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PV System Values: Solar Energy Needs Electrical Storage Now

By Joseph McCabe, PE
August 31, 2012   |   34 Comments

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Dramatic cost reduction in photovoltaics (PV), combined with lower electrical storage costs from batteries for the automotive industry, are creating new business opportunities for grid-tied PV systems that include energy storage. This article addresses the technical and economical justification for electrical storage with PV and what it means for the PV industry.

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34 Reader Comments
Comment
1 of 34
September 1, 2012
Joe, Nice article. From my perspective it points out that progress is being made... but there is still far to go. But, please, just don't fall victim to the V2G storage fantasy. That one's not happening, not now, not ever. Properly managed, PV will have its place, as will CSP and other technologies. None of these can be all things to the grid. What portion each can assume over time remains to be determined, and is probably fluid. Cost is an issue. In my opinion, public (taxpayer) funds are better spent on the R&D needed to bring down the cost of these new technologies rather than providing a subsidy (via ratepayer funds) to developers which only creates a false sense of grid parity. Regards, Rich Mignoga
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Comment
2 of 34
Anonymous
September 2, 2012
Regardless of whether the power is solar or wind generated, storage and load leveling are important problems to resolve if large scale RE is to be successful. However, some of the suggestions proposed in the article such as battery storage do not currently make sense economically, nor are they likely to anytime soon. The proposals for peak-pricing or real-time-pricing will not work for residential users with price controls, and they will only serve to drive away commercial power users.

The only proven, economical large-scale storage technology that currently exists is pumped hydro. The other cost-effective approach would be to encourage large industrial users of power to relocate closer to where there is excess power. Many of these large industrial users can ramp their manufacturing processes up/down each day to meet demand. And they would be happy to relocate for the promise of lower energy costs. More efficient usage seems smarter than storage.
Comment
3 of 34
September 3, 2012
Joe, at Firefly we now have a Micro Carbon Foam Battery which will be available in 4V 100Ah+ size, Flooded type. Now we offer this battery in 12V 100 Ah size. In Bulk, this battery will be available at below 300$/Kwh plus cost of BMS. Cost per kwh over life of the battery will be less than 0.15$. The designed life can be 20 years. This battery will immediately address many of the issues raised in the article. Small Energy Storage Systems using MCF Battery with capacity of 500Kwh to 5000Kwh will bring new market opportunities for Renewable Energy Market. Delivery of Renewable Energy at the Right Time is now possible. We would like to work with companies who deal in these activities. Thanks.
Comment
4 of 34
September 4, 2012
about storage costs I had already written: by using Air Hydropower (http://airhes.com) we can get a minimal cost for 1 kWh storage ~ $36-40 (2 km head, hydrogen price $2/kg) - 18 t water is ~100 kWh (3 day household) - compare with other ways here http://physics.ucsd.edu/do-the-math/2011/09/got-storage-how-hard-can-it-be/
Comment
5 of 34
September 4, 2012
Battery storage is a valuable tool for the customer and the utility, especially when it is coupled with solar energy. For the customer it provides back-up power for critical circuits and opportunities to lower their electric energy bill. For the utility it provides demand reduction, energy arbitrage and new revenue opportunities in the ancillary services markets. When combined with solar, battery storage is used for grid stability and to avoid cost shifts between customers. Speaking from an electric cooperative utility's perspective, I expect battery storage technology to succeed in the marketplace.
Comment
6 of 34
September 4, 2012
mukesh-bhandari - at $0.15/kwh (and that is over the lifetime of the batteries) - well, that is more than the cost of most residential electricity in the United States. While this MAY work for some large industrial users, it is, at this point, worthless for residential considerations whatsoever.

Here in New Hampshire we have some of the highest electric rates in the country. We pay just a little less than $0.16/kwh, BUT, not all of that is actual energy cost, part of it (near 50%) is the distribution cost, so, unless these are at installed at the point of use (i.e. at the residential customer) - that customer will still get hit with a distribution cost from the power company (they own the power lines). Tacking that $0.15/kwh PLUS any cost of actual power generation, then ALSO adding in distribution cost will make this energy cost prohibitive.

Don't forget - large industrial customers typically get price BREAKS based on amount of usage so they are paying LESS than residential customers.

