Yeah mon, checking in from the Caribbean!

[Tang Tonic]

Greetings forum,

I have been reading here trying to learn as much as possible because I have a deep desire to power some of my electronics from my favorite star - El Sol! I live on the island of St. Croix, US Virgin Islands where the cost of electricity is 0.46 per kWh. I've learned on this forum that pv power is about $1.00 per kWh. Down here with our high electric rates, it makes sense to supplement with solar. Another caveat: the second largest refinery in the US just closed and guess where it is- St. Croix. That means our already inefficient power company known as WAPA who already gets subsidized fuel from the refinery (Hovensa) will probably be raising rates in the near future. They will continue to get subsidized fuel until 2013 then they have to find a new supplier which means more $$$$. Plus they are terribly unreliable especially during hurricane season when we get hit with lots of tropical depressions and rain (for some reason rain causes power outages here).

So anyways, I have a kill-a-watt and I know the power demands of our various appliances (coffee maker is a serious power hog). My goal is not to live Off-Grid but to power as many small appliances as possible with pv. I know people on here say to figure out your demand and size accordingly. I am going a different route in that I have a certain amount I am willing to spend so I will power as much as I can based on my budget. I realize even with the high electric rates I will be looking at about a two year payoff if I spend less than $1,500 on my setup- I can live with that. My current electric bill is about $120 per month, so I'm hoping to cut that in half.

So here is what I am thinking - 2 or 3 Suntech panels at 175 watt, 35.2 Vmp . I will most likely buy from Sun Elec since they have a warehouse in Puerto Rico and shipping would be reasonable. If I could, I would support the sponsor of this site, but I need to go about this with my budget in mind.


Next, for a charge controller. I have decided to go with an MPPT controller since I will be charging a 12V battery bank and most panels I have seen in my price range have Vmp in the 35V range. I have been looking at the MPPT made by Isotronics ebay link: http://www.ebay.com/itm/US-MADE-Off-...item19d0012456
PDF link: http://www.intronics.com/products/pdf/MPPT25.pdf
Can anyone vouch for this controller? I like the fact that is US made and it does come with a 1 year warranty. I have also looked at Rouge but the price is $325 vs $185 for the Intronics.

Finally, for batteries I will go with the standard workhorse, (2) T-105 Trojans. I will bite the bullet for a Xantrex 600 watt true sine wave inverter to power my beloved vintage stereo, since music is my passion (no TV in this house mon).

The panels will be mounted on a wood frame I will build and be installed on the roof of the porch on the house I rent which gets unobstructed sunlight all day and has about a 5 degree tilt to the west. I would mount the panels in series and the CC would be about 10 feet or less distance away with the batteries another 5 feet or so. I would have a fuse in between panels and CC, and CC and batteries, not sure what size yet. I would also like to run some wires for DC into the three rooms of the house to power some 02 cool fans, charge cell phone and laptop, and some LED lights.

So I guess so far my questions are:

- Are there any other places to get cheap panels besides sunelec.com?
- Does the MPPT controller from Intronics seem like a good buy or should I be looking at the Rouge or even a PWM type?
- Are there any foreseeable problems with my proposed setup?
- Do you have any suggestions for me?

Once I dial in a few more details such as the exact panels I will be purchasing and exact distance wire runs will be, I will ask for some help on wire gauge sizes, fuse sizing, and how best to run some DC power to three rooms in my house. Thanks in advance for any help you can give me and I am glad to have found such a helpful place.

Aloha and Irie vibes from the Caribbean!

[Cariboocoot]

Welcome to the forum.
Whatever you do, don't spoil my romanticized visions of the Caribbean, okay?

I guess the first question would be: Does your utility allow grid-tie solar production? It's cheaper than off-grid and not far off your $0.46 / kW hour power.

The second question is going to be: how many total Watts & Watt hour do you want to supply? I know you don't want to do it that way, but sizing an inverter & battery bank is dependent on this info. You may find it advantageous to go up to a 24 Volt system if you A). need more than 2 kW peak power or B). need to store more than 2 kW hours (just as guideline numbers).

