Batteries and Portable Power

Japanese find HEMS plus PV Reduces Peak Electricity Demand by 42%

The HEMS Working Group, one of the household divisions of the Keihanna Eco-City Next-Generation Energy and Social System Verification Experiment Project in charge of HEMS, has initiated verification experiments for 14 households equipped with HEMS (Home Energy Management Systems) and solar power (PV) generators. These experiments are largely divided into two parts; reducing CO2 emissions by half or more by providing “visibility” for the amount of electricity consumed and advice on saving electricity, and responding to Demand Response (DR) requests issued by the CEMS (Community Energy Management System). The full-scale operation of these experiments started in fiscal 2013, and in addition to achieving excellent results, they have also added more clarity to the topics that need to be approached. The summer per-person target for the Peak Demand Reduction model implemented in fiscal 2013 was set at 0.100kW per person, which represents a 61% decrease in load over the 0.257kW per person set in 2007. The result of this was 0.150kW against the set target, and although the target was not achieved, a reduction of 42% was attained.

The reason why the target for the summer 2013 peak demand reduction DR experiment was not achieved has been analyzed by the person in charge of HEMS control in Omron Corporation, who claims, “The way in which the amount of electricity generated by the solar power systems was handled during the DR preparation period (morning) when the peak demand reduction DR signals issued by the CEMS were created was not sufficiently reconciled to CEMS in advance.”

The 14 households taking part in the HEMS verification experiments have solar panels with a capacity of between 3kW and 4kW installed on their roofs, and have been equipped with HEMS units for use in the experiment. The 14 households are divided into two types; those which operate only on electricity into which heat-pump water heaters have been installed, and those which operate on a combination of both electricity and gas into which home-use co-generation fuel cell systems (for both heat and electricity) and high-efficiency water heaters have been installed. Ten of the 14 homes are also equipped with storage batteries with capacities of 10kWh.

The type of DR verification experiments involving CEMS in a leading role to be implemented have been narrowed down to two project models in consideration of societal changes in the aftermath of the Great East Japan Earthquake. These involve a Peak Demand Reduction model to promote the reduction of demand (electricity received from the power grid) during peak demand periods, and a Power Supply and Demand Adjustment model that is operated in accordance with pre-planned power consumption (electricity received from the power grid). In the Peak Demand Reduction model, the greater the load (electricity received from the power grid) reduced against the baseline during specified periods and the greater the amount of electricity sold results in increases in the amount of incentives awarded to consumers. In the Power Supply and Demand Adjustment model, the closer consumers get to the values stipulated in the plan issued to them by CEMS with regard to electricity received from the power grid, the more incentives they receive.

The plan issued by CEMS during the summer 2013 peak demand reduction DR experiment placed the emphasis on maximizing the amount of electricity sold, and because of this the electricity discharged from the storage batteries was used to cover household power demands in the morning, and the surplus electricity generated by the solar power generators was placed on sale (a method known as the up-thrust effect). However, because the electricity stored in the storage batteries was discharged in the morning, the batteries reached their limit during the 1pm to 4pm peak reduction DR period. Had the surplus electricity generated by the solar power generators been used to recharge the storage batteries in the morning, it would have been possible to increase the amount of power discharged during the DR period in the afternoon.

In reflection of this, the peak demand reduction DR experiment implemented in the winter of 2013 was changed to a HEMS control method. The peak demand period in winter is from the evening through to the night. Instead of targeting the up-thrust effect for the surplus electricity generated by the solar power generators during the day, the peak demand reduction DR requests issued during this period call for the surplus electricity generated by the solar power generators to be used to recharge the storage batteries so that they have a capacity close to 100% by the evening. The use of discharged electricity is maximized and the amount of electricity received from the power grid minimized during the peak demand reduction period.

This resulted in the winter target per person for the Peak Demand Reduction model being set at 0.185kW per person, which represented a 58% decrease in load (electricity received from the power grid) over the 0.441kW per person set in 2007, and a reduction level exceeding 62% at 0.166kW was achieved.

