Backup Solar Inverter Question

[Spanky8601]

Currently I have a grid tied Solar Panel system. There are two arrays producing about 4kw per hour total at peak. The download volts per array is about 340 volts DC. The Inverter on the system is grid tied and shuts off with out Edison supplied power. (safety feature for the workers) I would like to be able to wire in an inverter prior to the grid inverter to be used for long term emergency power. This can either be as a manual switch and then to an inverter that I can plug in AC to. I would like to stay away from battery back ups if at all possible, due to space/location considerations. Thanks in advance for any ideals.

[Rivers]

We're just adding a solar array now, without batteries and tied to the grid. As explained to me, new batteries are coming and getting more affordable. These are lithium-ion and look something like an indoor wall heater unit. The new battery tech will make for higher capacity, longer life and less maintenance than the older battery tech. You may want to research this to see if the time is right to add batteries. We decided to wait for another year or two. In the meantime, we have our generator. Hooking that into the power is simple enough too.

[Spanky8601]

Rivers, thanks for the information. I currently have my contractor looking at a "Sunny Backup Set S. Not real sure if that will do it for me or not.

[ptoguy2002]

AFAIK, for solar power to work off-grid, you need batteries to store the power for the ups and downs in demand. Without them, your load would have to exactly equal your power production at any given moment, which is impossible without voltage drop or spike issues.

[rockdogz]

Interested in this too - let us know what you find out...

[chaunbot]

http://www.make-energy.info/bicycle-wheel-windmill/

[EWILKE]

same here have a solar system would like to get battery backup .let me know what you find.

[riprap]

We're just adding a solar array now, without batteries and tied to the grid. As explained to me, new batteries are coming and getting more affordable. These are lithium-ion and look something like an indoor wall heater unit. The new battery tech will make for higher capacity, longer life and less maintenance than the older battery tech. You may want to research this to see if the time is right to add batteries. We decided to wait for another year or two. In the meantime, we have our generator. Hooking that into the power is simple enough too.

^
This.
I have a 5 kw system and am patiently awaiting for the day....

[command_liner]

It is hard to store sunlight.

You can do a bit of trickery with inverters, inductors and
voltage limiters, but there is only so much one can do without
have a battery system.

4 KW means 4000 joules per second. "4 KW per hour" means almost
nothing. Your solar captures joules from the sun and turns them into
joules available on the electric line. Storing electricity generally
means you need a battery, but you can pump water or spin a flywheel
if you have those capabilities.

[parcours]

It's going to be a while before the battery system you really need is available.

We're evaluating storage systems at several levels: community level storage, where several large MW sized batteries will be placed around the utility distribution circuit and provide a "leveling effect" when system capacity cannot handle the demand. Substation storage, again large MW sized batteries will be placed within the utilities substation and add energy when the available generation is approaching 5% of the available capacity. And lastly, is home battery storage. The technology will be similar in all the batteries as the type and construction being evaluated requires minimal maintenance, etc.

The time is coming, it's just hot hear just yet. By 2020 our wonderful legislators have required all residential construction be Zero Net Energy (ZNE) meaning that what ever kWh you take from the grid you must put back within a calendar year.... Right now we can get "near ZNE" but the technologies available don't get us to be true ZNE...

Just wait when the utility will control all your appliances

[meaty-btz]

deep cycle batteries? Old tech but it can work.

[parcours]

deep cycle batteries? Old tech but it can work.

True, but not the the intent for load leveling. The batteries will be cycled constantly and even though batteries like Optima and Odyssey are built to handle this type of discharge and charge, the heating effect will kill them much faster than in an automobile application.

We're seeing batteries overheat very quickly when large demands are placed on them, For example, clear sunny day with a few clouds... The clouds move over the solar panel and where the panel and battery were handling the load without an issue, the battery now goes into a deep deplete without a recharge until the cloud cover moves away. Then once the sun is hitting the panels again, the battery goes from discharge to charge in an instant.

How much and how long do you think a standard deep cycle from today will last connected to the grid like this. I can tell you, not long, less than 3 mos.

This is why companies like A123 is developing battery systems to handle the large swings associated with grid connected storage systems.

[meaty-btz]

I agree with that limitation, was mostly thinking stopgap solution. A possible solution would be more batteries to reduce the draw on any single battery.

Ideally we want a better battery solution, no battery will live long under a heavy discharge/charge cycling. One would be better off with some of the modern capacitor solutions rather than a battery. Reserve limitations are the issue with the current generation of super-caps. No battery will do what is better served by advanced capacitors, they serve better at load balancing than any battery would, ever, at lower component stress.

$$$ are I think the real hold back on use of capacitors in the grid connected home systems. This is something I am currently doing a good bit of research on, wife is a ME and we are designing a closed loop steam generator for a ranch and orchard. Our design uses batteries for reserve capacity with capacitors for moment to moment load balancing though in our case, unlike photo-volatics, we can speed up or slow down our generation with demand but the caps are for power balancing to prevent spikes or brownouts. Current design is small, only 10KW. It might be scalable though.

[paul0660]

We're evaluating storage systems at several levels: community level storage, where several large MW sized batteries will be placed around the utility distribution circuit and provide a "leveling effect" when system capacity cannot handle the demand. Substation storage, again large MW sized batteries will be placed within the utilities substation and add energy when the available generation is approaching 5% of the available capacity. And lastly, is home battery storage. The technology will be similar in all the batteries as the type and construction being evaluated requires minimal maintenance, etc.

Please build my neighborhood nuke first, please.

[parcours]

I agree with that limitation, was mostly thinking stopgap solution. A possible solution would be more batteries to reduce the draw on any single battery.

Ideally we want a better battery solution, no battery will live long under a heavy discharge/charge cycling. One would be better off with some of the modern capacitor solutions rather than a battery. Reserve limitations are the issue with the current generation of super-caps. No battery will do what is better served by advanced capacitors, they serve better at load balancing than any battery would, ever, at lower component stress.

$$$ are I think the real hold back on use of capacitors in the grid connected home systems. This is something I am currently doing a good bit of research on, wife is a ME and we are designing a closed loop steam generator for a ranch and orchard. Our design uses batteries for reserve capacity with capacitors for moment to moment load balancing though in our case, unlike photo-volatics, we can speed up or slow down our generation with demand but the caps are for power balancing to prevent spikes or brownouts. Current design is small, only 10KW. It might be scalable though.

Have you considered Ultra Caps?

They are (were) form the cold war era, developed by the Russians and brought to the States by EPRI. I agree, the Cap idea is a far better solution however the cost is out of control. As you may know utilities (like SCE) use Caps as Volt/Var devices, adding Vars to the system in order to maintain voltage regulation.

Now, using Caps as a storage medium is a great idea and Ultra Caps offer the farad capacity needed to far exceed the same cross sectional area of an equivalent battery.

In the long term I think you will find that batteries do a good job load balancing any power system. The cost is far less and the reliability is quite good. Batteries don't have the issues of harmonic resonance like caps do on a grid connected system. With the increased deployment of inverters, harmonics will be an issue that is needing to be addressed. Inverters can be made to be very robust and handle most levels of voltage distortion caused by battery charging. Caps on the other hand are very susceptible to voltage distortion (ie. harmonics) and failure of the caps is usually catastrophic.