In over my head

[Tom Bradford]

Kia ora from New Zealand.

I do the techie stuff for a non-profit community trust that brings wireless internet to a remote and mountainous part of Middle Earth where wizards and commercial ISPs fear to tread. It's been hard enough getting my head around wireless networking but a couple of our relays are on mountaintops needing remote power so I'm having to get up to speed on controllers and panels and voltages and batteries and the rest, so any help from you guys would be appreciated.

It's clear that the batteries at one of our sites are struggling, tho' I don't understand why. We've two BP 80W panels and an unnamed 85W Chinese panel charging two 120 a/hr flooded 12V batteries. The two BP panels run through a Xantrex C35 controller. The Chinese panel came with its own controller and a single A4 sheet of unhelpful Chinglish and as I wasn't sure if you can mix 80 W and 85 W panels on the same controller we installed its own controller on the 85W panel.

Demand from the routers and radios is somewhere between 1.0 Amp and 1.5 Amps 24/7.

It's clear, tho', that the batteries are buggered as voltage being delivered to the routers drops off quickly once the sun goes down and we're getting to the point that they are failing by the early morning and only able to successfully boot-up once the sun is up.

As we're going into winter here I need to get on top of these problems , and clarify some issues.

1. Is it right that the 80W panels and the 85W one need separate controllers or can I run all three panels through the Xantrex? The C35 is rated for 35 Watts so it should be man enough?

2 Could the two controllers be working against each other and the reason the batteries are not charging?

We're replacing the 2 x 120 a/hr flooded batteries with a single 325 a/hr AGM which costs a fortune so I don't want to bugger it.

3. It's been suggested that we add a little 200W wind turbine on the site rather than another solar panel there's no room for, as the site can get clagged in by cloud for days but there's always wind.

4. I understand the three panels at maximum output would produce 13.6 Amps while the turbine will wind up in a gale to 336 Watts and 16V before it shuts down. That's 21 Amps which means that with both systems flat out they'll be presenting the 35 Amp C35 with 34.6 Amps. Is that too close for comfort or just a theoretical maximum we'll never get to?

5. I also think from what I've read that we'd need to switch the C35 into load diversion mode - and most of what I've read (and little that I understood) of this means we need something to absorb the dumped load. Articles usually mention water or air heaters at 120V AC but that's for the US. Here all the gear is for 240V AC. Does that make a difference? As we're talking less than 600 Watts to be dumped an electric kettle - jug to you - element could do it? Or not? Does it need to be in water?

6. The Xantrex manual says the device disconnects the battery from the panels at night to prevent reverse leakage of power. Can it do that when the solar panels are connected directly to the battery in diversion mode or will we need diodes?

7. What happens when the panels try to put 18V into a 12V battery, and the wind turbine is only producing 14V?

8. Both produce voltages higher than the controller's equalisation charge which I believe you're not supposed to give AGM batteries. So how can it be good for the battery?

Thank you for your patience.

[inetdog]

Kia ora from New Zealand.

I do the techie stuff for a non-profit community trust that brings wireless internet to a remote and mountainous part of Middle Earth where wizards and commercial ISPs fear to tread. It's been hard enough getting my head around wireless networking but a couple of our relays are on mountaintops needing remote power so I'm having to get up to speed on controllers and panels and voltages and batteries and the rest, so any help from you guys would be appreciated.

It's clear that the batteries at one of our sites are struggling, tho' I don't understand why. We've two BP 80W panels and an unnamed 85W Chinese panel charging two 120 a/hr flooded 12V batteries. The two BP panels run through a Xantrex C35 controller. The Chinese panel came with its own controller and a single A4 sheet of unhelpful Chinglish and as I wasn't sure if you can mix 80 W and 85 W panels on the same controller we installed its own controller on the 85W panel.

Demand from the routers and radios is somewhere between 1.0 Amp and 1.5 Amps 24/7.

It's clear, tho', that the batteries are buggered as voltage being delivered to the routers drops off quickly once the sun goes down and we're getting to the point that they are failing by the early morning and only able to successfully boot-up once the sun is up.

As we're going into winter here I need to get on top of these problems , and clarify some issues.

1. Is it right that the 80W panels and the 85W one need separate controllers or can I run all three panels through the Xantrex? The C35 is rated for 35 Watts so it should be man enough?

2 Could the two controllers be working against each other and the reason the batteries are not charging?

We're replacing the 2 x 120 a/hr flooded batteries with a single 325 a/hr AGM which costs a fortune so I don't want to bugger it.

