Thinking about adding some solar power

[meburdick]

I live in a town where there's pretty much no public water supply (almost everyone has wells for their home use), no public sewer (we all have septic systems), and constrained access to "entertainment" service providers (phone, Internet, television). On top of that, we pay RIDICULOUS electrical rates.

I've been reading a couple of threads that deal with alternative energy choices, and have been starting to wonder how I could go about adding solar power to my home to offset the commercial power costs. My initial "target" would be to deal with a constant expense that I have in a radon mitigation system - there's a fan that runs 24/7.

Label on the side says 120V, 60Hz, 1.0A max. Also says 1/30HP Max. I was thinking that I could install solar PV panels, with a charger, batteries, and inverter, that I could use to power the fan motor for continuous duty. If I ensure enough reserve power to run the motor continuously for, say, three days, that would mean I would need to be able to store about 8.6KW of power in the batteries. In addition, I would need to be able to provide panels that could accumulate the 2.9KW of power that this thing uses every day AND add charge to the batteries at the same time. In order to have enough power to charge the battery, I would need panels that could supply 120W of power to run the motor and something like 180W of power to go toward charging the battery. This essentially means I would need three 100W panels which are about $575 for three. Given that this motor alone costs me something like $135 / year to operate, it will take me FOREVER (over four years, actually) just to recoup my costs on the panels alone.

Am I missing something here? If I'm doing the math right, then NO WONDER people aren't switching over to solar for even supplemental power!

 

[KTurner]

1.0Amp max does not mean 1.0Amp continuous. You should find a way to measure the actual current/power draw of the device and start from there. If the devices plugs into an electric outlet, there are devices (kill a watt) that you could put inline that will track several things for you. 1 HP is about 750 watts, so 1/30th HP is about 25 watts (ignoring the spike for startup). That would cut all of your numbers by a big percentage, since you could rely on the batteries for startup requiring less panels and battery storage. One thing you're not factoring in is that your fan is 120v AC and your solar panels/batteries are putting out ~12v DC.

My understanding is that solar water heating is much more efficient than using solar to power an electrical device. And, solar water heaters can be built from scratch using commonly available items (like pipes, lumber and paint), unlike PV panels and batteries.

Taking something fully off grid is going to be more expensive due to the batteries. Another thing you could consider is a micro grid tie inverter (GTI). It plugs into the grid and matches the grid signal, but puts power onto the grid. If the power goes out, it does you no good. but it's a lot cheaper to start off with. No batteries and it takes care of the 12v DC/120v AC. Throw a single panel and a GTI up somewhere. Tinker with it, use it to figure out how well solar does at your location, etc.

I've not done anything yet with solar except some research, but will probably start tinkering with either solar water heating or a micro GTI at some point soon.

Keith

 

[meburdick]

I don't seem to recall asking for logic and reason to be brought into the conversation.

Seriously... Your points about max power versus continuous are dead-on. I knew that the "max" meant that wasn't continuous, but I forgot that the disparity between startup and continuous on motors is so large.

Since this is a continuous-duty item, there *is* no startup to have to consider (really).

I'm aware of the difference in voltages, and planned on addressing that with an inverter. "Watts is watts", so I'm not concerned about the voltage or anything when factoring how much power to generate and store. While it's pretty likely that the motor will draw about 25-30W continuous, I'll still need to use the "extra" from a 100W panel to charge the battery packs. Since I'll need batteries, a charger, and an inverter, I think I'm still looking at a 2-3 year recover for my costs.

I'll have to look into the GTI item you mentioned... It sounds like it goes in line with the grid power so that I can operate "off grid" when power is sufficient for my needs, "on grid" when there's no sun, and in a sort of mixed mode when there's sun but my needs are higher than what the panel(s) can produce.

 

[Traxx]

you can also replace the motor with a straight dc motor and elimnate the inverter.

 

[meburdick]

True... I wonder what the cost of that would be compared to the cost of the inverter, though... And, wouldn't the use of the inverter, ultimately, give me cleaner power to run the motor on?

 

[KTurner]

Your points about max power versus continuous are dead-on. I knew that the "max" meant that wasn't continuous, but I forgot that the disparity between startup and continuous on motors is so large.

I suspect this also means that your yearly operating costs for the fan, as it sits now, is much less than the $135 you mentioned. $135 around here will get me about 1,200 KWH - getting close to what my power usage is for an average month (1,400 kwh). We're at about 11 cents per KWH.

Good news / bad news. It's cheaper to run the fan than you thought, but that means it'll take that much longer to break even on your solar investment.

Keith

 

[meburdick]

Very true.

So, again, it seems that I understand why so few people take on solar energy for their homes (unless you're talking about solar water heating, which is a little more prevalent).

 

[Traxx]

No the inverter is a unnessary expense. A solar panel powers a battery the battery powers the fan, the only inverter needed would be from 120 to 12vdc for cloudy days. The best return for investment is the solar water heater like mentioned above. Or just a timer for your water heater turn it on for just a couple hours a day would save a good bit.

 

[meburdick]

Current water heater is oil-fired burner on a hot water tank. The "issue" I have with it is that the house is a ranch and the main tank is "far" from the master bedroom.

We go through a lot of hot water in a day, so not sure how much benefit I would get from a solar system where I would need to maintain two tanks (I'm going to be putting in a second one under the master bath).

 

[Alien]

I installed solar (grid connected) but I don't see it as needing to break even in x number of years. I know I used to get a near $500 energy bill every 3 months and my last bill was a credit of $4.87. It is nice to know that what I am using I don't have to pay for anymore.
If you are going to be running gear at night-time you do need batteries and if there is no sun for extended periods you need to be grid connected.
This inverter is the ducks nuts for both situations. I guess there would be something similar in your part of the world. I just thought the info may help you with your decision. Selectronic - On-Grid Inverters with Battery Backup