Friday, 3 July 2009


Renewable energy in your shed / workshop / out house / barn / stables or similar.

Below is what you need to know!

How much power do you require?

What you have to look at is how much power you want and for how long per day. Start off by listing everything electrical you are going to be using in your shed, for example:
1 x 600 Watt Power Drill
1 x 60 Watt Light Bulb
1 x 10 Watt Radio

Next thing to do is work out how long per day you are going to be in your shed per day, also whilst you are in your shed, how long are you going to be using each of your electrical appliances. Example below:

2 Hours per day in my shed on average. (Total time per day in Shed)
1 x 600 Watt Power Drill for 1 hour per day.
1 x 60 Watt Light Bulb for 2 Hours per day.
1 x 10 Watt Radio for 2 Hours per day.

Now for the simple math behind it all!

Drill - 600 Watts x 1 Hour = 600 Watt Hours or 0.6 KWA (Kilo Watt Hour)
Light - 60 Watts x 2 hours = 120 Watt Hours or 0.06 KWA (Kilo Watt Hour)
Radio - 10 Watts x 2 Hours = 20 Watt Hours or 0.02 KWA (Kilo Watt Hour)
Total use per day = (0.6 + 0.06 + 0.02) = 0.68 KWA Per Day

My rule of thumb is to double your estimate therefore 0.68 KWA x 2 = 1.36KWA

Calculating your Solar Panel size.

Lets assume that on average a typical location in the UK will receive 5 hours of bright sunshine per day (Wishful thinking I know!) Notice we are working with 2 known quantities now 1. Power (Watts) and time (Hours) this enables us to work out what we need easily.
Take our total load (1.36 KWA) and divide it by sunlight hours (5) = (0.272) This is the figure in KW that are panel will need to provide for 5 hours to enable us to place enough power in our battery bank to let us use our electrical equipment for designated time above (2 Hours per day) 0.272 KWA can be converted into Watts by x 1000 so: 0.272 KWA x 1000 = 272 Watts or a 272 Watt Solar Panel Is required!

Calculating your battery bank size.

We know from our calculation's above that our electricity demand is 1.36 KWA worst case, so our battery bank is required to put out a minimum of 1.36 KW for 1 hour (KWH) If we are going to use a 12 V (Volt) battery bank then we can start looking at the figures:
We know we need 1360 Watts for one hour.
We know we have 12 Volts DC from the battery bank.
Ohms Law states that P (Watts) = I (Current In Amps) x V (Volts)
So we have 1360 (Watts) = ? (I - Current In Amps) x 12 (Volts)
So without boring you too much if we divide 1360 by 12 We get 113.33 Amps!

Batteries are measured in AH (Ampere Hours) But note that the specified AH on a battery is normally measured over a 10 hour period so the drain on a measured AH is 1/10th over 10 hours!
Lets assume for our rule of thumb and to be sure we are going to double our needs so we require 113.33 * 2 = 226.66 AH (Amp Hour) at 12VDC. Easy!

Calculating Your Inverter Size.

(The thing that takes battery DC and makes domestic AC for use with household electrical equipment!
We know that we are going to be using a 12V DC battery bank to power the inverter so we know we require a 12V DC inverter!
We know we require a Max of 1360 Watts or 1.36 KW of power and lets factor in 100% to allow for losses and inefficiencies, this gives us 2.72KW.
So We would choose a 12V DC inverter at 3000 Watts or 3 KW.

Choosing a Solar Charge Controller.

There are many different kinds of solar charge controllers available in the current market, PWM controllers (Pulse Width Modulation Controllers) Electronic controllers and MPPT (Maximum Point Power Tracker) to keep this section simple you are best sending me an EMAIL with info on what you are wanting to do and I will suggest the best solution for your needs.

If you want more information please do EMAIL me and I will provide you with a free quotation for either supply only or supply & installation.

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