10 Kw NAMEPLATE utility limit question

Northforker

I'm considering installing a 10 Kw grid tied fixed rack system at my home in Indiana. Our electric service is provided my our county co-op. They buy solar on a net metering basis, essentially store credit, which isn't the best deal, but I'm still crunching the numbers. The co-op has a 10 Kw NAMEPLATE size limit.

My question is:

Is the nameplate capacity determined by the inverter rating(nameplate capacity), OR is it the total rated watts of the modules?

I'm thinking it is the inverter rating, but don't want to ask the utility a question that I don't already know the answer to.

I'm also thinking that I can install 14 Kw DC worth of modules and a 10 Kw AC inverter.

With the less than stellar solar resources in Indiana, the inefficiency of the modules, line losses, inverter conversion inefficiency, etc. the system will RARELY if ever produce more than the inverter is rated for, and it it ever does, the inverter dumps it.

Please enlighten me.

My electrical knowledge level = Electricity is invisible and it can hurt you!

2twisty

Re: 10 Kw NAMEPLATE utility limit question

I would think that the 10Kw would be the inverter since that's what ties to them. However, I would suggest just calling the local electric co-op and asking them. Seems to me that would get you the most precise answer.

solar_dave

Re: 10 Kw NAMEPLATE utility limit question

Have you gotten any sample interconnect documents from the utility, sometimes they spell it out in the docs.

CALLD

Re: 10 Kw NAMEPLATE utility limit question

Northforker wrote: »

I'm also thinking that I can install 14 Kw DC worth of modules and a 10 Kw AC inverter.

Be very careful - PV modules are capable of periodically putting out MORE than their nameplate capacity! I know this for a fact because mine often do so in partly cloudy weather. There is what is call an "edge of cloud effect". Sunlight reflects (or refracts) off the edge of a passing cloud, then what you get is 1xdirect sun + sunlight reflected or refracted. The effect can temporarily boost module output by up to 30% or maybe even more in certain conditions. The effect is more pronounced after the panels have cooled down during the cloud cover period. If your system cannot handle this surge or isn't protected you'll either fry it or it will keep cutting out wasting valuable power. Do check it out!

Cariboocoot

Re: 10 Kw NAMEPLATE utility limit question

It should be by the inverter rating because the inverter will not pass more than that. This allows for over-paneling to maintain peak production longer.

But that does not mean the utility involved understands this. As solar_dave said, get the info from the company as to how they define it - as well as all other info regarding their rules of installation.

Northforker

Re: 10 Kw NAMEPLATE utility limit question

Here is the applicationAttachment not found.

Northforker

Re: 10 Kw NAMEPLATE utility limit question

Here are the net metering rates and rules:

Single-Phase Service for residential consumers who have an RGS on their premises with a nameplate rating of 10kW or less.

Monthly rate

Consumer charge:
$33.17

Energy charge:
Purchased Power Energy: $.058*
Purchased Power Demand: $.01895
Distribution Demand: $.013

Availability
Available to any member of the organization located on its lines for residential buildings. This rate schedule will serve single-phase members.**

Type of service
Alternating current, 60-cycle, single phase, 120/240 volts or other industry standard voltages mutually agreeable to the member consumer and the corporation.

Minimum monthly charge
The minimum monthly charge shall be the following:

The consumer charge, and
A charge of $1.00 per kva of the member consumer’s required transformer capacity for all over 15 kva.
All bills are subject to Wholesale Power Tracker. See RATES page for explanation.

This APPLICATION should be completed and returned to a Hendricks Power Cooperative representative in order to begin processing the request. For more detailed information on our Net Metering standards, please click HERE.

*Rate for energy both sold to and purchased from Hendricks Power Cooperative. **The member must have an approved Renewable Generation System with a nameplate rating of 10kW or less. Members must comply with the Hendricks Power Cooperative’s approved Net Metering standard.

Northforker

Re: 10 Kw NAMEPLATE utility limit question

Here are the contract rules

Cariboocoot

Re: 10 Kw NAMEPLATE utility limit question

Note that you will also be limited in size by the NEC rules governing back-feeding service boxes. A 200 Amp service can have 40 Amp back-feed on it, which works out to 7680 Watt inverter with derating or 9600 Watt without. That could be your 10kW system with a 12kW array.

You'll need to do a plan and submit it, then adjust until they are happy. This may include additional (redundant) disconnects, array set-back requirements, wire type/sizing rules, etc.

Were it me I'd start with the service capacity maximum (which can be increased be derating the main breaker but that usually confuses AHJ's) and see if you can fit a 10kW inverter and appropriate array. Also work out just how large an array you can fit at your place, because if there is room for only 8kW or panels there's no sense having a larger inverter.

"Engineers don't make the rules, which is why the rules don't make sense."

Northforker

Re: 10 Kw NAMEPLATE utility limit question

This will be a ground mount array and I have ACRES, so space is not an issue. I agree that I will need to submit the application with my proposed equipment before committing to ANY of it. I work for a company that installs utility scale solar. We currently have over 800 MW under construction and all of it is being built at at least a 1.35/1.00 DC/AC ratio some as high as 1.45/1.00 which prompted my question about a residential grid tied system ratio.

In a perfect world, without considering cost, what would be your DREAM 10 Kw system.

Module watts
Module brand
Poly or Mono
voltage
array configuration
number of strings
Inverter
SCADA
more?

I should have stated that it will be a fixed rack system

Blackcherry04

Re: 10 Kw NAMEPLATE utility limit question

Here is from Florida power, but may not apply everywhere.

The Rebate: Amount varies depending on the DC rating of the solar panels:

$2 per direct current (DC) watt nameplate rating of the solar panel up to the first 10 kilowatts;
$1.50 per DC watt nameplate rating of the solar panel from 10 kW up to 25 kW; and
$1 per DC watt nameplate rating of the solar panel greater than 25 kW
For example, a 28 kW system would receive $2 per watt for the first 10 kW, $1.50 per watt for the next 15 kW and $1 per watt for the remaining 3 kW, totaling a rebate of $45,500.