3. It's been suggested that we add a little 200W wind turbine on the site rather than another solar panel there's no room for, as the site can get clagged in by cloud for days but there's always wind.

4. I understand the three panels at maximum output would produce 13.6 Amps while the turbine will wind up in a gale to 336 Watts and 16V before it shuts down. That's 21 Amps which means that with both systems flat out they'll be presenting the 35 Amp C35 with 34.6 Amps. Is that too close for comfort or just a theoretical maximum we'll never get to?

5. I also think from what I've read that we'd need to switch the C35 into load diversion mode - and most of what I've read (and little that I understood) of this means we need something to absorb the dumped load. Articles usually mention water or air heaters at 120V AC but that's for the US. Here all the gear is for 240V AC. Does that make a difference? As we're talking less than 600 Watts to be dumped an electric kettle - jug to you - element could do it? Or not? Does it need to be in water?

6. The Xantrex manual says the device disconnects the battery from the panels at night to prevent reverse leakage of power. Can it do that when the solar panels are connected directly to the battery in diversion mode or will we need diodes?

7. What happens when the panels try to put 18V into a 12V battery, and the wind turbine is only producing 14V?

8. Both produce voltages higher than the controller's equalisation charge which I believe you're not supposed to give AGM batteries. So how can it be good for the battery?

Thank you for your patience.

Let's hit the high points:

For 240AH of batteries at 12 volts, you would need by rule of thumb 240 watts of panels IF you use an MPPT controller. You are using a PWM controller which is costing you 1/3 or more of your available power.

The CC will never try to put 18 volts into the 12 volt battery. They regulate to prevent that. Maybe 14+ if doing equalization.

Your wind option may actually make sense, but no 200W turbine that I know of will both generate a useful amount of power and survive a year unattended with storms, etc.

You should NOT try to combine wind and PV through one controller, and for your situation a diversion (dump) controller connected to the battery is probably not a good idea.

An electric kettle without water in it will burn up. You can get air-cooled dump loads.

Numbers: 1.5A 24/7 (conservative end) means 36AH per day.
In winter you may only get 2 hours a day of full sun equivalent. So you need panels capable of 18A. 240Watts of panels at an output of 18 volts would only be 13 amps, and a reasonable derating factor would bring that down to only 10 amps.
The same panels with an MPPT controller would give you 240W / 12 volts = 20A. Better, yes?
If you need to make up 18A at peak charging, that would be C/13 which is actually a little low for FLA batteries and very low for AGM.

You do not need more or better battery, (well something to replace the dead ones, of course) you need at least a factor of two more panel watts.
Rather then spend money on a small turbine, large tower and expensive controller, you would be better off to invest the same money in more panels and an MPPT controller. My opinion anyway.
A good controller will have diagnostic (and maybe control) data connections that you can use to monitor everything remotely via your existing network infrastructure.

You say there is no room for more panel? You could probably get a more efficient larger panel that would fit where your current three panels are (unless you only have 3 small spaces) What is the space restriction anyway?

Avoid batteries in parallel if at all possible. Two 6 volt 240AH batteries in series, or a single 12 volt 240AH battery would be better.

It is Amp-hour (AH), Amps times hours, not A/h (amps per hour).

The Xantrex C35 is a capable, reliable, PWM controller. But a PWM controller is not what you want.

If you have room for a 200W turbine on a 30 foot or higher tower, you have room for more panels!

Dereck (Sunking) is very experienced (professionally) in reliable power for remote facilities, and may have some more specific suggestions for you.

[Sunking]

Well I do this for a living on a larger scale. I do Off-Grid Solar for Cellular Telephone so I kind of know what is going on. Your problem isd everything is udersized and you have no generators. If your batteries are dead by morning is telling me two things already.

1. They are ruined and need replaced already.
2. Both panel wattage and batteries are way undersized.

Now you understand why a commercial company will not touch those rural areas. No money in it.

What voltage are the radios operating at? I assume 24 volt? At 1.5 amps continuous they are using some 24 volt x 1.5 amps x 24 hours = 860 watt hours.

That means your panels at minimum for mission critical application must generate 1600 watt hours per day on the shortest winter day. Not sure what your winter insolation is but to get 1600 watt hours with a 4 Sun Hour day will require 400 watts of panels.

For the battery for mission critical you need a 10 day reserve capacity. So at 24 volts [860 watt hours x 10 days] / 24 volts = 358 AH battery @ 24 volts

A 400 watt panel operating on 24 volt battery demands a 15 amp MPPT Charge controller.

