Small off-grid system in Hawaii

[Sunking]

A few notes:

1) Wasting power. Going with a generator early on as your primary source of charging means you can care for a larger battery pack; a 2kW generator/charger means you can keep a 200-300 amp hour 48 volt battery happy. You will waste power towards the end of the absorb cycle because at that point the batteries won't be accepting full charge but the generator will still keep running. Your EU2000i has an eco-throttle which will help with that significantly, and if you plan your day so you run your other loads during the end of absorb you can avoid a lot of the waste.

2) Loads. Almost all your loads are DC 12V which is unusual. You'll have to consider either:

a) a DC/DC converter to convert 24-48VDC to 12V. There are purpose-made off-grid devices to do this but you are probably better off with a a straight DC-DC. The SD-500L-12 is about $150 and will give you 500 watts at 12 volts from an input of 19-72 volts. It has a somewhat high standby current (10 watts) but it's cheap and has decent protection.

b) Going to a 12V system. You will get lots of grief from people here for doing that because many people associate 12V systems with cheap thrown-together systems, and the wiring/protection to support high inverter power draws at 12V is insane - which is why you don't see 12V in "serious" systems. But in your case (low power, no inverter) it can make a lot of sense and at lower powers will work just as well as the higher voltage systems. You will end up with much larger cells (likely 6 2V 800Ah cells) ONLY consider this if you think your load analysis is accurate and your loads will not grow with time. Advantage is no DC/DC converter needed to run your loads, which saves you some power.

3) Protection. Make sure you use breakers/fuses rated for DC since most of your loads will be DC.

Once you do go to solar, find a dealer that will allow you to grow your array gradually; that mainly means making sure they will stick around for a while and continue to stock the panels you started with. (Much easier to grow an array if you can get all one type of panel.) You'll likely grow in both series (more panels per string) and parallel (more strings) as your system grows and you switch from cheapo PWM controllers to better MPPT controllers.

Jeff I do not disagree with anything you have said here. However you do appear to me to be glossing over something, or perhaps ignoring some facts about 12 volt systems. 12 Volts works great in RV's and boats no doubt.

Lots of 12 volt gizmos are made for that market right?
Many are high powered right?
Most are cheaply made, over priced, and inefficient right?
RV's are small footprints with respect square footage and cable distance right?
Batteries are stowed centrally in an RV which helps keep cable distances smaller and shorter right?
You know where I am going with this, and the OP has no clue what any of that means in the end right?
What does is take to overcome all the power losses using 12 volts in a home where cable distances get long.
How many extra circuits have to be ran because of low voltage?

ANSWER: A lot of money and exposing yourself to high fire risk on cheap equipment not made to last or use energy efficiently. When you look at the big picture in color things change.

[RedDenver]

Nope has nothing to do with individual conditions. FLA batteries should never be discharged more than 50% DOD. To get maximum service life and the most Watt Hours out of your battery for the dollar 20% DOD [per day is the sweet spot. So 5 day antinomy i sonly 3 days to CYA for cloudy days. After 3 cloudy days you have two options, Wait until you have 3 full sunny days to recharge, or run your generator.

A very popular battery is the Trojan T-105. To buy 1 up front will cost you roughly $180 delivered. It is a 6 volt 225 AH battery and has a capacity of 1350 watt hours. If you use 20% DOD per day you are going to get roughly 3 years or 1095 days. That yields you 295 Wh of usable energy. That energy in battery cost is $180 / 295 Kwh = 68-cents per Kwh. Or about 4 to 6 times what a utility company would charge you.

Take that same T-105 and do it your way and discharge it 50% DOD per day will get you roughly 1 year. That works out to 675 wh per day or 246 Kwh. Now your cost goes up to $180 / 246 Kwh = 73-cents per Kwh.. If you have a cloudy day you must shut down or run a generator.

Regardless any off-grid system requires a generator. But to get the most bang for your dollar, 5 day is minimum autonomy. Not only does it give you the best bag for your battery dollar, it also saves you big fuel bills running your generator every time you get a cloudy day.

I see where you're coming from, thanks for the explanation. I will quibble slightly in that what you just described is indeed based on individual conditions, like using FLA, how often you get 3+ days of cloudy weather, how expensive the generator fuel is, etc. But 5 day autonomy probably covers a great many cases.

[Sunking]

I've seen the 5 day autonomy a number of times. What is this based on? I'd think the autonomy is going to be based on the needs and conditions of individual systems.

Nope has nothing to do with individual conditions. FLA batteries should never be discharged more than 50% DOD. To get maximum service life and the most Watt Hours out of your battery for the dollar 20% DOD [per day is the sweet spot. So 5 day antinomy i sonly 3 days to CYA for cloudy days. After 3 cloudy days you have two options, Wait until you have 3 full sunny days to recharge, or run your generator.

