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Frequently
Asked Questions on Solar Energy made Simple
What
are Watts?
Watts indicates power output. Peak Watts is the output
at Standard Test Conditions. Amps on the other hand measures pass through
current or power in use.
Why are Volts rated differently?
Panels are designed to charge 12Volt batteries. The PV module voltage
is "open circuit" and is higher in order to lift the battery
voltage to a fully charged level, i.e. 13 to 14 volts. Solar power supplies
can be 12V, 24V or 48V depending on how the batteries are cabled (in
series to double up the Amp Hour capacity or in parallel to double up
on volts).
What's
the difference between DC and AC?
DC or direct current simply flows from the positive to negative (assuming
negative earth). DC doesn't flow over long distances without significant
voltage drops and fat cables. AC or alternating current swops the +ve
and -ve polarity 50+ times a second and can be transported over large
distances with no significant loss in efficiency.
What
Power can I Get from Solar?
Output is dependant on the amount of light energy impacting the solar
panel. Flat mounting panels are much less efficient than setting the
panel directly facing the sun - around 60 to 70o
from the horizontal. Also where several PV modules are set into an array
and wired in parallel, to increase the array voltage, shade on even
part of one panel will cause a drop across the array.
How
Reliable is a Solar Power System?
The reliability and life-span of a solar power system mostly depends
on two factors: its capacity to meet the demand required of it and how
well it, especially the batteries are maintained.
Should
I go for Wind + Sun?
Our experience indicates the following:
Single battery
low-power system - solar or wind will do fine.
Caravan, domestic
household and larger - use both where possible. You may get 4 hours
of sun a day in the UK, chances are the wind will supply power at other
times. We suggest using solar or wind as a top up for the other. Contact
the Met office for data averages.
How
Much Battery Capacity Will I Need?
The heart of the
system are the batteries. These store the energy supplied from solar
and/or wind. The Amp Hours rating must be sufficient for at least 3
days of average use without any solar and wind energy. Even so it is
possible for the batteries to become drained - requiring manual intervention.
~ When
the voltage drops below 11.7 Volts, switch to mains or mechanical
charging until the batteries are fully charged at 14.3Volts+.
~
Use the Lights and Power ONLY WHEN YOU NEED IT. SWITCH OFF!
To understand how
much battery capacity you need from a system, just make a list of equipment,
its power rating and how much time it is used on average per day and
total for a typical week:
For example:
Unit / Hours
of use: ................................................... Daily
Power Use:
9 x 80Watt strip
lights for 1 hour per day ................... = 720Whours
45Watt security
light for 10 hours .............................. = 450Whours
1 x 100 Watt
appliance for 1 hour per day .................. = 100Whours
Total average
for 1 day ................................................ = 1.27KwHrs
Total for 1
week .......................................................... =
8.89KwHrs
Allow 30% overuse
..................................................... = 11.56 KwHrs
Your battery capacity
needs to have three days of useable power before they are drained to
50% of their full limit.
i.e. 2 x 3 x
11.56 / 7 days = 9.9 KwHrs
Converted to Amp
Hours, (/Volts) = 825 AmpHrs. So you will need a battery bank of at
least 800 AmpHours.
Naturally the batteries
consume fluid over time, so if they are unsealed:
~ check
and top up with distilled water every 6 months. Also make sure the
ventilation ports are clear to disperse any possible gas.
How
much power do I need from an Inverter?
This is simply a question of the most power needed to be used at any
one time for as long as it is needed plus 25% safe margin. For example,
if you run 7 x 80 Watt strip lights plus a 400 Watt appliance at the
same time the total is 960 Watts, plus 25% gives 1200 Watts. Inverters
will handle surge currents to start certain equipment for short time-spans.
But their continuous rating must be equal or exceed the total.
What
Does a Regulator Do?
A Regulator serves to charge the batteries safely by dumping excess
power. Most Regulators also serve as a 12 Volt power supply. 12Volt
power is supplied down to a battery voltage of around 11.8 Volts when
the unit protects the batteries from further discharge by disconnecting
the 12V supply. !
DO
NOT DISCONNECT THE REGULATOR FROM THE BATTERIES UNLESS YOU FIRST DISCONNECT
THE SOLAR PV MODULES.
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