So it sounds to me like you need to start over from scratch. Forget the Wind TURDs. They are useless.

[Tom Bradford]

Thanks guys.

Some observations first. Yes, we know why the commercial folks avoid us. That's why we have to do it ourselves. And doing it to commercial specs would be prohibitively expensive for the few folk who use the network - and need it, as the only alternative is dial-up that runs at 1.5 kbps.

The site is a'top a mountain accessible only by quad which limits what we can get up there - and everything has to be done by volunteers, There's usually no problem getting bodies but getting the skills you need is another matter.

Establishing the site was a major operation with holes for the railway-iron frame having to be dug by pick in solid rock and packed with concrete + water hauled up the mountain. We built the frame to take 3 x BP 80W panels but started with two with room for expansion. When the additional gear that came with an expanding network suggested the third panel was required we discovered BP no longer made them and the 85-Watt Chinese panel was the only one we could find to fit the space available. Adding yet more panels would require a major community effort I can really only ask it to undertake if there is no alternative - and a wind-turbine did seem to offer an alternative.

Changing to an MPPT controller is feasible if it will substantially improve the situation. I've been bending the ears of the trustees for a Pentametric monitor with the ethernet unit so I can monitor the system from down here, but if we're going to get a new MPPT controller is there one with an ethernet/LAN monitoring function built in?

We've a new battery on order which should arrive with the next fleet if winds are kind. It's a 12v 325 AH AGM one weighing in at 70kg.

The routers have a voltage range of 12 - 28v. One of the early mistakes I made was to use 2 x 12v batteries in series to give 24v - as soon as the controller tried to give the batteries a bulk charge the over-voltage (>28v) protection on the routers cut in and we were off air until I could go back up the mountain to sort it out. SInce then we've used 12v. I would like to present higher voltage to the gear but it would seem to require limiting the bulk charge rate on the controller to 27.6v which doesn't help the batteries, I understand.

Putting up a tower for a small turbine will simply involve bolting a couple of meters of steel-pipe to the existing frame which is a much easier proposition than re-building the frame to take more panels, and yes I have my reservations about it but there are several around here on baches and marine farms that appear to be doing a good job and surviving. Perhaps more to the point the suggestion comes from one of the other trustees who is pushing it and prepared to pay for it. So given that I might be stuck with one, what would be the best way to incorporate it? If I get an MPPT controller for the panels could we use the Xantrex in diversion mode on the turbine?

[inetdog]

If I get an MPPT controller for the panels could we use the Xantrex in diversion mode on the turbine?

Yes, you could, but if it requires that the diversion load end up connected to the Xantrex in a way that dumps current from the battery side, it will not be ideal.
If it can be done so that the diversion somehow happens before the battery connection, it might be good. Need to look at the details of the X35's diversion mode.

For larger turbines, some folks swear by the Midnight Classic in wind turbine mode with the separate Clipper added on the turbine side to act as the dump load. It ends up being pricey but cast iron reliable and with networking capability as a simple option. In fact the Classic Light saves you money by leaving out the fancy direct control panel and using just the bus interface. Not quite sure what it takes to adapt that to IP, but it is designed for easy interface to computer, so how hard could it be?

Instead of 3x 80 watt panels, could you fit 1x240 on the existing frame? You can get a high voltage panel that needs an MPPT controller at a lower cost per watt than smaller battery voltage panels.
Can you give us the output specifications on the existing panels? You may not be getting best use from them as you have them wired now.

Only consider going to 24 volt if the equipment takes ~50% of the current when being run at the higher voltage, otherwise you are wasting power instead of saving it. (Although you could use a 24v to 12v switching mode converter and maybe get more reliable power to the routers.)

Make sure that the vibration from the turbine will not shake up the panels or other equipment in a harmful way. And think about where the blades will end up of they snap off. Free does not always mean low cost.

There are some good threads here on wind power, even though that is not a primary focus. You can find more information on that specific topic in some of the forums at Fieldlines.

[Sunking]

OK it is 12 volt, changes things by basically cutting things in half. However the root cause of your problem is you system is undersized. Until that is resolved you are dead in the water. You can use residential design practices but need to understand doing so means being off the air from time to time and more frequent battery replacement.

So 12 volts x 1.5 amps x 24 hours = 432 watt hours. New Zealand Winter Insolation = 3.8 Hours in June/July

Panel wattage required = ]432 watts x 1.5 efficiency factor] / 3.8 Sun Hours = 170 watts with MPPT. Use 200 watt GT Panel. With PWM controller you will need [432 watts x 2 efficiency factor] / 3.8 hours = 227 watts. With MPPT you must use the more expensive battery panels wired in parallel with a Vmp of approx 17 volts..

