SolPad: Portable battery, inverter, solar panel combined

[EllPea in CA]

Hello,

I haven't been around in a while, so apologies if this has already been shared...

While expensive, it looks like the power provided via this portable panel far exceeds what we can cobble together with a solar array. See article here:

https://cleantechnica.com/2017/01/16...orage-product/

[Jon Vermilye]

Originally Posted by Ellpea in CA

Hello,

I haven't been around in a while, so apologies if this has already been shared...

While expensive, it looks like the power provided via this portable panel far exceeds what we can cobble together with a solar array. See article here:

https://cleantechnica.com/2017/01/16...orage-product/

Don't be fooled by the hype. A 600 watt hour battery is the equivalent of 50 amp hours when rated the way we rate our batteries, and they don't give the amp hour rate. Even if they are using the standard 20 hour rate, the battery is much smaller than what comes with most trailers.

If you have the space & can deal with the weight, a pair of 232 amp hour (2784 watt hour) Interstate 6V batteries at $150.00 each and a $250.00 Renogy 100 watt portable panel would provide far more power for far less. Even if you combine the Renogy panel with your stock battery you will cover most user's needs and still have a system larger than the one Solpad provides.

[Larry C Hanson]

Hello,

I agree that it is better to build your own system.... so much
more for so much less.... At 50% discharge of the battery
(65AH x 12 V = 700WH + ) you would have a more robust
system. However, a bit more solar capacity would be required
to fully charge the battery it you routinely used 50% of its
capacity.

Example:

$165 Cynergy 160 W panel Ebay
300 Bluesky Solar boost 2000E MPPT Controller / Box
200 Trojan SCS225 Deep Cycle 130AH Battery Series 31
250 Samlex 600W Sine Wave inverter
100 Misc wire and parts
------
$1015 Total
====

The above prices were found without too much shopping
around. Lower prices can be attained with patient shopping..
My system ran about $800.

I have been using a similar setup for years and it has never
failed to provide enough power for my boondocking unless the
sun is blocked for several days. I run basic trailer LED lights,
Computer, phone charging, ham radio, satellite radio, coffee grinder,
juicer, etc. My rig has no microwave and the refrig does not
have electronic control... Just a little ventilation fan that runs
constantly on warm day using about .4 Amps.

It is interesting to note that these self built systems can
provide more performance at a lower cost than the ready made
systems. If you can live without your system talking to your
smart phone you might be satisfied with one you build yourself.
Also, consider the educational opportunity building your own
charging system would provide...

Of course, if you can't or don't want to take the time and effort
to put together your own system, a ready made system might be
better if you can live live with the reduced performance and
greater cost.

Good Luck, Larry H

[LaFille1]

Originally Posted by Jon Vermilye

Don't be fooled by the hype. A 600 watt hour battery is the equivalent of 50 amp hours when rated the way we rate our batteries, and they don't give the amp hour rate. Even if they are using the standard 20 hour rate, the battery is much smaller than what comes with most trailers.

If you have the space & can deal with the weight, a pair of 232 amp hour (2784 watt hour) Interstate 6V batteries at $150.00 each and a $250.00 Renogy 100 watt portable panel would provide far more power for far less. Even if you combine the Renogy panel with your stock battery you will cover most user's needs and still have a system larger than the one Solpad provides.

I am trying to find a 100W Renogy portable solar panel...have looked low and high for one of those...to no avail. Not even directly through the Renogy website itself! They are saying (Renogy company) these portable (especially 100W) panels are "back order" and let me tell you there are NOT $250 each. The last 100W portable set I saw through Amazon for $399.00? Huuu
So, where should we go for a $250. Dollars Renogy 100W portable solar panel? You tell us.

[Larry C Hanson]

Hello,

I have had good luck with Cynerygy panels.... Here is a portable one.

https://www.solarblvd.com/product_in...oducts_id=2754

I use a 160W Cynergy panel with home made legs.

