Small PV/battery system for extended power outages

[flick]

I'd like to have some backup power in case of an extended power outage, but
I don't need to be able to run much. As I found after Katrina, a gas or
diesel generator is a p.i.t.a. - it was dificult to buy fuel. I'd rather
not store fuel, I'm engine-impaired, and running a generator gets expensive.

I'm also electric-knowledge impaired. I've tried, oh how I've tried, but
when I read about setting up one's own pv power system, there are so many
variables that I'm just lost.

The prepackaged remote cabin systems are way out of my price range.

I only want to run a few things. A BIG fan for ventilation/cooling, and
also the desktop computer and satellite modem. If it would help enough to
make economic sense in terms of power savings and system requirements, I can
purchase a laptop, but I still need to run the sat. modem to connect to the
internet (all phones were out, so I want the computer & modem up for
communication). I have no idea how much power the modem uses.

I've seen the Xantrex Xpower battery packs. It seems like the 1500w model
would meet our needs. Plus, I could wheel it around the property and use
some power tools from it, which is a nice bonus.

Some stores sell the 1500w Xpower together with a 100w pv panel for about
$1500 - kinda pricey IMO. Looks like you can buy the two things separately
for around $1,000. How big a pv panel to *quickly* charge the Xpower 1500w?

If I buy the two things separately (Xpower and PV panel), do I need some
kind of limiting thingie (charge controller?) to keep from overcharging the
Xpower, or is that built in to the Xpower?

Can I do what I want to do for under, say, $1500?

Any info, ideas and suggestions welcome.

flick 100785

 

[Steve Spence]

I'd like to have some backup power in case of an extended power outage, but
I don't need to be able to run much. As I found after Katrina, a gas or
diesel generator is a p.i.t.a. - it was dificult to buy fuel. I'd rather
not store fuel, I'm engine-impaired, and running a generator gets expensive.

I'm also electric-knowledge impaired. I've tried, oh how I've tried, but
when I read about setting up one's own pv power system, there are so many
variables that I'm just lost.

The prepackaged remote cabin systems are way out of my price range.

I only want to run a few things. A BIG fan for ventilation/cooling, and
also the desktop computer and satellite modem. If it would help enough to
make economic sense in terms of power savings and system requirements, I can
purchase a laptop, but I still need to run the sat. modem to connect to the
internet (all phones were out, so I want the computer & modem up for
communication). I have no idea how much power the modem uses.

I've seen the Xantrex Xpower battery packs. It seems like the 1500w model
would meet our needs. Plus, I could wheel it around the property and use
some power tools from it, which is a nice bonus.

Some stores sell the 1500w Xpower together with a 100w pv panel for about
$1500 - kinda pricey IMO. Looks like you can buy the two things separately
for around $1,000. How big a pv panel to *quickly* charge the Xpower 1500w?

If I buy the two things separately (Xpower and PV panel), do I need some
kind of limiting thingie (charge controller?) to keep from overcharging the
Xpower, or is that built in to the Xpower?

Can I do what I want to do for under, say, $1500?

Any info, ideas and suggestions welcome.

flick 100785

For under $1500 you can get a deep cycle battery, an inverter, a pv
panel and a charge controller, but that's dependent upon what loads you
need to power. We need to know your loads.

Let's say you have 500 watts of loads you need to power for 8 hours.

8 * 500 = 4000 watt-hours.
4000 / 12v = 333 amp-hours

Since you only want to discharge a lead acid deep cycle to 50%, you'll
need a 670 amp hour pack. Six Walmart type 27 deep cycle batteries at
$55 each will do the trick.

A 1500 watt inverter will run you about $100.

In NY, we get about 3 hours of full sun best case scenario, so I would
need about 1500 watts of pv (about $7500) to charge that battery pack in
a day.

Three 60 amp charge controllers at $148 each and you start to get the
picture.

PV isn't going to economically replace a $500 gas generator any time
soon. But it is quiet, and pollution free.

 

[flick]

For under $1500 you can get a deep cycle battery, an inverter, a pv panel

and a charge controller, but that's dependent upon what loads you need to
power. We need to know your loads.

That will be a toughie. There's nothing on the sat modem to tell me what it
uses, and it isn't in the technical specs online. I've emailed the company.
Otherwise, a "typical" desktop computer with a CRT monitor. I have a fan of
the type I'd like to use, and it says 150w.

Let's say you have 500 watts of loads you need to power for 8 hours.

8 * 500 = 4000 watt-hours.
4000 / 12v = 333 amp-hours

Since you only want to discharge a lead acid deep cycle to 50%, you'll
need a 670 amp hour pack. Six Walmart type 27 deep cycle batteries at $55
each will do the trick.

A 1500 watt inverter will run you about $100.

In NY, we get about 3 hours of full sun best case scenario, so I would
need about 1500 watts of pv (about $7500) to charge that battery pack in a
day.

