Need advise from those who know more then me.

Joe94

I am in the process of building a earthship style home in the desert of eastern Washington. It is fully permitted and must pass inspections. I am ready to start designing the electrical system. I am building on shoestring budget and paying for everything as I go so I've been stretching every dollar I can. I've been reading through the forums and am at a bit of a crossroads. I won't be living in this home for a few years because of work and family. I will be be using it as a weekend get away but would like for it to become a full time residence as my obligations allow. It seems that since my plan is to use it part time for now a modest system would be better situated to my needs but I would like to have some typical amenities. I would like to run the lighting and water pumps on 12volt dc. I would like to run a small converted chest freezer for refrigeration. I estimate I could meet my power needs on about 1kilowatt per day for now. Would I be better off building small (inverters, batteries exe) for now and stepping it up when I'm ready to make it a full time residence or design a system that could facilitate full time living and let it sit idle most of the time? I'm looking for opinions from those who have been living with these systems and if you were in my situation what that system might look like.

westbranch

Re: Need advise from those who know more then me.

Welcome, You will need a generator anyway so look at the 2000w Inverter type gensets, Honda, Yamaha, for example. This will be the most economical way to build. For night lights get a 12 v deep cycle battery or retire a car battery and use it for a year or so. If you want something with more Ahr go for 2 golf cart batteries, you might want a cheap Box store MSW inverter to run some CFL lights, run the fridge off the generator in the day.

hth

BB.

Re: Need advise from those who know more then me.

For best bank for the buck--Design/build the small system. If you get 3-5 years out of the battery bank, you are making best use of the hardware (batteries are quite expensive).

For a larger system, you probably will need a 24-48 volt battery bank (different/larger batteries, larger/higher voltage AC inverter and AC Backup charger, larger genset for backup, and 3-6x more solar panels). The MPPT solar charge controllers can work well on 12/24/48 volt battery banks and will handle larger arrays at the higher voltages. However, you may not want to get the large "bells and whistles" controllers for your first small system.

Do a paper design for both types of systems. You will see how everything works out. Over sizing your off grid system for use 3-5+ years in the future is not doing you any favors... Larger battery banks are expensive to replace, need larger solar array to properly charge, larger backup genset+AC battery charger for backup, etc...

A 1kWH per day system is pretty minimal. If you need lights, chest fridge, 12 volt RV water pump--That is about it. Add a laptop computer+model--You need another 0.5 to 1.0 kWH per day.

You can stay with the small system, and use a small genset (like a Honda eu2000i 1,600 watt) to give you power during the day when needed (washer, vacuum cleaner, power tools), and use the battery system for night/quiet time.

Otherwise, if you are going to live there for ~9 months of the year, then you may want to look at a ~3.3 kWH per day system. That will give you a "near normal" electric powered life (standard energy star refrigerator, washing machine, well pump, laptop, energy eff TV, etc.).

The next size would be around 10 kWH per day (300 kWH per month)--That will be quite a bit of power for an off grid home (energy efficient, use some electricity for cooking, perhaps some A/C or heat pump).

In the end, get a Kill-a-Watt type meter to measure your average power (Watts) and energy use per day (Watt*Hours)... 1 kWH per day is not "camping", but it is pretty close.

Energy usage is a highly personal set of choices--My suggested values may not be what works for you--Just trying to set some expectations for planning.

Also, approximately where in Eastern Washington? Use PV Watts to figure out your average hours of sun per day by month.

-Bill

Joe94

Re: Need advise from those who know more then me.

