Hello Darryl,
I look forward to learning how you match solar production time with
consumption. I'm sure other wrenches do too.
Los Angeles has generally sunny weather with May and June coastal fog and
unpredictable clouds and rain from November until April. It hardly rains from
July through November so PV users can occasionally benefit from demand offset
from PV.
Here is a manual method for managing demand that others may find useful. A
cabinet making shop owner with a grid-tied PV system is able to control his
demand rate manually. Before he installed PV, he put a red light in the shop to
warn workers when demand was greater than his desired amount so workers could
manually shut off loads within the 15 minute demand period. PV has allowed him
to lower his demand goal, but they still has to keep an eye on the red warning
light.
Joel Davidson
----- Original Message -----
From: Darryl Thayer
To: RE-wrenches
Sent: Friday, March 19, 2010 6:24 PM
Subject: Re: [RE-wrenches] Demand Charge Reduction by PV
I do not agree. However I can not disagree with such logic. I hve done
some demand reduction, and I am doing some more. I did not say it was easy.
In fact it is hard, it is expensive, and in my area the energy saving for solar
for anyone on the general service rate (demand billing) is a fool to invest on
a ROI basis. HOwever if the demand can be reduced in my area it is more
valuable than the saving from energy reduction. My present customer has a load
factor of 10% I am studing this load profile on a fifteen minute recorder. I
hope to in about 2 weeks have enough data to make my predition as to energy
saving from the solar with demand reduction
As a note, I do not need to see the future, but the use structure has
to be known, so as matt says the unlikley day does not show up and ruenin the
month. Indeed not all buildings can be demand reduced. It is possible the
"electricity use profiles" in your location is different from Minnesota, .
Darryl
--- On Fri, 3/19/10, Matt Lafferty <gilliga...@gmail.com> wrote:
From: Matt Lafferty <gilliga...@gmail.com>
Subject: Re: [RE-wrenches] Demand Charge Reduction by PV
To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org>
Date: Friday, March 19, 2010, 2:26 PM
Wrenches,
I agree with Joel.
This is my policy on the matter: Consider any Demand Charge
reductions to be bonuses in favor of the customer. I think it is OK to say that
there MAY be some savings, but DO NOT try to guarantee or insinuate that there
WILL be any Demand related savings.
Here's why: UNLESS you have multi-year interval data for the site...
AND the ability to accurately interpret it.... AND the facility has a favorable
tariff... AND a site with a very predictable load (think in terms of being able
to predict the 15-minute interval which will set the Demand Charge within +/- 1
hour)... AND the 15-minute period which would otherwise set the Demand Charge
coincides with a period when the PV system is operating at a predictable
output.... AND your overlay of predicted generation on top of predicted load
indicates a FANTASTIC Demand reduction... AND your proposed system has multiple
inverters (the more the merrier here)... AND the weather is reliably
predictable around the 1-hour period you predict the "new" Peak Demand to
occur... Don't bother having the conversation or spending otherwise productive
time analyzing the matter...
If all the the ANDs above are true and you really want to go thru the
exercise, for whatever reasons you may have, be sure to consider the following:
In order to "prove" whether or not there was an effect on the Demand Charges
due to the PV system after the fact, you will need to have interval data for
both the generation and the facility. You will need to be able to evaluate
whether or not the customer's load profile, independent of the PV, changed from
the predicted values and, if it did, what the reasons for that were. For
example, if they increase or decrease their loads independent of the PV, the
net change is due to the customer's actions and the PV. Once you have
determined these factors, then you can begin to calculate the effective "value"
of the PV was on a Demand Charge basis.
It is possible and, in fact, likely that the PV will have some
positive effect on the Demand Charges for a given facility. It is, however,
very difficult to predict what that will be unless all of the ANDs noted above
are true. One of the keys driving the final calculation is the ratio of the PV
system's power rating to the customer's load coincident to the 15-minute
interval when the Demand Charges are set. The larger the system is, compared to
the facility load, the more likely and greater the savings will be. Embedded in
this relationship are the seasonal and hourly load profiles of the facility,
the reliability of the weather during this period, and how closely they line up
with the production profile. If you are intending to "guarantee" some number of
kW reduction, be sure you have multiple inverters on the project. The more
inverters you have, the more confidence you can have in your predictions.
