How to I compare system size rating to my electric bill?

[gte]

Can anyone explain how solar panel kwh ratings are calculated? If a system is rated at 5kwh, is that per 24 hour day of direct sunlight, or how is that rated? My electric bill is kwh per month and I would like to see what type of system I would need for 100% solar power (guestimation).

I was reading this article and trying to become more educated on this, and have not found a definitive answer explaining this yet.

http://americasmarkets.usatoday.com/2014/10/08/solarcity-lets-homes-buy-solar-with-no-upfront-costs/

Thank you

[J.P.M.]

Can anyone explain how solar panel kwh ratings are calculated? If a system is rated at 5kwh, is that per 24 hour day of direct sunlight, or how is that rated? My electric bill is kwh per month and I would like to see what type of system I would need for 100% solar power (guestimation).

I was reading this article and trying to become more educated on this, and have not found a definitive answer explaining this yet.

http://americasmarkets.usatoday.com/2014/10/08/solarcity-lets-homes-buy-solar-with-no-upfront-costs/

Thank you

I'll take a shot.

A 5 kW system will produce power at the rate of 5kW when the solar irradiance is crossing the plane of the solar array at the rate of 1,000 Watts/m^2. The solar irradiance is rarely at that high a level and is changing constantly. The 5kW rating is indeed for rating/sizing purposes, not unlike horsepower ratings for an ICE.

Look up and spend a few minutes with something called PVWatts. Read all the help screens first. Depending on a lot of stuff, a 5 kW sys. will likely produce REAL ROUGHLY somewhere between 7,000 and 9000 kWh/year +/- some if facing mostly south with little shade, depending on where you are located.

Do as you please, but a 100% offset of your electric bill is often not the most cost effective way to go. Read prior threads for logic/opinion/reasons why.

[inetdog]

Can anyone explain how solar panel kwh ratings are calculated? If a system is rated at 5kwh, is that per 24 hour day of direct sunlight, or how is that rated? My electric bill is kwh per month and I would like to see what type of system I would need for 100% solar power (guestimation).

I was reading this article and trying to become more educated on this, and have not found a definitive answer explaining this yet.

http://americasmarkets.usatoday.com/2014/10/08/solarcity-lets-homes-buy-solar-with-no-upfront-costs/

Thank you

As J.P.M. noted, PV systems are typically rated in kW (their rate of energy output at any particular time) and it is up to you to convert that to kWh (a unit of energy, not power) based on the sun conditions where you are.

If your POwer COmpany (POCO) has time of use or consumption tier based rates, then you may get the most bang for your buck offsetting the higher time rates and the higher usage tiers instead of trying to match 100% of your consumption. The difference is based on the fact that 50% of your consumption may be responsible for 90% of your bill.

PS: Welcome to Solar Panel Talk!

[gte]

Thanks for the replies and the welcome.

I found out that there are calculators online that do most of the work

If the 5kwh system cost me less than $75 a month I would be in the positive (at today's electric rates for my area)
If the 10kwh system cost me less than $149 a month I would be in the positive (at today's electric rates for my area)

Looking at my electric bill, I do not have tiered kwh rates based on time used, although I believe there is a program you can enroll in to take advantage of that.

Ideally, I would like to get a net meter and install my own solar system. Although I'm a newb here and to solar, I'm quite well versed in circuitry, dc electronics and wiring and a/c wiring and theory, but I don't know if this is feasible or what an uninstalled system would (approximately) cost.

http://pvwatts.nrel.gov/pvwatts.php

Here were my results

[gte]

Here is what an advertiser from the site says:

With this, I'd be around $187 per month (with them installing it) with no interest and system would average saving me $276 per month ... that's pretty solid. I imagine that if I installed a system, I could average $1200 a year in savings based on this information.


