Viability of Solar for emergency backup?

[Rusty123]

Short background: I live in a fairly conventional single family 2,500 SF home in a semi-rural area west of Seattle. Tall trees around perimeter of 1 acre lot. Propane heat (500 gallon leased tank on site). Electric dryer and kitchen range, but will replace with propane at some point. Deep well pump with 240 v power.

POCO feed is remarkably reliable (only one short (3 hour) outage in 15 years). And power is very cheap. So my design scenario is a large earthquake, of which we are at high risk, causing widespread outages and transportation interruptions lasting several weeks or months. Something short of SHTF, but I wouldn’t mind being prepared for that also. It’s just my wife and me, but I have kids and grandkids in the area who would probably ride out the emergency with us, since they don’t really have the financial ability to prepare much themselves.

I’m in the design phase of a holistic emergency backup system. By “holistic”, I mean that I’m trying to balance investment between the primary needs of heat, water, lighting, communication, sanitation, etc., rather that focusing too heavily on any one area.

I already have a hand pump for the well (Simple Pump, not yet installed) and a 12V/220AH battery bank for my ham radio and NIMH battery chargers, and 600 watt inverter for chest freezer.

I would love to go with solar as an electrical source, but even with minimizing the loads as much as possible, I can’t seem to get there on paper without significant investment, due to the poor solar energy in my area in winter (worst in the US, as best I can tell), coupled with trees. So I’m beginning to accept that I need to design my system around propane generation (increasing my tank volume), with solar (if any) being more of a fuel saver in the summer.

Knowing that the devil is in the details, does this all sound logical?

 

[GXMnow]

That is certainly a tougher situation than we have here in So Cal. With a lot of trees, there is not much you can do about having shadows hit panels.
If you didn't have the shading issues, I would have suggested a DC coupled system to efficiently charge the batteries. But to handle the shading issues, you would also need power optimizers on each panel which adds cost, and a Sol-Ark or Outback Skybox starts on the higher side on cost to include the solar MPPT controllers. So my thought was to use Microinverters on each panel. I have Enphase iQ7's and they are very efficient and have had no issues at all, but I have only had them 14 months now, so still pretty new. They are grid tie and just put out AC 240 volts which would normally just help feed your home on the grid. I have a lengthy thread in the Show and Tell section about adding storage to my Enphase system. The best part about the micro inverters is that each panel is being optimized to get as much power as it can even with shading. And they also take care of the rapid shut down at each panel, and the wiring is much safer, running just normal 240 AC like you already have in your house, not 600 volt DC which can pose some real hazards.

Since your main priority is for backup power, The Schneider inverters do work well. I have an XW-Pro, 6,800 watt with 48 volt battery bank. It is rock solid for backup power, the only issue I am having is trying to make it do time of use shifting, but that is a separate thread. How much power will you need while on backup? 6,800 watts is a fair amount, and if you need more you can stack 2 or 3. If you can get by with 4,000 watts, they have the much cheaper SW line that I almost went with, but the XW allows me to also sell battery power back to the utility. But this is not needed at all for a backup only system. There are several other battery based inverters that will also work for a system like this. We have others on this forum with a Sol-Ark, an Outback Skybox, the SMA Sunny Island, Enphase Ensemble, and I think even a Tesla Powerwall. All of which will work with AC coupled micro inverters. Enphase is probably the most popular micro inverter, but there are a few other companies making good ones.

If you did a setup similar to mine, it would work like this.

You need to install a separate breaker panel for the loads that you want to run from the backup battery system.
The battery based inverter (Schneider, Aims, Skybox, Sol-Ark, whatever) will have it's output feed this new panel.
The battery based inverter will also have an input which will get a feed from your existing panel. So grid power can run your loads normally
The solar panel micro inverters will also connect into the backup loads panel. When the sun shines, they will power your loads in the backup panel
Any power beyond what your backup loads need will also charge up the battery bank through the inverter, and if the solar is making more power than the charger is set to use, the remaining power will flow back to your main panel, and help power the non backup house loads as well. If you do not want to deal with a NEM (net energy metering) agreement with your power company, you can setup most systems to never export power back to the grid. But with a NEM setup, you could allow the excess solar to go back and reduce your electric bill even further once the batteries are fully charged.

