ISO examples of real-life solar calculations

[johnbro23]

I'm about a year out from buying my first home, and I really want to know if solar will make sense, even at an initial stage.

Can anyone share their own calculations for solar? I'm interested in details like cost of system, annual energy cost savings, electricity needs (are you also heating your home with electricity? Have an electric car?), state of residence (incentives? local energy cost? solar production capability?).

I'll be looking for a 3-4 BR on Long Island, NY - I'm optimistic that it'll make financial sense to go solar, but hoping I can learn from the community here. Thanks in advance!

 

[Ampster]

Try Google project sunroof. I recently bought a second home and it was one of the things I factored into the purchase.
Project Sunroof

 

[RedMS]

Try Google project sunroof. I recently bought a second home and it was one of the things I factored into the purchase.
Project Sunroof

How accurate did you find their estimates?

 

[GenSao]

How accurate did you find their estimates?

Their estimates are pretty close.

For my address, I had 5.7 KW Solar Array Installed. Using an average energy bill of $150 (My actual is closer to $160, but not an option), the website estimated a 5.5 KW System needs to be installed with an upfront cost of $20,732. My actual cost was just under of $21,000.

 

[Ampster]

How accurate did you find their estimates?

Very accurate as to square footage. Not enough history yet to say anyhing about production..

 

[BerTX]

Just be aware that utilities in some areas can change the rules at any time. Doing solar for economic reasons is not a sure bet. Do it for environmental reasons, and keep the economics as a bonus.Unless you are going off-grid, your economics can change with management change.

My system went from paying for itself in 8 years, to basically never doing so. Utility quit doing net metering. I had a "contract" with them, but they broke it.

 

[WannabeOwner]

I'm about a year out from buying my first home, and I really want to know if solar will make sense, even at an initial stage

The view from over this side of the pond is probably different, and we are higher latitude too ... so much less benefit from Solar in Winter ...

... but I would spend my first $ on insulation, and my second $ on Solar etc.

Energy is dirt cheap in USA compared to EU - pity IMHO as higher tax would kick-start more saving measures. So probably insulation too expensive to consider in USA. We have Passive House, needs virtually no heat in Winter (max day winter temperature here probably 10C, 0C overnight common, -5C overnight on a fair number of winter nights, and below -10C maybe once a decade), and is equally slow to overheat in Summer. The reckoning over here is that passive House adds (from memory) 7% to the cost of a new building, there is no central-heating system installed (that saving also contributes to the insulation cost), and of course no maintenance, replacement, nor heating fuel! for the lifetime of the building. Its hermetically sealed, so no draughts, and very comfortable - mechanical ventilation, with heat recovery, provides high number of [filtered] air changes, so better quality air than standard houses - and no damp / mouldy spots where air doesn't reach etc.

If the sums don't quite work for you then you might want to consider the difference as a charitable donation - the good news being that that charity starts at home! I appreciate that first time house buyer probably has no spare cash for such thoughts, but just thought I'd mention it.

 

[Ampster]

I agree, insulation is the low hanging fruit of energy conservation. In California we have a strict energy code that is moving toward zero net energy. (Title 24). It is a complicated calculation that looks at the entire building envelope.

 

[WannabeOwner]

moving toward zero net energy

Here in the UK the Building Regulations still allow really poor housing stock to be built. It annoys me, because in a few years time they are going to have to be upgraded, which is a much more difficult, and expensive, job than doing it at initial build. If we up'd the requirements for new build (same for everyone, level playing-field) we would reduce oil imports, and all the savings that go with that ...

... but we elect out Government for a 5 year term so nothing like this ever gets done ...

 

[bkp_duke]

Just be aware that utilities in some areas can change the rules at any time. Doing solar for economic reasons is not a sure bet. Do it for environmental reasons, and keep the economics as a bonus.Unless you are going off-grid, your economics can change with management change.

My system went from paying for itself in 8 years, to basically never doing so. Utility quit doing net metering. I had a "contract" with them, but they broke it.

Sounds like it is time to consider a Powerwall and give the big middle finger to the utility co.

 

[BerTX]

Sounds like it is time to consider a Powerwall and give the big middle finger to the utility co.

I keep trying to justify it, but it just doesn't work in my particular situation. Maybe in a few years when my lifestyle settles down.

 

[Ampster]

I keep trying to justify it, but it just doesn't work in my particular situation. Maybe in a few years when my lifestyle settles down.

The only insurance you can get from utilities changing the rules is to buy as little as possible from them that does not mean going off grid. It is simply about striking a balance. I have invested in future protection by installing batteries that I can program to load shift and arbitrage rates.

 

[BerTX]

The only insurance you can get from utilities changing the rules is to buy as little as possible from them that does not mean going off grid. It is simply about striking a balance. I have invested in future protection by installing batteries that I can program to load shift and arbitrage rates.

My situation differs. I would only save a small amount each month, and there is just no way to justify the expense of the batteries and I would still need a generator on top of that. I'm mad, not stupid.

