Wednesday, 24 December 2014

Summer bounty

One of the good things about summer is the fruit we harvest from the garden.

Right now we are feasting on apricots and plums



There's plenty of fruit that's still ripening, like the nectarines and peaches



Other fruits still have a way to go before they're ready for picking .....






So far it's been a good harvest!


Sunday, 7 December 2014

Installing batteries at PragSust HQ

We've started the design process to install batteries at our house in Melbourne's suburbs. We thought it might be useful to discuss why we're doing this and to describe the process so others can learn from what we find.

The electricity grid in suburban Melbourne is very reliable with generally very good quality power supply. But there are those pesky greenhouse gas (GHG) emissions. As most of Victoria's electricity is generated from burning brown coal or lignite, as judged by GHG emissions Victoria has one of the dirtiest electricity supplies on the planet. By installing PV's, efficient appliances and lighting, using Green Power and some behavioural measures we've gradually reduced our GHG emissions from electricity to zero. And we have an electric oven (with gas cooktop), instantaneous gas boosted solar hot water and an efficient wood heater so we use very little natural gas.

So why install batteries? The first point to emphasise is that we're not aiming at grid independence. We think grid independence is unrealistic as a standalone system with just batteries and PV's at our house. Mr PragSust has built a detailed multiple renewables and storage modeling tool as part of a research project. This can use cost and performance data from batteries, PV's and other intermittent renewables and despatchable renewables such as bioenergy systems to model what a system costs to meet energy demands. The tool matches energy demand and generation data at half hourly intervals over a year.  PV's obviously don't generate at night. Cloudy periods during the day or over many days in winter can reduce PV generation to almost zero. So the only way a PV system can meet demand when the sun isn't shining is to have storage. But coping with extended low insolation periods very soon shows that a very large array and storage capacity is required. Even though PV's have become much cheaper and battery costs are decreasing,  the capital cost of installing a large PV generation and storage system is still prohibitive for most. 10kW is 40 250W panels. Finding space on a suburban block to fit 40 north facing panels is challenging. Let alone where to put a large battery pack. We only have weather records since the 1800's in Melbourne. The climate change models predict significant changes in Melbourne's weather which some argue have already started. What would we do if we had sized a PV-storage system for 5 days with no sun but we had 6 days of low insolation?

People on rural sites in Australia with no grid power have been running Remote Area Power Supplies (RAPS) for decades. But these tend to have generator backup for periods without sun and often these homeowners will have a very strong focus on reducing electricity consumption. Everyone in a suburban street buying a good quality generator capable of charging batteries would be a very inefficient use of resources. And while PragSust strongly supports and practices reducing energy consumption, whether the good people of Melbourne are prepared to be as ruthless on their power consumption as many RAPS sites is moot. And does it make sense to tie up large amounts of money in a stand-alone system where most of its capacity is designed to be used only for a small percentage of the year?

To get serious about sustainability we need solutions that are scalable, cost-effective and widely implementable. PV's are an excellent example of a technology that meets these criteria. So how do we think batteries can be usefully deployed with PV's while still maintaining our grid connection?

New PV systems in Victoria will receive a feedin tariff of only ~6c/KWH from 2015. (Possibly with a topup from some retailers.) Typical electricity tariffs in Victoria are around 12-15c/KWH offpeak and 25-30c/KWH peak. And at PragSust HQ we've chosen to pay about 3c/KWH extra for Green Power. So even after energy losses charging and discharging the batteries, there can be a financial benefit from storing excess PV generation and using battery power to replace peak demand currently supplied from  the grid. The electricity bills for larger electricity users may contain charges based on their peak demand during a half hour over a billing period. This reflects the  cost to the electricity supply industry of having supply capacity large enough to cope with this peak. Batteries can supply power during these peaks. This is sometimes called  shaving the peaks. As well as saving money for the electricity customer by removing the peak access charges, smoothing these peaks has a powerful and profound influence on the overall cost of the electricity supply system. Total generation capacity can be smaller. This is a significant saving. Several billion dollars worth of generation capacity in Victoria is only used for small amounts of the year. But this generation capacity has to be paid for so electricity bills are higher to reflect this cost.  The transmission and distribution network has to be sized to meet these peaks. Again, this cost can be much lower if batteries are used to meet peaks. Electricity has become a lot more expensive in Australia over the last ten years. Much of this price increase is due to new transmission and distribution infrastructure. There is now a regulatory requirement to determine the lowest cost means to alleviate perceived electricity infrastructure constraints. Batteries are one viable technology in some situations.

We need more information from actual sites with batteries in Melbourne to help make informed decisions about high penetration and 100% renewable energy systems. While modeling is useful, factories can't run on a spreadsheet. Extensive monitoring and data collection can generate information of great assistance to other electricity users, policy makers and investors.

And going back to the micro from the macro, having a system capable of supplying electricity during the occasional interruption to our electricity supply is useful.

We'll describe our progress with the battery installation in later posts. We hope this will be interesting and useful to other people contemplating battery installation.