Simple Solar For A Simpleton

[Ex-Calif]

Originally Posted by VirtualVagabond

It's a tempting idea. It would be easier.
But I do like to try to get my head around this stuff if possible though, because if something goes pear shaped in the Pacific Islands I just may be able to find solutions... particularly if I can get onto the forum here and tap into the wisdom of the gurus

Most boat mechanics and electrics is about being able to put puzzles together using instructions. Not having the instructions is a real limiter. As is not having the right tools.

Troubleshooting requires experience, a methodical mind at problem solving and instructions can also help here.

Collecting the right tools allows you to do maybe 90% of the jobs on board. The tools required for injector and lift pump overhaul and most machining jobs are usually prohibitive for the average boater.

[tartansail]

Controller question: This thread resonates since I feel like a simpleton as well. Despite the cost, we're leaning towards zipping two 100 or 125 watt Solbian panels into our bimini. The reduced weight, no need to fabricate a frame and ease of mounting/removal are compelling. Bruce Schwab has been selling these with Genasun controllers which make sense for the smaller panels. However, with either 100 or 125 watt panels, the voltage shouldn't need to be boosted so the controller choice seems less certain.

I went over to HandyBob's site and read the battery charging puzzle. The RV Battery Charging Puzzle « HandyBob's Blog I came away with a headache and thinking that, with Lead acid batteries, it would be good to be able to run an absorption voltage of 14.8 volts. The Genasun MPPT isn't adjustable and runs absorption at 14.4 volts. Over at Morningstar, the Tristar PWM and MPPT are both adjustable up to 14.8. However, the MPPT is pricey. (Genasun MPPT and Tristar PWM are similarly priced. Tristar MPPT is more than double.) Questions:

1. Bob makes sense about the value of high voltage absorption, but is the difference between 14.4 and 14.8 as meaningful as he makes it out to be in real life?
2. How useful is MPPT with 100-125 watt panels in parallel? Is there a downside to just going with the PWM controller?
3. I've been planning to wire the panels separately since I expect there are times one or the other is shaded by the mast and keeping them separate will reduce the risk of losing all power that might occur with them in series. (The boat is on a mooring in season and will usually face into the prevailing SSW wind.) An alternative would be to wire in series, bumping the voltage so that there would be less voltage drop and then use a single Morningstar MPPT 45 to control the load. What are the pros and cons of those options?

All I'm really certain about is that HandyBob made my head hurt, but that solar on the bimini will make life aboard better.
Thanks for insights.

[noelex 77]

It is important to realise that we are talking about the last 10% of efficiency.
The difference between an absorption voltage of 14.4 and 14.8 is not great. I prefer to have adjustable absorption points, but this is generally only available in more expensive regulators. Gensun will custom set the absorption points for a small extra cost, but this is not subsequently adjustable. Trojan recommend high absorption voltages, but other battery manufacturers advise lower limits.

I like to go with the battery makers recommendations. When using high voltages make sure there is some temperature compensation.

Rogue make a very good controller with user adjustable set points that is worth considering at this size. The MPPT tracking of the Rogue is as good, or slightly better than the Gensun.

A non MPPT regulator will not give up much power. This is especially true of the slightly lower voltages of the Soliban 100 and 125w panels, but given the cost of the panels a MPPT is probably justified, but get a good MPPT regulator, or go for a more simple non MPPT regulator.

There is a lot of debate between series and parallel conection of panels like this and there is no clear cut answer.

[Dsanduril]

TartanSail,

Unfortunately, you can't believe everything you read on the internet , including here. HandyBob has some interesting information, but it has to be taken with a grain of salt. In particular, his comments on voltage. One item is quoted here:

VOLTS, VOLTS, VOLTS!! Also, the amps pushed into a battery at a higher voltage contain more power than those at a lower voltage. Remember, volts times amps equals watts, so amps pushed at 10% higher volts give you 10% more watts.