When the grid power does fail, the battery based inverter will disconnect from the grid and use battery power to supply power to your new backup loads panel. Any loads still back in the main panel will lose power. Since the micro inverters are in the backup panel, they will still see power as if the grid was still there, so they will still help power the house. And excess solar will still be able to charge the battery bank during the day. If the battery bank becomes fully charged, the battery based inverter will shift the AC frequency which will cause most newer micro inverters to reduce their output to keep from overcharging the battery bank. If the power does not drop enough, the frequency may shift far enough to shut down the solar completely, and once the battery comes down, it will take another 5 minutes to get them to connect again.

The only real problem with a purely AC coupled system like this is if the battery bank does run too low to where the battery inverter needs to shut down at night. It will not be able to produce the AC local grid to get the solar panels working again in the morning. The best solution is to have a low battery warning for you to reduce load, or even have a contactor to turn off some less important loads to preserve some battery for the morning. Most of these battery inverter will also output a signal for an auto start generator to come on and charge the battery bank. That will also prevent the run down issue. Some have gone to a dual system where panels that see shading will have micro inverters, and a few panels with less shade issues can be DC coupled which can keep charging the batteries even if the inverter shuts down from a low battery condition.

Since you are pretty far north, you will want to find a way to have your panels face south and be tilted to get the sun close to straight on the panel. There are several online calculators to find the best angle for your latitude. Being turned a little east or west will also shift the time of day of peak power. And with micro inverters or optimizers, having them at different angles can spread the peak power across a longer time.

To really start the design, figure out how much peak power (Watts), and how much energy (Watt Hours) you will need while in backup, and we can start to figure out how many panels that will take and see what can be done on your property. I was an evil person, I did cut down 3 palm trees that were killing my solar production in the winter. Palm trees grow like weeds here. I would not cut down old growth real trees for solar power. But a little trimming is not too evil.

 

[svetz]

Hi Rusty! Welcome to the forums!

...I would love to go with solar as an electrical source, but even with minimizing the loads as much as possible, I can’t seem to get there on paper without significant investment, due to the poor solar energy in my area in winter (worst in the US, as best I can tell), coupled with trees. So I’m beginning to accept that I need to design my system around propane generation (increasing my tank volume), with solar (if any) being more of a fuel saver in the summer.

Knowing that the devil is in the details, does this all sound logical?

If there is a three month outage, will propane trucks be able to get in to refuel you? There was an area in Colorado cut off months a few years back when the roads to access it were destroyed (bridges out).

Sounds like you have a well thought out plan, for example with the hand-pump you've all the basics: Water, food, shelter. But solar can add some luxuries (like not needing to lug water). If your lot is in a valley or something and it never sees sunshine solar might not work, but since you were thinking about it, I suspect there must be some.

Most homes, if not using power for heat or air-conditioning actually use fairly little energy (your well works against you there). The first thing you want to do is an energy audit. Then you'll know what consumes power and how much. If you share your audit some folks might have ideas on how to get around things. For example if you've an electric cooktop that just takes too much power, perhaps a $10 second-hand camping stove or one of those fancy gas grills can not only serve during the event but be the centerpiece for family barbecues?

Let's say your refrigerator is 150 Wh/d and your electric chain saw (so you can cut wood for heat) is 300Wh/d, and you want 4 hours of TV (200Wh/d), and 4 hours of 2 computers (4x2x80)=640 Wh. These are just made up numbers, from your energy audit you can setup a budget and match it to costs. But from just this, it's under 1.5kWh/d.

Solar insolation in Seattle averages about 3.57, low is 1.6 in the winter. Let's use the low number. 1.5 kWh/d / 1.6 insolation ~= 1 kW solar array. That's three 340W panels to get you 1.5 kWh/d in winter. On average throughout the year it would crank out 3.570 kWh/d.

Tesla advertises $1.49/W, so that's $1500. That's more of a DIY price as Tesla's smallest system is a 4 kW array. But, you'll also want enough battery for the night time, so let's toss in a powerwall... from their web site the solar and battery is $8000, or about $6000 after the tax incentive.

Hopefully this helps!

 

[Rusty123]

Wow! You all bring up some interesting systems and designs - really appeals to my engineering side.

