Retrofitting grid-tie system to off-grid in case of emergency

Sulfur

Hello, I have a grid tied solar system in Montana that I installed last year and have a question on retrofitting the system to off-grid in case of emergency.

SB7000 with 28 Sharp 240watt panels (ND-240QCJ) self installed

I am about to install another
SB7000 with 28 more Sharp 240 watt panels and a SB3000HFUS with 14 Sharp 240 watt panels
So a total of 70 panels and 3 inverters.

I have a net metering power meter and this inverter I am about to install also came with a Sunny Webox for improved data logging vs my current Sunny Explorer via blue tooth which is weak.

I only plan to use the system as grid tied but want to buy the hardware to be able to use solar power in case the utility power would go down for a long period of time. I have a generator that can power my house and enough gas for a few months, but want to be able to retrofit the system and have the hardware on hand to do so in case of longer power outage.

My current ideas are to get a Sunny Island and a 120VAC to 240VAC transformer (I am in USA so SI only puts out 120VAC) and some batteries, maybe eight 6VDC 200Ah batteries in series? but I don’t know what batteries are recommended, brand, voltage, How many amp hours, where to buy them?

Is Sunny Island the way to go for this backup plan? I would prefer not to rewire the panels in parallel for this emergency mode, although I think they are the correct voltage for 24VDC charge controller

Is it possible to buy these batteries dry and would they last indefinitely if stored dry?

Any ideas on how to design for this emergency mode would be appreciated. I realize that the SI only puts out 5000? watts but I could heat the water and house during the day with power directly from the SB's, if in this emergency mode. water heater is electric and house heat is geothermal heat pump, no natural gas or propane. I have never had a SI, so I am not sure if I am understanding there capabilities correctly?

Photowhit

Re: Retrofitting grid-tie system to off-grid in case of emergency

The Sharp are too low a voltage to charge 24V batteries without a MPPT Charge controller.

You say for a more than 2 month outage, that will just be a silly large battery bank if you want to have near the same amount of current your now using. Do you have an anticipated load?

Before you install the added array for your grid tied system, look into your local Power Companies(PC) and state law about the size of system. Many only do 'Net metering' for 10 Kw array and some require added inspections and restrictions for above 10 Kw Array's.

vtmaps

Re: Retrofitting grid-tie system to off-grid in case of emergency

Sulfur wrote: »

Is it possible to buy these batteries dry and would they last indefinitely if stored dry?

Any ideas on how to design for this emergency mode would be appreciated. I realize that the SI only puts out 5000? watts but I could heat the water and house during the day with power directly from the SB's, if in this emergency mode. water heater is electric and house heat is geothermal heat pump, no natural gas or propane.

All lead acid batteries deteriorate. Wet or dry, used or not used.

What you are proposing is quite impractical... you would need a truly massive battery bank to run an all electric house. My advice is to run your generator for the big loads and buy a small battery based back-up system wired to lights, radio, cellphone charger, etc. No need to use solar... you will be running your generator enough to keep the batteries charged.

--vtMaps

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

vtmaps wrote: »

All lead acid batteries deteriorate. Wet or dry, used or not used.

What you are proposing is quite impractical... you would need a truly massive battery bank to run an all electric house. My advice is to run your generator for the big loads and buy a small battery based back-up system wired to lights, radio, cellphone charger, etc. No need to use solar... you will be running your generator enough to keep the batteries charged.

--vtMaps

Thanks for your advice, maybe I don't understand the SI if this is impractical? My intention was to have the SB feed large loads to the house directly while there is sun, house loads would have to be reduced while there is not good sun due to constraints of SI and battery bank.
Running a generator while in this emergency mode may not be possible, because if the electrical grid is down for months at a time there will not be any gasoline available. I thought the SI allows the SB to produce 240VAC directly to my house while in off grid mode and then use any extra power to charge the batteries and if there is a shortage of sun then produce 120VAC from the batteries. and if there is too much power from the SB then the SB throttles back production from the panels, is the SI supposed to be able to do this? I am not intending to buy enough battery capacity to run the whole house, my intent is to feed heavy loads directly from the SB.