Charge Controller amps = 15 amps

12 Volt Battery capacity = [5 days reserve x 432 watt hours] / 12 volts = 180 AH @ 12 volts.

[Tom Bradford]

Yes, you could, but if it requires that the diversion load end up connected to the Xantrex in a way that dumps current from the battery side, it will not be ideal.
If it can be done so that the diversion somehow happens before the battery connection, it might be good. Need to look at the details of the X35's diversion mode.

I've attached a scan of the relevant bit from the C35's manual. Doesn't look like it does what we want.

For larger turbines, some folks swear by the Midnight Classic in wind turbine mode with the separate Clipper added on the turbine side to act as the dump load. It ends up being pricey but cast iron reliable and with networking capability as a simple option. In fact the Classic Light saves you money by leaving out the fancy direct control panel and using just the bus interface. Not quite sure what it takes to adapt that to IP, but it is designed for easy interface to computer, so how hard could it be?

How hard is brain surgery when you're a brain surgeon? Unfortunately I have to work with the turbine I'm given. The guy who swears by them and is donating this one says it doesn't need a controller. It just pumps down to the battery what the battery needs from moment to moment. What it does with the rest isn't clear. Fromk the manual: "In the same wind speed condition when the battery is becoming fuller and fuller the charging current of the common wind generator will become less and less." Any translation of that would be appreciated.

Instead of 3x 80 watt panels, could you fit 1x240 on the existing frame? You can get a high voltage panel that needs an MPPT controller at a lower cost per watt than smaller battery voltage panels.
Can you give us the output specifications on the existing panels? You may not be getting best use from them as you have them wired now.

It would mean a major rebuild of the frame to take something else - and I'd have to justify scrapping three perfectly good solar panels.

I know - or rather I think - only that they're BP 80 watt panels. When this site went up at the very beginning I was up to my eye-balls learning how to do wireless networking. Someone else took on establishing the site and the power supply and unfortunately he's no longer with us. I think the sticky id labels are still on the back of the panels and I'll note what they say next time I'm up there. I didn't even realise there were 'high' as opposed or 'low' or 'ordinary' or 'for suckers' panels.

Only consider going to 24 volt if the equipment takes ~50% of the current when being run at the higher voltage, otherwise you are wasting power instead of saving it. (Although you could use a 24v to 12v switching mode converter and maybe get more reliable power to the routers.)

Make sure that the vibration from the turbine will not shake up the panels or other equipment in a harmful way. And think about where the blades will end up of they snap off.

I must admit I've been toying with the idea of sticking on of those 'power-your-laptop-from-your-car's-cagarette-lighter' gismo's between the batteries and the gear to bump the voltage up to 18.

Oh, you can be sure that even if we set the wind-turbine up at the foot of the bloody mountain it would send a broken blade with unerring accuracy through the most expensive, delicate and vital piece of equipment we have.

432 watts x 1.5 efficiency factor] / 3.8 Sun Hours = 170 watts with MPPT. Use 200 watt GT Panel. With PWM controller you will need [432 watts x 2 efficiency factor] / 3.8 hours = 227 watts. With MPPT you must use the more expensive battery panels wired in parallel with a Vmp of approx 17 volts..

Charge Controller amps = 15 amps

12 Volt Battery capacity = [5 days reserve x 432 watt hours] / 12 volts = 180 AH @ 12 volts.

OK, I can very likely get the Xantrex swapped for an MPPT controller. But we're very likely stuck with the panels we have. Is there any way of finding out what their native Vmp is? If it's 17-18 volts - and I thought all 36-cell panels did that as the cells are always 0.5v - we've 240 or 245 watts of panel so shouldn't we theoretically be OK with a MPPT controller rather than our existing PWR one? Which would mean we could politely refuse the offer of the wind turbine. New battery is 325 Ahr C100 12v.

[Sunking]

Is there any way of finding out what their native Vmp is? If it's 17-18 volts - and I thought all 36-cell panels did that as the cells are always 0.5v

Should b eon the name plate, but if they are BP battery panels Vmp is going to be around 17 to 18 volts.

- we've 240 or 245 watts of panel so shouldn't we theoretically be OK with a MPPT controller rather than our existing PWR one?

Should work. If you go with MPPT rewire the panels in series. At 240 watt panel will require a 20 amp MPPT minimum.

[Tom Bradford]

If you go with MPPT rewire the panels in series.