But I’m afraid this all way far exceeds my design objectives (which I should have stated more clearly). Because my current POCO feed is very reliable and cheap, I have little interest in building a large scale solar system. Rather, I’m just looking to recharge a modest battery bank (2.5 kWh per day demand, approximately) in the case of months long outage caused by an earthquake. In fact, I’m not even planning to permanently mount the panels, but rather to store them in my basement until needed.

if I go with solar alone, I need to design for the worst case, which would be several days of clouds, in the dead of winter at 49 degrees north latitude, coupled with tall trees around the horizon. Based on my calculations, I could do it with solar, but would need 6-8 kW of panels (or more). But that amount of panels would generate high peak power on a clear day, necessitating a higher bank voltage, larger controller(s), etc., driving up the system cost.

alternatively, I could design around a small propane generator like a Honda eu2200i (I already have bulk storage on site), with a more moderate solar setup (maybe 1 kW), that would only play a significant role in the summer or in clear weather (making my propane last longer, which is not inconsequential).

Thoughts?

 

[svetz]

...alternatively, I could design around a small propane generator like a Honda eu2200i (I already have bulk storage on site), with a more moderate solar setup (maybe 1 kW), that would only play a significant role in the summer or in clear weather (making my propane last longer, which is not inconsequential).

That's my plan (well, grid-tied and the panels fixed to the roof to get some payback period on them), the generator is the backup to my solar/battery...at least until battery prices fall some more (once V2G (using your EV car as storage) or VPPs (making money from your powerwall) happen that might change/accelerate).

Of course, if I'm without power for more than a few hours I have to seriously curtail power use, for example AC in one room no hot water. What I'm lacking is a clean water supply. I have a BoB, but it'll only last a week. I'm not sure I'd get fresh water from a hand pump here so my backup is filtering water from a dehumidifier or distilling salt water (which would take a lot of power).

 

[efficientPV]

An emergency system should be doing something useful while it is waiting for that big moment. Heating water is what I would suggest. You can always do with a little less hot water in an emergency when power is diverted to other necessities. Those trees will be a serious problem though. If you really engineer a system it is amazing how little you can get by with.

 

[svetz]

You might also look into used panels as they can dramatically slash your costs. I don't have them but some people (@Craig - are you the one that likes these?) love 'em. I think the general recommendation is Santan solar or Craig's List (local is better, no shipping costs ;-)

 

[Rusty123]

You might also look into used panels as they can dramatically slash your costs. I don't have them but some people (@Craig - are you the one that likes these?) love 'em. I think the general recommendation is Santan solar or Craig's List (local is better, no shipping costs ;-)

Great comment - I haven’t really got to the point of purchase yet, but definitely don’t need the latest and greatest.

 

[Hedges]

PV makes great financial sense if you use them every day. Not so much for just backup. Propane generator would be best for that.
Trees around, but how many hours of sun on your roof? 1 acre is 200' x 200'. How tall are the trees? I think you should be able to get lots of sun (except you're north of where "people don't tan - they rust")

PV is good if it cost-effectively reduces your power bill, but bad it utility forces you on an unfavorable time-of-use plan and too little PV leaves you a net consumer. PV, grid-tie, in my area where I get 5.5 hours effective sun produces power for $0.05/kWh (amortized over 10 years.)

Battery systems are general more expensive, and battery storage costs several times as much per kWh as generation with PV. But a small battery system that works with PV can run A/C and everything else in your house while the sun shines. That with propane generator as backup would be ideal.

 

[Opusdei]

How about the foldable and rollable solar panels? P3Solar.com thin film solar panel was designed for rapid deployment allowing setup in minutes. 200W rollable solar panel and frames are lightweight so you can carry anywhere you have sunshine.

 

[Hedges]

How about the foldable and rollable solar panels? P3Solar.com thin film solar panel was designed for rapid deployment allowing setup in minutes. 200W rollable solar panel and frames are lightweight so you can carry anywhere you have sunshine.

They're ideal if you need a modest amount of portable power, for instance to charge cell phones, where you don't mind paying $8/watt

P3 Solar 125 Watt 12V, Portable Solar Charger Light Weight Foldable / Flexible

P3Solar’s P3 products are designed for United States and Allied Armed Forces personnel requiring the smallest, lightest, highest power density portable solar chargers in support of mobile forces operating in austere environments.

readymaderesources.com

Also expect lifespan of 5 or 10 years from thin-film flexible panels. (these have a warranty of 1 & 2 years)

For fixed applications and more power, we use rigid framed panels, cost $0.20 to $0.50/watt, expected lifespan 20 to 40 years.
We can make power this way for around $0.05/kWh (based on amortizing system cost over 10 years.) Sometime after than we might have to replace the inverter, so for next 10 years cost could be $0.01/kWh

 

[Opusdei]

In the original post, @Rusty123 wanted an emergency backup system in case of earthquake in rainy Seattle suburban area. 5 or 10 years is not a lifespan of thin film flexible panels, they are from the module vendor (also 1 or 2 years warranty).

