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Old 05-21-2015, 11:41 PM
Ironbeard Ironbeard is offline
Join Date: May 2015
Posts: 11
Default HELP! Brain FREEEEZE!!

Ok, I've downloaded tons of solar calculators, looked up and down charts until my eyes are having trouble focusing and I still can't figure out exactly what I need to design our new home's photovoltaic system. I must be doing something wrong?

Here's what I have to work with so far:

2880 sqft house
Built 1986, insulation on par with homes of that period.
Location: California, north eastern Central Valley, Sierra Nevada foothills.
All electric: HVAC, Water Heating, A/C, Cooking...yep everything is electric
Average Insolation (full sun hours per day): 5-6 hours
Average 220 Clear sunny days / year.

Past energy use:
Now the raw data below is based on the previous occupants energy history. It is an all electric home, well insulated, but all heating and cooking is electric. There is even an Electric Fireplace, which definitely is not an efficient use of electricity. We are planning on eventually converting much of the heating and cooking elements to propane and a wood burning fireplace. One of the first steps we're going to take is to convert all incandescent light bulbs throughout the house to LED. Ultimately we will add Solar Water heating, Grey Water Irrigation and so on, but Solar Energy Panels will be our first step.

So I wanted to figure out just how large of a system we'd need for an off grid stand alone system. using the highest historical use.

Summer: 2100-2500 kWh avg/mo
Winter: 1400-1800 kWh avg/mo

Avg Electric Bill/mo over 12 months: $395
Avg Electrial use/mo over 12 months: 2080 kWh

kWh used in summer/mo: 2300 kWh/mo = 76.67 kWh/day
Insolation Factor: 6

76.67 kWh / 6 = 12.78
Derate Factor: .77

12.78 / .77= 16.6

kW to Watts
16.6 x 1000 = 16,000 Watts

300 Watt solar panels: 16,600 / 300 = 55.33 panels needed

56 panels at $270 each = $15,120 cost for just panels? OMG!

Am I doing this correctly?

Last edited by Ironbeard; 05-22-2015 at 12:15 AM.
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Old 05-26-2015, 09:51 PM
Bones Bones is offline
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Join Date: Jul 2001
Posts: 2,634

Wish I could help. I do know that to try to buy enough Solar Panels to match my current power usage was not going to be possible. 12V man has the right idea Move to the land, make it more cost effective to put in panels than run power lines. Then live within the realm of your panels and add more when you can afford it. I had replaced all my bulbs with CFL/LED but many other energy hogs in our home.
" I void warranties"
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Old 05-27-2015, 08:33 AM
doc doc is offline
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Join Date: Apr 2013
Location: The Driftless Area, WI
Posts: 1,531

The average American household uses 30kW-hr of electricity each day, and only about 3 kW-hr of that is for lighting, so switching to LED hardly saves anything.

When figuring costs, don't forget to include "lost investment potential" in the calculations. That $30Gs (+ interest) shelled out up front for PV could be earning 5.5%/yr on average if invested just in the Dow over the 25 yr lifespan of the installation (a loss of ~$120,000). And after 25 years, you gotta shell it out again.

Go with alternative energy sources only if cost of connecting to the grid is more than ~half the cost of installing "free" alternates, or for energy security purposes.
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Old 05-27-2015, 10:38 AM
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12vman Male 12vman is offline
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Location: Tuscarawas County, Ohio
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Design for December and it will work year round..

In Redding, there is only an average of 1.64 hr's of usable sun in a day in December. Assuming an "Average" of 5-6 will mess ya up big time..
"Without Deviation from the Norm, Progress is not Possible".
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"Two roads diverged in a wood, and Ió I took the one less traveled by, And that has made all the difference"
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Old 05-27-2015, 11:09 AM
hunter88 hunter88 is offline
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Location: Nebraska
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The average American household uses 30kW-hr of electricity each day, and only about 3 kW-hr of that is for lighting, so switching to LED hardly saves anything.
You beat me to it. I figured if there were 50 lights in the house and they were switched to LED the savings might come to $36 a month, and in this case the OP says the average bill was $395, so LED's save slightly less then 10%.
Gun control: It's like fighting drunk driving by restricting the sober drivers.
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Old 05-27-2015, 11:10 AM
wywhitewolf Male wywhitewolf is offline
Join Date: Mar 2015
Location: Wyoming
Posts: 69

12v pointed out your biggest mistake. With off grid you need to calculate the worst case. In your case you will need to use winter usage and insolation for your array size and summer usage for your battery bank size.

Quick run of the winter numbers.

1800KWH/30days = 60KWH Per Day
60KWH/1.64/.77 = 47.5KW array size or about 3 times what you estimated.

Battery Bank

2500KWH/30days=83.3KWH per day

You should never use more than 20% of the battery bank in a day. That would also give you 2.5 days atonomy.

