Solar Charge Controller Help Please

[NYBurner]

Hi Everyone,
looking for some help as I am doing some experimenting with solar. I'd like to build a small solar garden lighting system this year to learn more about how solar works and whether it is worth investing more into next year. I know Home Depot/Lowes/Ace etc.... sell solar lights....but this is more for me to learn and experiment.
Is there a good quality MPPT charge controller that will allow me to also set ON/OFF times for the load with a budget of say $100 or less? Im looking to use a 50-100W panel with 3-4 LED floods (10-20W) for under tree/plant lighting.
Appreciate any guidance/help!

 

[begreen]

Not sure if a timer will show up in the charge controller but perhaps this will work?
http://www.amazon.com/uxcell-Digital-Power-Programmable-Switch/dp/B008999RYY

 

[BrotherBart]

If you aren't using batteries why do you care about on and off control? In fact for that application even if you are using batteries why do you care about on and off control? Suns out, batteries are charging. Sun's down. Batteries pick up the work.

 

[jebatty]

... to learn more about how solar works and whether it is worth investing more....

If that is your goal, just use a 12V deep cycle battery discharged to about 50% of capacity, use a voltmeter on the battery and ammeter on the charging circuit, all directly wired to the 50-100W panel, and observe what actually happens during charging, effect of clouds and effect of shading (simulate by passing your hand over the panel), V x A = W of actual output. I wouldn't worry about a "good" MPPT charge controller.

I can agree with experimenting to see if you want to get serious about PV. I did the same with a 30 watt panel, saw the effect of clouds, saw that rated panel output seldom was achieved, and sized PV a system based on PV Watts to annually supply about 75% of the household kWh use from the grid. I also chose micro-inverters for the panels.

 

[peakbagger]

Be careful that the panels are "12 volt" panels compared to higher voltage grid tied panels used for grid tied systems. There rarely is a benefit to go MPPT on small panels and many folks skip the charge controller if the panel is small compared to the battery. There are a lot of Chinese charge controllers on ebay labeled as MPPT, most are crude PWM mislabeled with incredibly high failure rates . Stick with Morningstar, possibly a Sunstar or Sun keeper

 

[NYBurner]

Not sure if a timer will show up in the charge controller but perhaps this will work?
http://www.amazon.com/uxcell-Digital-Power-Programmable-Switch/dp/B008999RYY

That looks great, thank you! If I cant find a integrated controller this could def be a winner.

I appreciate all the responses, this is just a fun project I'd like to try. Depending on the controller and options I'd either be using a small deep cycle or lithium battery in the design as well (I figured this was a bit obvious since I was asking about a charge controller, sorry). Accounting for loss and that I live in a fairly cloudy area is why I am looking at a slightly oversized setup.....not sure if I am approaching that wrong or not?

 

[peakbagger]

Avoid Lithium batteries, they require special electronics to get them to charge correctly. I would stick with a small 12 volt AGM FLA battery. Both are a lot more forgiving.

 

[iamlucky13]

Lead acid are also much cheaper for a given nominal capacity. I know of lithium-ion batteries with charge controllers built-in so they can take ordinary alternator input and properly charge the lithium-ion cells, but those are even more expensive. A Smart Battery Li-ion costs over 4 times as much as the equivalent Trojan AGM, although the Li-ions can be regularly cycled deeper, and Smart Battery claims a rather incredible 2000+ cycles to 80% discharge life (vs. Trojans, one of the best lead-acid brands, which are rated at 1000 cycles to 50%). You can save a bit more money and get more life with flooded batteries instead of a sealed type like AGM's, but you have to check the electrolyte levels monthly and add distilled water as needed.

I've been told that MPPT controllers are not really worth the added cost for most small installations (less than 200 W or so) compared to just adding more panel capacity to get the desired daily output. I've never tried to figure out how the performance actually compares, but considering a very basic 10A charge controller goes for $10-30 on Amazon, whereas similarly sized MPPT controllers start at around $60, I tend to believe it.

Also, is the planned demand 10-20W total, or 3-4 bulbs drawing 10-20 W each (up to 80 W total)? How many hours per day do you want to run these? Do you want them to run all year or just seasonally? I suspect you're underestimating what you need for a battery, and maybe for solar capacity, too.

 

[begreen]

For uplighting 12V MR16 LED bulbs should draw 5W and still be very bright.

 

[semipro]

I've been told that MPPT controllers are not really worth the added cost for most small installations (less than 200 W or so) compared to just adding more panel capacity to get the desired daily output.

I've read the same. Your project seems similar to PV apps for RVs that I've seen. You might want to investigate those apps.

