170 watts vs 340 watts

[tanglemoose]

We have a Keystone off the grid solar pkg, with 170 watts of solar, 2 6 volt wet deep cell batteries, 2000 watt inverter.

What would an additional 170 watts on roof give us?

We go south Jan. Thru May, do lots of camping with no hookups..

 

[DonTom]

What would an additional 170 watts on roof give us?

You answered your question in the question, so I have no idea what you're really trying to ask.

-Don- Cold Springs Station, NV (Hwy 50)

 

[tanglemoose]

Trying to figure out if we had an additional 270 watts would batteries get charged faster, stay charged, etc.... can I run coffee maker, what is reason people add more watts? To get benefit do I need agm batteries??

 

[Mark_K5LXP]

To answer the question one would need to know what your typical power usage is, or you want it to be. Part of it is the device (coffee maker) but another part is how long per day. This goes for all the devices in use, and what time of day (it makes a difference if they're being powered by the panels directly or from the charge in the batteries). "Double" the solar capacity is a nice gain but without knowing what the loads are it's a guess whether it will meet your expectations or not.

Mark B.
Albuquerque, NM

 

[Isaac-1]

340 watts of solar panels under optimal conditions,will be fairly close to providing the maximum optimal rate of charge acceptance for a pair of GC1 6V traditional lead acid golf cart batteries when in bulk charging (up to about 80% capacity). I have 400 watts of panels feeding a pair of 6V GC1 batteries on my coach and did the math for this a while back, with 400 watts being just a little above max optimal charge acceptance current.

 

[Ex-Calif]

170W / 12V = 14 amps X .8(efficiency_ X 8 (hours of collection in summer) = 90 amps theoretical collection per day.

So the second panel ups your theoretical collection to 180amps per day.

To understand if this is meaningful you have to do a power plan. The biggest "casual" offender to consumption are incandescent lights. LEDs are the way to go. Having said that...

Lights - 6 X 40W X 6 hours = 1440W
Smart TV - 40W X 6 hours = 240W
Water pump - 20W X 1 hour = 20W
Laptops/Phones charging - 4 X 30W X 6hr = 720W

Add other items you use in a 24 hour period especially big draw items.

In this example the daily draw is 2420W / 12V = 200 amps. If your batteries are 100amps then you are right at the limit of battery capacity and low on charging ability.

Don't panic I am guessing your rig has LED lights and they draw like 1/10th of incandescent so total draw is probably half of that.

 

[tanglemoose]

170W / 12V = 14 amps X .8(efficiency_ X 8 (hours of collection in summer) = 90 amps theoretical collection per day.

So the second panel ups your theoretical collection to 180amps per day.

To understand if this is meaningful you have to do a power plan. The biggest "casual" offender to consumption are incandescent lights. LEDs are the way to go. Having said that...

Lights - 6 X 40W X 6 hours = 1440W
Smart TV - 40W X 6 hours = 240W
Water pump - 20W X 1 hour = 20W
Laptops/Phones charging - 4 X 30W X 6hr = 720W

Add other items you use in a 24 hour period especially big draw items.

In this example the daily draw is 2420W / 12V = 200 amps. If your batteries are 100amps then you are right at the limit of battery capacity and low on charging ability.

Don't panic I am guessing your rig has LED lights and they draw like 1/10th of incandescent so total draw is probably half of that.

Hello, yes our 2021 cougar has LED lights, thankfully. We are collecting solar In winter time (snowbirds) guessing a lot less. I don't want to spend $1000 bucks for solar panel and...really not get more solar power to use.. with my current batteries... so add solar or AGM batteries?

 

[Mark_K5LXP]

If you're spending $1K for a 170W panel you're getting a serious hosing. Batteries don't add power, just storage. Per pound AGM has no more capacity than flooded but they are 2x the cost. If you say, double your battery bank you can run your loads longer but at some point any size battery bank will be depleted and need charging, and a bigger battery bank will need more charge to fill it. So the balancing act is to decide how long you want to operate your equipment from batteries, and then you decide what will do the battery charging and how quickly whether from solar, genset or shore.

Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

Mostly it adds charging capability, so recharges to 100% battery capacity faster if it is sunny. But your batteries only hold so many AH (210-230 AH for a pair on GC2 6v's), so you don't really have any more power to use. If your present panels are sufficient to recharge batteries to 80-100% on most days, then extra 170W gains little or nothing. But if you typically cannot get the batteries back to at least 80% before the sun gets low, then more panel wattage will benefit you.

If you add battery capacity as well as panel wattage, then you can store more power and thus have more power to use when the panels are not actively producing watts.

 

[Memtb]

We have a Keystone off the grid solar pkg, with 170 watts of solar, 2 6 volt wet deep cell batteries, 2000 watt inverter.

What would an additional 170 watts on roof give us?

We go south Jan. Thru May, do lots of camping with no hookups..

Many folks require more batteries/solar panel wattage .....as they wish to have more electronic conveniences or must run their forced air heat!

We have 600+ watts of solar and 6 batteries.....wish we had more. We boondock in cool (sometimes below zero) temps, with short daylight periods, use lots of battery power running the heater, and like tv and other “necessities” of our spoiler generation!

Summary: if you have warm temps, long daylight charge periods, and want to be minimalists......you should be good to go! JMO. memtb

 

[uchu]

Why pay so much more for AGMs compared to flooded? I get it, they are "maintenance free". Any other compelling reason?

