New system
Edwardo
Registered Users Posts: 16 ✭
I need to design an off-grid system for a small home we are building this year.Cost is concern,I would like to keep the solar budget under $10,000 and have the ability to expand if needed in the future.The cabin is 480sqft and in the future will become a studio/workshop when we have built a larger 1000sqft home beside it.I am doing all the construction work myself so this will come one step at a time.
I have tried to calculate our future power consumption,this is what I have come up with:
Fridge rated 570kwh year=1.56kwh per day
clothes washer rated 350w 3A 120v which we use 2-3 hours a week=150w
television 375w which we use 3hours per day=1125w
septic pump unknown not purchased yet=
60w light bulbs x 3 running 3 hours a day =540w
mac osx computer 18w x2=36w
Total estimated 120v loads=1852w + sewer pump
we also have a 240v Samsung energy star clothes drier and a 240v espresso machine
I must go dig some more water line now will continue this later.
I have tried to calculate our future power consumption,this is what I have come up with:
Fridge rated 570kwh year=1.56kwh per day
clothes washer rated 350w 3A 120v which we use 2-3 hours a week=150w
television 375w which we use 3hours per day=1125w
septic pump unknown not purchased yet=
60w light bulbs x 3 running 3 hours a day =540w
mac osx computer 18w x2=36w
Total estimated 120v loads=1852w + sewer pump
we also have a 240v Samsung energy star clothes drier and a 240v espresso machine
I must go dig some more water line now will continue this later.
Comments
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Re: New system
First thing we have to do is get straight on units. You're looking for the total Watts at any one time to size the inverter, and the total Watt hours per day to size the battery bank.
The second thing is: do NOT go by the numbers on the machine. Get a Kill-A-Watt and run everything through it one at a time. Multiplying the Amps times the Volts from the manufacturer's tag and then estimating time of use will not give you correct numbers to work with. Some things will use more than indicated, others will use less.
Then try to get some more economical devices. Your 'frige at 1.5 kW hours per day is on the high side. Is it large? Have a lot of 'extras' like ice maker? My 16 cu. ft. uses 1.2, and there are some that can do better.
TV: 375 Watts? Recycle it and buy an LCD or LED. You will be able to cut that number by 2/3rds.
60 Watt light bulbs should be switched for CFL's (others will say LED but you live in BC and we both know those are way too expensive here).
Clothes dryer? Forget it. Espresso machine? Pot on the (propane) stove. Lifestyle changes are necessary if you're going to go off-grid on a budget.
Off grid power comes at a hefty price; the more you can reduce your needs the better you'll be able to fit your budget.
Five years ago my system cost $8,000 (self installed). Today you could get a bit more power for a bit less money due mainly to falling panel prices.
You will also need to test some designs with PVWatts http://www.nrel.gov/rredc/pvwatts/grid.html (you may have to poke a bit to find the part which allows you to enter data relative to Vancouver Island) and see what kind of insolation you can expect. Winter time is a problem even where you are due to the short hours of daylight. This will inevitably mean more panel and/or back-up generator. -
Re: New system
Yes you need to conserve a lot otherwise you are going to need a huge array and battery bank.
since you are looking to go a step at a time, consider, once you have a good handle on your loads, just having a battery bank and inverter and a generator to start. This will allow you to see if you have the load calculations right....remembering Solar Rule #1 ..Loads will grow over time, rule #2 ..see Rule #1
Also consider the impact on your system size of powering the pump and clothes washer off the generator as they are heavy but intermittent loads.
I don't see any pump shown for domestic water delivery...?
hth
KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada -
Re: New system
A couple of points. Consider running your larger loads (wash/dryer) on a the genny, maybe at the time y need to run a charger.
Second, SERIOUSLY consider y lighting. Conventional incandescent bulbs are a non starter. Consider using CFLs or LEDs which. Umentation for lumen will run about 3-5 more efficiently. Then look at the TV. A modern TV might only draw ~150 watts, less than half of your current.
The old rule of thumb was, every dollar spent on conservation will save ~$10 in PV costs. Nowadays, with the price of CFLs and LEDs down, as well as the price of PV down, it probably isn't tht great a spread, but the general rule is still true.
