Off grid help

notes

Hi all, just bought a off grid camp in upper peninsula of Michigan. Runs on a Onan/cummins 5.5 kW propane generator. Wanting info on batteries and controls to charge a bank of batteries and a auto switch or inverter to run generator back and forth. Is this possible? I have run a load analysis on cabin and came up with 6359 watts a day in Winter and 5204 in summer. Camp will open in spring and shut down in end of November. Usually spend about 3-4 days at camp every other week and in fall up to 10 days. I have a lot of questions, but I am going to search first as to not wast anybody's time. Thank you all.
Andy

Cariboocoot

Re: Off grid help

Welcome to the forum.

Is it possible to get 6kW hours per day from batteries? Yes. Is it practical? Maybe not.

Looks a bit like this:
6000 Watt hours AC converted to DC plus inverter draw = 7150 Watt hours.
Divide by nominal 48 Volts and you get 149 Amp hours used. That's a minimum 300 Amp hour battery bank.

This amount of energy is fairly large for an off-grid application. I think you should re-examine your loads carefully and see what can be eliminated, changed out for a more efficient model, or shifted to other energy source (such as propane for heating something).

My cabin uses less than half that, just so you know, and has all the comforts. The smaller you can make the load requirements the smaller you can make the system and so the less it will cost.

That gen sounds like a fuel-guzzling monster too.

vtmaps

Re: Off grid help

notes wrote: »

I have run a load analysis on cabin and came up with 6359 watts a day in Winter and 5204 in summer.

Welcome to the forum,

Watts is a rate. Watts a day is a rate of a rate. I presume you mean 6359 wattHours per day. You also need to know your peak load which is measured in watts.

Usually for solar powered systems we size a battery so that you can go a couple of days without running the generator. In your case, since you are charging with a generator, you can get by with a smaller battery bank.

Another thing to consider is load shifting... that means scheduling your generator to run when you have large loads (pumps, laundry, vacuum, etc). You can get by with less battery if you don't have to run large loads off the battery.

How automated will the generator be... will you have an automatic gen start that triggers when the battery voltage dips from large loads?

--vtMaps

notes

Re: Off grid help

Thanks for reply, yes that is per day. I can bring my watts down by replacing electric water heater to propane and upgrading to a more efficient jet pump. Currently using 230/1ph. 3/4 hp. Already installed LED bulbs in all sockets. I do run 2 ceiling fans all day to move heat around from wood stove. I notice that is a large load. May need to look into something else. We also have a Onan/Cummins RS12000 genet on site but not connected. Is that more efficient than what I mentions in first post. I can get my daily watts down to 4000 bye changing the way we take grid power for granted and making some upgrade to be more efficient.

vtmaps

Re: Off grid help

notes wrote: »

We also have a Onan/Cummins RS12000 genset on site but not connected. Is that more efficient than what I mentions in first post.

I have no idea whether an Onan/Cummins RS12000 genset is more efficient than an Onan/cummins 5.5 kW propane generator. Generally, it is inefficient to run a genset at much less than its capacity, so I suppose that if you are running a 3 kW load, the smaller genset would be more efficient.

Efficiency is not necessarily what you should strive for... Aim for economy. Which costs less to run for an hour while fulfilling your needs? That may be the same answer in different locations.... depends on local pricing of diesel, propane, gasoline, etc.

I just reread your first post... what do you mean by: "a auto switch or inverter to run generator back and forth"?

--vtMaps

notes

Re: Off grid help

Yes my goal is to, aim for economy. Sorry about my explanation. I am trying to learn about other ways to power camp other than running a generator for power. I guess in short I thought I could install a bank of batteries and other controls to have generator charge batteries and keep generator off for a amount of time, maybe generator could run on larger demands, and get a system that I can add solar panels to in the future.

Cariboocoot

Re: Off grid help

notes wrote: »

Yes my goal is to, aim for economy. Sorry about my explanation. I am trying to learn about other ways to power camp other than running a generator for power. I guess in short I thought I could install a bank of batteries and other controls to have generator charge batteries and keep generator off for a amount of time, maybe generator could run on larger demands, and get a system that I can add solar panels to in the future.

