Solar questions

[Shawn & Ash]

So first off, I think it’s really cool that people offer their hard earned knowledge and time to people in the skoolie community. It’s really cool to be a part of!

Ok, I’ve done some research and I know that we want to have 1200 Watt solar panel array and 800 amp hour battery bank. We want to have a shore power Hook up and also have a connect to the alternator. Hooking it to a backup generator as well would be preferred considering we plan on frequent boondocking.

My first question arises from the Mppt charge controller. I gather we will need a 125 amp controller to allow for some wiggle room. Is this accurate? What’s the suggested brand? (I’ve heard Xantrax)

Also the Inverter/Charger. I believe we will need a 3000 Running Watt 6000 Surge watt inverter with auto switch considering our desired hookups and our wish to use a 6k OR 9k BTU a/c, an RV Fridge, outlets, DC hookups etc. is that an accurate size? What are the suggested brands?

Thanks so much. I hope I’m being specific enough!

[Ninjakitty]

We have 1400 watts (350w x 4 panels) connected 2 in series with each series in parallel. That runs to a Midnite Solar classic 200 mppt controller. This feeds our 800ah (4 x agm 200ah batteries in parallel) bank. Connected to that is an Aims 3000watt/9000 surge inverter charger with auto transfer and 120v pass through. That runs to our breaker panel for 120v items. Our 12 volt is fed from the battery bank from a fuse block.

We have a 30 amp inlet that runs to the inverter/charger. This allows us to plug into shore power and run our 120v items and charge batteries. We also have a 3400 watt champion duel fuel generator that runs on propane. If we are boondocking and need extra power (wash clothes, cloudy days, etc...) we can plug the generator into 30 amp inlet. It is basically a manual transfer switch. Very hard to mess up (can't plug in to shore and genny at same time that way).

Separately, we have a 15000 btu rooftop a/c unit that has it's own 20 amp inlet outside. This is set up so that by switching plugs, we can run the rooftop unit from genny or shore power (or from battery bank, but it's not a great idea to do so). (Right now, we are in North Dakota and stationary, so that 20 amp inlet is feeding a heater under the bed to keep batteries and water lines warm). I kept this system completely seperate with its own breaker box. I'll comment on appliances in a seperate reply.

[Ninjakitty]

We have a smart battery isolator but have not hooked it up yet. I'm not sure if it would work properly with agm house bank and fla bus bank.

Bus is ~27 ft interior from back door to windshield, exterior ~32 ft. It's a dognose.

We have a 12000 btu mini split (cl and mate right) on the back wall above the back door. It does a decent job of cooling the bus. The back does great but out back area isn't super open so some extra fans help move the cold air upfront.

We run a 120 volt magic chef fridge that is 9.4 cubic feet with a bottom freezer. Sticker says max draw is 1.5 amps. Ive never put the kilowatt meter on it, but it seems to work fine. It probably should have its own smaller inverter and breaker off the battery bank so we don't lose as much power leaving the inverter on all the time.

Hope some of this helps.

[Ninjakitty]

Also, this tool may help for your solar controller.

http://www.midnitesolar.com/sizingTool/

[john61ct]

Victron makes great gear in both categories, with optional centralized management / monitoring / logging everything together as a system.

Or just over BT with your phone. Excellent adjustability.

Magnum also is great for inverter / charger, higher end lines anyway.

Solar specialists also include Morningstar, Blue Sky, Midnight & Outback

[JDOnTheGo]

Originally Posted by Shawn & Ash

My first question arises from the Mppt charge controller. I gather we will need a 125 amp controller to allow for some wiggle room. Is this accurate? What’s the suggested brand?

I'm guessing that you are planning a 12V battery bank. That matters as it can relate to the amount of 'power' that the charge controller (CC) will pass. I.e 50 amps at 14 volts is a lot different than 50 amps at 24 volts. If true, you may find it less costly to go with multiple CC's vs one large one. Regardless, That 1200 watt array will probably produce something closer to 1000 in actual use (peak) so a 75 amp CC would probably be fine (1000 watt / 13.5v = 74 amps). So, 125 amps would seem to be a bit oversize. Nothing wrong with that and it is common to allow the addition of more panels down the road.

Name brand CC's are worth the extra cost. There are a handful of pretty good ones.