Just as an FYI, we live off grid, with 400 watts of PV, and we consume ~6-800 WH/day, which is a pretty well balanced system size wise. In the real world, my guess is that you will ikey use 2-3 kwh/day minimum and need a system ~1.5 kw to power it. Remember the cardinal rule of off grid, that is, all design considerations START and end with the load calculations. Any other method ends up with a square peg sytem. Define y loads carefully, add in some room to grow, (since loads ALWAYS grow with time) and find the proper size battery system. From there, the PV and charge regimen and hardware choices become clear.
Good luck and keep in touch,
Tony -
Re: New systemSecond, SERIOUSLY consider y lighting. Conventional incandescent bulbs are a non starter. Consider using CFLs or LEDs which. Umentation for lumen will run about 3-5 more efficiently. Then look at the TV. A modern TV might only draw ~150 watts, less than half of your current.
LED TVs (LCD TVs that are LED-backlit) are extremely energy efficient, 50 watts for a 32". -
Re: New system
It is a good idea to be mostly done with conservation efforts before you calculate the size of the system you need. Otherwise, it is very hard to estimate consumption. I didn't do it and I missed by a lot.
If you want to save money, your system will be different from what you could've had if you had unlimited resources. For example, if you only buy enough batteries to last for one day, you can save lots of money. Depending on how you use your systen, this may be a good money-saving decision, or it may turn out into a disaster. It is a good idea to figure out how are you going to live with your system day by day, or even hour by hour - when you run your big loads, when you run generator, what you do when it's cloudy etc. Good plan takes a lot of creative thinking. -
Re: New system
Thanks for your replys,I/we will give it more thought and research and get back. -
Re: New system
north guy,
doing the conservation figures first isn't as critical as you may think. he will still need to conserve, but any excess could be absorbed later on as most people tend to expand in their consumption. -
Re: New systemnorth guy,
doing the conservation figures first isn't as critical as you may think. he will still need to conserve, but any excess could be absorbed later on as most people tend to expand in their consumption.
That is absolutely right. Having a bigger system that will accomodate future growth is a very good idea.
However, when you're on a tight budget, properly sizing the system is the key to saving money. You do not want to build a system with underutilized capacity if you really can't afford it. -
Re: New system
A bigger system is fine within limitations. That said, if you reduce the design loads by say 65% because of efficiencies and conservation, then building a system three times as big may not make much sense.
My rule of thumb is, define the (conserved) loads, then design in a fair bit of head room, then designate a battery bank size, and a charge regimen to fit.
Tony -
Re: New systemA bigger system is fine within limitations. That said, if you reduce the design loads by say 65% because of efficiencies and conservation, then building a system three times as big may not make much sense.
My rule of thumb is, define the (conserved) loads, then design in a fair bit of head room, then designate a battery bank size, and a charge regimen to fit.
I had an Excel spreadsheet, with every load listed and separated by day/night summer/winter usage. I had current usage and projected usage. I did the best estimates that I could. We used to use 10MWh/year. My projection after conservation was 7+MWh/year. We're now less than 5MWh/year, and possibly will go lower than this. It is really hard to predict usage unless you have an ability to measure it with a KaW meter. If I knew that, I would've really saved some money and bought less batteries with an additional benefit that it would've been easier to charge them. -
Re: New system
We get a lot of overcast rainy days here sometimes for a week or 2.Would it be smart to have a larger array of panels with a 1 day(small) battery bank? -
Re: New system
That my friend is the 64000 kwh question? How big do you make your battery bank, and how many days of autonomy will that provide, and how big a charge system do you need to recharge? The answer is, how often do you want it run a genny either for power and for recharge. If it we me, I would try. I design around the worst weather. For example, cut on little production from Nov-Feb in the NW Coast and count on a genny for that time 3 weeks of little or no sun is a bear to design around for off grid. Do a search for Mtdoc in this forum. HE is located in NW WA and lives off grid. Perhaps he can give you some real world production numbers over e winters, as his climate is probably pretty close to the S. End of the Island.
Tony -
Re: New systemWe get a lot of overcast rainy days here sometimes for a week or 2.Would it be smart to have a larger array of panels with a 1 day(small) battery bank?
It depends on so many factors, so it is very hard to figure out.
First, you will never be able to have an array big enough to cover you completely during a dark cloudy day. You must have a generator for such occasions. Once you have a generator, you realize that you are capable to go through any weather just with generator - run it, charge batteries, stop it, live off the batteries until next day. But running generator is expensive (fuel, amortization), noisy, and it also has so many moving parts ... So, you install solar panels, which let you run generator less.