Solar Energy Services Inc.
Phone: 410-923-6090
4.97/5 from 33 Reviews
System Size: 18.55kw
Annual Power Generation: 23081 kw/hours
Executive Summary - cash purchase
Gross cost: $64,925
Clean Energy Grant Program - Residential Solar PV ($ 1k, 20kW max) -$1,000 » link
Federal Tax Credit (30% of Net Cost at Installation) -$19,178 » link
Net Cost of System after rebates and incentives: $44,747

Production Incentives
MD Clean Energy Production Tax Credit $196/year » link
Maryland Public Srvc Comm - SREC purchase: $ 0.13 per kWh (2014-2015 market rate) $2,997/year » link
Pay Back Time: 7.09 years
Internal Rate of Return (IRR) on Investment: 14.1%
This is an amazing return given the stock market has averaged only a 9.7% return since 1962 and money in the bank earns less than 2%.
Executive Summary - Zero Down Leased Option
Original Monthly Utility Bill: $300
New Monthly Utility Bill: $0
Monthly Lease Payment: $302
Monthly Production Incentives (average): $253
Monthly Savings after Lease Costs: $251
Monthly Profit/Loss Year 1: $3,010
Total Profit/Loss over the life of the system after all repayments: $75,256

[J.P.M.]

As J.P.M. noted, PV systems are typically rated in kW (their rate of energy output at any particular time) and it is up to you to convert that to kWh (a unit of energy, not power) based on the sun conditions where you are.

If your POwer COmpany (POCO) has time of use or consumption tier based rates, then you may get the most bang for your buck offsetting the higher time rates and the higher usage tiers instead of trying to match 100% of your consumption. The difference is based on the fact that 50% of your consumption may be responsible for 90% of your bill.

PS: Welcome to Solar Panel Talk!

I must correct an error to my prior post in the form of an omission: The temp. of the panels for the measurement process is 25 deg. C. Higher panel temps. will lower the output by something like .5% per deg. C. r so. I apologize for the error.

[J.P.M.]

I'm ignorant of MD incentive/SREC situation, but I'm curious about the assumptions used to get that rate of return. Often vendors use unrealistic assumptions or SWAGs that paint a rosy picture. As usual, Caveat Emptor. Also, ignorant of the MD situation or not, before I sprang for a system that met a 24,500kWh/yr. load, I'd have a serious conservation intervention. But, like I said, do as you please. Pay your money, take your choice.

[gte]

Again, I'm just learning, so no money would be spent for many months. I'm not willing to spend thousands without knowing exactly what I'm doing and being 100% confident in the results. I'm definitely not even close, but would like to purchase a system before the 30% credit disappears.

I'm ignorant of MD incentive/SREC situation, but I'm curious about the assumptions used to get that rate of return. Often vendors use unrealistic assumptions or SWAGs that paint a rosy picture. As usual, Caveat Emptor. Also, ignorant of the MD situation or not, before I sprang for a system that met a 24,500kWh/yr. load, I'd have a serious conservation intervention. But, like I said, do as you please. Pay your money, take your choice.

[gte]

Thanks for the replies JPM.

Another thing that is a little confusing, the credits.

The fed gives you 30% back of your installed price for a tax credit. Is this a direct refund, dollar for dollar or do you get to deduct that number from your AGI?

From my research, Maryland has a grant of $1000 for initial system purchase and Maryland SREC's are $132 per 1000 kwh, so if I produced ~23000kwh of solar, it is worth about 3k in SREC. It looks as if SRECS will plummet in price after 2018 or 2019 because the fee for not having enough SREC's will be around $100 in Maryland with the current legislation. So at the start of a calendar year, if I sell my SREC's, is it a lump sum? If so, that averaged $250 a month will be enough to offset my energy costs for the next few years while SREC's are still valued at around $130 per.

Is my understanding of the math correct, or am I wrong?

Also from my reading, it appears that time is of the essence to a point, and it would be financially foolish to wait a few years on this.

[J.P.M.]

Thanks for the replies JPM.

Another thing that is a little confusing, the credits.

The fed gives you 30% back of your installed price for a tax credit. Is this a direct refund, dollar for dollar or do you get to deduct that number from your AGI?

