Solar strategy in the east

[Snowman9000]

I'm from Illinois. Camping out in the AZ desert at the moment, I can see that solar is easy out here. Do the math, install it right, and you are golden.

Camping in the eastern 2/3rds of the US, in the summer, is more about finding shade. How should people who dry camp mostly in wooded sites think about solar?

1) Roof-mount 100w give or take, for battery health?
2) Load up the roof with panels; will you get anything out of it?
3) Portable solar, try to find a sunny spot for them?
4) Use the money to buy gas for the genset?

I need to try this at home this summer, but maybe someone can post their experiences... How many watts will a 100w panel put out when fully shaded by trees?

[12thgenusa]

I think at least part of the difference can be attributed to reduced cell temps in the shoulder hours. First, the ambient temp is lower in the morning and late afternoon hours (at least it is where I am). Second, the sun is considerably off-axis during those hours, both resulting in lower panel cell temps. So the "heat penalty" paid by MPPT might be as much as 11-13% at midday in Salvo's example, but could realistically be only 5% in the early and late hours.

[BFL13]

BFL13 wrote:
...

Salvo's graph here does show that the MPPT, by being say an amp over the PWM (same as panel direct connection he did)all day, is twice as good as PWM when PWM is getting 1 amp 🙂 and then when PWM is getting 8 amps mid-day, the MPPT is only a little better at 8.5 amps.

I suspect this is what "they" mean by MPPT doing better in less light, but don't know for sure. If so, it is another example of how you can "spin" statistics. Or maybe there is something real to it?

I still think the answer is in this somehow, where MPPT has a higher percentage above PWM in the shoulder hours than at mid-day. Suppose it were cloudy all day and the PWM never got over say 3 amps?

If the MPPT retained its sunny day shoulder hours worth of percentage advantage all day, then "they" could say it was way superior in daily AH haul on cloudy days.

Of course it would be "spin" because twice a little bit is still only a little, but the percentages look fabulous. "They" don't brag about the mid-day difference on a sunny day.

[12thgenusa]

Quite a bit of talk about voltage decrease under low light conditions, but the real problem is the decrease in Isc. Consider the fact that shading could be thought of as localized reduction in irradiance. Most manufacturers publish charts indicating performance at various irradiance levels. I haven’t quite figured out if these are specific to a particular panel or panel series or are more generic in nature. They are virtually identical for either “12-volt” or “24-volt” panels.

Below are a couple of such charts. The one on the left shows performance at discrete light levels. The one on the right is a normalized continuous graph.



It can be seen the Voc drops somewhat with decreased irradiance, but Isc has a greater than one-to-one relationship with irradiance. A 50% drop in irradiance results in slightly more than a 50% drop in current resulting in a corresponding decrease in power. I don’t believe either PWM or MPPT can “make something from nothing”.

I also found a chart for a Unisolar thin film “panel”.


It doesn’t appear much different from the above. It’s not that I disbelieve the claimed superior low light performance, but it would be nice to see some published data that verifies the assertion. Perhaps someone has some further info?

[Almot]

For those thinking of "going solar" I would suggest to max their panel size up to the limit of their roof (considering shading between the panels and roof structures as well), and only then decide on the controller. 20A controller could handle ~300W solar array, which should be enough for "going solar" in most of the Southern states if you keep at least 300-360 AH battery bank and limit the use of 120V devices other than electronics. Though it can get cloudy in Fl in winter, so it's better to have panel more than 300W.

Can't say if controller costing more than a panel is a "scam". Controllers used to cost less than panels, but solar panels prices have dropped significantly in the last 4-5 years. If they drop further, would this mean that any controller over $5 is a scam? :)..

The examples above - Rogue and Morningstar, even though not cheap, are well designed and well made units. If you want features and quality, you have to pay. Weak point of Eco-Worthy is not only 40V input, but also on-board temp-compensation. And I'm pretty sure there are other weak points in this unit, possibly - the way how it handles transition from Absorb to Float.

Panels and controller make the bulk of total cost of the system, but you will still have to spend at least few hundred more on other components.

[joelmyer]

BFL13 wrote:
I have an Eco-Worthy 20a MPPT controller ($102) that some other members here also have. It works very well on one 24v panel up to about 250w or a bit more, and you can adjust the set point voltages to suit your needs. It's weak point is the max input panel voltage it can take at 42Voc, so you can't use, say two 120w 12v panels in series as your one 24v panel (that would be two 22v Voc so 44v and over the 42. No problem on a panel with Voc about 37v like a single 24 like my Hanwha 230w.

A better choice to get more input voltage might be the Tracer 20a MPPT at 100Voc limit. ($140) We are waiting for a report from a member who got one of those. I saw one Youtube video on it from Oz where he seemed to say it has the high set point at 14.4v but I don't know if that is adjustable if you wanted higher.

In Key West it may be that 14.4 is plenty high for the prevailing temperature, don't know.

Thanks DFL et al
Key West December-February it says average high in the high 70s. Actually there is a lot of mid 80s.

I'm torn between "do it right the first time" and omg, that's more than the panel.

I'll probably start buying/installing next fall so I'll be watching the reports on the Eco-Worthy and Tracer.

Thanks again for all the expertize.

Joel

[pianotuna]

Hi BFL13,

To chose a controller one should pick the features and capacity needed. It isn't a scam if it costs more than a panel.

Where I am, a temperature sensor on the battery bank is a must do. If there were battery sense wires that would be a good addition, too.

Does this cost more? Yup! But four of my batteries are now nearly nine years old. The other four will be four years old in May 2014.

Should I replace my (aging) blue sky 3024di controller? No, because it is working well.

[BFL13]

When your controller costs more than your panel, you just know you are the victim of a huge scam. You don't have to do that to yourself, but being over 21, you are allowed to of course.

[EsoxLucius]

The new Morningstar TS-MPPT-30 is also a possibility.

[time2roll]

joelmyer wrote:
I've decided to go solar next winter for my annual three months in Key West.

I'm thinking 250 watt, 24 volt panel and mppt controller.

Which controller are you going to use?

Joel

For a single panel of about 250w I would go with the 20 amp Rogue.
Unless you plan on expanding.... then a 45 or 60 amp Morningstar.

[BFL13]

I have an Eco-Worthy 20a MPPT controller ($102) that some other members here also have. It works very well on one 24v panel up to about 250w or a bit more, and you can adjust the set point voltages to suit your needs. It's weak point is the max input panel voltage it can take at 42Voc, so you can't use, say two 120w 12v panels in series as your one 24v panel (that would be two 22v Voc so 44v and over the 42. No problem on a panel with Voc about 37v like a single 24 like my Hanwha 230w.

A better choice to get more input voltage might be the Tracer 20a MPPT at 100Voc limit. ($140) We are waiting for a report from a member who got one of those. I saw one Youtube video on it from Oz where he seemed to say it has the high set point at 14.4v but I don't know if that is adjustable if you wanted higher.

In Key West it may be that 14.4 is plenty high for the prevailing temperature, don't know.

[joelmyer]

BFL13,

I've decided to go solar next winter for my annual three months in Key West.

I'm thinking 250 watt, 24 volt panel and mppt controller.

Which controller are you going to use?

Joel

[Almot]

BFL13 wrote:
Aren't most of those little car battery chargers (10w etc) amorphous?

Yes. And most of them don't have a controller or any means of voltage regulation.

[BFL13]

Aren't most of those little car battery chargers (10w etc) amorphous?

[pianotuna]

Hi Almot,

It is my understanding that Amorphous panels come in a variety of voltages.