Originally Posted by Shawn & Ash

Also the Inverter/Charger. I believe we will need a 3000 Running Watt 6000 Surge watt inverter with auto switch considering our desired hookups and our wish to use a 6k OR 9k BTU a/c, an RV Fridge, outlets, DC hookups etc. is that an accurate size?

It's impossible to say if that is sufficient without knowing the actual current draw of these devices and which will be running simultaneously (energy budget). Air conditioning from battery is always a challenge so hopefully the goal is not to run it all night.

You can go with an inverter with internal switching or get an standalone transfer switch. The best option depends on your system design and personal preference.

[john61ct]

Yes more than 1-2 hours of aircon, plan on running a genset while off grid, no point in buying a huge battery bank just for a little time shifting.

Not saying it can't be done with tons of money, just that it isn't very practical IMO.

[Shawn & Ash]

That’s all great info thanks!

Depending on cost we hope to do 100 amp CC. The ability to expand is nice.

We went with the larger battery bank because they will be AGM and we would cut amp hour usage in half right? To prolong battery life?

[Shawn & Ash]

Is it stressful on the other components? To have a larger battery bank?

[john61ct]

Originally Posted by Shawn & Ash

Depending on cost we hope to do 100 amp CC. The ability to expand is nice.

That is Starter battery units there.

You need proper deep cycling batteries, capacity is measured in Ah "amp hour".

FLA is much better value than decent AGM.

The best battery value by far is Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH @12V pair from BatteriesPlus or Sam's Club. Deka labeled same batts also sold at Lowes.

Can't go cheaper without throwing your money away, you want the bank to last at least 4-5 years, and yes shallower cycling, avg DoD kept ~50% is needed for that, plus other care factors.

No "stress" from a bigger bank, but need a bigger charger to get back to 100% within 6-7 hours.

I would start with at least three pair with the loads you're talking about.

Do a proper energy budget, Ah per day @12V to try to reduce that.

[Shawn & Ash]

Originally Posted by Ninjakitty

Separately, we have a 15000 btu rooftop a/c unit that has it's own 20 amp inlet outside. This is set up so that by switching plugs, we can run the rooftop unit from genny or shore power (or from battery bank, but it's not a great idea to do so). (Right now, we are in North Dakota and stationary, so that 20 amp inlet is feeding a heater under the bed to keep batteries and water lines warm). I kept this system completely seperate with its own breaker box. I'll comment on appliances in a seperate reply.

When you say “kept completely separate” do you mean off of a totally different inverter? Or can there be two separate breakers boxes off of the same inverter. Do you have to buy an inverter with these specific capabilities? Or would it be wired similarly to a shore hookup?

[Shawn & Ash]

I’m coming up with questions that I’m sure have been answered but I’m struggling to find a definite answer. I’ve attempted my “energy budget” numerous times and I’m trying to comprehend actually how much everything runs a day.

Fridge in total is 400 Watts (AC+DC) How much power does it actually use during the day. I know it depends on the temps outside but what’s a rough estimate?

The 12v water pump I’ve also seen mixed answers. It’s about 16 Watts. How many hours a day does it run?

Do laptops themselves use power is it just the Wattage on the power charging plug to be considered?

ALSO. What’s the recommenced genset to have on deck for a 10 or 12k BTU AC Unit?

[Ninjakitty]

Originally Posted by Shawn & Ash

When you say “kept completely separate” do you mean off of a totally different inverter? Or can there be two separate breakers boxes off of the same inverter. Do you have to buy an inverter with these specific capabilities? Or would it be wired similarly to a shore hookup?

By separate, I mean its not wired to my main breaker panel, but to its own 20 amp breaker in a small breaker box. Out of the 20 amp breaker box is 10 ga wire with a 20 amp plug. I did this so I could manually switch the roof air between generator, shore power, or inverter (although, I don't plug into the inverter anymore, but I could).

I have two 20 amp outlets. One oulet runs to a 20 amp shore power hook up (20 amp plug-in inlet).

The other outlet runs to my generator. This outlet has 10ga wire to a 20 amp plug to plug into the generator.

If i need to, I can plug into shore power and plug the a/c into that outlet. Or, I can plug into the generator and plug the a/c into that outlet.

This way, I can choose where I'm getting power from. It also allows me to plug my rv into the generator if need be.

[john61ct]

Originally Posted by Shawn & Ash

I’ve attempted my “energy budget” numerous times and I’m trying to comprehend actually how much everything runs a day.

