Solar on a budget

[jflorey2]

My 2 kwh a day includes 10 hours a day on the laptop with a monitor running at the same time.

OK we can work with that. That means you need 166 amp hours a day at 12 volts, 83 amp hours a day at 24 volts or 41 amp hours a day at 48 volts. 3 days of autonomy - triple all that. Double it again so you will never drop below 50%. That gives you 288 amp hours at 48 volts. You can probably live with 220 amp hours at 48 volts, which is 8 T105 batteries in series (about $800, 3 months savings.) Or 8 in series-parallel for 24 volts.

The solar needed to support that is roughly C/10, or 1100 watts. That's about $1000 from cheap sources, so another three months.

I am the kind of person that plans for the worst. So I always have a backup and a backup for my backup (I have a second gen that is still in the box,never even been opened). So I will always make sure I have the ability to produce at least double what I am ever likely to need.

OK, great. See above.

No, you misunderstand, the battery is always connected to the solar. Only the load gets disconnected.

OK sorry, my mistake. I'm not sure I understand what you mean, then, when you say "then switch to another that is fully charged." Do you disconnect the inverter and move it? (same problems I mentioned before.) Do you unplug one AC appliance and plug it into another system? (you get hit by a lot of tare losses in that case.) Do you disconnect DC loads and rewire them to another battery? (also somewhat problematic)

The modular system is the best way I have found to be able to do this in a way that fits my budget and produces sufficient power to cover all or at least most of my power need.

And we are telling you that modular systems (of the type you describe) are more expensive and less reliable than a single larger system of the same (total) capacity.

[andyg]

That has nothing to do with the OP's application. A part time system has weeks to recover from abuse. You cannot do that with a daily use system.

Yes, I'm aware. That's why I made that clear. It's something to compare to.

[andyg]

Agreed, littleharbor. I've got the battery strings going to bus bars to somewhat balance the strain on the bank. Just wish decent power inverters weren't so expensive. We already want to see about adding a small refrigerator to the mix, ha ha. Which means more panels and batteries. So yeah, this would likely add to the challenge of working with mixed-aged batteries bumping up to 24v.

[Sunking]

Several years ago, we bought some hunting/ recreational property we go to about every 4 to 6 weeks for extended weekends, sometimes for a week or so (remote swamp land). At the time, we were new to using solar. Looks like we've broken some cardinal rules (best practices), ha ha, but our system is working pretty well after learning first-hand the limits of an off-grid system, to include being aware of the various inefficiencies, risks, and such.

That has nothing to do with the OP's application. A part time system has weeks to recover from abuse. You cannot do that with a daily use system.

[littleharbor]

One recommendation I would make for your next upgrade would be to move to a 24 volt inverter. This would enable you to decrease so many parallel battery strings. You will also be able to continue to enlarge your solar array without upgrading your charge controller.

[andyg]

We also have a similar mindset to start small and grow as we go using solar (on a budget).

Several years ago, we bought some hunting/ recreational property we go to about every 4 to 6 weeks for extended weekends, sometimes for a week or so (remote swamp land). At the time, we were new to using solar. Looks like we've broken some cardinal rules (best practices), ha ha, but our system is working pretty well after learning first-hand the limits of an off-grid system, to include being aware of the various inefficiencies, risks, and such.

We had a similar budget concept and didn't want to take out a loan either to front the cost of an ideal system. At the time, we weren't sure if the want/ need for electricity would be worth it for periodic short stays on remote land, and how much power we would want/ need to size an ideal system. We started with a small setup to see if it would even be worth it. Now, we're spoiled with it, and it would be an adjustment to go without. We're glad we have it.

As a comparison, we started with two 100 Watt Renogy Mono panels with a PWM 30A charge controller (~$330), two sligc110 (215AH) 6-Volt golf cart batteries ($84 - 10% discount + $22 core, ~$100 each at Batteries Plus), a Black & Decker 750 Watt Modified inverter (Walmart, bought many years earlier, $?), and related accessories (cables, wires, lugs, switches, breakers, fuses, grounding, etc....). Oh, and some learning-curve mistakes too, ha ha.

3.5 years later we've grown the system to eight 100 Watt mono panels (24v), a Solar Epic MPPT 40A charge controller with meter ($240), ten 6-Volt golf cart batteries (12v bank, 1075AH). We'd add a pair of panels & batteries about every 6 months or so, adding the new batteries to the same battery bank (I know that's apparently bad, but I'm also curious to see for my self and willing to take the risk/ cost if/ when it becomes a problem), a Samlex PST-1000 pure sine inverter ($220 on eBay, a lucky deal from a pawn shop); Also, we have a Tiger Claw 1500 Watt pure sine inverter ($200) as a backup.

