New to solar, installing on RV

Re: New to solar, installing on RV

Wayne,

1. The WFCO (World Freedom Company?) unit claims to be a three-stage charger, but the SB2000E is a two-stage charger (no float stage). Their various set-points may not be the same, and the SB2000E is (optionally) temperature compensated, while, to my knowledge, the WFCO is not. However, multiple chargers can generally coexist on the same battery bank. They may not operate at peak efficiency, but I doubt either will cause the other any harm. AGM batteries are sensitive to over-voltage charging, so you’ll want to follow Concorde’s instructions for the charger settings.

2. Your PV modules will run cooler on mildly overcast days, so their output voltage should be somewhat higher. Accordingly, the “extra” voltage should be converted to additional charge current on such days. Don’t expect miracles.

3. An MPPT controller’s main claim to fame is that it can convert most “extra” voltage (the difference between available PV voltage and battery charging voltage) into additional charging current. This extra voltage (which, times the PV current equals power, which, times time equals energy) is essentially lost when using a PWM controller (the PV array operates at battery voltage in the bulk charge mode).

However, this extra voltage has to be available for the conversion to be made. The largest % charge current boost is typically realized early on a very cold day (relatively PV voltage high) while charging a discharged battery (relatively low battery voltage). As the day progresses, the sun warms the PV modules (PV voltage drops) and the battery voltage increases, the extra voltage reduces considerably, which results in little current boost.

The Kyocera modules are fairly high voltage (STC Vmp = 17.4 V), and the Concorde AGM battery is a relatively low voltage battery (charging voltage = ~14.4 V), so you should see some current boost from the controller during the bulk charging stage, especially on cold days. This current boost should deliver a few extra Ah / day – perhaps 5% - 10% net after figuring the controller's internal losses (the SB2000E's eficiency spec is "typically 95% at 15 A output").

The absorption stage is constant voltage / limited current, so the MPPT function is typically of no value in this charge mode unless you’re powering a load in parallel to the battery.

In general, though, MPPT controllers are not cost effective in low-power configurations. The price difference between the SB2000E (and its optional enclosure and remote battery temp sensor) and, for example, a Morningstar SunSaver- or small ProStar controller could be invested in larger PV modules and you’d end up generating more energy. Ken Lenger originally included an SB2000E in his RV’s solar energy system, but he replaced it with a ProStar. You want to contact Ken and ask about his experience and rationale.

4. Tilting your modules towards the South is usually beneficial. A tilt of latitude minus ~15 degrees will help cool and clean the modules in Summer, and a tilt of latitude plus ~15 degrees will help boost energy production in Winter. A tilt angle = latitude works well for Spring and Fall.

5. Here’s a link to RV solar panel mounts available from NAWS, this site’s sponsor. Another possible source is RV Solar Electric.

HTH,
Jim / crewzer

Re: New to solar, installing on RV

BB,

Good point re the controller's own efficiency -- I just can't remember everything all the time! :roll: I've edited my post above to somewhat account for this point.

Speaking of the MX-60 and its operating efficiency, you may find these previous discussion topics to be of interest:

http://www.wind-sun.com/smf/index.php?topic=1034.0 (Paricipant "boB" is Bob Gudgel, the MX' original designer from Outback)
http://www.outbackpower.com/forum/viewtopic.php?t=952

Wayne,

Speaking of efficiency, good choice on the Concorde AGM battery! AGM battery Ah recharging efficiency is typically ~99%, vs. ~89% for regular ol' flooded-cell batteries.

Regards,
Jim / crewzer

Re: New to solar, installing on RV

Wayne,

Your collective post indicate that the SB2000E MPPT charge controller will be of no benefit to a very small benefit.

Correct.

This raises the question of will it simply not be effective on a small system (130 watts), or will it take away from a small system?

