Topping up 48v system using solar panels?

[grjfield]

I have a 48 volt electric propulsion system. 8 - 6 volt Crowns in series (235 AmH). I charge them using 2 24 volt chargers, each charger managing 4 of the 8 batteries. (Works great)

Once fully charged, I thought it might be safer (and greener) when I am away to unplug the chargers and hook up a few solar panels to maintain the batteries at 100%.

First question... does this make sense?

Second, since the solar panels are rated for 12 volt,
do I need to set up 4 (say 20 W)panels, each managing 2 - 6 volt batteries,
or can I set up 1 (say 100W) panel ...connected to only 1 set of 2 - 6 volt batteries?

If I use the 100W option, will the other 6 - 6 volt batteries also receive a topping charge as well, once the 2 - 6 volt solar connected batteries are topped up?

(I presume solar panels cannot be connected in series to produce a 48 v charge.)

Thanks.
Gerard

[Paul Elliott]

You can connect lower-voltage solar panels to some charge controllers that can boost the charging voltage for a 48V battery bank. This is probably your best bet. Here is an example: Genasun GV-Boost 105-350W Solar Boost Charge Controller with MPPTGenasun

With very few exceptions you do not want to connect panels to batteries without using a charge-controller.

What you call your "100W option" will not charge the other batteries, and will certainly cause problems.

[senormechanico]

Solar panels connected in series add the voltage while current stays the same.

The above assumes similar panels and no shadowing.

Panels connected in parallel adds current, but voltage stays the same.

[grjfield]

I will look into the Genasun GV-Boost 105-350W Solar Boost Charge Controller with MPPT. Sounds like a good product and can be connected for 48 V.

I have 4- 40W panels and 1 100W panel.
Am I better off hooking up 4 -40W in series to get 48V, or hook all 5 panels up in parallel to increase amps and have the controller raise the voltage to 48 volts to match the system?
Thanks
Gerard

[Paul Elliott]

You might be able to parallel all the panels, but they need to be well-matched in voltage characteristics. We would have to know more about your 40W and 100W panels to tell if this would work.

Putting your four 40W panels in parallel and connecting that array to the 48V boost controller would be my suggestion, or putting them in series (see below).

Putting the batteries in series would let you use smaller wires since the current will be less than in the parallel case. If you put the four 40W panels in series you would need a "buck" controller set for a 48V battery bank. Here is one from Morningstar: Morningstar ProStar PS-15M-48V Charge Controller - Wholesale Solar

This is a "PWM" controller, so not as efficient as the MPPT one I linked to before. I think it's cheaper though. For maintaining your batteries the lower efficiency probably isn't a big deal. There are probably MPPT 48V controllers out there as well. I don't know it the Morningstar controller is a quality product, perhaps someone else can comment, or suggest an alternative.

[Electric Ray]

Originally Posted by grjfield

I have a 48 volt electric propulsion system. 8 - 6 volt Crowns in series (235 AmH). I charge them using 2 24 volt chargers, each charger managing 4 of the 8 batteries. (Works great)

Once fully charged, I thought it might be safer (and greener) when I am away to unplug the chargers and hook up a few solar panels to maintain the batteries at 100%.

First question... does this make sense?

Yes Absolutely! Put up as many panels as you can afford/have room for and you may never need a genset again. We have 3500W of solar at home and NEVER use the genset for a 5 bedroom house with everymod con, our normal house battery is 1000Ah at 48v of Lead Acid (13 years old and still going strong) but at the moment we are running the whole house off a 400AH LiFeYPo4 Bank

Originally Posted by grjfield

Second, since the solar panels are rated for 12 volt,
do I need to set up 4 (say 20 W)panels, each managing 2 - 6 volt batteries,
or can I set up 1 (say 100W) panel ...connected to only 1 set of 2 - 6 volt batteries?

If I use the 100W option, will the other 6 - 6 volt batteries also receive a topping charge as well, once the 2 - 6 volt solar connected batteries are topped up?

