# Guesstimate my solar power potential

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I've been seriously considering uhm.... telling my parents that they should put solar panels on their roof :P I wanted to get a decent estimation as to whether or not the idea is silly. What kind of things should I look into to determine whether or not this will be a financially viable option? We live in Fresno, CA which is basically a freaken desert, we climb high up into PG&Es $.33/kWh bracket during summers, and I was hoping to get a company to install a small system, maybe 2kW, just to shave off enough power during the summer so that we're out of that killer bracket. I figure that would maximize the financial viability since we wouldn't be trying to become independent from PG&E. So I was wondering what kinds of things should I look into (I already will look into tax rebates and check out our roof's angle. I can even determine what direction the roof points with my new handy dandy compass I bought for totally different reasons :D So, solar geniuses of PF, UNITE!!! DISCUSS!!!!!!!!!!!!! I wuv you all <3 ## Answers and Replies Related General Discussion News on Phys.org Your solar power potential is. 6. Gold Member Your solar power potential is. 6. What are the units on that. Joules per solarpanel? I totally just checked it out and my room points at 346 degrees on the Northern slope. ZOMG I'm collecting data already! GO ME! Last edited: rhody Gold Member Peng Peng, Maybe you didn't see it but Chi Meson opened a thread on solar panels here. There is some good discussion here for you to think about. If I ever were to use solar it would be for a greenhouse for electricity and possibly heat, if I could heat and then store the heated water underground, but that's a stretch. You could PM and ask him about the good, bad and ugly of the project. Good hunting. Rhody... Gold Member Peng Peng, Maybe you didn't see it but Chi Meson opened a thread on solar panels here. There is some good discussion here for you to think about. If I ever were to use solar it would be for a greenhouse for electricity and possibly heat, if I could heat and then store the heated water underground, but that's a stretch. You could PM and ask him about the good, bad and ugly of the project. Good hunting. Rhody... No I can't pm him! He doesn't allow PMs :( SADFACE!!! That was my first idea. Then I thought PFF I WILL VISITOR MESSAGE HIM. Nope, no dice. He's punching my dreams of solar panels right in the face. Ivan Seeking Staff Emeritus Science Advisor Gold Member You have a lot of potential, Pengwuino. You're a bright young man. My understanding is that the price of panels is dropping so quickly that it makes sense to wait. Printed, thin-film panels, are coming soon. Gold Member You have a lot of potential, Pengwuino. You're a bright young man. My understanding is that the price of panels is dropping so quickly that it makes sense to wait. Printed, thin-film panels, are coming soon. Will solar panel companies drop their prices as well though? That sounds like an idea but I wonder if it will be one of those things like what happens with computer technology; you wait because prices are dropping but they're continually dropping so you continually wait :P. I heard, and Is wear Chi was the one who said this, that you only really need the panels + inverter + misc. mandatory electronics to run a system if you don't intend on it supplying 100% of your power. It apparently really drops the price down. Ivan Seeking Staff Emeritus Science Advisor Gold Member Will solar panel companies drop their prices as well though? That sounds like an idea but I wonder if it will be one of those things like what happens with computer technology; you wait because prices are dropping but they're continually dropping so you continually wait :P. I heard, and Is wear Chi was the one who said this, that you only really need the panels + inverter + misc. mandatory electronics to run a system if you don't intend on it supplying 100% of your power. It apparently really drops the price down. My understanding is that prices have and will continue to drop siginficantly. We had one thread where I was quoting online prices, and someone else was able to show that the newest panels were actually about 30% less expensive per watt, as I recall. What do you hope to achieve? [skip that, I hadn't completely read your first post] Last edited: Gold Member My understanding is that prices have and will continue to drop siginficantly. We had one thread where I was quoting online prices, and someone else was able to show that the newest panels were actually about 30% less expensive per watt, as I recall. What do you hope to achieve? World domination. Also, to cut down the power bill to where we are out of the highest priced tier during the summer. Paying$.33/kWh is pretty rough. The house is 2 story, 2200 sq ft with central air in the upstairs and we want to get it extended downstairs as well.

Ivan Seeking
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How did you come up with 2KW? If you know that's the number, it's a fairly easy problem. 2KW during daylight hours, or 2KW continuous?

