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I would like to be more sustainable and I am thinking of installing a solar panel on the roof of my apartment, my question is how cost effective I will be knowing that my current electricity bills are low (something about 50 USD per month) and the cost of solar panels are considerably high. Or shall i use solar heating only?

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    There are online calculators that allow you to put in your location, roof angle etc. and calculate how much power will be generated. You don't say where you are and they tend to be regional so I haven't found one for you. Unless you can get a tariff that credits you for electricity returned to the grid, you need to consider how much electricity you'll use when the sun is shining. – Chris H Apr 1 '16 at 6:46
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    JZF can you provide your location? Local conditions and regulations will very much determine the cost-effectiveness – THelper Apr 1 '16 at 13:38
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    Thanks @THelper . I am in Stockholm - Sweden (I know, it is not the best place to use PVs !) – JZF Apr 1 '16 at 13:55
  • Can we know your average power consumption? You should have the monthly use available on the bills, with luck even the daily power use. I'd like to calculate things for a more detailed advice. :) – Migz Apr 2 '16 at 9:31
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The amount of power you consume/power costs are surprisingly unrelated to the cost effective-ness of solar power. To be more accurate, they are "slightly" related.

When you install a solar panel you will start generating power. Then there will be four things that can happen.

  1. excess power will go directly towards your power supplier.
  2. excess power will be stored in some sort of battery and once this is full, direct the rest to the power supplier.
  3. excess power will be lost
  4. Excess power will be stored in some sort of batter until it's full and the overflow will be lost.

Selling to the supplier

What does it mean when power goes to your supplier? It means they will pay you for your excess power. This means that your solar panels may generate you profit. The thing you should note is that you will receive less money for the power you send to the supplier than the costs to receive power from the supplier. This is why it's always in your best interest to have a battery to power your house at night and rainy days.

This is why your electricity bill doesn't really have an impact on the effectiveness on the solar panel.

In the optimal situation, you will have a battery that will nearly always have power stored in it. This means you will never receive an "electricity bill". Instead you will receive money from this bill.

So I would advise to calculate how much sun/power you can produce with a solar panel at your location. Then inform yourself on how much power you use, get a battery that can hold x amount of power for Y hours/days. If you have good connections with your power supplier you will be able to strike a good deal on selling them power.

Note: you will be selling power, this will be a form of income, so I don't know to what degree income taxes are involved.

calculating effectiveness without selling

If you cannot sell to your supplier (see @Thelper's comment). Then you'll want to calculate this to be more efficient.

Many solar panels can only supply you with a certain amount of power per hour/day/month. What you'd want to calculate is how much you use during your "light" hour and how much you use during your "dark" hours. The larger your battery is, the less accurate you need to be with your calculations. Assuming you have a gigantic battery you will want to calculate how much power you use within an average day/month. And then look for a solar panel that can provide these amounts at your location.

Expect to need more power during the winter and less power during the summer. Look at the time period you wish to start benefitting from your solar setup. Chances are that you may not be able to get back the amount you invested until year X. Especially if you can't sell to your provider.

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    Net metering regulations vary widely from country to country, so without knowing the location of the OP you cannot say if he/she can sell any excess electricity back to the utility company – THelper Apr 1 '16 at 13:35
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    @THelper Gosh dang it, I did not think of that. I'll be editing to add/cover that in the answer. :) – Migz Apr 1 '16 at 13:41
  • A fifth thing can happen: excess power will be used by electrical consumers that are turned on automatically and do useful work. Such ass a water heater. For how to do this, see this question. – tanius Mar 31 '18 at 0:11

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