 

[Mark_K5LXP]

AGM's have an edge in some aspects of lead acid battery performance. Namely a bit better current delivery and charge acceptance, and a better resilience to the effects of deep discharges. They are also less tolerant of overcharging so require a more controlled charge regimen. Physically they require no user maintenance (watering) and because they don't vent they can be used and stored in living spaces. So it's not so much that AGM's are "better", they just offer some electrical and mechanical features that make them more suited than flooded when those features are desired.

Mark B.
Albuquerque, NM

 

[Isaac-1]

As mentioned above, if you are battery limited due to battery tray placement, etc then AGM can let you have more watts of solar panels than the same number of non-AGM batteries. Of course upgrading to Lithium Iron Phosphate batteries changes all that again. With the OPs pair of 6V GC1 batteries, he is effectively limited to charging at a rate of around 350 watts or so after charge losses are taken into account, so would likely not benefit much from more than 400 or so watts worth of solar panels. If he were to upgrade to AGM batteries, that would go up to about 600 watts worth of solar panels, though of course he would still be limited by total battery amp hours, the batteries would charge faster during the day. As to the price that seems very high to me too.

 

[DonTom]

wish we had more.

Is it possible to not want more, regardless of how much solar you already have on an RV?

There is a simple formula for how much solar you should have.

It is "N+200w", where "N" represents the wattage you now have. Who wouldn't want 200 watts more solar than they already have?

-Don- Cold Springs Station, NV

 

[Ex-Calif]

Hello, yes our 2021 cougar has LED lights, thankfully. We are collecting solar In winter time (snowbirds) guessing a lot less. I don't want to spend $1000 bucks for solar panel and...really not get more solar power to use.. with my current batteries... so add solar or AGM batteries?

Think of the solar panels like a garden hose and the batteries like a water tank.

As Gary says you have about 200amps in the water tank. Practically you can use 50-70% of that so call it 130 amps or 1500 odd watts. Based on my theoretically power plan (with LED lights) you can probably go a day or two reliably with "No Recharge" (i.e. rainy days)

So the system needs to be balanced. More storage means more days without recharging. But when you do need to recharge it may take days to do so if solar alone at 170W.

That's when you think about more solar (water hose) to charge things up. My rule of thumb is 2 days of power supply at least and the ability to charge it up in 1 X 8 hour sunny day.

Don't forget you also have a generator on board that will also recharge the batteries when it is running and of course when you are driving the alternator will also charge the batteries.

I'd go out and get some experience under your belt before I decided if I needed more solar or battery power.

 

[Sierranevada]

If your batteries are not getting totally charged during the day and if your charge controller can handle another panel, then add the panel. If your are getting full charge with one panel then add battery capacity and the second panel. George

 

[tanglemoose]

If you're spending $1K for a 170W panel you're getting a serious hosing. Batteries don't add power, just storage. Per pound AGM has no more capacity than flooded but they are 2x the cost. If you say, double your battery bank you can run your loads longer but at some point any size battery bank will be depleted and need charging, and a bigger battery bank will need more charge to fill it. So the balancing act is to decide how long you want to operate your equipment from batteries, and then you decide what will do the battery charging and how quickly whether from solar, genset or shore.

Mark B.
Albuquerque, NM

Yes, it was like 952 for the panel and installation from dealer. We can buy the panel for 599, but hubby not up to drilling holes in our new RV roof... it does have a plug in the roof for more panels... so... another debate.

 

[tanglemoose]

Mostly it adds charging capability, so recharges to 100% battery capacity faster if it is sunny. But your batteries only hold so many AH (210-230 AH for a pair on GC2 6v's), so you don't really have any more power to use. If your present panels are sufficient to recharge batteries to 80-100% on most days, then extra 170W gains little or nothing. But if you typically cannot get the batteries back to at least 80% before the sun gets low, then more panel wattage will benefit you.

If you add battery capacity as well as panel wattage, then you can store more power and thus have more power to use when the panels are not actively producing watts.

Thanks Gary, we typically are fully charged by nightfall we are not big consumers, but would like to watch more TV in winter...I am always panicking come evening that we have to keep our batteries at around 12.3 when we go to bed. As it seems that during night things still run in background, but most mornings we wake up to 12.2. But then the delimena do we turn TV on in am... until we get some charging happening?? Is is bad to be at 11.8 and be using power...??? Thanks. Donna

 

[Isaac-1]

$559 for a 170 watt panel in 2021, what is this thing made of gold? You can get a 175W flexible panel that you can glue down from amazon for $280 https://smile.amazon.com/Renogy-175-Watt-Volt-Monocrystalline/dp/B082FCZ4MD/ I am not suggesting going the flexible panel route, as they cost more and tend to only last 8-10 years if not abused vs 20+ for glass panels, just pointing out it could be an option for a lot less money. You can also get a glass front panel for about $1 per watt in this wattage range

 

[TonyL]

I just checked, we paid $265 in 2020 for 200 watt panel, 30 ft of cabling, cable inlet box, mounting brackets and controller, all at the Q show. We had to buy sealer, caulking gun, screws etc. Total came in at $300. If someone is going to drill holes in my roof, I want it to be me. At least I then know how it is sealed. If you have connections on the roof already, the only holes might be for screwing the panel down. I bet someone at the rally if you're going, would help out if you have any concerns.
$599 for a 170 watt, someone's wanting your hard earned money