After a hurricane, which is the most likely weather event to take out power
for an extended time here, the weather is typically clear and sunny for at
least a week and usually longer. In my case, i think it would be reasonable
to assume that we'd have 8 hours of sun a day. If we didn't, well, I
wouldn't be able to run as much or as often, and that would be okay. I'd
still have *some* power.

Would that mean I'd need 500+ watts of pv? Yikes.

Three 60 amp charge controllers at $148 each and you start to get the
picture.

PV isn't going to economically replace a $500 gas generator any time soon.
But it is quiet, and pollution free.

With our last power outage, which lasted two weeks, it was difficult to buy
gas. I'd like to be prepared to run these few things without having to buy
gas, even though the initial outlay will be more expensive than a generator.
Gas in the Katrina disaster zone abruptly rose to $3 a gallon, and where I
live you couldn't buy any for nearly a week.

Thanks for the info!

flick 100785

 

[bumtracks]

fwiw
my laptop a/c adapter usually is sitting at 20watts, as I load a webpage and
its graphics it will momentarily jump up to maybe 55watts.

 

[flick]

It's hard to say without more data as to your consumption figures. You
can
buy a meter for under $50, and plug your necessaries into it (one by one).
Moniter for a few days and you'll see what your consumption is.

But let's make some assumptions:

1. Laptop and satellite modem running 18 hrs/day
The satellite modem draws, if I recall correctly, about 60 watts,
and figure about 40-50 watts for the laptop. That's 1.8kWh/day.

2. Fan could be a big item. You said it was rated at 150W. Again, you
need to measure it to see but, if it is on 12 hours/day, that's another
1.8kWh/day.

3. A few compact flourescent light bulbs -- say four at 15Wea for 3 hours
= 0.18 kWh/day.

4. You did not mention a refrigerator? Are you planning to do without?
If not, you'll really have to measure that because their consumptions can
be all over the place. If you have a new model, that is efficient, you
might be drawing less than 1kWh/day. If you have an older model, it may
be
two or three times that. Let's assume a newer model at 1kWh/day for this
exercise.

We would do without lights hooked up to this power thing, and do without the
fridge. Doing without the fridge turned out to be no big deal for the two
weeks. We adapted. My son said it best - that it was like being on a
campout, with a house instead of a tent.

We were up at dawn, asleep soon after dusk. We used oil lamps and LED
headlamps. The heat at night was a BIG problem, though, hence wanting a
large fan. Instead of running a fan, perhaps I should just buy a
tent/screen room thing, so we can sleep outdoors where it's cooler, if this
ever happens again. They aren't expensive.

Those few items, being run for that period of time, total up to a load of
4.78 kWh/day. Since they are running off AC, after factoring in losses in
the inverter (assume 15%), you are up to a daily load of 5.623 kWh/day.

You could reduce this by significantly reducing the time your modem and
computer are on, but since you are using this for telephone service, that
may not be practical.

I should just use it it to send out and receive a couple emails a day, and
then it would be on for a much shorter period of time. 90 minutes a day
(?). Having absolutely no communications turned out to be a Real Big Deal.

Not sure exactly where you are, but in the New Orleans area, the worst
month for sun, considering only the hurricane season, has 5.18 effective
sun hours / day. Figure a 20% safety factor for system losses and so
forth, and you're up to quite a bit of money.

Consumption: 5.623 kWh/day
Safety Factor: 20%
kWh req/day: 6.748 kWh/day

Sun Hours 5.18

PV Panels required: 1303 watts

At present day costs, that's probably going to cost you upwards of $5,000
just for the panels. Inverter, charge controller and batteries would be
extra.

Again, yikes.

Does your state have any kind of rebate plan for PV installations?

I'm not sure, I'm going to look into it.

The Xantrex XPower Powerpack would not be appropriate for your purposes.
It only has a 60AH battery which means it would last, on average, about
2.5
hrs without needing to be recharged.

You probably need at least ten times that storage, and that's only if you
assume that every day is sunny.

So it would seem a generator would be cheaper. Perhaps you could store
diesel or propane fuel on site?

Diesel generators seem to be expensive. We have natural gas. Perhaps one
of those natural gas backup generators would be the best alternative for us
(?). I'd hate to get that bill afterwards...

Or run a laptop and the modem off my van's cig lighter (?). Of course,
there's a limitation there, as my van only holds about 20 gallons. That
could see us through a while, I guess, if we were real careful.

Many thanks for sharing your time and expertise on this.

flick 100785

 

[Douglas Siebert]

Let's say you have 500 watts of loads you need to power for 8 hours.

8 * 500 = 4000 watt-hours.
4000 / 12v = 333 amp-hours

Since you only want to discharge a lead acid deep cycle to 50%, you'll
need a 670 amp hour pack. Six Walmart type 27 deep cycle batteries at
$55 each will do the trick.

A 1500 watt inverter will run you about $100.

In NY, we get about 3 hours of full sun best case scenario, so I would
need about 1500 watts of pv (about $7500) to charge that battery pack in
a day.

Three 60 amp charge controllers at $148 each and you start to get the
picture.

