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Energy Storage Assignment

By

Mr. Steven Sweeney

Lecturer: Mr. Keith Moloney

Off-grid energy storage assignment Steven Sweeney (K00181764)

Submitted: 19/04/15

Table of ContentsList of Figures...............................................................................................................3

List of Tables................................................................................................................3

1 Introduction...........................................................................................................4

2 Determining the off-grid load demand...................................................................5

3 The chosen site.....................................................................................................6

3.1 Solar resource at the golf course...................................................................6

3.2 Wind resource at the site...............................................................................7

3.3 Wind speed at a 10m hub height...................................................................7

3.4 Log law formula..............................................................................................7

3.5 Average wind speed at Carrick Finn airport...................................................7

3.6 Wind shade effects........................................................................................8

3.7 Sizing the battery bank..................................................................................8

3.8 Sizing the PV array......................................................................................10

3.8.1 The Chosen PV panel...........................................................................10

3.9 The wind turbine..........................................................................................11

3.10 The battery bank..........................................................................................12

3.11 The inverter..................................................................................................12

3.12 The charge controller...................................................................................13

3.13 Estimated system cost.................................................................................13

3.13.1 Pay back check.....................................................................................13

4 Simulating the system using HOMER.................................................................14

4.1.1 Simulation optimum results...................................................................15

5 Optimum system layout.......................................................................................17

6 Conclusion..........................................................................................................18

7 References..........................................................................................................19

8 Appendices.........................................................................................................20

8.1 Appendix A: The bill for electricity................................................................20

8.2 Appendix B: Battery data sheet...................................................................21

8.3 Appendix C: Inverter data sheet..................................................................22

8.4 Appendix D: Charge controller data sheet...................................................23

8.5 Appendix E: Wind speed at Carrick Finn airport..........................................25

8.6 Appendix F: Solar resource at the site.........................................................25

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8.7 Appendix G the E160i data sheet................................................................26

8.8 Appendix G Homers Optimum hybrid solution.............................................27

List of FiguresFigure 1: Photo of the golf course................................................................................4Figure 2: Ariel view of the site......................................................................................6Figure 3: The wind resource at the golf course............................................................7Figure 4: The calculated reduction in wind energy.......................................................8Figure 5: The chosen solar PV panel.........................................................................10Figure 6: The chosen wind turbine.............................................................................11Figure 7: The systems chosen battery.......................................................................12Figure 8: The inverter.................................................................................................12Figure 9: The charge controller..................................................................................13Figure 10: Connected components in HOMER..........................................................14Figure 11: 0% capacity shortage results....................................................................14Figure 12: 5% capacity storage results......................................................................15Figure 13: The electrical data for the optimum system..............................................15Figure 14: Battery bank state of charge (SOC)..........................................................16Figure 15: The optimum system cash flow.................................................................16Figure 16: The optimum system configuration...........................................................17

List of TablesTable 1: Approximate break down of the electrical loads.............................................5Table 2: The solar resource at the site.........................................................................6Table 3: The average month wind speed.....................................................................8

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1 IntroductionThis is a report to see if it was financially feasible to supply a currently grid connected system with an off-grid renewable energy source. The load to be supplied is a portable cabin and shed on a small “pitch n putt” golf course located at sand field, Ardara in Co. Donegal. This site was chosen because it carries out seasonal business, running from April to October. The opening hours are from 10 o’clock in the morning to 7 o’clock in the evening. It has been decided to try and supply the load demand using a hybrid renewable system that will produce the required power from a combination of wind and solar energy resources. Because this is an existing grid connected system, the appliances run on AC and it would not make sense to change these appliances to DC which would have had the benefit of not having to purchase an inverter.

Figure 1: Photo of the golf course

As seen in figure 1 the cabin has a limited area of which to install the solar panels, leaving some restrictions on the amount that can be placed there due to the front PV panel shading the one behind. There is a hill located to the back of the cabin were a small 600W wind turbine can be placed. To the left of the turbine there are some fir trees which would cause an obstruction to the wind and decrease the energy output of the turbine.

