Designing new 12VDC Off Grid system. Many questions. (Midnite 150)

[vk4akp]

Hi,

I'm looking to put together a new 12VDC Off Grid system using Grid panels.

So far I have 2 of the following Panels. But plan on getting another two soon and eventually 8 all up.
They are 250Watt panels.
So 500Watts, then 1KWatt, & finally 2KWatt's is the plan.

CSUN 250-60M (250 Watt)  Voc[V] 37.3, Vmpp[V] 30.1, Impp[A] 8.31
http://www.chinasunergy.com/en/product/96

Here are my questions.

- I'm confused as to which is the best way to go as far as panel strings are concerned.
Do I string in series groups of 4? Or parallel up pairs of 2?
Which is going to give the better results?
I note that the web calc tool suggests that 4 in series is too high a Voc for the Midnite 150.?

- If I parallel up series strings of 2 how does it effect things if the different pairs put out different voltages due to shading etc?

- If you go up in size from the Midnite 150, 200 etc the current handling ability drops. But am I better off using the 200 model so I can run strings of 4 instead of two?

- Can I over size the panel array and just drive the Midnite 150 to full capacity sooner in the day without damaging it?

- Once the batteries are full, can I use the Midnite to divert output to a small Grid Tie inverter that takes a 12VDC input to pump back into the grid?

- Anyone know a good distributor in the USA that will ship to Australia. (Australian distributors are always way too expensive compared to the USA as specially with the great exchange rate currently).

- Are there any DIY MPPT Kits I could use as a temporary stop gap that could handle the initial 500Watts of panels? (The sooner I can save on Grid electricity the more money that can go into Midnite products).

Any help appreciated.
.-.-.

[Westbranch]

Unless you have a looong distance to send the PV output you would be better to put all 4 panels in (correction, too early)   parallel. 
That way there is the least amount of downshifiting (37v to 12V) for the 150 to do and thus more efficient overall
I don't think you will be able to do the GT along with a 12 V system

[niel]

for general speak here the expanding of the pvs is the easy part. the hard part is it's not advisable to gradually expand on a battery bank to match the pvs as batteries of mixed age really isn't a good idea to have and batteries need a certain charge % range to be optimal. design for 500w in pv now and you could overcharge later when you have 2kw in pv. or have a larger battery bank up front and undercharge it now. (edited to clarify and correct miswording)

it is also a good idea to go at least in 12v multiples for the battery bank voltage for every kw in pv up to 48v or so. it could go higher if an appropriate inverter is found to operate at the higher voltages. this means that for the 2kw goal you should minimally go to a 24v battery bank. higher battery bank voltages can be so, but i would say 12v may not be a good choice due to high currents being passed even though it can be done.

now off grid may be good if one wants to backup the grid tie connection from outages. if you don't suffer many outages or if they aren't too long, then straight grid tied pv is a good option. (no batteries) this would be more efficient that gt with battery backup. keep in mind generators can also back you up for some time too. the gt with battery backup can be done and there are inverters out there that can accommodate this arrangement. i believe outback power (not australian) and sma offer inverters that can work in this capacity, but they're most likely are others too that maybe i am forgetting about or that i am not aware of.

[Vic]

Hi VK4AKP,

Nice to see you here.

I am going to call you Ken  (perhaps am wrong).

Running 4 of the proposed PV modules in series is pushing things,  and,  will cause any of the MPPT Charge Controllers to run less efficiently.  This efficiency loss generates heat,  which is not good for any electronics.  As noted,  running your two initial PVs in series would be fine for a 12 or 24 volt system.

It is possible that you are almost in the exact geographic center of Australia.  I do not know the weather there,  but the lowest recorded low temps for the previous ten years or even longer is what determines the maximum Voc that will be presented to the CC.  But,  even is this woriks out below the Hyper Voc for the Cl 150,  the efficiency loss would probably dictate fewer than four PVs in series per string.

Some of us are attracted to 12 V systems,  because of the ability to run electronics directly from the 12 V batts.   In the case of many Radio transceivers,  transmitters  often work poorly directly connected to 12 V batts which are not being charged,  as these radios are designed to operate at about 13.8 to 14.4 V.

As niel stated  scaling batteries by adding more later is a bad idea,  and attempting to charge large battery banks with too few PVs also works poorly,  without a lot of fiddling with supplementary chargers.

In the US,  grid tied systems of any kind must be permitted and approved by the Utility.  It may be similar where you are.