Over these years, we've put about $3,500 overall into the system. It's working pretty well with minor issues here and there. Our typical power loads are various lights, 2 laptops, charge several smartphones, 2 box fans (one runs all night, ~60 watts), a 600 Watt water pump for taking showers and pumping water into a couple small water towers (via rain barrels), 27" flat screen TV (over-the-air antenna), cell phone booster, charge power tool batteries, and other small random stuff. We can even afford to forget to turn off something with less worry now, ha ha. We discharge the batteries about 30% to 50% or so a day. The more days we stay or if the Sun doesn't shine well, we may have to run the generator with a 60 Amp charger for a couple hours to charge the battery bank. Certainly better than running a generator continuously throughout the day. Especially, during hunting season.

NOTE: The rest of the time when we're not there, the solar power system is not really used. So we're not cycling the batteries everyday. But it's been suiting our purposes so far for our situation. I don't regret going with the 'start small and grow as we go' approach despite the "don't do it" warnings. Some of it depends on the scope and expectations of the system. It's been kinda nice having some kind of electricity available, being able to affordably do periodic upgrades, and figure out what we want as we go despite some of the trade-off's that might come with it.

[bcroe]

Your money would go farther if you used the most generic 250-300W PV panels instead those very expensive (per watt)
smaller panels. Arranging for your laptop to powered directly from a battery instead of going through the great inefficiency
of an inverter and AC supply would help, and running stuff mostly when the sun is out will lengthen the life of batteries.
Bruce Roe

[wpmasterdesign]

I suspect that staying with the generator and batteries will be the most cost effective solution given that you have a small load and meeting a small load w/PV gets pretty expensive per Watt. Given your self reliance, that ought to be a way to go, at least initially. You'll still need a gen set anyway, even w/ solar.

Get familiar w/ off grid solar to the point you're pretty sure what you need, price it up and prepare for sticker shock and a few surprises.

One of the reasons I left the city to live off-grid was to get away from the contant noise and pollution. Out here, there is little pollution and the noise is the song of nature. I do not intend to shatter that by using a gen 10+ hours a day. Thats why I want to use solar. And I am willing to pay as much as I am able in order to do so. Yes, I do have a strict budget that I simply cant exceed at this time.Thats why I am here talking to ya'll, so I can make the most of my budget.
I am well aware that my budget is well below what most of you feel is enough for this lifestyle, but I have confidence I can figure it out. The invaluable advice all of you are giving me is teaching me and increasing my determination to do this.
The modular system is the best way I have found to be able to do this in a way that fits my budget and produces sufficient power to cover all or at least most of my power need. Thanks to you all, I now know what to look for inmy equipment, how to best configure my system, and how to maintain each module for longe life/maximum performance

[J.P.M.]

Off grid is not really that big of an adjustment for me. I have always been a low energy consumer. I never leave anything plugged in that is not being used, I always by the most energy efficient modells I can afford. And all kinds of other things. Even when I lived in the city I used such a small amount of power in comparison to my neighbors that the POCO once showed up to ask if I was aving power problems and were suspicious when I told them I simply dont use much power. On top of that, I once sopent 6 months in the Oregon wilderness using 0 electricity.
So I KNOW I can do this. I just want to doo it in the most effieicient way I can and within my financial means.

I suspect that staying with the generator and batteries will be the most cost effective solution given that you have a small load and meeting a small load w/PV gets pretty expensive per Watt. Given your self reliance, that ought to be a way to go, at least initially. You'll still need a gen set anyway, even w/ solar.

Get familiar w/ off grid solar to the point you're pretty sure what you need, price it up and prepare for sticker shock and a few surprises.

[wpmasterdesign]

Don't do that. Keep all batteries connected, so that all batteries work together to keep average charge levels high. Nothing is worse on a battery than discharging it - then disconnecting it for a while until you get a chance to recharge it. Also, while most parts of a solar power system are protected against accidental short, batteries are not - they are the most dangerous part of the system and should not be connected and disconnected often. Plus, disconnecting/reconnecting batteries often leads to high resistance connections, with the resulting risk of poor performance, overheating and fire.

No, you misunderstand, the battery is always connected to the solar. Only the load gets disconnected. So there is no "till i get a chance to charge"

[wpmasterdesign]

Right. But if you still want to get good use out of the system, then you will either have to turn it off early or greatly oversize it. One larger system will tend to average your loads. Have a day you have to get a lot of work done on the laptop? You'll either drain small system #1 system to zero, or have to stop working on your laptop, or have to oversize it. Having a party for someone?* Then you will have to drain small system #2 to zero, or party in the dark, or have to oversize it.

Whereas if you have one larger system, it will handle both events just fine at a lower cost per watt-hour.

So give us a number in watt-hours per day.