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2 Determining the off-grid load demandInside the portable cabin there are several key appliances that must be supplied. There is a fridge, cash resister, clock radio, a fluorescent light and a socket for a phone charger. There is also an electric convection heater that might be turned on a very odd time in the early summer months and instead of this a small gas heater would suffice. Therefore, this heater was not included in the overall load demand. Also on site there is a small lawnmower service shed that is lit by 2 single fluorescent lights and joint on to the back of the shed is a toilet that has an energy saving CFL bulb lighting it. The cash register is on during the typical business hours (10 hours) and the fridge is estimated to be on for average 6 hours a day. There are some adjustments that can be done with the rest of these loads. The Fluorescent lights can be changed to low energy CFL’s or LED lights to help lower the energy demand which is a vital first step in trying to supply an electrical load from a renewable energy source. Also the light in the toilet can be connected to a motion sensor to ensure use only when required. A phone usually takes about 4 hours to charge and the clock radio can be turned on during business hours. Table 1 below gives an estimated breakdown of the entire electrical load demand and how long each appliance will be in use for. This information will provide a breakdown of the run time and electrical demand, which the HOMER software package needs to simulate and optimize this system.

Table 1: Approximate break down of the electrical loads

Appliance Rated power (W) Run time (hours) Energy usage( Wh)Fridge 410 6 2460Cash register 50 8 4004 LED lamps 20 3 60Clock radio 2 10 20Phone charger 7 4 28

Table 1 shows the estimated energy usage of the appliances i.e. power and run time, totalling an energy demand of 2968Wh. As seen on the bill from June to August which is the busy season, the usage for 63 days was 187kWh and this meant that the actual consumption was 2968.25Wh per day (see in appendix A).

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3 The chosen site

Figure 2: Ariel view of the site

This site has some large trees and several houses that will obstruct the wind speed reaching the turbine; therefore a roughness class of 0.2m was used in finding the wind at the hub height. The cabins dimensions are roughly 3m wide and 4m long which limits the amount of PV panels can be installed on the roof therefore other means of supporting more PV panels may be needed.

3.1 Solar resource at the golf courseThe PV array will (if possible) be placed on top of the cabin facing south west and at the optimum angle. Table 2 shows the solar resource data for this site. The lowest expected average daily irradiance falls in October (1.83kWh/m2), with the highest falling in May (4.12kWh/m2). These are reasonable figures for Ireland and suggest that solar PV would be a good fit for this seasonal load.

Table 2: The solar resource at the site

Month Irradiance kWh/m2/dayJanuary 0.95 February 1.74March 2.91April 3.87May 4.12June 3.88July 3.56August 3.24September 2.80October 1.83November 1.16December 0.82

(International Energy Agency, 2012)

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3.2 Wind resource at the site

Figure 3: The wind resource at the golf course

3.3 Wind speed at a 10m hub heightTo find this site’s unknown wind speed at a known height (hub height) the log law formula was used.

3.4 Log law formula

V2 = V1 * (Ln H 2z0 ¿/ (Ln H 1z 0 ¿

V1 = wind speed at the known height = 8.72m/s H1= known height from data recorded = 75m V2 = unknown wind speed at the turbines hub height. ? H2 = hub height of the wind turbine = 10m Z0 = roughness length at the golf course = 0.2m

V2 = 8.72 * (Ln 100.2

¿/ (Ln 750.2

¿ = 5.76m/s

The wind speed at the hub height is: 5.76m/s

3.5 Average wind speed at Carrick Finn airportThe nearest weather station to this site was Carrick Finn airport. From the wind finder website the average monthly wind speed was determined. This was a crude method of finding the average monthly wind speed and was done purposely for ease when working with the HOMER software. Highlighted in table 3 is the wind data for the months of business.

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Table 3: The average month wind speed

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecWindSpeedM/s

8.16 6.63 7.14

6.63 6.63

5.61 5.61

6.12 6.63

7.65 7.14

7.65

(WindFinder, 2015)

3.6 Wind shade effects

Figure 4: The calculated reduction in wind energy

(Motiva, 2015)

As seen in figure 4, due to the obstacle (trees) surrounding the cabin the wind energy was be reduced by 6% and the wind speed reduced by 2%.