ggunn

Re: Retrofitting grid-tie system to off-grid in case of emergency

Sulfur wrote: »

Thanks for your advice, maybe I don't understand the SI if this is impractical? My intention was to have the SB feed large loads to the house directly while there is sun, house loads would have to be reduced while there is not good sun due to constraints of SI and battery bank.
Running a generator while in this emergency mode may not be possible, because if the electrical grid is down for months at a time there will not be any gasoline available. I thought the SI allows the SB to produce 240VAC directly to my house while in off grid mode and then use any extra power to charge the batteries and if there is a shortage of sun then produce 120VAC from the batteries. and if there is too much power from the SB then the SB throttles back production from the panels, is the SI supposed to be able to do this? I am not intending to buy enough battery capacity to run the whole house, my intent is to feed heavy loads directly from the SB.

The SI is a pretty versatile machine. It can throttle back the production of a SB if the power from it has nowhere to go. It can control relays for load shedding when resources are low. It can fire up a generator. It has in integrated transfer switch. I'm pretty sure you could get it to make coffee for you.

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

Photowhit wrote: »

The Sharp are too low a voltage to charge 24V batteries without a MPPT Charge controller.

You say for a more than 2 month outage, that will just be a silly large battery bank if you want to have near the same amount of current your now using. Do you have an anticipated load?

Before you install the added array for your grid tied system, look into your local Power Companies(PC) and state law about the size of system. Many only do 'Net metering' for 10 Kw array and some require added inspections and restrictions for above 10 Kw Array's.

Thanks for your advice, I don't intend to design this emergency mode to be a huge Ah capacity since it may never be used, but my thought was to allow the SB to feed 240VAC to my house for heavy loads while there is sun and have some power available via SI and batteries while there is not sun. I was thinking about 1600 Ah of battery capacity but have not bought anything so just looking for other others advice, my normal mode of operation is grid tied.

My normal kwh usage in month is 1800 to 2500 but could get by with MUCH less if running in this emergency mode, for example the house can be heated with wood stove, probably could easily use 25% of what I use now, hot water is the biggest load and water could be heated while there is sun, directly from SB, I think?

good thought on the net metering limit, i checked and my limit is 50kw, so no problem there. Also, the SB 3000 will be installed at a different property for the next several years but the whole system will probably be in one location when I retire.

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

ggunn wrote: »

The SI is a pretty versatile machine. It can throttle back the production of a SB if the power from it has nowhere to go. It can control relays for load shedding when resources are low. It can fire up a generator. It has in integrated transfer switch. I'm pretty sure you could get it to make coffee for you.

does the concept of how I intend to use the SI make sense to you? can it feed the entire production from my SB's to my house, while there is sun? for heavy loads like heating water, stove, etc?

solarix

Re: Retrofitting grid-tie system to off-grid in case of emergency

1) lead-acid batteries don't store well even if dry.
2) The main purpose of the Sunny Island is to keep the GT inverters up and running during an outage by providing an "AC grid" for them to synchronize to.
3) The GT inverters then continue to feed your house directly. (during the day when the sun is up)
4) The rub comes when the GT inverters put out more power than your house needs - then the SI has to accept the difference. Because of this, the general recommendation is that the SI inverter has to be bigger than the GT inverter(s). If the SI inverter gets over powered, it won't be able to regulate the AC signal and will shutdown everything.
5) You can easily see how "whole house" off grid or hybrid systems get way expensive.
6) How about you put in your Sunny Island system and then shut off all but one GT inverter during an outage?

jaggedben

Re: Retrofitting grid-tie system to off-grid in case of emergency

Sulfur wrote: »

does the concept of how I intend to use the SI make sense to you? can it feed the entire production from my SB's to my house, while there is sun? for heavy loads like heating water, stove, etc?

