Buying Solar NOW

sasquatters · July 2017

Hello everyone,

We posted here a few months ago and never really got the advise we needed. We ended up calling a professional and he recommended a 24v system for our school bus conversion. After we thought about it some more, we decided that we HAVE to go 12v so that we can charge the batteries when we are driving since the panels will be on slide outs underneath the roof top deck and will only get sun when we are stopped and camp is setup.

I called the company again and they said that we can use 24v panels on a 12v system and get the full wattage from the panels because the MPPT controller can handle such a thing. Is this true? We are taking the bus on Friday to get the deck put on and I NEED to know what panels we are going to get since they will be welding the slide outs during the installation. I don't want to tell him measurements for panel X when they actually won't work and we needed to use panel Y.

I have been trying to put this off for as long as I could but this project needs to start moving again. I want to purchase the items we need without going through the company because they quoted us $1100 for 4 240w panels and I found them used online for $100 a piece used. Even new they were around $200 a piece. They wanted $4,500 for the whole system but said they would install it if I bought all the stuff for much less. I am more of a hands on learner so I need to purchase these items and mess with them a bit to fully grasp all of this. I go to school for environmental science and unfortunately there are no classes on solar or geothermal which is the whole reason I applied.

This is the charge controller I was thinking of buying.
This is the inverter I was thinking of buying.
These are the panels we are considering but they say off-grid and we don't know if they will work for 12v.

Thank you! Fast help greatly appreciated.

www.sasquatters.com

Estragon · July 2017

So fast, yes you can use a 24v panel in a 12v system with an mppt controller. Will have to look at the links.

Usually we start with loads. If a professional is recommending 24v, that suggests larger loads.

Estragon · July 2017

Again, with the caveat that we don't know anything about loads or batteries, 60a charge controller may be undersized.

westbranch · July 2017

yes those panels will work to charge 12 V batteries, by using an MPPT charge controller, but they will not work on a 24 v setup unless they are used 2 in SERIES, NOT PARALLEL. Reason is that the panel voltage is too low to charge a 24v battery, it has to be around 35 Volts.... Please do some reading on other MPPT charge controllers, to become familiar with the benefits of other makes, I am not familiar with the Renogy line at all... our sponsor carries a full line of reliable CC's and inverters, check out the store link at the top... just my experience talking.

sasquatters · July 2017

Loads will be low. We just want a lot of overhead. The biggest load will be our refrigerator. We plan to use a portable AC unit too but this will likely be run off of a generator. The professional is an Amish guy. Most people know Amish and electricity don't go hand in hand. At the same time they run their barns and shops off of solar only so.. :shrug: He is also a business man possibly trying to make the biggest system he can in the smallest amount of space.

So should we get the biggest wattage panels we can for the space we have? Why go 245w when we could go 315w if they all work for 12v systems. Right?

Again, thanks for the help. It's crunch time and I'm really feeling it.

Lumisol · July 2017

Yes it's true. I have 85volt panels and a 48 volt system.

sasquatters · July 2017

Thank you for the reply. I've never heard of 84v panels. Just out of pure curiosity, would 84v panels also work on a 12v system? Or am I being trolled? haha thanks again.

littleharbor2 · July 2017

The better MPPT controllers will take up to 150 Voc. The 85 volt panels above will work although they couldn't be series wired so multiple panels would need to run through a fused combiner box While the controller you have listed will accept up to 150 Voc. It can be had for considerably less than the price shown.

One advantage to using the 60 cell panels you referred to, over 72 cell, is that you can run 3 panels in series without over voltage into this controller. Also they, being a foot shorter than 72 cell panels, might fit better on your roof space. Maybe not.

The specs given for the refer show .712 Kwh. in controlled conditions. (no door opening?).You can buy an efficient energy star rated Full size refer that will rival those numbers, will cost much less and have a decent amount of usable space. 6 cubic feet is terribly small.

