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Solar Panel System

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Joined: 02 Jul 2007
Posts: 1
Location: UK

PostPosted: Thu Jul 05, 2007 11:54 am    Post subject: Solar Panel System Reply with quote

Hey people!

Can you guys give me some calculations as to what electricity can be produced from the following equipment cos I dont know too much about electricity and stuff.

Solar modules = 500w
Battery = 600Ah (12v)
+ regulator, inverter etc...

Sunlight 7 hours/day

This system would be installed in a hot climate like Pakistan. The stored electricity would be used as back-up in the summer, as the grid is often turned off.

Will there be enough electricity stored in the battery to power an appliance of 1000w (such as an air conditioner), and 5 low energy lights (10w each = 50w). The air con would be used intermittently. In winter the system could be used for all the lighting of the house and some appliances. Is this sort of system feasible? Any help would be appreciated!

Thanks in advance.
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Joined: 02 Jul 2007
Posts: 7012
Location: North Somerset

PostPosted: Tue Jul 10, 2007 9:29 am    Post subject: Reply with quote

Whilst it is possible to supply loads of 1,000 watts from a PV system, this requires a relativly large system if the load is to be supplied for an extended period.

A 1,000 watt air conditioner if supplied from an inverter will consume about 100 amps (can not give a precise figure without knowing the inverter efficiency)

Whilst it would appear that your 600 amp/hour battery could supply 100 amps for six hours, in practice it will be less for two reasons.
Firstly the ampere hour capacity of a battery is generally specified if discharged over twenty or one hundred hours. if discharged over only a few hours, the capacity will be reduced, perhaps to about 400 amp/hours (can not give a precise figure without detailed battery specidications)
Secondly, it is very unwise to regularly fully discharge a battery, this will drasticly reduce its life. for regular use the discharge should be less than half of the available capacity.
This suggests that the air conditioner could probably only be used for about two hours on a fully charged battery. doubling the battery size would more than double the run time, since the larger battery would be discharged more slowly and therefore be more efficient

If the air conditioner was only used during sunlight, the run time would be somwhat extended since some of the current would be produced by the PV modules and not taken from the battery.
your 500 watt PV array should produce, in practice about 25/30 amps into a 12 volt system (can not give a precise figure due to the many unknowns)

Use of the lights would of course reduce the run time but only slightly since the lighting load is very small compared to the air conditioner.

A few pitfalls to be aware of

1) to run a 1,000 watt air conditioner from 12 volts you will need a very large and expensive sine wave inverter. due to the heavy starting current of an a/c unit, it is likely that at least a 3,000 watt inverter will be needed. the cheaper "modified sine wave" inverters are seldom satisfactory for a/c units.

2) running such a large inverter to supply only a few low energy lamps will be very inefficient. it would be better to use 12 volt low energy lamps supplied direct from the battery.

3)you will need good qaulity deep discharge batteries for such a demanding application. vehicle starting batteries are not suitable.

4) Pakistan does indeed have a hot climate, unfortunatly the output of PV modules declines in hot conditions and the rated output is unlikely to be achieved.

5) such a large costly instalation will be totally uneconomic if used only for backup power. instead you should consider using it regularly, even when the grid is available, in order to reduce the electricity bill.
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