Have you been waiting for PV panels prices to drop?

[thatguitarguy]

I've been looking into this for awhile, and it seems it's about the controller. Without a good controller, you can quickly cook an expensive bank of batteries. You can't run an EV without a decent controller, can you?

I think the MPPT type are the way to go, but they are pricier.

[smokeyj]

These two components are not well matched.

The charger is a shunt type charger. The way this works is the charger absorbs excess panel power once the battery has reached full charge and dissipates it as heat.

That is a fine, simple technique that works OK if the battery voltage and the panel voltage are well matched.

In your case as I understand it, you have a 12V battery and a 60V panel.
So the panel and the battery have very different voltages.

If you look at the panel spec you see
Vopen circuit of 90V (no current flowing)
I short circuit of 1.2A (output terminals shorted)
and suggested operating point of 60V and 0.9A

Notice please that the panel puts out 0.9A at 60V and that current only increases to 1.2A into a dead short.

The panel is best thought of as a light dependent current source.

Your 12V battery is only going to charge at about 1.2A.
Well so what?
1.2A and 12V is 14W.

Net result is you will pay for a 60W panel and only obtain 14W of charge power, not so good.

Better would be to series two batteries to 24V and you will get about 30W of charge power into the battery.

Better yet would be to go for a panel with a lower output voltage of about 16V for your battery and the match will be darn good.

[Xringer]

I'm not so sure. If It charges a 12V battery at 5A, 12x5=60W, it would seem to be
the perfect match to a 60W PV panel.. Watt Wise anyways..

But, looking at the circuit diagram http://www.brightgreenenergy.co.uk/d..._EN%5B1%5D.pdf
I can't see how it's going to work with a high voltage panel, or any panel.. It looks like the fet T1 is shorting out the panel.?.

Maybe it was drawn by an artist, instead of an engineer.?.

Edit:
I just noticed the LVD function is only on the 6.6C model. Solar Cell, Solar Panel, Solar PV, Solar Products, Charge Controllers, Solar Trackers - Steca Solsum 6.6C 6A 12/24V Charge Controller With LVD

That Low Voltage Disconnect is a feature that I would want.. A extra couple of bucks? Yeah..

~~~

If these cheap chargers can't handle the HV of the K-60 module,
I would have to bite the bullet and get the MPPT250HV MPPT Charger.
The HV in the name means it can handle the K-60.
I think it might have been designed to use 2 K-60s. (It needs at least 68W).
http://www.bzproducts.net/sitebuilde...es/MPPT250.pdf

SOLAR PANELS: Ideally all of the solar panels in the system should be of the same type and power rating. The MPPT250 works equally well with mixed solar panels. The microprocessor control determines the operating point of the solar panels that produce the highest charge current to the battery.
See wiring diagram (last page) for solar panel wiring configurations. Maximum input power is 250 watts and minimum recommended input is 68 watts.

SOLAR PANEL VOLTAGE: The advanced microprocessor control of the MPPT250 allows a higher input voltage from the solar panels to charge a 12 volt battery. In many installations higher boost current over a greater operating range may be achieved by wiring the solar panels in series to produce a 24 volt PV input to the MPPT250. 100 volts maximum PV input voltage for model MPPT250HV. Nominal 12 volt solar input performs very well too. See wiring diagram (last page) for solar panel wiring configurations.

DO NOT EXCEED THE MAXIMUM SOLAR POWER OF 250 WATTS

[Ryland]

Originally Posted by brucey

Ahhh, that makes sense then. But then you have to buy a 120$ controller for a 100$ panel?

If you are buying a single panel then you can normally over size your battery so it's less likely to be over charged, or get a cheaper charge controller.
what are you going to do with a single panel in an off grid system?

[Xringer]

These chargers are 'smart' and shouldn't over-charge a battery, or let it get over-discharged.

I have a bunch of Ham stuff that uses 12VDC. And, every once in a while we need 12V for emergency lighting for a few hours.

If the outage goes on too long, I have a 5KW gas generator that can be used.

[smokeyj]

The FET will most likely be controlled to act not as a switch ie ON or OFF but as a variable resistor.

Its job is to absorb the excess power put out by the panel. So if the battery for its charging needs requires only 5W of power and the panel is putting out 14W the extra W will be absorbed by this FET and dissipated as heat.

This 60V panel is really intended to charge a 48V battery. In this case the panel and the load are well matched. This panel will only be able to put about 1.2A into a 12V battery which is about 14W of charge power.

If you read the panel spec it claims an short circuit current of 1.2A. No way no how will it put out 5A.

[Xringer]

Originally Posted by smokeyj

The FET will most likely be controlled to act not as a switch ie ON or OFF but as a variable resistor.

Its job is to absorb the excess power put out by the panel. So if the battery for its charging needs requires only 5W of power and the panel is putting out 14W the extra W will be absorbed by this FET and dissipated as heat.

This 60V panel is really intended to charge a 48V battery. In this case the panel and the load are well matched. This panel will only be able to put about 1.2A into a 12V battery which is about 14W of charge power.

If you read the panel spec it claims an short circuit current of 1.2A. No way no how will it put out 5A.

After looking it up, I see the light.

Pretty simple, and pretty wasteful IMHO.
Now, I'm starting to think the more expensive HV charger is the only one for these 60V panels.
I like all the neat features of the high dollar unit anyways.

[smokeyj]

It is not wasteful as it only shunts excess energy (that which would in fact damage the battery)

If the dump load instead of being a FET was say an element in a hot water tank then no waste at all.

I lost track of how much money you are plunking down on all this but the fancy chargers with MPPT (Maximum Power Point Tracking) features should extract more power from the panel.

If the panel and load are well matched like in this case a 48V battery and 60V panel the boost is maybe 10%. If the panel and load are mismatched like in your case the MPPT should get close to the 60W of charge power instead of 15W that you will see.

Is that worth the extra money??? You got to decide.

[Xringer]

Okay, what if I hang 4 of those 60W panels and just feed all the power into a 240 watt resistive heating element in my 76 gallon boiler?.

240 watts/h= 818.914 Btuh



I could epoxy a heater to the top of the boiler Under the sheet metal cover and cover it over with insulation. .
Build the heater using an 18 ohm resistor, clamped to an aluminum carrier.
18 OHM 225 WATT RESISTOR | AllElectronics.com

The panels would quickly pay for themselfs.. When heating oil hits $25 a gallon..


http://www.bfrl.nist.gov/863/pvsolar/pvwater/index.htm
"Solar Photovoltaic Hot Water System"

http://www.bfrl.nist.gov/863/pvsolar/fsec.html

[Ryland]

Originally Posted by Xringer

Okay, what if I hang 4 of those 60W panels and just feed all the power into a 240 watt resistive heating element in my 76 gallon boiler?.

That is why solar hot water panels tend to be cheaper, of course if you really are looking for a cheap dump load that you get the most bang for the buck out of, running your heat pump would be a good one, that heat pump could be as simple as a window a/c unit that cools your basement in the summer, or heats or cools a tank of water as water is a great way to store energy.