Renogy? Some 100W ones on Ebay for $300...

BTW... some panels come with built in controllers... I believe
that the controller should be near the battery as the controller
on the panel does not sense the correct battery voltage
because of the resistance of the wires between the panel/controller
and the battery.

Larry H

[gordon2]

$140 for 100 watts (Renogy and sans controller) but not very portable.. this is one of two panels I have.

The other panel I have is a flexible Chinese one that was $99 for 50 watts.. expensive but very light, portable and easy to handle. It seems to work fine as a short-term use portable panel, but if mounted flat on the roof I suspect it would die a premature death.

I am pretty sure that the two 50 watt panels in the Renogy suitcase need to be wired in series with their controller so that limits how you can reconfig them if you want to later.

For most Egg campers with solar, a MMPT controller is not a real advantage over a cheaper PWM one.

[Larry C Hanson]

Hello,

It can be agreed that PWM controllers are cheaper than MPPT
controllers. However, if one looks at what power one gets from
solar panels the MPPT wins hands down. If there is any cloud
cover or shading of the panel the MPPT is way more efficient.
It seems to me that a more efficient controller allows for
slightly smaller solar array saving money on that end.

Here is an interesting discussion comparing PWM and MPPT
controllers:

http://www.schams-solar.de/download/...n-mppt-pwm.pdf

I also favor movable panels instead of permanently mounted panels
as camping the shade beats having one's trailer in full sun for the
solar charging system to put out maximum power.

Larry H

[gordon2]

Originally Posted by Larry C Hanson

...

Here is an interesting discussion comparing PWM and MPPT
controllers:

http://www.schams-solar.de/download/...n-mppt-pwm.pdf

..

And here is another, copied from FAQ # C1 here:
Frequently Answered Questions - Bogart Engineering

C1. The debate rages: which controller is best PWM (Pulse Width Modulation) or MPPT (Maximum Power Point Tracking). Why did you choose PWM technology instead of MPPT for your SC-2030 Solar Charger? Click for answer

A very good question! They BOTH have good and bad. Plenty of hype has been written already. Here's my (Ralph's) view:

The "good" for PWM: It is simpler and lower cost technology. Under some common circumstances–it can actually deliver more amps to the battery. That could be when:
(1)days are moderate or warm, with few clouds.
(2) batteries are charging at over 13 volts, (in a 12 battery system) which they almost always are when actually CHARGING.
(3) Panel voltage is properly matched to the battery voltage, for example "12V" panels are being used with a 12V system.

PWM is actually more "power efficient" than MPPT–which means less total power loss in the controller itself. So heat sinks in the design can be smaller (and less expensive). Missing in most analysis of MPPT is that there is always a conversion loss with MPPT, which tends to be higher the greater the voltage difference between battery and panels. That's why PWM can actually beat MPPT under circumstances described above.

Some places that analyze MPPT assume that panels with 30V open circuit voltage are being used in a 12V system. Any good MPPT system will easily provide better performance in that case. They also may assume batteries are charging at 12 or even 11 volts, which is unrealistic. Lead acid batteries are typically below 13 volts only when discharging, or perhaps charging with very little charging current–meaning the actual potential gain in amps is not great.

The benefit for MPPT becomes apparent if you use panels not voltage matched for the battery. If they are not, MPPT will utilize more of the potential energy of the panels. For example, if you use 24 volt panels to charge a 12 volt battery system you must use MPPT, otherwise you would be using your panels very inefficiently. If you are trying to use PWM in that case, you are misusing the PWM technology.

Another potential benefit with MPPT is that if distance between panels and batteries is far, smaller wire can be utilized by running panels at higher voltage to the batteries. Running at twice the voltage reduces wire size to 1/4, which for a long run can be a significant saving in copper wire.

