PV Gap

Matthew Said:

i want to light up a building using solar panel what do i need?

We Answered:

Let's start from the simplest theoretical solution and work our way up to practicality.

Assuming you want to power 26W fluorescent bulbs (equivalent to 100W incandescent). You want to power 12 of them.
So total wattage requirement = 12 x 26 = 312 W
# of 80 W solar panels required = 312W / 80W = 3.9 ~ 4 panels
Now, the above calculations assume that your solar panels are exposed to sunlight while you are using bulbs, but if you want to use bulbs at night, you need a battery (or batteries) to store the energy and use it at night.

So, ideally if you charge your battery for 12 hours using 4 solar panels, you can use 12, 26W bulbs for 12 hours. Now this ofcourse assumes that your battery has enough capacity to store energy generated by 4, 80W solar panels during a 12 hour time period. This capacity is given in watt-hours.
For our case it would be, 80*4 W * 12 hours = 3840 watt-hours
For reference a typical laptop battery's capacity is around 100 watt-hour and that of a car battery is 700 watt-hour, so you need 39 laptop batteries or 6 car batteries.

Solar panels generate electricity in form of DC voltage and current. Batteries also store electricity in form of DC. But fluorescent bulbs need AC energy, so you need an inverter to convert DC energy stored in the battery to AC form.

Inefficiencies:
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Let's account for inefficiencies now,
- A solar panel rated at 80W would generate 80W max in ideal conditions I think. So if there is less sunlight, or intermittent sunlight, it would generate less energy.
- There will be some loss of energy associated with every device and component. So there will be some loss due to wiring, some due to battery and some due to DC to AC conversion in the inverter.

Lets add 1 extra solar panel and 1 additional car battery to cover inefficiencies.

Cost: (based on just a quick search on the internet)
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- 1 80W solar panel = $500, so 5 solar panels = $2500
- 7 car batteries = 7 * $94 = $658 (laptop batteries are more expensive, so we will use car batteries :-)
- 12 26W GE fluorescent bulbs = $35 approx
- Inverter, no idea, but guessing $200
- wiring probably another $200 assuming you will have to run long good quality wires from your backyard or roof to the room.

So you are looking at $3600 roughly

Fun fact:
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If you put $3600 in an online savings/checking account with interest rate of 3%, you get $108 a year in interest. Those $108 would probably cover the bill for running 12 fluorescent bulbs for 1 year (ofcourse the actual usage won't be 24 hours a day) off of the regular electricity.

Other ideas:
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Wind or water turbine would generate a lot more energy with low equipment cost, but you need to be fortunate to have good wind or a water spring near where you live.

Craig Said:

building a solar panel in montreal?

We Answered:

the first reference has annual average by location.
second reference has sun rise/set times, and sun path diagrams

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Chris Said:

I'm building a solar panel (60 Watts, 18V) How big a deep cycle battery do i need (How many Amp Hours)?

We Answered:

You have to make some decisions:

1. number of hours that you want the battery to operate when there is no sun

2. power used by the loads on the panel or battery in watts.

You will need an inverter and a charge controller.

If you want the battery to supply 60 watts for 10 hours, for example, that is 600 watt-hours. If the battery is 12 volts, than that is 50 amp hours.

Because of losses, I'd get a 60 or 70 amp-hour battery in this case.

If you could run the battery until it is fully or almost fully discharged, you need to get a "deep discharge" battery, as most lead acid batteries cannot be fully discharged without damage. Make sure this is a sealed battery for indoor use.

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