Need switching device controlled by insolation. Does it exist?

[Naptown]

Here's the point. You need to understand the difference between Net Metering and Net Billing when EXCESS production is involved. In a Net Meter situation (most grid tie situations CA, AZ and most other states) then you're right it does not make any difference where the electricity is used or when it is used. But in a Net Billing situation (like we have here in Indiana with our unregulated REMCs) then it make quite a bit of difference. You see I buy power at retail rates and sell my excess at wholesale rates. Thus it is to my advantage to use as much of my production as possible, thus I want to charge my EV with my excess power between 10am and 3pm when the sun shines. Now does it makes sense to you?

Ok that makes sense
What about a load management type system that would divert power to the EV during times when excess is generated.
This could get very complicated very quickly however.

[DanS26]

Ok that makes sense
What about a load management type system that would divert power to the EV during times when excess is generated.
This could get very complicated very quickly however.

I like simplicity and a load management system sounds complicated and expensive.

I just decided to just use a high amperage timer switch set to close between 10am and 3pm everyday is the best and most cost effective approach. Sure there will be cloudy days when I will be using grid energy during those times to charge the EV but I think it will be effective in the long run.

[theshadownose]

Here's the point. You need to understand the difference between Net Metering and Net Billing when EXCESS production is involved. In a Net Meter situation (most grid tie situations CA, AZ and most other states) then you're right it does not make any difference where the electricity is used or when it is used. But in a Net Billing situation (like we have here in Indiana with our unregulated REMCs) then it makes quite a bit of difference. You see I buy power at retail rates and sell my excess at wholesale rates. Thus it is to my advantage to use as much of my production internally as possible, thus I want to charge my EV with my excess power between 10am and 3pm when the sun shines.

Got the billing part- trying to figure out the usage part-- Unless there are literally 2 separate cables, one from your your company to you, one from you to your company, if you are producing 1000 watts, and you are using 2000 watts, why would 2000 watt come in to you? You would be drawing 1000 watts from them at that time, wouldn't you?

[DanS26]

Got the billing part- trying to figure out the usage part-- Unless there are literally 2 separate cables, one from your your company to you, one from you to your company, if you are producing 1000 watts, and you are using 2000 watts, why would 2000 watt come in to you? You would be drawing 1000 watts from them at that time, wouldn't you?

We're talking about the EXCESS power I produce. I just don't want to send that excess power back onto the grid. By doing that, I sell it at wholesale and then have to buy it back later at retail. So, if I can find a method to use up my excess power internally, at the right time, I have a better financial return.

What better way to use up my excess power (that I produce at $.058 kWh) than to convert it into gasoline gallon equivalent at 33.4 kWh or $1.94 per equivalent gallon. And before you ask, my installed cost is $2.04 per watt (which excludes my own labor, but includes the 30% tax credit). I made a large bet that the retail price of gasoline and coal generated electricity will increase in the near future. My real risk at this time is the unknown maintenance cost I will have on my solar power generating system.

[Naptown]

We're talking about the EXCESS power I produce. I just don't want to send that excess power back onto the grid. By doing that, I sell it at wholesale and then have to buy it back later at retail. So, if I can find a method to use up my excess power internally, at the right time, I have a better financial return.

What better way to use up my excess power (that I produce at $.058 kWh) than to convert it into gasoline gallon equivalent at 33.4 kWh or $1.94 per equivalent gallon. And before you ask, my installed cost is $2.04 per watt (which excludes my own labor, but includes the 30% tax credit). I made a large bet that the retail price of gasoline and coal generated electricity will increase in the near future. My real risk at this time is the unknown maintenance cost I will have on my solar power generating system.

How did you calculate your cost to generate. That number seems low or your production is very high. What is your system size and what is it producing per year?

[DanS26]

How did you calculate your cost to generate. That number seems low or your production is very high. What is your system size and what is it producing per year?

