Your Questions About Solar Panel Calculator

Lizzie asks…

science project help!!!?

i am trying to power a small light bulb(the small one) using solar if i use a solar panel from a calculator it will probably be not sufficient to provide that much how many solar panels form calculators do i need to do that?
this type of bulb.

ssadmin answers:

Go to radio shack and get an LED light. You cant use an incandescent bulb with such small solar cells. When you go to radio shack ask the dude for an LED and a solar cell. You should be able to light the LED with just 1 little solar cell, which is a little bigger than the type on a calculator.

Michael asks…

Where can solar panels be found?

what household and other appliances use them. e.g. calculators, cars, etc

ssadmin answers:

Solar panels are used in rockets, watches, lanterns, and way more other things

Ruth asks…

Do solar cells and panels run on artificial lighting as well?

Are photovoltaic and solar cells the same? And same question… do they all run on indoor artificial light like calculators' and watches' do?

ssadmin answers:

Probably a little bit, but very poorly.

Eg, if you had a 100w bulb, 5 feet away from a 1×1 sq ft panel, at 10% efficiency (it would really be far less), you'd get

100*0.1*1/(4*pi*5^2) =0.03 watts

that is, 100 watts in to produce 3/100 of one watt.
Worse, that assumes 10% efficiency, which is likely higher than you'd really achieve.

Mark asks…

Why don't cell phones have solar panels? They've been on calculators more than 20 years.?

seems like they could charge when not in use

ssadmin answers:

Because the amount of energy a calculator requires is minuscule to that of which a cell phone requires.

Betty asks…

Solar panels as an investment and saving – sounds too good to be true!…?

(Firstly I apologise for the length of this, but I wanted to explain the whole situation just so there's no ambiguity).

Here in Brisbane, Australia we get 7-8 sun hours per day on average (source: ); our household uses ~20kWh per day based on the average of all the power bills for 2009. Using this calculator ( … too lazy to crunch the numbers myself) it tells me the ideal system is 3.2 kW. Our house has a large north-facing roof so that is good enough for solar panels. For practicality (and to keep the numbers conservative) I sourced the figures for a 3.5kW system which is within the price range of $30-40k, but after selling RECs (Renewable Energy Certificates) and taking advantage of federal and state subsidies and offsets it is priced at ~$15-20k; I'll assume a worst case (say, $25k) to keep it conservative.

With a Home Equity Line of Credit Loan we currently have $220,000 in debt overall. At ~6.5% interest the monthly repayments are ~$1,190. If we were to throw the $25,000 for the entire solar setup onto the loan, the loan would increase to $245,000 and interest would be ~$1,330 per month, a $140 increase. Since we are currently paying $126 per month ($4.20 per day) in power bills, it seems it is not worth it. However, 3.5kW x 7.5 avg sun hours gives 26.25kWh daily, or ~6.25kWh more than is needed. When taking into account the 44c/kWh feed-in tariff that is a lowest possible return of ~$82.50 per month (I say “lowest” because it is real-time net metering, so if we have nothing running during the day it will send a lot of power priced at 44c/kWh to the grid; when we buy it back when we are back from work at night it will cost only 16c/kWh, so overall we will gain more than $82.50 per month).

So then if we had to pay $140 extra per month on the loan but that eliminates $126 per month in power costs and includes $82.50 at the minimum in feed-in credits, is that is effectively a saving of $68.50? I know it isn't really a saving per se since simply paying loan interest doesn't reduce the loan's size, but to me it seems to be a saving since the power cost of $126 per month will always be there so it may as well be moved from one account (elec) to another (HELOC loan) without making much difference financially; also the HELOC loan can be paid off and thus interest repayments become lower, while the cost of electricity is only set to rise (on top of inflation-adjustment each year, we are expecting sharp rise when the carbon trading scheme gets passed, and the generators were granted a 16% increase for January 2010 anyway!!!). Additionally when the 3 kids have moved out of home the power use will drop, leaving more electricity for the grid (so more money returns) in addition to less expenses overall (so the HELOC loan will be easier to pay off) – seems like a double win!

There are two major downsides that I can immediately see: variable interest rate rises and home valuation. However for the latter, I am not sure whether it is really a problem. For all I know, solar panels would most likely increase the value of one's home (seems to be logical anyway), which in turn means more flexibility regarding the floor of the HELOC loan if it is needed.

I am somewhat naive regarding how HELOC works so that is my main concern in this plan. So is this too good to be true, or have I missed something (I generally don't believe in “too good to be true” hence why I am asking).
Naive re HELOC; I am one of the 3 kids mentioned in the question (19yo) so this is just for me to propose to my parents as an idea.

ssadmin answers:

Not bad. I'll answer with what I know about California (USA) – it may or may not apply to where you live.

If your power utility offers net metering on an annual true-up basis, then less sun in the winter doesn't matter. You would theoretically build up a credit on your power bill in the summer, and draw it down in the winter.

If your utility offers time-of-use metering, where the rates are higher during the sunny hours, then you may not need to size your system so large.

The value for sunlight hours – was that “peak equivalent sun,” intended for sizing solar systems? In the winter here, the sun is out for 10 hours, but the equivalent sun is only about 2 hours, when dawn, dusk, and overcast weather are taken into account.

If your utility is set up such that they will never pay you cash for power, then it's pointless to size your system so large that you might generate more than you use over the course of a year. This is in fact how the utility works where I live. The first year that our system was installed, we generated $80 more electricity than we used. We didn't get a check for it, the balance was just set back to zero at the end of the year, as a donation to the grid.

What you should do is ask a professional installer to look at your house and make a quote. They will probably know about the financing angle, too. Then decide whether it's truly a value, or whether they're trying to do a sales job on you.

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