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#201241 - 05/01/10 03:02 AM Re: Determining how much solar power is enough [Re: MartinFocazio]
Art_in_FL Offline
Pooh-Bah

Registered: 09/01/07
Posts: 2432
Cost for line power from the POCO (power company)is roughly $.06 to $.10 per kWh depending on where you are and what they are using for fuel at the time. Solar is running $.10 to $.15 per kWh. Mostly more to the high side. It would seem to be a losing proposition.

But there are other considerations. Like how much is it worth to you to be able to completely avoid summer brownouts and outages and being independent? Also, many POCOs buy back power so while you're using little power your meter spins backward. POCOs typically spend extra money on peak load generation. They are willing to pay a premium to cover peak load requirements. Currently utility buy-back is the standard rate but computerized meters and changes in the regulations may see POCOs paying peak rates for power they buy back from you during peak times.

The ability to remove your house from peak summer load motivates many sun belt POCOs to subsidize solar installations. Last time I asked the local company was contributing a dollar per watt of solar pane installed up to 20,000 watts.



It also has to be noted that future trends are that central POCO generation is going to get more expensive. The shift from coal, resort to expensive nuclear power systems, or the need to pay for coal and other high CO2 sources, is going to see the price per kWh rise.

Whereas solar systems are becoming ever more efficient, easier and quicker to install. Purchase price per watt of generation capacity is going down as efficiency is going up. Yes, a bank of solar panels is a major investment but longevity is expected to be 12 to 20 years. A losing proposition on its face the kicker is often tax breaks, or subsidies from the POCOs or government.

There are also sometimes unexpected returns. A local family covered the south side of their roof with panels and saw a 10% to 15% reduction in air conditioning cost due to shading from the panels. A benefit even the POCO engineers had overlooked.

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#201253 - 05/01/10 04:00 PM Re: Determining how much solar power is enough [Re: Art_in_FL]
Susan Offline
Geezer

Registered: 01/21/04
Posts: 5163
Loc: W. WA
The average cost of residential power in 1970 was $0.02 per kWh. Today, it's four times that. Just since 2000, rates have escalated 6 to 8% per year. Extrapolating rate increases at 8% per year (if they don't go higher than 8%), we're looking at $0.17/kWh in 10 years, $0.37/kWh in 20 years.

My use of 1528kWh last month would cost, respectively, about $260 in 2020, and $565 in 2030 (flat rate, no reduction for off-peak hours).

There are always more things to consider than today's knee-jerk-reaction prices.

Sue

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#201276 - 05/02/10 04:53 AM Re: Determining how much solar power is enough [Re: Susan]
frediver Offline
Enthusiast

Registered: 05/17/04
Posts: 213
Loc: N.Cal.
I would be happy with a small solar battery installation.
Something that would put out 500-1000 watts@12v an inverter
that would handle any 120v load I can connect to it ( 2 sockets )
and a battery that will support my home for 4-6hours for brown outs. I figure I would only need to run my freezer for 1-1.5hr/day
to keep my food. The fridge would likely take twice that because it will be used more often. other than those items I can shut down our home as needed to cut consumption. Lights are CF, comp.
runs thru a battery, cell phone charger, no heat needed we have a fireplace.
I checked out mysolarbackup and the power it provided for the cost
was prohibitive, IIRC the internal battery only has the capacity to run my freezer for 15-20 min until it is totally dead.

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#201292 - 05/02/10 10:46 PM Re: Determining how much solar power is enough [Re: Art_in_FL]
philip Offline
Addict

Registered: 09/19/05
Posts: 639
Loc: San Francisco Bay Area
Originally Posted By: Art_in_FL
... such rough estimates won't replace a detailed engineering study, but it is remarkable how many times such a quick and dirty estimate is within a few percentage points of some very expensive professional analysis.


Yeah, well, I can't afford a detailed engineering study, so it's nice to get a more nearly accurate ballpark estimate instead of relying on the numbers published by the manufacturer.

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#201296 - 05/02/10 11:50 PM Re: Determining how much solar power is enough [Re: philip]
JohnE Offline
Addict

Registered: 06/10/08
Posts: 601
Loc: Southern Cal
So far as powering the freezer, you can either get enough solar panels to produce enough power coupled with enough battery capacity to keep it running continuously or you could increase the battery capacity so that a smaller solar panel will keep them charged enough for short term, part time usage.

You don't need a whole house system to run only a couple of circuits.

Any pre-built or pre-assembled kit is gonna cost more than doing it yourself.

It's fairly simple to figure out the needs for a single use emergency system, it's watts, amps and ohm's law.

One quick and easy thing anyone can do for use in an emergency, pick up a pack of solar powered lawn decoration lights with LED bulbs. For $50-$100 you've got a temporary, battery powered lighting system for use when the grid goes down. Keep the batteries charged up or replace the ones that come with such a kit with some low loss Eneloop type batteries and Bob's your uncle.

The problem with a lot of comparisons of replacing grid fed power is that the infrastructure that is required for the grid fed systems are rarely taken into account. I've read of numerous examples where people thought that it would too expensive to use solar power, the only fair comparison would be to include the hidden costs of those power poles and lines outside your home, along with the guys in the bucket trucks who come along periodically and keep the system working.

