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Old 05-13-12, 05:08 PM   #1
strider3700
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Default what size system do I really need?

I'm anal about tracking my power usage but not amazingly frugal about it although my wife would disagree.

Anyway's yesterday was my lowest single day's usage ever. 14 kwh in a 24 hour period. This was the first real spring day this year, with no Heating at all, no clothes in the dryer(clothesline was in use) and quick reasonable showers. I didn't have specific tracking of the hot water power usage but looking at my past records the lowest it could have been was 4 kwh which happens on days where we're not home. More likely it accounted for 6 of that 14 kwh. I know the computer never went into sleep mode and accounts for 2.4 of the remaining 8. fridge, freezer, a bit of lighting and vampire must account for the rest.


When I move to my new house, I'm seriously thinking of putting in a solar setup to cover a good chunk of the houses usage. Electricity there is expensive compared to here at roughly 18 cents/kwh Also on the plans are solar hotwater, and a wood boiler for heat of both space and domestic hotwater.

So if I can get and keep the houses usage near 10 kwh/day how big of a system do I really need to be 100% solar in a grid tied system, making excess during the summer and drawing in the winter? I'm sure there must be info on how to calculate this but I haven't seen much from the sites trying to sell me the equipment.

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Old 05-14-12, 07:57 AM   #2
Ryland
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You first need to figure out how many sun hours per day you get at your location, then you figure out what your shading is going to be, calculate the type of mounting you are going to have (fixed, adjustable for seasons, or tracker) then you take the amount of sun that you have left per day and use that to figure out how many panels you need based off your electrical use, it used to be that you would also figure in losses for inverters and so on, but with the new micro inverters and with maximum power point tracking you figure your output is going to be right around your rated output of the panels.
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Old 05-14-12, 01:31 PM   #3
strider3700
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Let's go ground mount, non tracking seasonal adjust rack, no shading, 46 degree's N latitude, 1905 hours of bright sun yearly which is about 5.2 hours/day.

How do I work out the loss from the rack?

<edit>

I just found this site
http://rredc.nrel.gov/solar/calculat...ATTS/version1/

I'm assuming when you say micro inverters mean we can ignore the efficiency loss that means I can set the DC to AC derate factor to 1.00 or .99?

<edit>

Last edited by strider3700; 05-14-12 at 01:38 PM..
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Old 05-15-12, 09:44 AM   #4
Ryland
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Sun Isolation Hours in Canadian Cities - Solar Store

That site seems to say that you have 4.9 sun hours per day, with that figure and because you said you don't have any shading at all, I would give an educated guess at 2,100 watts of panels to give you 10kwh per day.

Yes, with Micro Inverters that have MPPT (maximum power point tracking) you don't have to derate them because the MPPT squeezes a little extra power out of each panel, making it operate at it's peek and that makes up for the losses in the inverter, you also have shorter runs of low voltage wire, so again you cut your losses.

I don't remember how to figure the different mounting options and trackers, it was around 5 years ago that I took the class on solar site assessments and it's starting to get fuzzy, so your best option is to have someone come out to the site that you are planing to install solar and have them look at it first hand and to look at your needs, but with 4.9 sun hours per day (rather good) and $.18 per kwh you would be dumb not to install solar, worst case you have a 15 year return on your investment and all of the equipment tends to have a 25 year warranty and should last 50 years, but worst case everything stops working the day the warranty runs out and your electric rates never go up you've still saved over $6,000, but electric rates go up and I haven't seen any solar panels that don't outlast the warranty by double.
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Old 06-25-12, 11:57 PM   #5
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There is android app SolarMeter from VisTech.Projects on Google Play, that simulates solar cell behavior based on your GPS location while moving your android device arounda and also makes calculation for the annual energy distribution at your location, based on panel orientation and tilt. So you basically can put the device on a roof, touch couple buttons and it will automatically detect your roof orientation and tilt, then you can play with area parameter and panel efficiency to estimate size of the system to cover your consumption:


