Optimum panel configs for Midnight Solar Kid

Uncle Dave · September 2014

Hello!

New member to this forum.

I tried looking before posting this question - is there a section for, or does anyone have an optimum (or close to it) panel configuration for this controller?

Im redoing my RV solar and have enough space to max out a Midnight solar kids capacity, but am struggling with finding the optimum panel config to get to 30 amps without going over.

Rather than entering panel after panel into the string calculator I figured I might as well ask if anyone has "gone here" yet and if you have, can I lean on you for info?

Thanks everyone.

Uncle Dave

Cariboocoot · September 2014

Re: Optimum panel configs for Midnight Solar Kid

Welcome to the forum Dave.

A bit short on info there, such as what system Voltage? On an RV probably 12.

You don't really have to worry about going over by a little bit: it won't matter.

Have you tried MidNite's string sizing tool? http://www.solar-electric.com/inverters-controllers-accessories/chco/misoclchco/midnite-solar-classic-sizing-tool.html

In general 12 Volts @ 30 Amps will be an array of about (12 * 30 / 0.77) 468 Watts minimum. Plus or minus a bit won't matter much because panels do not put out their nameplate rating most of the time anyway. The usually less-than-ideal insolation found in RV applications (can't always get the panels pointing directly at the sun) reduces this further than even the typical derating. The "upper end" of the array size could be as much as 100 Watts more.

westbranch · September 2014

Re: Optimum panel configs for Midnight Solar Kid

Also location of use if you are trying to max out the panels to get 30A. In cold winter areas your panels will produce more volts and the MPPT will convert that excess to amps...
What is the reason you want 30A? battery size? It is OK to use the kid at max but you are playing on the edge, most electronics do not like to be pushed to the limit ALL the time... Max stress is a good thing to avoid on any CC...

Uncle Dave · September 2014

Re: Optimum panel configs for Midnight Solar Kid

Cariboocoot wrote: »

Welcome to the forum Dave.

A bit short on info there, such as what system Voltage? On an RV probably 12.

You don't really have to worry about going over by a little bit: it won't matter.

Have you tried MidNite's string sizing tool? http://www.solar-electric.com/inverters-controllers-accessories/chco/misoclchco/midnite-solar-classic-sizing-tool.html

In general 12 Volts @ 30 Amps will be an array of about (12 * 30 / 0.77) 468 Watts minimum. Plus or minus a bit won't matter much because panels do not put out their nameplate rating most of the time anyway. The usually less-than-ideal insolation found in RV applications (can't always get the panels pointing directly at the sun) reduces this further than even the typical derating. The "upper end" of the array size could be as much as 100 Watts more.

Thanks Cariboocoot.

12 volts it is. I have too many "taps" into it for various 12V devices to change that now.

I'm using (the same) Midnight string tool to choose panels, and going to be using flat mounts so Ill likely never see that max theoretical the system will be capable of with "X" panels anyway.

I put solar on this RV a decade ago with dinky 2x40 Watt panels and a PWM controller whose name escapes me and a lone 5 watt panel with no controller connected to the 2 8D starting bank. It works but the yield tiny.

Thanks.

Uncle Dave

Uncle Dave · September 2014

Re: Optimum panel configs for Midnight Solar Kid

westbranch wrote: »

Also location of use if you are trying to max out the panels to get 30A. In cold winter areas your panels will produce more volts and the MPPT will convert that excess to amps...
What is the reason you want 30A? battery size? It is OK to use the kid at max but you are playing on the edge, most electronics do not like to be pushed to the limit ALL the time... Max stress is a good thing to avoid on any CC...

Thanks westbranch.

Im in so cal so we never get really cold. It gets down to around freezing but not much lower.

Im shooting for 30 as thats the recommended max size, but I wouldn't be averse to 27-28 or just under.

Midnight solars string tool recommends a second kid at anything over 1.2 Kids worth of amperage - so it seems to me that 30 is safe based on their own data.

I was just wondering if anyone had already "been there".

Thanks!

Uncle Dave

ILFE · September 2014

Re: Optimum panel configs for Midnight Solar Kid

Hi Dave,

I have been there. I have over paneled my Beta Kid (one of the units shipped to beta testers before the Kid was released to the general public) and it performed fine. I live in Cambodia, where we are not lacking in sun hours.