The max AC input on the SI is 6.7kW. So you cannot connect any of your SunnyBoys to it except the SB3000HFUS in an AC-coupled arrangement. Maybe with a transformer (and losses in between) you could connect one of your SB7000s, but I'm not sure about this. You'd need to ask SMA, since it's right on the line. Maybe someone here knows the answer.

Simplest approach (besides doing nothin) would be to connect the SI only to the SB3000HFUS and your critical loads (e.g communication and safety lighting). The two SB7000s would be offline, though. If you want more power, you would need to re-design other parts of the system, or use multiple SIs.

The SI is not the only product to look at. There are also Magnum and Xantrex products that will AC couple to your grid tied systems. In each case though, I'm pretty sure you will be limited by the input current rating of the product. I'm not sure there are any that will do 7000W.

BB.

Re: Retrofitting grid-tie system to off-grid in case of emergency

From our host's battery FAQ, even dry charged batteries should be activated withing 18 months.

Lifespan of Batteries
The lifespan of a deep cycle battery will vary considerably with how it is used, how it is maintained and charged, temperature, and other factors. In extreme cases, it can vary to extremes - we have seen L-16's killed in less than a year by severe overcharging and water loss, and we have a large set of surplus telephone batteries that sees only occasional (10-15 times per year) heavy service that were just replace after 35+ years. We have seen gelled cells destroyed in one day when overcharged with a large automotive charger. We have seen golf cart batteries destroyed without ever being used in less than a year because they were left sitting in a hot garage or warehouse without being charged. Even the so-called "dry charged" (where you add acid when you need them) have a shelf life of 18 months at most. (They are not totally dry - they are actually filled with acid, the plates formed and charged, then the acid is dumped out).

-Bill

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

BB. wrote: »

From our host's battery FAQ, even dry charged batteries should be activated withing 18 months.



-Bill

so it sounds like you do not recommend storing an unfilled battery? but do think that a battery that is kept charged all the time will last a long time? did I understand that correctly?

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

jaggedben wrote: »

The max AC input on the SI is 6.7kW. So you cannot connect any of your SunnyBoys to it except the SB3000HFUS in an AC-coupled arrangement. Maybe with a transformer (and losses in between) you could connect one of your SB7000s, but I'm not sure about this. You'd need to ask SMA, since it's right on the line. Maybe someone here knows the answer.

Simplest approach (besides doing nothin) would be to connect the SI only to the SB3000HFUS and your critical loads (e.g communication and safety lighting). The two SB7000s would be offline, though. If you want more power, you would need to re-design other parts of the system, or use multiple SIs.

The SI is not the only product to look at. There are also Magnum and Xantrex products that will AC couple to your grid tied systems. In each case though, I'm pretty sure you will be limited by the input current rating of the product. I'm not sure there are any that will do 7000W.

Thanks for your advice, I think the house loads only need to pass through the SI when in grid tie setup, when in an off grid setup, it seems like the SB's should be able to feed the house loads directly and the SB's should be able to throttle back the panels as needed. Am I understanding that correctly?

icarus

Re: Retrofitting grid-tie system to off-grid in case of emergency

I am sort of wondering what you might be planning for, with the potential of multiple months of no grid power, no gas station fuel etc? End of the world, Armageddon type scenario? If this is the case then it might be the life style choices that would reduce consumption dramatically to "make it through". For example, a 100# propane tank or two, would provide a LOT of hot water through a small demand type water heater, or a REALLY big LOT using a Zodi camp water heater.

I guess my point is if you truly encounter an end of the world scenario, you life style is probably going to change dramatically anyway, so reasonable planning now for reduced life style issues probably make sense.

Tony

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

solarix wrote: »

1) lead-acid batteries don't store well even if dry.
2) The main purpose of the Sunny Island is to keep the GT inverters up and running during an outage by providing an "AC grid" for them to synchronize to.
3) The GT inverters then continue to feed your house directly. (during the day when the sun is up)
4) The rub comes when the GT inverters put out more power than your house needs - then the SI has to accept the difference. Because of this, the general recommendation is that the SI inverter has to be bigger than the GT inverter(s). If the SI inverter gets over powered, it won't be able to regulate the AC signal and will shutdown everything.
5) You can easily see how "whole house" off grid or hybrid systems get way expensive.
6) How about you put in your Sunny Island system and then shut off all but one GT inverter during an outage?