That's his major argument for increasing the voltage, and it's just wrong. Here's why. Amps is a measure of how many electrons are moving past a point (6.24x10^18 electrons/second is one Amp). Doesn't matter how much you increase the voltage, the number of electrons is measured in Amps.

The voltage tells you how energetic those electrons are. The higher the voltage the more energetic they are. So, you say, that jibes with Bob's theory. Batteries, in their simplest sense, store electrons. If you put in 10 electrons you can only take out 10. If you put them in with more energy they don't magically multiply so that you can put in 10 and take out 11. What really happens is you make the battery warm (by reversing the chemical reaction that occurs when you take out the electrons).

So, you put electrons in at 13.8 to 14.4 volts, and you take them out at 12.2 to 12.6 volts (typical LA battery voltages). That works out to about 15% power loss, which ties in with the industry standard of 85% round-trip efficiency in charging LA batteries. The rest is lost to heating the batteries, and you simply can't get it back, it's gone.

There is something to be said for higher voltages when running equipment. If you can run equipment (fridge, radio, whatever) at that charging voltage they can make use of the greater energy, their current draw drops. In addition, they don't lose 15% to going into and then coming out of the battery. Always a good idea to time your highest electrical usage to the time when the solar panels are putting out the most power. Using it directly is always better than a charge/discharge cycle.

Having said all of that:

1. Go with what the battery manufacturer recommends. If they recommend 14.8 then you may want to go there, but only if you will be reaching close to 100% SOC during your charge cycle. If not, then not nearly as critical.

2. MPPT can net you 10-20% more power from your panels. That "can" is important, it is really based on panels that are performing well, which is frequently not the case on sailboats. If you have the space more panels will almost always be a better return than MPPT controllers. Not having the space, if you can afford it MPPT will probably give you more power, but, in my experience, on boats not a lot more. I still use MPPT wherever I can.

3. For these panels I would probably wire then in parallel. Especially if you think the sun conditions can be different on different panels. Only wire in series if all panels are matched in terms of current output and will be operating under the same conditions. If you go PWM you only need one controller, it manages the output voltage, so will connect/disconnect both panels just fine. The diodes in the panels should prevent an under-performing panel from affecting the other one. MPPT is different, if the MPPT conditions for one panel are significantly different than the other then you may not get the maximum available power - you'll get the best it can with the aggregate rather than the best possible from each panel. These controllers assume that with multiple panels connected they are all working under the same conditions.

Hope that helps, and remember, don't believe everything you read here, I could be just as full of s**t as I think someone else is.

[tartansail]

Many thanks to both of you for the responses. I agree with the need to take everything on the Internet with a grain (or pound) of salt, but getting different perspectives helps me move from simplistic confusion to a path forward. I appreciate the expertise reflected in both your answers. It was scary to see that 6.24 X 10^18. Something about Faraday or Coulombs? Physics was a looonnnng time ago, but I understand what you were saying. Despite that quote, I think Bob's main point about absorption voltage was that it was good to push in amps to the battery's tolerance. Stopping short was giving away useful capacity and, potentially, impacting battery life. The advice to follow the manufacturer's recommendation makes sense. If/when my batteries are toast, I'm planning to replace them with Trojans so the ability to adjust the absorption seems worthwhile. Since we are not liveaboards, the boat often has several days with good sunshine and trivial draw so it seems like we'll have a shot at getting close to 100% SOC. I like the idea of being able to start full when the fridge goes on.

Given that MPPT will have some benefit, it seems worthwhile when we're spending time on the boat as long as I can find one that's not too pricey. It sounds like the Rogue would be a good one to consider given its price and adjustable absorption voltage. It seems like it may be penny-wise pound-foolish to spend the $$ on the panels and then not be able to fully use the output.

It sounds like there is no disagreement that the controller should have temperature compensation, especially at higher voltages.

[Dsanduril]

It sounds like there is no disagreement that the controller should have temperature compensation, especially at higher voltages.

