Solar Power system for my Unimog expedition truck

[Iain_U1250]

I have decided to go 4 x 85W BP Solar Panels. Their dimensions are 354x1207mm - so the fit the sloping sides of the roof nicely and I'll have one either side of the skylight/hatch.

I have also decided on 4 x Optima 31T batteries 75AH - one for starting, and the other three for the "house" batteries. The main reason is that the Optima's are a tough battery, very suitable for off road / corrugations.

Now the big question is the solar regulator/charger. Combined, the 4 panels can just about push out 21Amps - I will have one side hinged so I can tilt them up if we are parked for a while to get max power. So I'm looking at a 20-30A solar regulator.

This is where my knowledge falls short - anyone got recommendations. Most of my systems on the truck are doubled up - so I always have redundancy. How reliable are solar regulators, should I be looking at running two?

 

[billwilson]

solar

solar:
i actually know alot from 1st hand experiance

being in Brisy, you will have a good bit of Mr. Sun, so you are good there

Some thoughts:
- tilting panels
one more thing to break
have to climb up rig to get to
added watts by tilting not worth it IMHO

- determine your usage
tv, radio, hair dryer :ylsmoke:, fridge
each thing will translate into wattage or amp hours
determine your full load per day
ex: tv requires X number of watts times 2 hours per day = X number watts per day

i caclualted mine for my rig to run for 3 days off batteries with NO sun
(hey, it DOES rain in California

i have 400 amp hours of AGM batteries
one 4d and two group 27 plus the starter batterie

i have two 180 watt kyocera panels
run thru a Blue sky controler with MMPT
MMPT is some vodoo that when the panels are spitting out juice, the MMPT amplifies the input
ex: if i have 5 coming in, i get about 8 going to batteries
not as good as a ice cold tinny on a hot day, but not bad

the panels run thru a controler to the battery
the controler has to be rated for the amout the panels put out
call or email the good folks at Blue Sky
thier specs were different than my local guys, i bought the right one

it is a bit confusing, read a bit and you will figure it out
dont rely on my opionon, get the facts yourself, you are going to spend some premium dollars, get it right

also check out www.affordable-solar.com, i bought stuff for two rigs from them
some great info on thier site

i am sure you have some local sources for the gear

pm me if you want some more info

bw

ps
send pictures from beyond the Black Stump

 

[Iain_U1250]

Thanks Bill - I had never heard of MMPT before, and it looks like the way to go instead of tilting the panels. It seems a good way of getting the most out of the panels.

I am now thinking of running 2 x Sunsaver MMPT regulators - one for each pair of panels in parallel, and running the two panels in series.

I have done all the calculation of load etc, and hence the need for the 4 x 85W and 300AH of battery. This will allow me to park up for 3 days as well. If I need more battery power, I will fit it later as I have a few spare spots on the truck.

 

[Steve F]

I'm in Sydney and run a single 24V 167W (46V Open circuit panel) panel with a MPPT controller from ebay, you can buy them here but 3 times the price. They are a lot cheaper than the sunsaver and you can also get an LCD display for them which tells you everything that is going on with your panel and the input into the battery.

I left my panel sitting flat at Easter, in average conditions the panel was only putting out 1.1A but at 36V which meant it was putting over 3A into the battery. The MPPT controllers work really well if there is a big voltage difference between panel and battery and will optimize the output for both, one reason I have a 24V panel.

Anyway, you can get the controller form ebay here

MPPT Regulator and display

Cheers
Steve

 

[Iain_U1250]

Thanks Steve - lucky for me I can get solar panels and regulars at "reasonable" prices. The Sunsaver MMPT 20A only costs me a bit more than the ones off e-bay. I will wire up the 12V panels in series to get 24V input to the MMPT for the reasons you describe.

 

[OptimaJim]

Iain, that sounds like a very cool project. One of the first things I learned about batteries when I started working for Optima is that the wiring order of batteries in banks of three or more should be rotated periodically (similar to rotating tires), to ensure even use and charging characteristics on all the batteries in the bank. When Reid Stowe used our BlueTops on his world record-setting voyage, he rotated several banks of three BlueTops during the 1,152 continuous days he was at sea. I look forward to seeing your finished project.

Jim McIlvaine
eCare Manager, OPTIMA Batteries, Inc.
www.facebook.com/optimabatteries

 

[dwh]

A few thoughts...