Welcome to this Forum.  Guessing is about over.  Vic

[vk4akp]

Hi, Thanks for all the good advice.

I think I need to explain  my background and planning ideas a bit better to give you guys an idea on what I am trying to achieve.

We currently have here a 5KWatt Grid Tie system  using an Aurora inverter and 20x 250Watt CSUN Panels. (I bought two extra for the 12VDC Off Grid project.

See: http://forums.energymatters.com.au/solar-wind-gear/topic3608.html

I also run a Ham Radio station here and a Web server. I will be adding a M4-ATX 12VDC ATX power supply to the server PC shortly to convert it over to 12VDC operation.

For these services it's important to not have any down time during grid outages.

I also have a lot of other equipment. TV's Routers, Cable Modem, Network Switches, Serial servers, AA/AAA battery chargers, lighting, etc that were all purchased specifically for their 12VDC compatibility.

Our feed in tariff is 50 cents a KW. Grid power 24Cents, Controlled (Hotwater etc) 13 Cents.
So it's better to pump power into the grid during the day instead of using it.

For this reason I can also add a top up charger for the solar battery bank that cuts in on the Off Peak 13 Cent tariff from 11PM - 8AM every day.

We are also limited in that the government does not allow us to have a larger grid tie inverter without forfeiting our 50 cent FIT and dropping to only 8 cents (new laws sadly).

Getting lost yet? LOL

However if the battery bank does fill during the day dropping another say up to 500 Watt's into the grid from an extra small in home grid tie inverter would not be noticed as the existing large system never really runs to capacity.

Now lastly I expect at some time in the future I hope to set up a container home on land on a semi local hill top and will transfer the 12VDC Solar system to it. In fact if I am lucky I may even design and build the container home locally and then transport it later.

I do realise 24Volt & even better 48Volt is the way to go. But since I have based all my devices on the 12VDC system as it's been very easy to obtain over the year I'm sort of locked into that.

Perhaps I should aim for only a 1KWatt Solar array and buy batteries accordingly. (I have to look into batteries yet).

But the ongoing cost of things I will have to build in modules.

I am also looking at getting one of these 400 Watt MPPT Wind Generators off eBay (China), and possibly some sort of LPG Stirling electric / Hot Water generator to supplement things.

If I ever win the lotto it will make things a lot easier as far as design wise! LOL

.-.-.

[vk4akp]

Hi Vic,

Sorry I replied right at the same time you did. LOL

Must be fate!

Yes it would be good to have a chat with another semi local Ham and get the good juice on things.

OK Must run. Chat more soon.

~Ken~
.-.-.

[Vic]

Hi Ken,

OK  we have a better understanding of what you are doing ..  I do not necessarily know exactly what the items are,  but know well enough.

I do not know of a GT inverter that works on 12 V,  but they may well be on FeePay or elsewhere.

The  additional comments that I have are that Flooded batteries (ones with removeable caps)  need to be Equalized on occasion.   The EQ voltage usually exceeds 15.5 volts -- even higher with cool/cold batts.   Some  12 VDC equipment can be damaged by this higher voltage.   Some 12 V Inverters  will shut down above 15 VDC  etc.  All of the items that you have and will be using may well take this EQ V.  And some sensitive items could be disconnected,  and so on.

Sorry for the tardy reply -- we have had a Heat Wave,  and have been distracted trying to get batteries recharged  while extracting every last watt for A/C systems.

Thanks for the added info.   Good Luck,  73  Vic  K6IC

[niel]

ken,
you will need to figure the loads the items on 12v will draw over a 24hr period. this draw is critical from a design standpoint as otherwise you can overshoot or undershoot your goals. overshooting is the better thing to do, but it is more costly too. the loads required by your server are more consistent and predictable, but ham radio is trickier with variable tx times, power levels, and modes of operation that affect the draw. i hope to assume no linear will be involved in this equation or everything is out the window in the requirements area.

it may be better to go for all solar and not count on wind power.

[vk4akp]

OK My turn to apologise for the late reply. I'm about 1/2 way through the worst flue I've ever had in my life. Bed ridden and coughing blood up even over the past week. Very scary.

So the Midnite Classic 150 at US$615 from http://www.wholesalesolar.com looks the go so far.
.AU direct prices as expected no where near realistic sadly.

All items are designed to run from a car at the very least.
So 13.8VDC Given is easily safe. I doubt an extra 1.2VDC (15VDC) will worry anything.

