GM Volt Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
Has anyone out there designed a stand-alone off-grid solar system that relies on charging up an array of batteries during the day, and then using that stored energy to charge up a Volt at night?

Yes, yes, I understand that it would cheaper to use mains power, but this is not an ROI calculation.

I understand via this forum that it takes ~10 to 14 kWh to charge the car? What would I need via a stored array to meet those requirements?

Thanks,

RedVolt... Car on order, status 1102.:cool:
 

·
Registered
Joined
·
857 Posts
You might want to take a look at Homepower magazine. They have a interesting library of articles describing all kinds of on-grid and off-grid photovoltaic options.

The link to the mag is: http://homepower.com/home/

WVhybrid
 

·
Registered
Joined
·
5,486 Posts
Simple formula is to take the Solar array size and compute an average output of 2.2 times that per day. So, imagine 10kWh Solar system - that's about 22kWh on average. Some days it would be 40kWh but others under 20 if it's rainy, really hot, really cloudy, etc.

Would you consider an on-grid system instead? It will be much more cost effective.

You wouldn't use the power just to recharge the car. It would be to power the house too, right? You need to know your home's kWh usage on a monthly basis now and figure in the additional 12.5kWh per day driven or about 375kWh/month if driven 30days/mo. 375kWh = ?? today on your electric bill. Mine would be 375*.18=$67.50 (but I also don't drive every day, so for me it differs)

An off-grid system of about 10kW (appx. 45 * 235W panels) would do it - but then batteries are the key. I've heard that the 2 Volt batteries are best for off-grid but I think that is for 12v homes (like cabins in the mountains). 120v would be better with 12v or higher voltage batteries. The # of batteries and their capacity is what needs to be looked at. Keep in mind that 1000 50% discharge cycles is about what the batteries are rated for. That is "only" 3 years of recharging the car daily and normal home use, perhaps. If that is how the system is used, it may require new battery sets every 3-4 years. I just don't see the cost-effectiveness of Off-grid solar for our EV and full home use in modern society. Off-grid is best for standby-power in case the grid goes down. As a "battery backup" when you have Solar PV as your primary power during the day but use grid power at night. Off-grid is also good for very rural homes or mountain cabins. If you have an On-grid solar system, your electric bill can be zero for the year if you size it right. But that's before adding the Volt to the equation.

The problem with battery storage on a daily basis is their wear. I believe that there is technology for Solar farms that will store power in underground salt pits or caverns full of compressed air (a bit like a water reservoir for hydro). But battery chemistry wears out and thus just like the Volt is only warrantying the battery for 100,000 miles (a few thousand recharges) - an Off-grid solar storage system cannot last forever if discharged daily.

http://www.renovusenergy.com/battery_bank_sizing.html

Notice there that 10kW systems would output an average of 28kWh a day - half for the Volt and half for the house. I hear that off-grid systems don't really like to fully-cycle their batteries every day. Just like the Volt, running within a middle-band of discharge is best for longevity of the storage batteries. So "more batteries, the better" to limit the discharge depth. If your daily load on the storage pulls 1/2 the charge normally, that is better than pulling daily 3/4 or 7/8th storage. The reason is that the Sun may not fully recharge the batteries every day. It will be cloudy. You should size the system based on Average solar storage and not maximum.

www.wholesalesolar.com is a good site to look at "parts pricing". Add about 30-40% to such prices for installation by a reputable installer.

I priced out a 6.5 kW on-grid system here in PA. It was $33,500 installed (had another quote of $42k - so your results will vary). That would have gotten me about 8000 kWh of power per year - which is about $1520.00 of local power company costs/year. Minus incentives such as 30% federal and yearly "Solar RECs" which also help pay back the system -- without incentives, you have like a 20 year pay-back for an on-grid solar system. Off grid prices are approximately double that of on-grid due to battery costs, charger cost and a little more maintenance. My payback computation (doing it my way not the installers) for an on-grid was 7.5 years. Of course, it would require financing so that ROI cost goes out to 8.5 to 9 years with the added interest. Installers praise the SRECs and super-high rate of increase of kWh on the grid - but they lie (don't sales folks lie as a rule?? :) )

My guess for you for a well-sized system would have to be at least $50K for a large enough system to go off grid for the house and to recharge the Volt daily. I really think you should do that rather than "just for the car" charging. You can definitely benefit from powering the house on Solar - I don't think the Federal tax credit is available for a utility system (just-for-car) but is for a full-house system. On-grid discounts for off-peak charging is very good incentive to get a 2-meter setup with the local power company to charge at night at what may be sub .10/kWh.

I learned a lot attending the Pennsylvania Renewable Energy Festival in 2010: http://www.paenergyfest.com/ There, I learned that "Solar is good but not cost effective". If you want to be green, don't mind the up-front costs and want to deal with selling Solar Credits every year for the next 10+ years (and they may go away) then go for it.

