planning a system to cover over 100% of current electricity usage

[halfmonkey]

I have a question about these solar companies designing a system and how they decide on the kW they account for. I've told every company that has come by that I want to cover 100% of my current electricity usage and actually go over to account for my kids growing up and using more electricity. I also explained to them that the readings/usage that our electric bill is showing is what it is because we're being cautious when using space heaters, a/c, and other big energy draws. I explained that once we have the solar panels installed, we may be a little more liberal in some of the uses so our electricity usage may increase.

It seems though whenever I mention that I want to have a system that covers maybe 110% or even 120% or 125%, they're all hesitant to go that high. One even mentioned that if he went too high, the local utility may not approve the permit request. Is this accurate? I ask because since we've been interviewing quite a few different companies, some have actually provided bids with more panels than others and they seem to have been confident that getting the permits would be no problem as they didn't even mention anything about permits and such. In other words, separate companies were designing systems using the same components but one would estimate 19 panels whereas another one would recommend 21 panels.

Does anybody have any information to share regarding exceeding my current usage or is it simply I can request up to whatever my wallet is willing to pay?

[Mike90250]

Most power companies, don't pay for "surplus" power when you offset your bill by 110%. It's money wasted. If you can show that next year, you will be adding a refrigerated room to your house, and expect your bill to increase 20%, you may make a sell-able case. Another block, is many areas have a 10KW limit to solar PV, any larger and you become a "Major" pain the in Grid.

[Volusiano]

Most utility companies, even when they pay for your surplus solar credits at the end of the year, would only pay you wholesale rate (if anything at all) -> dirt cheap rate compare to how much they sell their energy to you. So it doesn't make much economic sense to oversize your system, because you'd end up spending your hard-earned money to "subsidize" the utility company.

Another limiting factor is what the size of your circuit panel is. For example, if you have 200A service, there's only so much you can size your system before you start having to derate your service panel main circuit breaker, and only derate down to a point or you'd have to spend major $ to upgrade your circuit panel to a higher service.

[snic]

Most utility companies, even when they pay for your surplus solar credits at the end of the year, would only pay you wholesale rate (if anything at all) -> dirt cheap rate compare to how much they sell their energy to you. So it doesn't make much economic sense to oversize your system, because you'd end up spending your hard-earned money to "subsidize" the utility company.

That explains why some companies may have been unwilling to provide quotes for systems that produce >100% of current usage. But the OP is very clear that he expects his usage to increase.

To answer the OP's specific question: the size system that it makes financial sense to install depends on what state you are in and what utility you have (i.e., what are their rules governing system size and retail vs wholesale pricing for excess power you produce beyond what you use). You can find this info out from the state, the utility, and from a reputable local solar installer.

I my case, living in NY state and having Con-Ed as the utility, the state rebate applies only to systems that generate <110% of expected usage. Excess power is purchased by Con-Ed at wholesale rates. I'm installing a system that will generate about 106% of my needs in an average year. Even if we had room on the roof for more panels, it would not have made financial sense to install a larger system even though we anticipate greater power usage in coming years. That's because the rebate would not have been as big for such a large system.

[SUN Advisor]

There are different reasons as to why different solar companies would rather not oversize a PV system: 1. Increased monthly cost of system 2. Your local utility company might not pay you for the excess energy you produce. 3. The size of any local rebates is dependent on historical usage. 4. Certain municipalities will not issue a permit unless you provide them with electrical usage. 5. If you are leasing the equipment, the leasing company will not allow you to oversize the system. If you are buying the system, then it is easier to oversize the system as there are no restrictions, unlike a leasing company. By using TOU (time of use, if offered by your utility) you can generate larger credits with a smaller system.

A lot of it depends on area and utility company. Who are you with? What city?

[Volusiano]

By using TOU (time of use, if offered by your utility) you can generate larger credits with a smaller system.

This is very true and this is my strategy when I decided on how to size my system.

I'm on a TOU plan where I pay about 7 c/kwh during off-peak summer hours but 21 c/kwh (3x) for on-peak summer hours (1-8pm weekdays). I decided to size my system and place my panels on the west facing roof so that I will have maximum summer solar production during on-peak hours. Then I can use my solar energy for the AC and EV car charging as needed during on-peak hours and not have to buy on-peak energy from the utility company at 3x the cost. That means my solar generation has 3x the value (21 c/kwh) during on-peak summer generation, as opposed to just 1x value (7 c/kwh). This help shortens my payback period because I optimize my solar production to when it has the most value.

