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Solar Soluciónes

Estimating Daily Electricity Use

Every solar installation is unique and professional installers have to obtain many specific facts and figures that have to be evaluated and calculated to ensure that the final system design will meet the customers particular requirements. To estimate the size of equipment needed for any installation, it is necessary to calculate as closely as possible the amount of electricity likely to be used on a daily basis. For most circumstances the time of year when most electricity is used will be during the winter months, we spend more time indoors and need more hours of artificial lighting, usually so we can see whilst using some other electrical device. Every system has to be designed to the customer's particular requirements, if for example the customer uses more power in the summer months, perhaps on a cooling system, of course the system would be designed to supply the electrical demand during that period, not for the whole year .

With the information and tables below it should be possible for you to get an idea of the amount of electricity you use on a daily basis , and from there be able to estimate the amount of Solar Panels and size of other important parts of the complete system .

To estimate the amount of Watt/Hours/Day required to provide the lighting system, we have to estimate the amount of time (in Hours ) each known light source (Rated in Watts ) will be used. The same is true for parts of any system; lights, computer, etc.

Multiply Watts by Hours of each independent light source and then add together the totals to give the total Watt/Hours /Day

Using the table below as an example , it will be possible to calculate your personal Watt/Hour/Day requirements.

Light fitting site	Watts (bulb size)	Hours (per day)	Total Watt/Hours/Day
Living Room	4 x 15W 60 w	6	360
Dining Room	4 x 15W 60 w	1	60
Kitchen Main	1 x 15W	2	30
Kitchen specials (see note)	4 x 50W 200 w	1	300
Bathroom Main	1 x 15W	2	30
Bathroom specials (see note)	2 x 50W 100 w	1	100
Bed 1	2 x 15W 30 w	0.5	15
Outside Lights	1 x 150W	0.5	75
Grand Total			870 Watt/Hours/Day or 0.87 Kw/Hours/Day

Note: Any special lighting such as spotlights, cooker hood etc.

All electrical equipment should have it's power rating indicated upon it , usually on the back or bottom although sometimes on the plug , you will find a small printed or stamped label with numbers and letters on it . For our calculations we need to find the number immediately before the word WATTS or the letter W or maybe even Kw, if the appliance uses a large electrical load (1Kw is equal to 1000 Watts).

Sometimes the manufacturers give different information on their products and then we have to do a little maths to find the Watts figure we need. For example if the label has written on it something like:-

210/240V ~ 1.5 A ( This is saying it will work with an input of anywhere between 210 volts and 240 volts ,and that it will need no more than 1.5 Amps).

To find the amount of Watts needed we have to multiply the Volts by the Amps .

Thus... 210 volts multiplied by 1.5 amps is equal to 315 WATTS

We need to find the Total amount of Watts used for the Total amount of Hours , per day .

So if we use the above example of 315 Watts for 2 Hours per day, the total Watt/Hours is 315 multiplied by 2 so 630 watts for 1 hour , every day, or 630 w/h /d.

Using the table below as an example , you can get an idea of what we need to do to get the daily total. Watts/Hours

Note:- To get Total Watt / Hours required for Lighting, you will have to add together the power / time requirements of all parts of your lighting system.

Electrical Load	Rated power in watts	Hours per day use	Total Watt/Hours/Day
Lighting total (from above)			870
Telephone/ Internet	175	6	1050
Computer Equipment	250	4	1000
Television/Satellite	125	3	375
Refrigerator/Freezer (see note 1)	185	12	2220
Stereo	85	1	85
Vacuum cleaner	2000	0.10	200
Kitchen tools (inc. microwave , coffee maker)	1750	2	3500
Dish washer	2500	1	2500
Washing machine	3000	0.5	1500
Water pressure pump	500	1	500
Borehole / Well pump	3000	0.1	300
Swimming Pool Equipment	3000
Fans / Air conditioning	3000
Tools workshop/garden	1000
Grand Totals			14,100 w/h/d or 14.10 Kw/h/d see note 2

Note 1: Equipment such as freezers do not need their full rated Watts all the time, only when they are trying to alter the internal temperature, when it is down to temperature the freezer does not use much energy. In this table I have assumed that the equipment is only using its rated amount of Watts for the equivalent of 12 hours during a typical day. (50 Percent) Technically speaking this is called the "duty cycle " of a piece of equipment.

Note 2: Realistically this figure should be increased by around 20% to account for the inevitable power losses within the system itself. Every day each piece of equipment in the system (inverter, regulator, cabling) will take some power (coming from the panels) to operate. Therefore the 14,100 w/h/d in the table above becomes 16,920 w/h/d.

The table above is only an example and it is possible that with some mounting systems, the number of panels and bank notes required can be reduced. Contact us for an assessment of your individual needs.

The BIG Question:- HOW MANY PANELS DO I NEED ?

To try and avoid confusing customers with too many calculations and equations, I suggest that with the information supplied above we (the system designers) can now estimate accurately how many solar panels may be required .

As an example :-

1 x 130 Watt "Kyocera" made SOLAR PANEL would have an expected Daily output of around 0.45 Kw/h (or 450 watt/hours)

So now we know how many Kw/h one panel will supply , all we have to do is Divide the TOTAL Kw / Hours (from the bottom of the table) by our known figure of 0.45 .(Kw/h/d per panel)

16.92 Kw/h/d Divided by 0.45 Kw /h /d is equal to 37.6 so a system of around 38 panels would be required to run the equipment listed in the tables.The example above is a very simplified way of sizing a system and is meant to be used only as a very basic guide . It also assumes that the clean solar panel is mounted on a fixed bracket, facing south, angled to capture the winter sun, the sky is clear and that the panel is not shaded by anything during the day ( in mountainous areas , particularly in winter, the sun may not reach the panels until much later in the day than panels on flatter land with no obstructions) Also worth mentioning at this point is that the type of mounting structure used to support the panels can have dramatic effects on the daily power output from them, all panels have to be supported on something and it is another cost to be met by the customer.