Thanks for your advice, when in an off grid setup, it seems like the SB's should be able to feed the house loads directly(as you mentioned) and the SB's should be able to throttle back the panels as needed, but maybe there is some limit on its throttling ability?. Am I understanding that correctly?

Is it the SB or SI that throttles the panels, seems like it has to be the SB, since they are connected to the DC from the panels.

If I had to, I certainly could shut down 2 of the SB's when in this emergency mode, as you mention in your 6) comment

stephendv

Re: Retrofitting grid-tie system to off-grid in case of emergency

solarix wrote: »

4) The rub comes when the GT inverters put out more power than your house needs - then the SI has to accept the difference. Because of this, the general recommendation is that the SI inverter has to be bigger than the GT inverter(s).

According to the manual, the SI can accept 2x it's own capacity in sunny boys. So with a 5kW SI you can connect 10kW of SB.

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

icarus wrote: »

I am sort of wondering what you might be planning for, with the potential of multiple months of no grid power, no gas station fuel etc? End of the world, Armageddon type scenario? If this is the case then it might be the life style choices that would reduce consumption dramatically to "make it through". For example, a 100# propane tank or two, would provide a LOT of hot water through a small demand type water heater, or a REALLY big LOT using a Zodi camp water heater.

I guess my point is if you truly encounter an end of the world scenario, you life style is probably going to change dramatically anyway, so reasonable planning now for reduced life style issues probably make sense.

Tony

I do have propane stored as an alternative energy source but my questions here are how to retrofit my solar system to make use of the solar power I have; without a utility grid.

BB.

Re: Retrofitting grid-tie system to off-grid in case of emergency

Batteries do not store well--And batteries designed for float service (say emergency power for a telephone central office) will not usually last as long when used in deep cycle service...

From the battery FAQ:

• Starting: 3-12 months
• Marine: 1-6 years
• Golf cart: 2-7 years
• AGM deep cycle: 4-8 years
• Gelled deep cycle: 2-5 years
• Deep cycle (L-16 type etc): 4-8 years
• Rolls-Surrette premium deep cycle: 7-15 years
• Industrial deep cycle (Crown and Rolls 4KS series): 10-20+ years.
• Telephone (float): 2-20 years. These are usually special purpose "float service", but often appear on the surplus market as "deep cycle". They can vary considerably, depending on age, usage, care, and type.
• NiFe (alkaline): 5-35 years
• NiCad: 1-20 years

Your best bet may be forklift/industrial batteries--Although, they will use more water and need a 10-20% larger solar array to make up for higher self discharge/slightly less efficient charging.

Making use of "unused" solar--Find a job that it can do with variable available power... Typically that is water pumping to a cistern/storage tank. Some people use for water heating--But resistance heaters tend not to be very efficient for domestic water heating (solar thermal panels or an "electric" heat pump type water heater can do better).

With any standby system--Knowing that it is still good months (or years) between major usage is always an issue... You can keep charging your battery bank and never know if it will actually work. Or you can cycle once a month to 50% discharge (or whatever you like) and see that everything works (which then wears on the battery a bit--plus requires you to actively do the cycling/monitor the state).

Add that I would plan on replacing inverters/charge controllers/electronics about every 10+ years (may last longer--but have money in tank, spares on shelf "just in case").

For true emergency usage--I would buy a Honda eu2000i genset every 5 years, recycle 20 gallons of gas every year (with fuel preservative). Cheap, portable, extra fuel can be used for "bugging out" (in my area, earthquakes is probably going to be our "end times"). If you can store propane--think about a propane conversion (if you have natural gas, frequently a good fuel source for emergency power too--but in a "true" regional failure, natural gas may go away too).

But you need to focus on the basics... More or less I use the "3 until I die" rule of thumb:
3 minutes for air
3 hours for shelter (assuming you are in a serious winter storm or something)
3 days for water
3 weeks for food
3 months, Zombie time?