Not all MPPT charge controllers are equal. Many of the Chinese units sold on eBay are actually PWM units with an MPPT decal stuck on them. Those that are in fact MPPT, are not using the highly efficient proprietary algorithms developed by Morningstar, Xantrex, Outback, Midnite, Blue Sea, Steca, Rogue and others.

In the real world, MPPT is probably going to get a 10% overall improvement over PWM, which isn't a lot on a small mobile system. The big gains from MPPT come when the battery is low (bulk stage charging), but on a system designed to keep the battery up over 50%, the charge controller doesn't spend quite so much time in bulk stage.

The Morningstar Sunsavers can have a remote meter added to them. They can also have a remote battery temperature sensor. That RBTS is an important bit of kit, so the charge controller can adjust the charge voltage according to the battery temp. A quality PWM with RBTS will probably do a better job than a cheap MPPT without it.

I wouldn't say that using an MPPT instead of a PWM would be a replacement for tilting. The way you're mounting your panels, I'd still want to be able to raise them up so they lay flat so all 4 can get sun at the same time. Even better would be to make them go higher, so you could park north/south and have all panels tilted east in the morning and west in the afternoon. Or park east/west and have all panels tilted north.


A common misconception is that the bigger the difference in voltage between the PV and the battery, the greater the benefit of MPPT. It is true in a way, but not true in another way, which is why it's misleading.

Watts is watts. MPPT doesn't make more watts - all it does is maximize the watts that get into the battery by adjusting the voltage. In Steve's example, his PV was putting out 1a, and the MPPT was putting 3a into the battery. If his PV was the same watts but rigged to output a lower voltage, then instead of the charge controller seeing 1 in and 3 out, it might look more like 2 in and 3 out. If his PV put out twice the voltage, but the same watts, then it would look like .5 in, 3 out - which *looks like* a bigger benefit - but really isn't; the ultimate output is still only 3 since that's all the watts that the PV can produce.

I mention this because you talk of wiring your panels into two series strings. I imagine your reasoning is to maximize the voltage differential between PV and battery. If you do so, then yes - you'll see a better looking ratio on the meter, but it won't get any more watts into the battery.

If all you've got is 170w of PV, then there won't be more than that going into the battery no matter what. When there is a big voltage differential, such as say a 36v PV hooked to a 12v battery - there is a lot of wasted power due to the voltage differential. Even with a "12v" PV hooked to a "12v" battery (which is really more like a 16Vmp PV to a 14.4v battery), there is some wasted power. All MPPT really does is minimize the waste.

By rigging for a higher voltage on the input side of the MPPT, you are creating a larger differential, and so there is more waste to be eliminated - and so when the MPPT eliminates the waste, it *appears* to be a greater "gain". But there is no actual gain...170w is still only 170w.

As long as the PV voltage is higher than the battery voltage, then the MPPT is going to get the 170w into the battery in the most efficient manner - but it'll never be more than 170w. Doesn't matter if the input voltage is 16v or 160v - it's still going to be 170w at battery voltage on the output side.

Thus, it is not necessary to create a larger voltage differential by wiring the PV modules in series - all that is necessary is that the Vmp of the PV is higher than the battery voltage.


Rigging PV modules for a higher voltage can be beneficial in that a higher voltage allows the use of thinner wire between the PV module and the charge controller, and/or has less voltage drop on the same size wire. Of course, if you are trying to charge a 24v battery, and you have PV modules rated at 12v nominal, then you must wire them in series to get the voltage up above the battery voltage.

But rigging PV modules in series also has a serious drawback (cheezy pun intended), which becomes especially important on a mobile system; In a series string, if one PV module gets shaded (or partially shaded) it drops the voltage output of the entire string. If the modules are wired in parallel, then shading on one panel causes the voltage of that one panel to drop, but the unshaded panel is still putting out full voltage.

Partial shading is quite likely in a mobile system, so I personally would not wire modules in series on a camper unless there were some reason which required it, such as charging a higher voltage battery bank or because the PV modules were some oddball voltage.

Also, you mention redundancy. If the PV modules are rigged in series and one quits working - then the whole string is out of commission. If they are rigged in parallel and one quits - the other keeps working.

 

[Tony LEE]

if one PV module gets shaded (or partially shaded) it drops the voltage output of the entire string.

Which WILL happen on this rig most times whenever the front hatch is fully open

 

[Iain_U1250]

Thanks for the detailed replies guys - you are right about the reason for wiring them up each side in series was to increase the output voltage to help the MMPT. If wiring up in parallel will be better, then that's what I will do. I think some testing will be required.