Response to Power Supply and Demand Adjustment DR requests operated in accordance with advance plans for power consumption (electricity received from the power grid) in advance achieved a coverage level that exceeded an average of 80% for ten households in which storage batteries had been installed during both summer and winter. The term “coverage level” is the percentage of households that achieve +/-200Wh per 30 minutes against the targeted values on the load curve notified by CEMS during the 16-hour period between 7am and 11pm when power supply and demand adjustment DR requests are in effect. The coverage level of households with storage batteries installed reached 82% in summer, and the households not equipped with storage batteries reached 63%. In winter, households with storage batteries installed reached 83%, and the households not equipped with storage batteries reached 71%.

The targeted values on the load curve notified by CEMS are based on the amount of electricity to be received from the power grid predicted by HEMS in accordance with past load data, past power generation data and the weather forecast for the following day. This is then revised by CEMS, so in most cases the values used are almost the same as the predicted values. Consequently, the coverage levels are determined by the accuracy of the predicted values calculated by the HEMS and the precision of supplementing power from storage batteries when the predictions are inaccurate. The person in charge at Omron Corporation pointed out that, “Achieving 80% coverage levels with HEMS predictions and storage batteries is a huge success.”

Another topic being tackled by the HEMS Working Group is to cut CO2 emissions in half by providing advice on energy-saving measures. The target has been set at “CO2 emissions of 490kg per person/per year.” This value has been set to reduce by approximately 60% the 1,210kg of CO2 emissions per person/per year recorded in Kyoto City in fiscal 2007. Advice on energy-saving is being provided in 2013 to attain a total of 595.8kg of CO2 emissions per person/per year between January and December of the same year, representing a reduction of approximately 51% over fiscal 2007 figures.

Committee meetings explaining energy-saving methods (briefings for local residents) involving the entire committee and for individual households have been implemented on two occasions respectively. The person in charge at Sharp Corporation explains that, “although we didn’t meet our target, the advice provided resulted in large reductions in certain cases, and we gained much.”

The CO2 emissions target for each household was set before energy-saving advice was provided. The CO2 emissions for each person differed greatly in accordance with the number of people in the family and lifestyle customs, etc. Households with minimal levels of CO2 emissions before the experiment had little room for further reductions. Because of this, imposing uniform reduction rates against the past results of CO2 emissions for each household would lead to discrepancies in the level of effort that would need to be put into reducing consumption.

Taking this into account, calculations were made to include a combination of pre-determined percentages of CO2 emission results for each household during the previous year and the average CO2 emissions of the population of Kyoto City, and having totaled this figure, targets for the per-person level of CO2 emissions attainable throughout all households were set for each household. Leveling off the past results of each household’s CO2 emissions with the average value of CO2 emissions for the population of Kyoto City enabled the level of effort required of each household to be set at a similar standard.

Once the individual targets were set, advice on energy-saving measures that matched up with each household was then provided. The ways in which this was carried out were divided into the following three main methods: (1) Promoting modifications to appliance settings; (2) Promoting changes to family member activity patterns; (3) Recommending the replacement of household appliances with high-efficiency models.

The measures promoted in (1) included setting heat-pump water heaters to the energy-saving mode with which a minimal amount of water is heated, weakening the temperature setting of freezers and refrigerators when residents are away from the house and when sleeping, and switching off the quick-start settings on televisions and BD/DVD recorders, etc. The measures promoted in (2) included reducing the number of times the dryer on dishwashers is used by washing crockery and cutlery in bulk, and reducing the amount of time note PCs are used every day by one hour, etc.

The measures promoted in (3) achieved the greatest results with freezers and refrigerators. The HEMS operation patterns have been changed for fiscal 2014. In further detail, the HEMS have been operated up until now with the emphasis placed on patterns that attain the largest levels of reduction in CO2 emissions, but verification experiments will now be carried out to discover if residents are able to operate effectively when offered patterns that provide the most economic benefits, patterns aligned to the optimization of power supply and demand for the local community, and patterns that involve a combination of both of these. Making the best use of the results acquired up until now, verification experiments into HEMS operations that conform to the most realistic situations are scheduled to be implemented.

Japan Smart City
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