It's not free though.
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Old 09-08-12, 03:24 PM   #6
creeky
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For your 10kw something less than 3 kws would do. In fact I suspect Ryland was pretty close with 2.1kw.
My not terribly relevant baseline is derived from generating 4 kw avg. daily with an offgrid 1kw system. At 12v the system overcurrents at around 850 watts but in lower light conditions the larger array creates more power (cloud, haze, morning, full moon.
Being offgrid my system throws away power after the batteries are full. I tested a 13.5 amp a/c for kicks and generated 5-6kw daily.
With an ongrid application you should do much better.
I have a friend building an ongrid 3kw system. What inverters have you been impressed by?
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Old 09-23-12, 06:21 PM   #7
classradiance
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Default Solar Pad - estimate your setup - lights on time

HOW TO CALCULATE YOUR MONEY SAVING SYSTEM for Home / Boat / Caravan / Shed
1.Add up the hours that each light will be on for to get the Total of Energy Consumed.
2.From that you can Calculate everything you need IE: Solar Panel / Battery / Regulator
------------------------------------------

My Calculations
3 Zones
1 X LED SPOT @ 10W + 2 x LED FLOOD @ 15W
on for (SEE CHART) hours per night
...................

-Watt/Hour Chart- - Only ever use 12 volt LED lights -

3 Room scenario

kitchen/Diner 15W on when required daily average use -- 3 hours = 45wh
Bedroom 10W on when required daily average use - 2 hours = 20wh
front Room 15W on when required daily average use - 8 hours = 120wh

Total usage per night in Winter = 185wh/d
-----------------------------------------------------------------------------------------

-Load and Battery -

House Lights Consumption = 185Wh
185 watt-hours divided by 12 volts = 15.42 amphours taken from system in 1 night

Because we can only use half the energy in a lead acid battery without harming the battery,
the minimum battery size is 15.42 amps x 2 = 30.84 amp hours.

I want my system to be reliable if we have four consecutive days of cloudy weather,
4 days of autonomy x 30.84 = 123.36 amp hours for the battery. = 124 + amp hour battery
(Required Battery Bank = 1 x 130 Ah True Deep Cycle


-------------------------------------------------------------------------------------------

-Charging Battery from Panel-
This installation is in a location that gets 5 hours of full sun per day.
Check the charts for this depending on the month in the Season.
To recharge the battery for one day of use we need 30.84 amps in 5 hours = 30.84 / 5 = 6.17 amps from a 12 volt solar panel array.
------------------------------------------------------------------------------------------------------------------------

-Solar Panel -
Most load calculations include a discount factor for the inefficiency of recharging the battery.
20% is typical. 6.17 / 0.8 = 7.71 amps.

A single 140W solar array that has an Impp (amps maximum power point) of 7.7A would be suitable

------------------------------------------------------------------------------------------

-Charge Controller Rating in AMPS-
The 140W solar array has a short circuit amp rating (Isc) of 8.2A 8.2A x 1.25 = 10.25A
use a 10.3A or larger charge controller with this array to charge the battery.

Cheap example - 20A Unit
For best efficiency to charge use an MPPT Type.
------------------------------------------------------------------------------------------

- estimated Cost of mentioned Materials - 20 years / $450. = $500./240 months = 2.08 month = .52 per week ....wow

Have seen 140w poly panel on Net for $170 inc delivery
Have seen 130Ah Varta Leisure Battery 12V 130Ah for around $150 inc delivery
20A Charge controller $20 - $60 - mppt prefered of course
3 QUALITY External (For in or out & VERY BRIGHT) LED Lights 2 x 15w/1 x 10w = $60
100m of .75mm twin and earth from wholesalers = $30
Mounting Bracket for Panel = $20

Estimated Total = $500ish

Also required - Fuse box / switches / bits ..


-----------------------------------------------------------------------------------------
-Solar Panel specification-
STK-140P6-A ...... manufactured by 3E
Related power
140W
Open circuit voltage Voc(V)
23V
Short-circuit current Isc(A)
8.2A
Optimum operation voltage Vmp(V)
18.3V
Optimum operation current Imp(A)
7.7A
.......................