I'll have the 4 PV's and the regulators here next week - I'll do some testing out the front of the shed and report back the differences of series/parallel - parts shade/angles etc.

I could make the PV panel system so that I can tilt them when parked up - not to much extra work.

 

[whatcharterboat]

being in Brisy, you will have a good bit of Mr. Sun, so you are good there

Iain......work on an average of 5.5 Peak Sun Hours around Brisbane. Google "PSH charts" and you'll find plenty online if you want any more accuracy. Kimberlies get the highest PSH in Oz...about 7.0 PSH if I remember correctly. PSH charts work on average amount of sunlight for a given latitude and also take into account the maximum cloudy days , rainfall, etc. for that location.

Also don't forget to take into account the efficiencies of everything in the system when you do your calculations especially the charge efficiency of the batteries. Ah in does not equal available ah out. Most batteries (good ones) are closer to .85% efficiency.

One more thing to watch is that with poly and especially mono crystalline panels you allow an air gap under the panel when mounting. They are both effected by high cell temps and with our high ambient temps here in Oz, it's a good idea to allow some cooling. BTW Amorphous panels are virtually unaffected by high cell temps so they can be stuck straight down on the roof.



DWH...excellent rap on regulators. BTW I was told at tech years back that MPPT's were originally designed for applications such as solar pumping were there is no battery at all and that in a normal power system such as we are talking about, the PV array voltage should always match (as close as possible) the system voltage rather than rely too heavily on a MPPT to bring it into line. Pretty much what you are thinking.

 

[dwh]

DWH...excellent rap on regulators.

Thanks. Having read many of your posts here concerning solar - coming from you, I consider that a high compliment indeed.

BTW I was told at tech years back that MPPT's were originally designed for applications such as solar pumping were there is no battery at all and that in a normal power system such as we are talking about, the PV array voltage should always match (as close as possible) the system voltage rather than rely too heavily on a MPPT to bring it into line. Pretty much what you are thinking.

Yea, originally to accommodate motor startup loads. Turned out to be quite useful for grid-tie systems as well. Expensive, but justifiable in certain situations. Finally they got the price down to where it became reasonable to use for small systems.

For large systems, rigging the array for higher voltage to reap the benefits of less voltage drop is the preferred way to go. The limit is whatever the max input voltage the MPPT unit can handle. It seems the trend these days is to build MPPT units with ever higher input voltage capability. Kicking up the array voltage and using smaller wire can save a lot of money on copper for a large rig.

But I don't see that it makes much difference on a little mobile solar rig - and surely not a big enough difference to overcome the shading drawback of a series array.

But that's just my opinion. And you know what they say about opinions...

 

[Iain_U1250]

Thanks John, I have over sized the array for our needs based on a relatively low PSH. I want to be able to stay in one place for 3 days with minimal sun. - if we need more solar panels, I will have plenty of space on the flat part of the roof, but that will reduce the "roof rack" space. The panels will have a 25-50mm air gap under them, so that should help a bit.

Regarding the regulator, I've been reading the Sunsaver MPPT manual, and it does not recommend running two regulators in parallel - so I will have to look at a single Tristar MMPT which can handle 45A. That give me a fair bit of extra capacity up my sleeve.

Is there any other brands available here that I should be looking at? Plasmatronics, STECA?

Iain......work on an average of 5.5 Peak Sun Hours around Brisbane. Google "PSH charts" and you'll find plenty online if you want any more accuracy. Kimberlies get the highest PSH in Oz...about 7.0 PSH if I remember correctly. PSH charts work on average amount of sunlight for a given latitude and also take into account the maximum cloudy days , rainfall, etc. for that location.

Also don't forget to take into account the efficiencies of everything in the system when you do your calculations especially the charge efficiency of the batteries. Ah in does not equal available ah out. Most batteries (good ones) are closer to .85% efficiency.

One more thing to watch is that with poly and especially mono crystalline panels you allow an air gap under the panel when mounting. They are both effected by high cell temps and with our high ambient temps here in Oz, it's a good idea to allow some cooling. BTW Amorphous panels are virtually unaffected by high cell temps so they can be stuck straight down on the roof.



DWH...excellent rap on regulators. BTW I was told at tech years back that MPPT's were originally designed for applications such as solar pumping were there is no battery at all and that in a normal power system such as we are talking about, the PV array voltage should always match (as close as possible) the system voltage rather than rely too heavily on a MPPT to bring it into line. Pretty much what you are thinking.