Vic · July 2017

Hi sas..,

Personally, would be suspect of that particular Charge Controller (CC). While Renogy is not necessarily a bad brand, that CC has NO safety agency Listing, and there appears to not even be a manual available for that product. Furthermore, it is not inexpensive. AND, there appears to be an error in the Maximum amount of Solar input on a 12 V system. This CC appears to be a new product, and might not even be shipping yet.

Here is an example of a top-notch CC -- the MidNite Classic:
https://www.solar-electric.com/mnclassic.html

For RVs, you might want to be a bit more selective in choosing your CC, as most CCs use a relay, and some, like the Classic has fans, so noise made from these, would either affect where the CC is placed, or exactly which CC you would want to choose.

A fridge is not normally a small load.

For RVs, 12 V systems are often convenient. But for medium-sized systems, 24 V may be better, overall.

BUT, how would anyone know even the best system voltage, without more info about all of your loads? The design of a system needs to flow from data on what it needs to do, and the expectations/needs of the users of that system.

Rushing a system design often has disappointing results, as one may need to live with the consequences of inadequate data on loads for some years. Designing systems for RVs can be a bit more complex than stationary systems, so they often require considerably more time to get a that is correctly sized, fit into the available spaces.

As has been stated above, s l o w ing down may pay dividends in the future, if you are able to figure out more about your loads on the system.

Just more opinions, Vic

sasquatters · July 2017

I've spent months look for refrigerators that will fit the height of the bus. We would really like to find a bottom freezer unit and that one I listed is the best we came up with. We will have a refrigerator, a 32" Samsung LED tv, some LED lights, and a water pump. That's about it. We have to go 12v because as I stated, we won't be able to charge by the panels while driving since they will be under the deck. If you think that charge controller is a better option I will go that route.

Vic · July 2017

sas,

OK on the need for 12 V. CCs are usually rated on the maximum output current. When the system voltage is doubled, generally the amount of power that the CC can produce will also be doubled. Good MPPT CCs are expensive, so needing more than one CC can be expensive. Also, inverters that operate on 24 and 48 V, are generally more efficient, and 12 V systems need larger cables, for the same level of power, so just something to keep in mind.

If the noise from fans in a CC might be a problem, the Morningstar MPPT series of CCs might be better. Believe that most of these CCs probably do not use a mechanical relay. Often there is a bit of relay clicking around the beginning and end of the day. This can annoy some, if the CC is in the living space.

Here is a Link to one
https://www.solar-electric.com/motr60ampmps.html Morningstar CC:

It is possible that this discussion should be moved to the RV/Caravan topic, as perhaps many members here that have done RV systems might not look in the Off Grid topic, ...

FWIW, Good Luck, Vic

Vic · July 2017

In Post #57 in the following Discussion, sasquatters does mention some numbers, assume that the individual numbers are probably for the proposed RV system:
http://forum.solar-electric.com/discussion/351459/building-a-skoolie#latest

FWIW, Vic

sasquatters · July 2017

Thank you. We will have a "garage" area in the rear of the bus but this will be right behind our heads as the other side is the bed. Here is a photo. You can see the bed in the rear and the solar components hopefully will be behind that in the back right (of the photo) corner.

Dave Angelini · July 2017

I really did not look at your refrigerator but it looked like it might be hard to support if you get a failure (Chinese?). Here is something else you could consider. These probably would not be easy to get parts in a failure but they they are German built and I have been using them for my clients for 12 years and none have even had a hiccup. In other words they don't fail.
https://thesolarstore.com/steca-pf166-solar-refrigerator-or-freezer-12v-or-24v-dc-58cf-p-95.html
If you could fit one it can make enough ice to keep a cooler cold for a refrigerator. One of my clients uses this to drive 200 mile to costco and keeps the Fish/Meat down low and the top does not run long enough to freeze the non freeze items.