Thanks for the advise. Bill, I would get as little as 2.24hr of sun in Dec and as much as 6.83hr in July. Hth that is basically what I've been doing. I have a 4000 watt generator. I am to the point that I need to wire the house and it needs to meet code or at least pass inspection. The local inspectors dont seem to know too much about off grid wiring. My plan is to have 2 electrical panels one 110v AC and one 12v DC. The dc will run lights and pumps. My cistern gravity feeds to a small RV style pump and a traditional pressure tank. On the small side I've considered a about 500 watts of panel at 24v run thought a Morningstar mppt controler charging 4 210ah golf cart batteries (2 in series 2 parallel) 12v. A Suresine inverter. I doubt seriously if I would be able to run even a 5cuft chest freezer with this setup but TV, laptop, phone exhaust van exe would run fine. For a mid size setup I would maybe do 750 watt of panel, 6 210ah batteries 3 parallel strings, and a magnum MMS-1012. On the large side I might go with 1000 to 1200 watts of panel, midnight solar mppt controler, 8 Dekka L16 2 parallel strings 24volt. Magnum MS-2024. It sounds like from Bills recommendation that the later would be a bit overkill for now.

BB.

Re: Need advise from those who know more then me.

Joe94 wrote: »

Thanks for the advise. Bill, I would get as little as 2.24hr of sun in Dec and as much as 6.83hr in July.

Sounds like a fair amount of sun. You may look at 4 hours of sun as you "break even point" (usually I suggest using generator, as needed, for ~3 months of year--And use pretty much pure solar array for the rest of the year). 2.24 hours of sun is not very much--And it will be your choice if you want more solar panels for less genset use in the winter.

If you have seasonal power variations (water pumping, A/C, etc.), you may be able to adjust the solar array size vs loads (i.e., higher summer loads when you have lots of sun).

Hth that is basically what I've been doing. I have a 4000 watt generator. I am to the point that I need to wire the house and it needs to meet code or at least pass inspection.

You can wire the house as a standard AC system. You do have a choice if you use 120 VAC only, or 120/240 VAC split phase. If you have some heavy power needs and/or farther distances to reach (remote well pump, out building/work shop), 240 VAC can be nice.

If you do choose 120/240 VAC wiring (hot/hot/neutral) but run a 120 VAC inverter/generator for now--There is an issue of "home running" Neutral (white) wiring.

With true 120/240 split phase, the Hot+Hot currents cancel each other out in the Neutral wiring. But if you connect the Red+Black wiring together on a 120 VAC system, the Black+Red current adds together and causes excessive current flow in the common neutral (if you use Romex with Black+Red+White+ground on a 120 VAC system, you will have problems with a "jumpered" Black to Red on a 120 VAC inverter/generator).

The local inspectors dont seem to know too much about off grid wiring. My plan is to have 2 electrical panels one 110v AC and one 12v DC. The dc will run lights and pumps. My cistern gravity feeds to a small RV style pump and a traditional pressure tank.

Think hard about the 12 VDC panel... In general, 12 volt has a lot of current requirements and supports very little voltage drop (remember P=V*I -- if voltage is low, then current must be high). So--12 volt loads should be very close to the battery bank. Any remote loads should be 120 VAC.

Another issue, for smaller systems (like a 1 kWH per day system), 12 volt inverter and battery bank will support upwards of 1,200 watts of continuous power. One a 12 volt battery bus, 1,200 watts is > 100 amps -- A lot of current that requires lots of short/heavy copper wiring.

If you go much above this power level, you will have to look at 24 volt or 48 volt battery bank.. Which then causes issues with your existing "12 volt" panel and loads.

You cannot pull 12 volts from a 24/48 volt battery bank directly (splitting the bank)--That causes battery equalization and charging problems (basically very hard on the battery bank). There are solutions with balancing power supplies--But that is about as much costs/hassles as just choosing to go with all 120 VAC loads (water pumps, low power lighting, etc.).

On the small side I've considered a about 500 watts of panel at 24v run thought a Morningstar mppt controller charging 4 210ah golf cart batteries (2 in series 2 parallel) 12v. A Suresine inverter. I doubt seriously if I would be able to run even a 5cuft chest freezer with this setup but TV, laptop, phone exhaust van exe would run fine.

Yep--You need around a 1,200 to 1,500 Watt AC inverter to reliably start most refrigerators/freezers. As soon as you want a refrigerator (or even a chest freezer conversion), you are looking at a 24x7 AC inverter which requires a bit more power (or some other fancy switching to conserve power by only turning the inverter on when the refrigerator needs power, etc.).