83.3*5/48v= 8677AH battery bank at 48V or 416.5KWH battery bank.

At $330 per KWH for quality batteries you're looking at $137,445 that'll need replaced in 8 to 12 years.

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Old 05-27-2015, 04:04 PM
doc doc is offline
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Originally Posted by wywhitewolf View Post

At $330 per KWH for quality batteries you're looking at $137,445 that'll need replaced in 8 to 12 years.

Cripes. That translates to a lost investment potential in 7 figures over 25 yrs.

The problem here is that this home is large and relies on electricity to heat & cool it. Most homesteaders go with smaller homes and avoid energy use where possible. Whoever built this place apparently wasn't into "roughing it." Looks like Ironbeard has his work cut out to try to correct things.
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Old 06-21-2015, 10:41 PM
RochBear Male RochBear is offline
Join Date: Apr 2015
Posts: 56
Default conservation is the first thing to do


the first thing to do is "conserve", in looking at the amount of power you are using, there must be things you can do to cut back. You stated, you had an all electric house. Anything with a heating element is going to kill you, if you are trying to do it in an off grid system.

Areas, you could invest in, would be solar hot water. That should greatly reduce your over all power consumption. The electric stove would be the second thing. (switching to an LP stove, is the most common way to not loose function, but would greatly reduce your electrical use).

Using a clothes line vs an electric dryer is another great way to reduce your electrical usage.

Once you've gotten rid of the all the 220 V heating appliances, THEN, you could consider going to an off grid type of system.

What I've done is set up an off grid system, I have it running ONE circuit in our house. Yep, you might have guessed it, It's running this computer! That way, you have some solar power, and the ability to run the freezer, a radio, a light or two, and other absolute essentials, if the power grid were to go down. While not spending 6 figures.

My system will produce about 3 KWH/day on a good day. But it does run the deep freeze most of the time, and we don't have anywhere near the 220 clear days that you do (I live in Minnesota. And yes, I do have to go and sweep the snow off the panels in the winter time)

I hope this helps you.

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Old 10-25-2015, 10:50 PM
JeepHammer Male JeepHammer is offline
Join Date: Oct 2015
Posts: 39

That is the best possible money you can spend,

Insulation in the attic will pay you back many times over and it's cheap if you do it yourself.

Get that old 1986 cracked/missing calking around the windows/doors off and put in new, soft calking.
You can do the entire house for $35 and a wet finger...

If you can afford it, look into a higher thermally efficient window set,
Doors too.

Don't forget things like ceiling fixtures, wall outlets, light switches.
The average thermal leak around inside fixtures adds up to two bricks missing from a wall!
There are little foam gaskets made to seal up those face plates/work boxes.
REAL cheap and easy.

Don't forget lighting, It's well worth the money to use CF or LED lights where you can. Living in CA, I'm sure it's actually hard to find an incandescent light bulb anymore...

If you have 'Security' lights, consider converting them to LED, you will see a substantial drop in the bill just for that alone.

If it's 1986 A/C or 'Heat Pump' then it's time for something more efficient,
Say at least 16 SEER rated or higher.
Again, with your electric rates, it WILL pay for itself, and there are some serious rebates/credits available for upgrading.

There are also tax credits available in CA for windows, doors, insulation, ect.



ANYTHING you put in the sun will reduce your bill.
Remember, you have the best tax credits in the country out there!
About 80% of what you install you will get back!

In specific, Grid Inter-Tie (no batteries) with Micro Inverters.
EXPANDABLE! Just plug the new panels/inverters in and go when you expand.

In the daytime, when the sun is shinning, the panels/micro-inverters pump power into the home,
Any excess you produce hits the grid, turning your meter BACKWARDS, giving you credit for when the sun IS NOT shinning...

Dark days or night, you draw off the grid like normal, the meter moves forward.

You have to remember, you are in one of the FEW states that is REQUIRED to buy any excess power you might produce at the end of the year,
They have to pay you a PREMINUM for that power since it's 'Clean' & 'Renewable'.
This would be an incentive for me to put in as many panels as I could swing!

I would get a bank Personal note if I had to, and get this rolling!
Get paid back for just installing the system
(Tax Credits! I don't know what tax bracket you are in, but my bracket is WAY TOO MUCH!)
And get a premium for any excess I could produce!

Wouldn't it be nice to get a check FROM the electric company for a change?
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Old 10-26-2015, 07:09 AM
doc doc is offline
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Location: The Driftless Area, WI
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I have mixed emotions about taking advantage of tax subsidies. It's like cheating at cards. If you're the only one cheating, you're taking advantage of the others at the table and you win. If everyone is cheating, nobody has an advantage.

That said (oops--let me pick up that ace that just fell out my sleeve) I did take the tax credit when we installed a new furnace/AC a few yrs ago.

Remember-- Robin Hood didn't rob from the rich and give to the poor. He robbed from the govt and gave tax money back to the taxpayers.
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