off grid solar project

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haklesup
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off grid solar project

Post by haklesup »

I'm upgrading a shed to be a detached office thanks to working from home during the pandemic. One feature I would like to install is a small solar system mainly for lighting but maybe also for small AC loads depending on how much capacity I have left over after the lighting is selected and a run time is determined.

Most of this is fairly straightforward with the usual number of design choices one might expect. I'm going with two 100W panels, a 60A MMPT controller (overkill but room to grow) and 2 lead acid deep cycle batteries (100Ah each) and a few single pole DC breakers here and there. At this point I am working out 2 aspects. What kind of lighting and which battery

1. I would like to use the 12VDC directly from the battery for the lighting and skip the efficiency loss of an inverter and LED Drivers in between. Problem is LED low profile lighting is predominately AC with a current source in line and the only predictable 12V lighting is for RV. I could go with conventional screw base fixtures with 12V bulbs, that's going to work but I want the color selectable LED recessed or surface mount type.
1A. What are people doing here, what's the conventional solution for off grid interior room lighting
1B. can I just remove the AC to DC current source and direct wire to the battery, seems like brightness would vary uncontrollably and annoying dimming after dark. I couldn't find a 12V DC-DC current source specifically designed for Solar direct to LED. I did find plenty DC-DC buck boost converters, maybe that's the way to regulate, any opinions please?



2. Batteries. Its not in the budget for Lithium so I am looking at two Marine deep cycle batteries which are $65 to $130 at walmart. MCA (similar to CCA) is the only clear spec on the batteries and there are models with 600 to 950 MCA all in the 24DC or 27DC size. I understand that MCA roughly relates to the max load it can deliver, I doubt I would ever need hundreds of amps for lighting a car amplifier or even a PC running off an inverter.
2A. The question is does anyone know if there is a trade off between MCA and capacity or any other performance criteria. These all are close to 100Ah but I can't find all online and most don't show capacity. Any advice on battery selection appreciated.
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CeaSaR
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Re: off grid solar project

Post by CeaSaR »

Hey, what do I know?
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dacflyer
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Re: off grid solar project

Post by dacflyer »

I've built a few of my own DC led lights. with good results. I'm sure you could hack any AC led light to run off of DC.
I didn't like the stock bulb dome lights in my van, i tried the led replacement leds, they just didn't give enough light, and the color was an icy cold blueish light. So, i took some salvaged led strips from a 2X4 grid ceiling light fixture. the color was a nice bright white (like cool white fluorescent lamp )
i had some boost converters i used that boosted up to 30VDC. the leds were in 7 led sections...I think.
anyway, these were way brighter for what i wanted.. So, i gutted the stock dome lights and made these small strips fit in. I was very pleased with the results.
Then i also took and old RV style fluorescent fixture ( 15" size T5 Lamp ) I gutted the fixture and added in the led strip and the little converter fit inside nicely. it is brighter than the fluorescent lamp was. These little power supplies also have a dimmer ( voltage control )
I can give you the info on the power supply later on if you like..

In my house i have some of them small 12v 10W halogen puck lights, like you use in a china cabinet or under the counter.
I later found some 2w led replacements for them. and they give off just as much light.
there's all kinds of options for 12v lighting.. and even better they do make Edison base led bulbs, so you can use a regular fixture or a lamp.
options are endless.

As far as batteries and solar, 200w of solar will not be enough to charge 200Ah worth of batteries.
I am running a 24v system, and i have 3 in series panels ( 3x 295W) and a MPPT charge controller. it charges the batteries at about 20A hr. in full sun.
battery bank is 266AH in 24v config. and my inverter is a recycled 900W APC UPS LF inverter. I have this temporarily running all the lights in my house, and this gives me about 2 days running on average if no sun. the system as is,, i think the system could use another 100AH. but it does fairly well for now. I'm saving about $20.00 - $25.00 a month on my electric bill.
I'm working to build a bigger system for isolated circuits in my house to run things like my fridge, microwave, lights, attic fan, and the tv etc.
i bought a big lithium battery bank out of a BMW. The system will be running a 48v system. a 2KW Inverter, that can surge 6kw for 20 seconds, for starting big loads or compressors etc. 3kw for 30 min.
my bank will be 6 banks of 48v li-ion.
I hope to have it all up and running sometime soon,, I need to mount the new panels on the roof, 295W, i already took the older 100W panels. was 24 of them.. They are up for sale..
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jwax
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Re: off grid solar project