I met a guy there with a Tesla, electric lawn mower and a 14kW home solar system. He has spent over $150K on Solar and Electric things like the Tesla roadster. Total gear-head in terms of going green. Everyone has their incentives and his was getting off foreign oil and being responsible. Plus, seemed to have the resources to do it.

Thinking about it more - you may want to find out if there is a DC-charging option? It would be far more efficient to go DC all the way - the Volt recharges off 110v/220v AC but converts that to DC. It would be great to have a Solar system store in a battery array in your garage and then do a DC charge directly to the Volt (or any EV). Switching from stored DC batteries up to AC and back to DC is very lossy. Staying DC directly would save possibly 1kWh during recharge (that's just a guess).

I'm no expert but I've learned the above by doing some research (yes, homepower.com is well worth the subscription costs). Also ran RC car racing for a few years and that taught me a lot about DC battery charging, LiPO and NiMH batteries and so on. It transfers somewhat nicely to today's EV world.

Bottom line - I wouldn't buy an on-grid PV Solar system unless I can get it installed for under $5 per Watt. That day will come, but just not here yet. I wouldn't buy an off-grid battery-storage solar system for recharging an EV due to the continuous need to buy batteries every 4 years or so. What I would do to go green is what is most easily attainable - conservation. Get a Kill-a-watt device, find out where your electric usage wastes are and cut back. I've already dropped 800 kWh hours off my monthly bill by doing this and being smart with power consumption. That's enough to recharge a Volt every day.
 

·
Registered
Joined
·
10 Posts
I have a 4kw grid tie net metering solar system on my home. It generates about 7500Kwh/year in Northern California. The season is very important. This power varies with a sine wave over the year reaching a minimum geneated per day of about 9Kwh/day and climbing to about 30kw/day in the summer. You can definitely see the day of minimum and maximum sun. So if you only use it for the volt it would either be very oversized or lacking in the winter. I've had my volt (#231) for a month today. I'm planning on a seperate meter for low rate 220 charging offered in N.California.
 

·
Registered
Joined
·
857 Posts
Bonaire, that was an excellent summary. :) You've obviously spent a lot of time and effort to understand the technology and the market. Waiting a few more years may be beneficial. Prices have come down a lot lately. Seems like the switchgear (inverter, disconnect, etc.) cost about the same as the solar panels these days.

WVhybrid
 

·
Registered
Joined
·
5,486 Posts
Solar panels are still a large portion of cost. I priced out my 6.5kw system (that I didn't install) with 235W panels from a US-made supplier (Motech, located in Delaware). Each panel would be $531 * 30 for almost $16K. THe inverter was at $3K. Wiring, meters, installation and all that making the remainder of the $33.5K total price. So, panels are 1/2 the cost and labor a necessary evil but the state won't pay the rebate without a certified installer on their list.

There is a lot of engineering, township building permits and state forms to fill out to get into the PA sunshine program in order to sign up for the rebate. I just didn't see saving $200 a month on electricity worth that amount of up-front cost. I found a savings of $100/mo or so by conserving and trying to cut back on power waste. For example, my wife used to leave a desktop PC and LCD monitor on at all times but rarely use it. And our multi-function fax/printer was also a high consumer. I cleaned our two refrigerator coils which helped. I also educated my kids on turning off lights in rooms when not in them, etc. A Kill-a-watt device is great to know what's going on.

Also - side note. My sister-in-law and her husband put in a 1.8 kW system. That's 8 panels on their roof. And they paid too much. The installers I talked with said it's not cost effective to do a Solar system under 2.5 kW if you intend to "save money" over your local utility and get a good ROI. You would only do it if you wanted to be green in your power usage. The larger the system, the more cost-effective it is.

If you're in a state like WV or KY which have good kWh prices for electricity, Solar also doesn't make "monetary sense" either. Unless, again, you want to cut back on your "carbon footprint" and all that. In places like CA, where kWh costs go up - Solar is big. Some installers take advantage of that and jack up their system prices because of this so be careful and bargain hard.

http://www.green-energy-efficient-homes.com/how-much-does-electricity-cost.html
 

·
Premium Member
Joined
·
14,156 Posts
Simple formula is to take the Solar array size and compute an average output of 2.2 times that per day. So, imagine 10kWh Solar system - that's about 22kWh on average.
...
I priced out a 6.5 kW on-grid system here in PA. It was $33,500 installed (had another quote of $42k - so your results will vary).
...
Bottom line - I wouldn't buy an on-grid PV Solar system unless I can get it installed for under $5 per Watt. That day will come, but just not here yet.
Your production will vary depending on the location so a single formula won't work very well. Where I am the actual number is more like 4.25x rather than 2.2x. I'm in a sunny area but location isn't ideal (too close to the water) although the roof is well situated and has a pretty good slope. So in your 10kW example where I am you'd expect 42 kWh on average.

