FAQ:Solar Panel without the Technical Stuff

[John61CT]

There is no way such an SoC meter can be accurate.

But for the price you get maybe a decent ballpark guesstimate, and that's certainly better than nothing.

For people familiar enough with their setup, used to guessing via voltage or hydrometer, likely will be an improvement.

[Socal Tom]

The original goal of this thread was to take the technical details out of the discussion, I think we broke that goal. I posted the 18$ meter because knowing your electricity usage is helpful for determining if you even need solar , and how much you need if you do. I consider $18 a cheap investment, now we are looking at stuff that costs $120. ... not really in line for folks that may not need solar.


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[absolutsnwbrdr]

Victron SmartSolar MPPT solar charge controllers have built-in Bluetooth that can be monitored with a Smartphone ap, VictronConnect.

Prices at Amazon.com are $129.95 (as of 12/04/2017) for a Victron SmartSolar Charge Controller with Built-in Bluetooth - MPPT 75/15 that will work with a 12 volt solar panel up to 220 watts.

VictronConnect is the Smartphone ap used to get instant data, a 30 day history, and to change settings of a Victron MPPT charge controller.

Just bought a Victron SmartSolar 100/20 MPPT for my Scotty build! I can't wait to hook it up to some 12V and try it out! I'll have it hooked up to two 120W flexible panels, which should take care of me pretty well. It'll be interesting to see how it handles my camping trips compared to my Morningstar PWM charge controller.

Speaking of....



For a quality charge controller with no configuration and zero frills, I'd highly recommend a Morninstar Sunsaver 20. I think they are less than $100 these days. Paired with a cheap r/c power meter, you can't go wrong. Install it and forget it. I had this setup in my X-Cubed, with two 100W panels. Worked great!

You don't have to spend $200+ for a charge controller, but you will absolutely be disappointed with a $10.99 ebay special, and you may end up burning down your camper. If you're going to delve into solar, be prepared to spend a few dollars on something that has a proven track record, and that will last you a few years.

The whole point of this thread was keeping it simple. Watch your voltage, and don't waste your power. This doesn't have to be rocket science. We don't need to open up the batteries to test the chemistry to make sure the state of charge was measused after 24857 minutes of resting, with an ambient temperature of 68.936-71.36 degrees fahrenheit. Yes, power in vs power out will give you a much better idea of whats going on with your system, but is unnecessary in such simple systems. There's one guy on this forum that swears you have to spend $2324893.45 on a 10' camper. "Oh you MUST have this, and you HAVE to buy that, otherwise I won't camp in the same state as you." He'd probably criticize buying a $200 Victron charge controller just because there was another company that has one that costs four times as much. The phrase more money than brains comes to mind.

Anyway... dive in with a simple setup first, continue to do your research, and expand when you're ready. And Bruce's information in the first post is still very pertinent stuff.

Here's my Morningstar SS-20 and my $15 power meter in the galley of the X-Cubed...

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And my simple voltage meter in the headboard...

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[bdosborn]

MPPT controllers are cool and to quote the guys on Big Bang theory "everything's better with bluetooth!". But I'd pass on an MPPT controller; they're generally so expensive that the $/watt for the extra power they deliver is way higher than what additional panel capacity would cost. For a small system like a teardrop, PWM controllers with larger PV panels is going to deliver the best bang for the buck.

Bruce

[John61CT]

Victron 75/15 is a very cost-effective MPPT at ~$100, but yes BT is extra.

Match with a higher-voltage panel 200-250W in size, maybe 300W if very cheap, and that's a lot of bang for the buck.

[John61CT]

If people are talking about those $30 SCs from China on eBay or included with a kit, of course that's different, and maybe "good enough" for some.

[Esteban]

MPPT controllers are cool and to quote the guys on Big Bang theory "everything's better with bluetooth!". But I'd pass on an MPPT controller; they're generally so expensive that the $/watt for the extra power they deliver is way higher than what additional panel capacity would cost. For a small system like a teardrop, PWM controllers with larger PV panels is going to deliver the best bang for the buck.

Bruce

MPPT charge controllers have come down in price enough to be a worthy choice for many of us. They're worth buying when you're well informed about what works best for your wants, needs, budget, available space on the roof, or storage space for portable solar panels.

Roof space on most teardrops is very limited. Few have enough space for mounting more than one solar panel. Or for a large high power solar panel.

I think it's very worthwhile to pay the small difference to use a MPPT controller instead of a lower cost PWM controller. A MPPT controller will harvest ~10 to 30% more power from solar panels. It makes more efficient use of the limited roof space. Having more available power enables you to camp or travel more comfortably and enjoyably. You can save money by having less, or no, need for camp $ites with electric hookups, which often cost extra.

A few years ago a Morningstar Sunsaver 15 AMP Solar Charge Controller was the most affordable good quality MPPT controller available. Today (12/05/2017) the Morningstar Sunsaver MPPT costs $243.00 from Northern Arizona Wind & Sun.

Much more affordable MPPT controllers are now available. For example: Victron's Blue Solar controllers (without built-in Bluetooth) start at $80.90. Victron's SmartSolar controllers (with built-in Bluetooth) start at $119.95. genasun.com controllers start at $65.00.