Post by jwax »

Years ago, I lived in Campbell, CA, and there was a "surplus" solar provider near where I lived.
https://www.mlsolar.com/
Maybe you've talked with them.
They had incredible deals on panels, probably still do.
In designing the system, go for way more solar power than you think you'll need.
Forget them producing much power in your cloudy winter there in silicon valley.
As for storage, buy as much as you can afford.
Cool project! :)
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solar3000
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Re: off grid solar project

Post by solar3000 »

I've done a side off-grid solar system.
I have some panels outside the house. They are for 12 volt systems. I have it set up quite simply really.
[solar] -> [controller] --> [12v lead acid]
Simple, right!
I have connected, some LCD clocks, LED night lights, other misc [on/off] lights, USB phone charger, and other misc 12 v toys like UV lights and flashing L EDs.
So, when the power goes out, I mess with my solarts. [solar arts].
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haklesup
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Re: off grid solar project

Post by haklesup »

Thanks for the info, the link had some general perspective advice that was useful. I'm still collecting components, installation won't be for a month or two since I can only work on this during weekends (until daylight savings time at least when there is enough time after work). I've only just completed the framing changes and still need to install doors and siding. I'm keeping it small so nobody decides I need a permit.

While it may be hard to charge 200Ah on 200W of panels, I doubt I will deplete them very often, I only have like four 14W and five 10W floodlight fixtures planned so far. If its not enough to top them off regularly, I can add a panel or battery later

For lamps, I got some low profile color selectable, 14W, 800lm, LED from HD and not until I got it home and could find the label inside the J box where the regulator is did I learn that the operating voltage is 28~36V, 350mA. That's attainable using a 60W variable buck boost regulator in constant current mode I got on ebay for $6 each. Add to that the cost of low voltage 2 pin connectors to mate with the lamp $2 each (I don't want to cut the leads off the included ballast yet). Note that ~12V fixtures use the barrel connector but higher voltage will use a 2 pin connector and the gender may vary depending on AWG of the cable attached. Whether that's more efficient and justifies the conversion cost ($8 per lamp) than just powering them off a salvaged UPS inverter remains to be seen, I'll have to do some bench testing later when I have it more setup. I also need to verify of the color selector still works properly with a substituted ballast module (the switch is small and I suspect its just a resistor network, not sure how that works yet)

I also got this neat buck boost regulator with color display and wifi to experiment with. at least it will get me a cheap flexible bench supply or maybe an overkill lamp dimmer with phone app remote (lookup XYS3580 on ebay).

The regulator modules look pretty versatile, I may be able to repair some 30W LED floods that had the ballasts burned out, I was going to repair for 120V but now maybe 12 or 24V is a worthwhile. (when I say ballast, I really mean current source module)

I'll try to get over to ML solar and take a look someday. I got the panels from Lowes who had a great price on some windy nation components. Still processing the technical difference between single crystal and polycrystal solar cells, the prices and specs are not that far apart. If this works well, I may add a 30W panel to my 93 Explorer so I can unplug the battery maintainer from the house (not used often)
qeuker
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Re: off grid solar project

Post by qeuker »