 

[Maast]

Short background: I live in a fairly conventional single family 2,500 SF home in a semi-rural area west of Seattle. Tall trees around perimeter of 1 acre lot. Propane heat (500 gallon leased tank on site). Electric dryer and kitchen range, but will replace with propane at some point. Deep well pump with 240 v power.
POCO feed is remarkably reliable (only one short (3 hour) outage in 15 years). And power is very cheap. So my design scenario is a large earthquake, of which we are at high risk, causing widespread outages and transportation interruptions lasting several weeks or months. Something short of SHTF, but I wouldn’t mind being prepared for that also. It’s just my wife and me, but I have kids and grandkids in the area who would probably ride out the emergency with us, since they don’t really have the financial ability to prepare much themselves.
I’m in the design phase of a holistic emergency backup system. By “holistic”, I mean that I’m trying to balance investment between the primary needs of heat, water, lighting, communication, sanitation, etc., rather that focusing too heavily on any one area.
I already have a hand pump for the well (Simple Pump, not yet installed) and a 12V/220AH battery bank for my ham radio and NIMH battery chargers, and 600 watt inverter for chest freezer.
I would love to go with solar as an electrical source, but even with minimizing the loads as much as possible, I can’t seem to get there on paper without significant investment, due to the poor solar energy in my area in winter (worst in the US, as best I can tell), coupled with trees. So I’m beginning to accept that I need to design my system around propane generation (increasing my tank volume), with solar (if any) being more of a fuel saver in the summer.
Knowing that the devil is in the details, does this all sound logical?

I'm just to the south of you in a similar semi-rural area outside Gig Harbor in a similar situation (kids & grandkids will come here in an emergency). I'm implementing a 3 phased plan that you might gain some value in, even though I'm investing considerably more money.

IMO there is a point where if you dont put enough into it you're just wasting time and money and should just go with a straight generator backup and forgo the battery and inverter. I think you need at least a 5kwh battery unless all you want to do is keep a couple of LED bulbs going at night.

In place:
Phase 1: Eight 135AH SLA batteries (14kwh, 7kwh usable), 48v 2200 watt inverter/charger, 6000w diesel generator, 300 gallons of treated diesel in phenolic lined 55 gal drums. Got a hell of a deal on the batts from Budget Battery and saved a couple thousand. Batts are 7 years old and pretty much shot at this point. Inverter/charger is connected full time to gas furnace, garage door opener, fridge and freezer. Has really paid off during the few multi-day power outages we've had and multiple 6-8 hour outages. Three various 1000-1500w 24V inverter chargers in UPS mode w/ two 100AH SLA batteries each protecting one home server, two computers, two TVs & 1 TIVO.

Actively assembling, have all parts on hand:
Phase 2: Eighteen 3.2kwh BYD modules (58kwh, 55kwh usable), 8kw Split Phase inverter charger, house tranfer switch, same genny, 600 gallons stored diesel, 1 car and truck is diesel. 21kw 24v Planar diesel forced air heater. Inverter/charger (Radian) and batt bank will be configured as whole-house backup.

Moved tree line back 80 feet to clear roof solar line-of-sight line-of-sight in winter. Cut down about 50 douglas firs and cedars which paid for itself and more when sold to the lumber mill. I'm a 53yr old man, did about half of the logging myself, amazing what a snatch block or two and a truck winch can do.

Future within the next 2 years:
Phase 3:
9.5kw solar array. Panels to be set at 50 degrees to optimize for winter production. BYD batt bank, same genny, heater, and diesel. Have plans on building a 500W thermoelectric generator for planned wood stove.

I'm a full-up prepper so I also have a truly stupid amount of beans, rice, etc sealed in mylar bags in the basement. I figure we'll be feeding the neighbors too in a Cascadia quake and beans and rice are cheap.

Yeah, I'm one of those.....

 

[Rusty123]

Duplicate

 

[Rusty123]

I'm just to the south of you in a similar semi-rural area outside Gig Harbor in a similar situation (kids & grandkids will come here in an emergency). I'm implementing a 3 phased plan that you might gain some value in, even though I'm investing considerably more money.

IMO there is a point where if you dont put enough into it you're just wasting time and money and should just go with a straight generator backup and forgo the battery and inverter. I think you need at least a 5kwh battery unless all you want to do is keep a couple of LED bulbs going at night.