My winter on-peak hours from November through April, on the other hand, are 5-9am and 5-9pm, when there will be minimal solar production. So any excess on-peak summer credit I have will roll-over to the winter months and I can use these excess on-peak summer credits for heating (I don't have gas, only electric heat pump) in the winter on-peak hours when there will be minimum solar production. My utility company resets the year at the end of April and buys back any excess credit for dirt cheap at that point. I plan to have used up all the credits at that point so I'm not forced to sell my solar credits back to them for next to nothing.

I would not have considered an investment in solar if I could only use it to offset the 7 c/kwh cost I must pay to the utility company. That's just too low of a payback value for me. But if I can design it to offset the 21 c/kwh cost I would have had to pay to the utility company for the most part, now that's 3x the payback and a lot more justifiable an investment to me.

If you size your system to offset your entire electrical demand, then you don't want the TOU plan but want the basic plan instead, because at that point, it doesn't matter whether you pay $10/kwh or 1 c/kwh to the utility company. Everything nets to 0 and the utility price is no longer relevant as long as you're in the basic plan. But what's relevant is that you'd have a very bad investment if you size up your system for 0 net metering if the utility company charges you only 1 c/kwh. But it'd be a very good investment to size up your system for 0 net metering if the utility company charges you $10/kwh (I know it's an exaggeration here, but it helps drive home the point).

In my situation, I can't size up to 100% of my demand without having to beef up my 200A home service at considerable cost. So I only sized as high as I could (70% of my demand) without having to beef up my 200A service (I had to derate it down to 150A). Then I stick with the TOU plan and placed my panels where it'd give me the most production during summer on-peak time to maximize the value of my on-peak solar production.

As you can see, there are a lot of variables to consider and they vary greatly for individual situations. So you'll have to consider a strategy that works best for your case and not apply other people's strategy to your case because it may not fit. But usually the one rule of thumb that would apply in most cases is that you don't want to oversize your system needlessly. Even sizing it for 0 net metering should require careful consideration to make sure that you maximize your solar investment and not minimize it.

[SoCalsolar]

If you are connected to the Utility

If you are connected to the Utility then they will have much to say as far as the size of the system.
Which Utility are connected to?

[itnetpro]

Estimates

I told my Solar company that I was planning to get an electric car. They asked what kind and how many miles I was planning to drive and calculated that into my proposal for PECO. I was telling the truth and bought the electric car. You can use same angle with your guys and get what you want. The company I used was Astrum Solar. we estimated about 3,500Kwh per year for the car and so far we seem to be on target. Besides all these solar companies that guarantee your yearly output under estimate any way so they don't have to pay you the difference and in my case they were under by about 1,500 KWh.

John

[Naptown]

I believe Pa is similar to Md in that you are allowed to go up to 200% of historical use and they are required to allow it.
I have one starting today that is almost 200% of 5 meters which will be virtually aggregated. To stay within the 200% I had to have a rental
Unit on the property changed back to the owners name and account.
He will be selling electric to them.
Better than the wholesale he would have gotten

[SoCalsolar]

In CA some

In SoCal some utilities cap you at 100% some at 120% if you want to go above that they usually require a load justification, meaning receipts for a permanently attached device or electric car.

[OvertheSun]

Sdg&amp;e?

In SoCal some utilities cap you at 100% some at 120% if you want to go above that they usually require a load justification, meaning receipts for a permanently attached device or electric car.

SoCalsolar - do you know what the cap is for SDG&E? I would like to know because we are considering adding solar and a new HVAC system, but will probably do only one or the other in the next year. I'm thinking we should do solar first, for a number of reasons, but any cap on solar would obviously be affected by a more efficient HVAC system.

Our electric bills have been outrageously high - as in the HVAC contractor who gave us an estimate said he would have expected to find a marijuana grown in our attic with bills as high as ours (there is none), and many of the people we've talked to recently have told us it is the highest they've ever seen! My husband has just complained about it, never realizing how much higher it was than comparable houses. I've been taking a more active role over the past few months and have put everything on the table. Nevertheless, I would like to avoid being told what I can and can't do by SDG&E.

[J.P.M.]

SoCalsolar - do you know what the cap is for SDG&E? I would like to know because we are considering adding solar and a new HVAC system, but will probably do only one or the other in the next year. I'm thinking we should do solar first, for a number of reasons, but any cap on solar would obviously be affected by a more efficient HVAC system.

Our electric bills have been outrageously high - as in the HVAC contractor who gave us an estimate said he would have expected to find a marijuana grown in our attic with bills as high as ours (there is none), and many of the people we've talked to recently have told us it is the highest they've ever seen! My husband has just complained about it, never realizing how much higher it was than comparable houses. I've been taking a more active role over the past few months and have put everything on the table. Nevertheless, I would like to avoid being told what I can and can't do by SDG&E.

