Solar104!! Solar yield

[GallenH]

Parenthetically, Friday night is Mexican at our house. Tonight smoked chicken enchilladas Christmas style. Margaritas flow, so I apologize.

I still haven't got a handle on solar yield. I know that theoretically in the best possible conditions a 100w panel should yield 8.33A for an hours time in the sun. But I know that's not real life. And I know that it varies considerably throughout the day and is dependent on what time of year, where you are and the temperature.

Can anyone give me a decent estimate of daily AH yield from real life experience.

gracias.glenn

[booster]

Originally Posted by GallenH

Parenthetically, Friday night is Mexican at our house. Tonight smoked chicken enchilladas Christmas style. Margaritas flow, so I apologize.

I still haven't got a handle on solar yield. I know that theoretically in the best possible conditions a 100w panel should yield 8.33A for an hours time in the sun. But I know that's not real life. And I know that it varies considerably throughout the day and is dependent on what time of year, where you are and the temperature.

Can anyone give me a decent estimate of daily AH yield from real life experience.

gracias.glenn

The old standard estimate we usually heard in the past and even now is about 30 amp hours of energy from 100 watts of solar. We have seen others that get more, usually in the south under very good conditions, IIRC over 40 amp hours in at least one case. In poor sun, drizzly/rainy/cloudy we have seen as little as under 5 amp hours per 100 wates, but on average do probably come pretty close to the 30 amp hours in good sun, mostly in the northern areas of the US for use over the spring/summer/fall period. We have 300 watts in parallel because the Blue Sky controller wouldn't be able to handle the 60+v maximum voltage the panels could put out on an MPPT controller.

[GallenH]

Thanks, booster, for all of your replies. Extremely helpful as always!

glenn

[jrobe]

Doing the math on solar panels is discouraging. I have always seen the 30 amp hour number also for a 100 watt panel but this is probably for a perfect sunny day in the summer. A cloudy day may be more like 10 amp hours. The cost / benefit ratio is pretty low.

Compare this to a second alternator with minimal driving. It takes me about 8 minutes of driving in a day to achieve 30 amp hours of battery charging (or 16 min every 2nd day, 24 min every 3rd day, etc.). Solar would have been a complete waste of money for the way we use our van.

[GallenH]

Originally Posted by jrobe

Doing the math on solar panels is discouraging. I have always seen the 30 amp hour number also for a 100 watt panel but this is probably for a perfect sunny day in the summer. A cloudy day may be more like 10 amp hours. The cost / benefit ratio is pretty low.

Compare this to a second alternator with minimal driving. It takes me about 8 minutes of driving in a day to achieve 30 amp hours of battery charging (or 16 min every 2nd day, 24 min every 3rd day, etc.). Solar would have been a complete waste of money for the way we use our van.

If I posted another thread on this topic it would be "solar vs 2nd alternator" because that's something that's in my mind as well. So I appreciate your observations.

How we use our van (load-wise): water pump, LED interior lights, ceiling fan in warm weather/heater fan in cold. Period. No inverter, no microwave, no TV, etc. From that perspective 200w of solar panels, even producing only 10AH@/day would always cover my daily use without driving anywhere.

However, I'm considering/anticipating adding a compressor fridge. I figure that my total usage would be more in the range of 50AH/day with that setup.
So if I'm looking at 200AH of battery of which 160AH is usable, I could go 3 days (w/o solar) before I would need to do some driving to charge the batteries. With 200w solar and even only a 20AH/day solar yield, my total daily consumption would be 30AH and then I could go 5 days without driving.
We rarely camp more than 3 days in one location before moving on. That's my current thinking on that anyways.

Costwise: I can get a 200w solar kit with either a MPPT or PWM controller for c.$400. It looks like a 2nd alternator is c.$1000 plus the cost of a Balmar controller ($400?). So I'm not sure if the cost/benefit is better with the 2nd alternator.

But I'd appreciate your take on my situation as I could easily have missed something here.

thx.glenn

[booster]

Originally Posted by GallenH

If I posted another thread on this topic it would be "solar vs 2nd alternator" because that's something that's in my mind as well. So I appreciate your observations.