Sorry - I just don't see this being economically viable - at least not yet.
Comment
7 of 34
September 4, 2012
What is the true potential of flywheel storage? Why do we hear so little about it? Can someone please enlighten me? Specifically I am thinking of a small off-grid community of say 10,000 people - would it be viable?
Comment
8 of 34
TK
September 5, 2012
The only large scale 20MW Flywheel storage is in Stephentown New York. The supplier Beacon filed for chapter 11 before completion of the project. It was supposed to be commissioned last year. Flywheel is more suitable for frequency regulation not for small off-grid system. A VRB redox flow battery system is most suitable for small micro grid applications. Charging of VRB can be carried out from any renewable or clean energy sources. It is versatile enough to balance the intermittent supply as well as to supply power to off grid community over long periods.
Comment
9 of 34
September 5, 2012
The article makes an obscure and not particularly compelling case for the necessity of 'solar load control,' before segueing to a list of ARPA-E funded solutions. What we need is load control for the entire grid within which solar is presently a bit player. For the record, pumped hydro is the only current grid-level solution. It depends on optimum geology (elevation differential near a water source) and takes years of planning and construction. Perhaps one or more of the ARPA-E funded solutions will pan out. Another grid-scale storage possibility is a mag-lev weight system, where large cement blocks are transported up an elevation on tracks. The concept seems plausible and within reach: www.youtube.com/watch?v=OE92_Ds6XvI
Comment
10 of 34
September 5, 2012
Before any energy is stored as electricity, as much energy as possible should be stored as thermal energy. That is: hot water, cold water and/or ice. Water storage can be installed for less than $1.00 per gallon. 21 gallons ($21.00) of water is 175 pounds. Water at 120 F used for heating a building will cool 20 F as it passes through the heating coil. 175 pounds X 20 F is 3,500 btu which is equal to 1 KW for only $21.00. What is the shelf life of water? Thermal storage can be used for potable hot water, space heating and clothes drying. Cold water is used for air conditioning; ice is used for air conditioning and 40 F refrigeration. Thermal energy storage will provide excellent load leveling by turning the heat source or cold source on and off and using the stored energy when the wind is calm or the sun is not shining. I am an inventor looking for partners or sponsors who are interested in intellectual property that will provide a vehicle to expand into new markets. I have developed technology in air-to-air heat recovery, solar heating and cooling, dehumidification in industrial freezers, desiccant dehumidification, thermal electric systems, improved ground source heat pump systems, improved solar distillation, lumber drying, crop drying and desiccant dehumidification and cooling.
Comment
11 of 34
September 5, 2012
Rich Mignoga - V2G storage fantasy V2G works well I have run my house off my EV several times during power outage i guess V2House. i can send to grid also. But why? My furnace worked while others in the neighborhood had no heat Where V2G and Solar does not work is with smart grid as smart meters deployed in California Are not compatible with either. smart meters are not capable of Net metering 2 way flow of electricity. In CA when you get solar the smart meter has to be changed out to a non smart meter NEM meter. Rod N - yes I think valuable for Industrial customer. I had a customer on a solar bid a few years ago that his demand charges were over one half of his bill. Solar wouldn't help him as high demand was early in the morning. But if he had battery pack,charge at $.05 kwh, pull high demand off pack he would save $2,000 a month. Think I'll run some numbers. I think 2 year payback give him $48,000 pack @ $400Kwh current LiFePo Kwh price Elite power solutions, if need that large pack as only need to draw start up welding units. I think a battery pack would save him more than solar and faster pay back lower initial cost. bob-plugh1 - yes large users pay less per Kwh but they have to pay demand charges which increase cost above case add total bill instead of $.05 Kwh customer paying $.11 kwh. mukesh-bhandari - are those FireFly batteries commercially available yet? christina-nelson-45845- where can i find more info on solar heating cooling? small scale mostly
Comment
12 of 34
September 5, 2012
@ christina-nelson-45845 and Joel_Fairstein The PV people totally ignore the solar thermal industry. The addition of thermal storage to a solar thermal collection system is very low cost and provides all the 'solar load control' you will need... the solar peak can also be matched with the load peak too and eliminate a lot of the need for make-up energy that fuel and hydro dams provide allowing solar to contribute close to 90% of the electricity needs of a grid (10% being extreme rapid use fluctuations - flywheel storage would be good to fix that). This does not address the fluctuations of PV and Wind inputs though but adds extra economics to go with solar thermal over PV for large scale operations. Note that Spain has been leading the way with this form of storage for years and now most new solar thermal collection systems include some thermal storage. Regarding the "mag-lev weight system", most rocks are similar to aluminum in density but iron is much higher (about 2.5 times the densest common rocks as in 7.87 compared to 3.1 g/m^3). I had the idea of lifting the house with hydraulic rams for weight-elevation storage.
Comment
13 of 34
September 5, 2012
I don't want my EV or PHEV's battery to be available for GRID demand as increasing the charge/discharge cycles will shorten battery life. However I WOULD like to have it as a plug-in battery bank for grid outages. Are there any residential inverters that offer this plug & play "sometimes" battery bank option?
Comment
14 of 34
September 5, 2012
Whoever figures this storage thing out at a grid level is going to be rich. it is the last big technical bottleneck preventing more widespread rewnewables deployment (politicies and financial issues aside).