A very popular battery is the Trojan T-105. To buy 1 up front will cost you roughly $180 delivered. It is a 6 volt 225 AH battery and has a capacity of 1350 watt hours. If you use 20% DOD per day you are going to get roughly 3 years or 1095 days. That yields you 295 Wh of usable energy. That energy in battery cost is $180 / 295 Kwh = 68-cents per Kwh. Or about 4 to 6 times what a utility company would charge you.

Take that same T-105 and do it your way and discharge it 50% DOD per day will get you roughly 1 year. That works out to 675 wh per day or 246 Kwh. Now your cost goes up to $180 / 246 Kwh = 73-cents per Kwh.. If you have a cloudy day you must shut down or run a generator.

Regardless any off-grid system requires a generator. But to get the most bang for your dollar, 5 day is minimum autonomy. Not only does it give you the best bag for your battery dollar, it also saves you big fuel bills running your generator every time you get a cloudy day.

[jflorey2]

A few notes:

1) Wasting power. Going with a generator early on as your primary source of charging means you can care for a larger battery pack; a 2kW generator/charger means you can keep a 200-300 amp hour 48 volt battery happy. You will waste power towards the end of the absorb cycle because at that point the batteries won't be accepting full charge but the generator will still keep running. Your EU2000i has an eco-throttle which will help with that significantly, and if you plan your day so you run your other loads during the end of absorb you can avoid a lot of the waste.

2) Loads. Almost all your loads are DC 12V which is unusual. You'll have to consider either:

a) a DC/DC converter to convert 24-48VDC to 12V. There are purpose-made off-grid devices to do this but you are probably better off with a a straight DC-DC. The SD-500L-12 is about $150 and will give you 500 watts at 12 volts from an input of 19-72 volts. It has a somewhat high standby current (10 watts) but it's cheap and has decent protection.

b) Going to a 12V system. You will get lots of grief from people here for doing that because many people associate 12V systems with cheap thrown-together systems, and the wiring/protection to support high inverter power draws at 12V is insane - which is why you don't see 12V in "serious" systems. But in your case (low power, no inverter) it can make a lot of sense and at lower powers will work just as well as the higher voltage systems. You will end up with much larger cells (likely 6 2V 800Ah cells) ONLY consider this if you think your load analysis is accurate and your loads will not grow with time. Advantage is no DC/DC converter needed to run your loads, which saves you some power.

3) Protection. Make sure you use breakers/fuses rated for DC since most of your loads will be DC.

Once you do go to solar, find a dealer that will allow you to grow your array gradually; that mainly means making sure they will stick around for a while and continue to stock the panels you started with. (Much easier to grow an array if you can get all one type of panel.) You'll likely grow in both series (more panels per string) and parallel (more strings) as your system grows and you switch from cheapo PWM controllers to better MPPT controllers.

[RedDenver]

You need a minimum 5 day autonomy on the battery.

I've seen the 5 day autonomy a number of times. What is this based on? I'd think the autonomy is going to be based on the needs and conditions of individual systems.

[littleharbor]

Propane fridges do work fairly well but can get expensive to operate. If the fridge doesn't already have some sort of fan blowing over the coils do your self a favor and find a 12 or 24volt, (whichever voltage you go with), computer muffin fan to move some air over the coils. I tapped into the output of my solar panels with one. It only runs when the sun is out and draws only a negligible amount of power. Made a big difference in performance. This is in my 5th wheel so I did put a switch inline to disable it when not in use.

[mia.da]

Bala- Ahh yes, the first law of stuff dynamics! "Your stuff will expand to fill any container you decide is big enough to hold your stuff." Sounds like a garage we used to have.

I guess, at least we come from that end of the spectrum rather than never having been there- we had a bigger house way of living and then went through the process of downsizing, and have kept it up- but yes, stuff has a way of sneaking back in!

LETitROLL, very true about us continuing to see what else we can divert to other energy sources. We have another friend here who used a propane fridge for many years- ha, I should see what he's up to with it now! I know he recently got a large DC chest fridge because he upgraded his off-grid system.

And thank you both for suggestions on timing tasks accordingly. Has a large impact overall.

Definitely feeling out the natural economic thresholds with different systems, and their size limitations. Logan's suggestion of staying within 112.5 amp hours is something I'm going to think about.

[Bala]

The lifestyle of travel and renting for most means you do not have a lot of possessions. Once you have some where to store stuff you tend to accumulate and after time tend to want to add a few little luxuries. So as suggested most will tend to load up their system over time.

