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Solar Electric
Fundamentals Basic
Principles
Sunshine at high noon at the equator on a cloudless day delivers about
one kilowatt per square meter of radiant energy that can be converted
into electricity. Solar panels at present can convert about 10% of this
sunlight to electricity. Thus a one meter square solar panel will
produce about 100 watts of electricity. At present, such a solar panel
will cost about $600 from WSE.
During the day the sun moves across the sky and the sunlight must
travel through different amounts of the atmosphere and in doing so
loses some of its energy. If the panel does not face directly at the
sun it will also produce less energy. If the panel is not on the
equator both of these effects are exaggerated. The amount of sunlight
also varies with the season and amount of clouds.
On a typical summer day a one meter square solar panel might be exposed
to sunlight for 8 hours at 60% of its maximum capability and will thus
capture about 500 watt hours of energy (100 watts x 60% x 8 hours = 480
watt-hours).
Of course, a solar panel only produces energy while the sun is shining.
If electricity is desired at other times some sort of storage is
needed. Most solar electric systems use batteries to store the energy
from the solar panels. The size of batteries needed for a particular
system depends primarily on the number of days the system must operate
without sun
The daily energy capacity of the solar panel must be at least equal to
the daily energy usage requirement plus the amount needed to fully
recharge the battery after it is discharged during several sunless
days. A typical number of sunless days to design for is three and a
typical recovery period is five days.
Solar Electric Design Rules of
Thumb
Energy Requirements
The total daily energy usage requirement is the sum of the daily energy
used by all appliances (fans, lights, electronics, etc). Each
individual appliance energy is found by multiplying the appliance power
rating by the number of hours it is used.
| Ea = Pa x Ha | where
Ea
= Daily Energy used by an Appliance (watt-hours)
Pa = Power
Rating of Appliance (watts)
Ha = Daily Hours of use of
Appliance |
Add the Daily Energy used by all Appliances to get Et (Total Daily
Energy Used)
Battery Size
All of the solar energy will be generated during the day but most of
the energy will be used at other times. The battery is usually sized to
store several days of energy so that energy is available during days
when the sun does not shine.
| Eb = Ds x Et | where
Eb
= Battery Energy needed (watt-hours)
Ds = Days without Sun
Et
= Total Daily Energy Used (Watt-hours) | | |
| AHb = Eb / Vb | where
AHb
= Amp Hour Rating of Battery (amp-hour)
Eb = Energy Rating of
Battery (watt-Hour)
Vb = Battery voltage (volts) |
Solar
Electric Panel Size
The solar panel must be able to supply the daily energy required plus
recharge the batteries after several sunless days.
| Ep = Et + Er | where
Ep
= Total Daily Energy from Panel (watt-hours)
Et = Total Daily
Energy Used (watt-hours)
Er = Energy Required to Recharge
after Sunless Days
(typically 5 days so Er = Eb / 5) | | |
| Pp = Ep / (Hs x
Eff) | where
Pp = Panel Rated Power (watts)
Hs
= Hours of sunshine per day
Eff = Panel Effectiveness
(typically 0.6) |
Usage
Requirements Example
We have a particular usage requirement, what size of solar panel and
battery storage do we need?
| Energy Usage | power
(watts) | usage
(hours/day) | energy
(watt-hours) |
Lighting4 - 60 watt lights
2 - 10
watt compact fluorescents |
240
20 |
4
6 |
960
120 |
Entertainment
TV
Radio |
60
10 |
4
8 |
240
80 |
Stove
oven
burner |
1500
500 |
1
1 |
1500
500 |
| Refrigerator | 250 | 2 | 500 |
| Water Pump | 250 | 1 | 250 |
| Furnace (fan) | 250 | 4 | 1000 |
| Total Energy Use per day
(watts-hours) | 5150 |
| Number of days without
sun | 3 |
| Battery capacity
required (watt-hours) | 15450 |
| | | System
voltage (volts) | 12 |
| Amp-hour capacity
(15450 / 12) | 1288 |
| Each battery amp-hour
capacity (typical) | 225 |
| Number of batteries
(1288 / 225) | 6 |
| Battery cost (6 x $250) | $1200 |
| | | Solar
Panel Size (to fully charge the batteries in 5 days) | |
| Daily Energy
Requirement (watt-hours) | 5150 |
| Recovery Requirement
(watt-hours) (15450/5) | 3090 |
| | | Total
Energy per day (watt-hours) | 8240 |
| | | Hours
of sunlight | 8 |
| Panel effectiveness | 60% |
| | | Panel
Size (8240 / (8 x 0.6)) | 1700 |
| Panel size (10%
conversion efficiency,
1000watts/sq.m) | 17
sq meter |
| Panel Cost ($6 per
watt) |
$10,200 |
Small Solar
Energy System Example
We have a small solar panel, what sort of appliances can we use?
| Panel
Size (watts) | 200 |
| Panel Size (2 meter x 1 meter)(6'x3') | |
| Panel Cost |
$1200 |
| Energy Per Day (8 hours @ 60%
effectiveness)(watt-hours) | 960 |
| Battery size (3 day capacity)(watt-hours) | 2880 |
| Number of batteries (12 volt, 225 amp-hour = 2700
watt-hour) | 1 |
| Battery Cost | $250 |
This will allow the following use per day:
| power
watts | usage
hours | energy
(watt-hours) |
Lighting
4 10 watt
compact fluorescents |
40 |
4 |
160 |
Entertainment
TV
Radio |
60
10 |
1
6 |
60
60 |
| Small Refrigerator | 100 | 2 | 200 |
| Water Pump | 250 | 1 | 250 |
| Total
Energy Usage (watt-hours) | 730 |
| Daily Energy available for recharging battery (960
- 730) (watt-hours) | 230 |
| Number of days to recharge battery after 3 days
without sun | 12 |
Ready to order or have some questions?
Simply pickup the phone and call 1 306 244 8808 or if you would like us to contact you, simply email us at info@wsetech.com
Barry ext 242
Trevor ext 232
Brayden ext 239
Grant ext 230
For Dealer inquiries
Linda ext 226
WSE Technologies
303 - 47Str. E
Saskatoon
Saskatchewan
Canada
S7K 5H2
Ph: 1 306 244 8808
Fax: 1 306 244-9970
We accept Visa and Master card.
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