Smaller battery bank at off-grid cabin...

[calebc]

I'm upgrading my solar system at my off-grid cabin. I'm looking at this kit: https://www.solar-electric.com/outba...620-watts.html with a few minor adjustments. Currently my power needs are pretty small, about 650 watt hours a day, but I expect that to increase once I get a reliable solar system in place (currently I have a small 35W panel that charges a bank of batteries which means we end up using the generators to keep the batteries charged most of the time).

On to my question. Since I know it's expensive to maintain a battery bank, I'm wondering if it's reasonable to supplement my solar system to a hydro system (I'm fortunate and have a year round "creek" that flows 100+ gpm even at the low point of the season) and only have smaller battery bank instead of what would actually be needed to sustain me for multiple days? I'd still have something (probably what comes with that kit linked above) but wouldn't need to grow it over time is the hope. Since the solar is plenty for my needs, the hydro would really just be to offset cloudy days and the minimal night time use. The cabin is used generally every other weekend so plenty of time for the batteries to recover between visits.

Or is this overkill and I should just rely on the generator to top off the batteries when solar isn't enough? I like the idea of not being reliant on the generator though. Thoughts?

[Wy_White_Wolf]

Who's going to monitor/repair the hydro system when you're not there? Solar is for the person that is passively involved in the generation as there is little to upkeep/maintain. Mechanical systems such as hydro and wind are for people that want to be actively involved in there power generation.

I have a weekend system like yours for our cabin. Batteries are sized to use 50% of there power over the weekend. Panels are sized to replace that in 5 days. With being there every other weekend I've never had a shortage for power. Sounds more like your panel is just undersized and increasing it would be a better option than adding a mechanical system to deal with.

WWW

[SunEagle]

Just a note. That kit is for a 24volt battery system not a 12volt one. It will also generate over 10kWh or at least 3kWh a day without discharging it more than 30%.

That is a lot bigger then what you currently have and may be overkill in size and cost based on what you really need in daily Watt hour usage.

[calebc]

Thanks for the feedback. I'm really new to all the renewable energy stuff. I've done a ton of research, reading, etc on solar and feel I have a preset good understanding of the systems but I'm still trying to wrap my head around wind and hydro. However, if it requires a daily or semi-daily interaction then yeah, it definitely won't work for me.

[calebc]

Just a note. That kit is for a 24volt battery system not a 12volt one. It will also generate over 10kWh or at least 3kWh a day without discharging it more than 30%.

That is a lot bigger then what you currently have and may be overkill in size and cost based on what you really need in daily Watt hour usage.

Thanks. Yeah, I know it's significantly larger than what I have and what I currently need. I've been targeting 1.5-2kWh for size, but going from a system of that size to this system is minimal cost savings. I've though about going from 6 to 4 panels on that system. That would save ~$400 and if I went the next size down on the inverter, it'd save $100. Not that significant. I know once I get our electrical system squared away, my wife is going to want more nice-ities than we currently have (she's a city girl, I can't fault her too much ) like TV, appliances, etc so I'd rather be a little oversized (thus making it a little less efficient) than have to re-buy the more expensive pieces. However, I may be over thinking it and may not need anything in addition to this system. I should probably get this bought/installed and then re-evaluate.

[SunEagle]

Just make sure whatever system you decide on has a good balance of solar panel wattage to battery Ah rating. You want to stay within the C/8 to C/12 charging rates of the batteries where C= total Ah rating.

That first system was a 24volt 428Ah system so with 1620watts of panels you could get a peak generation of 67.5amp (1620w / 24v = 67.5A) which is a little high for that battery system but should work if you do not have a lot of sun isolation hours.

[Sunking]

However, I may be over thinking it and may not need anything in addition to this system. I should probably get this bought/installed and then re-evaluate.

That can bite you in the butt. Most who come here way underestimate what they really need and learn they have to spend a lot more money.