There are several mitigating factors here. One is that the 2000E’s operating efficiency is less that 100%. In addition to its “Charge On” power requirement (90 mA x ~14 V = 1.26 W), its specs also indicate that the power conversion efficiency is 95% at 15 A output. So, you’d need something between a 2% and a 5% current boost just to break even.

Another factor is that any MPPT charging benefit is limited to the Bulk charging stage. The charger’s Absorption algorithm is fixed-voltage and declining-current, so there’s no MPPT benefit realized in this stage.

A third factor is the PV module specs. The Kyocera KC-65’s STC Vmp spec is 17.4 V. Its typical Vmp will be lower, especially in your location, but there should be some “extra” voltage available for the 2000 to convert into additional Bulk stage charging current.

Is the SB2000E the same as the other controllers, except has the MPPT technology?

It’s certainly similar. Other features include two-stage charging (Bulk and Absorb) plus EQ, and temperature compensation via an optional remote battery temp sensor. For AGM batteries, the EQ function is essentially useless.

The Morningstar SunSaver-20 is a 20 A, two-stage PWM (non-MPPT) controller with a local temp sensor, which is fine if the controller is located in the same general environment as the battery(ies).

If I wired the two 65 watt panels in series, would this give the MPPT more voltage to convert to amps?

Do not do this with your particular system. First of all, wiring the two modules in series may add their voltage, but their current is not added, and, when accounting for conversion losses, the net result would be less power. Also, the series voltage of the two modules would exceed the 2000E’s input voltage spec (30 Voc), and you may well damage the controller. Some controllers (i.e., Outback MX-60, large Blue Sky models) have a DC-DC step-down capability in addition to MPPT, but the SB2000 does not.

My interest in the MPPT charge controller, is to increase the charge to the AGM during overcast days, using the 130 watts of panels I have. My panel space is limited. For three days per week, I am camped forty feet from the bay of San Francisco. It is seldom above 80 degrees in summer, typically 40 to 60 degrees with frequent overcast in winter. I will be able to tilt the panels to the south, but would prefer to have them flat.

I have experimented with one panel flat on the ground. With the MPPT turned off, is shows 3.6 amps. Turned on it is 4.2 amps. I did not time how long it would do the 4.2 amps. Later in the day, it was at 3.8. I elevated the panel about 6-inches, it went back to 4.1 amps. I really do not know what the gain would be in a day, but considering I only need about 25 to 30 amps a day, that little gain could worth while. However, it I loose it because the controller some how takes away, then obviously there is no gain.

Since you already have the MPPT controller, stay with it and make the best of it. I doubt that it “takes away” (uses/loses more power than the MPPT function provides), especially considering the KC-65’s decent output voltage. Just makes sure to follow the controller’s instructions and get the MPPT function optimally calibrated.

The Sun is relatively high this time of year, so you won’t see much gain from tilting the modules. However, the collective benefits of a small tilt are worthwhile, as the module will generate more power, will run cooler (=even more power), and rain will help clean the module rather than letting dirt and water pool on top of the module. The tilt benefit will be more noticeable in the Winter hen the Sun is relatively low and you may see your energy demands increase as the nights grow longer.

When I purchased the controller, I was told I did not need the battery temperature monitor with the Lifeline AGM.

What do the instruction that came with/on the battery say?

An AGM battery is a beautiful thing to waste. AGM batteries are susceptible to thermal runaway, so remote battery temp sensors and a temperature-compensating controller are generally considered a must, particularly in hot environments. In a cool- or cold environment, the BTS helps provide the higher charge voltage required. So, assuming your battery compartment doesn’t exceed 80 F, you may be able to get away with no BTS in the Summer, but the battery will be undercharged in the cool Winter, and that will lead to reduced capacity and shortened life.

Actually, I am at San Quentin State Prison, in the parking lot.

Here’s a link to insolation data for San Francisco.