How we use our van (load-wise): water pump, LED interior lights, ceiling fan in warm weather/heater fan in cold. Period. No inverter, no microwave, no TV, etc. From that perspective 200w of solar panels, even producing only 10AH@/day would always cover my daily use without driving anywhere.

However, I'm considering/anticipating adding a compressor fridge. I figure that my total usage would be more in the range of 50AH/day with that setup.
So if I'm looking at 200AH of battery of which 160AH is usable, I could go 3 days (w/o solar) before I would need to do some driving to charge the batteries. With 200w solar and even only a 20AH/day solar yield, my total daily consumption would be 30AH and then I could go 5 days without driving.
We rarely camp more than 3 days in one location before moving on. That's my current thinking on that anyways.

Costwise: I can get a 200w solar kit with either a MPPT or PWM controller for c.$400. It looks like a 2nd alternator is c.$1000 plus the cost of a Balmar controller ($400?). So I'm not sure if the cost/benefit is better with the 2nd alternator.

But I'd appreciate your take on my situation as I could easily have missed something here.

thx.glenn

With only two AGM batteries, you really won't need a second alternator IMO. They are only going to like accepting about 80 amps max and even with chassis loads about 100 amps from the alternator. At most you could get an aftermarket higher output and durability alternator as the primary and be in good shape.


You must have lead acid batteries so having the solar is a good thing even if the solar doesn't cover you loads all the time. Solar does a great job of doing the last 20% SOC when the current gets low enough for the solar to keep up with. You only need to top off once ever week or 10 days so should get good sun in that time period. Just run the alternator until you get to 75-80% SOC and then let the solar finish if it is sunny. If it isn't sunny just run it down again do it again when the batteries get low. Once you get full sun you can get back full the same way but the solar will top you off. It is what we do with our 440ah bank of AGMs and 300 watts of solar.

[MsNomer]

This is a dumb question because I don’t remember what your rig is, but why not just a B2B on your original alternator?

[jrobe]

At one time I debated getting a portable solar panel that I could place in the direct sun. We would never pick a campsite in the sun in the summer if we could choose one in the shade. I wouldn't want to even have the thought in the back of my mind that I better find a sun spot to charge my batteries. Of course, then there is the issue of where to store a portable panel. I dropped that idea fairly fast.

[HarryN]

If you are wanting to just trickle charge, then 200 watts is ok, but not really a serious amount unless you live in NM or AZ.

In this area (roughly San Jose, CA) don't bother unless you are willing to put 400+ watts on.

Don't goof around with those little renogy 100 watt panels - go buy some ~ 180 - 200 watt size panels - they fit better anyway.

As a rough estimate (for this area) I use:

(solar panel name plate rating in watts) x (50% ) x (6 hrs / day) = ~ watt-hrs collected per day.

It is far from perfect but a decent indicator.

(400 watts) x (50%) x ( 6 hrs / day) ~ 1200 watt-hrs / day, which will usually be enough to run the fridge, fans and some lights.

If you are going to use a relatively small battery pack < 400 amp-hrs @12 volt equivalent, then put on even more panels, because you won't have enough storage capacity to carry much power from one day to the next.

[GallenH]

I follow your calculations, HarryN, but you indicate the daily yield of your panels
is c.1200WH or c.100AH. If that's barely enough to run your fridge and a few lights you must have one large fridge! How many AH do you generally use in a day?

Given 200W solar and following your formula I'd come up with c.50AH. I see how that might be a trickle charge to a 400-800AH battery bank, but on a 200AH bank it's a significant gain.

[GallenH]

Originally Posted by jrobe

At one time I debated getting a portable solar panel that I could place in the direct sun. We would never pick a campsite in the sun in the summer if we could choose one in the shade. I wouldn't want to even have the thought in the back of my mind that I better find a sun spot to charge my batteries. Of course, then there is the issue of where to store a portable panel. I dropped that idea fairly fast.

I actually use a portable 100W panel right now. On my 97 PW it fits nicely in it's case strapped between the spare tire and rear door. I can see how that might be an issue for some vans, though.