In theory, the amount of electricity you need should be in support of the above rules... I.e., electricity to pump water, a little bit of light, and perhaps a week or three for running a fridge/freezer until you are out of fresh food (obviously, if you have frozen meat and access via hunting/farming to more, longer freezer runtime may be worth while--But then you could also go old school with smoking/drying meats, salting, etc.).

In many areas (urban), three weeks without electricty means no sanitation (sewer pumping, garbage, fresh water) and such--So doing these types of efforts for the suburban home (to spend months/years without utilities) is probably not the first place to spend money.

Obviously, if this is rual area--then being isolated from external services is a bit more practical--as you don't use most of them anyway. But understanding your true "minimal" electrical needs and getting good equipment that supports those needs (at a $$$$) vs just some less expensive genset/batteries/support equipment with larger power numbers) can really affect your budge and long term survival plans.

-Bill

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

I called Russel Kyle (his contact info below) at SMA and he tells me that I can feed my house with all 3 SB's in the off grid configuration that I have been describing. and that the SI will only draw the required current from the SB's. So if anyone knows for sure that this is not correct, I would like to hear that.

So that leaves me still with some questions on batteries, which I don't know much about at this point nor do I own any. any recommendations on these for what I am trying to do would be helpful. My plan is to not use the batteries unless the grid goes down, so probably just let the SI maintain a charge on them? but not let the SI put out any 120VAC unless the grid was down.




Russell Kyle
SMA America, LLC
Technical Support Representative
6020 West Oaks Blvd, Suite 300
Rocklin, CA 95765 - 3714
U.S.A.
Tel: +1 916 625 0870
Fax: +1-916-625-3588
Service Line +1 877 697 6283 (Toll Free)
Email: Russell.kyle@SMA-America.com
www.SMA-America.com

westbranch

Re: Retrofitting grid-tie system to off-grid in case of emergency

here is an off the wall idea...what about using a VOLT car or similar vehicle as you battery bank. Use it daily and then plug it in if needed. there are several strings on the topic of 'other uses' for those Li batteries in a car...

hth

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

BB. wrote: »

Batteries do not store well--And batteries designed for float service (say emergency power for a telephone central office) will not usually last as long when used in deep cycle service...

From the battery FAQ:

Your best bet may be forklift/industrial batteries--Although, they will use more water and need a 10-20% larger solar array to make up for higher self discharge/slightly less efficient charging.

Making use of "unused" solar--Find a job that it can do with variable available power... Typically that is water pumping to a cistern/storage tank. Some people use for water heating--But resistance heaters tend not to be very efficient for domestic water heating (solar thermal panels or an "electric" heat pump type water heater can do better).

With any standby system--Knowing that it is still good months (or years) between major usage is always an issue... You can keep charging your battery bank and never know if it will actually work. Or you can cycle once a month to 50% discharge (or whatever you like) and see that everything works (which then wears on the battery a bit--plus requires you to actively do the cycling/monitor the state).

Add that I would plan on replacing inverters/charge controllers/electronics about every 10+ years (may last longer--but have money in tank, spares on shelf "just in case").

For true emergency usage--I would buy a Honda eu2000i genset every 5 years, recycle 20 gallons of gas every year (with fuel preservative). Cheap, portable, extra fuel can be used for "bugging out" (in my area, earthquakes is probably going to be our "end times"). If you can store propane--think about a propane conversion (if you have natural gas, frequently a good fuel source for emergency power too--but in a "true" regional failure, natural gas may go away too).

But you need to focus on the basics... More or less I use the "3 until I die" rule of thumb:
3 minutes for air
3 hours for shelter (assuming you are in a serious winter storm or something)
3 days for water
3 weeks for food
3 months, Zombie time?

In theory, the amount of electricity you need should be in support of the above rules... I.e., electricity to pump water, a little bit of light, and perhaps a week or three for running a fridge/freezer until you are out of fresh food (obviously, if you have frozen meat and access via hunting/farming to more, longer freezer runtime may be worth while--But then you could also go old school with smoking/drying meats, salting, etc.).