Incidentally, Morningstar makes a nifty 115 VAC 300 Watt inverter: http://www.solar-electric.com/mosu300wasiw.html

If you've only got 10 feet from the array to the controller, and you use panels with a Vmp that suits the system Voltage (17.5 or so for a 12 Volt system, about 35 for a 24) you don't need an MPPT controller. Your biggest problem is probably going to be power loss from high panel temps as that midday Caribbean sun is not know for being cool.

For a couple of Trojan T105's you'd be looking at about 350 Watts of panel for recharging.

Lots of options here. At some point you'll have to start making the decisions that determine all else.

[vtmaps]

I know nothing about that charge controller except what I read in the pdf that you referenced. It does not appear to have remote temperature compensation. It will assume the batteries are the same temperature as the controller.

I do see problems with your proposed setup. The controller is rated 25 amps at either 12 volts or 24 volts. Therefor it will handle twice the power at 24 volts. You indicate that you want two or three 175 watt panels. At 12 volts that controller will not be able to handle two panels, let alone three. You need to go with a 24 volt system.

One more thing, you indicate that the panel Vmp is 35.2 volts. The number you need to know is Voc. The controller has a max input voltage of 80 volts. The Voc of two panels in series may exceed 80 volts and destroy the controller. Also, the Voc of panels increases as they get cooler than standard conditions. I don't know the Voc of those panels, and I don't know how cold it can get in St Croix, but I would guess that this controller is not suitable for two panels in series.

--vtMaps

[Cariboocoot]

And just so we're clear, that 35.2 Vmp will not work with a 12 Volt system without an MPPT type charge controller. But they would work with a 24 Volt system and PWM type controller.

Complicated, isn't it?

[reddog]

Greetings forum,

Next, for a charge controller. I have decided to go with an MPPT controller since I will be charging a 12V battery bank and most panels I have seen in my price range have Vmp in the 35V range. I have been looking at the MPPT made by Isotronics ebay link: http://www.ebay.com/itm/US-MADE-Off-...item19d0012456
PDF link: http://www.intronics.com/products/pdf/MPPT25.pdf
Can anyone vouch for this controller? I like the fact that is US made and it does come with a 1 year warranty. I have also looked at Rouge but the price is $325 vs $185 for the Intronics.


So I guess so far my questions are:

- Does the MPPT controller from Intronics seem like a good buy or should I be looking at the Rouge or even a PWM type?


Aloha and Irie vibes from the Caribbean!

Hello Everyone,

I have the same question on the Intronics vs Rouge vs Morningstar MPPT charge controllers. I would like swap out my junk charge controller that I bought..

Thanks in advance for the input.

[BB.]

Reddog,

Welcome to the forum.

Before we can really give you answers, I have some questions...

What is the size of battery bank (voltage/Amp*Hour rating)?
What is the size solar array you have/are planning for?
How far from the array to the battery/controller location?
Where, roughly, is the system installed (to figure out hours of sun per day)?
What are you expecting it to power (Watt*Hours/Amp*Hours per day at what voltage/AC/DC/etc.)?

Solar products generally cover narrow ranges of power/voltage and a good controller for a smaller system will not be the same as a controller for a larger system.

-Bill

[reddog]

Hello BB,

Thank you for the welcome.

Well I would say I have a very basic system. two Sopray 140W mono panels in parallel on the roof of the house (Atlanta, GA). Distance is about 20ft to the basement where two Marine Energizer band E27DC 12v batteries connected in parallel. I have attempted to find the charging spec but have not found it. I am attempting to run a 400W inverter for 24hrs a day via the 12v supply of the batteries..I know that most likely will not happen so I have purchased a LVD high current switch to protect the batteries from a complete discharge. I get a min of 5-6 hrs of sunlight here during the winter must more during the long summer months.