 

[whatcharterboat]

Is there any other brands available here that I should be looking at? Plasmatronics, STECA?

Hi Iain,

Yeah.....well the Tristar is defintely a quality reg but what are you doing for info display? I always like to see amps out quickly. Do you intend to use another battery monitoring unit like a Xantrax or a BEP or similar? Some of these battery monitoring units are really accurate at doing the Peukerts (bad spelling) equation to give you a state of charge expressed as a % based on ah in and ah out and the battery type. If you are going that way then sure....good choice but alot of coin.

The Plasmatronics PL regs with a shunt adaptor kit do well too and have the benefit of a full function LCD display and even a 30 day data logging history. I used to wire a lot of yachts that way (and most of our early motorhomes too) and didn't have too many problems. A tip with the PL's ... always throw in a catch diode across the load terminals if you use them. I did a 40' cat with a PL that kept seizing up .......disconnect power from it and it would be OK again but I realized that they didn't like any power spikes back into them from relays shutting down, etc. A simple catch diode fixed it any way. If you use a shunt adaptor kit it will be OK but still use the load terminals to hook up a warning light if the units go into "Low Volt Disconnect" mode......even though the actual load of course will still come straight off the battery through the shunt and not through the reg.

Actually I would recommend doing that no matter which reg you opt for. Easy to do ....just hook the load terminals through a relay so that if the unit goes into LVD a light comes on somewhere prominent. Most regs will LVD well before a fridge will (presuming you have a LVD function on your fridge).

Used to wire up plenty of the big Morningstar regs too. Very reliable in a mobile situation and all those early Phoenix caravans used them and they were the toughest things ever towed behind 4bie in the Australian bush. We did about 50 of those vans a year and don't ever remember a reg fault in the years I was there.

Afraid that I don't have alot of experience with too many other brands of regs other than these and the units that we use at work now. They are very simple units by comparison but extremely robust. I think I showed them to you when you dropped in to our stand at the Brisbane Camping Show last year.

At the end of the day , I guess you want to work out exactly what you need the reg to do and keep it as simple as possible. With out making this a War & Peace post ......think about what will happen if it fails. How will effect your travel plans? If the batteries have an alternative charge source then the solar reg may not be so critical. A lot of yachts carry spare regs but that's another story.

 

[dwh]

Regarding the regulator, I've been reading the Sunsaver MPPT manual, and it does not recommend running two regulators in parallel

This manual?

http://www.morningstarcorp.com/en/support/library/SSMPPT.IOM.EN.02.pdf

I don't see anywhere in that manual where it prohibits two regulators in parallel, except on page 29 where it says:

"Do not wire multiple SunSaver MPPT load outputs
together in parallel to power DC loads with a current
draw greater than 15A. Equal current sharing cannot
be guaranteed and an over-load condition will likely
occur on one or more controllers."

That refers to the load connections, which are to feed power to some device, such as a refrigerator. The load connections are protected by an internal LVD (low-voltage disconnect) which will disconnect the load before the battery is totally flat.

You cannot combine two load feeds (for instance to supply a 30a load). If you had two regulators, you could however supply two different 15a loads - such as powering a fridge from one and some fans and lights from the other.

The LVD protected load terminals are simply an added option for convenience. Nice to have, but you aren't required to use them.

But that's completely different than the battery connections.


In solar rigging, it's perfectly acceptable to have multiple charging systems to a single battery bank, such as an alternator, mains powered charger and a solar regulator. It's also acceptable to rig two solar regulators from two separate solar panels or arrays to the same battery bank.

The no-no is to rig two regulators being fed from a single solar panel or array. For instance if you have one solar panel and two different batteries such as engine and house, then you can't just tap two regulators off the single solar panel - you need a special regulator that can feed two batteries.


And actually - though this doesn't apply to your specific installation - it is permissible to use two Morningstar (dunno about others) regulators to charge two batteries from a single solar source (panel or array) IF blocking diodes are used to keep the regulators from backfeeding each other - as shown in this document from Morningstar:

http://www.morningstarcorp.com/en/support/library/ALL.APP.1_array_isolated_banks.01.EN.pdf

(Take that with a grain of salt - it's an older document and may not apply (likely doesn't) to MPPT units, but it certainly does apply to PWM units.)


I might also mention another random bit of info; There is some convincing anecdotal evidence that the pulsing of battery "desulfators" can interfere with the proper operation of MPPT units.