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**Ampster** · 07-12-2022, 01:04 PM

Originally posted by petitout

Hi,
.....
Total : $37982 (before tax credit)
what do you think?

A back of the napkin calculation, would put the solar component just above $3.00 per Watt. My assumption is that the installer is not Tesla, since Tesla Powerwall installs were, coming in at around $10,000 when you could get them. Tesla certified installers were charging about $17,000 for single Powerwall installs. A few months ago I was talking to a Sunpower dealer in Southern California who told me that demand is such that he is not doing any solar installs without installing Powerwalls.

**petitout** · 07-12-2022, 01:17 PM

Yeah , the solar alone (panels+inverters) is $23.4k
so the battery cost is $14.6k

is it too much?

**J.P.M.** · 07-12-2022, 02:03 PM

Since you're asking, $14.6K/13.5 kWh storage capacity seems kind of steep, but then, most such storage seems cost ineffective to me at least at this time.
So, the question is storage at what price, not who's the least first cost.
Also, how long will 13.5 kWh last you in a crisis power outage ?
What are your design goals for the project ?
You on some type of NEM ? If so, what's the max/min POCO cost/kWh spread ?
Or, are you off grid ?
Have you done any cost analysis for the storage yet ?
Meaningful questions if you want meaningful answers.

**Ampster** · 07-12-2022, 02:48 PM

Originally posted by petitout

Yeah , the solar alone (panels+inverters) is $23.4k
so the battery cost is $14.6k

is it too much?

Since you are only asking about costs, I will assume you have done your own analysis about the value of the system to you economically. In the California rate and regulatory market, battery systems have become one way to acquire a hedge against erosion of Net Energy Metering benefits. Your mileage may vary.

I do not know the installation market in Colorado so I can only give you similar metrics for California. The Powerwall quote is below the market is California and the panels and inverters is approaching $4 per Watt, which is above the market. On balance the only way to know is to get another competitive bid. My metrics are a year old and reports of an increase of installers backlog may point to a less competive market.

**petitout** · 07-12-2022, 03:00 PM

Thanks all,
In Colorado, we have a 1 for 1 credit. However Xcel energy (our provider) is going to roll out Time Of Use (see this doc)
the TOU peak hours are from 3pm to 7pm (and the sun is getting down very early here in Colorado)
So the battery is a way to store energy during off peak hours and use these during peak hours.

**Ampster** · 07-12-2022, 04:24 PM

Originally posted by petitout

Thanks all,
In Colorado, we have a 1 for 1 credit. However Xcel energy (our provider) is going to roll out Time Of Use (see this doc)
the TOU peak hours are from 3pm to 7pm (and the sun is getting down very early here in Colorado)
So the battery is a way to store energy during off peak hours and use these during peak hours.

Yes that is the trend in California as well. It seems that the objective payback and ROI models for evaluating solar when we were on flat rates are not sufficient now that TOU rates are becoming more prevalent. I am envious of your rates in Colorado. My peak rate is $0.55 per kWh but my battery and hybrid inverter allows me to not consume much at that rate so I can put the solar energy into the bank at those rates even though those time windows have shortened .

**J.P.M.** · 07-12-2022, 04:28 PM

Originally posted by petitout

Thanks all,
So the battery is a way to store energy during off peak hours and use these during peak hours.

Which is the reason I asked about the min/max POCO cost/kWh spread.
If cost effectiveness has any place in your deliberations, that differential will affect the decision making and calculations. Big enough spread makes storage more cost effective and conversely.

**petitout** · 07-12-2022, 04:55 PM

Another question about my quote, it is expected that this 6.4kw system will produce a 11.5kWh yearly.
It seems a lot, especially seeing other quotes, which for the same expected production, started at a minimum of 7.7kW
Thoughts ?

**Ampster** · 07-12-2022, 05:30 PM

Originally posted by petitout

Another question about my quote, it is expected that this 6.4kw system will produce a 11.5kWh yearly.
It seems a lot, especially seeing other quotes, which for the same expected production, started at a minimum of 7.7kW
Thoughts ?

That seems high using my rule of thumb. The best source for an estimate based on your expected configuration, is PVWatts. It needs location, tilt and compass direction that the panels will be facing.

**petitout** · 07-12-2022, 05:36 PM

Originally posted by Ampster

That seems high using my rule of thumb. The best source for an estimate based on your expected configuration, is PVWatts. It needs location, tilt and compass direction that the panels will be facing.

Thanks !
Actually PVWatts gives an estimation of 10.5 kWh

**petitout** · 07-12-2022, 05:46 PM

Actually, I'm leaning towards getting more panels with no battery so that the over-production that Xcel buys back covers our daily need (even for peak hours).

**J.P.M.** · 07-12-2022, 06:25 PM

Originally posted by petitout

Another question about my quote, it is expected that this 6.4kw system will produce a 11.5kWh yearly.
It seems a lot, especially seeing other quotes, which for the same expected production, started at a minimum of 7.7kW
Thoughts ?

Since you ask:

1.) What are your proposed array azimuth and tilt ?
2.) What's your zip ?
3.) Depending on array orientation and altitude above mean seal level, and if your azimuth is maybe +/- 30 deg. of true south or so, that specific annual output (11.5 kWh/yr.)/(6.4 installed STC kW) = 1,800 kWh/yr. per installed STC kW doesn't sound unreasonable (to me anyway). Most of CO is pretty sunny.
Just keep in mind that whatever the number is, it's a long term average. Most models will suggest any year's annual output may be +/- 10% or so of that long term average with most of the annual variation due to the weather.
4.) I'd check my inputs (and use a 10% system loss factor instead of the 14 % default value) and go with whatever PVWatts suggested.

FWIW, my array long term (8+ yr.) average specific annal output is ~ 1,740 kWh/yr. per installed STC kW, and from what I think I might know of it, depending on your array orientation, you probably have more annual irradiance than I do and possibly lower ambient temps.

**J.P.M.** · 07-12-2022, 06:41 PM

Originally posted by petitout

Actually, I'm leaning towards getting more panels with no battery so that the over-production that Xcel buys back covers our daily need (even for peak hours).

I'd still check the POCO rate differential, high to low. Even though I think residential electricity storage isn't ready for prime time just yet, depending on your numbers and goals, planning for some storage in the future may be worth the effort down the road. You can always add storage as it becomes less expensive and more standardized.

As for oversizing an array to cash in on rates, be careful. Most POCO's pay spit for excess production, maybe 10-20 % of the NEM rates. Mine's about 10%, roughly. I'd be very careful about checking what Xcel pays for excess production. Usually, most POCO's pay a LOT less for excess production than NEM rates.

If cost effectiveness matters in your calculations, I'd size the array so that the mix of array supplied power and POCO bought power PV results in the lowest overall long term cost of providing power to your residence. If you're interested, look up the term "Levelized Cost of Electricity" for more details. NREL and others have a lot of info on it.

**petitout** · 07-12-2022, 06:55 PM

What are your proposed array azimuth and tilt ?

180 and 30, I also put "premium" module and 10% of loss and I arrive at 11.2kWh which seems in line, thanks !

As for oversizing an array to cash in on rates, be careful. Most POCO's pay spit for excess production, maybe 10-20 % of the NEM rates

Xcel in Colorado is 1 for 1 credit if you elect the "continuous rollover credit) (see here : https://www.xcelenergy.com/staticfil...TOU-FAQ_P3.pdf)
So I don't think I need a battery, especially as I share the same point of view about getting 1 later down the road when it's more mature

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