The controller will not be more than 3-4 feet from the batteries in the basement...I have an el cheapo crapo charge controller that is only good for telling me what power I get from the panels..at peak sun the panels kick out 15 to 16 amps...it just seems my current controller goes to sleep or does not know what to do to charge the batteries...

Looking to upgrade to a good controller but do not want to take out a loan for one..any input is greatly appreciated.

[BB.]

Not really the best to use Marine batteries as deep cycle... Anyway, assuming your batteries are around 100 AH @ 12 volts each. The recommended solar array to charge a 5% to 13% rate of charge would be:

• 2x 100 AH * 14.5 volts charging * 1/0.77 panel+charger derating * 0.05 rate of charge = 188 watt minimum
• 2x 100 AH * 14.5 volts charging * 1/0.77 panel+charger derating * 0.10 rate of charge = 377 watt nominal
• 2x 100 AH * 14.5 volts charging * 1/0.77 panel+charger derating * 0.13 rate of charge = 490 watt "maximum cost effective"

Assuming 200 AH battery bank @ 12 volt for 2 days of backup (no sun; 1-3 days recommended) and 50% maximum discharge, your useful storage per day would be:

• 200 AH * 12.5 volts * 0.85 inverter eff * 1/2 days no sun * 0.50 max discharge = 531 WH per day at 120 VAC (inverter)

Using PV Watts for Atlanta Ga, fixed array tilted from horizontal, we get:

Month    Solar Radiation (kWh/m 2/day)
1      3.86     
2      4.67     
3      5.21     
4      6.17     
5      5.95     
6      5.81     
7      5.82     
8      5.83     
9      5.21     
10      5.51     
11      4.42     
12      3.72     
Year      5.18

Using February as the "break even" month, you get 4.67 hours of sun per day (average).

• 531 Watt*Hour per day * 1/0.52 end to end system eff * 1/4.67 hours of sun = 218 Watt solar array minimum

For a small system, I would suggest a MorningStar 300 Watt 12 volt TSW inverter. It is really nice for these smaller systems/load. Pretty efficient and includes "search mode" (goes to low power standby if <6 watts of AC loads) and has a remote on/off switch.

A very nice mid-sized MPPT solar charge controller (with good reviews here) would be the Rogue 30 amp 12/24 volt controller (around $325 + shipping from Oregon). My recommendations for a the maximum "cost effective" solar PV array with a 30 amp controller on a 12 volt battery bank:

• 30 amp * 14.5 volt charging * 1/0.77 rate of charge = 566 Watt PV array "cost effective maximum"

You can run a Vmp~35 volt array and keep the wire gauge/voltage drop to a minimum for the 20 foot run.

Personally, I would change out the pair of 12 volt marine batteries in parallel to a pair of 6 volt golf cart batteries (around 220 AH @ 12 volts) in series. Running batteries in parallel runs into problems and increased maintenance issues (I would suggest that 2-3 strings in parallel would be the maximum unless there are other limitations that force higher numbers--and you are prepared for the extra maintenance/monitoring issues).

Note there are still a lot of details to work out. For example, smaller inverters typically draw 6-10, and even as much as 20 watts just "on" with no other AC loads... Running one 24 hour per day will draw 6w*24h=144 WH per day--about 1/4 of your power capabilities with a 218 watt array.

Anyway, that is the 50,000 foot view of what I see right now. Your thoughts and questions?

-Bill

[reddog]

Hello Bill,

I really appreciate you taking the time to pull those details together for me. So it appears I made a couple mistakes in developing my system and did not do enough research.

I was looking at the Morningstar MPPT controller..only because of price points as it appears at a min in addition to the controller I should swap out my batteries and go with golf cart ones. Any reason to stay clear from the Morningstar controller?

I was also planning to put up a 600w 3 phase Windturbine to help the panels.

[Cariboocoot]

Any reason to stay clear from the Morningstar controller?

Yes: $500 for the MPPT 60 vs. the same money for the new MidNite Classic Lite http://www.solar-electric.com/misoclli150m.html

A wind turbine will need its own controller, and be really sure you have enough wind to make it worth the investment.