[jrobe]

We have a small 2.7 cu ft refrigerator (probably holds the equivalent of 2 cases of pop) that as I recall probably uses about 40 amp hr on a typical summer day. On a warmer day, our fantastic fan probably uses 10-12 amp hrs if we ran it the warmest part of the day. We could use 10-15 amps making a little keurig coffee, lights, etc.. Assuming we didn't use our TV, microwave, etc., I would probably need 60 amp hours as a bare minimum. This means I would need 200 watts of solar if it was a perfectly sunny day and I was willing to camp in direct sunlight. If it was cloudy and we parked in the shade, I would probably need to triple this.

The other alternative is to drive 15 min or so with our alternator (which we would usually do anyway) and never give the slightest thought to charging batteries, the weather, parking in the sun, etc..

[GallenH]

I guess I wasn't very clear in my OP. I wasn't trying to put up a solar system that would recoop a days use of power. I was thinking about a system that would recoop some thereby extending the time needed before any kind of alternator (primary or secondary) charging.

I agree with the campsite: we like to find shade. A lot of the time in AZ and Utah, that's actually impossible. The last trip we took to NM, none of the 3 campgrounds had much shade.........trees in the SW aren't like elsewhere. But we also often find ourselves parked at a trailhead for 4 hours while we hike. That's always in the sun.

My current setup is small: 100AH. With the loads that I described earlier and my 3-way fridge, I've never had issues. The portable solar gets the battery to full within hours.

But I haven't ruled out the idea of some type of alternator upgrade, be it, as booster suggested, a more powerful primary or as you are suggesting a 2nd alternator.

[HarryN]

Originally Posted by GallenH

I follow your calculations, HarryN, but you indicate the daily yield of your panels
is c.1200WH or c.100AH. If that's barely enough to run your fridge and a few lights you must have one large fridge! How many AH do you generally use in a day?

Given 200W solar and following your formula I'd come up with c.50AH. I see how that might be a trickle charge to a 400-800AH battery bank, but on a 200AH bank it's a significant gain.

My own van use is perhaps somewhat different than people who are using it as a camper.

I own a small business in Livermore, CA that builds and installs van electrical systems, so my suggestion was based on what is working out for customers in this region - which actually covers quite a range of weather conditions.

For instance just 30 miles west along the San Francisco area, it is quite overcast year round. A combination of 400 watts of solar + 4 x 100 amp-hr LiFe batteries will keep a 12 volt refrigerator going and keep the batteries charged up pretty readily.

A system with 200 amp-hrs of batteries and 200 watts of solar, in roughly the same area won't.

Some of my customers live in WA state near the Canadian border with similar setups ~ 450 watts of solar and 4 x 100 amp-hr of AGM - and this is also usually enough for their use.

My own van is really more of a work vehicle than a vacation vehicle. My shop is completely off grid so I need to gather enough power each day to run all of the power tools, heat gun, etc each day. If there is not enough sun light (due to weather or fire season smoke) then I plug in at home.

I am using the total output of 300 watts of solar on the vehicle x 400 amp-hrs of AGM, and then I also have 600 watts of solar panels at the shop that are used for various testing, power, etc. Even with that I am not running a refrigerator, but my heat gun is 1800 watts and it gets a lot of use.

My van is older and has only a small alternator, so I can't really tap into the alternator for significant power. Depending on your vehicle and alternator, it might be feasible to pull 400 watts or more.

My personal view is that a van should have sufficient solar to power the fridge and most loads from solar, and then supplement with the alternator as needed for problematic conditions - unless it is for running an air conditioner. In that case, a heavy duty aux alternator is really a requirement.

This is somewhat a philosophical concept - there are a lot of opinions about what is better.

As a practical matter, the "total installed time and cost" of 200 watts of solar vs 400 vs 600 watts really isn't all that different. It all still takes a mounting setup on the roof, a charge controller, wiring, etc.

The bogart previously mentioned can easily handle 400 watts on a 12 volt system in your area.

I use those all of the time with 24 volt systems, so (30 amps) x (24 volts) can easily work with 600 watts of solar panels. Even 800 watts is not a problem in this area.

The really great thing about those is that they will work even when the lighting conditions are lousy.

[GaryBIS]

Hi,
As you say, solar depends on where you are, what time of year it is, and if the panels are tilted.

