Solar Regulators

[GordMay]

Solar (PV) Charge Controllers and Regulators:
*** A very Basic Primer ***

There are 4 main components that make up a complete solar system:
- solar modules
- charge controller(s)
- batteries
- inverter(s)
The solar modules produce DC power, which is wired through a charge controller, before it goes on to the battery bank, where it is stored and/or utilized.

The main function of a controller or regulator is to fully charge a battery without permitting overcharge, while preventing reverse current flow at night. If a (non-self-regulating) solar array is connected to lead acid batteries, with no overcharge protection, battery life will be compromised. Simple controllers contain a transistor that shunts the PV charging circuit, terminating the charge at a pre-set high voltage and, once a pre-set reconnect is reached, opens the shunt, allowing charging to resume.

The circuitry in a controller reads the voltage of the batteries to determine the state of charge. Designs and circuits vary, but most controllers read voltage to control the amount of current flowing into the battery as the battery nears full charge.

There are many different types of charge regulators available on the market, the simplest switch on/off regulators, PWM charge regulators which charge the battery with constant voltage or constant current (they are the most often used regulators in PV systems), to the most complex MPPT charge regulators. The first 70% to 80% of battery capacity is easily replaced, but the last 20% to 30% requires more attention and therefore more complexity.

Pulse Width Modulation (PWM) is an efficient charging method that maintains a battery at its maximum state of charge and minimizes sulfation build-up by pulsing the battery voltage at a high frequency. When the battery voltage reaches the regulation setpoint, the PWM algorithm slowly reduces the charging current to avoid heating and gassing of the battery, yet the charging continues to return the maximum amount of energy to the battery in the shortest time possible. The result is a higher charging efficiency, rapid recharging, and a gentle mixing of (stratified) electrolyte.

Maximum Power Point Tracking (MPPT) is a newer charging method designed to extract the most power possible out of a solar module by altering its operating voltage to maximize the power output.

Maximum Power Point Trackers (MPPT) allow a PV charging source to operate at Vmp (maximum power voltage*). When operating at Vmp, the array produces the maximum power possible for a particular light and temperature condition. When operating at other voltages, such as a battery float voltage or the voltage of a discharging battery, array power is reduced. Using solid state dc-dc converter circuits and a power comparing algorithm, MPPT charge controllers allow the array to operate at Vmp on the input side while maintaining the proper battery voltage on the output side.

* The Maximum Power Point is the point on the current-voltage (I-V) curve of a module under illumination, where the product of current and voltage is maximum. For a typical silicon cell, this is at about 0.45 volts.

ie: Shell Solar’s SP75 is rated at 4.4 amps @ 17 volts (4.4 times 17 = 74.8 watts)
But this 75 watts does NOT equal 75 watts of charging capacity, since your battery is only charging near 13.5 V. The output of a solar module is characterized by a performance curve of voltage versus current known as its I-V curve. For crystalline modules, the current remains fairly constant as the voltage changes relative to the voltage of battery it is charging. A battery charging at 13 V is only using 57.2 watts of power not the full 75 watts - a loss of about 24%. In an extreme case, such as a fully discharged battery at 10.5 volts, you would get nearly 7 amps at 10.5 volts from the MPPT into the battery!

MPPT's are most effective under these conditions:
1. Cloudy or hazy days - when the extra power is needed the most.
2. Cold weather - solar module output increases in cold temperatures during the winter when sun hours are low and you need the most power.
3. Low battery charge - the lower the state of charge in your battery, the more current a MPPT puts into them - another time when the extra power is needed the most.
4. With higher voltage solar arrays of 300 Wp or more.

------

Don’t confuse “Smart” Controllers or Regulators with Blocking & Bypass diodes or Shunt Devices:

Blocking Diode - A semiconductor connected in series with a solar cell or cells and a storage battery to keep the battery from discharging through the cell when there is no output, or low output, from the solar cell. It can be thought of as a one-way valve that allows electrons to flow forwards, but not backwards.

Bypass Diode - A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.

Shunt Controller - A charge controller that redirects or shunts the charging current away from the battery. The charging current is controlled by a switch, connected in parallel with the photovoltaic (PV) generator. The controller requires a large heat sink to dissipate the current from the short-circuited photovoltaic array.

[sv_makai]

Since we have been cruising, I have added one other item to the componets list (covers more than solar)

Wiring/connections.

We have seen a very large number of boats and talked with several who have spent much time researching and installing solar panels and the releated componets then install wiring that was to small for the application. Then on top complain about wiring related issues.

I believe that the correct wiring not only helps the efficency but is a safety issue. It is poor economics or incomplete knowledge to choose the incorrect wiring.

Makai has 4x120 Kyrocea pannels, RV Power Products MPPT contoller with 1 size larger than recommended for the 2 way run. It charges great with no problems after a year out.

[GordMay]

Captain Bill is absolutely right - one of the biggest problems with Boat Electrics is undersized wiring, and poor (high resistance) connections.

