Solar Panels For Air Conditioner ??????

Re: Solar Panels For Air Conditioner ??????

You need to look at how much power you wish to consume... Assuming you are in the SF Bay Area (Oakland?), you don't need near as much power for A/C here as you would in the central valley...

For example, I live pretty close to you and have ~$30,000 worth of Grid Tied solar and that, during the summer, generates roughly 500 kWhrs per month ($60 worth of electricity)...

Say, you want to run an A/C unit that can cool several rooms (in a well insulated home). Assume that it takes 20 amps @ 120 VAC... How long will 500 kWhrs run that unit?

500,000 Watt*Hours / (20A*120V) = 208 hours per month or about 7 hours per day...

Is that worth $30,000 (about $20k after state and fed rebates) to run a good sized room A/C unit a few months out of the year? Probably not.

That $30k system has 20 solar panels (175 watts each) and a 3kWatt Grid Tie inverter mounted in my garage.

Basically, $2,000 will just pay for the solar installation permit in many cities around here (some are better, some may be worse).

And, to be honest, a Grid Tie system is the most cost effective way to drive an A/C unit. You could go off-grid, but your power will cost you, at least, 4x the cost of a grid tie system, which itself (without rebates) already costs 2x base tier pricing of PG&E ($0.12 per kWH for PGE, ~$0.25 per kWHr for Grid Tie in our area, and $1.00+ per kWhr for off grid+battery system). (note: numbers are very approximate for a "retail installed system" that has an estimated 25 year life and includes new batteries for the off-grid system).

If you want to cool a cabin in a hot / dry climate--using a couple of solar panels plus a swamp cooler (batteries, or not--depending if you need cooling after the sun sets)--solar works nicely...

But, to actually be cost effective, you want to use the solar power for 9-12 months out of the year... If you only use it 3 months out of the year and it sits unused for the other 9 months--many times, it would be cheaper just to use a small generator by the time you add all of the costs up.

In the end, conservation is where you should first do your investment.

In California, we have tiered rates, and if you use more than, roughly 1,000 kWhrs per month (for a natural gas fed home), solar grid tie can save you some money. But, as you can see, to offset 1,000 kWhrs per month is not an inexpensive system.

-Bill

Re: Solar Panels For Air Conditioner ??????

That is wonderful conservation... In our home of four, I got down to around 175 kWhrs or so a few times (we use natural gas for heating, no A/C or heavy loads, usual appliances for a 3 bedroom home). Normally it is around 200-300 kWhrs per month.

A normal home around here is around 600 kWhrs per month (according to our power company for a similar sized home and no A/C).

For an off-grid system, people aim at less than 100kWhrs per month energy usage... When the power usage is that small, the off-grid system costs are much smaller too.

You could probably get away with a 1kWatt grid tie system and just about zero out your energy usage (if you are around 150kWhrs per month).

The reason I keep talking about grid tie solar is that--it is the cheapest and more practical way to generate and consume solar power.

There are only two major parts. The solar panels (plus mounts) and the Grid Tied inverter. Some conduit from the panels to the inverter, and some more conduit from the inverter to your AC breaker panel. And you are done.

Trying to do this "off grid" and generating AC power--adds a whole bunch of equipment (and costs). Still the same solar panels and wiring (although, about 1/3 larger because of the losses of an off-grid inverter and storage batteries), wired to a solar charge controller--which feeds a bank of storage batteries (which need to be replaced every ~5-10 years). From the storage batteries you connect to an Off-Grid Inverter which feeds a new sub circuit panel for your off-grid loads. You may also need to wire from your utility power to charge the batteries when there is no sun. And, you may even want a generator for emergency power (always nice to have)...

The advantage with the Grid Tie system is the electrical utility supplies regulated power for your home, and acts like a "perfect" almost infinite sized battery (can "store energy" from summer for use in the winter through "net metering"). Any reasonably sized off-grid system can only store about 3 days of power.