I used PV Watts to calculate my annual production. I assumed a 25 year life of the panels with a 1% degradation per year. A 10 year life on the inverter. So, total cost of system net of tax credits divided by 25 years of production results in cost of kWh to generate. I did not assume any maintenance costs which I hope to avoid.

I'm not sure how accurate PV Watts is but I hope it is not too over optimistic. My output was slightly lower in Dec and Jan but right on in Feb. In a few more months I should have a better feel for true return vs projection.

[russ]

Depending on location PV Watts is based on a 10 or 20 year average - at any point in time it is highly unlikely to be 'correct' but over time it will probably be quite close.

[DanS26]

[ATTACH=CONFIG]1802/ATTACH]

How did you calculate your cost to generate. That number seems low or your production is very high. What is your system size and what is it producing per year?

Here's a pic of my array. It should give you an idea of system size, etc.

[Oilrich]

Thumbs up

[DanS26]

Thumbs up

Thanks.

We need to get the word out. Residential solar power is near parity. I live in Indiana where we have cheap coal power electricity. I am producing power at below the retail rate to purchase from my local utility. I achieved this only by taking advantage of three things:

1. I designed and installed the system myself, so my costs were only for the parts.
2. I was able to take advantage of the 30% tax credit. (Good until 2016)
3. The purchase price of solar panel have declined 75% in the last three years.

Now is the time to strike, before tariffs send the price of solar panels back up.

[Oilrich]

Dan,

I like what you're sayin. I'm really fascinated with designing and installing a PV system.
I live in tx, where no benefits are passed out, so I'm finding it hard to justify such a large cost. I also don't see anything at the federal level either. Where are u getting a 30% credit, state or fed? I'm getting all my info from http://energy.gov/savings.

[DanS26]

Dan,

I like what you're sayin. I'm really fascinated with designing and installing a PV system.
I live in tx, where no benefits are passed out, so I'm finding it hard to justify such a large cost. I also don't see anything at the federal level either. Where are u getting a 30% credit, state or fed? I'm getting all my info from http://energy.gov/savings.

Check this site out. It also will list all credits and rebates for all states including Texas.

http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=US37F

As with all Federal tax credits, you have to have the income to support a credit of this magnitude. Note that unused credits are carried forward to future years. That helps a lot and I took advantage of this tax feature.

[billvon]

I just decided to just use a high amperage timer switch set to close between 10am and 3pm everyday is the best and most cost effective approach.

How about just a very small 12V panel driving a 12V relay? Add a variable resistor in parallel if you want to set an on/off threshold. No sun = relay open. Sun = relay closed.

[DanS26]

How about just a very small 12V panel driving a 12V relay? Add a variable resistor in parallel if you want to set an on/off threshold. No sun = relay open. Sun = relay closed.

I believe in simplicity. I already have an 8.5kwh solar system feeding my distribution panel and thus the grid. My garage is fed by this panel with a 60 amp feed. Simple, just have a timer to feed my EV when the sun is shining.

After researching this topic at length, I ran into many problems with photo voltaic relays. Main problem is that they switch off and on rapidly based on insolation, such as when the sun is shaded by a passing cloud. Some devices have a delay but that adds complications. Just for simplicity, I just scrapped the idea of having insolation trigger a switching device and decided on installing a timing device.

As a side note to all you lurkers, make sure your switching device is rated for the proper amps. You could burn your garage down including your brand new EV.

Also for all you EV future purchasers, the Chevy Volt incorporates a timing capability that allows you to determine when power is downloaded to the battery. Nice job Chevy.

[DanS26]

Depending on location PV Watts is based on a 10 or 20 year average - at any point in time it is highly unlikely to be 'correct' but over time it will probably be quite close.

Russ,

I'm resurrecting an old thread but I wanted to give you an update on my PV Watts experience now that I have about 16 months of real data.

You were quite right that in the long run PV Watts will be accurate. My actual generation is within 1% of PV Watts prediction.