Published on July 4th, 2014 | by Guest Contributor


Solar + Battery Hybrid Inverters That Read Weather Forecasts

July 4th, 2014 by  

Renew Economy

By Matthew Wright

We know solar works, we know it is a billion dollar industry, but how is it going to evolve in the future? To answer this question we only have to look at the activity around batteries and the talk of grid independence, which is pervading all corners of the energy industry.

Solar with Battery Hybrid inverters (formerly known as Grid-Tie with Battery Backup or what the CEC calls multi-mode) have actually been around for a long time.

I, personally, got my hybrid inverter system installed back in the year 2000, and it cost a bomb. But systems were available for a number of years before then, from early movers such as Power Solutions Australia (whose product range was acquired by Selectronics and re-badged SB Pro), and Xantrex (which has now part of the Schneider Electric solar division).

In early systems, such as mine, the batteries were there primarily to bolster supply reliability. They stayed charged most of the time until there was an interruption in the grid (something that happens rarely on Australian’ grids, especially in cities with regulated service levels, meaning grid power must be supplied for 99.9+% of the time) at which point the household supply would seamlessly transition from the grid to solar and batteries or just batteries at night. This type of system was a niche product back then – for enthusiasts, but certainly not for the general public.3de7e42a0d50786fa5ca9f7c75c391b7

Fast forward to 2014, battery inverters are now being released by almost all inverter manufacturers, and their prices are dropping fast. Most of these units are converging on a number of capabilities beyond working as a simple “Solar UPS”.

Likely standard capabilities include the ability to timetable when the batteries will be charged from the grid, when batteries will be charged from solar, when the inverter will satisfy a customer’s on-site self-consumption by drawing on the batteries in preference to the grid (usually during peaks and/or critical peaks) and the ability to limit grid exports to a maximum amount, to keep grid operators satisfied (should they place a cap on household solar power exports) and also limit imports to a maximum rate.

Grid operators in future may only allow 3kW, 4.5kW, 5kW or 10kW maximum feed-in rate, but a hybrid inverter could have a higher rating itself (to both feed-in and satisfy local self-consumption) and be configured so as not to exceed those grid operator-imposed limits. In addition, grid operators could also mandate the maximum amount of energy that can be drawn from the grid through such an inverter. In this case the new hybrid inverters can be set to only ever pull say 3kW max from the grid (a requirement for battery inverters in some parts of the South Australia).

Such intelligent power management is the way that a solar hybrid inverter competes with the old energy industry – i.e. by maximising self-consumption of cheaper solar energy that you’ve generated whether it be consumed at the time or withdrawn from the inverter’s battery.

But next-gen hybrid inverters can save you even more money with just a simple software update and an Internet connection.

The third generation of hybrid inverters (very few people in Australia even have a first or second generation solar hybrid inverter) is hitting the market lead by the Bosch Power Tec’s BPT-S 5 Hybrid. Not (upfront) the cheapest solution but a premium, high quality one, and one that is showcasing weather forecasting technology.

What is weather forecasting technology, you ask? Well, without weather forecasting, a customer with a hybrid inverter and a decent sized battery bank to easily match his evening, night-time and morning demand on a day of low solar contribution would have to rely on the grid at some time during the evening peak (paying higher rates) and, if the next day was also to be a very low solar day (i.e. heavy rains and cloud), then they’d also be relying on the grid during that day and the next again paying higher peak usage rates.).

Enter weather forecasting by your hybrid inverter. A hybrid inverter with weather prediction capability generates solar during the day and uses approximately 30-50% of it on-site in real-time, depending on the time of the year. During the night the inverter downloads weather data from the Bureau of Meteorology or some third party aggregate of that forecast data. If at 11pm if it looks like the next day is going to have very little solar generation potential the inverter then decides to recharge the batteries based on that knowledge of tomorrow’s weather forecast at cheaper overnight off peak rates, which are often 50% or more cheaper than peak rates.

The net result is overall cheaper energy for the solar customer as any peak time usage will now just cost a small premium (losses in charging and discharging) over off-peak power instead of the full inflated peak power price.

Therefore weather forecasting reduces peak power consumption (peak power brings in more revenue for the conventional energy industry, including networks and generators) and causes more of old energy’s revenues to go to the solar PV juggernaut, which keeps it moving along as more volume and a bigger market decreases prices for everyone.

The hybrid inverter industry is moving fast and we can expect that within 12-24 months every offering on the market will be capable of processing weather data and making the decision to recharge our batteries on off-peak power if grid power is required.

In the future, with dynamic power pricing potentially matching 5 minute or 30 minute activity on the electricity market these kinds of inverters could become very reactive to price with minor updates to their software, something that would minimise costs to power consumers further.