 

[TheTalkingMule]

There's no straight answer to this question. As others pointed out, it purely depends on the whims of your state utility commission. Those whims are often dictated by legacy fossil fuel interests, so figuring out your payback is tough.

Where do you live?
Who is your utility provider?
Is your governor a scumbag?

Solar itself is extremely inexpensive, but the in's and out's of the buying decision are super complex. Not many states provide their citizens financial certainty at the point of sale, so calculating your compensation from the grid IMO is impossible in half the markets in the US.

All that uncertainty also adds cost to your purchase. Sales cost can be $3-6k or up to 35% of your purchase price.

Since only 20-30% of the electricity produced on your roof is actually consumed by your home, the whole equation depends on how much you're compensated for pushing juice to your neighbors. That's the question you need answered.

 

[robynum]

The solar equation is not a simple one. There are lots of variables:

1. The orientation of your house (south facing is best).
2. What type of roof do you have...hip roof is the worst, basic a-frame is good, flat roof is the best.
3. What state do you live in? States like California promote renewable energy, provides incentives, and forces the utility companies to cooperate.
4. How many sunny day do you get a year...cloudy days are not good.

Additionally, you really need to do your homework so you understand what you're getting because all solar installations are not the same. As mentioned above, only about 20% of the energy produced by the panels actually get used by your house, therefore you want to get the best equipment. The panels produce direct current (DC) but your house uses alternating current (AC). Solar installations use an inverter to convert DC to AC, therefore the efficiency of the inverter is key. Some systems use a single inverter with the panels strung in series, some use enhancers on each panel to a single inverter, and some apply an inverter to each panel to produce a parallel configuration (which i think is optimal).
The panels themselves have differ ratings as well...currently there are two companies producing 360w panels which may improve in the future.

The amount of energy you use, the size of your system, the cost and the relation with the utility company will determine the length of your payback window. I live in California and I'm in the process of getting my second system installed...different residence from the first.

I'm a believer!

 

[NuShrike]

[snip]As mentioned above, only about 20% of the energy produced by the panels actually get used by your house, therefore you want to get the best equipment.
[snip]

You mean < 20% of the sunlight? If sized 1:1, most of the energy produced by the system is used by the house.

~97% (depending on inverter efficiency) of the energy produced by the panels get used by the house.

For insolation estimates, PVWatts (esp with the TMY data). There's also SAM if you want to get into extra detail.

 

[GenSao]

NuShrike,

One can't directly use solar power at 1:00 a.m.

To clarify, I believe TheTalkingMule was referring to 20% of the solar produced would DIRECTLY be used by the house at the time of production. The other 80% of solar produced would generally: (1) be sent to the grid and used as credit for power use at a later time based on a Time of Use (TOU) Agreement or (2) stored locally in a battery for use at a later time.

 

[Gwgan]

You can probably find nearby real-world comparables at PVOutput
Pay for solar now if you have the money and don’t pay for electricity later (good plan if the price of power goes up).
First Insulate, then insulate some more and then add an HRV because the house is so tight. Then you can live off a small solar roof.

 

[Brovane]

I'm about a year out from buying my first home, and I really want to know if solar will make sense, even at an initial stage.

Can anyone share their own calculations for solar? I'm interested in details like cost of system, annual energy cost savings, electricity needs (are you also heating your home with electricity? Have an electric car?), state of residence (incentives? local energy cost? solar production capability?).

I'll be looking for a 3-4 BR on Long Island, NY - I'm optimistic that it'll make financial sense to go solar, but hoping I can learn from the community here. Thanks in advance!

I found this website at NREL to be very helpful for my PVWatts Calculator my calculations.

 

[kc_moses]

This is the calculator I use to determine solar production capability, and it's very close to the the KW that the solar installer quoted me:

How to calculate the amount of kilowatt hours (kWh) your solar panel system will produce - Solar Power Rocks

When I first sit down with the solar sales person, we went through the numbers, like how many KW I use per month, from that number, we determine the number of solar panels I need. Once we know the number of panels I need, then the next step is the cost (panels+inverter+hardware+labor). Then take that number minus the Federal Tax Credit, divide by the number of months to finance the panels, and that's the amount I would pay/month.

When I first see the number, it wasn't that impressive because it doesn't show a significant amount of saving. However, if you look for long term, it may change the perspective. For example, your local utility company may be charging 6 cent/Kwh, but in 5 years, they might raise the price to 15 cent/Kwh (inflation, high fossil fuel cost etc) , so you are at the mercy of the utility company. By going solar, I might be paying higher than 6 cent/Kwh at this instant, but I lock in that rate for the next 15 years (my solar finance term). And once the 15 years is up, I don't have to pay "any utility" provided I have the Powerwall battery.

I don't know about your utility company, I have been through many utility companies who raise their rate 10-17% per year.

Bottom line, if you stay in the house long enough, you will get some return of investment, if you don't plan on staying in the house more than 10 years, probably not worth it. I talked to appraisal company, having solar panel do not increase your property/resell value.