Getting PV quote in San Diego (SDGE territory) : some questions

soylentgreen · September 2012

Hi All, I've got an estimator coming this week to give me a quote on a grid-tie PV system. I want to be forewarned so I can ask some intelligent(er) questions.

SDGE Net Metering - I think that SDGE calculates net metering on an annual basis, so that if I have a credit in the summer, I can draw down that credit in the winter. Am I right? If not, would seem to change how big of a PV system to install.
Heat Pump vs. Natural Gas - our house is pre-wired for an air conditioner, and our furnace is 25 years old, so strongly thinking of just getting a heating/cooling heat pump instead. I ran some numbers and it seems that if we got a good heat pump (with 3.0 COP) then our winter heating needs would cost about the same as we are paying for natGas. I know that using heat pumps for heating in southern california is fairly rare, which I assume is due to expensive electricity and cheap gas. Any other things to consider?
TOU and electric car - we have an electric car, so we could get EV-TOU2 metering. Can we have that along with net-metering? The rates seem better than the solar TOU rates. Any gotchas?
Critical load battery backup - I would like to have a separate circuit that would provide a small amount of battery backup to a few systems (some lights, fridge, and a few computers). I understand this is pricey, so may not do it right away, but would like the ability to add later. Are there any makes / models of grid-tie inverters that would make this easy vs. impossible?
Bad roofline - most of our roof is E and W oriented. I've seen at least one system described where the PV was put on both E and W roofs, and then 2 separate grid-tie inverters were used. Why would you do this, vs. just putting all the PV on one side and using a single inverter?
Monitoring - I'd like to have performance data monitored, but am not sure about having that be public information, or want to pay a service fee to an outside company. Any recommendations for monitoring systems that can be self-contained? Or any third party companies that are cheap and seem to handle issues such as privacy/security well?

Thanks in advance for your thoughts & advice

BB. · September 2012

Re: Getting PV quote in San Diego (SDGE territory) : some questions

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soylentgreen wrote: »

Hi All, I've got an estimator coming this week to give me a quote on a grid-tie PV system. I want to be forewarned so I can ask some intelligent(er) questions.
SDGE Net Metering - I think that SDGE calculates net metering on an annual basis, so that if I have a credit in the summer, I can draw down that credit in the winter. Am I right? If not, would seem to change how big of a PV system to install.

This is a very good question... California, in general (I am in northern California with PG&E), has very complicated rate plans. And depending on how you use power, they can be a big help or an expensive burden with solar power.

At least for me, the meter is read once a month, and either it moves "forward" (charge you) or backwards "credits you". And for us, we have several meter readings: Off peak, partial peak, and peak.

The utility then chargers me based on the tier (the more power we use, the higher the kWH rate--from $0.09 to $0.52 per kWH depending on tier and OP, PP, or Peak power.

If the value is "negative", the $$ is placed into your account (credit) and if the value is positive, money is pulled from your account. For me, I am usually "negative" for off peak (night, mornings, weekends), and positive for Peak (M-F, noon to 6PM). So, I get charged $0.09 per kWH off peak, and I receive around $0.15 to $0.30 per kWH (winter/summer) during peak times.

I have to pay the minimum bill during the year (~$5-$6 plus gas), and at the end of the year, if I "owe", I have to write them a check. Or if I am positive (money in account), it is simply reset to "zero" (in October for me).

A new thing is based on excess kWH "generated" (if I generate more kWH than I use during the 1 year period). I will get a ~$0.05 per kWH "credit" (seemed to be about $30 this time). Remember, I can have a "credit" in $$$ in my account, and yet still have <0 kWH credit (on "average", I get paid $0.30 per kWH in summer peak, and pay $0.09-$0.12 per kWH off peak/winter--so I can still have "money" in the account but not get a kWH credit at the end of the year).

So--just remember that "money in the account" is "fictional". It can be used for "credits anytime during the 1 year net metering period--but "goes away" if there is excess, and if "negative", I would have to pay the full amount at the end of the year.

In California, the program is setup for people to "net zero" dollars (other than a connection fee) over the one year period. Because California requires GT Solar folks to use Time of Use/Seasonal billing--You need to understand your load profile vs the solar generation profile.

For example, if you use a lot of power during Peak times/season (more than your solar array generates), you are now "forced" to by power at 2-3x the rate you normally do now.

And your power generated during "off peak" times, is not "worth as much" as a credit to your bill... When this first started, there were folks that got "just a little" GT solar to see how it worked. They ended up with higher power bills, not less (because they used a lot of power during summer afternoons, and paid dearly for it with TOU metering).

Heat Pump vs. Natural Gas - our house is pre-wired for an air conditioner, and our furnace is 25 years old, so strongly thinking of just getting a heating/cooling heat pump instead. I ran some numbers and it seems that if we got a good heat pump (with 3.0 COP) then our winter heating needs would cost about the same as we are paying for natGas. I know that using heat pumps for heating in southern california is fairly rare, which I assume is due to expensive electricity and cheap gas. Any other things to consider?

