Please critique/comment on/improve my solar plan

[weboughtabus]

Originally Posted by JDOnTheGo

I'm afraid I do not understand this. Perhaps I haven't had enough coffee yet today.

I agree that parallel is ideal.

The link to the proposed panels is no longer working so please allow me to assume they output about 6 amps @ 50 volts. Three of them wired in parallel would result in approximately 18 amps @ 50 volts.

There are many charge controllers that can handle this so I'm confused by your statement above.

I'm running four, 435 watt panels in parallel, thru a Morningstart TS-MPPT-60 and into a 24 volt lithium battery bank. Nearly twice the total wattage that you are talking about. That charge controller cost me $530.

The Morningstar TS-MPPT-30 is all that you would need (more than you need) and it costs something around $390. In my way of thinking, one $390 name brand charge controller is less expensive than three $209 controllers.

I did not download the manual for the listed controller but I assume you have confirmed that they can be networked so that they operate "together" to properly charge a single battery bank.

Where did my number crunching go wrong??

Don't assume your thinking is wrong - all I know is based on little bits of information from a million different sources, so it's almost certain that I've gone astray somewhere. I'll have to do some more research and plan things out better!

[JDOnTheGo]

Originally Posted by john61ct

Victron 75/15 is usually ~$125

Not a lot here for the OP to go on. I think you are agreeing that there are many charge controllers that can handle the OP's system and one charge controller is better than three. You may also be saying that this particular charge controller, while limited to 15 amp output, is probably sufficient for an ~18 amp array as the real world output is going to be less than the published numbers. However; this controller does not provide any room for expansion - that may or may not be a factor in the OP's decision.

Am I close???

[john61ct]

Originally Posted by brokedown

I stand by my earlier post. Connecting 3 charge controllers to a single battery bank sounds like a mistake. Electricity doesn't just flow downhill like water.

Wut?

There is no problem at all with that technically, just a question of space, wiring etc.

Don't even need to be same type or voltage settings.

No idea what that downhill metaphor might mean

[john61ct]

Originally Posted by JDOnTheGo

I think you are agreeing that there are many charge controllers that can handle the OP's system and one charge controller is better than three

No, I was not addressing the OP, just responding to a later comment that getting three separate controllers must necessarily be more expensive than one big one. That is not how Victron's pricing works.

The ideal for partial shade handling is 1:1 ratio, each panel gets its own MPPT optimization.

For that to be economic, the panel should ideally be selected to match the SC spec limits.

In the case of that Victron 75/15, a voltage over 40Voc helps give the MPPT some headroom to optimize, and 220W in theory, up to 300W if the panel $ / W is a great bargain.

Of course in a mobile context W/square area might need to be optimized more than cost.

[weboughtabus]

Originally Posted by JDOnTheGo

I'm running four, 435 watt panels in parallel, thru a Morningstart TS-MPPT-60 and into a 24 volt lithium battery bank. Nearly twice the total wattage that you are talking about. That charge controller cost me $530.

The Morningstar TS-MPPT-30 is all that you would need (more than you need) and it costs something around $390. In my way of thinking, one $390 name brand charge controller is less expensive than three $209 controllers.

JD have you experienced any issues with having a 24v bank? Are you primarily running 24v appliances or inverting to 120v AC? Originally my plan was to use a 24v battery bank in order to use a single charge controller. At 12v the charge controller you recommended is limited to 400w or 800w at 24v, so if I proceed with my current plan of 2-3 panels I think I'd have to upgrade, unless I'm seriously misunderstanding these spec sheets.

[JDOnTheGo]

Originally Posted by weboughtabus

JD have you experienced any issues with having a 24v bank? Are you primarily running 24v appliances or inverting to 120v AC?

Zero issues. From the voltage perspective, I designed my system (http://jdfinley.com/electrical-system-design/) for 24VDC and it works just swell (http://jdfinley.com/24-volt-battery/). From a battery perspective, I am very happy with the 24V lithium bank (http://jdfinley.com/lithium-battery-lfmp-missy/). For my use, it is amazing and worth the cost.

Originally Posted by weboughtabus

Originally my plan was to use a 24v battery bank in order to use a single charge controller. At 12v the charge controller you recommended is limited to 400w or 800w at 24v, so if I proceed with my current plan of 2-3 panels I think I'd have to upgrade, unless I'm seriously misunderstanding these spec sheets.