You are the opposite. Based on just the batteries of 4 x Rolls S550 can support up to 3 to 4 Kwh per day. What I am driving at it sounds like you spent a whole lot more money than your needs.

[685eric]

If you only need 650 watt hours a day, you do not need to spend that much money. I have a similar setup with an off the grid cabin. 180 Ah batteries at 24 volts ($300), 200 watt solar panels with controller ($450), 2kw automatic inverter/charger 24v ($800). Now, the solar does not always keep up with our usage throughout the weekend, but we can leave on Sunday and return the following Friday and the batteries will be fully charged again and last all weekend. Under hard usage the batteries will drain to about 50% before we leave on Sunday. So it all depends if you are staying at the cabin 24/7 or just a certain amount of time. Don't buy more solar panels than you need, more batteries is probably a better investment if you will only be there a short amount of time. Just my opinion.

[calebc]

If you only need 650 watt hours a day, you do not need to spend that much money. I have a similar setup with an off the grid cabin. 180 Ah batteries at 24 volts ($300), 200 watt solar panels with controller ($450), 2kw automatic inverter/charger 24v ($800). Now, the solar does not always keep up with our usage throughout the weekend, but we can leave on Sunday and return the following Friday and the batteries will be fully charged again and last all weekend. Under hard usage the batteries will drain to about 50% before we leave on Sunday. So it all depends if you are staying at the cabin 24/7 or just a certain amount of time. Don't buy more solar panels than you need, more batteries is probably a better investment if you will only be there a short amount of time. Just my opinion.

Thanks. I would tend to agree with you. That system is definitely oversized for my needs as they sit today. However, I KNOW that will change drastically once our power situation is solid. Right now, we don't hardly ever use power, we go to bed early because there isn't much light, etc. So there are many things that will change, as I mentioned above, I know my wife wants to add a TV in the front room and maybe one in our bedroom, I know she wants to add several lamps (so we can enjoy staying up and playing games, etc). So I'd rather over buy than under buy and I'm not terribly concerned about the price tag of that system. I'll see if the battery system that comes with this setup is enough, if it's not, then I'll definitely invest in to more batteries.

[Sunking]

If you only need 650 watt hours a day, you do not need to spend that much money. I have a similar setup with an off the grid cabin. 180 Ah batteries at 24 volts ($300), 200 watt solar panels with controller ($450), 2kw automatic inverter/charger 24v ($800). Now, the solar does not always keep up with our usage throughout the weekend, but we can leave on Sunday and return the following Friday and the batteries will be fully charged again and last all weekend. Under hard usage the batteries will drain to about 50% before we leave on Sunday. So it all depends if you are staying at the cabin 24/7 or just a certain amount of time. Don't buy more solar panels than you need, more batteries is probably a better investment if you will only be there a short amount of time. Just my opinion.

+1. That is solid and well thought out.

The difference here is you are talking about an occasional use system vs say a home off grid system used everyday. You are talking about systems like a weekend cabin, camp site, or an RV, etc.

Standard practice for a daily use system is to size the batteries for worse case 5-day reserve capacity, and worse case sola rpanel wattage based on shortest day of the year to fully recharge the batter every day. That gets expensive and not required for occasional use system.

Now for a occasional use system say up to 4 days you can downsize the battery to 3-day reserve which gets you 2 usable full days without sun. But one requirement must still be met, with any Pb battery system, and that requirement is to provide a minimum charge current. That minimum is C/12 to C/10.

So for example let's say you need 800 to 1000 Watt Hours per day you would want a pair of 6-volt 225 AH gold cart batteries. To meet at least C/12 charge current is roughly 19 amps, and 23 is perfect at C/10. With a MPPT controller is a 200 to 275 watt panel system.

Now if this is a cabin or camp site a generator is a must for two reasons.

1. Cloudy days.
2. Battery Preventative Maintenance Routine. Solar is not capable of providing an proper Equalization charge. Now you can take the batteries home with you to do that.

So OP keep your generator around, you are going to need it.