Some of the items I will run.
Note: * Indicates that I can not find info on power tolerance specs yet.

- Motorola Surfboard SB5101 Cable modem - 12VDC 1.25A (From Power supply) *
- Billion 7404VGPX - 10-15VDC 1.6A. *
- Medion MD86407 1.5TB NAS - 12VDC 1.5A *
- 8 port generic 10/100 Network Switch - 12VDC *
- Digi Portservber TS-3+M Serial Servers (4x) - 9-30VDC 0.5A(Max@12VDC)
- Boltek LD-250 Lightning Tracker - 11.8-18VDC 0.8A
- Maha PowereX MH-C9000 Battery Chargers (2x) - 12VDC 2A *
- Yaesu FT-890AT HF Multi band Transceivers (2x) - 13.5VDC +/- 10%  1.5A RX, 20A TX. (Max values).
- Yaesu FT-212RH VHF Transceivers (3x) - 13.8VDC +/- 10% 0.5A RX, 10A TX. (Max Values)
- Kantronics KAM-XL Packet Radio TNC's (2x) - 10-18VDC 0.15A
- Linksys WRT54GS WiFi Routers (2x) - 5-20VDC 3A(@3.3VDC)
- Minitar SB-2200G WiFi Amps (2x) - 12VDC 1.25A *
- M4-ATX DC Server Power Supply - 6-30VDC 250Watts (To run an Intel i5 based server).
- Vivid AJ-15LE1 39cm LED TV - 12VDC 3A *
- 240VAC Inverters (Yet to purchase some larger ones but have a few smaller ones).
- 12VDC 500Watt Grid tie inverter (Variable Current limited)
- DTMF / RS232 / Ethernet DC Switching device to switch units in and out. (Home Brew)
- + Possibly other items.

Current ratings are Max only and often most of these devices don't even draw 1/10th the amount.

I'm going to look into getting another 2x 250Watt panels and start out with a 1KWatt system I think.
Then later on add a wind turbine to help in low solar times.

.-.-.

[niel]

ken,
you need to determine what you will typically need over your average 24hr period to determine the minimum battery bank size and that determines your minimum pv size. for instance the maha charger may draw over a 2hr period to fully charge some batteries. are you doing this 24/7, 6 hrs every day, or 2hrs every 3 to 4 days? this  time interval has a direct impact for every load on your list. some you may want to run 24/7, but most you don't want to. even a router going 24/7 costs quite a bit in pv power needed because that small load is constant over 24hrs, but your solar production may only be over about a 5hr period. don't confuse this with the amount of daylight hours you have because the early morning and early evening hours do not have strong sun. you may get this strong sun the pvs are rated at for a few hours around solar noon. the rest is from lowered amounts of sun insolation added together to equal that of the total full intensity sun hrs. think in terms like amp hours or watt hours. i like to call them full sun hours, but i forget exactly what the proper term is.

btw, if you wish you can save $5 and go here,
http://www.solar-electric.com/misocl.html

[vk4akp]

Hi Thanks for the good lead on the other company.

Their online ordering system seems much easier in that it allows for PayPal etc as well.
I'm yet to work out how to get the freight costs displayed there though before checking out.
This is something I would need to be sure of before committing to pay.

Now as far as power usage. Well that would be a big ask to work it all out exactly.
Using the monitoring software though I will basically work around What I have available and go from there.
It may be that I will have to bring in the night charging from the mains in off-peak hours or instigate timer / battery voltage based auto shut down of some systems as necessary. We'll look at all that as time goes by.

The server will be the biggest draw I'm sure. But it too will have green modes etc that it can be kicked into.

Looking at what I currently have hanging off the DC supply I see idling at 1.5A @13.7VDC.
That being - The Router, Network Switch, Boltek LD-250, Digi TS3+M, & Kam XL TNC.

Kick in the VHF Radio (1.7A), then the HF Radio (3.3A).

But it's OK. If I have to make sacrifices that's life.

.-.-.

[vk4akp]

Still haven't heard back from that company with a shipping quote to Australia.

I guess they don't want my cash $$$'s !!

Any other good places to shop state side?

.-.-.

[Halfcrazy]

You may try www.altestore.com

Ryan

[niel]

hmmm. i'm surprised. did you try calling them?
Tel: 800 383-0195 (928 526-8017 Outside USA)

[vk4akp]

Yep, that's how I contacted them.

Called got their answering service. Left my details including phone number and email address.

They have the best price so far so are my preference really if the freight is reasonable.

.-.-.