Thanks to everyone who places information out there so I could put all this up
Hope the above can inspire you, cause the Bills r going up !!
Not mentioned above are Switches, Inverters, Distribution, Heating, Health & Safety,
etc ... Caution -12V Batteries can Cause Fire if not Fused or Stored Correctly-

- Battery info -

Deep cycle batteries are designed to be discharged down as much as 80% time after time,
and have much thicker plates. The major difference between a true deep cycle battery
and others is that the plates are SOLID Lead plates - not sponge. This gives less surface
area, thus less "instant" power like starting batteries need. Although these can be cycled
down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about
50% discharge.

Battery life is directly related to how deep the battery is cycled each time.
If a battery is discharged to 50% every day, it will last about twice as long
as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times
as long as one cycled to 50%. Obviously, there are some practical limitations on this
- you don't usually want to have a 5 ton pile of batteries sitting there just to reduce
the DOD. The most practical number to use is 50% DOD on a regular basis. This does NOT mean
you cannot go to 80% once in a while. It's just that when designing a system when you have
some idea of the loads, you should figure on an average DOD of around 50% for the best storage
vs cost factor. Also, there is an upper limit - a battery that is continually cycled 5% or less
will usually not last as long as one cycled down 10%. This happens because at very shallow cycles,
the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film.

If this has helped you in any way, let me know . . good luck
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Old 09-23-12, 08:58 PM   #8
Ryland
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My parents sized their battery bank to only be discharged to 20% DOD and are planing for it to last 20+ years, 14 years in and everything seems good so far, every once in a while they drop down to 30% or even 40%, so at 40% they used twice what they planed... if you plan to discharge to 50% you don't have that wiggle room for a bad week of no sun or wind and no back ups, like after an ice storm where you can't get the generator fired up, power lines to their grid tied system are down, blades on the wind turbine are iced up and it's not sunny to melt the ice of anything, at that point it's nice to have the fan on the furnace work to keep the house warm.
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Old 09-24-12, 03:46 AM   #9
classradiance
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This is my effort, and I hope it can help you in some way.

HOW TO CALCULATE YOUR MONEY SAVING SYSTEM
1.Add up the hours that each light will be on for to get the Total of Energy Consumed.
2.From that you can Calculate everything you need IE: Solar Panel / Battery / Regulator
------------------------------------------
My Calculations
14 Zones
15 X LED SPOT @ 10W + 1 x LED FLOOD @ 15W
on for (SEE CHART) hours per night
...................
-Watt/Hour Chart- - Only ever use 12 volt LED lights -
Down Stairs
kitchen 15W on when required daily average use -- 3 hours = 45wh
bed1 10W on when required daily average use -- 7 hours = 70wh
bed2 10W on when required daily average use - 7 hours = 70wh
hall 20W on when required daily average use - 2 hours = 40wh
toilet 10W on when required daily average use - 4 hours = 40wh
bed3 10W on when required daily average use - 1 hours = 10wh
utility 10W on when required daily average use - 2 hours = 20wh
front Room 20W on when required daily average use - 8 hours = 160wh
outside front 10W on when required daily average use - 1 hour = 10wh
outside back 10W on when required daily average use - 1 hour = 10wh

Up Stairs
stairs top 10W hardly used daily average use - 2 hours = 20wh
toilet 10W on when required daily average use - void as 2 exist
bed4 10W on when required daily average use - 8 hours = 80wh
bed5 10W on when required daily average use - 4 hours = 40wh

