Small off-grid system in Hawaii

[mia.da]

Hi there!

I made an overview of what I'm trying to plan out in the new members introduction section, but for summary here, my partner and I are moving to an ag lot on the Big Island of Hawaii and will be roughing it while we develop our property over the next few years. We have several friends in the area who have done the same, and we've been living in Hawaii for a little while, so we know a bit of what's ahead for us. We're also young-ish, are no strangers to roughing it, and have sustained a minimalist lifestyle for quite a few years now.

I'm also a total newbie, I steamrolled through as much as I can learn this week on off grid & solar power system, so bear with me if I'm completely missing something! Any and all advice welcome.

First, for a quick analysis of what it would take to get grid power where we are:

- Average delivered residential rate on Hawaii Island is between 35-45 cents per kWh, depending on time of year. (Ahh, welcome to Hawaii!) (Don't know if I can add links yet for my sources)
- Our distance from the nearest power pole means hookup could be $10,000+, and we don't even have a building yet. Some neighbors have been told by Helco that there's a year-long waiting list.
- To get even a temporary power pole, would still need building permits. That would be a year-plus away as well.

So, we think that an off-grid system is our best bet. And, nothing purchased yet!


We would like to begin with a Honda EU2000i generator, portable propane tankless water heater (Eccotemp L5), and propane stove. We already have a Suntactics S-Charger 14 and small battery pack for our cell phones. No need for heating or air-conditioning. We're around 2000ft in elevation so it ranges from 60-80's in daytime to 50's at night (°F).

The initial energy needs (to complement generator use for short-duration AC power) will be:
4 LED lights DC (12v/5W) .42A
<4 hours/day
total Wh: 80
total A: 1.68

2 LED light strings DC (7.5v/4W) .53A
<4 hours/day
total Wh: 32
total A: 1.06

2 USB outlets (5v/5W each) 1A
<3 hours/day
total Wh: 30
total A: 2

1 water pump DC (12v/90W) 7.5A
1-3 hours/day (2x20min max showers, intermittent kitchen sink faucet use, possibly feeding into a pressure tank)
total Wh: 90-270
total A: 7.5
Total daily Wh: up to 412
Total max Amps: 12.24

412 Wh x2 for 2 days back up: 824 Wh
824 Wh x2 for 50% DOD: 1648 Wh
/12v (still vetting if I can stick with 12v power, I understand that it means thicker wiring to handle more amps):

~138aH battery bank

Seeing approximately how many aH we need, and if we can stay under the economic threshold of jumping up to a larger system, I was wondering if we could add a Sundanzer DCR50 to this. We were willing to ice chest it for a long time but ha, I can foresee that we'll get tired of that real quick. I know a DCR50 is pretty small, but we can upgrade it to be our freezer at a later date by switching the thermostat.

Sundanzer DCR50:

runs on 12v or 24v
Typical use: 114wH/day at 32°C/89°F, 9.6 aH/day at 12v, 32°c/89°F

Couldn't find out exact specs, but the larger models have the same compressor and list this:
Power: typical-max 40-80W
Fuse size: 15A @ 12v, 7.5A @ 24v

Whew! That is where I am so far.

Speaking of power, I forgot my laptop charging cord today- posting this now and then switching to my phone!

Thanks,
Amelia

[Logan005]

yea, I have a few recommendations, go with a 24 volt battery bank and get the better sundanzer that runs on 24 volts. use your power wisely and learn to use gas instead of microwave and or electric coffee pot. if you do transfer to a carafe and turn off the inverter. the less you have to run the inverter the better. You can do this but you must learn to use much less electricity than most would consider. chest style refrigerator is most ideal for energy, but hard to get used to, Try keeping eggs on the counter as they don't need refrigeration anyway.

[Sunking]

You need a minimum 5 day autonomy on the battery. You want no less than a 24 volt system, preferable 48 volts. So if 2000 wh/day your battery capacity is

400 AH @ 24 volts
200 AH @ 48 volts

[Logan005]

with battery replacement and upkeep, you may still end up spending as much or even more than going with the POCO in HI. Yours is a better case thank most, with much lower POCO rates.

[mia.da]

Thank you for your responses! I'm crunching on your suggestions. Hmm, 24v...

Just for more parameters, there is a time factor that we are facing. It is undeveloped land, no structures, so it'll be a few years before we get through the building planning, applying for permits, and then actual construction of our home, in order to connect to grid power, and that would be if we start right away. So it would be possibly a very long time on solely generator power if I choose no solar. I guess I should do a price breakdown of that too, the generator is definitely useful for many things, but maybe inefficient to have it running every evening for hours to run low power lights, etc.

There are so many variables! Thank you for lending your eyes on this potential plan.

[Logan005]

for off grid 12 volts is a joke, and the joke will be on you. like already said, 24 volts is a min. 48 will allow more common luxuries. This a crucial choice.

[mia.da]

No, I agree, I'm seriously taking both of your advice to go to 24v at minimum.

[Logan005]

very good then, This single choice is the difference between a toy and a serious power source.

[Logan005]

now depending on your budget you have to chose batteries. they come in 2, 4, 6, 8 and 12 volts. never wire batteries in parallel, always series. stick with common easiest to get on the island. 2 or 6 volt batteries though I think you will be greatly served by 4 T-105 style 6volt batteries in series for 24 volt nominal. since you already plan to have and run a generator, I would advise charging your batteries from it. when you are using for other electrical demand, and week to week to condition. and keep plenty of distiled water on hand. if you cycle these batteries they will need checked often and water added. you can add solar at any time as budget permits.

[Logan005]

keep in mind if you get the 6 volt and should have bought the 2 volt, you have to replace the whole battery bank. so learn to live with less power first, so you can change your life style to fit inside 112.5 amp hours and you won't need the 2 volt or the L16 style batteries. before you buy any solar build the battery bank you need first and learn to care for them, you will really need to be involved in their care, for long lasting batteries.

[mia.da]

That is excellent, Logan- yes we are constrained by budget. Not having high rent in Honolulu anymore will be really great, but we don't have savings to help us with large upfront costs. An option to slowly build a system would be amazing. In my (brief) research on using a generator to charge batteries, it said that using it to get batteries to 80% charge is efficient, but the absorb/float is where it gets inefficient, so then I thought I would have to wait until we can afford both batteries and panels at the same time. But, if all I have to do is kinda eat the extra gas and run the generator for longer, for just a few more months until panels... that's a possibility?

[mia.da]

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

[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]

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!

[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.