For a mid size setup I would maybe do 750 watt of panel, 6 210ah batteries 3 parallel strings, and a magnum MMS-1012. On the large side I might go with 1000 to 1200 watts of panel, midnight solar mppt controler, 8 Dekka L16 2 parallel strings 24volt. Magnum MS-2024. It sounds like from Bills recommendation that the later would be a bit overkill for now.

Be careful here--I really like to design from the loads--That drives the rest of the system design.

If you pick something else (XXX AH of battery bank, or $x,xxx system cost), we can give you an idea of what that sort of system would be configured to support (i.e., you pick the battery bank, the rules of thumbs tells us how much power per day you can get from the system, how much starting load for power tools can be supported, etc.).

You have to good understanding of your loads (reasonably accurate measurements). And many times, it is the 24x7 loads that drive you to larger a system design.

For example, say you have a 60 Watt higher end laptop computer that you run 12 hours per day (lots of computations, graphics, gaming system). And a 1,200 watt microwave you run 20 minutes per day.

60 watts * 12 hours = 720 Watt*Hours per day (laptop computer)
1,200 watts * 1/3 hour per day = 400 watt*Hours per day (microwave)

Add a chest freezer conversion--That will add another 250-500 Watt*Hours per day...

And we are up to ~1,620 WH per day.

Loads add up quickly. And energy usage is a highly personal set of choices. I can give you some rough ideas--But what works for me, may not for you.

-Bill

Joe94

Re: Need advise from those who know more then me.

Great thanks for the advise. So my current line of thinking is since I don't live there go small and rebuild as the demand requires. It seems like to over build now and waste power on a large parasitic draw from my equipment would be foolish. I'm going to have a 12v panel for the lights and pumps because that is already how I run these things. I don't see a reason to swap them out for 120v now. I've actually been living/camping on weekends out there for almost 9 months now on a very modest PV system. I'm just looking for the best way to address setting up the house for more permanent wiring and my electrical inspection. If I abandon the idea of the chest freezer for now the only draw I would really have is TV, phone/ipad possibly a laptop charging for now. My thought is to go with 4 210ah golf cart batteries, that would give me 420ah at 12 volt or about 2500 Watts at 50% draw down. That's 1250 watts per day that I'm usually there. I feel like that is plenty for my current demand. Next I was thinking I would add two 240 watt panels 24v in series through a mppt charge controller. My thought is to go with a midnight solar classic because as I grow the system down the road I can still use the controller on a larger system as well as the panels. I figured on just using a suresine inverter for my 120v power as it would supply my current needs and doesn't use a lot of power while on standby. for the 5 days a week that I'm away. I have a 4000 watt generator that I can use to supply additional power when I would like to use a microwave or other large draw equipment. I haven't given much thought on a battery charger from my generator yet or if I should even include one for now. One question I would have is how would I set it up to bypass the inverter and switch to the generator when I run it. Do you guys with experience living with this stuff see any major flaws in my current line of thinking that I should reconsider before I'm committed?

BB.

Re: Need advise from those who know more then me.

Joe94 wrote: »

Great thanks for the advise. So my current line of thinking is since I don't live there go small and rebuild as the demand requires. It seems like to over build now and waste power on a large parasitic draw from my equipment would be foolish. I'm going to have a 12v panel for the lights and pumps because that is already how I run these things. I don't see a reason to swap them out for 120v now. I've actually been living/camping on weekends out there for almost 9 months now on a very modest PV system. I'm just looking for the best way to address setting up the house for more permanent wiring and my electrical inspection. If I abandon the idea of the chest freezer for now the only draw I would really have is TV, phone/ipad possibly a laptop charging for now.

Wire up the home/cabin with full 120 (or 120/240 VAC split phase) wiring. Even put a main panel with a meter socket in it. It will be "legal" and you will have AC outlets/power where you needed (or will need it when you go full time). Wiring is "easy" now with open walls/no insulation. Once you button up the home, it will be much tougher to drop wire where you need it (You do have the trade off of lots of copper/electrical in a weekend home--If you have issues with theft in the area, I would almost be tempted to drop conduit it and don't pull any wire (not sure it would save any money) and use "plastic water piping".

