Eschew Obfuscation: Can Battery Backups Make Money?

Can Battery Backups Make Money?

Max Dunn — Wed, 23 Jan 2008 10:12:00 -0800

I don’t have a lot of confidence in PG&E. It seems that every time we have a big storm, our power goes out. Once, it took 3 days for them to get the power back on! So I have been considering installing a battery backup system for my house to get through these power outages.

If I install a battery backup system, I was wondering if it would be profitable to charge up the batteries at night when electricity costs are low, at $0.05/kWh, and then use it during the day when electricity costs are high, at $0.11/kWh to $0.29/kWh [9]?

"Can Battery Backups Make Money?" by Max Dunn

Fri, 01 Feb 2008 10:16:58 -0800

Flywheels

It turns out the flywheels might be a viable way of storing energy for a house battery backup system.

They can be up to 90% efficient, can have capacities up to 133kWh, and have long lifetimes with little maintenance.

However, while some commercial and industrial flywheel storage systems are available today, there doesn’t appear to be any for sale to individual users, and the initial cost is about 50% higher1 than a battery system, although the total cost is lower over time.

1 Pentadyne VSS Brochure

"Can Battery Backups Make Money?" by Max Dunn

Thu, 31 Jan 2008 11:30:25 -0800

Carl,

Wow, paying $0.33 kWh is a lot! If you could put up solar panels, they would probably pay for themselves in 10 years. But I am guessing in your condo, this is not an option, so let’s go back to battery backups.

The first question is whether you want a system that will tie into your house power circuit and come on automatically when the power goes out. These are certainly the most convenient, and people that use them say that they often don’t even know that the power went out, until they look at their neighbor’s houses that are dark.

The downside to these systems is that they are more expensive and require an electrician to install, which adds another $1000 or so to the price.

If that is what you are looking for, then a Gridpoint, Gaia or Xantrex system would fill your needs.

For a lower cost system that doesn’t require an electrician, you could look into a UPS like the Xantrex PowerHub 1800 This lists for $900. Batteries are extra and the run time isn’t very long, but two of these each with the extra battery might be able to fill your needs and the total cost including batteries would likely be less than $4,000. This system also has the advantage that it can be connected to solar or wind generators to recharge the batteries.

You could also look into Sentinel systems. You can get a 7.2kWh system with batteries for about $4000. Most of these need to be hardwired into your home electrical system, but I recall seeing one that offered a plug outlet.

Good luck with this, and let me know what you end up doing.

"Can Battery Backups Make Money?" by Carl

Thu, 31 Jan 2008 05:57:32 -0800

I’m in the USVI where the cost of electricity it $.33 KvH. I can live with that - but the government-owned power system goes off line 3-4 times per mon th in good weather (max = 1 day) and it can be really bad during hurricane season. How about your initial premise - which was not to save money, but to provide a “backup generator” capacity? We cannot have any large generator in our condo. (2500 = max) So…..I’ve looked at Gridpoint and Gaia systems—both 10 KwH total capacities. To cover my fridge, small a/c unit and bedroom (including tv, lights and computer stuff) I draw a max of 2 KwH, with actual usage closer to 1. But the systems are $12,000. Any thought or observations would be GREATLY appreciated !!!!

"Can Battery Backups Make Money?" by J.R.

Wed, 30 Jan 2008 15:37:42 -0800

It’s great to see the numbers – thanks for calculating it thru. Here’s another one for you – how about a giant flywheel in your garage? I love the answer for storing water – I’m just imagining 20 swimming pools on your roof!

"Can Battery Backups Make Money?" by Max Dunn

Thu, 24 Jan 2008 17:24:26 -0800

Hydrogen

Using hydrogen to store energy is only 20%-25% efficient [1]. This is about 3 times less efficient than storing the electricity in batteries [2].

[1] Does a Hydrogen Economy Make Sense?

[2] Wind-to-Wheel Energy Assessment

"Can Battery Backups Make Money?" by Max Dunn

Thu, 24 Jan 2008 16:58:20 -0800

Air

Storing 10kWh of energy as compressed air would take only about a 300 liter tank [1], but the efficiency of compressing the air and getting it out will likely be less than 25% [2] and even in ideal situations, still less than 40% [3].

[1] Compressed Air Thermodynamics of the MDI Air Car

[2] Physics of isothermal compressed air storage

[3] Thermodynamic Analysis of Compressed Air Vehicle Propulsion

"Can Battery Backups Make Money?" by Max Dunn

Thu, 24 Jan 2008 16:01:31 -0800

Good question, let’s look at other ways of storing energy. First, let’s look at water.

Water

To determine the amount of electricity water can produce, you can use this equation from reference [1]:

watts = (Height [ft] * Flow [USGM]) / 9

or to change to kWh and solve for Gallons:

Gallons = 540,000 * kWh / Height

So if you have tank on your roof that is 10 feet high and you want to produce 10kWh of electricity you would need to 540,000 gallons of water. For comparison, the average swimming pool holds 25,000 gallons so this would be equivalent to over 20 swimming pools!

However, this is probably the most cost-effective way of storing energy being 70% to 85% efficient [2].

[1] Micro Hydro Equations

[2] Pumped-storage hydroelectricity

"Can Battery Backups Make Money?" by J.R.

Wed, 23 Jan 2008 21:44:15 -0800

Are there more efficient or less costly ways of storing energy? How about if you use the cheap night electricity to pump water to a tank on your roof, then let it generate electricity on its way back down. Or run an air compressor at night to pressurize a 50 gallon drum. Or create hydrogen thru electrolysis?