HTH,
Jim / crewzer

Re: New to solar, installing on RV

I purchased the panels and controller from NAWS. Nice guy in sales, but it would appear he doesn't know much more about this than I do.
He ask the owner if I needed the battery temp sensor, and the answere was no. My AGM is inside with me and the controller, so it is at the same temperature as I am, maybe a little cooler due to it being closer to the floor.

You say I should get the battery temp sensor. With my setup, is it to protect the AGM, increase the efficiency of the charger/battery or both?

My recommendation for using the remote BTS is to protect the AGM battery and prolong its useful life.

What is the "EQ function"? I have read and reread, and I am missing it.

Bill’s write up on EQ is pretty good. However, AGM batteries are usually not equalized, especially if they’re properly maintained. My advice on EQ’ing an AGM battery is to only do it in strict accordance with the manufacturer’s specific instructions.

The controller has a switch that turns the MPPT feature on or off. If there is a difference in amp output (MPPT on or off), it can be seen in the amp display. I do not think I would need the MPPT feature (if it works) in the summer months. Should I turn it off in the summer months?

I’d leave it on all the time.

It is extreamly rare for me to bring the AGM below 12.2 volts, usally two days in the winter. If I use 25 amps per day (from a 100 amp AGM), it appears to me that the 7 amp panels would produce an excess of 30 amps per day in the summer months. It is my understanding it is designed not to over charge the battery. Do I understand this correctly?

Yes. Properly adjusted, the controller should not overcharge your battery. Follow Concorde’s instructions for your Lifeline AGM battery.

The charge voltage is factory set at 14.0 volts. I am considering lowering it to 13.8 volts. It is my understanding that the AGM will handle the 14.0 volts or 13.8 just fine. I would think the 13.8 would give just a little more voltage for the MPPT and a little more safety margin for the AGM. What is your thought on this?

I think 13.8 V ~ 14.0 V at 77 degrees F is too low for your battery. The result will be an undercharged battery that will not provide optimal daily service or long life. Concorde says to use 14.2 V ~ 14.4 V. FWIW, my charger is set at 14.35 V ref 77 F (measured at the battery terminals near the end of the Absorption stage).

Finally, while I do know a bit about some of this stuff, I don't know everything about all of this stuff. Objective discussion and debate is healthy and encouraged!

HTH,
Jim / crewzer

Re: New to solar, installing on RV

Tilt is very important in the winter, you want to tilt them up 45-60 degrees or Latitude+23.5 degrees.  Summer should be flatter, lat-23

now when it is the beginning of summer it would be 40-23.5 or 16.5 degrees. now in the beginning of winter it is 40+23.5 or 63.5 degrees and is more vertical.

For a reference tilt angle = latitude, increasing PV array tilt in the Fall and Winter, within limits, can lead to improved Winter energy production. Similarly, decreasing tilt angle in the Spring and Summer helps as well.

However, I submit that increasing an array’s tilt angle by +/- 23.5 degrees is too much and therefore is a less than optimal adjustment.

A Fall and Winter tilt adjustment of +23.5 degrees will result in optimal solar noon alignment on just one day: December 21. There will be a tilt (declination) error on all other days, with a maximum of 23 .5 degrees. Similarly, A Spring and Summer tilt adjustment of -23.5 degrees will result in optimal solar noon alignment on just one day: June 21. There will be a tilt (declination) error on all other days, with a maximum of 23 .5 degrees.

In general, a compromise seasonal adjustment of +/- 15 degrees works better. Solar noon alignment will be correct on two days in each six month cycle, and the maximum error will be just 15 degrees. As a result, the array will be able to produce more total seasonal energy than if using the +/- 23.5 degree adjustments.

The National Renewable Energy Laboratory (NREL) included +/- 15 degree offsets for their 30-year solar radiation data collection used to create their Solar Radiation Data Manual. You can also model the differences between the +/- 23.5 degree and the +/- 15 degree solutions using the PV Watts calculator.

HTH,
Jim / crewzer