(I presume solar panels cannot be connected in series to produce a 48 v charge.)

Thanks.
Gerard

Solar Panels can be connected in series or Paralell, in just the same way batteries can to achieve the same results

Just get a 48v MMPT and string at least 65v volts (or whatever the MPPT classes as the minimum solar voltage) together in series. Forget PWM controllers as they are no where near as efficient as MPPT controllers. We use a Victron MPPT 150/70 which means max 150 Volts (solar)/70 Amps(Battery). We have 3 type/sizes of panels in series/parallel strings, the MPPT handles the differences and chooses the optimum voltage for that moment in time.

[Fog Bank]

If looking for a 48v MPPT option, you might see if Rogue has any 3048's remaining in stock. It was discontinued, but is a quality built unit.

[finnarne]

I have a Genasun boost controller connected to my 48 volt battery bank. Now for the winter, I have only one old 20watt solar panel connected to keep the batteries topped up. The batteries installed in my boat now is old and varies in size, but it does the job now for the winter. I will replace both the batteries with 4 new equal batteries, and 3x30watt solar panels connected in parallel.

I also have a 5kw 48 volt EP-system.

I'm now looking at a way to charge one 12 volt battery from the 48 volt bank, to keep my charging as simple as possible. That way, I can connect everything that runs on 12 volt to this single battery (or maybe later a battery bank).

My 20 watt solar panel manages to keep my bank at 50.4volt or better now during the winter, even if there is only a few hours of sun (if there are sun at all...)

But it's not that much electricity used now.

[Electric Ray]

Try to keep your systems as simple as possible. There are various low power DC to DC converters available, essentially you want one that will happily do the 48v-12v conversion and a small 12v regulator to do the charge regulation if you need a 12v battery for higher intermittent loads like a 12v winch.

The DC converters are available in various sizes up to at least 240W output (20A at 12v) this is more than enough for most house loads.

[socaldmax]

I think all of the better quality MPPT charge controllers (Rogue, Morningstar, Victron, Midnite Solar, Apollo, Outback) are capable of charging 48 volt battery banks. As mentioned above, you need to connect the panels in series so that your PV voltage is above 65v or so.

I wouldn't bother with a bunch of smaller panels, anything under 100w is worth the labor to screw it in. Solar panels aren't really 12v or 24v, their MPPT V is usually 18v, 29v, 37v, 65v etc depending on how many cells are in the panel. All of the quality controllers mentioned above can accept PV input voltage of up to 150v. A recent system I installed for a customer used 4 panels totalling 1120w and pumping up to 92A (46A per controller, 2 controllers) into his system, it's now his main source of power.

If you shop around, you can often find 230 -300w panels for as low as 60 cents per watt. Install 4 of them where you were going to install the 5 much lower power panels and enjoy the benefits of up to 1200 watts of free power keeping everything charged all of the time. Just connect each pair of panels in a series string then connect each string to a 45 or 60 amp MPPT controller. Considering how cheap the panels and controllers are these days, it's a pretty small investment by normal boat standards.

[grjfield]

I went with the recommendation and picked up a
Genasun GV-Boost 105-350W Solar Boost Charge Controller with MPPT from Bluesky.
(48 volt model- rated for up to 8 amps)

I have 4 - 40W panels. I was told hooking up 4 panels in parallel would hit about 9 amps...too high for the Genasun. And 4 panels in series would produce about 68 volts - again too high apparently for the Genasun.

When I spoke to the salesperson at Bluesky he suggested I should hook up 3 40W panels in parallel as it would give me 17 volts @ approx 7 amps ~~ about 117 watts.
Is there any reason why this would be preferred over 3 - 40W panels in series giving 51 volts @ approx 2.3 amps...for again about ~~ 117 watts.

Or better still... why not go with 2 sets of 2 - 40W panels in series...each set giving 34 volts @ 2.3 amps, then connect the sets in parallel, yielding 34 volts @ approx 4.6 amps ~~ 156 Watts.

And regardless of which configuration, should there be breakers in the wiring anywhere?