No matter how hard you try, you cannot make a Kid produce more than 30 amperes. It will limit itself to that, even if you have over paneled the charger. For example, for a 12v configuration, you could easily add 600 or 700 watts worth of panels with no worries. (You do have an option of manually setting the output limit of the charger, as well.)

Use This Sizing Tool for sizing the Kid controller.

Also, do you have the Most Current Manual for the Kid?

Now, my question to you is, would you really want your controller (any controller) to produce it's maximum output, day in, day out, continuously? I wouldn't, personally. I would think we would get more life out of them if we were to not drive them to full capacity, except when necessary. Just my thought on it.

Uncle Dave · September 2014

Re: Optimum panel configs for Midnight Solar Kid

ILFE wrote: »

Hi Dave,

I have been there. I have over paneled my Beta Kid (one of the units shipped to beta testers before the Kid was released to the general public) and it performed fine. I live in Cambodia, where we are not lacking in sun hours.

No matter how hard you try, you cannot make a Kid produce more than 30 amperes. It will limit itself to that, even if you have over paneled the charger. For example, for a 12v configuration, you could easily add 600 or 700 watts worth of panels with no worries. (You do have an option of manually setting the output limit of the charger, as well.)

Use This Sizing Tool for sizing the Kid controller.

Also, do you have the Most Current Manual for the Kid?

Now, my question to you is, would you really want your controller (any controller) to produce it's maximum output, day in, day out, continuously? I wouldn't, personally. I would think we would get more life out of them if we were to not drive them to full capacity, except when necessary. Just my thought on it.

Hello Ilfe,

Let me try asking a different way -

Im not asking to the kid to give me 30amps all day long - just at peak hours - and want to find a good panel combo for its comfortable range.

Ive spent several hours on both Arizona Sun Winds site's kid calculator as well as midnight solars sight running panel combos through the calculator for it.

Ive come up with a number of combos that work, but was looking to see if one of you guys had a particularly sweet combo for power Vs dollar.
I can continue looking everywhere for it myself or ask what you guys came up with and compare notes.

Ive also run the numbers on morningstars ever popular sunsaver 15 mppt and the newer tristar 45 and find the kid optimal for what I'm looking for.

Uncle Dave

Cariboocoot · September 2014

Re: Optimum panel configs for Midnight Solar Kid

I'm not surprised: at 30 Amps maximum the Kid is an 'ideal range' controller for basic systems built around the venerable and inexpensive 220 Amp hour 6 Volt GC2. If you have those for batteries you really only need 22-25 Amps of peak current and the Kid can manage that without being at its limit with about 343 Watts per 12 Volts.

BTW the better charge controllers can handle full output rating for all sun hours, but are unlikely to achieve it due to the nature of insolation. This is not the same as using them for a turbine which really is 24 hour full power; in my opinion a controller used like that should be derated some to reduce heating. But over the course of 4-6 hours "equivalent good sun" running maximum current should not be an issue.

Uncle Dave · September 2014

Re: Optimum panel configs for Midnight Solar Kid

Cariboocoot wrote: »

I'm not surprised: at 30 Amps maximum the Kid is an 'ideal range' controller for basic systems built around the venerable and inexpensive 220 Amp hour 6 Volt GC2.

Ding ding ding- winner - (or close enough for gov work) - the basic 4 X Trojan T106's 225ah each. Standard RV setup.

I might just go with someones single "300 something" and be done with it.

I've seen various sources saying trojan calls for 14.8V vs the 14.4 the string calculator is set at , but Im guessing Ill just get a bit fewer amps at 14.8.

Uncle Dave

Cariboocoot · September 2014

Re: Optimum panel configs for Midnight Solar Kid

Uncle Dave wrote: »

Ding ding ding- winner - (or close enough for gov work) - the basic 4 X Trojan T106's 225ah each. Standard RV setup.

I might just go with someones single "300 something" and be done with it.

I've seen various sources saying trojan calls for 14.8V vs the 14.4 the string calculator is set at , but Im guessing Ill just get a bit fewer amps at 14.8.

Uncle Dave

Buzzzzzzzzzzzz.

Four T105's in a 12 Volt configuration is 450 Amp hours: 30 Amps peak really isn't enough

Trojan's high Absorb Voltage won't affect the maxim Amps but rather the Amps @ Absorb. It takes longer to get higher and the EQ Voltage can trigger problems with some 12 Volt equipment. On the whole the cheaper GC2's may be a better choice.