In 2014 we already have the technology (with more coming) to really decouple our power capacity requirements (maximum grid power ‘upload’ or ‘download’) and our power usage requirements (kWh units used and billed) which now will allow us to always get our power at the cheapest price possible this also makes the risk premium that we are currently paying retailers for managing supply demand matching almost redundant which should lead to a further lowering of prices.

Source: Renew Economy. Reproduced with permission.

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  • Matt

    You don’t have to be off grid for this to be useful. In some location self-consumption is a must. Of you can be in a location that has common mini drops. In my USA location when storms go thru we get many .1-10 second drops. Or you could be in a location where the off peak to peak price delta is very high (say Texas). And the current prediction is for all people to see more power outages caused by extreme weather events. This type system allows you to keep running during those times, if you turn down you main power hogs.

  • JamesWimberley

    Why put the intelligence in the inverter, which is only one piece of the home management pie? What we want is an electronic concierge or janitor – a “janitroid” – that will manage our house and every one of the dozens of connected appliances in it. “Jeeves” or “Chiron” will learn from experience like Nest, respond to voice commands and requests like Siri, and handle authorised interventions from the grid to shed loads or draw down batteries.

    • Bob_Wallace

      Avoid mutli-function devices. That’s my advice.

      Modular components so that they can be individually updated/sent in for repairs.

      • JamesWimberley

        That way you end up with 30 devices each as complex to operate and program as the proverbial VHS recorder that an 8-year old boy can operate – but no adult. I don’t understand my microwave and stereo amp, you are proposing to make the problem much, much worse.
        To make an intelligent home possible, every device must have a controller chip with a network connection. My comment was about where you put the intelligence and the user interface.

        • Bob_Wallace

          30 devices with a standardized communication system would allow for a central nervous system and replaceable/exchangeable appendages.

          I’m coming from the position of someone with a very heavy combo inverter/battery charger whose battery charger failed. It would have cost more to ship the combo for repair than to purchase a standalone battery charger plus the days without electricity.

          I’d rather have components that could be replaced when they fail or when something significantly better is introduced.

  • sault

    This setup might make sense in high electricity rate markets like Hawaii, etc., especially where utilities are getting outright hostile to distributed generation. Allowing homeowners flexibility in when they draw off the grid and how much power / kWhs they take can help maximize the benefits of installing solar while minimizing the utility’s ability to gum up the works.

    In areas where utilities are embracing distributed generation (or state regulators are making it worth their while), it’ll be a harder sell. And this setup would have to compete with any energy storage projects the utilities themselves would install, putting it at a disadvantage because utilities can tap into vast economies of scale that individuals cannot. A giant, train-sized flow battery serving 10,000 customers or whatever is going to be cheaper per kW, kWh or whatever compared to 10,000 individual systems, for example. But as a counterpoint to my own argument, utilities will never pass on all the cost savings of a setup like this to their customers, so there might still be a trade space for solar hybrid setups even in utility service areas that are more accepting of distributed generation. While the utility would be interested in capturing as much peak demand as possible by filling in the morning and late afternoon peaks seen in high solar deployment areas that displace the long midday peak seen normally, customers with hybrid setups would mostly try to avoid all the peaks throughout the day and try to use the grid at night as much as possible.

  • Vensonata

    Question: what is the price of the bosch storage system in Australia? It does not seem to be available in Canada or the u.s. lithium battery banks are definitely the future. As an aside I also have an idea (untried) that we who already have large lead acid battery banks with pv could benefit from a small lithium pack addition of about 10% of the lead acid bank. The lithium can absorb simultaneously with the lead bank but can slow feed the lead bank the last 10% to meet the necessary 100% charge for lead acid, which lithium does not require. Hence much greater efficiency and a not too expensive bridge to the day when all lithium is affordable. Engineers and off -gridders, feel free to steal my idea!

  • spec9

    Don’t buy batteries for your solar PV system unless it is a remote off-grid cabin. If you want to buy batteries, buy an electric car which puts the batteries to good use.

    • Offgridmanpolktn

      It isn’t really right to make a blanket statement like that. The systems described in the article will help make overall costs cheaper for people using solar on rainy/cloudy days that have high daytime peak rates when the electric car is with the homeowner at work or meeting appointments.
      Or for someone using the electric car as their backup on a cloudy day, and then doesn’t have sufficient charge to get to a night job.
      Systems like these will allow everyone to get their power at the lowest cost whether or not they have an EV, and according to their specific situation.

  • Dee Kay

    If you want to see sophisticated battery backup technology with time of day pricing, weather forecasting, etc. check out SonnenBatterie from Germany – very interesting software/battery system for solar self consumption.

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