In many areas (urban), three weeks without electricty means no sanitation (sewer pumping, garbage, fresh water) and such--So doing these types of efforts for the suburban home (to spend months/years without utilities) is probably not the first place to spend money.

Obviously, if this is rual area--then being isolated from external services is a bit more practical--as you don't use most of them anyway. But understanding your true "minimal" electrical needs and getting good equipment that supports those needs (at a $$$$) vs just some less expensive genset/batteries/support equipment with larger power numbers) can really affect your budge and long term survival plans.

-Bill

I live in the country, septic tanks, well water and have food and legal weapons to last a long time. So this part of the solar project is figuring out how to make use of the solar power without a utility grid. thanks for your good comments. does 1600Ah of batteries sounds like an appropriate amount? would 1000 be more appropriate, I don't envision a LOT of power need while the sun is down. I do have a few generators and gas as a backup. Your comments on the importance of cycling the off grid system periodically are wise. To make sure it works.

westbranch

Re: Retrofitting grid-tie system to off-grid in case of emergency

"will a 1600 or 1000 Ah battery work?"

It all depends on your loads, I planned my system on 3 kwh per day and have a 900Ah battery, 24v system in progress...

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

westbranch wrote: »

here is an off the wall idea...what about using a VOLT car or similar vehicle as you battery bank. Use it daily and then plug it in if needed. there are several strings on the topic of 'other uses' for those Li batteries in a car...

hth

I don't have enough money right now for a Volt car and have enough vehicles but thanks for the comment. what voltage are those LI car batteries?

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

westbranch wrote: »

"will a 1600 or 1000 Ah battery work?"

It all depends on your loads, I planned my system on 3 kwh per day and have a 900Ah battery, 24v system in progress...

have you ever replaced the electrolyte in those NiCd's you have? i have access to some old wet NiCd's and was wondering if they can made good again by replacing the electrolyte, I can get the POH for this. they currently foam when charged and don't seem to hold charge that good. I will probably also get some lead acid's even if I can make those work.

how many Ah of battery are recommended per kwh of discharge from the batteries?

BB.

Re: Retrofitting grid-tie system to off-grid in case of emergency

What is enough battery/solar/etc... Depends on your needs and your ability to fund.

As a starting point, I would suggest around 3.3 kWH per day as a nice "cabin" sized system. Enough power for an Energy Star Fridge+lights+laptop+computer+washer+well pump (all run efficiently). Or 100 kWH per month.

You could build out this system to learn more about solar, and how to maintain it. Plus, this could be your "backup" off grid power system in case the main system goes down (or if you have a small cabin on the property).

Most people probably use closer to 1,000 kWH per month--10x that amount of power. (and that would not even be with air conditioning and electric heating/cooking for many folks).

From my "city home" experience--It is pretty easy to run a home on 200-300 kWH per month (natural gas for all heating/cooking/hot water)... But you have to keep an eye on those numbers as they tend to grow if not watched (kids, wife wants freezer in shed, everyone wants a computer for schoolwork, etc.).

In general, it is cheaper to conserve power than to generate it.... Refrigerators and Well Pumps are two pieces of equipment that tend to be "really hard" on off grid systems. High surge current for starting, and fairly large power usage (1-4 kWH per day for a fridge, 1-2 HP for a well pump and a lot of power if used for irrigation, etc.).

There are off grid capable well pumps that can run off of a few hundred watts of solar panels (pump to cistern, use small AC or DC pump to pressurize home plumbing) that run $2,000+ for a 900 watt well pump. Think "slow pumping" for low power draw and efficient kWH/gallon pumping.

These days, modern Energy Star rated refrigerators are pretty efficient (nearly as efficient as the "off grid" fridges at 1/3 the price) and have no frost, ice makers, etc.... The drawback tend to be that they require 120 VAC 24x7 as the defrost timers tend to reset if the power is cut when the compressor is not running (requires a couple hundred watts of solar panel extra + battery storage to keep inverter running 24x7).