The PVWatts calculator will give you estimated solar for any part of the world, anytime of year and any orientation of the PV panels. It uses actual average weather for any location you run it in.

It takes a little manipulation of the solar output numbers it that PVWatts produces, but its easy.

Step by step:
- Run PVWatts in your browser
- Enter your location into PVWatts
- Fill in the data for your solar array
= fill in your solar panel size in KW (so, 400 watts is 0.4 KW)
= if your panels are flat to the roof, change the tilt to 0 deg
= thats really all you have to change, but you can look at the rest
- Go on to the output - you will get a table that looks something like this:




You get an estimatef your solar array output with average actual weather by month.

The first column tells you the average intensity of the solar radiation at that location. Its kind of interesting to look at the variation, but not of much practical use.

The 2nd column called AC energy gives you the average number of KiloWattHours your solar will collect for each full month with average weather.

You can turn this into how many average amp-hours per your solar panels will collect for an average day each month.

Do this as follows.
If you look at (say) Sept, for this 315 watt PV panel, the average harvest is 32 KWH.

Divide this by 30 to get the average per day, or 1.07 KWH.

Convert from KWH to watt-hours by multiplying by 1000, so 1070 watt-hrs on average per day.

Convert to amp-hrs for a 12 volt system by dividing by 12 volts, or 89.2 amp-hrs.

This says that for an average day in Sept in Bozeman, MT, and with one 315 watt PV panel, you will get 89.2 amp-hrs to your batteries.

Of course, you put in your size panel, your location to get your amp-hrs.

PVWatts is not perfect, but its very good - it was developed by NREL and its used by many commercial PV installers.

It won't cover the case where your battery is too full to accept all of the solar in a day, but then you probably don't have a problem then

edit: oops - I entered 32 KWH as 23 KWH - its fixed now.

Gary

[GallenH]

thanks, Gary. I've got it bookmarked.

[UKDude]

My own experience if it's of any use:

I used to have a Sprinter with a miserable 50 watt solar panel and the most it ever yielded was 3.5 amps, and that was in summer, middle of the day.

Now I have 1000 watts of solar and the highest yield I've seen was 58.0 amps, again in summer, middle of the day.
This is ample for my own use; I never use hookups, and it keeps my 800 amps of Lithium fully charged, usually by midday unless I'm using the AC.

[8milimeter]

In my system I have 4x100 watt panels and 3x100 AH lithium batteries. I'm using the RENOGY DCC30S 30A Dual Input DC-DC On-Board Battery Charger with MPPT. That limits the alternator charging load to 30 amps max. I added a switch activated solenoid to access the alternator if and when I need it. Very little stress on the factory alternator. I rarely ever need to use the Alternator unless I have multiple cloudy days.

[GallenH]

Originally Posted by 8milimeter

In my system I have 4x100 watt panels and 3x100 AH lithium batteries. I'm using the RENOGY DCC30S 30A Dual Input DC-DC On-Board Battery Charger with MPPT. That limits the alternator charging load to 30 amps max. I added a switch activated solenoid to access the alternator if and when I need it. Very little stress on the factory alternator. I rarely ever need to use the Alternator unless I have multiple cloudy days.

Just to be clear: My impression of dual input Dc-Dc chargers was that they are usually wired so that if the engine is on, your batteries are charged by the alternator and if the engine is off, your batteries are charged by the solar.

Are you saying that in your system you've added a switch so that when you are, say, stationary the alternator and solar inputs are combined so that the batteries are simultaneously drawing from both?

[8milimeter]

I added a switch at my dashboard that activates a solenoid (1amp). The solenoid connects the vehicle Battery/Alt to the Renogy DCC30S. Lets me control when I want the alternator energy. If the vehicle is not running and the switch is on it will draw from the vehicle battery. I have read that it does back feed the vehicle battery if it is a lower voltage then the van lithium batteries.

NOTE: The DCC30S can only charge 30 amps max. If it has input from the solar and the vehicle alternator it splits the power so 50% comes from each. So if the solar is only supplying 7amps the vehicle alternator only supplies 7amps, 14 amps total. Not sure why this is so, is a complaint that people have about this unit. In my system I can switch the solar off if I want the full 30 amp capacity from the alternator.