"Robust" means it works even when the weather isn't great, or you forget and leave a light on for an extra hour, or you have an unexpected load.

Obviously you can do whatever you want. But I think you will be happier overall with a good (single) battery system, a good (efficient/reliable) inverter/charger, and solar added as you can afford.

(* - I have no idea if you ever have parties, or ever have to get a lot of work done on a laptop. But almost no one's use per load is perfectly constant.)

My 2 kwh a day includes 10 hours a day on the laptop with a monitor running at the same time. The laptop is only plugged in foir an hour at a time to charge, a total of about 3 hours a day.
I dont have parties that require power. A grill burns wood.
I will always have the gen as backup in the event I do not have enough sun to power my system.
I already have one of these modules built and have used it for about a month. In that time, I have had to run my gen a total of 4 and a half hours. Solar has covered the rest. So if I add another module, I think that will more than cover my needs.
I plan to build 3 of these modules. Combined, they will produce nearly triple my current avg needs. So no, my needs, like anyone elses are not constant. But the 3 modules together will cover fluctualtions to a large degree. But if they don't here and ther, I have the gen as backup.

I am the kind of person that plans for the worst. So I always have a backup and a backup for my backup (I have a second gen that is still in the box,never even been opened).So I will always make sure I have the ability to produce at least double what I am ever likely to need

[wpmasterdesign]

Off grid is not really that big of an adjustment for me. I have always been a low energy consumer. I never leave anything plugged in that is not being used, I always by the most energy efficient modells I can afford. And all kinds of other things. Even when I lived in the city I used such a small amount of power in comparison to my neighbors that the POCO once showed up to ask if I was aving power problems and were suspicious when I told them I simply dont use much power. On top of that, I once sopent 6 months in the Oregon wilderness using 0 electricity.
So I KNOW I can do this. I just want to doo it in the most effieicient way I can and within my financial means.

[jflorey2]

Rather I use 1 battery down to the 11.9 (80%) mark, then switch to another that is fully charged.

Don't do that. Keep all batteries connected, so that all batteries work together to keep average charge levels high. Nothing is worse on a battery than discharging it - then disconnecting it for a while until you get a chance to recharge it. Also, while most parts of a solar power system are protected against accidental short, batteries are not - they are the most dangerous part of the system and should not be connected and disconnected often. Plus, disconnecting/reconnecting batteries often leads to high resistance connections, with the resulting risk of poor performance, overheating and fire.

[jflorey2]

Over discharge is not really an issue as I have a voltage monitor connected at all times, which has an alarm that will alert me when the battery hits 11.9.

Right. But if you still want to get good use out of the system, then you will either have to turn it off early or greatly oversize it. One larger system will tend to average your loads. Have a day you have to get a lot of work done on the laptop? You'll either drain small system #1 system to zero, or have to stop working on your laptop, or have to oversize it. Having a party for someone?* Then you will have to drain small system #2 to zero, or party in the dark, or have to oversize it.

Whereas if you have one larger system, it will handle both events just fine at a lower cost per watt-hour.

I think your idera would be good IF I used more power. But I use a very small amount of energy . . . .

So give us a number in watt-hours per day.

so my modualr systems are low cost (under 300 ea) and each will last 20+ years, except batteries. I dont NEED a "robust" system. Read the entire thread, and you will see that. I need to produce less than 3kjkwh/day/ One of my modular systems does more than half of that.

"Robust" means it works even when the weather isn't great, or you forget and leave a light on for an extra hour, or you have an unexpected load.

Obviously you can do whatever you want. But I think you will be happier overall with a good (single) battery system, a good (efficient/reliable) inverter/charger, and solar added as you can afford.

(* - I have no idea if you ever have parties, or ever have to get a lot of work done on a laptop. But almost no one's use per load is perfectly constant.)

[wpmasterdesign]

Well I agree that at only 2kWh/day you are definitely using very little so maybe living off grid is something that you will be able to handle.

Just try to understand that whatever way you do it any system you build will have to be a stand alone and sized exactly for a specific set of loads. I would not try to combine the systems but you will need to keep an eye on the batteries and be careful not to discharged them more than 25% for each cycle or they will not survive long.

Yes Suneagle, you are correct regarding needing to design each module for specific loads. But at the same time, they will be more scalable than a larger system. If I ever need to add more capacity, I can add more panels or more batteries easily because they are not interconnected via a bank or array. Rather I use 1 battery down to the 11.9 (80%) mark, then switch to another that is fully charged. Besides, although I do not know what the future might hold, at this point, I do nto imagine my power needs growing by all that much.
As for monitoring, I will have voltage monitors connected to each, with an alarm set to go off when the battery hits 11.9. Plus, the entire set is disconnected from the battery when not being actively used. But I agree, it will be essential to be vigilant in order to et maximum life.