Lumisol · July 2017

I personally do not like midnite and would definately go with Morningstar instead for your charge controller. Some say midnite is fine, I disagree with that assessment.

littleharbor2 · July 2017

Lumisol said:

I personally do not like midnite and would definately go with Morningstar instead for your charge controller. Some say midnite is fine, I disagree with that assessment.

Your tirade on Midnite Solar is still fresh in some of our memories. Your problems with their combiner boxes were well documented. So now you have a dislike with their whole line if products?
Opinions are like, you know what's, and everybody has one. You are definitely in the minority here though.

jonr · July 2017

I'd look into adding a second, 24V or 48V alternator to the bus.

sasquatters · July 2017

We have looked at freezers to use as refrigerators and that is just not an option. We want to have a nice tiny home, not a hunting cabin. Why do you recommend adding another alternator jonr? I imagine our giant diesel engine's alternator is sufficient.

mcgivor · July 2017

The suggestion to add a second alternatoris is probably to enable the use of a 24V or 48V nominal system rather than the less desirable 12V.

sasquatters · July 2017

Our bus's engine is basically underneath the front and any mechanical work of those types of buses gets expensive fast.

Photowhit · July 2017

I had a long post that appears lost in the ether...

Several things. Of course...lol.

While you are looking at a nice tiny home, what you have is a bus, I would embrace it rather than dismiss it! Looks like you intend to keep the windows, you won't have much insulation. When you look at a generator, look for small quiet ones. It will be difficult to air condition, even parked in the shade. Perhaps insulating blinds would be in order. You will be at opposition with your self. With a poorly insulated home it will be hard to air condition if left in the sun, but your solar will not work at all in the shade. Something to keep in mind.

It would be nice to be able to charge when driving and higher voltage systems tend to make more sense. Along with the mobile and poor insulating aspects of a bus I would not recommend the Midnite Classic due to fan noise. I own 3 of them, they live in their own power center away from the house. (Midnite has been very reliable and trustworthy company) If attached you will hear them! Morningstar makes a reliable MPPT charge controller that will handle 60amps (as Vic suggested). If you go to 315 watt panels you would likely need 2 of them on a 12 volt system. Another reason 24 volt systems work out better, Charge controllers are based on the output amps. At 12 volts with a 1260 watts of array works out to about {(1260x.75derating for NOCT) ÷ 12} = 78.75 amps. I believe Magnum makes a 100 amp MPPT type charge controller that is rated at 100 amps. It is also air cooled I believe. I have never used them. I just checked it does have internal fans.

I don't have anything against the Renogy 60A Commander, just no experience with it and knowing the Morningstar is reliable would suggest it instead. Really not much cost difference. Understand that this works for the 240 watt panels on the margin, but would not work for 315 watt panels.

https://www.solar-electric.com/motr60ampmps.html

A point of reference, It appears that the refrigerator you have suggested was rated with no door openings. Doors are opened in energy start ratings 24 times. I can't recall the ambient temps, but their ratings would look favorable to them without the door openings. So when you are comparing fridges, you might keep that in mind.

I suspect you will have some other loads, laptop(s), wifi, Phone charger, music, fans (O2cool makes a nice low power 10 inch, I have 2 running now) Guess you will heat water, cook, and heat with propane?

Panels should be angle toward the sun in general, you will lose some efficiency with flat mounted panels. Some solar isolation calculators will allow you to take that into account.

Looks like an interesting adventure! Have fun.

mcgivor · July 2017

An inverter charger may be a good to have, that way shore power or generator, could be used to supplement the solar if needed, some/all?, allow for pass through of AC~ to support loads, they cost a little more than a reasonable quality inverter, but have a built in charger and results in a tidy installation, with a matching charge controller some can communicate with each other giving better control and monitoring capabilities.
https://www.solar-electric.com/catalogsearch/result/?q=inverter+charger

sasquatters · July 2017

I hate writing long posts that mysteriously disappear. I find myself copying my posts before I submit them on several forums.