My thought is to go with 4 210ah golf cart batteries, that would give me 420ah at 12 volt or about 2500 Watts at 50% draw down. That's 1250 watts per day that I'm usually there. I feel like that is plenty for my current demand. Next I was thinking I would add two 240 watt panels 24v in series through a mppt charge controller. My thought is to go with a midnight solar classic because as I grow the system down the road I can still use the controller on a larger system as well as the panels.

Yep--That is a nice sized system that will probably do everything you need (real close if it can run a chest fridge--Perhaps you can go with a propane RV fridge or one of the 12 volt RV refrigerators with a "real" compressor (watch costs--Refrigerators designed for 12/24 VDC can be scary expensive--Get a "regular" 120 VAC energy star fridge and put the extra money in a few more panels/batteries/larger inverter.

Start with your 2x240 Watt panels and add a few more when you need the extra power (4 panels would probably be the "cost effective" maximum for you system unless you have a lot of daytime loads to burn off "excess" charging capacity for the array (or really need more power in deep winter).

I figured on just using a suresine inverter for my 120v power as it would supply my current needs and doesn't use a lot of power while on standby. for the 5 days a week that I'm away. I have a 4000 watt generator that I can use to supply additional power when I would like to use a microwave or other large draw equipment. I haven't given much thought on a battery charger from my generator yet or if I should even include one for now. One question I would have is how would I set it up to bypass the inverter and switch to the generator when I run it. Do you guys with experience living with this stuff see any major flaws in my current line of thinking that I should reconsider before I'm committed?

You can go with a manual transfer switch between Genset and Inverter--Or you can go with simple automatic transfer switch (basically a relay with a time delay).

There are larger multiple circuit manual transfer (and even automatic) switches that can be use to switch various outlets in your home between AC Inverter and AC Generator.

Lastly, I still think that you can make good use of a smaller Honda eu2000i genset (1,600 watt), or Yamaha inverter-generator type genset if you think you will need more power at times. They are quiet and pretty fuel efficient (~4-9+ hours of run-time per gallon of gasoline depending on load).

If/when you go with a larger AC Inverter/off grid power system--There are versions that are combined AC Inverter-Battery Chargers. They will share generator output between battery charging and AC loads when the genset is running, and even include an AC transfer switch internally. Pretty much like a large computer UPS system with external battery bank (and some very sophisticated configuration/programming/generator auto-start options for many of them).

-Bill

arby

Re: Need advise from those who know more then me.

Joe94 wrote: »

I am in the process of building a earthship style home in the desert of eastern Washington. It is fully permitted and must pass inspections. I am ready to start designing the electrical system. I am building on shoestring budget and paying for everything as I go so I've been stretching every dollar I can. I've been reading through the forums and am at a bit of a crossroads. I won't be living in this home for a few years because of work and family. I will be be using it as a weekend get away but would like for it to become a full time residence as my obligations allow. It seems that since my plan is to use it part time for now a modest system would be better situated to my needs but I would like to have some typical amenities. I would like to run the lighting and water pumps on 12volt dc. I would like to run a small converted chest freezer for refrigeration. I estimate I could meet my power needs on about 1kilowatt per day for now. Would I be better off building small (inverters, batteries exe) for now and stepping it up when I'm ready to make it a full time residence or design a system that could facilitate full time living and let it sit idle most of the time? I'm looking for opinions from those who have been living with these systems and if you were in my situation what that system might look like.

No expert here, but My friend across the lake on 12 V solar installed two LED 12V tracklights. For fun, we checked the difference on the Trimetric between the draw on 12V dc, to the draw on 120V ac going through the small transformer back to 12V DC. The difference did not measure on the Trimetric, which reads in 1/10ths of an amp. Seems the difference is definitely not worth having two voltage systems.
One caveat I have noticed is: I have an LED lamp in my bedroom with the little transformer on the plug. This transformer draws even with the lamp switched off.