Absolutely none. The higher you go in voltage, the closer you get to the maximum tolerance of the battery, and the more critical the temperature compensation becomes so that you don't exceed that tolerance. If you always charged at 13.8 or 14 I would say not too critical, but as you move up the voltage scale it becomes more and more a necessity.

[foggysail]

Originally Posted by tartansail

If/when my batteries are toast, I'm planning to replace them with Trojans so the ability to adjust the absorption seems worthwhile.

Given that MPPT will have some benefit, it seems worthwhile when we're spending time on the boat as long as I can find one that's not too pricey.

OK, appears that you have some consideration to cost so I want to address Trojans.

This topic was discussed earlier in a different thread, the essence of the discussion was not about Trojan's quality but about cost. Further, we learned that the golf cart 105's are available in the Fort Lauderdale area in the $80 range. NOT BAD! Here in my Massachusetts area the least costly source I found wanted $220 a pop!! Further, Sams Club where I finally did purchase my 4 new golf cart batteries, Duracells for only $88 each which have a 230AH rating.

My only point is that there are many good lead acid batteries out there. The technology is over 100 years old. There are few surprises facing the manufacturers. I suggest that you keep an open opinion regarding new batteries until the time you need to say goodbye to your bucks.

Foggy

[Jimbo485]

Can one of the "experts" please answer this question?

If a cruiser has, hypothetically, 400 W of solar panels and requires more energy, he can:

1) buy another 100 W panel for $150. This will increase his solar charging capacity by 25%.

Or

2) buy an MPPT controller for, say, $400 and the increase in charging capacity will be 10% - 20% (ie. 40 W - 80 W).

Why do so many recommend the second choice when obviously the first choice is cheaper and more efficient????

(I regard the second choice as ludicrous, unless he runs out of physical space for additional panels.) What am I missing?

[Dsanduril]

unless he runs out of physical space for additional panels

That is usually the problem with a boat installation. You install all the panels you can find room for (that's definitely the most bang for the buck), then you find out they still can't keep the batteries fully charged, and you look for ways to get more power out of them.

MPPT controllers are really good when you can connect multiple panels to the same controller, then the cost per Watt may be less than a new panel. But most boat installations don't fit that mold. However, when you've filled up all your space, and you want to get the absolute most out of what you have...

What you really have to compare the cost of the MPPT to is the cost of installing/running the generator/engine to charge things vs. the additional Ah you can get out of the controller.

[ExRonin]

Jimbo

You need to consider the total cost of installing that "$150" panel. In general, mounting rails/hardware, wiring, etc are significantly more costly than that $150 panel. I recently added two Kyocera 140 W panels (a good deal at about $200 ea), but the cost of everything ancillary to those panels was easily 4 times the cost of the panels. Thus, if you can gain, as you say 40-50 W with an MPPT, it will be 1) far cheaper in total cost 2) faster and simpler to install. That said, doubtless someone on this forum will say they can mount a dollar panel with a couple u bolts from home depot and used scrounged romex wire, but I am attempting to answer your question in a more general/practical way appropriate for a sea going vessel and compliant to ABYC recommended standards.

[noelex 77]

Originally Posted by Jimbo485

Can one of the "experts" please answer this question?

If a cruiser has, hypothetically, 400 W of solar panels and requires more energy, he can:

1) buy another 100 W panel for $150. This will increase his solar charging capacity by 25%.

Or

2) buy an MPPT controller for, say, $400 and the increase in charging capacity will be 10% - 20% (ie. 40 W - 80 W).

Why do so many recommend the second choice when obviously the first choice is cheaper and more efficient????

(I regard the second choice as ludicrous, unless he runs out of physical space for additional panels.) What am I missing?

Most of our points are correct, it's generally more cost effective to mount more (or more effecient panels) than the extra cost of MPPT.
As others have said you need to take the cost of mounting into consideration and many boats have no more room for extra panels.

A factor that has not been mentioned is that more expensive controlers have much better and adjustable battery algorithms. This can make a big difference to battery life and health and given the high cost of batteries the extra life can pay or the higher cost of a better controller. More expensive controllers also have better monitoring, reporting AHrs in, time on absorption etc. This information helps in monitoring the battery bank.