This is perfectly normal: battery bank powers loads through inverter, is recharged by generator as needed and/or when generator is run to accommodate large loads the inverter can't handle. Solar for charging batteries can be added later. No problem, and I've often advised people to do just that.

I understand what you mean about an "auto switch": automatic transfer switch that will connect the loads to the gen whenever it is running. Again normal, and yes some inverters have them built-in. This would be as opposed to a system where the generator only charges the batteries and loads are always run through the inverter (less efficient that powering AC loads directly from the gen).

As vtMaps said the generator's functional efficiency depends on how it is used. Efficiency drops off as the load demands do: a 12kW generator having to supply only 2kW is not going to be efficient. Larger is not automatically more efficient, neither is smaller. The only way to tell what size is right for your system is to calculate the needed battery size and know the anticipated loads. That will give you a Wattage that the gen must be able to supply.

Blackcherry04

Re: Off grid help

notes wrote: »

Yes my goal is to, aim for economy. Sorry about my explanation. I am trying to learn about other ways to power camp other than running a generator for power. I guess in short I thought I could install a bank of batteries and other controls to have generator charge batteries and keep generator off for a amount of time, maybe generator could run on larger demands, and get a system that I can add solar panels to in the future.

All you need is a bank of batteries and a Inverter / Charger with AGS if you want to auto start the generator. You have to decide if you a 12, 24 or 48 Volt system, there reasons to for each. 24 v, with 8, GC-2 Golf Cart batteries is a medium system, the Transfer switch is built into the Inverter. Then a 3000 watt Inverter your in business. You set the Inverter to start the generator when the batteries reach a certain level and enjoy. if you find that the 8 batteries are not enough, add 4 more.

upa123

Re: Off grid help

This is a tough one, as no matter how you crunch the numbers to make your current part time off grid camp more "efficient" it don't look too pretty. As already mentioned the cheapest option is conserve your current electrical demands as much as possible(great idea about getting rid of resistive heating loads) and keep your current small generator as prime power or perhaps substitute it for a smaller Honda inverter generator(keep in mind it likely wont spin up your current jet pump). I used my Yamaha ef2000 inverter generator for 3 years as prime power at my off grid residence. I had my total daily loads under 3kw and it ran at a partial load up to 12hrs on a gallon of gas. Now once you get in to good quality inverters(with pure sine and auto switching) and battery banks to off load some generator use plan to bring $3-5K to the party, add solar and its going to be more like 10k. You quickly realize that current fuel bills may not be so bad. I don't want to discourage you but if you really want to go down this road don't do it piecemeal, or think you can just upgrade stuff later, trust me you will just end up wasting money down the road. My honest advice is to make a plan, figure out a way to pay for it and make it happen and then forget it.

BB.

Re: Off grid help

With generating power--There is a lot of inefficiencies involved... Just to "run" a battery bank:

0.80 typical AC charger efficiency * 0.80 typical battery efficiency * 0.85 inverter eff = 0.544 = ~54% end to end efficiency

Your battery system will probably save you fuel if your off peak AC loads are less than ~25% of generator capacity. And for much of the time they will be--Just some lights, perhaps one of those newer LED flat screen TVs, laptop computer, etc... Efficient fan to move warm air around, etc...

In the end, reduce your off peak loads (LED, efficient appliances, energy star rated devices, etc.) to get the battery loads as small as possible.

And for your peak loads--Try to keep those to shorter time periods (and run the AC battery charger off the genset during these times).

Solar is difficult to justify for seasonal camps... Conservation will be your best friend here.

You can get more complex... Generator Support capable AC inverter/chargers is very interesting... You use a smaller genset running many hours per day--But when the AC loads exceed the generator output, the AC inverter can support those loads with battery power (say running a well pump, power tools, or even an induction hot plate/microwave, etc.).