1.) I do not believe SDG & E limits the size of a solar electric system as long as it's less than one MEGAWATT, per their literature. That's much larger than any homeowner is likely to ever need. I'm aware of many oversized and thus non cost effective systems that have been approved and are running in San Diego county. Check the SDG & E website, including the net metering portions.

Perhaps a dirty little secret is that utilities may have discovered that overall usage (not bills) for solar electric owners goes up, thus making any bill reduction perhaps less than anticipated over time. If something costs less, people tend to use more of it. Possible bottom line: bills drop, usage increases.

2.) The good news is your bills are high probably at least partially for reasons you can mostly control yourself. Get an energy audit ! Not knowing why your bills are high means you will have a harder time finding cost effective solutions if that's what you're after. My experience is that high usage is often the result of lifestyle choices and ignorance with respect to energy use.

3.) SDG & E already has the ability to know what you're doing if they take the time to look (if they want), and will tell you what they want regardless of what you want to avoid.

4.) Throwing expensive solar at a high electric bill is like buying a bigger, very expensive pump for a leaky boat when it may make more sense to find and plug the leaks first.

5.) It's almost always less expensive to not use something than it is to get more of it. reduce your use and conserve first.

[OvertheSun]

[QUOTE=J.P.M.;92056]1.) I do not believe SDG & E limits the size of a solar electric system as long as it's less than one MEGAWATT, per their literature. That's much larger than any homeowner is likely to ever need. I'm aware of many oversized and thus non cost effective systems that have been approved and are running in San Diego county. Check the SDG & E website, including the net metering portions.

Perhaps a dirty little secret is that utilities may have discovered that overall usage (not bills) for solar electric owners goes up, thus making any bill reduction perhaps less than anticipated over time. If something costs less, people tend to use more of it. Possible bottom line: bills drop, usage increases.

2.) The good news is your bills are high probably at least partially for reasons you can mostly control yourself. Get an energy audit ! Not knowing why your bills are high means you will have a harder time finding cost effective solutions if that's what you're after. My experience is that high usage is often the result of lifestyle choices and ignorance with respect to energy use.


Thanks so much for your response! I'm already there with the energy audit and energy efficiency steps. I am now a huge proponent of LED lighting. We've replaced most of 65W BR30 bulbs in recessed lights and within the next month or so will have replaced nearly all the lights in the house with LEDs. The only ones left are those that are more difficult to find LED replacements for, like bi-pin halogens and some candelabra base incandescents. We've also added dimmers, occupancy sensors, dehumidstats for bathroom fans, window film and started adding reflective barrier. In just a couple months, we've had more than a 50% decrease in kWh/day (75% on some days).

In our climate, the effect of countering the heat generated by incandescent light bulbs with AC is even more significant than the light itself. We have enough can lights in this house that when they were all turned on using incandescent 65 W bulbs it raised the temp by about 10 degrees F in one hour (calculated and observed). With LEDs, the temp increase is negligible and the energy use with dimmers is probably 3-5 Watts/bulb. Overall, our house, which is only 11 years old, is pretty well sealed and insulated. The energy audit analyses for those areas indicated only small, incremental increases in efficiency by adding more insulation and if we sealed much more, we'd need to add mechanical ventillation. Of course there are other things we can do, but with diminishing returns.

The biggest remaining issue is our HVAC system. Not only is the equipment inefficient, but the ductwork was not sized properly to distribute the air to all the rooms of the house evenly. I work from home and to keep my office cool enough to tolerate, much of the rest of the house is too cold. So I've added a room AC to my office, but its only a stop-gap measure and it is noisy. We have 2 zones now (upstairs and downstairs), but that's as far as we can go with our current equipment. I'm looking at an iQdrive split system with modulating compressors and blowers and up to 16 individually controlled zones. We would also replace most of the ductwork and add more returns, which have been recommended by at least 5 different HVAC contractors and the energy auditor. It should pay for itself in energy savings in a few years, but it has a pretty hefty upfront price tag and there are fewer incentives and rebates than for solar.

I want to eventually replace both the HVAC system and install solar. I know the conventional wisdom is to replace the HVAC before adding solar, but with the tax incentives set to expire in 2016 and the reallocated CSI funds available to CCSE/SDG&E customers for residential solar limited, it seems sensible to me to do the solar first, even if we can only guestimate our final load after eventually replacing the HVAC, too. My very crude approximation is that we would need about an 8-12 kW system for 100% solar after all the other energy efficiency measures, including HVAC, and that has the same ballpark net pricetag as the new HVAC system we're looking at.

Do you think this reasoning makes sense?