If temperatures are low enough, the slightly less power efficiency of MPPT will be compensated by the higher panel voltages, which will result in a little more battery current. But in actual measurements we made using a commonly sold MPPT solar controller, this would occur at temperatures less than 55 F degrees (in full sun, when charging at more than 13 volts), where there is a slight advantage to MPPT in my location (Boulder Creek, near the California coast). As temperature drops below that (in full sun) MPPT will get some advantage, such as could occur at high elevations in Colorado in the winter. Potentially this would be maximum about a 2.5% improvement in amps output for every 10 degrees F lower in temperature (or 4.6% per 10 degrees C colder. I'm using data from Kyocera KD-140 panels.)

There can be theoretically optimal situations (that I don't personally experience where I live) where MPPT could give some advantage: that is when solar current is present, but the batteries are quite low in charge–but because loads are high and even greater than the solar current the batteries are still discharging despite the solar current. Under these conditions the voltage COULD be at 12.5 volts, or even lower. Again, using data from Kyocera panels, ("Normal Operating Conditions") there is a theoretical maximum gain over PWM of 20% current assuming NO MPPT conversion loss and no voltage drop in the wires to the panels, at 20C (68F). With PWM, the voltage drop in the wires in this case would not affect the charging current. Now if in addition you lower the temperature to below freezing at 28 degrees F (while sun is shining) you might actually get up to a THEORETICAL nearly 30% gain while the batteries are discharging.

The only REALLY BAD part of MPPT, is all the hype surrounding it–for example one manufacturer advertises "UP TO 30% OR MORE" power harvested from you panels. If you are using solar panels properly matched to the batteries, 30% ain't gonna happen unless it's EXTREMELY cold. And your batteries have to be abnormally low in charging voltage–which tends not to happen when it's cold (unless you assume the battery is still discharging while solar is happening). Virtually all the analyses I've seen touting MPPT on the Internet ignore the conversion loss, assume really cold temperatures, assume unreasonably low charging voltages, assume no voltage drop in the wires from panels to batteries, use STC conditions for the panels (that the marketing types prefer) rather than more realistic NOCT conditions, and in some cases assume panels not voltage matched to the batteries.

The other thing that is misleading about MPPT, is that some manufacturers make meters that show both the solar current and the battery current. In almost all cases for a well designed MPPT type the battery current will be greater. The engineers making these know better, but it is implied (by marketing types?) that if you were NOT using MPPT you would be charging your batteries with only the SOLAR current that you read on their meters. That's not true, because the PWM BATTERY current should always be higher than the MPPT SOLAR current. It is the nature of the MPPT that maximum power occurs when the current is lower than the maximum, so they must operate there to get the maximum power. So to properly compare the two you need to compare MPPT with an actual PWM controller in the same circumstances.

Finally, the reason we went to PWM is that I was anticipating that panel prices were going to drop (which they certainly have over the last 5-10 years!) and that the small advantage of MPPT (under conditions where the correct panels are used for the batteries) would not justify their additional cost and complexity. So my thinking, for more total benefit per $, put your money in an extra panel rather than a more expensive and complex technology.

[Raz]

A few years ago we had a discussion of MPPT controllers. At that time I did a little reading. It was a good time to get information as it seemed every EE student was doing a MPPT controller as a senior project. Basically these units obtain the I vs V characteristic of the panel and attempt to set the operating point at the knee of the curve, which is the max. power point.

As solar input varies the characteristic, the controller attempts to keep up. Beyond the input circuitry the rest of the controller is a standard PWM charging circuit. Increases of up to 10% output are claimed.

For a megawatt solar installation this might be a worth while effort but to gain an extra 1/2 amp from a 100 watt panel??? And that's if it is doing what is claimed. How would you know?

I bought a Morningstar 6 amp PWM controller for my 60 watt panel. Works fine. How do I know? Because I periodically measure the charging current with my $10 multimeter. As long as the battery is charged by the end of the day, I really don't care how long it takes.

There is big money (much of it provided by the tax payers) in solar these days and lots of hype to go with it. Caveat Emptor