For 30 Amps @ 14.8 Volts you'd have 576 Watts of array. A single "300 something" panel such as a KD315 would produce about 20 Amps; enough for a single set of the batteries but not double.

Uncle Dave · September 2014

Re: Optimum panel configs for Midnight Solar Kid

hmmmm is just 10 amp hours diff between the 105 and gc 2 a breakpoint?

Sound like It'd be better to spend less on batteries - or up the controller if I want to keep the 106's

I have the roof space for the panels and my budgets can cover an upgrade......I have a hard limit on space for batts.

Thanks! Great input.

UD

Cariboocoot · September 2014

Re: Optimum panel configs for Midnight Solar Kid

30 Amps on 450 Amp hours is 6.6% peak charge rate. That's pretty low; 1.6% above the recommended minimum, and that's not including the reduction in actual charge rate from load demand.

If the battery bank is going to be 450 Amp hours, up the controller and up the panels. You won't regret it.

BB. · September 2014

Re: Optimum panel configs for Midnight Solar Kid

So--Basically you have several choices:

Design the Battery bank to support your loads (AC and DC); design the charging system(s) to supply the daily loads+keep battery bank happy.
Pick a battery bank then design a 5-13% rate of charge (10-13% rate of charge is a "healthy" amount of solar array for the bank).
Figure out how many panels will fit on your roof, then take that Array and work "backwards" to size the battery bank+loads that it will support.

In the "olden days", people would over size the battery bank to support their loads. Was not a great idea but solar panels were expensive and batteries were cheap.

These days, solar panels are cheap and batteries are expensive--So having more solar array on a battery bank (10-13%) is a good investment for longer battery life.

If this was a weekend cabin/RV, you may get away with down towards 5% rate of charge--But it would not be "our" first choice.

In the end, without knowing your loads (and load profile--Do you use most power during the day for computer/tools/battery charging for cameras, etc.--Or at night to run computer+TV+lights+etc.--More power directly from battery bank).

And how much storage--I.e., 1-3 days of storage and 50% maximum discharge is recommended for Lead Acid batteries (2 days of storage and 50% discharge 4x daily loads--Is good starting point).

If weight/size of battery bank is important, then a LiFePO4 Battery Bank (Lithium rechargeable) is gaining a lot of popularity in the RV/Boating world (Li batteries are not cheap--But do have really nice electrical characteristics and should have a good long life too).

Anyway, more questions than answers at the moment.

-Bill

Uncle Dave · September 2014

Re: Optimum panel configs for Midnight Solar Kid

Thanks Bill-

Vehicle serves double duty as a leisure and business device making a load chart inapplicable - this also makes trying to shoot for a number of "days" of storage just a wild guess.

Im going to play around some more to see how many AH I can fit in my battery tray and work the solar backwards into that number and keep the rate of charge in the 10% range. I have the roof space and budget to accommodate that number. I have a trimetric in the RV now to monitor SOC.

I have a commercial vehicle with 440AH of AGM 's on an outback fx2012 inverter charger with an autostart, and an alternator charging system I am familiar with outback, and may just use a flex instead of a midnight solar.

Im not confident in the off the shelf chargers and inverters using lifpo's yet- maybe next round.

Uncle Dave

ILFE · September 2014

Re: Optimum panel configs for Midnight Solar Kid

Uncle Dave wrote: »

Im not confident in the off the shelf chargers and inverters using lifpo's yet- maybe next round.

I haven't been overly confident myself, concerning them. However, if you are interested in taking the time to view it, here is a guy who has been using them for more than a year, along with a Midnite Classic 200:

http://youtu.be/voxecvn09j8?t=9m43s

It should start for you at 9 minutes, 43 seconds, to take you to the part of the video where he explains it a bit.

Uncle Dave · September 2014

Re: Optimum panel configs for Midnight Solar Kid

Great clip Paul - thanks.

Here is another reference about a couple that built their own and struggled with the components being able to properly adapt to the various lifepo parameters.
He's using a victron inverter with a third party charger. Balancing the cells seems to be particularly tricky

http://www.technomadia.com/lithium/

After a year of living with it Chris seems sold, but Im still a bit skeptical.
People don't tend to publish failures so Im wondering what the average guys success rate is.

I love the concept and believe its the future. I Love almost no Puekert, and no slow absorption charge, but just want to see a few others go down this road with off the shelf components so I can follow a known path when I "flip."

Uncle Dave

Optimum panel configs for Midnight Solar Kid

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