Net cost of going solar
 

I live in Phoenix so we've no shortage of sun, and during summer A/C is not a luxury (though keeping it under 80 is)

A former coworker mentioned to me he recently had a 4.8kW solar system installed on his house, he pays $43/mo for it and it has generated ~$170 worth of power since it went online 24 days ago.

I wasn't able to get much more information from him on the topic.. don't know if he leased or financed the panels or what... but he did send me a link to his monitoring account

http://img683.imageshack.us/img683/1206/solarp.th.jpg

At the rates I pay, that many kWh still adds up to >$110/mo which is less than the $170 it supposedly saves him but more than twice the $43/mo he pays for the system.

My average monthly electric bill over the past 12 months comes out to $104..

So my question is, am I doing my math wrong here? The way it looks to me is if I'm presently paying around $100 and I generate around $100 worth of juice on average, and I pay the solar co. $43/mo for the panels... that makes my net electricity cost per month $43 right? Or am I reading that wrong? Plus the panels shade my roof which should slightly reduce A/C load, plus it improves the value of my home, plus it is presumably better for the environment....

Are there any hidden, down the road "gotcha" problems I'm not thinking about?

You need to figure out exactly how much you pay per kWh and how much your electric company will pay you per kWh.

First step is normally to have a site assessment done, we can speculate all we want here and would get some what accurate if we looked at your kwh per month use (not dollar amount) and your sun hours (hours of full sun per day) that you get, but someone who works in your area, has the info for your area and is looking at your house in person is going to give you 100% accurate info, we are not.

Werd, I'm planning to have a consultation with them but figured my very first step would be to ask around for others' opinions, to see if there are any good reasons not to even bother - so as to avoid taking a half day off work to meet with a consultant on their schedule (this particular company apparently doesn't do weekend/evening consultations, which is fine their employees deserve days off too)

http://img686.imageshack.us/img686/6493/energym.jpg

My home is 2 story (among mostly single story neighbors) and gets 100% roof exposure at angles available to the sun from dawn to dusk. The overall size, orientation, amount of sun exposure, etc that my home gets is very similar to that of the ex coworker whose solar setup got me inspired... I use less electricity than him in general and pay a lower kWh fee (between 7 and 12 cents per kWh depending on time of year/day)

I know that folks on a forum can't give me a detailed breakdown of exactly what I'm going to pay, that's not what I'm looking for... just asking if there are any unforseen considerations to this because what it looks like is if the system costs $43 per month and offsets $44 per month worth of grid power, it's saved me a dollar no matter how you slice it. Is that correct? :D

Probably not. You'd need to know for sure what the $43/mo figure is. Is that just the monthly payment for the loan he took out to buy the system? Was there a down payment? When the loan matures, how much equity will be left in the solar system?

If there are enough tax credits available, the numbers might work out in your favor. And even if the system doesn't save money, you'll still feel good about it.

Let us know the results of the assessment.

The numbers sound reasonable enough to be sure. I'd say the only gotcha I could think of is a month with little sunlight.

If I had the opprotunity to do that, I'd insist on an oversized solar setup to maximize the credit to my electric bill. Depending on the costs, it might make the return on investment quicker.

There are no real hidden cost in solar electric systems and if I remember correctly you should average around 7-8 sun hours per day and to be a bit more clear on that wording, it's the amount of sun you would get full output from, not the amount of time it's "light out", the other thing is, solar output tends to match peek loads, sunny days tend to be peek days for A/C, it has been a few years sense I have asked about installed system costs, but costs have gone down, rebates have gone up and the panels them selves should last the rest of your life seeing as how they have a 25 year warranty on their labeled output and 50+ years of real life testing, some companies used to put a 30 or 35 year warranty but when I asked them why this was no longer the case I was told it was because some countries have restrictions on warranty time spans, so instead of having a warranty that varied by country they cut it back to 25 years, but we have some solar panels that are getting close to the 30 year mark, well past the warranty they had 30 years ago and are still producing at their output.

Arizona sounds like a great place to use evaporative cooling. It shouldn't be very difficult to modify an evaporative cooler to run on solar.

is there such a system that is a combination evaporative cooler and heat exchanger? It's bloody humid in Arkansas so evap coolers would make it worse, but if a heat exchanger was used to bring the cool into the house, it would be like a regular ac unit.

A friend of mine is working on a hybrid A/C that uses evaporative cooling to cool the condenser of a normal A/C. The prototype gets a SEER rating in the low 30s. It uses distilled water as the refrigerant. Main problem is that the "turbocompressor" (basically a modified turbocharger driven by a switched reluctance motor) is not a mass produced part.

I think I'll try to build my own hybrid A/C in the future, but with a conventional refrigeration loop using ES-22a.

Not to rain on anyone's parade, but my rather ordinary, inexpensive Frigidaire window A/C has a COP of 10.5, or a EER of 36 and probably a SEER around 40. I hope he didn't worsen the COP by trying to evaporatively cool the condenser.

Where did you get that A/C? Even high end central units are lucky to get 20 SEER. 30-40 SEER is about where geothermal is.

A simple fan can have an effective SEER rating much higher than 40, as can evaporative coolers. But evaporative coolers don't work in all areas and fans might not be enough on the very hot days.
Alternative to Air-con - EcoRenovator

Fantasyland. I'm a metric man living in a mixed-units world! Sorry, it's an EER of 10.5, for a COP of 3.1. I'm now properly impressed by that prototype condenser chiller.

EER i assume is energy efficiency rating, but what is COP?

My burning question is the difference between using evaporative cooling to aid a heat pump type compressor and just using ambient air. if it makes a big enough difference I'd be all over it. Theoretically evaporative cooling will drop the temp by 10-12 degrees F regardless of humidity.

Coefficient of Performance. It's the amount of heat energy moved from the A/C's cold side to its hot side, divided by the amount of electrical energy required to do it.

An EER is the same figure, but with one of the terms in BTU/hr and the other in Watts, and the units carelessly lopped off before doing the division. EER = COP * 3.413.

Product Downloads | Coolerado Cool News
Looks like there's already a hybrid A/C in production. It appears to be roughly as efficient as the prototype unit my friend is working on. However, it is only available as a rooftop package unit instead of the more common split system. It must also be really difficult to install as it weighs almost as much as a small car! There's also no mention of price.

Last time I crunched the numbers a grid tied (no batteries) system that size cost arround $25,000.

For the area I live in figuring a 20 year life span the power the system would produce would cost $0.20/kwh, or about double what I pay now. Arizona gets a little more sun than we do so that would reduce the costs, and I think Arizona has some extra deductions that we didn't get when I last did my calculations.

Before you get on me about using 20 years for a life span, its not that I don't think the panels can last 20 years, but that the chances of something damaging the system in 20 years is pretty good, be it a freak hail storm, neighbors kids with rocks etc... so I use a conservative 20 years.