Off-Grid Power Systems - How Much Power Do You Need ?

What Do You Want To Power ?

With any off-grid power system, careful selection of the devices to be powered can massively reduce the size and cost of the system required to power them. Efficient devices often make all the difference to the viability of a project.

To demonstate how dramatic these savings can be, listed below is a simplified comparison of two ways to acheive the same overall goal. One scenario costs almost 10x as much to power as the other.

For the purposes of this example - let us assume that each device needs to run for 5 hrs per day in winter in the UK - imagine a very small off-grid home office.

Example Office - Scenario 1 - Normal Mains Appliances	Example Office - Scenario 2 - Highly Efficient Appliances
Desktop PC @ 100w x 5hrs = 500 whrs	Laptop PC @ 20w x 5 hrs = 125 whrs
A/B Class Stereo Amplifier @ 25w x 5hrs = 125 whrs	Digital Class Amplifier @ 3w x 5 hrs = 15 whrs
Incandescent 100w Light x 5hrs = 500 whrs	CFL Light Bulb @ 18w x 5 hrs = 90 whrs
Total per day = 1125 whrs + 20% Inverter Losses.	Total per day = 230 whrs (+ no inverter losses if devices are DC).

The difference in the costs to power these two simple scenarios is huge, Scenario 2 will cost about 10% or 15% of the cost of Scenario 1. The first scenario would require approx 6x the size of solar array, battery bank, cabling, support structure, delivery & installation costs ... as well as an inverter.

Therefore you can see why it is so important to select high efficiency devices. As shown in the example above, with careful planning, this is where you can save serious money on the cost of a remote power system.

To make these high efficiency devices easier to source, we now offer some of the more ultra-efficient dc lighting, audio and ventilation equipment in our product range.

How Much Power Does It Use ?

It is important to take the time to establish how much power each device uses. Most mains devices can be easily tested using a simple, low cost, plug-in energy meter.

The power figure from the energy label on the back of the device or the manufacturers specification sheet is often peak power, which is normally far higher than the average. Conversely, many mains powered devices draw power even when they are supposedly 'switched off'.

Testing smaller DC powered devices may need a multi-meter or the manufacturer may be able to supply some data for average power use. Our experienced system design team can help if you get stuck here - we have figures for many appliances.

When Does It Need To Run ?

To minimise running times throughout the system, use timers, PIR motion sensors and well designed controls with your appliances. These convenient devices offer huge opportunities to reduce energy requirements.

Recently a new type of energy saving multi-plug has appeared on the market. These 'smartplugs' shut down multiple devices based on one. For example, when a PC is turned off ... the printer, scanner, speakers and possibly network equipment is all automatically shut down as well.

On small off-grid power systems we recommend trying to avoid the need for an inverter to be running 24/7. All inverters use power on standby and also loose power in conversion from DC to AC. Therefore DC lighting, fridges, freezers and IT equipment all cost less to power from DC.

How Critical Is The Supply ?

What are the consequences of running low on power ? Critical systems tend to be designed with a higher spare capacity. This can also be supplemented with a larger battery bank and the entire system can be backed up by a diesel generator.

A well designed off-grid solar or wind energy system, correctly installed, is highly reliable. Maintenance involves an occasional clean of the solar panels and checking of batteries, with very occasional change of bearings on a wind turbine.

With modern technology - it is even possible to send a text or phone warning alert if a critical system is running low on power, thus enabling preventative action. Online system status web pages are also possible.

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