Ah. Penny drops. That's what you mean by high voltage panels, yes? And the ampherage you need from an MPPT controller relates to the amps it's putting out to the batteries at 12v rather than the amps it's receiving from the panels at a higher voltage.

But how does that relate to your comment above - "With MPPT you must use the more expensive battery panels wired in parallel with a Vmp of approx 17 volts."


I've fallen in love with the Midnite Solar 'Classic Lite' MPPT controller - looks great, lots of how-to videos on their web-page and what looks like a great LAN monitoring facility. In our store the 150v model is rated for 96 amps and the 200v model is rated for 79 amps, at the same price. Given that either would be hardly breaking a sweat with what we'd put into it - 20 Amps - is there anything to choose between them?

[inetdog]

But how does that relate to your comment above - "With MPPT you must use the more expensive battery panels wired in parallel with a Vmp of approx 17 volts."

Small typo, I think. That should have read "Without MPPT....."

[Sunking]

But how does that relate to your comment above - "With MPPT you must use the more expensive battery panels wired in parallel with a Vmp of approx 17 volts."

That is a typo. Should read with PWM, you must use more expensive low voltage battery panels. With MPPT you can use higher voltage less expensive GT panels.

Once panel wattage gets to about 200 watts, a MPPT system is less expensive for a given amount of energy. A 200 watt panel and 15 amp MPPT controller with 4 sun hours generate roughly 550 wh/day and cost around $475 to $500. To get the same amount of power out of a PWM and battery panels requires a 300 watt panel, 15 amp PWM controller that cost around $550 to $700.

That i swhy I give folks such hard time when they say that have a 40 amp PWM controller with say a 600 watt battery panels. Their answer is always the same ignorant answer: "I cannot afford MPPT". Truth is they wasted money and could have done the same job using a MPPT controller with GT panels like 400 watts of inexpensive GT panels and saved a few hundred dollars.

I've fallen in love with the Midnite Solar 'Classic Lite' MPPT controller - looks great, lots of how-to videos on their web-page and what looks like a great LAN monitoring facility. In our store the 150v model is rated for 96 amps and the 200v model is rated for 79 amps, at the same price. Given that either would be hardly breaking a sweat with what we'd put into it - 20 Amps - is there anything to choose between them?

Midnight Solar makes the best MPPT charge controllers hands down favorite.

[Tom Bradford]

Their answer is always the same ignorant answer:

I'm sure that it is often, as in my case, just ignorance. Now that I understand the difference I think it is worth ditching the PWM in favour of an MPPT to get the best harvest from the panels but when we were putting this site up in a hurry it seemed like the difference between PWM and MPPT - if you just read the brochure and listed to the manufacturer's pitch - was like the difference between a Honda ABC and a Suzuki XYZ, ie a drinks holder, an extra bit of chrome here and there, a smidgin of additional bird-pulling power and a couple of hundred bucks.

This has been a very useful and informative thread for me, for which I thank you.

[Sunking]

I'm sure that it is often, as in my case, just ignorance. Now that I understand the difference

That is how Obama got elected. Nothing you can do now except suffer or hope for Impeachment. Then we are stuck with JOE Blow. At least Joe would be a Lame Duck and marginalized.

[Naptown]

That is how Obama got elected. Nothing you can do now except suffer or hope for Impeachment. Then we are stuck with JOE Blow. At least Joe would be a Lame Duck and marginalized.

I don't think a Kiwi is much interested in American Politics.
They have Middle Earth to worry about

[Tom Bradford]

I don't think a Kiwi is much interested in American Politics.
They have Middle Earth to worry about

You'd be surprised. I was exhilarated with hope when Obama was elected for the first time and my disappointment and despair at his turning out to be just a Saruman is deep. There'd be a lot less for us here in Middle Earth to worry about if you Yanks would get your act together and ride to the rescue like you did in '41.

Some follow-on: If we get this wind-turbine donated by a well-meaning member we will be required by community politics to utilise it. How would I do this? Do I:

1. just feed it in series to the Classic 'Lite' along with the panels?
2. connect it directly to the batteries, and the panels through the 'Lite'?
3. feed its output to the batteries through the shortly-to-be-redundant C35 in diversion mode, parallel to the panels and 'Lite?
4. quietly not connect it to our system at all but use it for recharging the batteries in Galadriel's vibrator?
5. other.

And a query touching on fundamentals - when you connect panels in series does it have to be AXBXCXY where Y is the controller and X is + to - and vice versa, or can it be AXY BXY CXY?