some components need replacing, I anticipate that there will be much more efficient and cheaper alternatives available.

[Outbackshackhack]

Advice on choosing batteries

I'm looking at 2 different types of battery online, both should provide similar capacity I think, but you guys pls speak up on that point. Here are the 2 options:-

6v, 1000Ah Flooded @ $1500 per piece (x4 = $6k)

6v, 395Ah heavy duty deep cycle @ $517 per piece (x8 = $4.2k)

The 1000Ah is at C100, and at C20 this happens to be 792Ah.

The 395Ah is at C20, so this seems to be equal to half of the 1000Ah battery, but 1/3 the price.

So is a 24v system of the 1000Ah better or worse in reliability, capacity, rechargeability than a 24v system using 8 of the 395Ah batteries?

The bonus to me for the smaller batteries is much easier handling and cheaper cost, although the smaller ones need a lot more cables to be made.

The other comment I have is about weight, the smaller ones total 440kg whereas the bigger ones total 652kg and as far as I know, capacity is all about weight in this case. Are the C20 rates actually the same for the 2 systems even though the weights are so different? I need 12 of the smaller ones to equal the weight of 4 of the bigger ones, then that would give a C20 of 1185Ah.

Also, is C20 worth thinking about as the system is designed around the C100 figure (4-5 days), but I don't know the C100 for the smaller batteries. It all depends on plate thickness I think.

Discuss please?

[Sunking]

OK I will try to sort this out for you and fill you in a little on batteries.

I have no comment on the first battery because I do not see a manufacture or model number on it. With that said would be enough for me to reject it.

As for the second battery Crown makes really good batteries. However this one is a low end product line. The 1-year warranty would scare me off. Even a cheap Walmart solar battery comes with a 2 year warranty. Really good batteries come with 7 and 10 year warranty.

OK battery manufactures play games with AH capacity as you have now noticed. You need to know what is going on. Battery AH capacity is expressed as Amp Hours at a given discharge rate. As you noted one specified it at 100 hour discharge rate, while another specified it at a 20 hour discharge rate. They are not giving Bogus number as it might appear, but it can lead you astray if you do not understand Peukert Law.

Peukert Law states in layman terms expresses the capacity of a lead acid battery in terms of the rate at which it is discharged. As the rate increases, the battery's available capacity decreases. Click on this link to a popular battery made by Rolls model 4CS17P. Scroll down the bottom half spec sheet and take note of the AH capacity of the battery at various discharge rates.

100 Hour Rate = 770 AH
20 Hour Rate = 546 AH
1 Hour Rate = 186 AH

That is Peukert Law in action the same battery can be specified as high as 770 AH and as low as 186 AH for the exact same battery.

You are correct about battery weight, heavier the better, and I have another good example to show you. Have you ever heard of Trojan Battery? For years the T-105 was king in the solar world, but not today. The reason it was popular was because 20 years ago no one made true deep cycle batteries for RE applications. So people used golf cart batteries. Golf cart batteries are hybrid aka Marine which means it has thicker heavier plates than a cranking battery, but not as thick and heavy as a true deep cycle battery. So in the last 2 years Trojan released the RE series. So now take note and click on the T-105 and T-105RE battery. Look at the weights. They are both in the same BCI group GC2 casing, but one has more lead in it.

[Outbackshackhack]

Thanks for the explanation, Sunking.

It is difficult to compare apples with apples.

What about these? Surrette Batteries 6-Cs-25Ps 6V, 820Ah (20Hr) Flood L-Acid

4 of those should be at least as good as the no-name brand - do you agree?

[Sunking]

Thanks for the explanation, Sunking.

It is difficult to compare apples with apples.

What about these? Surrette Batteries 6-Cs-25Ps 6V, 820Ah (20Hr) Flood L-Acid

4 of those should be at least as good as the no-name brand - do you agree?

Surrette is second to none and makes excellent batteries. The 5000 series carries a 10 year warranty.

[Mike90250]

And here's another way to look at it.

Most people ruin their first battery bank.

Would you like that to be a cheap bank, or an expensive bank ?

And in 2 years when you go to replace it, there may even be a better battery out there, some advance is possible, but not really likely. But, battery bank #2, would be the one I spend money on, and get something cheap & serviceable to learn on.

[Outbackshackhack]

And here's another way to look at it.

Most people ruin their first battery bank.

Would you like that to be a cheap bank, or an expensive bank ?

And in 2 years when you go to replace it, there may even be a better battery out there, some advance is possible, but not really likely. But, battery bank #2, would be the one I spend money on, and get something cheap & serviceable to learn on.

You know I damn near killed my present (1st) set of batteries, but they are hanging in there! And they were used and tired when I bought them for $600 more than 2 years ago. They still provide me with enough power to run my home for 2-3 days.

I allowed my batteries to sit for 6 months without charging, I allowed them to lose too much electrolyte and run flat, and I have no idea what the sg is. Also the charger is not fully up to the job either. They still work!

That said, I would like my next set of batteries to be well maintained for maximum performance and lifespan.

So I'm still battery hunting and making an effort to obtain the best bang for buck I can. It seems I will be up for around $6k, possibly a bit less depending on what some of the online sellers say when they get back to me.

[Outbackshackhack]

Exide Batteries

Now also looking at Australian made Exide Energystore batteries (it's a pdf). Specifically the Energystore 6RP1080
6V 1080Ah battery. 4 of them. I have a price of just under 6k just waiting on delivery rate.

I think I am keen on these, but I might be swayed toward the Surrette 6-CS-25PS as they have slightly more capacity and are slightly cheaper and have the same weight. More importantly the Surrettes have a better warranty (3+10) than the locally made Exides (1+4), and I will be letting them know if they lose out, that it was due to the pithy warranty.

Sorry the content of the post is a bit jumbled, but I'm researching still whilst writing the post and finding specs and stuff so things evolve ya know?

Geez I'd be mad not to go with the Surrettes wouldn't I? Except if the chick selling the Exides has nice tits. Then it could still go either way.

[Sunking]

Surrette are superior to Exide. If the Surrette is the same or less price for a given capacity makes it a No Brainer.

[maple flats]

You know I damn near killed my present (1st) set of batteries, but they are hanging in there! And they were used and tired when I bought them for $600 more than 2 years ago. They still provide me with enough power to run my home for 2-3 days.

I allowed my batteries to sit for 6 months without charging, I allowed them to lose too much electrolyte and run flat, and I have no idea what the sg is. Also the charger is not fully up to the job either. They still work!

That said, I would like my next set of batteries to be well maintained for maximum performance and lifespan.

So I'm still battery hunting and making an effort to obtain the best bang for buck I can. It seems I will be up for around $6k, possibly a bit less depending on what some of the online sellers say when they get back to me.

If you are going to continue treating your batteries that way, you should just get a generator to run when you need power. Regardless which battery you chose, it will not give to it's ability if treated like that. Batteries need TLC to get the most from them. The battery bank is by far the most expensive component of an off grid system even if treated with TLC, but it gets far more costly with poor maintenance. With poor treatment you might be lucky to get half the expected life published. Might be a flooded lead acid is not for you, some other types cost more but might take poor treatment better.