Solar Panel Question?

Question

My electric bill per month averages 1800 kWh per month. I am looking at 165W solar panels. How many panels would I need to make my bill come to zero? I realize I also need an inverter to convert dc to ac.

Answer 1

There are 720 hours in a month (30 days) but only about 1/2 of those are in *full* sun

1800 kW hr / 360 hr = 5 kW.

5000 W / 165 W / panel = 30 panels minimum
and that's based on full sun during the day (no clouds, rain, etc).

Besides an inverter you'll also want a bank of batteries to operate at night. OR, you can get about 35 - 40 panels and sell power back to the utility during the day (meter runs backwards), and use power off the grid at night.

Suprise! solar power isn't cheap, is it? Figure on taking advantage of some government and public utility rebates, though to lessen the cost.

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Answer 2

There is always a lot of confusion on this question so I built a webpage to show people how to do the math and pick the right system size.

Most all public utilities will trade you kWh for kWh and then either settle up with you at the end of the month or every 12 months.

So one week you might have all rainy days but the next 3 weeks you have 10 hours of bright sun even in the winter. This means you have no need to put batteries on your system unless you have a lot of power outages. Then you only need a few hours of battery backup power. At most 24 hours. While the power is out you are not going to fire up everything in the house. Well you might but you will learn pretty quick not to do that. Backup power is backup power not give it all you got power.

You have to take the avg sun hours for the whole year and divide that by 365 to get the avg daily sun available. You will not never get that amount but some days you will get more and some you will get less. It averages out.

So if you use 1800 kWh per month divided by 30 days you have 60 kWh per day. If you get 5 avg peak sun hours a day you divide 60 by 5 and you need a 12 kWh system.

A 12 kWh system is going to cost you around 150 Grand to install and unless you have a very large roof or yard you will not have the space to put all the solar arrays. You could save 100 Grand of that money just by doing a few things to your home. It is cheaper to buy a new energy saving A/C unit then but on an extra 5 kWh of solar modules.

I am thinking you must be very wastefull on your power usage and have a total electric home. I think you should start by putting a little money in the home first. Get some energy star appliances in your home. Put some insulation in the walls. Get some better windows and plug those air leaks. Put in some CF lights and and turn them off when not in the room. Learn that you don't have to have all 4 tv sets on at the same time. Put in power strips so you can turn off things when you are not going to be using them. A TV set uses as much as 12 watts of power turned off, computers are the same way. If it has a remote it uses power when it is off.

Check out this link it might help. http://www.oynot/solar-info.html

Answer 3

If you fully want to offset your energy bill, you will need 1800kWh/month/30days/month=60kWh/day.

A typical value for insolation

http://en.wikipedia.org/wiki/Insolation

will give you on average 4-5 hours worth of sun at full solar constant (i.e. that's when your panel will produce the 165W that it is rated at). So one panel produces roughly 165W*5h/day=825Wh/day=0.825kWh/day.

Which means you would need at least 60kWh/day/0.825kWh/day=72 panels. Not counting inverter losses, that is. In less fortunate parts of the country, it will be closer to 100 panels. Your local installer will estimate this much more precisely than I can.

Your main problem, as I see it, is not that you need this many solar panels. Your main problem is that you consume WAY too much electricity. You should probably cut your energy consumption in half BEFORE you invest in solar because it will be way more economic to eliminate the main consumers than to generate that wasted energy.

I, for example, need no more than 180kWh/month for a household of two. My big ticket items were the fridge and the washer/dryer. Changing the lights did the rest.

My comments are for a household, of course. If you are a small business, your electric bill is probably OK. I am not trying to be critical, just pointing out the economic realities of energy where conservation is always cheaper than generation.

Hope this helps.

PS: the two previous answers WAY overestimate insolation. One seems to assume that the sun shines 24/7, the other one uses 12/7. In reality the sun does not always hit your panels at 90 degree angle (unless you have them follow the sun which for most rooftop solar makes no economic sense) and there are plenty of days with clouds (unless you do live in Nevada). 20% of full solar constant is a good estimate. The geometric average for the surface of the Earth without cloud cover is only 25%, but that includes the polar regions.

Answer 4

It depends very much on where you live. If you live in Nevada, Arizona or California solar panels might be a good idea. If you live in Canada don´t expect to get your bill to zero...

1800 kwh/month means an average consumption rate of about 2500 watts. 16 panels would cover that. But your energy consumption isn´t cosntant and nor is your energy production from the solarpanels. If you go off to work during the day when your panels produce the most then you probably produce excess electricity. Check with your utility if it is possible for you to sell off that electricity by putting it on the grid. Then you buy back electricity when you´re watching tv and surf the web at night. You loose money and electricity like this (or by using batteries as suggested above) so I would underdimension my solarpanel capacity. It makes sense if it is cheaper to just buy electricity at night.

The retailer and the manufacturer should have charts showing how much their 165 watt panels really produce at different times of the day and the year for your location.

Oh, and I´m sure there are ways in which you could reduce your electricity consumption. Smart lights, energy efficient lights are easy ways.

Answer 5

I like TBS101's answer, but 5KW isn't going to hack it. We don't live life on the average. If you turn on the oven, the dryer, the iron, a bunch of lights, and the TV, you are going to shut the system right down. You should not count on running everything with solar cells, but the most critical circuits.

And you are lucky to have 25% of a day in optimum solar alignment for photocells.

You need to think outside the Al Gore crazy box. Our modern way of life requires a lot of power! If you switched to coal or wood for cooking and heating and ironing, sunshine for drying clothes, heating the hot water heater, and for daytime lighting, then you could use the photocells for some lighting and the washing machine and anything electronic. You might stand a chance.

Answer 6

Build Home Solar Power - http://SolarPower.duebq.com/?sWz

Answer 7

I suggest you find someone in your area that has a system and look at there data. I live in Florida, have a system and publish my data. I am in my first winter and dealing with some trees that are reducing my performance. Any local installers should be able to give you names of customers that have systems.
I have 2.6kw grid-tied system. Some days it gets up to about 50% of my power requirement.