The more panels you have, the less generator hours you need. The relationship between the amount of panels that you have and number of hours of generator runs is very complicated. Generally, you'll see diminishing returns. When you don't have any panels, adding even one panel will decrease the generator runs by a lot. But when you already have relatively big solar array, adding an extra panel may only scratch couple of generator hours. So, at some point, adding more panels doesn't benefit you any more. The problem is to figure out where that point is. -
Re: New system
Edwardo, I just looked at what you want again. as I see it you have conflicting objectives, small studio, small system, larger house (3 X original sq.ft.) at least 4 x power demands plus full time home issues.
I am thinking that you should get your feet wet by assembling a small PV system for the Studio section. This will get you started into Solar power. Leave the main house power for later. run the fridge and other heavy loads on the gen, a bit inconvenient but it can work. Oversize your charge controller and battery charger to use later when you upgrade, with the 'full system' on the back burner. That's the best I can come up with for a transition strategy. Of course the wiring, plumbing, etc you do in the 'studio' will have to fit with the final 'house' plans.
hth
e
ps you should look at one of the inverter gen sets like the honda 2000i type.
KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada -
Re: New system
You can get an idea of cloud cover amounts, sunshine hours and daylight hours through the environment Canada website as well. This is climate data for Victoria.
http://www.climate.weatheroffice.gc.ca/climate_normals/results_e.html?stnID=118&lang=e&dCode=1&StationName=VICTORIA&SearchType=Contains&province=ALL&provBut=&month1=0&month2=12
For my system, I'm counting on significant generator time from about late November though to early February, due not only to cloud cover, but mostly due to the very short day light hours. Natural gas is very inexpensive where I live, so fuel expense is not a big factor. (It's actually less than what they charge us for power to generate your own). So you may want to factor in your generator cost versus having extra panels as North Guy mentioned.
What I have done is started with a small system as westbranch suggests, and figure out what the system will supply over the course of a year. If you can go that route, you will have an easier time deciding on the size of system to suit your needs. I find that my overall efficiency is about 70 %. If I generate 10 kwh through my charge controller, I make use of about 7 kwh on average, so you will be factoring losses in as well. Good luck with your system planning! -
Re: New systemWe get a lot of overcast rainy days here sometimes for a week or 2.Would it be smart to have a larger array of panels with a 1 day(small) battery bank?
After doing a lots of different calculations based on different needs... I think Cariboocoot's (Marc's) usage of 2 days of backup power and 50% maximum discharge (during normal operation) is about the best "balanced" design point (that is 4x your daily average load).
It gives you two days of "no sun", lots of reserve power (starting a well pump, septic pump, microwave, etc.) and allows you do dump a lot of current into recharging (sun+generator or a larger genset+AC charger) to quickly recharge back >80% SOC for those runs of dark days. A too small of battery bank--You cannot recharge that fast and need a lot of time on charge to get the battery back to >90% SOC (that could be 8-16 hours of charging--lots of generator run time). During a time when you have no sun anyway.
I would not go with a 1 day/50% maximum discharge unless this was a summer cabin or mostly small loads that you can live without when needed.
-Bill "my two cents" B.Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Re: New systemA too small of battery bank--You cannot recharge that fast and need a lot of time on charge to get the battery back to >90% SOC
I don't understand this. In my mind, given the same energy available, the smaller the bank the faster it charges. -
Re: New systemI don't understand this. In my mind, given the same energy available, the smaller the bank the faster it charges.
Peukart effect.
You can fill the large portion of a larger battery bank faster than getting the last 20% (equivalent power) into a smaller bank.
And in the case of generator charging efficiency is best with the gen well loaded, so a smaller bank becomes much more expensive per Watt hour recharging than a larger bank.
Pain in the anatomy, but there it is. -
Re: New systemCariboocoot wrote: »You can fill the large portion of a larger battery bank faster than getting the last 20% (equivalent power) into a smaller bank.
If you take a 500AH bank and 1000AH, both 50% discharged and then connect to equal solar arrays (or generators), the 500AH bank will charge up faster. Correct? -
Re: New systemIf you take a 500AH bank and 1000AH, both 50% discharged and then connect to equal solar arrays (or generators), the 500AH bank will charge up faster. Correct?
What do you mean by "equal"? The current required for the larger bank to recharge at all will be higher than that needed for the smaller bank.
Likewise the array for a larger bank could charge a smaller one too fast and cook it.