FWIW your estimate was only a small amount above your $5/watt target. Panel prices are dropping at a rate of roughly 1% per month so you might be there if you check again.
 

·
Registered
Joined
·
500 Posts
I may look into going solar after my next renovation is done. In Ontario, they are really trying to encourage rooftop generation; the provincial energy board is buying power from residential rooftops at a rate of 80.6 cents/kWh, with a 20-year guaranteed contract. Considering that the most expensive peak rate is about 16cents/kWh, it's a no-brainer to sell everything back to the grid here.

The only problem is that solar only generates power here for 8 months of the year. I don't even know how I would prevent snow from piling up on the panels in the winter.

Luc
 

·
Registered
Joined
·
462 Posts
Is it a 2 story home? I would say a nice long squeegy or something should be able to pull the snow from the panels. I don't think there is any way to do a heat method of quick melting the snow off, which would undoubtedly eat into your profits too. :)
 

·
Registered
Joined
·
5,486 Posts
Luc,
In Ottawa you do have limited winter sun, but it won't be zero. Summer is very good. You will be affected a little bit by the lake ontario clouding. I love Ottawa, BTW. Great town.

In Sarnia Ontario, they opened the largest solar generation plant in N. America at 80 MW recently. However, they are using thin-film collectors - a little cheaper per-panel but less power per panel. http://www.cbc.ca/technology/story/2010/10/04/sarnia-enbridge-solar-farm.html

.80+ or more cents per kWh is Insanely good - if I were offered that for 20 years, I'd be all over it right now. Anyone with a South-facing roof without a lot of trees should jump on it. In fact, farmers could indeed make some money on using a portion of their land to produce electricity given the payback per square foot would be quite good at that rate.

Here, they incent with federal monies and state rebates. I'd rather see incentive from the power company like that with the per-kWh buy-back - I'd fill my roof with panels and start selling excess back. No, wait - I'd fill my back-yard with panel racks and sell even more. In my state of PA, you sell back at retail rate (about .18/kWh) and then once you have a zero-net energy bill, they buy-back at wholesale rate of about .08/kWh. Nothing like Ontario.

My guess of 2.2 times panel output is for a low-average. The reason is your daily output average day across the whole year is approximately 2.2 times on the low side during cloudy days or winter. Summer would be 3, 4 or up to 5x your peak power output per-hour. If the solar system is meant to recharge an EV - it needs to be able to do it year round so use the worst of the averages. Another example above is the 4kW, system noted above, outputting only 9 kWh during winter months.

Sounds like a combination of Solar incentives along with EV incentives would make Ontario a great place to be going with those technologies. It's a very progressive province and some times I am a little sad that I didn't go north rather than south from my hometown of Niagara Falls, NY. I work with people from Toronto all the time, know people near Ottawa and enjoy everyone I've met up that way.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #11 (Edited)
Thanks to everyone for your helpful advice, especially Bonaire & WVhybrid.

I inadvertently left out “battery” in my last question, which would help clarify things here: What would I need via a stored battery array to meet those requirements? (…of say ~10-14 kWh)

Per the threads below, again thanks - Yes, I would indeed need a fairly large solar system to produce ~14kWh of power to charge the car on a daily basis throughout the year. (and at that cost, one would defiantly want to do more with it than just charge the car – i.e. house, Grid Tie, etc).

But what if we changed a significant variable, that being TIME?

I work at home, so I drive maybe 5 miles a day. Subsequently, I don’t need to charge the car every day. I need to charge the car every “nth” day, like every 3rd to 5th day. This could hopefully, reduce the size of the solar array needed, by stretching out the time required to charge the solar batteries. A second efficiency may be in the use of a solar tracker with pole mounted panels at high wattage. But that's not critical yet. The big question of course, is how much battery do I need, and how long does it take to charge it at “X” voltage.

I’ve been out to a few battery manufactures to try and spec requirements for batteries, but unfortunately it’s a bit challenging, especially when you consider charging voltage, duty cycles, amperage, etc… At any rate, I’d like to keep discharge of the batteries to about 40%-50% to preserve the life of the system.

Any solar battery experts out there?






Has anyone out there designed a stand-alone off-grid solar system that relies on charging up an array of batteries during the day, and then using that stored energy to charge up a Volt at night?

Yes, yes, I understand that it would cheaper to use mains power, but this is not an ROI calculation.

I understand via this forum that it takes ~10 to 14 kWh to charge the car? What would I need via a stored array to meet those requirements?

