Why is grid-tie battery backup not an easy addition to a grid-tie solar system?

The standard grid-tie solar system will not work when the power grid is down.  Grid-tie inverters shut down as soon as they lose the AC signal from the energy grid and hence grid-tie inverters do not accommodate grid-tie battery backup.  That is because government regulations and electrical codes mandate that solar systems never put power onto an energy grid if the grid is down.  Those laws are meant to protect power line workers from electrocution.  Hence, grid-tie inverters have always complied with these laws and it has caused problems for solar system owners.

So, owners of solar installations suffer the same bad effects of losing grid power as non-solar users.  The sun might be shining away, but it doesn’t matter if the grid-tie inverter shuts down when the grid does!  Many people who buy solar systems are surprised to find that their lights go out when their neighbors do with a widespread blackout.  The fault all lies with the design of the grid-tie inverters that meet the government regulations.

Grid-tie battery backup ideas that work around government rules legally.

I am not nearly so worried about regulations as I am about the very real risk of electrocutions.  Thus, I assure you that anything I am going to try in the near future and will describe to you violates neither laws or lives.

Let us discuss the simplest system first as I have it all in place waiting for my electrician friend to wire it up to the grid.  Though I am an electrical engineer, I do not understand or know all the electrical codes.  I rely on my friend to get me over those hurdles.   This is all going to be fairly technical, but I will try to make it as easy as possible for the layperson.

Phase I of my grid-tie battery backup system will provide about two days power off grid.

I designed and built my Phase I grid-tie battery backup system to keep  emergency loads going two days.  At least I will be ahead of all the other neighbors who do not have backup generators.  But I will be in no better shape than those who do have the backup generators.  Those with the generators can purchase extra gasoline to stay energized for a few more days.  I will not be able to purchase more solar energy, nor will I be able to use my solar panels to re-charge my batteries.  That is not until I test and complete Phase II plans.

We have already purchased and installed all the Phase I equipment in the shop.  A battery of two volt AGM (Absorbent Glass Mat) cells makes up a 48 volt 30 kWh energy storage system.  I placed all the cells on two shelves of a substantial industrial storage rack along with an 8kW inverter/charger unit.  I like the several advantages the AGM batteries offer.  Several years ago I started using them in my fishing boat because normal lead-acid batteries were lasting only about a year for me.  They designed AGM batteries specifically for deep cycle service which fits a backup application perfectly.  You can store the cells in any position because they are sealed and do not leak.  Most lead acid batteries do leak and they cause a lot of corrosion problems.  Battery corrosion creates performance degradation besides just being annoying.

I plan to configure my 48 volt battery backup system with the grid soon.

All the actual equipment for Phase I is now wired into the emergency breaker panel and the grid.  I did that with the help of my electrician friend Mike Egbert.  I am inserting a diagram of how I plan to connect this backup system to the grid.  RV readers might recognize this scheme as being similar to what their motor coach has.  Our coach provides us with an almost identical system.

The block diagram below will give you a picture of how the Phase I system now operates.  First let me explain the normal operation of the solar system when the grid is up (properly functioning).  In that mode, the solar panels feed 350 VDC energy to the three power inverters.  Those inverters detect the 240 VAC energy at the main breaker panel and start producing 240 VAC energy they feed to the main panel.  The main panel supplies 240 VAC energy as needed by the house and the other two panel loads.  Any surplus is fed to the grid and the smart meter runs backwards.  If the total loads consume more energy than the three inverters supply then the meter will run forwards .  The forward running meter subtracts any energy credits we have stored up.  The backwards running meter stores up energy credits we can use later.

We got the Phase I battery backup system going the first week in March and by the middle of March we had a power outage that lasted for about two hours.  Our system performed flawlessly and until I turned on a light switch that was not on an Emergency Panel circuit, I didn’t realize the grid was down!  All our important appliances kept running without giving a hint that something was wrong!  This will work well in place of a generator, but it still will not work in the event that the grid goes down for more than a few days.  That will require the ability to make the Grid-Tie Inverters work when the grid is down so that the backup battery bank can be charged so long as the Sun is up.  It sounds easy, but there are complications that someday I hope to overcome in the form of Battery Backup Phase II.

 

Phase I grid-tie battery backup system schematic diagram.

Schematic diagram of Phase I grid-tie battery backup system.

Aims Power 48 VDC charger and 240 VAC inverter for grid-tie battery backup system.

48 VDC battery bank for grid-tie battery backup system.

The Rest of Phase I grid-tie battery back up system 48 VDC battery bank for a total of 24 two volt cells.

Phase II of the grid-tie battery backup system will follow after experimentation.

I have worked up a paper design that utilizes the same equipment as the Phase I plan uses.  This new plan might work out great if the three solar people (from different companies) I have talked with are correct in their affirmative statements.  Once I have applied the changes I plan to do an update following this sentence on this page!

Protect your expensive solar system from a nuclear or solar EMP.

Most people today are aware of the term Electro Motive Pulse (EMP).  These dangerous critters can literally cripple most electronic and even some higher powered electrical circuits.  This includes most all solar systems and their battery backup circuits. Generally, EMPs can be caused either by the super high energy pulse generated during a nuclear bomb event.  They may also be caused by a direct hit from a solar flare which is an extremely remote chance, but is yet a finite possibility.  Solar events are a usual occurance, but they are very directional when given off by the surface of our Sun.  The chance of a very powerful flare actually hitting the Earth is very slight, but possible.

When such an event happens, it creates a very large voltage spike in most electrical or electronics circuitry.  If the circuits are connected to the grid, all that connected wire acts like one huge receiving antenna that can deliver an extremely high voltage, short-duration energy pulses to all connected devices.  The trick is to prevent any such pulse from ever entering your home in the first place.

There appears to be an affordable solution to this very real potential problem.  Any EMP energy pulse if of very high energy, but only for a very short (nano second to microsecond duration).  This new protection product will protect any home whether you have a solar system or just a traditional on-grid (only) home.

You really need this kind of protection if you want to sleep nights without having to worry about having your life being destroyed by a (planned) nuclear or (unplanned) solar flare event.  For more information on this protection systems, go to My EMP Shield.  I have not personally seen or used this system (YET)!  However, I am looking forward to installing one to protect my home and solar investment soon.  There is a ton of useful information on this web site along with contact information if you still have questions.

I have been aware of the EMP threat for over 40 years, but the people who have come up with this solution are light years ahead of any thinking I have done on the subject.  I can tell you from my engineering experience that the inventor of the device sounds more than credible in my limited telephone conversation with the man.