-Bill

notes

Re: Off grid help

Thanks for all your help. I guess first we need to get an exact load on our camp. My brother works for local electric company and has kilowatt meters we can install and graph our usage next time we go up. I see what you are saying on inverter generators. Question, are they able to convert to propane. Cannot find any info on Honda web site? Also can we install two and run them both when demand is high and only one when load is low. Seems like my dollar is going to propane co. 750.00 for 300 gal. Should start there and upgrade to energy star equipment first. I can change jet pump from 230 volt to 115 volt but amps increase. Will have to look for eff. Pump.

Blackcherry04

Re: Off grid help

notes wrote: »

Thanks for all your help. I guess first we need to get an exact load on our camp. My brother works for local electric company and has kilowatt meters we can install and graph our usage next time we go up. I see what you are saying on inverter generators. Question, are they able to convert to propane. Cannot find any info on Honda web site? Also can we install two and run them both when demand is high and only one when load is low. Seems like my dollar is going to propane co. 750.00 for 300 gal. Should start there and upgrade to energy star equipment first. I can change jet pump from 230 volt to 115 volt but amps increase. Will have to look for eff. Pump.

The Honda EU 2000 is easily converted to Propane, you lose a little power, but no big deal. The pump could go either way, if you can use a transformer on it and step up the voltage. There are 100 different options to power use and re-charging the battery bank and you can add in some solar to finish off the charge when your not there. I size most of my installs where the nights are free from generator use, thats a sizing issue and knowing the level of charge it requires. Charging can be slow and steady or with a big generator you can pump in a lot of amps in a short period of time.

BB.

Re: Off grid help

Here is one thread on propane conversion of the small Honda gensets (another thread referenced inside):

Propane conversion for Honda EU3000is

This company seems to have a good reputation for conversions:

http://www.generatorsales.com/

There is always the question of running propane in "ice box" conditions (keeping cylinder pressure up, keeping vaporizer from icing up--If not gas feed from tank, possible hard starting, etc.). But if you avoid winter--You are probably OK. Gasoline vs Propane--Just which ever makes sense for your area.

A very active Yahoo Group for eu2000i recommended by others:

Honda_EU2000_Generators - Yahoo Groups

-Bill

notes

Re: Off grid help

Thank you all for your comments and suggestions. Lots of info. Got some books from library to read up on to make a better decision. One more thing came up today talking with my Carrier rep, he sells solar thermal heaters for domestic hot water and some space heating. Sounds interesting but when sun is down no heat. Storage tank would have to be large enough to provide heat at night. I was thinking, I know not good, but if I have a propane water heater with a close loop from panels full of glycol, could I use water heater as heat source when panels become inefficient? I would need a 3 way valve to stop flow to panels and send to base board for space heating. Just a thought. Again thanks,
Andy

techntrek

Re: Off grid help

You'll need far more heat for space heating than your water heater will provide. Look up www.solarhouse.com for one example of solar PV and solar thermal (space and water) done right.

Working on your overall efficiency first is the right path. For years I used two 4 inch 12 volt "biscuit" fans to move heat from my wood stove around my house, mounted at the top of door frames. Cheap to buy and little amperage to run.

I learned the hard way that going big with a genset as a single source of power is a bad idea because of operating costs. Go with a smaller inverter genset on one sub-panel for your base loads and some discretionary loads - lights, wood stove fans, fridge, tv. If you add in an inverter + battery have the inverter run these loads 24/7 and use the genset to recharge the batteries with an AGM as mentioned before. Size the genset so the battery charger takes up 70-80% of the capacity at its max load for best efficiency. Then use your 5 kw genset for the well pump and water heater as-needed.

I've been down this road for backup power. Started with a 12 kw Generac, then added a 22 kw battery bank so I could keep the genset off at night and middle of the day, then ran the Generac for a few hours for the water heater, well pump and battery charging for best efficiency. Then I switched to the type of configuration I mentioned above.