In the end--I suggest measure your loads (both peak/average watts, and hours per day of usage for Watt*Hours or kWH consumption numbers) conservation, more conservation, and even more conservation... Then recalculate your power needs. Finally start design the off grid power system that will meet those needs.

-Bill

PS: Amp*Hours is not enough information... Amp*Hours at what voltage? 100 AH at 12 volts is 1,200 WH; 100 AH at 48 volts is 4,800 AH of storage.

The Volt and Prius batteries tend to be around 200 VDC... There are inverters out there that run at these votlages (mid sized computer room backup units and such).

Note that for larger systems, you want higher battery voltages. 100 amps at 12 volts is only 1,200 watts... 100 amps at 48 volts is 4,800 watts. So with higher voltage you use smaller wire and can support longer cable runs. And, over all, you may end up paying less to build larger systems at higher voltages.

westbranch

Re: Retrofitting grid-tie system to off-grid in case of emergency

here is a cheap Li battery http://cgi.ebay.com/ebaymotors/130826602917

user 'Solar-Dave' has several threads on electric cars, as well as others, there is a house runoff a Prius mentioned too.

re NiCd's, what brand do you have?

No, have not needed to change the electrolyte in the ones I use. They were part of a 75 cell lot I obtained and the ones I use were from the ones that passed muster. a week long charge regimen is needed...

email me for more info re rehabilitating them

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

BB. wrote: »

What is enough battery/solar/etc... Depends on your needs and your ability to fund.

As a starting point, I would suggest around 3.3 kWH per day as a nice "cabin" sized system. Enough power for an Energy Star Fridge+lights+laptop+computer+washer+well pump (all run efficiently). Or 100 kWH per month.

You could build out this system to learn more about solar, and how to maintain it. Plus, this could be your "backup" off grid power system in case the main system goes down (or if you have a small cabin on the property).

Most people probably use closer to 1,000 kWH per month--10x that amount of power. (and that would not even be with air conditioning and electric heating/cooking for many folks).

From my "city home" experience--It is pretty easy to run a home on 200-300 kWH per month (natural gas for all heating/cooking/hot water)... But you have to keep an eye on those numbers as they tend to grow if not watched (kids, wife wants freezer in shed, everyone wants a computer for schoolwork, etc.).

In general, it is cheaper to conserve power than to generate it.... Refrigerators and Well Pumps are two pieces of equipment that tend to be "really hard" on off grid systems. High surge current for starting, and fairly large power usage (1-4 kWH per day for a fridge, 1-2 HP for a well pump and a lot of power if used for irrigation, etc.).

There are off grid capable well pumps that can run off of a few hundred watts of solar panels (pump to cistern, use small AC or DC pump to pressurize home plumbing) that run $2,000+ for a 900 watt well pump. Think "slow pumping" for low power draw and efficient kWH/gallon pumping.

These days, modern Energy Star rated refrigerators are pretty efficient (nearly as efficient as the "off grid" fridges at 1/3 the price) and have no frost, ice makers, etc.... The drawback tend to be that they require 120 VAC 24x7 as the defrost timers tend to reset if the power is cut when the compressor is not running (requires a couple hundred watts of solar panel extra + battery storage to keep inverter running 24x7).

In the end--I suggest measure your loads (both peak/average watts, and hours per day of usage for Watt*Hours or kWH consumption numbers) conservation, more conservation, and even more conservation... Then recalculate your power needs. Finally start design the off grid power system that will meet those needs.

-Bill

PS: Amp*Hours is not enough information... Amp*Hours at what voltage? 100 AH at 12 volts is 1,200 WH; 100 AH at 48 volts is 4,800 AH of storage.

The Volt and Prius batteries tend to be around 200 VDC... There are inverters out there that run at these votlages (mid sized computer room backup units and such).