From my research, Maryland has a grant of $1000 for initial system purchase and Maryland SREC's are $132 per 1000 kwh, so if I produced ~23000kwh of solar, it is worth about 3k in SREC. It looks as if SRECS will plummet in price after 2018 or 2019 because the fee for not having enough SREC's will be around $100 in Maryland with the current legislation. So at the start of a calendar year, if I sell my SREC's, is it a lump sum? If so, that averaged $250 a month will be enough to offset my energy costs for the next few years while SREC's are still valued at around $130 per.

Is my understanding of the math correct, or am I wrong?

Also from my reading, it appears that time is of the essence to a point, and it would be financially foolish to wait a few years on this.

You're Welcome.

IMO, All good questions. What follows is mostly opinion given with the caveat that I am NOT a tax advisor or accountant. I suggest you consult your tax advisor for better information on tax questions/matters anyway.

On tax credits, the fed. tax credit is indeed a tax credit, not a deduction. However, you do not get a refund check specifically for the solar tax credit. The credit comes off the bottom line of fed. income tax owed. The fed. solar tax credit amount is reduced by other state/local credits and adjustments from utility or vendor rebates. Again, I'm ignorant of MD opportunities/requirements. Perhaps others more knowledgeable can clarify or input more complete/accurate info with respect to MD.

The future of SRECs everywhere, like the future of utility rates, is a crap shoot. Educated guesses are always possible and may or may not be reasonable or accurate. I'd only suggest that anyone who claims they know for certain what the future holds has a better crystal ball than I. In general, the farther into the future I gaze, the thicker my cataracts get.

On the question of waiting: Like everything else, and without trying to duck the question, "it depends". Moving now (up/running before 01/01/2015) will get you 3 years to chew up the fed. tax credit rather than 2, so that may involve some tax planning. On the other hand, it's getting a bit late in the year and haste makes waste. Hussling up to get in this year may cost extra in money and also result in lower quality.

I'd consider possible acceptable, or at least tolerable life style adjustments to reduce the bill, and then study up on conservation measures that make sense to you and then implement those changes before solar electric. If you want the most cost effective path to a lower bill, that, IMO, is the best road to take.

Depending on how one sees life, it's possible for most folks to live comfortably using a lot less elec. It saves the most money, and as an often overlooked benefit, it reclaims some control given to the utilities by the profligate overuse and waste of electricity that results in dependence and consequent loss of some freedom of choice. But, to reiterate, it's a free country. So, pay your money, take your choice. I'd only suggest that you use your brain to read, study, think, learn, and repeat the process so that when you do make a choice, you walk in with your eyes and brain open.

[gte]

Well I have contacted Solar City and will await a reply from them.

They are going to size the system based on my last years electricity usage at a delivered price of about 13.6 cents a kwh, which is

09/2013 - 2088kwh/$303
10/2013 - 1464kwh/$213
11/2013 - 2245kwh/$312
12/2013 - 4319kwh/$589
01/2014 - 4678kwh/$629
02/2014 - 6176kwh/$828
03/2014 - 3752kwh/$506
04/2014 - 2401kwh/$326
05/2014 - 1621kwh/$223
06/2014 - 1626kwh/$221
07/2014 - 2048kwh/$264
08/2014 - 1729kwh/$224
09/2014 - 1808kwh/$246

[inetdog]

With those bills in winter months, it looks like you may be using electric resistance heating. If you are, then spending a few thousand on a heat pump could pay back the investment faster than the same amount of money on solar PV. Or are the winter temperatures too cold for an air source heat pump?

[gte]

It's a new heat pump, it was very cold last year, especially that month. Normally the coldest months are a little less than $600 or approximately 4500kwh.

Is there a preferred DIY solar panel seller? Or a list of panels that are recommended?

[J.P.M.]

It's a new heat pump, it was very cold last year, especially that month. Normally the coldest months are a little less than $600 or approximately 4500kwh.

Is there a preferred DIY solar panel seller? Or a list of panels that are recommended?

So are last winter's bills with the old heat pump or the new one ?

[gte]

The new one

So are last winter's bills with the old heat pump or the new one ?