Watts, Voltage and Amps

Ohm's law calculations
can be useful for calculating your battery storage limits
and the power delivered to it from the solar panel(s) against
the power needed to run the lights and the electrical equipment
you require.

P (watts) = Amps
x Volts

I (Amps) = Watts ÷ Volts

V (Volts) = Watts ÷ Amps

Example 1 - using the
calculation for Current I=P/E

Lets assume you have an
100 amp hour leisure battery with one 30 watt solar panel
charging it, to find how many amps the solar panel will deliver
in a full sunshine hour we need to do our calculations. We
need to convert the solar panel output watts to amp hours,
so to find the amps we need to divide watts by volts (I=P/E,
I (amps) = P (watts) ÷ E (volts)):-

i.e. 30 watts (solar panel) divided by the panels nominal
voltage17.5 Volts (approx) = 1.7 Amp's per hour. This would
be under exceptionally good circumstances (brilliant sunny
day, not to hot or cold) and the most likely average in usual
weather would be closer to 1.25 Amp's per hour.

If your total energy requirement is say a total of 200 watts,
if we convert this to amps (Watts ÷ Volts) = 16.67
amp's per hour we can now work out how many hours we will
get from our storage battery. We can see clearly that if using
the 100 amp hour leisure battery mentioned above that we can
maintain our power requirement for between 5 and 6 hours.
This of course would not
be recommended as it would bring the battery to a very low
point and may mean permanent damage has been done.

*Screen
shot from 'the12volt.com website*

the12volt.com
Is a good website for working out or verifying your Current,
Power, Resistance or Voltage calculations

Example 2

Often domestic electrical
equipment is stated in amps (or milliamps) especially when
the consumption is low. Ohms Law calculations can be useful
to convert all the milliamps into watts to match the other
electrical equipment you are trying to calculate your usage
for.

Good additional reading:

energy.gov

bbc.co.uk

thegreencarwebsite.co.uk

Ohms Law - (defined)

Ohm's Law defines the
relationships between P ((P) power), E ((E) voltage), ((I)
current), and R ((R) resistance). One ohm is the resistance
figure through which a single volt will maintain a current
of a single ampere.

Current (I)
is like a garden hose and is what flows on a wire or conductor.
Current is measured in Amps or Amperes.

Voltage (E)
is the measurement of electrical potential between two points
in a circuit. It is the strength or pressure behind the current
flow.

Resistance (R)
is the measurement of current through a circuit or component.
Resistors are used to control voltage at current levels. High
resistance reduces the amount of current flowing and is measured
in Ohms.

Power (P)
is the amount of current multiplied by the voltage level in
a circuit and is measured in watts.