Over the years, I've spent plenty of brain-damaging hours (weeks &
weeks) working on this. For utility companies, large integrators, and small
integrators. Before and after installation. With and without complex load and
generation profile data. On facilities with loads of all magnitudes and
hourly/seasonal profiles. The end result is the same... The effective Demand
Charge savings due strictly to the PV is relatively small and terribly
difficult to predict from year to year. I've had to analyze and report on "why"
the mucky-muck MBA & Engineers' predictions were so far off from the actual
experience after the projects went in. In the minds of these folks, it seems
like a no-brainer and just another column in their spreadsheets during the
sales cycle. It's a lot more complicated than that. I know of several
institutional customers who bought into paying the integrator for these Demand
savings on projects and have walked away from doing it on future projects. The
ones who have bought into paying for projected future Demand reductions in the
up-front cost of the project have regretted it. The ones who have agreed to pay
for it as a line-item on a PPA bill, aren't doing it in the future. It's simply
too much brain-damage. Too complex. If they are going to have to pay somebody
for it, it's a lot easier to pay the utility company.
I've had to analyze and report on cases where the facility Demand
Charges have increased after installation of PV systems. After you isolate the
load and generation factors, and demonstrate that the customer's load profile
has changed from the historical (generally larger loads later in the day when
the PV can't help as much), you can do the dance of trying to show them that
they avoided something and trying to quantify exactly what that is/was. A lot
of Demand tariffs actually punish lower kWh consumption, so you have to factor
that negative impact into the value analysis. A LOT of time goes into this when
you consider all the communication, data gathering, analyisis, presentation,
and negotiation. Remember, it only takes one 15-minute period that occurs
outside of your effective generation curve to blow the whole theoretical thing
up.
IF you are set on going thru the exercise with the intent of
predicting/promising something, you need a facility with a very stable load
profile that occurs during peak PV periods, stable utility voltage, a tariff
that doesn't punish lower consumption, reliably predictable & favorable weather
coincident with facility peak demand, a large PV to Load ratio (>50%), and
multiple inverters. The combination of requisite weather, PV:Load ratio, and
favorable tariff pretty much makes the number of facilites, which you can model
accurately, very small.
I recommend going to the beach or mountains instead.
$0.02001
Solar Janitor
----------------------------------------------------------------------
From: Joel Davidson
Sent: Thursday, March 18, 2010 7:47 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Demand Charge Reduction by PV
Hello Peter,
I have seen 40% to 70% monthly demand charge reduction for some
southern California PV projects for some months, but it is still a crap shoot.
15 minutes and 1 second of clouds during the peak demand period will trump a
client's energy management efforts unless they are willing and able to shed
loads during cloudy periods. I tell clients that they cannot rely on the
weather to cooperate, to monitor and control their demand, and to think of any
PV savings on their monthly demand charge as a windfall.
Joel Davidson
----- Original Message -----
From: Peter Parrish
To: 'RE-wrenches'
Sent: Thursday, March 18, 2010 9:38 AM
Subject: [RE-wrenches] Demand Charge Reduction by PV
I failed to clean up the subject line on this post a few minutes
ago. Please respond to this post so that we can keep track of the topic
properly.
Esteemed wrenches,
I have been wrestling with this concept about as long as we have been
in business. How to estimate how much a pv system will reduce the demand charge
for a customer.
I know the “worst case” goes as follows:
(1) Demand is based on measuring the consumption every 15 minutes
and keeping track of those numbers for the entire billing period.
(2) The customer gets socked with a demand charge that is based
on the highest 15 minute consumption for the entire billing period.
(3) The customer also gets soaked with a “facilities charge” that
is equal to the greatest monthly demand number for the trailing 12 months.
(4) Now you have a solar system pumping out Wac varying over the
familiar bell-shaped curve during the day.
(5) In the southwest US, peak demand typically occurs early in
the afternoon in the summer, during the week. Our LADWP has a mantra that goes
something like this, “Peak demand occurs at 3pm PDT on the third Thursday in
August!” I believe them.
(6) So one would expect something like 40% of the peak Wac to
offset the peak demand, but what happened if the sun goes behind a cloud for
those 15 minutes? Answer, “Bad luck. Your demand is back to what it was before
you bought your solar system.
(7) It is actually worse than that. Peak demand recurs with
approximately with the same value with some regularity for an extended period
of time, so the sun will have to shine with full intensity every day when peak
demand is expected to occur, which in LA could be every day (M-F) of the 30 day
billing period.
I have always taken the position that we can’t guarantee that any of
the demand charge will be reduced with a solar system. But what do other PV
integrators tell there customers? Better yet is there any actual data on demand
reduction with PV systems? It seems to me that occasionally the monthly peak
demand will in fact be shaved by PV production, the question is how often in
practice?
I once thought of taking actual insolation data and comparing it with
actual demand data and doing a Monte Carlo simulation (throwing the dice =
randomly matching up demand data with solar production data) – but I haven’t
retired yet.
I would love to hear what others are doing about this.
- Peter
Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave. , Los Angeles , CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parr...@calsolareng.com
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
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