Hello considering the same Can anyone help unanswered questions: Design of solar panels vs charger 12V system
1. Seems eg If you buy a single 110W panel nomnal 12V THEN you will be very disappointed in winter/ no sun as insufficient voltage generated for teh charge controller to work ? So we need a " mix and match" of panels/ chargers for off grid so that on less sunny days there is still enough voltage to generate SOME current to the batteries Yet in high summer avoid total voltage overload ? So how do we juggle these variables / panels / solar chargers so we get something on not so sunny days too ?
2. No matter what : We must protect your batteries against over discharge and destruction So please what gizzmo must we buy for this ? How much are they ? What are they called ? How many legs does it have ? No the protections in a typical inverter will NOT do.it. No the average lower cost solar charge dc output ( eg for running lights ) will not do it either.
Direct DC efficiency vs AC convert . For me its the equation of "pleasure for effort ratio. " Every manufacture of electrical stuff has their own power supplies for their kit ( eg pc's) invariably AC. I wish there was an abundance of dc options There is not ? So I cant be mucking about with modifying this and that. Pleasure for effort ratio too much against

Love to know how to "juggle " the low sunshine / high sunshine equation ? Particularly as I'm in the UK

somwhere between heaven and Primark ciao MsO
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Externet
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Re: off grid solar project

Post by Externet »

Hi.
Am happy to report two weeks ago finished my solar implementation; next energy invoices will be credits piling up monthly until winter heating comes.
Not off grid, am on grid. That is my storage 'battery'
Six 2 metres x 1 metre each 390W 40VDC 10A DC series string panels, twice on the roof make 12 panels for almost 5 KW at 240VDC / 20 Amperes into an inverter feeding me and the excess going into the grid.
Roof.jpg
- Abolish the deciBel ! -
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jwax
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Re: off grid solar project

Post by jwax »

Congratulations Externet!
I'm glad you went with waaay more than 200 watts solar! Lot less hassle without storage batteries too!
I had net metering at my last house, with 4.6 KW of panels, and waited to get a check from the power company. In New York, they "even up" once per year to see what the net energy flow was. Turns out that buying from the grid cost $0.16/KWH, but selling to the grid yields you $0.03/KWH! So don't expect too much payback!
Nice installation!
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jwax
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Re: off grid solar project

Post by jwax »

qeuker- What is required is a "Solar Charge Controller"- it charges the battery when the battery needs it, and prevents overcharge.
As to getting the most out of low sun/high sun, that takes a Maximum Power Point Controller. It optimizes the panel output depending on incoming sun intensity.
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Externet
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Re: off grid solar project

Post by Externet »

Hi John, thanks.
In Bourbonland the KWh is 10 cents and the electric utility is forced to pay (credit) my generated energy on net metering at same 10 cent /KWh for the next 25 years by decree no matter if rates increase or decrease ---> yes, sure, decrease... One extra reason that made me jump onto it, the program was supposed to expire June 30. My last bill for June came down to $22. Will see how much credit I get for July. Will report.
Besides, 26% of the installation cost to be deducted from taxes next filing also helped to jump onto it. Actually should be like 20% because I paid 6% sales tax for the equipment.

At $0.43 per Watt of new panels warranted 25 years, $0 shipping / local pickup, couldn't resist. Murphy lives with me, but hope this rare time was caught asleep. Will see...

Another good thing... I did not fall from the roof, no hospital bills, no ambulance. 100% installed by me, no ripoff from installers.
- Abolish the deciBel ! -
roryjim1
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Re: off grid solar project

Post by roryjim1 »

I am looking to buy a fridge for my home but I need the best fridge that has good quality and a reasonable price. Please tell me your opinion about it. If you will help me then I shall be very thankful to you.
dyarker
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Re: off grid solar project

Post by dyarker »

A reasonable question for somewhere. But what does it have to do with a year old thread (last post 8 months ago) about solar power in an electronics magazine's forum??
Dale Y
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CeaSaR
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Re: off grid solar project

Post by CeaSaR »

The absolute vagueness of the post is such a flag. It is technically off topic and could be reported.

Still haven't heard anything back from Sean about all of this.
Hey, what do I know?
dyarker
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Re: off grid solar project

Post by dyarker »

His last visit here was 30 December. I doubt you will hear back.
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