Note that for larger systems, you want higher battery voltages. 100 amps at 12 volts is only 1,200 watts... 100 amps at 48 volts is 4,800 watts. So with higher voltage you use smaller wire and can support longer cable runs. And, over all, you may end up paying less to build larger systems at higher voltages.

thanks for the good comments, oops I see your point, I was not thinking when talking about Ah, I would want a 48VDC battery system. So how many Ah of battery capaicity would be recommended for a 48VDC system that can comfortably pull 5kwh per night, assuming SI can fully recharge them each day.

ggunn

Re: Retrofitting grid-tie system to off-grid in case of emergency

Sulfur wrote: »

does the concept of how I intend to use the SI make sense to you? can it feed the entire production from my SB's to my house, while there is sun? for heavy loads like heating water, stove, etc?

Yes, because your protected loads panel (the one that is live when the grid is down) would be between the SI and SB, so you would not be limited by the passthrough capacity of the SI. The thing is, though, if your loads exceed the capacity of the SI and SB working together (or the SB alone once you have reached the acceptable SOD of your batteries) the system will shut down. The other thing is, unless you are running a generator as well, your daily energy consumption plus some accounting for battery inefficiency cannot exceed the daily production of your PV system, else you are not running sustainably. Getting a SB, SI, and genny all playing together nicely will take some finesse, the right equipment, and a lot of help from SMA tech support. The SI can be a complicated beast.

ggunn

Re: Retrofitting grid-tie system to off-grid in case of emergency

Sulfur wrote: »

thanks for the good comments, oops I see your point, I was not thinking when talking about Ah, I would want a 48VDC battery system. So how many Ah of battery capaicity would be recommended for a 48VDC system that can comfortably pull 5kwh per night, assuming SI can fully recharge them each day.

Well, off the top of my head, assuming 50% maximum depth of discharge and 85% storage and retrieval efficiency from your batteries... (cipher, cipher)

(5000)(1/.5)(1/.85) = 11,764 W-h per day. At 48V that's 245Ah. Is that right? Something seems screwy. Anyway, if that's right, will your SB provide enough power to both charge your batteries and power your loads during the day?

DISCLAIMER: I have some experience with SB/SI systems, but it's not really my area of expertise. I enjoy participating in these discussions, but for actual advice you'll get better info from others in here.

jaggedben

Re: Retrofitting grid-tie system to off-grid in case of emergency

Sulfur wrote: »

Is it the SB or SI that throttles the panels, seems like it has to be the SB, since they are connected to the DC from the panels.

The SI controls the SBs in the off-grid situation. Remember the SI is the 'grid' to the SBs in this situation. The SI varies the line frequency and the SBs need respond to that signal.

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

ggunn wrote: »

Yes, because your protected loads panel (the one that is live when the grid is down) would be between the SI and SB, so you would not be limited by the passthrough capacity of the SI. The thing is, though, if your loads exceed the capacity of the SI and SB working together (or the SB alone once you have reached the acceptable SOD of your batteries) the system will shut down. The other thing is, unless you are running a generator as well, your daily energy consumption plus some accounting for battery inefficiency cannot exceed the daily production of your PV system, else you are not running sustainably. Getting a SB, SI, and genny all playing together nicely will take some finesse, the right equipment, and a lot of help from SMA tech support. The SI can be a complicated beast.

Since I am not planning on ever using the SI in a grid tie mode, other than to keep my batteries charged, I was not planning on having a protected loads panel, the house has a 200amp transfer switch that I can throw and power the whole house from a generator, this requires not turning on too many things at once of course. So my intent is to connect the output of the SI to this transfer switch aux side that is normally used for generator, that way utility is still protected from SI. Therefore the SI can power all circuits as long as I don't turn too much load on for the SI and SB can throw their full capacity of up to 16kw at the house when there is sun and if the house needs it.

Sulfur

Re: Retrofitting grid-tie system to off-grid in case of emergency

jaggedben wrote: »

The SI controls the SBs in the off-grid situation. Remember the SI is the 'grid' to the SBs in this situation. The SI varies the line frequency and the SBs need respond to that signal.

I believe that is the same description as what Russel Kyle told me, thanks for verifying that for me