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**ButchDeal** · 03-03-2019, 12:47 AM

your systems sizes should be in kW not kWh so the Tesla one is 7.63kW

Comparison is based on $/W pre tax not $/kWh estimate (estimates are not worth much often).

Yes you still want to use as little as reasonable possible during expensive TOU hours. You could use the more expensive battery but Tesla does not have any more battery incentive.

Lets try to compare these two properly first though.

Bid 1 Tesla

ok you states 26 PV modules at 325W or 330W either Panasonic or Hanwha?
in any case 26 X 325 = 8.45kW (what did you mean by system size of 7.63kWh??)
Guessing the price was ~$45.8k or $5.42/W

Bid 2 local company

29 PV modules LG Neon R (several sizes there but guessing 360W) so size of 10.44kW
coming to about $3.68/w still high but high end PV modules.
seems like large system.

What is the azimuth of the array? is it shadowed?

**J.P.M.** · 03-03-2019, 01:19 AM

For starters, if your goal is to reduce your electric bill as much as possible, start by using less. That is the single, most cost effective and foolproof way to reduce your energy bill as much as possible. Not as easy as throwing PV at a high electric bill, but much more cost effective. PV is the most expensive way to reduce a bill and therefore, with all elcse being equal priority, ought to be the last thing done. Almost no one around ere understands or does that in any serious fashion. That's my pitch for conservation.

Also, while you're at it, download the green button data from the SDG & E website. You'll need it to make intelligent choices about which tariff rate to choose.

Please provide system sizes in kW for each bid and total system prices before any tax credits or rebates. Don't pay much attention to panel wattage or number of panels. And don't compare prices per kWh (if that's what you mean to be doing). Use total prices from the vendors after any rebates but before fed. tax credit for the entire system divided by total system size in STC watts for all price comparisons. What you've provided so far is confusing and inaccurate. It's hard to give a meaningful opinion with the information supplied here so far.

Also, forget about vendor estimates. They underestimate output for several reasons, some good, but most are B.S. cons to oversell product. Download PVWatts, read the help screens a couple of times before you start, use a 10 % system loss parameter (you'll get that defined by the help screens) and make a few runs. Most vendors around here underrqate output (in effect oversizing systems) by ~ 10 % or so. Around here, a mostly south facing 20 deg. tilt roof mounted array with not much shade ought to generate ~ 1,700 kWh/yr. per installed STC kW of PV. Get your orientations as close as you can and have fun.

Before you go further, get a copy of "Solar Power Your Home for Dummies". It's a bit dated but still has a lot of stuff you'll find useful. There's a free online download for the looking, or a hardcopy at bookstores or amazon for about $20 +/- a bit. Either way, it's a good investment of a few hours of education. You'll need it.

Next, and there's no easy way to say or do this, get familiar with SDG & E's tariffs and how they work. When you do, you'll get frustrated and confused as hell. However, if you don't, you will be at the mercy of your ignorance that will be fertile ground for others to make money at your expense. Don't shoot me, I'm only the messenger. Start by Googling: "Current and effective tariffs + SDG & E". Then click on "residential rates".

After PV is added to your residence, you may also have "DR-SES" as rate choice. It's similar to TOU - 2. It's a rate for PV system owners and similar to TOU-2 that MAY (or may NOT) be the best deal for you. There are others besides TOU - 2 or TOU - 5. Your rate /tariff education will go a long way to straightening that out.

FWIW, TOU-2 and TOU-5 are different in that TOU - 5 has an ~ $0.14/kWh lower super off peak rate than TOU-2, but TOU - 5 also has an additional $16.00/billing period service charge, meaning if you use (i.e., charge a vehicle) more than ~ $16.00/$0.139/kWh ~ = 115 kWh/billing period, TOU 5 may be a better deal. Next, the going rate for a non battery residential PV around here is ~ $3.00/ STC W - $3.25/STC W.

A little factoid you'll only find out here: With any of the 3 rates discussed above, every installed STC kW of a grid tied PV system in San Diego that has not much shading (maybe 5-10% or so) and faces mostly south at ~ a 20 deg. tilt or so will offset ~ $420 to ~ $460 of an electric bill figured by one of those three tariffs (provided the system is sized for less than 100 % usage offset).

So, as an example, a 7.6 kW system as broadly described above will offset ~ $440*7.6 = $3,496 of an annual bill. Use all your electricity at peak time and you'll have a higher residual bill. Use less and/or use it at off peak times and you'll be able to use more for a lower bill. For those tariffs, a PV system can be considered as a revenue generator separate form usage and bill generation with the revenue confind to being used to only offset electric bills.

Another tidbit: Never oversize a system. More than 100 % generation is a waste of money.

Lastly, PV panels are now a commodity. Know the beyond some basic level of quality, all equally (electrical) sized systems and fit for purpose designed systems in the same location, orientation and duty will generate approx. the same amount of electricity per year, probably within a couple of % of one another for as long as you'll own a system. LG and Panasonic are good products, but no better than other quality products that are less expensive. Don't be B.S'd by peddlers.

Welcome to the forum of few(er) illusions

J.P.M., Zip 92026

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