AM Solar does high quality RV solar installations. Their DIY Instructions diagrams and videos are helpful and very informative. amsolar.com sells both the Victron and Genasun brands of MPPT solar controllers.

You might choose to buy a Renogy 100 watt 12 volt starter kit with a PWM controller for a teardrop that currently costs $180.99 from Amazon.com.

Instead you could buy a 100 watt panel for $106.99, a Victron BlueSolar MPPT 75/10 Charge Controller for $80.90, mounting brackets for $9.59, and a pair of 10 guage cables with MC4 connectors for $21.98. Total cost $219.46.

The $38.47 cost difference is minimal between the two example 100 watt kits. With careful shopping the cost difference might be lower.

I bought a 160 watt solar panel to mount on my teardrop's roof to have enough power to operate the lights, recharge a cell phone or other electronic devices, and use an AC/DC fridge/freezer. I'll most likely buy a Victron SmartSolar 75/15A MPPT controller which works with up to 220 watts of 12 volt solar panels.

[John61CT]

+1 to all that

Just note you won't actually get any MPPT performance improvement until voltage goes way higher than that of nominal 13V panels.

Choose the SC and its panel to match each other to get the most out of both.

The little 75/15 at under $100 is great to do 1:1, best partial shade optimization.

I believe ~40V, up to say 65 max in that case.

Don't just settle for what's available on Amazon, there are 100's of great better value panels out there, maybe some within driving distance, it's the shipping that kills pricing.

[bdosborn]

Roof space on a teardrop is very limited. Few have enough space for mounting more than one solar panel or for a large high power solar panel.

I think it's very worthwhile to pay the small difference to use a MPPT controller instead of a lower cost PWM controller. A MPPT controller will harvest ~10 to 30% more power from solar panels. It makes more efficient use of limited space on the roof.

That's were I think MPPT isn't the bargain that I thought it would be. I run two arrays through two different controllers, one an MPPT and one a PWM, and both Sunsavers. The two arrays are similar in size but I haven't noticed much difference in performance between the two controllers - more like 10% better with the MPPT controller and usually in cooler weather. Jump on to some of the Solar forums and you'll see similar performance numbers. So if the MPPT controller is around 10%-20% more expensive than a similar capacity PWM, the performance gain merits the additional cost. Otherwise, you're better off buying a bigger panel to get more capacity instead of an MPPT controller. UNLESS, you're running a panel with a voltage higher than 12V. In that case, it's a no brainer, the MPPT is going to support double the panel capacity at 24V over a 12V PWM. So you're right, careful selection is best when selecting components but I still think PWM is going to be the cheapest $/watt for a small, simple 12v system.

Bruce

[Esteban]

I bought a Grape Solar 160 watt solar panel. The pdf specs show it has a 18.5 Vmpp V and an Open Circuit Voltage of 22.2 V. That should work well with a MPPT solar controller. It's 58" long by 26" wide. I changed my plans to build my teardrop 64" wide to make the solar panel fit on the roof with drill-free glue on solar panel mounts.

Grape Solar now sells a 180 watt panel that is the same size as a 160 watt panel. Its Vmpp is shown to be 19.67 V with an Open Circuit Voltage of 24.06 V. If I hadn't already bought the 160 watt panel I'd be a little tempted to buy a 180 watt one instead.

Home Depot sells Grape Solar 180 watt panels and others too. Sometimes their Special Buys are very competitive. If you do a store pick up there is no additional shipping cost.

[John61CT]

All of those are "12V nominal" panels, have to be over 18V even with PWM

Where you see bigger gains from MPPT is with "nominal 24V" panels, double the volt specs you're referring to, and higher, as with panels designed for "grid-tied" home systems.

Since occasionally conditions can drive volts higher than Voc, best to leave some headroom, so for the 75/15 Victron, I wouldn't go over 65Voc.

And while you *can* put panels in series to multiply voltages, that's usually not as good as one big one for handling partial shading issues.

[Socal Tom]

Walmart now sell renology 100w panels for under 100$. I’ve got two 50 w panels, and a 20$ PWM controller. Last trip I used about 200 watt hours of power before my panels started working. By about noon the battery was back up to full voltage. My panels are in a a foldable configuration. I wouldn’t have seen any benefit from an MPPT controller, unless I use more power.
Tom


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[bdosborn]

Anyone who has gone to a solar forum or an RV forum knows there are a lot of different ways to skin this cat and some of the discussions can get prickly. That was the point of this post originally; give some direction to the guy who wants to use solar panels without having to spend hours doing research. You shouldn't have to know how to build a watch to tell time.

Bruce

[John61CT]

Yes, absolutely right, MPPT adds nothing to that setup.

And true many people don't want to learn unless they perceive a real need to do so.

[absolutsnwbrdr]

.... some of the discussions can get prickly....

Who you callin a prick?



I'll admit that the only reason I spent a few extra $$ for the Victron SmartSolar, was for the Bluetooth feature. Because gadgets are cool.

It was a 20A controller, and I paid $156 for it. Yup, could have saved $60 and bought another Sunsaver-20. But I've been there, done that. Time to play with something new.