There are also some very nice "hybrid" systems that have the advantages of both Grid Tied and Off Grid emergency power (plus the drawbacks of a battery bank, generator, extra costs)...

It really depends on what you want for your home. A Grid Tied system for your home that would offset 150 kWhrs per month would be about 1.166 kW worth of solar panels and cost you somewhere around $10,000 installed (yes, you can save some money doing some work yourself, and there would be a ~$1,000 state check at this time).

And you would sign up for net metering rate plan (1 year period). You might need to run Time of Use billing--which means your electricty will cost you $0.30 per kWhr during the day and $0.10 per kWhr at night... If you are generating power during the day--you get paid $0.30 per kWhr and at night, you buy $0.10 per kWhr...

Unfortunately, it is a bit more complex than I said above--but it will give you some ideas of the options out there for you.

Feel free to ask more questions, and let us know what it is you really need.

-Bill

Re: Solar Panels For Air Conditioner ??????

B',

You need to look at your last 1 year power bills (some utilities put your 1-2 year usage on the web--just uses your customer ID and phone number or some such thing).

I used the information for San Diego and this website to calculate how many watts of solar panels you would need to off set your yearly kWhr usage (based on the one number you gave). You can also look through these PDF files to get an idea graphically how things work.

I came up with an estimate of 1.166 kWatts of solar panels and very roughly $8-$10 per peak watt installed (all costs). If you use more power other months/total year--the system would go up porportionally (2x power, 2x size).

My own system is over sized for our current usage--I lose, roughly, $265 every year in unused electrical billing credits (1 year net metering, I pay if I used more, any positive balance is wiped off the books for the next year)... I planned on using more power for a portable A/C (wife hates hot weather) and, hopefully, a decent around town electric (or hybrid electric) vehicle.

And, into the details. California has a very complex set of requirements for solar PV...

First is how to qualify for the rebates, and at what level they are right now... (currently around $1.19 per PTC kW rating--about 1kW for "your system). Is going down (from a high of ~$2.80 per watt last year).

Next is the billing plan you have now vs what is required for solar... For northern California, there are three residential plans E1, E6, and E7...

E1 is the flat rate plan ($0.12 per kWhr all year round). E7 is a Time Of Use plan where I pay/receive $0.29 per kWhr noon-6pm Mon-Fri ("summer" 6 month period), and ~$0.09-$0.12/kWhr the rest of the time.

E6 is a much more complex TOU plan... So complex, I am not sure anyone could actually accurately estimate their power bill (only half kidding here).

And, depending on the tea leaves--E6 may be the plan you are required to use...

I like E7 (no new connections in PG&E land), and would probably fall back to E1 flat rate to avoid E6--but again, depending on a whole bunch of stuff, you may not be able to use E1 either...

That leaves E6. Which punishes mid-day to 8-9pm energy usage with higher rates. But, I don't get much solar after about 4-5pm in the summer--so cooking for dinner (lights, fan, oven, etc.) usually cannot be pushed back to cheaper rate periods. (E7, cheap rates start at 6pm).

You may work out OK, because the higher rate costs start earlier in the day--when you do have solar to offset your evening usage--but it does make it rather hard difficult to push power usage into the 9pm to 10am weekday periods.

And, lastly, there are base line rates... For my area, ours is set to about 300kWhrs per month... If you go above those levels, the rates go up higher (and the cheap off peak rates go up very quickly to near the costs of the peak rates when we get to near 1,000kWhrs per month). But for me (and it sounds like you)--those upper rates are never an issue.

In the end, you have to figure out how much power you use--and for plug in 120 VAC appliances, a Kill-A-Watt meter will be your best $30 investment ever.

Once you know how much power you need--things become much clearer.

The whole California Solar PV structure is for you to try an zero out your power bill (in dollars). Too small of system--you may get killed by TOU billing. To large of system, you will never get credit for the amount you over generated.

-Bill