We do plan on keeping the windows. The reason we wanted a bus was to have a bus. Several people sheet metal over them and add new windows. While that is cool, it no longer looks like a bus. Plus the light is wonderful. Despite that, our bus actually stays decently cool in the shade. We have 3.5" of spray foam insulation in the walls, and 2.5" of insulation in the roof, and the roof will also have a deck over that so the air will flow between to keep it cool as well as shade the roof. We do plan on using insulating/blackout curtains and so far we think we will be fine in that area.

Thank you Photowhit for the advice on the Midnight controller. Not sure if you saw our photo but the "garage" solar area will be right behind out heads and we do not want to hear a loud fan running all the time! I think we are going to stay around 215-245w panels due to size since they will be sliding in and out and with the roof hatches there are size restrictions for width. If you could explain your calculation better ( {(1260x.75derating for NOCT) ÷ 12} = 78.75 amps.) I would really appreciate it just for the knowledge. I am pretty sure we will be around 940w or so.

Thank you for the information about door opening on refrigerators. I never knew that. Seems to be hidden from consumers? We certainly do not open the refrigerator 24 times a day. We were looking at a very nice bottom freezer unit but it was 434kwh/yr and apparently that is quite high. We then found the one I posted above which is also a bottom freezer unit. After more and more consideration and people telling us to look elsewhere, I guess we will probably be going with a more efficient smaller unit with a top freezer. Not sure why the bottom freezer units are not as efficient as the top freezer unites.

We will be heating water with an on demand propane unit as well a cooking with propane but we will be heating with a wood stove made for boats. Our thoughts behind this are propane is a wet heat and we will likely have condensation with out single pane bus windows. The wood stove should keep the air dry enough that we do not have water pouring off the 16 windows.

We we going to have each side of the bus's solar panels on their own tilt mounts but we were informed that they will only draw in as much as the lowest panels is without having two charge controllers.

I have never heard of an inverter/charger but we are very new to this. Anything we can combine into a single unit to save space sounds great. We really want a fully automate system other than having to potentially plug in a 50amp service.

Thank you all for your help. This is obviously a huge investment so please keep the information coming! Truly appreciated.

Photowhit · July 2017

sasquatters said:

If you could explain your calculation better ( {(1260x.75derating for NOCT) ÷ 12} = 78.75 amps.) I would really appreciate it just for the knowledge. I am pretty sure we will be around 940w or so.

Solar panels are rated at what is called STC - Standard Test Conditions. In thin manner all have a basic exposure for a short amount of time and measured. The amount of light is higher than typical and the panels are not allowed to warm up. Panels produce less voltage and to some degree less current when warm. There is often another set of number call NOCT - Normal Operating Cell Temperature values which are much more representative of the normal out put of panels well angled to the sun. (Something that is often hard to do with an RV.) These NOCT values are typically 75% of the panel rating.

As an example you say you will have 940 watts of panels or @ 4 235 watt panels. I found a site that has published the NOCT values for a 235 watt Canadian Solar panel CS6P-235P similar to those you linked to;

http://www.solarsystems-usa.net/solarpanels/canadiansolar/cs6p-235p/

This is what they say the panel will produce normally.

So under normal conditions the panel will produce about 174 watts or 174÷235= 74% of the panel rating.

sasquatters said:

We we going to have each side of the bus's solar panels on their own tilt mounts but we were informed that they will only draw in as much as the lowest panels is without having two charge controllers.

This is bad information, if I'm understand you correctly. It takes very little light for the panels to produce voltage, if you have the panels on one side on their own string, the other side, if not in the sun, will not reduce the output of the side in the sun. They just won't add to the current (amperage) It might create some little confusion for the MPPT charge controller, but it shouldn't be a problem. If the panels on both sides were in a single string, it would create a problem. That would be a string with 1 or more panels in the sun and 1 or more panels in the shade. In fact I would run separate strings for each side and you should be fine.

sasquatters said:
I have never heard of an inverter/charger but we are very new to this. Anything we can combine into a single unit to save space sounds great. We really want a fully automate system other than having to potentially plug in a 50amp service.