I will jump in with others in saying that pumped hydro looks to be one of the best tried and true solutions we have,... but finding the physical space for those hydro projects is a big challenge, and we need a lot of them to address the problem at grid scale.
Comment
15 of 34
September 5, 2012
How's this for scale: Only 10,000 homes with 5,000 gallons of hot water storage. Each house has 245 kw of storage for hot water and space heating. 10,000 homes would have 2,445,780 kw of storage which is 2,446 MW or 2.4 GW.
Comment
16 of 34
September 5, 2012
Interesting concept Christina, and I can see some advantages to thermal storage, but markets will demand more flexibility than that. Somebody is going to want to turn on an (electric) light at night, so we've got to find a way to store electric energy, and ultimately get it all (or a portion of it) back as electric energy.
Comment
17 of 34
September 5, 2012
The thermal energy consumption of a home is more than 55% of total energy consumed. This would greatly reduce the amount of electrical storage required. Now, if a house or commercial building had hot and cold thermal storage, then a low temperature freon turbine (Ormat already does this with solar ponds) could be used to make the eletricity.
Comment
18 of 34
September 5, 2012
erikkiehle - Silent Power, Inc., Baxter, MN makes a residential battery storage unit that can sometimes be used for grid management and can serve a critical circuits panel during grid outages
Comment
19 of 34
September 5, 2012
an idea I came up with but will never be able to capitalize on is to use street lamp poles to hold storage batteries and grid interconnections (smart charging and inverter systems controlled by the utilities). The poles are hollow, have grid wiring, good ventilation, secure, on public land, and located all over residential areas. Powering street lighting during an outage might also have significant value for public and traffic safety. Large spiral designed batteries are known to last longer and be relatively cheap to make but few applications like round batteries... but this use would love round batteries to fit in poles.
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Comment
20 of 34
Anonymous
September 6, 2012
One of the technologies considered under former President Reagan's Strategic Defense Initiative, popularly known as "Star Wars" was an enormous laser of some kind -- electron laser or fusion laser or something -- that might be used to pick off incoming ballistic missiles and zap them out of the sky. The thing would require an enormous amount of energy at a moment's notice, and the Initiative tried to come up with a way of storing electrical power on a power plant scale. An old man's memory fails, but it seems to me that they awarded a contract to somebody at Duke University to assess the feasibility of building a huge "battery," something that might be several miles in diameter and run like one of these atom smashers. Does anyone know what ever came of that?
Comment
21 of 34
September 6, 2012
Rich Mignogna - yes Firefly is selling 12V 95-100Ah Group 31 Blocks in tens quantities for evaluation. By early 2013, larger quantities will be available. 2/4V 100- 300Ah blocks are undergoing testing and could be available in third quarter of 2013. Please see Firefly website for phone/address etc. Thanks.
Comment
22 of 34
September 6, 2012
erikkiehle - in EV already have DC-DC converter from pack voltage to 12 volt. I just hook up a cheap 12v DC to 120 V AC inverter. plug into house circuits I want to run. no big deal.
Comment
23 of 34
September 6, 2012
>erikkiehle - in EV already have DC-DC converter from pack voltage to 12 volt. I
>just hook up a cheap 12v DC to 120 V AC inverter. plug into house circuits I want
>to run. no big deal.

