Solar Panels

[lawjohnson]

Good evening all,

I have a HR Class A that we purchased used. It has three solar panels on the roof that are stationary. The solar system is charging the batteries, (4 6V GC 140Ah units new this year)

Question:

How do I tell what the wattage is of the installed panels? We are going to AZ in November and would like to do a bit of boondocking but I'm concerned that I may not have enough power.
I remember seeing somewhere there was a way to measure it but for the life of me I can't find the article.

TIA

Larry

[lawjohnson]

Ivylog wrote:
1000 sq inches of panel will be aprox 100W.

That's what I was looking for! Thank you!! :B

[Ivylog]

1000 sq inches of panel will be aprox 100W.

[CA_Traveler]

grumpy3b wrote:
if you do need to update the solar charge controller I'd suggest to get an MPPT type controller. They are far more efficient that the PWM controllers.

FYI It depends: PWM controller use the full panel amps which go slightly up with increasing temperature. Panel power used for MPPT controllers decreases much more with increasing temperature. So depending upon panel temperature there may not be any significant difference between the 2 controllers.

This is for 12V batteries and 12V panels. 12V batteries and 24V panels require MPPT of course.

Lower temperatures have the opposite effect on the panels.

Plus there is about a 5% efficiency loss with MPPT controllers.

Check your panels temperature coefficients. Amps will have a positive value. Voltage or power will have a larger negative value.

12V panels with larger lower loss wiring would help with the power produced by an MPPT controller.

Lots of factors.

[grumpy3b]

Odds are there are 3 100w panels gicen the battery bank capacity (remember really should use no more than 50% of that 280AHr)

if you do need to update the solar charge controller I'd suggest to get an MPPT type controller. They are far more efficient that the PWM controllers.

Added consideration:
How many watts do you plan to use daily? Lead acid batteries are in efficient taking a good long time to charge up their last 25% give ir take. So knowing your estimated daily needs will help manage expectations.

LiFePO4 batteries can be charged from nearly completely depleted to full in 3-10hrs depending on the amount of sun. Meaning a ton more rapidly. If you have a couple drop-in replacement LiFePO4 types (meaning you just buy 'em, tske old out & put new ones in) they allow you to use them all night then have them fully charged again by noon, 3pm pessimistic case. But the batteries aren't inexpensive at $650-$950 depending per 100AH battery. And 200Ah batteries don't give us a break so just double the cost.

I only mention new batteries to help understand how long your lead acid batteries can take to charge. Remember too if it's a cloudy day and yoi need to use the generator to charge your batteries it will take days ti get lead acid charged even with a 5KWh generator. The LiFePO4 w8ll charge in 3-5hrs. That is the part where if you Boondock a lot ir for a couple weeks at a time you save on fuel to charge, fuel to run back & forth to get more fuel...plus the time factor. Yhe LiFePO4 batteries will last 2000-7000+ charge cycles compared to 500-700 for lead acid. again it all depends on your needs. Ho slowly until you really gey a sense how well your current system works for you. Then if you need new batteries consider a switch. Oh, you might even manage with a single 100AH LiFePO4 that's recharged a 1-3x daily.

[CA_Traveler]

Do you have a gen? What size charger? Magnum charger/inverter? 140Ah battery is on the small size as 230Ah flooded is the basic standard size. What make/model?

Recommend you spend some time boon docking like you expect in AZ before traveling. Even better if power is available and you can plug in if needed.

Consider installing a battery monitor so that you can determine your loads and (or reduce them) plus charging. Better ones are $200 but there are posts on very workable $40 variety on this board.

My first solar purchase was a battery monitor about 9 months before solar purchase. A battery monitor takes the guess work out of a energy audit which is recommended for understanding boon docking power usage.

[Lwiddis]

Does the solar controller indicate what the panels are offering on amps and volts? If it doesn’t, it’s ancient.

[CA_Traveler]

The sun in December is at it's lowest level for the year - ie less solar power. Plus some appliances like a propane furnace fan draw significant amps and for longer periods of time in higher elevations. At lower AZ elevations it's certainly much milder than Lake Stevens.

[CA_Traveler]

1. Use a mirror and see if there is a label.

2. With full bright noonish sun disconnect the panel input wires to the controller and measure the voltage. A voltage of about 18V indicates 12V panels and use a value of 14V. Next short the wires and measure the amps. Now multiply 14V by the amps to get watts. The value is about what you can expect but not the panel amps or watts. I use a value of 67% of the mfg watts for 5 hours as there are light and wiring losses.

Now the fun begins due to weather and location. 67% is likely to high due to the lower sun elevation in Lake Stevens with your flat mounted panels and other factors but will give you a ball park estimate.

A panel cell is 1/2 volt so count the cells. 36 cells is 18V and a 12V panel. 60 cells is 30V and marginally a 24V panel, etc but this doesn't tell you the mfg watts.

Enjoyed watching GD ride her horse in a Lake Stevens event last week.