PV isn't going to economically replace a $500 gas generator any time
soon. But it is quiet, and pollution free.

Call me crazy, but it sounds like his best option if he wants to avoid
being dependant on a generator would be to figure out his power needs
and buy enough of those $55 batteries to cover all use for the entire
power outage and keep them fully charged via utility power (and possibly
his generator when he has gas for it or even his car assuming he gasses
it up before the hurricane arrives) and forget the PV for a few years
until it comes down in price.

PV isn't even cost effective today with a net metering arrangement, but
it is really bad when used only as emergency supplemental power. For
the prices it sounds like he'd be paying for PV, he could afford to have
a big pile of gas generators and run each until it runs out of gas and
then move onto the next

 

[[email protected]]

I only want to run a few things. A BIG fan for ventilation/cooling, and
also the desktop computer and satellite modem. If it would help enough to

The satellite modem is an interesting thought. My friend in Ft. Lauderdale
was watching DirecTV long before the local cable was back.

On the other hand, cellular service was back before the power was.

I occasionally use my cellphone to connect my laptop to the internet.
Depending on your location, Cingular GPRS or EGPRS might be 50-150Kbps.
I've thought about the new Verizon cingular data service at 400K as an
off-grid replacement for Starband.

I have a single Walmart tractor battery on a 15 watt solar panel. I had my
laptop and cellphone powered from that for several hours.

 

[flick]

Call me crazy, but it sounds like his best option if he wants to avoid
being dependant on a generator would be to figure out his power needs
and buy enough of those $55 batteries to cover all use for the entire
power outage and keep them fully charged via utility power (and possibly
his generator when he has gas for it or even his car assuming he gasses
it up before the hurricane arrives) and forget the PV for a few years
until it comes down in price.

PV isn't even cost effective today with a net metering arrangement, but
it is really bad when used only as emergency supplemental power. For
the prices it sounds like he'd be paying for PV, he could afford to have
a big pile of gas generators and run each until it runs out of gas and
then move onto the next

You don't sound crazy to me at all. I had no idea that what I wanted to do
would be so expensive.

Thanks for your time .

flick 100785

 

[flick]

The satellite modem is an interesting thought. My friend in Ft.
Lauderdale
was watching DirecTV long before the local cable was back.

On the other hand, cellular service was back before the power was.

It was the other way 'round here, I guess because we had such an extensive
power outage.

I occasionally use my cellphone to connect my laptop to the internet.
Depending on your location, Cingular GPRS or EGPRS might be 50-150Kbps.
I've thought about the new Verizon cingular data service at 400K as an
off-grid replacement for Starband.

I'm going to look into that, too.

I have a single Walmart tractor battery on a 15 watt solar panel. I had
my
laptop and cellphone powered from that for several hours.

I think I'll go with keeping the van gassed up, and running some few things
off it for a little bit of time, just long enough to send and receive a few
emails daily. And the portable screen room, to escape the heat at night.

flick 100785

 

[flick]

Fan: 150W for 12 Hrs = 1.8 kWh/day

Laptop and Sat Modem: 100W for 90 min = 0.15 kWh/day

Consumption (includes inverter losses): 2.294 kWh/day
Safety Factor: 20%
kWh req/day: 2.993 kWh/day

Sun Hours 5.18

PV Panels required 578 Watts

That's still around $2,500 just for the panels.

Obviously, I need to do something different than PV for a power outage!
Thanks so much for illustrating this for me.

If you decide to get a NG generator, be sure to size it properly.
Generators work most efficiently when operating at close to full output.
Some of the units designed for home backup have sound reducing enclosures.
The biggest problem I see is that people do not regularly (weekly or
monthly) exercise their generators. Then, when there is an emergency,
they
don't work.

Also, consider whether your NG lines continued to function during the
hurricane, so that won't be an issue for you.

The NG lines were okay.

Thanks again . You folks in here are great.

flick 100785

 

[Steve Spence]

That will be a toughie. There's nothing on the sat modem to tell me what it
uses, and it isn't in the technical specs online. I've emailed the company.
Otherwise, a "typical" desktop computer with a CRT monitor. I have a fan of
the type I'd like to use, and it says 150w.

A $30 Kill-A-Watt meter will tell you the consumption of each of your loads.

After a hurricane, which is the most likely weather event to take out power
for an extended time here, the weather is typically clear and sunny for at
least a week and usually longer. In my case, i think it would be reasonable
to assume that we'd have 8 hours of sun a day. If we didn't, well, I
wouldn't be able to run as much or as often, and that would be okay. I'd
still have *some* power.

Even Sunny CA doesn't get 8 "Full Sun" hours, more like 6.

 

[bumtracks]

a stationary exercise bike
rig up a car altenator
30 minute quick charger.

 

[Steve Spence]

a stationary exercise bike
rig up a car altenator
30 minute quick charger.

you are only good for 50 to 100 watts for less than an hour or so, so
this is a non-starter. fun for experimenting.