Feedback on proposals for San Diego: LG/Hanwha + Solar Edge

[jd31]

By going with SE7600, do you have to derate or upgrade your main panel? or similarly what ampage of breaker are you installing? For SE6000 you can live with 40A, but for SE7600 you will need 50A (32A*1.5 = 48A, according to code) which some times requires you to modify your main panel.

Good question. I'll double check, but I'm fairly certain my breaker doesn't need to be upgraded (200 amp panel). I was originally looking at a 7,700 /watts system (or thereabout) and when the installer checked my breaker, he said I didn't need to upgrade it.

[thejq]

By going with SE7600, do you have to derate or upgrade your main panel? or similarly what ampage of breaker are you installing? For SE6000 you can live with 40A, but for SE7600 you will need 50A (32A*1.5 = 48A, according to code) which some times requires you to modify your main panel.

[ericf1]

I'd like to keep the option open to expand. On the horizon is possibly an electric car and possibly a pool/spa. I've asked the installer for an "option to buy" that I could exercise later at the current $/watt, which the installer seems amenable to.

That said, do I lose anything by over sizing with the SE7600?

I don't think you lose anything as far as features or efficiency, and expanding will be much cheaper than if you need a new inverter or a whole second system. My installer ran the electrical conduit directly under the roof area where I would install any additional panels, making it easy to add on.

[thejq]

Here's what I'm looking to pull the trigger on; hopefully sign an agreement this Friday:

- 6,325 watt system (109% of projected usage)
- LG 275 panels (qty 23) + SolarEdge 7600 DC Optimizer
- $/watt before tax incentive: $2.75*

* the actual cost is $22,074 or $3.48 /watt; however, that price includes a re-roof (separately quoted at over $4K from another roofing company) on the roof planes where the solar will be installed and other roofing work I need done. After removing those costs, my net cost for solar is $2.75/watt before tax incentive and $1.9/watt after.

Good price indeed. Good luck with the installation.

[jd31]

Nice deal! The SE7600 is a bit of overkill for your array size and $450 more expensive than the SE6000. Planning on expanding later?

I'd like to keep the option open to expand. On the horizon is possibly an electric car and possibly a pool/spa. I've asked the installer for an "option to buy" that I could exercise later at the current $/watt, which the installer seems amenable to.

That said, do I lose anything by over sizing with the SE7600?

[ericf1]

Nice deal! The SE7600 is a bit of overkill for your array size and $450 more expensive than the SE6000. Planning on expanding later?

[DanKegel]

Damn, that is a fine price!

[jd31]

Here's what I'm looking to pull the trigger on; hopefully sign an agreement this Friday:

- 6,325 watt system (109% of projected usage)
- LG 275 panels (qty 23) + SolarEdge 7600 DC Optimizer
- $/watt before tax incentive: $2.75*

* the actual cost is $22,074 or $3.48 /watt; however, that price includes a re-roof (separately quoted at over $4K from another roofing company) on the roof planes where the solar will be installed and other roofing work I need done. After removing those costs, my net cost for solar is $2.75/watt before tax incentive and $1.9/watt after.

[gregvet]

And another question about system size. My goal is for 100% offset. In general, do people aim for 100% offset or a higher percentage for overhead? 7,150 is over producing by 123% of my estimated need. I've only been in the home for 6 months so I'm devoid summer usage numbers. Using some projections, a 5,800 watt system would likely cover all my needs. I also have an old refrigerator I will be replacing and changing out windows. I know there's no right/wrong answer, but is there a general rule of thumb I should consider?

For my net metering, since there is always a minimum monthly charge regardless of whether I am making more than I use(kWh), it is a poor way to offset 100% of my electric bill. I would rather have a very small bill at the the true-up month rather than be paid wholesale or less for the excess energy I might have produced. It would be a long ROI time on the amount of extra expense of additional production capability to offset the monthly minimum charges.

[J.P.M.]

Sorry I should have clarified that I can, and likely will, have them install it over the existing tile roof. The shingles is an option that they prefer for aesthetics, which I told them is not at the top of my priority list.

My question is more about the benefit of redoing the roof membrane. For a 4% difference ($609 difference on a 7,150 watt system), it seems like a good option. Curious what other think in case I'm grossly missing something.

And another question about system size. My goal is for 100% offset. In general, do people aim for 100% offset or a higher percentage for overhead? 7,150 is over producing by 123% of my estimated need. I've only been in the home for 6 months so I'm devoid summer usage numbers. Using some projections, a 5,800 watt system would likely cover all my needs. I also have an old refrigerator I will be replacing and changing out windows. I know there's no right/wrong answer, but is there a general rule of thumb I should consider?

1.) The up and coming cheap out method is to remove the tiles from the area where the array will be and put composition shingles in their place, creating the potential for a lot of problems. It saves a few $$ for the vendor and provides no benefit for the owner. What you don't want is a sump under an array or a way for water and the crap that gets carried with it to get under the tiles. A uniform roof surface with all penetrations properly flashed is a tried and true method of helping to ensure a leak tight roof.

2.) The smart money does the conservation first or have a good idea what the for-sure conservation measures will be before buying any solar. That way, the solar will be sized with the new and (hopefully) smaller load. That way, the array will not be oversized.

3.) The future, as it has always been, remains uncertain, but usually and often, it is not cost effective to offset 100% of an electric load with solar. Reason: Doing so usually replaces the cheapest electricity you buy. Solar, being a relatively expensive way to supply electricity, is best suited to replacing the most expensive portion of what you must buy. That's also why conservation is almost always cheaper (more cost effective) than solar.

4.) Therefore, under most current rate schemes and tariffs, offsetting more than 100% of a bill makes even less sense than a 100% offset which, again, may not be justifiable from a cost effective perspective.