3.7 Sizing the battery bankThis load was seen non-critical type and really the business could still function without any power, but for good practice it was decided to allow for two days autonomy to allow for any dull or calm days.

Energy Demand = 2970Wh Systems Voltage = 12V

Charge (Q) = Current (I) * Time (T)

The daily charge demand is determined by the energy demand and the system voltage.

Q DEMAND = Energy demand(Wh)Systemvoltage (V )

= 2970Wh12V = 247.5Ah

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The daily battery capacity is found by dividing the charge demand by how much the battery will be allowed to discharge. For this application 50% depth of discharge (DOD) was used. Any more than this is not advised as it shortens the batteries life time.

C DAILY = Qdemand

Dept of DISCHARGE = 247.5 AH0.5 = 495Ah

Therefore to allow for two days back up.

C TOTAL = #days * C DAILY = 2 * 495Ah = 990Ah

To determine the total current drawn simply divide the total power that can be consumed at one time by the systems voltage.

Total current = Total PowerSystemVoltage = 489W12V = 40.75A

Therefore the battery bank must be configured to meet the voltage and charge requirements found in these calculations. A summary of the results is listed below.

Voltage = 12 V Current = 40.75 A Capacity = 990 Ah Discharge Time = 10 hours (estimate)

Therefore the batteries must be configured to meet the voltage and charge requirements to make up the battery bank.

N SERIES = SystemVoltageBattery Voltage = 12V6V = 2 batteries in series

N PARALLEL = QTotalQBattery = 495 AH225 AH = 2 batteries in parallel

Charge = current * time

Time = ChargeCurrent = 450 Ah40.9 A = 11 hours

Therefore by placing two 225Ah batteries in parallel means a combined charge capacity of 450Ah. This means that the battery now has a storage capacity that will discharge to 50% in 11 hours. This would be sufficient as the golf course is only open for 10 hours each day.

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3.8 Sizing the PV arrayAs October has the lowest daily irradiation of 1.83kWh/m2/day. Then the PV array must be sized to be able to charge the battery bank on days like this one.

Energy OUT (Eout) = Power MAX (Pmax) * Daily Irradiation in peak sun hours (PSH)

1 PSH = 1000Wh/M 2 Irradiation

Eout = 2970Wh PSH = 1.830 Pmax =?

There will be losses associated with a PV system of roughly 20% due to the inverter, PV panel array and the battery bank. This means that the PV array will need to produce 20% more energy (Egross) to supply the energy required (Enet).

ENET = EGROSS * (1-Losses)

EGROSS= Enet

1−losses = 2970W h1−0.2 = 3712.5Wh

Pmax = EoutPSH = 3712.5W h1.830 = 2028.69 W

2028.69W is the amount of power that the PV array must output to meet the loads daily requirement. It is not possible to get one PV module to fit this size therefore a series of modules need to be combined together to make up an array.

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3.8.1 The Chosen PV panel

Figure 5: The chosen solar PV panel

(Amazon, 2015)

To supply the system with only PV it would be necessary to purchase 8 of these solar panels. Therefore by adding another power source would be essential in a load that required a power supply all year round as the solar resource in the winter is a lot less. To see how the system runs as a hybrid, a small e160i 600W wind turbine was added as a power source. It was estimated that installing the e160i wind turbine as well would allow a requirement for only 4 250W PV panels. This gives a cost for the PV array of €1244.

3.9 The wind turbine

Figure 6: The chosen wind turbine

(Ilios Energy Solutions, 2015)

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To help reduce the need for as many solar panels, installing a wind turbine would be very beneficial. It would be hoped that combing both these components would also increase the chances of keeping the batteries topped up most of the time. The turbine selected was a 600W turbine with a 1.6m diameter rotor as seen in figure 6. The wind turbine costs €1750 (excluding shipping and installation costs).

The annual energy output (AEO) of the turbine can be found. As found earlier in figure 4 the wind speed was reduced by 2% due to obstacles and had to be deducted from the original figure (0.02 * 5.76 = 0.1152m/s).