The industry standard formula for calculating minimum Wire Size for a given Voltage Drop is:

CM = (K x A x L) ÷ VD]

Where:
CM = The Circular Mil cross sectional area of the wire
(See Table 1, and ABYC Section E-8, Table III) *
K = 10.75 Representing the Mil-Foot Resistance of Copper Wire @ 78o F.
L = The Total Length of the wire in Feet
(This is the ‘Round Trip’ length of both Positive + Negative wires)
VD = Permitted Drop in Volts
(Ie: 3% VD @ 12.5V = 0.375 ED -or- 3%VD @ 25V = 0.750 ED)

For an explanation of Voltage Drop & Wire Sizing, see “Ohm’s Law & Boats” at: http://cruisersforum.com/showthread.php?s=&threadid=372

or
“Good Old Boat Magazine” March/April 2003 (Issue 29)
[url]www.GoodOldBoat.com/electrical.html[/url

* I have a Wire Sizing Chart, which presents all this in a convenient, easy to use format.
I can Fax a copy to anyone who sends me < Gord@BoatPro.zzn.com > their Fax number.

HTH,
Gord

[Rick]

PV panels made with high quality silicon exhibit extremely low leakage currents in the absence of light. This specification is referred to as DARK CURRENT and is rarely seen on the data sheet for the panel. Nonetheless you can measure it for yourself using your battery and a DVM or ammeter. If the dark current for your panel is on the order of 10mA (milli-Amps) for a 50Watt panel there is no need to suffer the voltage burden imposed by the insertion of a blocking diode. You MUST, however, protect the wiring with the use of a fuse located close to the battery connection to protect from inadvertent shorts.

Peak-power-point tracking regulators will, therefore, deliver an optimum amount of energy to the battery without the burden of the blocking diode.

NOTE: with good quality panels even the slightest ambient light, like starlight, will overwhelm the dark current so that if the panel is never actually physically covered there will be a net positive current flow out of the panel instead of a drain on your battery. Again, use your DMV to verify this for you if you wish to obviate the need for a blocking diode.

[rleslie]

Gord, Bil & Rick

Excellent information and presentation. Thanks

Will you please explain the most effecient manner to connect two 90W panels to the same battery bank? Will two regulators be required and should they be fed into two seperate battery posts or can they be combined and fed through o a single regulator?

Thanks

[Rick]

The least energy loss will be to parallel the panels (assuming 12V panels and battery bank) feeding them through a switch-mode peak-power-point tracking regulator set to a voltage appropriate for the battery's state of charge. The line feeding the regulator from the battery would probably be from a fused connection (fuses have, in general, lower voltage burdens at rated load than do breakers) attached to a positive (and negative) power distrubution point appropriate to the wiring layout of your electrical system.

Verify for you own edification that the dark current of either panel is insignificant or that the switching regulator does not allow bidirectional current flow.

[Alan Wheeler]

Sorry to dredge this thread up again. But I was talking to a freind today about this site and the fantastic thread on charging etc etc. We bantered around all the charging methods and device's and concluded that a DC system was really expensive, IF, you wanted to do it right. Anyway's I mentioned to him, Sooooo, why can't you have say, one smart regulator. Say a Solar regulator, seeing as they have to do the most complex regulation of the input supply than most other regulators. Then have some form of an islolator/switching mech that could then select varying supply sources. For instance, connected to shore power, you have a simple AC/DC Power supply and you switch it to the charge regulator. This can then be coupled to the Genset when at sea.When running the motor, the regulator could be switched to Alternator supply. Solar panels could be switched in to the system, when nothing else is supplying a voltage. So what am I missing here??? Am I not considering something important?

[GordMay]

Do you know anything about these devices - your comment/opinion is valued ?

Paneltronics Introduces Intelligent Mosfet Battery Isolator
Paneltronics, Inc. announces the introduction of its ICS-060, Intelligent Mosfet Battery Isolator. The unit features Solid State Design, Optional CAN Interface, Microprocessor based Monitoring and Control, Onboard Self Diagnostics, Auto-detection of 12 VDC or 24 VDC battery systems, Watertight construction, LED mode and status indicators, Ignition Protected UL 1500, SAE J1113 Compliant, Programmable charge current limits from 10 Amps to 100 Amps, Corrosion Resistant, Studs are 3/8 – 16 for maximum current transfer and Stub boots are included (ABYC E-11.5.2.7.5).

The benefits of the unit, permits total isolation between two batteries or battery banks and multiply charging sources, full charge of two batteries or battery banks with one charger and or alternator, provides solid state over current protection to the second battery, shutdown feature protects the ICS –60 against over temperature and over voltage and extends the battery life of both the Primary and Secondary batteries.

The unit works as a “Gateway” between Primary and Secondary Batteries. It provides total electrical isolation between two batteries or battery banks while permitting one or more charging sources (including alternators, battery chargers, wind generators or solar panels) to fully charge both batteries, or battery banks to their maximum capacity. In contrast to Diode based battery isolators presently available on the market that have up to a 1.4 volt internal voltage drop (at 10 Amps), the ICS-60 has less than a 30 millvolt drop making it possible to fully charge batteries with resulting extended battery life.

The units will be available for sales in Late February 2005. For further information and/or user manual contact Paneltronics, 11960 N.W. 87th Court, Hialeah Gardens, FL 33018; Tel. 305-823-9777; Fax. 305-823-7802; www.paneltronics.com .

[Alan Wheeler]

Gord!, your bloods worth Bottling Mate!
Your just a wealth of resource information. I can't believe you can come up with so much. It must be cold winter Evenings over your way Huh? Nothin to do, but sit in front of the computor and a warm fire roastin close by.