In place:
Phase 1: Eight 135AH SLA batteries (14kwh, 7kwh usable), 48v 2200 watt inverter/charger, 6000w diesel generator, 300 gallons of treated diesel in phenolic lined 55 gal drums. Got a hell of a deal on the batts from Budget Battery and saved a couple thousand. Batts are 7 years old and pretty much shot at this point. Inverter/charger is connected full time to gas furnace, garage door opener, fridge and freezer. Has really paid off during the few multi-day power outages we've had and multiple 6-8 hour outages. Three various 1000-1500w 24V inverter chargers in UPS mode w/ two 100AH SLA batteries each protecting one home server, two computers, two TVs & 1 TIVO.

Actively assembling, have all parts on hand:
Phase 2: Eighteen 3.2kwh BYD modules (58kwh, 55kwh usable), 8kw Split Phase inverter charger, house tranfer switch, same genny, 600 gallons stored diesel, 1 car and truck is diesel. 21kw 24v Planar diesel forced air heater. Inverter/charger (Radian) and batt bank will be configured as whole-house backup.

Moved tree line back 80 feet to clear roof solar line-of-sight line-of-sight in winter. Cut down about 50 douglas firs and cedars which paid for itself and more when sold to the lumber mill. I'm a 53yr old man, did about half of the logging myself, amazing what a snatch block or two and a truck winch can do.

Future within the next 2 years:
Phase 3:
9.5kw solar array. Panels to be set at 50 degrees to optimize for winter production. BYD batt bank, same genny, heater, and diesel. Have plans on building a 500W thermoelectric generator for planned wood stove.

I'm a full-up prepper so I also have a truly stupid amount of beans, rice, etc sealed in mylar bags in the basement. I figure we'll be feeding the neighbors too in a Cascadia quake and beans and rice are cheap.

Yeah, I'm one of those.....

It does sound like we have pretty similar situation (I’m 53 also). But it sounds like your power grid is less reliable than mine (I’ve only had one outage of a couple hours in the last 15 years). For that reason, I’m having a hard time justifying a big expense that will essentially never be used unless/until something big happens (like an earthquake).

So I’m taking a more minimal approach, basically making sure that I can provide bare essentials of life (water, heat, food/cooking, communications, battery powered lanterns, that sort of thing. And maybe light refrigeration, but that’s optional). Basically, a SHTF/Prepper approach.

For lots of reasons (no fuel, quiet, reliable, etc.), it would be great if I could do this with solar only, but because of our dismal winter conditions (as you know), I’m not sure that solar only would cut it, at least not without a couple weeks (or more!) of autonomy. And that sort of battery investment will buy a small generator (or two).

 

[Supervstech]

The two big pluses of battery are silent, and on hand.

The costs do bite a bit.

A nice 400Ah LiFePO4 bank stored in a basement at 50%charge will last for years, and you can setup a timer to trickle charge the bank once in a while to offset the minuscule self discharge of them.
That and a small 1500W LF inverter will keep refrigerators and deep freezers chill for quite some time, drag out a few 250W panels, and you should be able to keep minimum loads happy for weeks.

This should be doable under $2500

 

[Supervstech]

But, yeah...

A decent 15KW generator would be less...

 

[Rusty123]

The two big pluses of battery are silent, and on hand.

The costs do bite a bit.

A nice 400Ah LiFePO4 bank stored in a basement at 50%charge will last for years, and you can setup a timer to trickle charge the bank once in a while to offset the minuscule self discharge of them.
That and a small 1500W LF inverter will keep refrigerators and deep freezers chill for quite some time, drag out a few 250W panels, and you should be able to keep minimum loads happy for weeks.

This should be doable under $2500

I assume you’re referring to a 12v 400Ah battery. But even at that, $2500 seems very inexpensive for a battery like that (not to mention the peripherals). What sort of cells/setup do you have in mind?

Also, what does “LF” in LF inverter stand for?

 

[Supervstech]

LF is for low frequency.
High quality inverters have a Low frequency steel transformer design that allows huge surge abilities, often 3 times continuous load spec, and can produce this output for 30 seconds or more.
The HF inverters use tiny inductors, and switching mossfets to produce current, and surge is only twice the rated spec, and then only for a few nanoseconds... useless for startup loads.

 

[Supervstech]

Yes, 12V 400 Ah, simple to maintain, and low cost for the output abilities.

$2500 should cover the cells, BMS, wiring, and the inverter/charger setup.