AEO = ƞ* PAVG * Area * Run time Efficiency (ƞ) = 20% (small scale efficiency) Area (A) = πr2 = 3.14 * 0.82 = 2.512m2

Run time (T) = 0.95 * 8760 = 8322 hours Average power density (PAVG) = 1.91 * 0.5 * ρ * V3 = 1.91 * 0.5 * 1.225 * 5.643

= 209.88W/m2

AEO = 0.20 * 209.88 * 2.512 * 8322 = 877.51kWh

Without the obstacles interference the AEO would have been 934.70kWh.

3.10 The battery bank

Figure 7: The systems chosen battery

This system required 4 Trojan 6V T-105 225Ah batteries. This gave a combined total cost of €935. The data sheet can be seen in appendix B.

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3.11 The inverter

Figure 8: The inverter

(Alibaba, 2015)

The Inverter converts the variable direct current (DC) output of the PV array into the alternating current (AC) at a frequency (50Hz) safe for appliances. The inverter chosen for this project was a solar hybrid wind turbine inverter and costs roughly €380. The data sheet can be found in appendix C.

3.12 The charge controller

Figure 9: The charge controller

(Sun Store, 2015)

The charge controller as seen in figure 9 is an essential component of any off grid system. A charge controller monitors the power being delivered to the battery bank from the PV array and the wind turbine. This is very important because the charge controller will stop the power being forced into the battery bank once fully charged, preventing damage to the battery. The charge controller for this project costs €208. The data sheet can be seen in appendix D.

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3.13 Estimated system costAfter researching and pricing all the required components, it was found that the estimated overall cost to install this system (excluding labour costs) was €4517. The price that the golf course pays for 2 months of electricity is €78.50 (€39.25/month) (see appendix A for the bill). Therefore the annual cost of electricity including the 5 months of no business (€16/month PSO levy) is .€284.70/year.

3.13.1 Pay back check

Payback = Totalcost

net annual income = € 4517€ 284 .70 = 15.87 years

This is a relatively high payback time and wouldn’t be that appealing to implement this system based on this figure.

4 Simulating the system using HOMER

Figure 10: Connected components in HOMER

HOMER is a very useful piece of software to use in optimising the best system to install at a site such as this golf course. The golf course is a non critical load with the worst case scenario being that the drinks are not chilled for customers. Therefore there was room to allow the system to run out of charge very rarely if need be. HOMER was allowed to work with two simulations, one with a 0% capacity shortage (not allow the load to run out) and the other was a 5% capacity shortage (meaning allow load to run out for 5% of the time). This could significantly reduce the size and cost of the battery bank required.

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Figure 10 shows the connected components in HOMER. HOMER is a useful tool to optimise a system because it can search for the least number of batteries. It can also give the best way to install components for hybrid systems such as this one. An example of this would be to see if it would be cheaper to install two turbines and no PV or all PV and no turbines.


Figure 11: 0% capacity shortage results

Figure 11 shows the system running with 0% capacity shortage meaning that the battery bank must never run out of charge. This simulation suggested that for the optimum system is to leave out the wind turbine and install a PV array of 7. There was also a need for a battery bank of 10 batteries which increased the cost of the system.

Figure 12: 5% capacity storage results

Figure 12 shows an allowance of up to 5% capacity shortage, therefore 4% showed not to include the wind turbine and use a PV array of 7, with a battery bank of 6 instead of 10. This system allowed for 4 batteries less which would save €936. As this system was the cheapest, it was chosen as the optimum system that would be best suited for the golf course.

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4.1.1 Simulation optimum results

Figure 13: The electrical data for the optimum system

Figure 13 shows the electricity production data. There is a significant amount of excess electricity being produced totalling 63.2%. This was due to no load demand outside the season, April to October. February and March have considerable amounts of electricity produced with no demand and are the main contributors to this large figure of excess electricity. There is 3.1% of the yearly electricity demand not met, which was a trade-off with saving on installation costs.

Figure 14: Battery bank state of charge (SOC)

Figure 14 shows the state of charge (SOC) of the battery bank. The mean SOC stays above 80% for the first 2 months of business in April and May. The mean SOC gradually deceases as the summer wears on and in the final 2 months of business in September and October the mean SOC is just above 60%. If this was not a summer business then the solar PV would not be sufficient to charge the battery bank for the winter months and the wind turbine would need to be included also (see graphs of hybrid system in appendix H).