Fridge in total is 400 Watts (AC+DC) How much power does it actually use during the day. I know it depends on the temps outside but what’s a rough estimate?

Also depends how cold you set the thermostat, ventilating the hot bits, added insulation how often opening, added contents pre-chilled, kept how full. . .

Roughly? Between 15Ah and 60Ah per day.

Really you need a 12Vdc coulometer measuring to get a closer number, ideally in real world conditions.

The nameplate mfg ratings mean nothing.


> The 12v water pump I’ve also seen mixed answers. It’s about 16 Watts. How many hours a day does it run?

That will depend on you.



> Do laptops themselves use power is it just the Wattage on the power charging plug to be considered?

Same again, useless, need to actually measure. An addicted gamer or professional graphics / video guy (YouTuber) might use 150Ah per day, someone doing email light web browsing under 15Ah.


> What’s the recommenced genset to have on deck for a 10 or 12k BTU AC Unit?

With an EasyStart a single Honda EU2200i might be enough if you pay for one very energy efficient.

e.g even a Webasto 16,000 btu unit

Companion version in parallel will help with noise & longevity, maybe don't need the soft start.

[JDOnTheGo]

Originally Posted by Shawn & Ash

I’m coming up with questions that I’m sure have been answered but I’m struggling to find a definite answer. I’ve attempted my “energy budget” numerous times and I’m trying to comprehend actually how much everything runs a day.

No doubt, it can be very difficult without some actual RV type experience. Hang in there!

Originally Posted by Shawn & Ash

Fridge in total is 400 Watts (AC+DC) How much power does it actually use during the day. I know it depends on the temps outside but what’s a rough estimate?

Yes, depends on many factors (duty cycle). Does it have one of the typical "Energy Star" labels on it? If so, it will list it's expected annual power use (400kWh or something like that). In my one experience (Samsung refrigerator/freezer), I found that number to be reasonably accurate. You can divide it out to month or day as needed. No, it won't be precise but it is something based on data which is always better than a guess.

Originally Posted by Shawn & Ash

The 12v water pump I’ve also seen mixed answers. It’s about 16 Watts. How many hours a day does it run?

16 watts seems low to me. The ones I've had seem to pull about 60 watts (5 amps @ 12VDC). Run time varies wildly. I'd guess that mine runs a minimum of 2 minutes a day up to maybe 10 minutes?? I have an accumulator though so the pump doesn't have to run every time I crack a faucet open. The big water consumer is typically the shower. If you have several people that don't know how to take Navy showers, it may run an hour every day. Hard to know.

Originally Posted by Shawn & Ash

Do laptops themselves use power is it just the Wattage on the power charging plug to be considered?

I did some research on this a while back. My results are here. In general, a laptop is always consuming power when plugged in. How much varies with the state of its battery.

Originally Posted by Shawn & Ash

ALSO. What’s the recommenced genset to have on deck for a 10 or 12k BTU AC Unit?

The roof mount RV style A/C and heat pump units in the 13.5k-15k btu range generally draw around 1500-1600 watts running and have a rather high "Locked Rotor Amps" rating (of 60-40 amps). I'm not certain about the 10-21k but units but probably slightly less. As far as I am aware, they are all 120VAC. So, that means the pull about 15 amps @ 120VAC when running (1600 watts / 120VAC). The larger problem is the startup power - that is the locked rotor amps thing. It is only momentary but if trying to run from an inverter or noise maker (generator), it has to be sized to handle the load. However; there are some "soft start" accessories to help with this. Note that there are some differences between hi and low as well as outside conditions (how hard it has to work to cool the air).

[Shawn & Ash]

Thank for all the great info.

This is sort of off the rails but I’m trying to understand the difference between watt hours and amp hours. If I have 400 amp hour battery bank (lithium batteries) and 1200
Watt solar array. Let’s say we have four 300 Watt panels. How long will it take to charge my batteries if the panels are taking in as much power as possible. I’m sure it depends on the panel and the amount of volts they generate. I’m bringing it to 12 Volts through the Mppt.

Does this mean I have 400ahs to consider for my “energy budget?” (I know on a very sunny day in Florida the batteries could be charging while running appliances aswell) But for those foggy days when we need to conserve.

If there are any recommended links please post!
I’ve done my research but the clarification is comforting from the knowledgeable people 🙏🏼

[PNW_Steve]

Originally Posted by Shawn & Ash

Thank for all the great info.