There's a similar disconnect when talking about using alternatively fueled vehicles, when one adds up the real costs of the transportation system right down to the roads which are subsidized, then you realize that the alternatives don't actually cost that much more at all. I realize that the alternative fuel vehicles would be using the same roads but there's a huge amount of unseen and usually uncounted costs that have been paid for to allow us relatively cheap fuel and power.
_________________________
JohnE

"and all the lousy little poets
comin round
tryin' to sound like Charlie Manson"

The Future/Leonard Cohen


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#201299 - 05/03/10 01:33 AM Re: Determining how much solar power is enough [Re: JohnE]
Art_in_FL Offline
Pooh-Bah

Registered: 09/01/07
Posts: 2432
Quote:
Any pre-built or pre-assembled kit is gonna cost more than doing it yourself.


The bad point of a kit system is that they invariably, good capitalists all, get their profit margin off the top. This is far less an issue in mass produced systems where wholesale purchase of parts more than makes up for the profit margin. But solar is still a small sector of the energy market and while it is growing even large marketers are selling systems by the hundred, as opposed to the thousands.

On the other side kit systems assembled by major retailers have a lot of experience and engineering behind them. Buying one you often pay a bit more but you also sidestep a lot of mistakes and teething problems. They are sort of the equivalent of training wheels. A small starter system that has parts selected to assemble easily and work well together, that is pre-engineered for you, backed by customer support goes a long way toward making getting started in solar easy. It makes parting with the cash a little easier.

A small starter system is often a good way to get your feet wet. Once you get to know the technology such small systems can be added on to. Or they can be re-purposed for use on the barn or cabin if and when you install a larger system on the house. Or they can be reworked to make a portable emergency power system to keep some combination of communications, lights, a small refrigerator for medical supplies running.

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#201319 - 05/03/10 03:43 PM Re: Determining how much solar power is enough [Re: frediver]
LCranston Offline
2
Member

Registered: 08/31/09
Posts: 172
Loc: Nebraska
Example- Harbor Freight has a 45 watt kit for 199.00 US
(3*15 Watt panels - 12 volt @ about 1.5 Amps each)

includes panels, controller, 2 DC lights NOT BATTERIES

at 6 hours full light, that is 270 Watts possible, more likely 220 watts per day

I found 75 AMP hours 12 Volts for 40.00 each (military surplus, used 2 years of 10 years rated, AGM, Woo hoo!) Bought 4, so 120.00.

So, we have 300 AMP/Hours, or 3600 Watt Hours storage. (300 Amps * 12 Volt= 3600 Watts)

I have an inverter already (no extra cost) But to buy a new one capable would be ~100.00 (1000 watt continuous, 300 watt surge)

If I use 50%, or 1800 Watts, I can run my 18Ft/ Fridge (500 Watts) for 3+ hours. It would take me 8-10 days to recharge the batteries to full. Cost 320.00 ( or 420.00 with Inverter)



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#201322 - 05/03/10 04:46 PM Re: Determining how much solar power is enough [Re: LCranston]
Am_Fear_Liath_Mor Offline
Carpal Tunnel

Registered: 08/03/07
Posts: 3077
Quote:
If I use 50%, or 1800 Watts, I can run my 18Ft/ Fridge (500 Watts) for 3+ hours. It would take me 8-10 days to recharge the batteries to full. Cost 320.00 ( or 420.00 with Inverter)


500W for a Fridge!! Your energy bills must be enormous especially if you need aircon to remove the heat generated by your fridge.

Thats 4380 kWhrs/year!! That would cost me around $800-900 a year to run in the UK.

The Vestfrost SE225 A++ Chest Freezer @ 8 cubic feet is available for 172 kWhrs/year whilst another Vestfrost SE225 operating as a chest fridge would work out around 36 kWhrs/year. The Vestfrost SE225 also has a 50 hour specification for the internal temperature rise from -18C to ambient temperature.

http://www.builditsolar.com/Projects/Conservation/chest_fridge.pdf

Total Yearly energy usage would be less than 250kWhrs/year or around 16-17 times less than your current refrigeration.



Edited by Am_Fear_Liath_Mor (05/03/10 04:50 PM)

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#201323 - 05/03/10 04:48 PM Re: Determining how much solar power is enough [Re: LCranston]
JohnE Offline
Addict

Registered: 06/10/08
Posts: 601
Loc: Southern Cal
A refrigerator/freezer doesn't draw power like that continuously, it's intermittent. I think your math is off a bit. If I estimated correctly, you could get about 36 hours of usage out of those batteries before they'd be at 50% capacity.

It gets more complicated when you have the panels running at the same time you have the batteries being used. You'd be adding less than you take out obviously but you'd still be adding some.

I could be wrong about the figures but I think you're low on how long those batteries would power the fridge.

You also have to figure in how much power you're losing with the inverter. Depending on how efficient it is, you could be giving up as much as 50% converting the 12v source to 120v.

Top of my head guess, I think you could get approx. 18-24 hours of use from those batteries at those power levels.

Somebody please double check the math...!!!
_________________________
JohnE

"and all the lousy little poets
comin round
tryin' to sound like Charlie Manson"

The Future/Leonard Cohen


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#201324 - 05/03/10 05:14 PM Re: Determining how much solar power is enough [Re: JohnE]
Am_Fear_Liath_Mor Offline
Carpal Tunnel

Registered: 08/03/07
Posts: 3077
Most American Style refrigerators typically have an annual load of around 500-600 kWhrs/year for the A and A+ rated European market. So I would estimate around 2kWhrs/day worst case. So 18-24 hrs would be about right. But then again the refrigerator might be an older inefficient model where it could easily be 3-4kWhrs/day so 9-12hrs might be a typical run time using the batteries especially if the inverter is a low efficiency model i.e 50% even when used with a modern refrigerator design.

Is the 3 hrs quoted an empirical or experimental test?



Edited by Am_Fear_Liath_Mor (05/03/10 05:27 PM)

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