I'm not an electrician so I could use some sage advice.

Would anyone care to comment on the best way to go. (I also have 1 100W panel, but figured I start with common panels until I know what I'm doing.)

Thanks
Gerard

[Dsanduril]

Originally Posted by grjfield

Or better still... why not go with 2 sets of 2 - 40W panels in series...each set giving 34 volts @ 2.3 amps, then connect the sets in parallel, yielding 34 volts @ approx 4.6 amps ~~ 156 Watts.

This one. Stays within the 8A input limit and maximizes the use of your existing stock of panels.

Only caveat, each string should have similar sun exposure to get maximum benefit (but if it is just for maintenance then not such a big deal). If one string is shaded while the other is not the MPPT controller will have a hard time getting the best out of things.

[Electric Ray]

Originally Posted by Dsanduril

This one. Stays within the 8A input limit and maximizes the use of your existing stock of panels.

Only caveat, each string should have similar sun exposure to get maximum benefit (but if it is just for maintenance then not such a big deal). If one string is shaded while the other is not the MPPT controller will have a hard time getting the best out of things.

Ageed,

This configuration will stay under the maximum PV voltage of 43v of the Genasun whilst halving the current, for such a small array a simple in line fuse rated for the cable but above the MPPT max (say 10A) between the panels and the MPPT would protect from short circuits (not that they would be damaging). There should be a fuse rated for the load and or cabling between the battery and the busbar to protect the battery and cabling from shorts, It would normal to have a fused or breaker protected switch panel between the busbar and the associated circuits assuming you have a few:-)

[socaldmax]

Originally Posted by grjfield

I went with the recommendation and picked up a
Genasun GV-Boost 105-350W Solar Boost Charge Controller with MPPT from Bluesky.
(48 volt model- rated for up to 8 amps)

I have 4 - 40W panels. I was told hooking up 4 panels in parallel would hit about 9 amps...too high for the Genasun. And 4 panels in series would produce about 68 volts - again too high apparently for the Genasun.

When I spoke to the salesperson at Bluesky he suggested I should hook up 3 40W panels in parallel as it would give me 17 volts @ approx 7 amps ~~ about 117 watts.
Is there any reason why this would be preferred over 3 - 40W panels in series giving 51 volts @ approx 2.3 amps...for again about ~~ 117 watts.

Or better still... why not go with 2 sets of 2 - 40W panels in series...each set giving 34 volts @ 2.3 amps, then connect the sets in parallel, yielding 34 volts @ approx 4.6 amps ~~ 156 Watts.

And regardless of which configuration, should there be breakers in the wiring anywhere?

I'm not an electrician so I could use some sage advice.

Would anyone care to comment on the best way to go. (I also have 1 100W panel, but figured I start with common panels until I know what I'm doing.)

Thanks
Gerard

I'm not sure I see what the problem is. It's a 350w controller, and you're only connecting 160w of panels, so...

it doesn't look to me like you're exceeding any current limit. 8A @ 57.6v = 460.8 watts max. output. So you're about 300 watts short of blowing it up. LOL You will never see 160w out of the panels, even under perfect conditions. Depending on your proximity to the equator, TOD, which month it is, you'll see the sun lower in the sky with a corresponding lower panel output.

I also agree that connecting the panels 2x2 is the best configuration. I'm not a fan of low power panels, I prefer 230w - 300w+, but if 4 x 40w will do what you need, then by all means.

Don't skimp on the cable size, and keep the runs as short as possible to minimize voltage drop (power loss.)

[Dsanduril]

Originally Posted by socaldmax

it doesn't look to me like you're exceeding any current limit. 8A @ 57.6v = 460.8 watts max. output. So you're about 300 watts short of blowing it up.

Because it is a boost MPPT controller rather than the typical buck controller the GVB has a maximum rated input current. You can put in 8A at 13V to get 105W, or you can put in 8A at 44V to get 350W, but the boost controller requires that you limit input current, even if you are within the Watt rating of the unit.