 

[begreen]

Here are some kit options
http://www.wholesalesolar.com/rv-marine
(broken link removed to http://bhasolar.com/?page_id=391)

 

[NYBurner]

I'm figuring 3 floods, 10 or 20w each going about 4 hours. 3 season use, I know winter won't be feasible for me in NY.
For 20w lights it would be 60w x 4 hours 240w hours. 12v system would be drawing about 5 -7 amps. Am I wrong that a single 50-100 watt panel could handle this with single 100 amp hour battery?

 

[woodgeek]

If you search for cheap MPPT controllers, be wary. There are a bunch out there on Fleabay and Hamazon that claim to be MPPT, but clearly are not....I have only found non-MPPT when I looked for <$80 units.

 

[NYBurner]

ok thanks for the heads up....is there an easy to identify true MPPT or is pay and pray?

 

[peakbagger]

Dont waste your time if you want MPPT you are going to pay for it. You are better off going with a larger panel than going MPPT . If you want MPPT, stick with Morningstar

 

[begreen]

Good suggestion. The Morningstar Sunsaver MPPT has timer sequences for pv lighting.

 

[iamlucky13]

I'm figuring 3 floods, 10 or 20w each going about 4 hours. 3 season use, I know winter won't be feasible for me in NY.
For 20w lights it would be 60w x 4 hours 240w hours. 12v system would be drawing about 5 -7 amps. Am I wrong that a single 50-100 watt panel could handle this with single 100 amp hour battery?

Ok, accepting that you won't run all night long or expect similar performance in the winter makes this much more viable than what I was concerned your expectations might be. Your suggested specs are actually in line with what I'd recommend.

NREL's solar resource maps suggest the average daily summer production in NY is 5 kW-hours per kW of capacity. So divide the required kWh per day (240W-hr = 0.24 kW-hr) by that to get necessary Wattage. That suggests you should consider 50 W your bare minimum panel size under optimal conditions. Larger helps keep the battery from getting drained too far during multiple cloudy days in a row, as well as make up for charging losses. 100 W should keep you going through spring and fall.

When you said "small" deep cycle battery, I was concerned you were thinking of something much smaller than a car battery. 240 W-hr per day is 20 Amp-hours for a 12 V battery. Because you want to design your battery system not to drain below 50% charge on a regular basis, you should at least double that. 50-75 Ah sounds good, which is about the size of a car battery. If you want to spring for a 100 Ah battery, that gives you more capacity to play with. Again, multiple cloudy days in the row in the spring are when a larger battery helps you the most. If you've got a way of monitoring your state of discharge erring towards the smaller range of your battery options can be done safely by running the lights less when production is lower. Many charge controllers also serve as the point of connection for your load, which allows them to shut off the load if the battery voltage drops to a point - usually corresponding to 10% or 20% state of charge. Some of the nicer models might let you set the cutoff voltage. You don't have to always avoid going below 50%. Just avoid doing it regularly and the reduction in battery life should be small.

 

[simple.serf]

All I'll add as someone who has tinkered with solar power for the last 16 years (and who has just started another project today, in fact ) is to just buy good stuff from the beginning. Morningstar, Xantrex, Trojan, etc. Also, as someone who lived with PV only for a period of time, plan at least 50% larger than you think you need.

 

[iamlucky13]

I've read the same. Your project seems similar to PV apps for RVs that I've seen. You might want to investigate those apps.

Almost identical except he probably won't also have a 120V battery charger to charge the batteries from "shore power." However, I'm pretty sure there's a lot of poorly designed RV systems out there that don't do much more than keep the batteries topped off when not in use.

Perhaps the biggest mistake is putting the charge controller where convenient, then running a long length of wire sized to code between the charge controller and the batteries. Working at 12V makes any voltage drop 10x as significant as at 120V, and dependence of batteries of having a certain voltage to charge effectively (which the charge controller usually monitors at its terminals, not the battery terminals at the other end of the wiring) can have even more of a significant effect.

Without going into the engineering details, it ends up being extremely important to locate your charge controller as close as practical to the batteries, and to oversize the wire. Electrical code for wiring sizes is based on safety. Efficiency and utility factor for a solar and battery system has its own implications. A 12V charger connected to a 100 W panel can be safely hooked up to the batteries with 14 gauge wire, but 10 gauge or even bigger will help ensure the batteries actually see the intended charging voltage, and as a result, draw as much of the available current as possible.

Note that I'm discussing a separate issue from that addressed by MPPT controllers. Those handle optimization between the panels and the charge controller. I'm talking about optimization between the charge controller and the batteries.

Locating the panels close to the charge controller and over-sizing that wire is also very beneficial, but if it comes down to a choice between getting the charge controller close to the batteries, or the panels close to the charge controller, do the former.

 

[NYBurner]

Awesome information, thanks so much for sharing. The logistics of 'hiding' the controller/battery is something I also need to figure out. Out back near the pond should be fairly easy.....if I try to do something out front, the wife will be a lot more critical of the aesthetics haha