It's more about the power difference in the "top 20%" of the battery capacities and being able to get that amount from a larger bank at a lower SOC than taking the extra time to 'refill' the smaller bank to 100% in order to have the equivalent power available.
10 Amp hours @ 12 Volts is 120 Watt hours. If taken from and put back the <80% SOC of a larger bank it can be done in less time than if the same amount of power is utilized from the >90% SOC of a smaller bank because inevitably the charge rate will be different at those two SOC. You cannot get constant current charging in a solar power system (as of yet).
This is the principal Bill is trying to describe and no it will not be true or viable in 100% of cases. But if the application is in an area where the weather can't be counted on all the time being able to run a larger bank in the "above sulphation but below full charge" range has advantages. -
Re: New systemCariboocoot wrote: »What do you mean by "equal"? The current required for the larger bank to recharge at all will be higher than that needed for the smaller bank.
Likewise the array for a larger bank could charge a smaller one too fast and cook it.
Yes, I meant "Equal". Batteries can be charged with a wide variety of currents, from C/20 to C/5. Sure, if the current is too high or too low, it will kill the batteries. But, within limits, you can vary the size of the battery bank. To figure out what is the effect of smaller (or large) battery bank on performance characteristics (charging time in this case), you need to keep all other things equal.Cariboocoot wrote: »If taken from and put back the <80% SOC of a larger bank it can be done in less time than if the same amount of power is utilized from the >90% SOC of a smaller bank because inevitably the charge rate will be different at those two SOC.
That's the part I don't understand. You seem to imply that larger battery bank is normally bulk-charged (< 80% SOC), while smaller bank is in absorption(> 90% SOC).
If anything, I would expect it to be opposite. Say, if you take 100A from 400AH bank, it'll be 75% SOC (bulk). If you take the same amount from bigger 800A, it'll be 88% SOC (absorption) . -
Re: New system
No, it's more about not being able to meet the full charging of the small bank at the lower current of the Absorb stage due to lack of time when the same power can be put back in Bulk with a larger bank because the current rate is higher.
Can't think of any other way to explain it. -
Re: New systemCariboocoot wrote: »No, it's more about not being able to meet the full charging of the small bank at the lower current of the Absorb stage due to lack of time when the same power can be put back in Bulk with a larger bank because the current rate is higher.
Can't think of any other way to explain it.
I understand that Absorb current is lower and therefore it takes longer. What I don't understand is why you associate smaller bank with Absorb and larger bank with Bulk. -
Re: New systemI understand that Absorb current is lower and therefore it takes longer. What I don't understand is why you associate smaller bank with Absorb and larger bank with Bulk.
I think what Cariboocoot is trying to say is that a smaller bank of batteries (for a given size solar array) will be sooner to go to absorb, spending more time there. If you have a bigger bank, then it can absorb more energy through the bulk stage. Does that make any sense? In any case, it's important to size the array to the battery bank size, as you and others likely know. -
Re: New system
It sounds to me what cariboohoot is trying to say is; If you use power you can use more cheaply with a larger bank cause an 80 percent charge is about amp for amp. If you have a smaller bank with no latitude then to get the same use you have to charge the batteries to 95%. When you charge to 95% you are no longer getting one amp out for one amp put in. the current is also reduces due to resistance so that you can't charge as fast which means it is not there to use. Cari.... can correct me if I am misquoting.
Cheers
gww -
Re: New system
Yep--The "small battery" that operates from 100% to 50% state of charge will have to spend ~2-4+ hours to get from ~85to ~100% state of charge (charging current will be much less than solar array maximum output during "absorb" stage from ~80-100% state of charge).
With a battery bank that is 2x larger... And if significantly discharged (during bad weather)--The batteries are near 100% efficient in terms of Amp*Hours. So, the first day you discharge to 75% SOC, and the second day you discharge to 50% SOC.
The third day, you either have a bunch of sun and/or a good sized generator that output ~10% rate of charge or more.
Charging from 50% to ~85% state of charge will be simply (for a first approximation):
Amp*Hours used / Charging Amps = Hours of Charging.
So, with a 10% rate of charge, you can recharge from ~50 to 85% in about 3.5 hours... And easily be able to "survive" another "day of darkness" on only 3.5 hours of charge time. And that is over 1 day of energy usage (25% discharge per day, 35% recharge).