MPPT regulators will also work with a wider range of panels. Many of the high efficiency panels are also high voltage and need a MPPT regulator.
So often it's worth getting a better controler to extend the life of the batteries.

Better non MPPT controlers are available with the above features, but they are generally not much cheaper than MPPT.

[Jimbo485]

Ok, thanks for the comments. I know from my own experience that each panel required 2 pieces of aluminium angle, 16 screws, Sikaflex and about 2 metres of cable. Nowhere near 4 x the cost of the panel. More like $50 more for each panel.

I still remain unconvinced and maintain that an MPPT is a consumer rip-off UNLESS you have run out of available space.

Using a generator is totally uneconomical while cruising in tropical and sub tropical regions UNLESS you run out of space for more panels.

So I return to the original question. Assume you have sufficient space. Why would you be silly enough to spend more on an MPPT than more panels???

FWIW, we have 970 W of solar panels, no generator, no alternator, 880 Ah of batteries. We live onboard permanently, run 3 computers, radar, autopilot, watermaker, fridge, etc etc. No problem. If we ever felt the need for more power, there is still no way we would install an MPPT. We would simply add another panel or two.

Nevertheless, your comments are appreciated, even though I do not agree with the logic!

[Ex-Calif]

Originally Posted by Jimbo485

FWIW, we have 970 W of solar panels, no generator, no alternator, 880 Ah of batteries. We live onboard permanently, run 3 computers, radar, autopilot, watermaker, fridge, etc etc. No problem. If we ever felt the need for more power, there is still no way we would install an MPPT. We would simply add another panel or two.

What controls your panels now? Aren't we really talking about the delta cost between a good controller and an MPPT controller?

At the time of planning and purchasing the first controller aren't the benefits of an MPPT controller to be considered.

I really am asking out of ignorance...

[Jimbo485]

Originally Posted by Ex-Calif

What controls your panels now? Aren't we really talking about the delta cost between a good controller and an MPPT controller?

At the time of planning and purchasing the first controller aren't the benefits of an MPPT controller to be considered.

Yes, it could be the delta cost, unless you already have some sort of basic controller on your boat. All depends...

340 W of panels from the previous owner run thru a simple 3-stage PWM controller in our case. We use a Xantrex Link 10 for monitoring. The remaining 630 W of panels are connected directly to the batteries via some breakers in the cockpit and are controlled by us humans.

I turn them off gradually when the B&G instruments in the cockpit show the voltage approaching 14.4. I almost always turn them all off when we leave the boat and therefore let the controller and the 340 W panels handle everything. But today, for example, I left all the panels on while the watermaker was running and we went ashore for a few hours. Around noon, the watermaker was sucking out its 15 A, the fridge was sucking 3 or 4 A and there was still a net 15 - 20 A running into the batteries which were at about 90% SOC.

Works for us, but I see people still buying MPPTs when they have more deck space and I can't understand it.
Then again, many bought pet rocks a few decades ago and I couldn't understand that either...

In the case of Victor he bought panels with an extremely high voltage (54 V?), so he can't connect them directly to his batteries and therefore needs more controllers. But for your normal panel with a Voc of 17 or 20 V, what is the problem???

I still remain mystified by human behaviour and curious of electrical behaviour.

[noelex 77]

I am glad its working for you Jimbo, but i would not suggest anyone copies your set up.
It's very hard to this sort of self regulation without inadvertently feeding the batteries inappropriate voltages.
This becomes expensive in terms of battery life. It can even become dangerous and damage other electronics if the voltage is allowed to climb too high.

The crude step wise regulation of switching panels off and on is also much less efficient. These sort of inefficiencies are really only viable on cat where the the room for a very large solar array is possible.

If starting from scratch a smaller solar array with a good controler that can handle the whole solar array (not necessarly MPPT ) would be a similar price, give longer battery life, be easier and safer.