westbranch wrote: »
here is a cheap Li battery http://cgi.ebay.com/ebaymotors/130826602917
user 'Solar-Dave' has several threads on electric cars, as well as others, there is a house runoff a Prius mentioned too.
re NiCd's, what brand do you have?
No, have not needed to change the electrolyte in the ones I use. They were part of a 75 cell lot I obtained and the ones I use were from the ones that passed muster. a week long charge regimen is needed...
email me for more info re rehabilitating them
BB. wrote: »
One way to size the battery bank is to use 1-3 days of storage and 50% maximum discharge, along with 80% inverter efficiency to give you a "balanced" system design. So, using 2 days of storage:
5,000 WH * 1/48 volt battery bank * 1/0.85 inverter efficiency * 2 days of no-sun * 1/0.50 max discharge = 490 AH battery bank.
With a 490 AH @ 48 volt battery bank (flooded cell) and 5kWH per day of AC usage (charge during the day, use power at night), you can:
490 AH * 1/8 hour discharge rate * 48 volt battery * 0.85 inverter efficiency = 2,499 Watt recommended max continuous load
490 AH * 1/2.5 hour discharge rate * 48 volt battery * 0.85 inverter efficiency = 7,997 Watt recommended max surge/starting load
Recommended DC charging current range is 5%-13% and never exceed 25% (usually AC charger). For 13% to 25% rate of charge, you should have a remote battery bank temperature sensor to reduce the chances of thermal run-away (if deeply discharging and fast charging backup).
The DC charging range would be (again, everything I am using here assumes flooded cell battery bank--But will work fine with AGM too--AGM can source/sink more current than flooded cell and are slightly more efficient--And the numbers are not that exact--just carrying out numbers so you can reproduce my math and reduce rounding errors):
490 AH battery bank * 0.05 rate of charge = 24.5 amps minimum
490 AH battery bank * 0.10 rate of charge = 49 amps healthy nominal
490 AH battery bank * 0.13 rate of charge = 63.7 amps max recommended no thermal management (and max cost effective solar recommended)
490 AH battery bank * 0.25 rate of charge = 122.5 amps never exceed using thermal management for deep cycling recharge
The typical AC genset to run the above AC chargers (assuming worst case of 80% efficiency and 67% power factor (again, there are lots of AC charger options--the below should be worst case--largest minimum genset VA rating):
24.5 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 2,697 VA rated generator minimum
49 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 5,394 VA rated generator minimum
63.7 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 7,012 VA rated generator minimum
122.5 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 13,484 VA rated generator minimum
Typical solar array sizing using 0.77 derating (not sure of GT back feeding AC inverter--might be a bit more losses):
24.5 amps * 59 volts charging * 1/0.77 panel+charger eff = 1,877 Watt Array minimum 5% rate of charge
49 amps * 59 volts charging * 1/0.77 panel+charger eff = 3,755 Watt Array nominal 10% RoC
63.7 amps * 59 volts charging * 1/0.77 panel+charger eff = 4,881 Watt Array "cost effective" 13% RoC for solar
Note--I would suggest there is a maximum solar array to battery bank ratio--that if exceeded, can cause the battery bank to over voltage with Solar MPPT charge controllers (solar array can "overwhelm" the battery charging when MPPT sweeps are performed). I would suggest that is our standard for 100 AH @ 48 volts for every 1kW of solar array capacity--Or roughly 4.9 kW solar array... If the solar array is much higher than that, it appears that you can run the risk of over voltaging the battery bank/inverter electronics (exceeding ~72 volts). MPPT controllers run "sweeps" every so often to figure out the Pmax=Vmp*Imp ... And it is possible for a nearly fully charged battery to refuse to accept the sweep current (it has to go somewhere for a few seconds)--My theory to explain a few "odd ball" events we have talked about here before.
Again, the above are all starting rules of thumbs. Once you have the needs nailed down and start picking hardware, can recheck/adjust as needed.
NiCad and NiMH batteries are amongst the hardest batteries to charge. Whereas with lithium ion and lead acid batteries you can control overcharge by just setting a maximum charge voltage, the nickel based batteries don't have a "float charge" voltage. So the charging is based on forcing current through the battery. The voltage do do this is not fixed in stone like it is for the other batteries. This makes these cells and batteries difficult to charge in parallel. This is because you can't be sure that each cell or pack is the same impedance (or resistance), and so some will take more current than others even when they are full. This means that you need to use a separate charging circuit for each string in a parallel pack, or balance the current in some other way, for example by using resistors of such a resistance that it will dominate the current control.
The coulometric charging efficiency of nickel cadmium is about 83% for a fast (C/1 to C/.24) charge, and 63% for a C/5 charge. This means that at C/1 you must put in 120 amp hours in for every 100 amp hours you get out. The slower you charge the worse this gets. At C/10 it is 55%, at C/20 it can get less than 50%. (These numbers are just to give you an idea, battery manufacturers differ).
So how many Ah of battery capaicity would be recommended for a 48VDC system that can comfortably pull 5kwh per night
Eric L wrote: »
I get that at night from my 360 ah flooded lead acid bank (48v), which drops the bank to about 75% SoC. A 25% depth of discharge (75% SoC) is an economical "compromise" depth of discharge for long battery life versus cost.
I probably missed something above, but I'm not understanding why you're looking at these exotic batteries. They are likely to be complicated, expensive, and easy to damage from a new user. What's wrong with a big, inexpensive and locally-sourced flooded lead acid bank? It's very likely to be the least expensive route, will give you many years of service, and if you make a mistake and damage them, as some new users do, you won't be out huge amounts of $$$.