This is sort of off the rails but I’m trying to understand the difference between watt hours and amp hours. If I have 400 amp hour battery bank (lithium batteries) and 1200
Watt solar array. Let’s say we have four 300 Watt panels.

It's as easy as P=I*E

Power in watts is equal to current in amps times voltage in, you guessed it, volts.

If you have a 12 volt battery and place a load on it that draws 2 amps then you are consuming 24 watts. If you operate the load for 1 hour then you have consumed 24 watt/hours.

Given that you are drawing 2 amps from the battery, if you operate the load for 1 hour you will have consumed 2 amp/hours from the battery.

[john61ct]

Watt hours are consistent and comparable when there are different voltages involved.

Whereas Ah are the best unit for measuring storage capacity and usage over time, but you need to know the voltage involved.

If your 400Ah LFP bank is 12V (4S), then that 1200W panelage will be able to completely recharge it in one day in good insolation conditions, even with some loads concurrently running.

[JDOnTheGo]

Adding to what Steve and John have already said....

The output of your solar array varies by location, time of year, and weather. One day you may be in the sunny southwest with excellent insolation, long days (many hours of sunshine), and cloudless skies. Your array will charge your battery bank by 10 am and you will wonder why you have such a large array. The next day you may be in the northeast with lousy insolation, short days, and clouds. Your array will struggle to fully charge your battery bank before the sun sets. You will wonder why you didn't install a larger solar array. Of course, there are dozens of variations with clouds, trees/shade, etc.

Ideally, your battery bank would be sized to allow you to live normally from battery power alone for your target number of days. You get to define what all those things are/mean. Some of us want hot coffee, computer, microwave, etc... regardless of sun or rain - for 3-4 days. Others are happy to have less/something else. Based on all that, you size your battery bank. So, if you energy budget has you consuming 200Ah per day and you want to exist three days before having to plug in/start the noise maker, you need 600Ah of usable power. For a FLA battery bank, that is about 1200Ah in size and about 700Ah for lithium (assuming everything in good condition).

The thing that then often occurs is that one realizes they cannot afford that size battery bank and/or cannot fit that size solar array. So, you begin making compromises. Compromises are totally fine and absolutely necessary. IMO, it is far better to have a 'small' solar/battery setup that does what you need 80% of the time but have to fire up the noise maker if it is thick overcast two days in a row. (I say that having camped near people that have ONLY a noise maker for power - listening to that thing for six hours every day would drive me insane.)

Depending on your goals, about all you can do is construct a system that matches either your expected conditions OR your budget($$) OR the space you have available (array and battery bank). My goal was to live exclusively from solar - mostly because I strongly dislike noise and I have never heard a generator that didn't make lots of it (never mind smell, vibration, and cost). That's just me though - everyone get's to pick their own goal.

Originally Posted by Shawn & Ash

If I have 400 amp hour battery bank (lithium batteries) and 1200 Watt solar array.

Assuming clean, flat mounted, and a good solar insolation; that 1200 watt array could produce something around 960 watts (80% - my observed number). Assuming it is a long summer day, it may produce 'near' that amount of power for 6 hours per day. However; as the sun rises and falls, it will produce power but it will ramp up/down. Lets' go with just 6 hours to keep it simple. So, over 6 hours, it will produce 5760 watts. If that is going into a 12V battery bank at 13.8 volts, we get a total output of about 417 amps. Of course, it will only do this if there is somewhere for the power to go. When the bank stops accepting all that power, the charge controller/array throttle back. If during this time, you fire up your microwave, the charge controller will see the demand and throttle back up (until the demand decreases). It is during this period that you do what you can to use this 'free but soon to be wasted power'. Some people turn their freezer way down (lower temp) during this period (so it runs less when back to running on battery power), others turn on their electric water heater, charge laptop, etc.

I'm not sure if all that rambling answers your question but hopefully it helps a bit.

[Shawn & Ash]

Im unsure on what breaker box i need to install for my solar setup.

Ill have 3 15 amp circuits but id like to have the capability to add at least one more. When i go to home depot i see models that are 200 bucks all the way down to like 40.

I have determined that ill need around a 75 amp breaker box but im not sure exactly what i'm looking for. Im sure an electrician could answer this but i figured id see if anyone had a link to one they have used on a similar system.