With a "small" battery bank. The first ~50-85% only recharges in 3.5 hours (yes, with a 1/2 sized array and/or 1/2 sized genset). But the next 15% will take 2-4-maybe 6 hours to recharge. That is more sun than most people have in winter and/or running the genset for many hours at low output levels (less than 50% loading on a genset is less fuel efficient). And you have to complete the charge to 100% to get a "full charge" for the next "dark day".
In the end, assuming a genset (for this example). With a larger battery bank, a 2x larger genset running 3.5 hours (or less) after a couple dark days... Vs a smaller genset that runs 6-9+ hours every day to get the battery bank fully charged for the next dark day.
Of course, there are other ways to run/design a system, but that was the basics of what I was trying to say earlier.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Re: New systemOf course, there are other ways to run/design a system, but that was the basics of what I was trying to say earlier.
I see. There are two different things mixed here
1. You can cycle your battery differently. One method is 50-85% cycling, avoiding absorption, and doing it once a week. Let's call it "efficient" method. Second method is to fully charge every day. Let's call it "full" method.
2. You can have smaller or larger bank.
Bill and Coot think that smaller bank must be charged with full method, while larger bank must be charged with efficient method.
I don't think bank size is so closely related to the charging method. Any bank can be charged with either method.
If you use full method (full charge every day) then you need to put back everything that you have discharged. With the same loads, smaller bank will get discharged to 50% SOC, so there's a considerable amount of bulk charge it can take. Bigger bank may get discharged to 75% SOC, so there's almost no bulk, only absorption.
If you use efficient method then during cloudy periods you simply need to run generator more frequently for the smaller bank, for example, every day. With large bank, you run it less frequently, for example every other day. In both cases it'll charge from 50 to 80% SOC. Assuming the same charging current, the total number of generator hours will be the same. Of course, smaller bank should still be big enough to be able to accept the current. -
Re: New systemI see. There are two different things mixed here
1. You can cycle your battery differently. One method is 50-85% cycling, avoiding absorption, and doing it once a week. Let's call it "efficient" method. Second method is to fully charge every day. Let's call it "full" method.
2. You can have smaller or larger bank.
Bill and Coot think that smaller bank must be charged with full method, while larger bank must be charged with efficient method.
I don't think bank size is so closely related to the charging method. Any bank can be charged with either method.
If you use full method (full charge every day) then you need to put back everything that you have discharged. With the same loads, smaller bank will get discharged to 50% SOC, so there's a considerable amount of bulk charge it can take. Bigger bank may get discharged to 75% SOC, so there's almost no bulk, only absorption.
If you use efficient method then during cloudy periods you simply need to run generator more frequently for the smaller bank, for example, every day. With large bank, you run it less frequently, for example every other day. In both cases it'll charge from 50 to 80% SOC. Assuming the same charging current, the total number of generator hours will be the same. Of course, smaller bank should still be big enough to be able to accept the current.
That is true, but the issue is bank size relative to a fixed size of solar array (or generator). To make use of a given amount of power per day from a solar array, a small battery bank won't be able to operate with the "efficient" method. It will have to go to full to take it all in. A larger battery bank, however, can avoid the "full" method and make more use of the "efficient" method, due to the larger capacity. -
Re: New system
NG I think if you look at the use in Ahr as well as % it makes more sense.
a big bank can be more shallowly discharged by X Ahr than the bigger bank can, thus if we want to replace X Ahr in the big bank it will (hopefully)all be done in Bulk, whereas the small will not only be in bulk ans Absorb but can also be in Float too, the latter 2 at a much lower rate (%) of charge. As bill said Bulk is the cheapest rate of charge, float the most expensive.
hth
KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada -
Re: New systemnortherner wrote: »That is true, but the issue is bank size relative to a fixed size of solar array (or generator). To make use of a given amount of power per day from a solar array, a small battery bank won't be able to operate with the "efficient" method. It will have to go to full to take it all in. A larger battery bank, however, can avoid the "full" method and make more use of the "efficient" method, due to the larger capacity.
There's no doubt that the system with properly sized battery bank will work better.
However, batteries are very expensive. If you cannot afford or do not want to spend on a big bank, it is quite possible to organize your system to work well with smaller bank. And also it is possible to use part of the money saved on batteries to compensate for a small bank with "cheap" panels.
That's like houses. Big luxurious house is definitely better. However, people who cannot afford or do not want to pay for big ones, live well in smaller houses with less amenities.
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