Yes, heat pumps for heating and even hot water (either from the A/C or a "hybrid" heat pump stand-alone water heater) can be the same or less than natural gas (or even solar thermal hot water--One installer I talked to said that solar hot water has about died in central California for his company--they are installing hybrid hot water heaters these days).

Maintenance--Don't know. I just installed a new 80% efficient forced air furnace in my home (we had wall heaters before)--I did not even bother with looking at heat pump system. I did not want to deal with the external heat exchanger with small home and smallish/standard sized lot--Perhaps I should have at least asked.

Gas water heaters here cost about $600 for a 50 gallon heater--and they don't heat too fast these days (efficiency and pollution laws). One of my kids can "empty" the 50 gallon heater even with a 2 GPM shower head (the burners on the new water heaters here are 1/3rd to 1/2 the BTU of my older water heaters).

TOU and electric car - we have an electric car, so we could get EV-TOU2 metering. Can we have that along with net-metering? The rates seem better than the solar TOU rates. Any gotchas?

YES!!!!

A few years ago, there was a real confusion about mixed billing (home and EV metering) and "tiered" power rates. An electric vehicle would push the billing tiers up several notches in the rate plan--So instead of paying $0.09 per kWH, people were paying $0.30 per kWH to recharge their vehicles.

This was in Northern California (PG&E), and was really bad news for awhile. People were disconnecting their EV meters because of the confusion and that the utility used the confusion to figure out how to "play the numbers" with Tiered quantities and rate plan (if I understood correctly, they charged very high tier for EV meter, eventhough there was a net credit for the other home meter from GT Solar).

It was "fixed" a few years ago (applied to PG&E, don't know about your region)--But I would still make sure that the utility explains (in writing) how the Residential/EV separate meters will work for you (tiers, shared credit to all meters/tiers/etc.).

Critical load battery backup - I would like to have a separate circuit that would provide a small amount of battery backup to a few systems (some lights, fridge, and a few computers). I understand this is pricey, so may not do it right away, but would like the ability to add later. Are there any makes / models of grid-tie inverters that would make this easy vs. impossible?

SMA, Outback, and Xantrex/Schneider (and others?) make "hybrid" Inverters that can do GT when the utility power is up, and Off Grid when the utility power is down. Unfortunately, you need to have the Hybrid Inverter+Battery bank installed together.

There is a way of installing a GT Inverter now, and installing the hybrid inverter+battery bank later--This is when the GT inverter is tied to the "protected output" of the hybrid inverter. Grid power is up--everything works as normal. Grid down, GT inverter is connected to the output of the hybrid inverter, and can share AC loads or even back-drive energy into the hybrid inverter and recharge the battery bank.

This is neither trivial or saving you much in costs (hybrid inverter needs to be larger kW rating than the GT inverter to "absorb" AC power to recharge the battery bank.

We can talk more if you want.

Bad roofline - most of our roof is E and W oriented. I've seen at least one system described where the PV was put on both E and W roofs, and then 2 separate grid-tie inverters were used. Why would you do this, vs. just putting all the PV on one side and using a single inverter?

Separate GT inverters are used to optimize the power collection (MPPT--Maximum Power Point Tracking). If you have two "different" arrays (temperature, power output due to orientation, etc.), paralleling the arrays into one MPPT GT inverter will collect less than optimum power. There is an argument to be made on how much difference this will make (i.e., >>10% or <<10% difference). People who should know and have tested recommend separate MPPT inputs (one for each array/plane).

You can use PV Watts and try the East vs West array and see what gives you most power.

Remember, if you have TOU billing plan--The "West" facing array may generate less kWH per day, but since you are paid 3x as much for each kWH (in summer peak), the "minor" losses with a west array may be still much better in the end because of more "money" into your account (for example, in Florida an East array will collection more KWH than a West array because of cool morning temperatures an no afternoon thunderstorms/clouds--However, the west array being paid 3x as much for power still gives more credit in the end (this is based on California rate plan, not Florida)).

Monitoring - I'd like to have performance data monitored, but am not sure about having that be public information, or want to pay a service fee to an outside company. Any recommendations for monitoring systems that can be self-contained? Or any third party companies that are cheap and seem to handle issues such as privacy/security well?

There are a few threads here about monitoring... Have you picked an inverter/company/style (central vs micro inverter for example) yet?

-Bill

bill von novak · September 2012

Re: Getting PV quote in San Diego (SDGE territory) : some questions

I have used two grid tied systems in San Diego so a few basic answers for you:

Net metering. Our first system was net adjusted yearly, so we'd get charged a service fee every month and then it got trued up once a year - so you could carry over generation in June to December when generation was lower. Now that's changed since we are now on a feed-in tariff; I'll take a look at our bill to try to break that down.