Most high end inverters are also charger when connected to "Shore power" or a generator. In fact the one you linked to is!
Samlex EVO-2212 2200 Watt 12 VDC Pure Sine Wave "Inverter/Charger"

It won't replace you charge controller but will charge from a generator...

littleharbor2 · July 2017

If you are concerned about how much power you will get from 235 watt panels keep in mind you can get wattages up to and above 300 watts in 60 cell panels exactly the same size as 235 watt panels.

fratermus · July 2017

westbranch said:

yes those panels will work to charge 12 V batteries, by using an MPPT charge controller, but they will not work on a 24 v setup unless they are used 2 in SERIES, NOT PARALLEL. Reason is that the panel voltage is too low to charge a 24v battery, it has to be around 35 Volts.

I don't understand. Nominal 24v panels won't charge 24v batteries? Why are nominal 12v panels able to charge 12v batts?

A spot check of several 24v PV shows Vmp in the 35-36v range. Maybe I am missing something.

mcgivor · July 2017

240W panels would more than likely be 60 cell panels which are not recommended to charge a 24V nominal system with a PWM controller, because the voltage output, VMP is considered too low at ~30v, as the panels get hot this voltage may drop below the requirements needed to charge ~29v. So with an MPPT the panels could charge a 12V nominal system because the voltage is high enough, but for a 24V nominal system 2 panels, or more in series, depending on the controller, would be required to keep the voltage sufficiently high enough to allow the controller to track the maximum power point. It's a common mistake to assume 60 cell panels are good for 24V nominal with PWM, but they are not, a 72 cell panel is a true 24V nominal panel, just like a 36 cell is a 12V nominal panel. The 60 cell panels were primarily used in grid tied systems, but became popular with MPPT users due to the lower cost of the panels, lower cost was due to the larger demand of grid tied over off grid. Hope this explains it to some degree.

sasquatters · July 2017

When I stated

"We we going to have each side of the bus's solar panels on their own tilt mounts but we were informed that they will only draw in as much as the lowest panels is without having two charge controllers. "

I meant that we were told that if the panels on one side of the bus are drawing 100w, the panels on the other side, even though they may be getting more sun, will not charge above the lower 100w side. This is why we were told we needed two charge controllers. One per side. We really want to get an inverter/charger with an auto generator on function. If anyone is local to the Hagerstown MD or Harrisburg PA area we would really love for you to come out.

fratermus · July 2017

mcgivor said:

It's a common mistake to assume 60 cell panels are good for 24V nominal with PWM, but they are not, a 72 cell panel is a true 24V nominal panel, just like a 36 cell is a 12V nominal panel. The 60 cell panels were primarily used in grid tied systems, but became popular with MPPT users due to the lower cost of the panels, lower cost was due to the larger demand of grid tied over off grid. Hope this explains it to some degree.

Very well explained; I appreciate it.

sasquatters · July 2017

Big Update!

Bought 4 of these Canadian Solar 255w CS6P-255P panels yesterday and they were delivered today. We are dropping the bus off tomorrow morning to get the deck put on the roof, taking a little vacation, and then picking the bus up and installing the solar panels on their slide outs. The next step will be to figure out the rest of the electrical and pick out a charge controller and inverter/charger.

More opinions and videos are very helpful!

sasquatters · September 2017

We have been doing more reading about setting up our panels in the coming weeks. Most recently we found out that, like batteries, you can wire solar panels in series or parallel. What is recommended for 255w 24v panels? We will be running them on a 12v system (when we figure out how) so that we may charge while we are driving since the panels will be hidden during that time.

Buying Solar NOW

Comments

Categories