Total usage per night in Winter = 615wh/d
-----------------------------------------------------------------------------------------
-Load and Battery -
House Lights Consumption = 615Wh
615 watt-hours divided by 12 volts = 51.25 amp hours. Because we can only use half the energy in a lead acid battery without harming the battery, the minimum battery size is 51.25 amps x 2 = 102.5 amp hours.
(only do this if using a Lead acid Battery)
I want my system to be reliable if we have four consecutive days of cloudy weather,
4 days of autonomy x 102.5 = 410 amp hours for the battery. = 410 + amp hour battery
(Required Battery Bank = 2 x 220Ah or 4 x 110Ah or 8 x 55Ah
Autonomy allows for No charge over 4 days flat
------------
-Charging Battery from Panel-
This installation is in a location that gets 5 hours of full sun (insolation) per day.
Check the charts for this depending on the month in the Season.
To recharge the battery for one day of use we need 102.5 amps in 5 hours = 102.5 / 5 = 20.5 amps from a 12 volt solar panel array.
-----------------------------------------------------------------------------------------------
-Solar Panel Array-
Most load calculations include a discount factor for the inefficiency of recharging the battery. 20 percent is typical. 20.5 / 0.8 = 25.7 amps.
A (5 panel) 500W solar array that has an Impp (amps maximum power point) of 25.7A would be suitable
The Panels SUM ( Impp ) must be more than the 25.7A ( 5 x 5.79A = 28.95A)
-----------------------------------------------------------------------------------------------------------
-Charge Controller Rating in AMPS-
The 500W solar array has a short circuit amp rating (Isc) of 5 X 6.46A = 32.3A. 32.3A x 1.25 = 40.375A
use a 41A amp or larger charge controller with this array to charge the battery.
Cheap example - 50A CM5024Z JUTA PWM Charge Controller
For best efficiency available for charging the batteries use a MPPT charge controller for lead acid.
-------------------------------------------------------------------------------------------------------------
-Cost of mentioned Materials - 20 years / 2k = 8 month
100w watt poly solar panel = 80 + 15 delivery x 5 = 475 UK delivery
50A CM5024Z JUTA PWM Charge Controller = 85
Yuasa 12v 220Ah Cargo Batt For trucks 234.47x 2= 468.94 + shipping
1 x 15W Flood = 20, 15 x 10W Spot = 180 -- Total = 200
Twin & Earth 1mm x 100m = 29.58 from Electrical wholesaler
Max Length for 15w@12V = 6m of .75/Max Length for 10w@12V = 9m of .75
Total Cost can be either + or - dependent on your Budget . 2k / 20years = 8 per month
---------------------------------------------------------------------------------------
-Solar Panel specification-
Related power
100W
Open circuit voltage Voc(V)
21.5V
Short-circuit current Isc(A)
6.460A
Optimum operation voltage Vmp(V)
17.3V
Optimum operation current Imp(A)
5.79A
.......................

Thanks to everyone who places information out there on the WEB
Hope the above can inspire you.
Not mentioned above are Switches, Inverters, Distribution, Heating, Health & Safety,
etc ... Caution -12V Batteries can Cause Fire if not Fused or Stored Correctly-
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Old 09-25-12, 08:04 AM   #10
classradiance
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Default 14 years on

Quote:
Originally Posted by Ryland View Post
My parents sized their battery bank to only be discharged to 20% DOD and are planing for it to last 20+ years, 14 years in and everything seems good so far, every once in a while they drop down to 30% or even 40%, so at 40% they used twice what they planed... if you plan to discharge to 50% you don't have that wiggle room for a bad week of no sun or wind and no back ups, like after an ice storm where you can't get the generator fired up, power lines to their grid tied system are down, blades on the wind turbine are iced up and it's not sunny to melt the ice of anything, at that point it's nice to have the fan on the furnace work to keep the house warm.
Hi Ryland

Can you tell me what the size was of the System, and what power was consumed each day as w/h/d as a Comparison.
LED Lighting is so interesting as a Low Power alternative to what we all grew up with, and I like to see what people think and say about it all.
I am being shocked by looking at the Solar Forums where it seems most people are only interested in Solar as a means of investment. If only they realized that renting the space above the roof is not what this is only about.
They repeatedly mention investment returns as being oversold scam ... etc.


Last edited by classradiance; 09-25-12 at 08:10 AM..
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