Yes you can do EV-TOU along with net metering. We don't do it (we have a Leaf and a 10kW system) but we'd save a bit if we did. There is much debate over the value of doing what when; one EV user at my company determined that it's cheaper to do BOTH and move the plug for the charger between the net metered and the EV meters, depending on time of charging.

Direction - in San Diego June gloom is a big factor. The "ideal" orientation for a coastal San Diego system is about ten degrees west of south since you almost never get sun in the morning May-July. So I'd max out the west array before adding any on the east.

However both my houses have had SW and SE arrays; they still work.

Battery backup - if you want cheap now and expensive later (i.e. you want to minimize money now but are OK spending a lot more later) then I'd start with a straightforward grid tie system then switch to a HV MPPT (around $1000) with a hybrid system later. For slightly more money now but a lot less later I'd go with an Enphase-like AC system now then go AC coupled later. This is more complex but lower cost. You might also consider a small battery size hybrid system based on something like a GTFX inverter. Undersizing the battery system will make it much less effective during power outages but reduce maintenance costs, since you will have to periodically replace them.

rollandelliott · September 2012

Re: Getting PV quote in San Diego (SDGE territory) : some questions

Power One Aurora Grid Tie inverters have dual MPPT tracking so you can use ONE GT inverter to control Different facing arrays, one east one west, I don't know of any other GT that does this.

Also TED (the energy detective) is a good AC monitoring solution that is in house.

solar_dave · September 2012

Re: Getting PV quote in San Diego (SDGE territory) : some questions

For Monitoring I use a TED. You can have up to 4 lines monitored and combine them in lots of different ways for figuring you current net.

You can look at my link in my signature for mine. I have 3 different loads (main house, new building, EV chargers) and one generation for the solar setup on it. BTW it is fun to look at the EV chargers, I get a kick out of solar charged cars.

Be forewarned, it is not trivial to get it all working like dial tone. If you have any other wireless transmission via power line like X10 you will need to look at filters. TED uses wire-line transmissions to send data to its web/data-collection appliance. Don't put the appliance on a UPS or plug strip. There was some rumble that some CFLs can mess it up, but it seems to work fine here with all CFLs. It has a 10 mbit Ethernet port to put it on your home network. Be prepared to debug the comms stuff. If your network switch can't dynamically set just the one port to 10 mbit then the whole switch might slow to that speed, but most late model ones should be fine. I did have an old 100 mbit that was that way. Good excuse to hit gigabit on the home network as most of those will step back cleanly.

That being said, mine has worked pretty flawlessly for about 18 months after the initial grief. I was keeping up with the code releases but not looked in a while because anything that I use works well on the current version. Plus Flashing firmware always make my heart skip a beat while it is in progress (fear of bricking syndrome).

soylentgreen · October 2012

Re: Getting PV quote in San Diego (SDGE territory) : some questions

Thanks to all the replies. We had the initial quote, and it looks good to us : plan to put about 5KW worth of the 235W Sharp panels on our west-facing roof, which should be able to more than cover our current usage as well as do a good job of covering our planned (heat pump) and possible expansion (using the electric car more often).

Our west roof is about 260 degrees, so PVWatts says we'll only get about 80% of maximum possible capture, but that portion of the roof is nearly invisible from the street so we like it for aesthetic reasons.

Almost certain we'll go with a single inverter (although I really like microinverters in theory, we have a very steep & hard-to-access roof, so the idea of doing any replacements there doesn't sound good). The single string inverter will be mounted in an insulated garage so it should be pretty babied in terms of environmental exposure. The Power One aurora inverter was recommended as we have some late-afternoon shading issues from a tree so the plan will be to wire two banks of panels (shaded, and unshaded) with its two MPPT inputs.

The actual roof survey hasn't been done yet, but we don't expect any big surprises. I'll update with more info as it comes.

I'm pretty amazed at the pricing so far: with all the rebates, tax credits, and a special San Diego rebate, it's looking to be about $3-$4 watt installed. We may need some roof work too, so that may bump the price up, but that's not necessarily fair to consider as part of the cost for a normal install.

soylentgreen · October 2012

Re: Getting PV quote in San Diego (SDGE territory) : some questions

Update 2 - our initial quote turned out to be optimistic, as the roof location we want to use is just a little bit too short to get 3 rows of panels on. The options were to go for a much smaller system, or upgrade to higher efficiency panels (SunPower E20 327 watt panels).

We are leaning towards that - yes, the panels are crazy expensive (more than 2x per dollar per watt) but we think in the long run it's a more elegant design.

For the moment we are punting on the idea of battery backup, we may revisit that topic later (and I may want to do that as a DIY project for the fun of it).

Getting PV quote in San Diego (SDGE territory) : some questions

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