[jd31]

Since you ask:

Putting different roofing material under an array is, IMO, and for reasons detailed several times, a very bad idea.

Sorry I should have clarified that I can, and likely will, have them install it over the existing tile roof. The shingles is an option that they prefer for aesthetics, which I told them is not at the top of my priority list.

My question is more about the benefit of redoing the roof membrane. For a 4% difference ($609 difference on a 7,150 watt system), it seems like a good option. Curious what other think in case I'm grossly missing something.

And another question about system size. My goal is for 100% offset. In general, do people aim for 100% offset or a higher percentage for overhead? 7,150 is over producing by 123% of my estimated need. I've only been in the home for 6 months so I'm devoid summer usage numbers. Using some projections, a 5,800 watt system would likely cover all my needs. I also have an old refrigerator I will be replacing and changing out windows. I know there's no right/wrong answer, but is there a general rule of thumb I should consider?

[J.P.M.]

Update on my situation.

I have a revised bid from one of the installers (roofing background) that puts me at $3.52 /watt installed before tax incentive. That includes a new roof (titanium membrane) where the solar will be installed, which is about 30% of my total roof. I have a cement S tile roof and under the solar they will replace with shingles.

So the net net is, after the tax incentive it's about 4% higher than the next bid without replacing the roof. Seems like a good idea?

Since you ask:

Putting different roofing material under an array is, IMO, and for reasons detailed several times, a very bad idea.

[jd31]

Update on my situation.

I have a revised bid from one of the installers (roofing background) that puts me at $3.52 /watt installed before tax incentive. That includes a new roof (titanium membrane) where the solar will be installed, which is about 30% of my total roof. I have a cement S tile roof and under the solar they will replace with shingles.

So the net net is, after the tax incentive it's about 4% higher than the next bid without replacing the roof. Seems like a good idea?

[SunEagle]

To put it correctly, glygol or usually water/glycol mixtures are referred to as a heat transfer fluid or working fluid, not a heat exchanger. A heat exchanger is what the working fluid(s) go through, not the fluid itself.

There is (was ?) a chicken parts factory that had a line freezing nuggets using liquid N2. We did some refit work, took out the old line, replaced it with a bigger one. As part of the refit, took out a floor heater as you describe, replacing it with what was essentially a large slab of rigid foam insulation. Worked better and needed little maint. cost a lot less too.

I'm very familiar with glycol as a heat transfer fluid. Designed industrial systems for many power applications and others, including sanitary food and drug manufacturing equipment of the type you speak of for years.

What I was referring to in this thread was the application of removing heat from beneath a solar array, using piping, pumps and required support equipment and controls. What you'll probably get back with such a scheme ain't worth what you'll put in, in engineering, capital cost and maint. requirements.

As for glycol, or usually glycol/H2O mixtures' abilities as a heat transfer working fluid, while glycol/H2O has a lower freezing temp., and usually a somewhat higher vapor pressure (--> "boiling" temp.) than H2O by itself, what are called its transport properties - sp. gravity, sp. heat, viscosity, thermal conductivity and to some extent surface tension make it's ability to transfer heat inferior to plain old water. Sometimes glycol/H2O is required for the application, but H2O is the fluid of choice as a coolant wherever possible. Glycol H2O is used in lieu of H2O when required by that application, but not for its superior heat transfer characteristics.

I agree that the cost of using just about any type of fluid to transfer heat from a solar panel will not be cost effective. The savings by keeping the PV panel within heat specs would be minimal.

As you stated H2O is a better coolant but having Glycol mix allows you to use a lower temperatures in the fluid without the possibility of freezing the pipes. This allows you to get a faster (although not necessarily more economical) Delta T during the cooling cycle in a pasteurizer.

It all comes down to what is important to balance costs and production requirements. Glycol is ok for food processing but not a good fix for keeping solar pv cells happy.

[J.P.M.]

I never tried to determine the true cost associated with using glycol as a heat exchanger. So maybe in that area it is a loser.

I can tell you that is it used in many Food processing industries mostly in equipment like pastuerizers, filling machines and just about all equipment that transfers a food product that requires cooling without contamination.

It is also used in under floor heating systems to keep the ground beneath a food freezer from building up ice which will cause the floor to heave.

IMO I would say it transfers heat very well.

To put it correctly, glygol or usually water/glycol mixtures are referred to as a heat transfer fluid or working fluid, not a heat exchanger. A heat exchanger is what the working fluid(s) go through, not the fluid itself.

There is (was ?) a chicken parts factory that had a line freezing nuggets using liquid N2. We did some refit work, took out the old line, replaced it with a bigger one. As part of the refit, took out a floor heater as you describe, replacing it with what was essentially a large slab of rigid foam insulation. Worked better and needed little maint. cost a lot less too.

I'm very familiar with glycol as a heat transfer fluid. Designed industrial systems for many power applications and others, including sanitary food and drug manufacturing equipment of the type you speak of for years.

What I was referring to in this thread was the application of removing heat from beneath a solar array, using piping, pumps and required support equipment and controls. What you'll probably get back with such a scheme ain't worth what you'll put in, in engineering, capital cost and maint. requirements.

As for glycol, or usually glycol/H2O mixtures' abilities as a heat transfer working fluid, while glycol/H2O has a lower freezing temp., and usually a somewhat higher vapor pressure (--> "boiling" temp.) than H2O by itself, what are called its transport properties - sp. gravity, sp. heat, viscosity, thermal conductivity and to some extent surface tension make it's ability to transfer heat inferior to plain old water. Sometimes glycol/H2O is required for the application, but H2O is the fluid of choice as a coolant wherever possible. Glycol H2O is used in lieu of H2O when required by that application, but not for its superior heat transfer characteristics.