Danger
Gold Member
Hello, beaked one.
I'm with Rhody on this one. I can honestly say that I don't know anyone who has an air conditioner (aside from those which are included in vehicles as standard equipment). For heat, I would actually go with black ABS or PVC piping as opposed to photovoltaic devices. You apparently live in a climatic zone that is not normally conducive to penguin longevity. Wanna trade?

Gold Member
How did you come up with 2KW? If you know that's the number, it's a fairly easy problem. 2KW during daylight hours, or 2KW continuous?
Oh I just vaguely guessed at it. I remember Chi saying his house was fully powered by a 7 kW system and he sounds like he doesn't use much electricity in the first place so I figured 2 might be a non-stupid guess. I should actually check the bill!

So when people say they're giving you a 2kW system, what does that actually mean? I mean, is that how much it will produce in direct sunlight? Does that only apply during summer when intensity peaks? Does it include variables like roof slope? Is it some kind of average? AHHH!!!

Danger said:
Hello, beaked one.
I'm with Rhody on this one. I can honestly say that I don't know anyone who has an air conditioner (aside from those which are included in vehicles as standard equipment). For heat, I would actually go with black ABS or PVC piping as opposed to photovoltaic devices. You apparently live in a climatic zone that is not normally conducive to penguin longevity. Wanna trade?
Yes, we live in an area that regularly tops high 100s and low 110s during the summer. Even the biggest swamp coolers can't handle it.

Ivan Seeking
Staff Emeritus
Gold Member
Oh I just vaguely guessed at it. I remember Chi saying his house was fully powered by a 7 kW system and he sounds like he doesn't use much electricity in the first place so I figured 2 might be a non-stupid guess. I should actually check the bill!

So when people say they're giving you a 2kW system, what does that actually mean? I mean, is that how much it will produce in direct sunlight? Does that only apply during summer when intensity peaks? Does it include variables like roof slope? Is it some kind of average? AHHH!!!
The panels are typically rated according to their maximum output. You have to derate from there according to angle, panel temp, and so on.

I would look closely at the break point for the high price, how much you need to reduce power, and during what hours. The rates can even vary with the hour of the day, but I don't know if this applies to you.

Gold Member
The panels are typically rated according to their maximum output. You have to derate from there according to angle, panel temp, and so on.

I would look closely at the break point for the high price, how much you need to reduce power, and during what hours. The rates can even vary with the hour of the day, but I don't know if this applies to you.
PG&Es site says we're on a plan where they do not charge based on the time of day. So during the summer it looks like we're using 1000 kWh into the $.33/kWh tier (yes, our bills can hit nearly$800 on a really bad month). Maybe a 3kW system would be able to keep us out of that super high range as much. Our winter electricity usage drops to around 1kW during the day since we have a gas heater, so going beyond 3kW would seem to be adding more cost with no benefit to be gained during the off-months.

I really can't figure out jack from solar company websites. It's always "Enter your monthly bill and your area code and we'llt ell you how much you can save :D" with figures such as how much the actual stupid system they're installing costs if you buy it upfront or what the generation would be or anything.

Danger
Gold Member
Yes, we live in an area that regularly tops high 100s and low 110s during the summer. Even the biggest swamp coolers can't handle it.
And here I be, up to my *** in snow. It's currently -8°, which Dave mentioned a while back is considerably warmer than the point at which we Canuks have to put on a hat when we go oot and aboot. It's T-shirt weather.

Ivan Seeking
Staff Emeritus
Gold Member
PG&Es site says we're on a plan where they do not charge based on the time of day. So during the summer it looks like we're using 1000 kWh into the $.33/kWh tier (yes, our bills can hit nearly$800 on a really bad month). Maybe a 3kW system would be able to keep us out of that super high range as much. Our winter electricity usage drops to around 1kW during the day since we have a gas heater, so going beyond 3kW would seem to be adding more cost with no benefit to be gained during the off-months.

I really can't figure out jack from solar company websites. It's always "Enter your monthly bill and your area code and we'llt ell you how much you can save :D" with figures such as how much the actual stupid system they're installing costs if you buy it upfront or what the generation would be or anything.
So it sounds like you need to reduce your usage by at least 35 KwHrs per day. You would want to do a formal check on the losses, but just shooting from the hip, you are probably into a 10KW panel, or so. Then you need to figure out how to apply it in an independent mode. When I feel like thinking harder, if you haven't worked this out yet, I'll check back. Right now my brain is still fried from running budget numbers.