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Figure 15: The optimum system cash flow

Figure 15 shows the cash flow corresponding to the PV only system. The red bar shows the initial investment at the start which included the PV array, the converter and the battery bank costing €3676. The next cost for the golf course would happen 10 years after installation when the life time of the batteries was reached and therefore must be replaced (seen as a pink bar). This has a cost of €1404 (€234 X 6). The next component to reach its end of life was the converter at a cost of €380 (seen also as a pink bar). There is a salvage value to be gained at the end of the projects lifetime represented as a positive yellow bar.

5 Optimum system layout

Figure 16: The optimum system configuration

Figure 16 shows the complete system configuration with all the components wired in place. The PV array converts the solar energy from the sun in to electrical energy and delivers it to the charge controller. The charge controller feeds the electrical

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energy to the battery bank at a controlled rate to provide over charge protection. The charge controller can also extract charge from the battery to supply any DC loads such as LED lighting. Also spurred off the battery bank terminals is the DC/AC inverter that rectifies the 12v DC in to 230V AC that is suitable for the golf courses appliances. This system has one particular advantage over the hybrid system proposed earlier in this report in the way no dump loads are needed, whereas wind turbines do require a dump load.

6 ConclusionAfter using the HOMER software package to optimise this system, it was found that the most suitable system for the golf course was to use standalone solar PV. The PV array consisted of 7 250W solar panels with a battery bank of 6 225Ah batteries and a 1kW converter. The optimised result differed from the hand calculations made previous, which sized the system for 8 PV panels and 4 225Ah batteries. If the system wasn’t optimised with HOMER, the battery bank would have been insufficient. The total system had an estimated payback time of less than 16 years and by this time the life time of the converter and battery bank would have been exceeded and they would have had to be replaced. The golf course at present is grid connected and even if it wasn’t, it would still not cost that much for grid connection to be installed as it is located on the road side near other houses. Therefore it would not be a good investment to go completely off-grid for this application, unless there is a sharp increase in electricity prices in the future. From completing this report it seems that an off-grid system would only be viable in remote locations were grid connection is non-existent or would cost too much to install.

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7 ReferencesAlibaba, 2015. Solar hybrid wind turbine inverter. [Online] Available at: http://www.alibaba.com/product-detail/Solar-hybrid-wind-turbine-inverter-1kw_1810758655.html[Accessed 31 March 2015].

Amazon, 2015. solar panel 250w. [Online] Available at: http://www.amazon.co.uk/motorhome-caravan-household-off-grid-Germany/dp/B00HHVO5CO/ref=sr_1_1?ie=UTF8&qid=1428329991&sr=8-1&keywords=solar+panel+250w[Accessed 6 April 2015].

Ilios Energy Solutions, 2015. E160i Wind Turbine. [Online] Available at: http://iliosenergy.co.za/wind-turbines/26-wind-turbines-off-grid-600w-3500w.html[Accessed 12 April 2015].

International Energy Agency, 2012. Photovoltaic Geographical Information System - Interactive Maps. [Online] Available at: http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php#[Accessed 30 March 2015].

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Motiva, 2015. Wind shade calculator. [Online] Available at: http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shelter/index.htm[Accessed 11 April 2015].

Sun Store, 2015. 12v Solar Charge Controllers. [Online] Available at: http://www.sunstore.co.uk/12v-Solar-Charge-Controllers/[Accessed 6 April 2015].

WindFinder, 2015. Wind & weather statistics Donegal Airport/Carrickfinn. [Online] Available at: http://www.windfinder.com/windstatistics/donegal_airport_carrickfinn[Accessed 11 April 2015].

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8 Appendices

8.1 Appendix A: The bill for electricity

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8.2 Appendix B: Battery data sheet

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8.3 Appendix C: Inverter data sheet

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8.4 Appendix D: Charge controller data sheet

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8.5 Appendix E: Wind speed at Carrick Finn airport

8.6 Appendix F: Solar resource at the site

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8.7 Appendix G the E160i data sheet

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8.8 Appendix H Homers Optimum hybrid solution

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