That's one way to do it but still keeps your PV/wind system and inverter offline. Why can't the Inverter utilize an EV battery pack instead of the grid and utilize the PV/wind source as available for house or EV recharging.

Essentially in a grid-tie, no battery system if the grid is down your house is without power. I want to know if there's an inverter that can use the EV as a plug-in battery bank restoring full function.
Comment
24 of 34
September 6, 2012
"For the record, pumped hydro is the only current grid-level solution. It depends on optimum geology (elevation differential near a water source) and takes years of planning and construction."

Many, probably most, hydro-electric power plants could be converted to pumped=storage facilities. There would long-term be a need for bigger grid-tie, and often a below-facility reservoir size increase, but the capability could be added slowly: most such plants have several turbine-generators, so one at a time could be converted to bidirectional turbine-pump generator-motor operation, as needed.
Comment
25 of 34
September 6, 2012
This is an important article, and storage is the holy grail of electricity. Companies such as AES (VA) and Axion Power (PA) are fielding large containerized battery banks tied to electric utility lines. Arbitraging lower cost electricity to meet electric loads at other times is critical. Storage can also relieve electric line congestion or constrictions and provide high electric power quality (less surges, sags, and transients. The cost issue for storage is totally reliant on scale of deployment. Just like energy efficiency, federal and state regulators need to build in ways to monetize storage if such technologies improve electric power rate stability, power quality, and overall electric grid reliability. Scott Sklar


Scott Sklar
President
The Stella Group, Ltd.
E-mail: solarsklar@aol.com
Web site: www.thestellagroupltd.com

The Stella Group, Ltd. is a strategic technology optimization and policy firm for clean distributed energy users and companies. Scott Sklar is Chair of the Steering Committee of the Sustainable Energy Coalition and serves on the (non-profit) Boards of Directors of, the Business Council for Sustainable Energy, and the Renewable Energy Policy Project, and The Solar Foundation. Sklar is an Adjunct Professor at the George Washington University teaching a unique multi-disciplinary sustainable energy course.
Comment
26 of 34
TK
September 6, 2012
Scott,
I totally agree with you that MW storage is going to be the holy grail of electricity companies but what AES is doing is playing with fire. Large capacity lithium systems have inherent safety issues that are still not fully resolved. Individual cell capacity of lithium systems are still too small to be used in MW storage application. The more cells you link up together, you increase the chances of having something going terribly wrong.

In this MW storage race, everyone is still at the same starting line. Betting on lithium, is like playing with fire.

TK
Comment
27 of 34
September 7, 2012
The term we need to use instead of storage is 'arbitrage'. Private investors should build (if that is necessary) grid extensions to the remote renewable sites; Once the connection is made the need for storage declines, since gas turbines can react to short-term demand. Rather than spending so much R&D $ on all varieties of renewables and storage (ALL of which have significant 'unintended' consequences .. the kind 'we dont know that we dont know') > why not quieter micro turbines at home or community level. Wonder if someone can do (or has done) the arithmetic on the viability of small scale gas turbines vs. PV etc. Hydro storage has a round-trip efficiency of about 70% > better than most battery technologies. That alone is the practical alternative ... others, such as CAS, are very risky ... no matter what anyone says >>> I would NOT want the EPA-type rules to apply there" The harm has to be proven before something can be banned. I would rather use the FDA rule (as misused as it is) 'prove efficacy and safety before you can sell.'
Comment
28 of 34
September 7, 2012
Xantrex WX do anything ya want Solar charge battery pack house Grid tie, off line run off house pack Charge EV pack automatic grid shut off Should be able to hook EV pack to Generator hook up, draw from pack I'd have to reread manual WX do just about any function you can think of.
Comment
29 of 34
September 7, 2012
Thanks to everyone for all the great comments thus far. Here is a recent Bloomberg article that expands upon energy storage options: http://tinyurl.com/9gc4hgv . I knew there would be flavors of choice comments for storage; keep them coming.