YehoshuaAgapao

Re: Off grid help

For efficiency, the 22 inches of insulation I had blown in a year ago is working great. The heat pump hasn't turned on at all yet and the lows have been getting into the low 40s this week.

niel

Re: Off grid help

YehoshuaAgapao wrote: »

For efficiency, the 22 inches of insulation I had blown in a year ago is working great. The heat pump hasn't turned on at all yet and the lows have been getting into the low 40s this week.

insulation makes a great difference as you found out. am i to assume that was 22 inches added in the attic area as few have wall cavities that span 22 inches? did you add in the wall cavities too as this makes for a far greater result than many in warm climates realize? solar guppy used to tell everybody just to add it in the attic, but heat infiltrates through the walls too be it outside to inside or inside to outside depending on the season.

YehoshuaAgapao

Re: Off grid help

Attic only. Walls are expensive and disruptive (ripping out drywall, most wall space is not attic accessible). I did do the duct seal and air seal (seal off airflow spaces between attic and walls). Temps are going to be ~55 high and 30-35 low all week.

niel

Re: Off grid help

years ago they used to blow insulation into walls through a high up hole in the wall for each cavity and then they'd patch the hole and paint over the wall. some had troubles with the walls sweating due to the lack of vapor barriers. they may have solved this as i'm talking some 30yrs ago with that trouble. might be worth your looking into it later.

Cariboocoot

Re: Off grid help

Just be sure that when they blow in the insulation it is done correctly, not randomly so that it block off air circulation from the eaves to the vent. I know because I spent weeks correcting this sort of mess on our old house - and adding blocks to the joists which were open from eave to eave and let the air blow through under the 2nd story floor. And sealing off the exposed fibreglass on the 2nd story walls (Tudor style house - miserable things to insulate properly if it is not done at the time of build).

Cariboocoot

Re: Off grid help

niel wrote: »

years ago they used to blow insulation into walls through a high up hole in the wall for each cavity and then they'd patch the hole and paint over the wall. some had troubles with the walls sweating due to the lack of vapor barriers. they may have solved this as i'm talking some 30yrs ago with that trouble. might be worth your looking into it later.

The problem with this method is that there are often obstructions in the wall cavities that prevent the insulation from filling it evenly and completely.

Depending on the siding type, insulation may now be added outside in the form of rigid foam boards. Not cheap or easy, but what is these days?

niel

Re: Off grid help

yes i know as fire breaks, pipes, wires, and electrical boxes can do that and it certainly is better than nothing. it may not be worth his trouble in a temperate climate. the insulation boards are a good idea, but depend on the exterior wall type he has. these insulation boards are best used on wood frame types with siding for cost effectiveness and least amount of work involved. stucco or brick exteriors require a new exterior wall of some sort to be made whereas the siding would be able to be reused in the type with it. it is expensive to do in any case so he may opt to not do this. with 22 inches of insulation in the attic it would be futile to add any more up there and even with the 22 inches that may have been unnecessary to add that much with walls that are uninsulated. the reason for this is that the losses presented by the walls would look like there's a big opening like a door or a window. the heat flows so readily through the walls that it doesn't see the ceiling area hardly at all. think of water flow. if there are 2 branches off of a river and one has a blockage, it will push most of the water through the other open waterway. doubling that blockage, just like doubling of insulation, will have very little effect on the water flow because it is exiting out the other channel.

solar_dave

Re: Off grid help

One new method for fixing home insulation is to do the re-foam regime. They pump a low expanding foam into the walls from the outside to seal them and increase the insulation. I have been considering having this done for a while, but my budget is holding me back.

niel

Re: Off grid help

good point dave. i forgot about that one.

YehoshuaAgapao

Re: Off grid help

They did block everything, but when I had the roof redone, I went overkill on the attic ventilation. After a couple of windy days, the even the stubborn vents unclogged themselves. I have ridge vents on all roof ridges, more than twice the requirement, and replaced all the bird blocker holes with vents that are mostly just screen rather than one or two small holes (because ridge vents with inadequate intake don't work). The ridge vents are baffled so they can be wind powered in addition to passive convection (which usually doesn't work as intended on retrofits).