Refrigeration in the tropics is a big draw, we survive without aircon but need a fridge and freezer. For off grid you need to buy the most energy efficient which are usually the most expensive.

Another consideration is if you work. We both work full time five days a week so clothes washing can only be done form solar on weekends, if its raining then its generator, if we want to do it during the week its generator. In the wet season if we get good rains we need to run the clothes dryer to get things dry.

If their is someone home all the time then you can utilize the sun better.

So just saying that things will change over time and time will go fast, make sure you budget for new batteries on their expected life not what you hope to get.

[LETitROLL]

As you are use to conserving, and already looking to propane water heating and cooking, you can make this happen just fine, Just develop a small solar/battery system for nighttime use of lights and electronics, etc. (all low draw stuff) and the generator will have to handle the bigger stuff. Most people do not realize the dramatic difference in size and price of solar as you increase your WH needs, it is thousands of dollars difference in initial system purchase when you step up from just running some lights and electronics, to adding just the water pump, so try and figure out how to use the pump on genny only and pump into pressure tank for nite use, or some other holding tank. Also 12v systems are OK (sometimes preferable) if kept small like just for lights and electronics which don't need inverters, etc and can be very simple and inexpensive, and work well (less maint. and items to fail). Most people try and cheat and start adding in small appliances and then of course is when all the trouble starts. The only other real issue you have is refrigeration, costs too much to run off solar, they make propane ones (they are expensive to buy, but much cheaper after that), can find small used ones over here out of camp trailers for cheap sometimes.

[mia.da]

I also figured that if I can come up with something that passes the SPT test, then it's rock solid! Haha.

[mia.da]

Thank you Bala. You have extremely valid points for everyone considering off-grid power. I believe we have relatively low needs in general- and we're very willing to cut anything we need to. For a tiny example of who we are, we're used to traveling for many months on end, and I personally go backpacking for weeks every year- where my only electrical needs are a headlamp and a camera. Our lifestyle is flexible and can adapt. I'm definitely not a hair dryer kind of girl! It's just two of us, in a tropical climate, diverting our only two heat-producing items to propane (tankless water heater and a propane stove) and any short-term higher-power AC use (like tools or our beloved Vitamix) to our generator. No coffee, no hair dryer, have never owned a TV or a microwave. Haven't had an oven in a few years because a lot apartments in Honolulu don't seem to believe in them, lol! We're acclimatized to having a minimalist lifestyle (everything we own can fit in a pickup truck, we fit it in a couple of checked bags when we first moved out here). We're both handy and can take on the complexities of caring for such a system.

To connect to grid, if we chose that path towards building a permitted house now and not later, would take us 3-5 years as owner-builders. We will begin living on our property soon. It would be nice to have an energy solution other than just generator for those years, for LED lighting, a DC water pump, and possibly a DC chest style fridge, but if we needed to, we would adjust to something less.

So yes, off-grid will be more expensive for us than if we could just connect to grid, but if you factor in that we'd have to build a house in the first place in order to get grid ($150,000+), the barrier to entry for off-grid is much lower. To compare, one of our friends has had his nearby farm for 7 years. He's just starting to build a small house now. He only had an outdoor kitchen with a shower off the side, a deck with a nice tent on it, and a composting toilet, for all that time. We will be doing a similar setup.

[Bala]

People can generally come up with a math equation that justifies off grid V getting the grid connected.

What is not considered is that the off grid system is not a direct replacement.

Even a reasonable off grid system with a 3kw inverter can only supply some of that 3kw some of the time.

A grid connect system can supply 15 to 20kw every hr all day if needed.

Really consider the long term cost and lifestyle choose you are making before taking the step.

[mia.da]

To backtrack a few things- Sundanzers can take in between 10-31VDC, same model, not separate models. But obviously running a system at 24v is better!
And I might have failed at how to express the average power rates out here- Hawaii is notorious for very high electrical bills? They have some crazy decoupling charges and other things. But either way, the cost of solar off-grid blows it out of the water. Our specific obstacles are time and infrastructure- grid power is cheaper per kWh than off-grid, but we'd have to build a house first. Whew, that won't be happening anytime soon!

And this is out in the boonies of Hawaii- these aren't typical neighborhoods. There are many people who live in shacks indefinitely, with zero running water or power. We're almost glamping in comparison!

[mia.da]

That's the one thing about the generator, I'm trying to find ways to divert using it for long-term low power needs and occasional small needs, and if I can avoid running it at night (obviously with as little power usage as possible)- everything a battery bank could help buffer.

[mia.da]

And yes, I've definitely been digging through all the stickies on battery maintenance! Thank you guys for the great resources!