Thanks,

RedVolt... Car on order, status 1102.:cool:
 

·
Premium Member
Joined
·
14,156 Posts
I work at home, so I drive maybe 5 miles a day. Subsequently, I don’t need to charge the car every day. I need to charge the car every “nth” day, like every 3rd to 5th day. This could hopefully, reduce the size of the solar array needed, by stretching out the time required to charge the solar batteries.
You do realize that you're talking about installing a solar array and batteries in order to save ten cents a day? You'll spend more on an inverter alone than you'd save over a lifetime. If you really want a solar array, this spring they're selling some that you can just plug into an electrical outlet. They're small units, 1 kWh or less, but they'll have an inverter built in and will be more than enough to charge the Volt and you can do the labor yourself. Look for them at Lowes, which is one of the places you should be able to find them.

Until batteries come way down in price only the grid-tie system makes any sense.
 

·
Registered
Joined
·
471 Posts
Has anyone out there designed a stand-alone off-grid solar system that relies on charging up an array of batteries during the day, and then using that stored energy to charge up a Volt at night?

Yes, yes, I understand that it would cheaper to use mains power, but this is not an ROI calculation.

I understand via this forum that it takes ~10 to 14 kWh to charge the car? What would I need via a stored array to meet those requirements?

Thanks,

RedVolt... Car on order, status 1102.:cool:
If you are in an area with utility power, on-grid makes a lot more sense both economically and environmentally.

1. With an on-grid system your excess generation during the daylight hours benefits the community by reducing the need for commercial power generation, even though by a small amount.

2. You won't incur the cost, space requirements, or hazardous materials involved in purchasing, installing, and maintaining a rather large battery bank. The grid becomes your storage.

3. You will be producing power at peak usage times and consuming it at off-peak times, which can result in a substantial cost savings and may even result in the electric utility paying you. Also better for the environment.

4. The complexity and design of the required electronics will be much simpler, and the specifications of the inverter required to deliver clean power to the Volt will be a lot tighter than an on-grid inverter.

5. If the array and batteries are sized to ensure sufficient reserve to charge the Volt during extended overcast conditions, you'll be capable of producing substantially more power than you can use for most of the year. This is a waste of battery and panel capacity. If they're not sized to ensure this, you'll need to use grid power (or gasoline) during cloudy weather.

Unless you simply don't have utility power or it is so horribly unreliable as to require an off-grid solution, on-grid is likely to be a better choice from a number of aspects, not just financial.
 

·
Registered
Joined
·
471 Posts
The only problem is that solar only generates power here for 8 months of the year. I don't even know how I would prevent snow from piling up on the panels in the winter.

Luc
In the northern latitudes the panels are going to want a fairly high tilt angle. That coupled with the slick glass surface and dark color should cause the snow to slide off rather quickly once there's enough sunlight to have the panels do anything useful.
 

·
Registered
Joined
·
471 Posts
Seems like the switchgear (inverter, disconnect, etc.) cost about the same as the solar panels these days.
WVhybrid
I went with the Enphase micro-inverters. Single inverter per panel mounted to the roof racking underneath each panel. No DC wiring or disconnect. No equipment to mount in a closet. No need for specific number of panels to make a string. A single panel with shadow, dirt, bird-doo, etc. doesn't take down a whole string. Individual monitoring per panel, in real time.

Click here to see stats on my solar system.

 

·
Registered
Joined
·
5,486 Posts
As I mentioned on page 1 - don't use a battery storage off of Solar to re-charge the car. You would need a quite-large # of batteries to afford the storage - at least 30 kWh of storage since you never want to discharge past 50%. Let's say you need 40 kWh of storage at 120V to be safe. To charge that up with Solar, from 50% to full is 20 kWh or about 10 hours of a 12-panel Solar array on a good day. The cost to buy into such a small system is still quite high - at least $20K due to the inverter and batteries.

What you are saying is you want a small solar system to trickle-charge a battery-standby power system to re-charge the volt off stored battery power. This is very inefficient and costly.

What you want is not really affordable nor "normal" for Solar array setups. You want a trickle charger to put in the 3kWh a day you need to go about 9 miles or less. This still is very cheap using grid power - the Volt uses a 110v wall plug and pulls what, about 13-14A while charging? That is 1500-1600 Watts and over 8 hours, that equals about 12 kWh. That costs $1.00-1.50 and if you do it at night, the power grid has that available in excess and could charge you less than daily rate.

The Volt is a great car but don't let this Solar battery thing stop you from going Volt. You could and should consider a Grid-tied Solar system (without batteries) as a first-step in building a renewable energy plan. Unless you really really require battery standby - there isn't much reason to do it. Use the solar to "sell back" to the grid during the day and use the grid's excess power at night to charge the Volt. That's what Solar users are doing now.
 
1 - 16 of 16 Posts
Top