I will use the comments from this part to help develop the next part, which should be finished after SPI. Let me know if anyone wants to discuss this at SPI. Thanks again. -Joe Mc.
Comment
30 of 34
JHB
September 7, 2012
I am not too deep into this electric storage and have always wondered why we are using high voltages to provide our household and industrial appliances. Why don't we simply convert to twelve or twenty four volt battery power so that all our appliances can provide us with our needs without the National Grid and all the other rubbish that is costing us a fortune to have the use of. Each dwelling could then be independant of the state once we have purchased our method of renewable energy.Perhaps some people are already using this method, so please tell me how I can do my cooking using low voltage. Thank you. Joe.
Comment
31 of 34
September 7, 2012
Joe, there is a big movement here for DC current, just like ib you car or an RV which would be very feasible, look at www.nextek.com which has a great video on it. Scott Sklar
Comment
32 of 34
September 7, 2012
@ JHB : the biggest problem with low voltage is the amperage squared is used to calculate the energy loss in the wires. If you drop the voltage by 10 times (125v to 12.5v), you increase the energy loss in the wires by 100 times (10 x 10) or with a wire that is 100 times as thick in cross-sectional area will have the same loss as the original wire using the 125v. This can be solved by putting the battery close to or inside the appliance using the energy but you still have to connect the batteries to the source (solar? wind? fuel burning generator?) so you are still stuck with a high amperage, thick-expensive wire problem. I am hoping to design units for homes that provide light (LED), occupancy detection (turns on the lights and heat/cool only when needed), fire alarm, and a small sealed battery with charging circuitry. This unit would receive 125 v AC from a "micro grid" of the solar panels that only is powered when the sun is shining and the small battery would take care of the lighting in the rooms. Some inverters will detect electrical need so plugs can be hooked to such inverters and they will only operate when someone plugs stuff in (and powered by bigger batteries located in a protected box outside the house). More things can also be powered by rechargeable batteries (like power tools) and only charged up when an energy source is available. Like what has already been mentioned in this thread, thermal storage can keep your refrigerator cold over night and your hot water tank hot all night and only be using energy when the sun is shining. This local storage is great for customers of the grid but only if they pay different rates based on solar or wind energy availability. Otherwise, it is not part of the discussion of grid management but rather how to no longer need the grid (which power companies obviously do not like to hear).
Comment
33 of 34
JHB
September 8, 2012
Ann, thanks for that very informative post. Once you have developed your Led lighting system please tell us all about it and how much you require to light a three bedroom home.
Scott, may I also thank you for your information, I did not realise that the idea would be feasable. I will look up the site shortly.
Comment
34 of 34
September 8, 2012
@ JHB : The idea with these lighting units is to have one in each room (with the fire alarm optional for rooms like the bathroom) and to have the house heating/cooling/HRV(heat recovery ventilation) controlled separately for each room by this same unit. An infrared detector could be incorporated in it to measure the floor temperature (and internal ceiling temperature measured) to get an accurate temperature profile of the room. CO2 detection is part of CO detection so can also be used to detect air quality along with humidity detection to control the ventilation through the HRV. HRV units usually use brushless electronically controlled DC motors (many times as efficient) and last longer) so HRV fans can be located in each room instead of in HRV unit (a flow detector can be used to match the flow of the opposite flow) or an even more radical idea of an HRV for each room (they are a bit expensive so the increase in efficiency is likely not enough to justify the extra expense). This idea came to me on a quest to make houses without the need for utilities and using high insulation and high air-tightness to compensate for the lack of solar in city homes with a building 4 feet to the south of your house. In such a situation, there is a bit of solar but only for a short time in the day on the roof so electrical energy is at a premium and so is concentrating thermal solar for hot water and some heating. It can still be applicable to grid customers though for safety and security during power outages and of course building energy efficiency (no matter the source of the heat). An interim system I am planning to use incorporates a tankless condensing natural gas water heater as the source of thermal energy to be replaced later with concentrating thermal solar panels later. A stratified hot water storage tank will store the 'used' hot water in the HRV that replaces the furnace until I add the radiant floor heating in each room. check out PassivHaus and "1 watt house"
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Joseph McCabe

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About: Joseph McCabe is a solar industry veteran with over 20 years in the business. He is an American Solar Energy Society Fellow, a Professional Engineer, and is int... more »

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