Depending on where you are located and how the panels are mounted, you can expect to get less than 100% of the rated output from the panels. If flat mounted, I've found that 90% in the southwest summer is the maximum. About 60% in the winter (very roughly). The charge controller (CC) has some conversion losses - not huge but they exist. A 24VDC battery bank needs about 28 volts for charging (exact number varies by battery type and charging stage). So, a CC that is limited to 30 amps will deliver a maximum of 30 amps at whatever the current voltage requirement is. Let's assume your batteries will accept 28 volts. To max out the 30 amp CC that I mentioned, an array that is producing about 840 watts (30 amps x 28 volts) is required. Add another 10% for best case and an array of 925 watts will just barely max out the CC. As far as I am aware, all of the better MPPT CC's are happy to clip excess power (up to some limit) - this is important to understand. This means that you could have an array of 1200 watts (for example). In the best of times, it will clip off 260 watts of the array output. In reality, that array will probably never produce more than about 1000 watts. That drops to more like 700 watts in the winter. This summer vs winter 'reality' is one of the reasons that most of us install an array that sounds too large. Yep - my 1720 watts is a LOT of power. However; that same array produces more like 1000 watts during the winter and that is not a lot of power (it's all relative, of course).

I apologize for all the about/approximate nonsense - there are too many variables to speak in absolutes in regard to solar array output.

[weboughtabus]

Originally Posted by JDOnTheGo

I apologize for all the about/approximate nonsense - there are too many variables to speak in absolutes in regard to solar array output.

Thank you very much for all of your insights. I used the MidNite calculator recommended in this thread and found that the MidNite Solar Classic 150-SL should be able to handle the panels I'm looking at (you have to enter the specs for the panels, as well as the number and configuration) and a 12V Battery Bank, so I may go with that setup. It simplifies things since I'll only need one charge controller and will still be able to maintain a 12V Battery Bank.

[john61ct]

Yes important when sizing inputs and load demands to work closer to "worst case scenario" than ideal conditions.

Then in bright sunny weather with lighter loads, you can come back and ask "what do I do with all this excess power", nice first-world project to have

[Ninjakitty]

Originally Posted by weboughtabus

Thank you very much for all of your insights. I used the MidNite calculator recommended in this thread and found that the MidNite Solar Classic 150-SL should be able to handle the panels I'm looking at (you have to enter the specs for the panels, as well as the number and configuration) and a 12V Battery Bank, so I may go with that setup. It simplifies things since I'll only need one charge controller and will still be able to maintain a 12V Battery Bank.

I went with the midnite classic 200 as it fit my needs. The classic was easy to install and set up as well.

[weboughtabus]

I'm sure someone has asked this question before, but I perused a bunch of threads and tried to do a Google search, but I'm having a hard time finding a straight answer. How does powering 12V devices from solar work? Is there a way to have them powered directly off of the charge controller when the sun is shining and then draw off of the batteries when it's not? Is that something that the charge controller does automatically?

Originally Posted by Ninjakitty

I went with the midnite classic 200 as it fit my needs. The classic was easy to install and set up as well.

Fantastic! I think it was your recommendation that I check out the MidNite Classic calculator. I appreciate your recommendation and experience.

[john61ct]

Originally Posted by weboughtabus

How does powering 12V devices from solar work? Is there a way to have them powered directly off of the charge controller when the sun is shining and then draw off of the batteries when it's not? Is that something that the charge controller does automatically?

Yes but.

Yes any loads small enough to run from incoming watts do not touch the battery.

If the load draws more than input, then it also draws the battery down.

Only watts left over from loads' needs are going into charging the battery.

So for example if you run an aircon unit off your 1200W of panels, very little will go into recharging the bank.

All this is nothing to do with solar, just as true of generator, mains whatever sources.

[weboughtabus]

Originally Posted by john61ct

Yes but.

Yes any loads small enough to run from incoming watts do not touch the battery.

If the load draws more than input, then it also draws the battery down.

Only watts left over from loads' needs are going into charging the battery.

So for example if you run an aircon unit off your 1200W of panels, very little will go into recharging the bank.

All this is nothing to do with solar, just as true of generator, mains whatever sources.

Thank you. I'm not planning on installing an air conditioner right away, so my primary 12v loads (which would likely be intermittent) during the day will be a vent fan, phone charger and our water pump and then our fridge will be run off of the inverter.

[john61ct]

Actually the aircon bit was just a **very** extreme example.

Rarely practical, certainly not worth trying off batteries for most rigs.

Use a quiet genset, and even then pay more for high efficiency.

And insulate very well.

Even better do without.

[weboughtabus]

Originally Posted by john61ct

Actually the aircon bit was just a **very** extreme example.

Rarely practical, certainly not worth trying off batteries for most rigs.

Use a quiet genset, and even then pay more for high efficiency.

And insulate very well.

Even better do without.

Yeah, we're planning on rigid foam for the floor and a minimum of 2" spray foam on the ceiling and walls (2 windows deleted will also be sprayed). We're also planning on doing some insulated curtains for the side windows, at the very least.