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So it sounds like you need to reduce your usage by at least 35 KwHrs per day. You would want to do a formal check on the losses, but just shooting from the hip, you are probably into a 10KW panel, or so. Then you need to figure out how to apply it in an independent mode. When I feel like thinking harder, if you haven't worked this out yet, I'll check back. Right now my brain is still fried from running budget numbers.
Holy chit, 10kW? :-/ Why so much?!?

Ivan Seeking
Staff Emeritus
Gold Member
Holy chit, 10kW? :-/ Why so much?!?
35 KWHrs per day over say 6 Hrs effective, is 5.8 KW. Then factor in additional losses due to angle and temp, and system losses after that.

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35 KWHrs per day over say 6 Hrs effective, is 5.8 KW. Then factor in additional losses due to angle and temp, and system losses after that.
Sadface. I read that systems are around $7/W. So that's like.... ridonkulous. Ivan Seeking Staff Emeritus Science Advisor Gold Member Sadface. I read that systems are around$7/W. So that's like.... ridonkulous.
I would take a hard look at getting a deal like Chi has, where you pay a fixed amount every month and have a complete system.

Obviously the negawatt [saving energy] approach is the place to start. You guys are total power hogs.

Ivan Seeking
Staff Emeritus
Gold Member
You are probably a slam dunk for a passive solar heater for your water. The ROI on that would probably be good.

rhody
Gold Member
Peng,

How about one of these beauties, Geothermal heat pump, good for heating and cooling, high tech solution, and we love high tech (affordable) solutions now, don't we ?!
The geothermal pump systems reach fairly high Coefficient of performance (CoP), 3-6, on the coldest of winter nights, compared to 1.75-2.5 for air-source heat pumps on cool days.[5] Ground source heat pumps (GSHPs) are among the most energy efficient technologies for providing HVAC and water heating.[6][7] Actual CoP of a geothermal system which includes the power required to circulate the fluid through the underground tubes can be lower than 2.5. The setup costs are higher than for conventional systems, but the difference is usually returned in energy savings in 3 to 10 years.
Rhody...

Earlier in the thread I think it was Ivan who said that solar panel costs were decreasing rapidly, and I'd have to agree with that. I'd hold off for at least the next couple of years and see what kind of potential the market has. I would be hesitant about installing a large panel or set of panels unless California offers to buy energy from you. Meaning that you connect the panels to the grid and any power that you can't use goes to into the grid.

Up here in Canada we call it the microFIT program, and they are offering about a dollar per kWhr.

Chi Meson
Homework Helper
Hi!

Sorry for not allowing PMs, but it's due to the condition of being a teacher; I got swamped early on with students (not my own) who saw I was a HS teacher and said "this guy will answer my questions without posting in the HW section...

Anyway, I tried to read all the posts heretofore, and I'll recap:

0th priority: location. You pass.

1st priority: roof slope facing south. Even in Sunny CA, an east-west orientation makes roof-mount not effective. But with a little property, a ground-mount can be very useful.

2nd priority: roof tilt. If the first 2 priorities are passed, then any roof tilt will be good. Generally, optimal tilt is your lattitude +10 degrees. But with south-facing roof, or close to it, where you are even a 20 degree tilt will be fine.

3rd priority: thermal panels are cheaper, quicker and most efficient in payback, compared to photovoltaic, no matter how your water is heated currently. If you are in a no freeze zone, it gets even cheaper and you can consider in-line evacuated tubes (even if it freezes a couple of times in your location, its worth it if you can drain-down the tubes before the temperature drops). Heck, you could put a black plastic bag on the roof and get all the hot water you will ever need.

For photovoltaic, if you're going for 2kW, might as well go for 5kW. The inverter is a big chunk of money, up to half of the total price. WIth the inverter, you will get the grid intertie, and you don't need the batteries to store your electricity. Inverters must be sized to the kW of the system, so you can't decide to "add-on" later without getting another inverter; lesson: go large as possible at the start.

I don't know how CA does it, but if you put an 8kW system on your roof, you might be getting paid by the utilities for producing more than you use.

Ivan Seeking
Staff Emeritus
Gold Member
If you tie to the grid, your system will operate at max potential as a function of load. If you don't tie to the grid, then you have to worry about matching the load to the source, which is a constantly moving target. This is where small dedicated systems can lose a lot of efficiency.

In the end, the ROI should drive your choice. Payback can take decades if not done correctly.

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