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Hybrid Solar Power Systems

Hybrid Solar Power Systems

Do you love the idea of generating electricity from a modern decent sized solar power system?, do you strongly dislike old school last century fossil fuel addicted power companies?, have you thought to yourself "Wouldn't it be great if I could generate electricity from solar panels during the daytime and store it in deep cycle batteries for night time use?"

That kind of thinking seems perfectly logical and practical, and if not for the cost factor it would be the way to go for everyone on the planet.

At this point in time (mid 2016) with energy storage technology and its associated costs being what they are, going completely off grid is probably not the most economical power solution for everyone, although some in and ouside the solar industry will dissagree. There is an interesting article written by Australian solar guru Finn Peacock that explains the pros and cons of going off grid here - Does An Off Grid Solar System Make Sense For You?.

What is a hybrid solar power system?

A hybrid solar power system is a solar system that has both a connection to the mains power grid and a bank of deep cycle batteries used to store electricity generated from the solar panels.

A hybrid system is more expensive to buy and install than a grid connect system but not as expensive as a full off grid system.

With a hybrid system you get the best of both worlds, energy from the solar panels can be stored for use whenever you choose, if you run out of battery power then the grid is always there as a back up. Alternatively it could go the other way, if the grid goes down the deep cycle batteries could takeover the supply of electricity to your home or business. If you operate critical machinery this this would be a very reliable system for maintaining 100% up-time.

Hybrid Solar Power System Diagram

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Below are some reasons for considering going hybrid:

1. A backup power supply when there is a blackout

All grid connect solar power system installed in Australia have a shut down mechanism that is activated when the grid goes down. This is for the protection of line maintenance workers that may be carrying out repairs or maintenance somewhere along the power lines. A grid connect solar system can send current down the line making it live again and a danger to line workers.

A well designed hybrid solar system should have the ability to disconnect your home safely when there is a blackout, power will then be supplied by the home energy storage systems deep cycle batteries.

2. Solar power system size limits imposed by electricity companies

Power companies are in the business of making money, nothing wrong with that business is business. Solar power systems are the enemy of power company profits, for this reason some companies will place a limit on the kW size solar system permitted to connect to the grid. This policy has forced many home solar power system owners into installing a PV system that is much smaller than what they require to offset their electricity bills.

A hybrid system can work around the size restriction by using a smart power inverter that has the ability to set a limit on the amount of grid export power, for example a 10kW hybrid solar system running at maximum output could export 3kW to the grid and divert the remaining 7kW to the deep cycle batteries making your 10kW system appear to the power company as a 3kW system remaining with in their greedy limitation.

3. Revenge for near worthless feed-in tariff rates

Most states in Australia have very low feed-in tariff rates on average 6 to 12c per kWh for grid exported power. With batteries installed there is no point in exporting any power at all because you will only need to buy it back for much more than you sold it should the batteries run out of charge. Best option is to use as much solar power as possible be it directly from your solar panels during the day or the stored solar energy from the batteries at night.

4. Take advantage of time based power rates

Power companies in some states of Australia charge a higher rate for electricity when its consumed at peak times and lower for off peak times. With a hybrid system you could switch over to batteries during those peak periods and avoid paying the higher rate. If there is not enough sun for your solar panels like in the middle of winter for example you could use the grid to charge the batteries on lower cost off peak power then use the stored battery power during peak time, once again avoiding the higher power prices.

Can deep cycle batteries be retrofitted to an existing grid connect system?

Yes this is possible, however it will require more than just the batteries alone as other system components may need to be upgraded to accommodate the batteries. A system size of at least 5kW is recommended so that there is enough panel output to charge the batteries in winter or on overcast days.

If your system is under 5kW, consider installing more solar panels, although if your home is small and power efficient you may not need many batteries. The inverter will need to be upgraded to match the extra capacity.

It is good practice to oversize a solar panel array to a power inverter. More kW will not damage the inverter provided the voltage and electrical current specifications are maintained. Your local accredited solar panel installer can advise if your power inverter will need to be upgraded based on the capacity you need.

Installing a modern hi-tech battery storage unit like the Tesla Powerwall you should be able to continue using your current inverter, however it may not have the backup function which is what hybrid inverters a designed to do.

The compatibility of the inverter and the BMS or battery management system will determine their ability to match up, generally the more modern and expensive the inverter the higher the compatibility will be. Older model inverters are unlikely to be able to connect with the Tesla Powerwall.

If you are installing older pre-Tesla Powerwall style deep cycle batteries then they will probable need their own inverter with islanding functionality to enable some home appliances to run if the grid fails.

How much does hybrid solar power cost?

Comparing the cost of a hybrid solar power system to a standard grid connect system the price fully installed is about double. The main factor in a hybrid system price is the size and type of batteries you choose to install.

Today a decent 3kW grid system will set you back around $5,000, add a battery storage system to that with 4kWh capacity and its up to $10,000. 4kWh should be enough to last one night with sensible use.

Australian homes are power gluttons though so a 5kW system may be more suitable. With no batteries 5kW systems are selling for around $8,000 fully installed, add 8kWh of battery storage to that and your looking at $18,000.

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Hybrid solar batteries and battery service life

Two basic types of batteries can be used in a hybrid system:

1. Lead acid type batteries

The sealed lead acid type are best as they require less maintenance. This type of battery should last for 1000 to 3000 cycles @ 60% discharge, so the service time could be up to 8 years depending on quality and build. Operating temperature will play a role in battery life, cool is better.

2. Lithium Ion and Lithium Iron Phosphate

These types of batteries can serve up to 6,000 cycles @ 80% discharge with a service life of 13 to 18 years and are much more expensive to buy roughly double the price of lead acid.

The Tesla Powerwall Lithium Ion battery started selling in Australia in May 2015 priced at $8,000 with a daily discharge of 7kWh and represents good value for money for its performance and type.

For more information about hybrid solar power systems including up to date prices visit