I plan on always being connected to grid and these batteries are for emergency use only, so there is an advantage to have batteries that can sit unused for a long time without killing themselves.
Sulfur wrote: »
Panels are wired in 2 strings of 14 into the one SB7000 that is in service right now.
Sulfur wrote: »
when I last posted my system was a SB7000 and 28 240 watt Sharp panels, I ended up buying a Sunny Island 6048 and eight 6VDC golf cart batteries from Sam Club. I plan to only use the system as grid tied and the SI and batteries are only to be able to utilize the solar system if the grid goes down. I wired it so I can power the whole house in an off grid scenario, so normally I leave the SI off and not connected at all. Using a 200amp transfer switch to eliminate possibility of backfeeding down grid. I have tested it and it easily powers the house including a hot water heater when the sun is shining, I only have 208 Ah of batteries at 48VDC so I would not be able to let the house use much power at night if the grid were to go down.
When in off grid mode and a large load turns on, the SI will draw that load from the batteries until the SI changes the frequency of island grid which increases power production from the SB7000 or if it was charging the batteries then it just immediately slows or stops that charging and inverts power from batts if needed in conjunction with SB7000 feeding house. So the power from the SB7000 feeds the house directly at 240VAC and does not pass through the SI. I am using an Outback 120VAC to 240VAC transformer to step up and down between the SI and my house panel. I bought another SB7000 and 28 more panels and will have them installed within a month hopefully.
It would be nice if the SB and SI could provide better real time trending options, the sunny portal data update is usually delayed by several hours, the Sunny Webbox does allow nice real time snap shot data but not real time trending, that needs to be improved by SMA.
My current panels are mounted facing South at 17 degrees from horizontal, the max power they could produce at winter solstice was 4300 watts, now they are producing about 5400 watts max, I did not have them installed during summer solstice, so not sure what the system max will be. The next 28 panels will go in yard at 30 degree angle, which SMA software says is ideal for my area. 6700 watts is supposed system max. I bought SB7000's on ebay, 1 used and 1 new old stock, $2200 each. The panels also bought from ebay for $0.80/watt, now you can get them for $0.75/watt. Panels are wired in 2 strings of 14 into the one SB7000 that is in service right now.
I had to cut down a tree that was giving me shade once we got into winter time, so I recommend measuring winter time sun angle so folks know what shade problems they will run into.
My area has a good net metering program. So far I am happy with the system, it has been a fun little science project.
Sulfur wrote: »
I used the SMA configuration software to determine that 14 panels was ok for my min temp, 15 panels however was supposedly too many. I should measure the max voltage on a cold sunny afternoon with the DC disconnect from the inverter, I don't think I have ever seen it over 500 volts once the inverter is on.
Sulfur wrote: »
Hello, I have a grid tied solar system in Montana that I installed last year and have a question on retrofitting the system to off-grid in case of emergency.
SB7000 with 28 Sharp 240watt panels (ND-240QCJ) self installed
I am about to install another
SB7000 with 28 more Sharp 240 watt panels and a SB3000HFUS with 14 Sharp 240 watt panels
So a total of 70 panels and 3 inverters.
I have a net metering power meter and this inverter I am about to install also came with a Sunny Webox for improved data logging vs my current Sunny Explorer via blue tooth which is weak.
I only plan to use the system as grid tied but want to buy the hardware to be able to use solar power in case the utility power would go down for a long period of time. I have a generator that can power my house and enough gas for a few months, but want to be able to retrofit the system and have the hardware on hand to do so in case of longer power outage.
YehoshuaAgapao wrote: »
There is a growing market for AC-coupled battery backup retrofits to existing grid-tie-only systems. The incompetent foreign and fiscal policies of America and just the growing tendency toward tyranny, and the out of control money printing could be having a role in this.
For the first time in recorded history, we have nearly every central bank printing money and trying to debase their currency. This has never happened before. How it’s going to work out, I don't know. It just depends on which one goes down the most and first, and they take turns. When one says a currency is going down, the question is against what? because they are all trying to debase themselves. It’s a peculiar time in world history.
I own the dollar, not because I have any confidence in the dollar and not because it’s sound – it’s a terribly flawed currency – but I expect more currency turmoil, more financial turmoil. During periods like that, people, for whatever reason, flee to the U.S. dollar as a safe haven. It is not a safe haven, but it is perceived that way by some people. That’s why the dollar is going up. That’s why I own it. Will I own it in five years, ten years? I don't know.
ggunn wrote: »
The SI is a pretty versatile machine. It can throttle back the production of a SB if the power from it has nowhere to go. It can control relays for load shedding when resources are low. It can fire up a generator. It has in integrated transfer switch. I'm pretty sure you could get it to make coffee for you.
inetdog wrote: »
But if you rely on SB's to deliver the majority of your load power and this includes some individual large loads, there could be some uncomfortable problems when a cloud goes by and the SI itself does not have enough capacity to make up for the lost power from the SBs. You could end up with your large load finding itself shed unpredictably.
You should also make sure to size the battery bank for you SI sufficiently large to provide surge power, as for motor starting, since the SBs simply cannot provide any power beyond the limit of the instantaneous DC input from the panels. Also make it large enough to supply any critical loads during the night.
ggunn wrote: »
Yeah? I still bet you could get it to make coffee.
inetdog wrote: »
I think that is a given.
And a rather significant benefit. If it would toast bagels too, it might be enough for comfortable survival.
However, a modern hyper-coffee-pot with solid state timer might not be as happy as a simple single burner hotplate. :-)