Firstly we need a dwelling. For this example our dwelling is again located on the southwest coast of Ireland because of the levels of solar radiation that is available, the building is orientated due south to maximise the capture of solar radiation and there is no over shading concerns from any direction.

The image below shows the yearly total of global horizontal irradiation for the island of Ireland.

Source

Dwelling Energy Use

Next we need to get a base load for the energy consumed by the dwelling. In this case we are assuming that the occupier has applied the basic energy saving techniques to the dwelling such as:

-Low energy bulbs
-Design for natural Illumination
-Eliminate standby power
-Minimise/Eliminate electrical immersion
-Boiling water for immediate use
-High Efficiency appliances.

The dwelling was audited for electrical consumption for daily, weekly and quarterly consumption and the averages calculated from the readings to give the base load for the dwelling. The base load per day is calculated at 6.51 kWh/day which gives a monthly usage of 201.66 kWh/month.

Solar Radiation

If we take the solar radiation at the location and plot this against the consumption per m² for a 24 hour period we can see that the peak electrical consumption for the dwelling occurs several hours after the peak in solar radiation. This pattern will help define the type of system that we should be installing for maximum payback.

Hourly radiation per m2 and consumption pattern of the dwelling during a normal day.

The first system uses a battery pack to store the energy for use during the peak load while the second systems is connected to the grid to feed power back when it is not consumed by the dwelling and power in the evening is puuled from the grid.

If we use a larger data set from the Valentia Island Meterological station located approx 40 miles from the dwelling location we can calculate the total solar radiation available per unit area that can be used to drive generation for the dwelling. The data is converted to kWh/m² and corrected for the roof inclination. When the figures are calculated it gives us 1159 kWh/m² over the year.

This data has been broken into total radiation per m2 and total consumption of the dwelling per m2 of roof space available to generate electrical power from. Using this method we can straight away determine what energy is available to be harnessed, albeit prior to conversion to electrical energy and excluding system losses. Straight away it can be seen that this is all down to efficient conversion of solar energy into electrical energy.

The best way to view this data is to look at the ratio of consumption to radiation per unit area of the roof space at each month. This ratio will tell, broadly, the entire system efficiency required to satisfy the monthly base load conditions. This is graphed below and it clearly shows that months January, November and December are months with low solar radiation and that total system efficiencies of 15-20% would be required to satisfy the consumption patterns measured. For all other months a total system efficiency of approximately 10% would suffice to satisfy load conditions.

PV Collectors

The selection of a PV system configuration was somewhat simplified due to government initiatives for a renewable energy feed in tariff (REFIT) of 19cent per kWh for micro generators which was introduced early in 2009 (www.esb.ie). The aim of the project is to promote micro generation of all renewable technologies throughout the country and in particular technologies suited to areas with geographical differences. Seeing that this REFIT can be availed of, then the easiest and cheapest option for a dwelling is to feed its produced energy into the grid and consume as you require. This eliminates the need and cost for a battery storage system and also insures that you always have power as a stand alone system would not be the preferred choice if mains power connection is readily available. As shown above the maximum radiation and consumption pattern for the dwelling are time shifted by approximately 5 hours, therefore power is not available when most needed at the location. In additional, this grid tied system can be cash positive, due to the REFIT being greater than the cost of electricity that you purchase from the grid. Every kWh you export makes you 4.47cents more that the cost of every kWh you consume when there is no PV power available, such as during the late evening and night. The table below shows the current price comparisons of imported electricity and electricity generated and fed to the grid under the REFIT scheme.

Grid tied PV systems are by far the most popular systems world wide having nearly 70% of the over all PV systems installed in this manner, measuring some 1000 MW of an installed base in 2002. This REFIT scheme allows the public to integrate a PV system of less than 6kWp (www.cer.ie) into a dwelling. During times of low power production, electricity can be imported, and during times of excess electricity production over consumption, energy is fed into the grid and the user gets the benefit of receiving the higher feed in tariff. This tariff is targeted as an incentive for micro generation throughout the country.

Multiple PV systems were examined for selection from the multitude of panels available on the market. Key performance parameters must be looked at for selection which includes output, efficiency and cost. The main criteria can be summarized as below.

Source

The above systems have been compared excluding BOS components required so that criteria on the panel performance may be first evaluated and a superior panel may be selected. From this data the best panel from a cost perspective per kWh is the Solarcentury were selected due to the inherent advantages such a system incorporates, which include reduced labor costs and material build costs as these are installed as a replacement for roof tiles, zero glare factor and the aesthetically integration of the system into the dwelling. This system also has grid connection capabilities and uses the same system components as a conventional solar PV panel system.

The two types of systems were directly compared. A table from suppliers was drawn up for the standard on roof panels where key parameters such as ouput, efficiency and cost were examined. From this the most appropriate panel was chosen and then compared with the BIPV system. Initial data, shown below, would suggest that the on roof system is superior in cost of produced electricity, but other factors must be taken into account.

System Components

As the system will be grid tied, an expensive battery pack is not required. Being grid tied reduces the over all capital cost of the PV system, maintenance over the operational lifetime and ensures that during days of low solar radiation mains power is at hand to use and conversely, during periods of high solar ardiation, power can be exported to the grid availing of the REFIT scheme described earlier.

Source

The remaining components of the system are the import/export meter which is freely installed by the ESB due to the REFIT scheme currently available (www.seai.ie). Apart for this the main component is the inverter which is responsible for converting the DC power produced by the PV array to AC grid voltage regulated specification. This power may be then used by the dwelling electrical devices or exported to the grid. There are many inverters on the market to choose from and four configurations possible, namely (a) central inverter, (b) string inverter, (c) module integrated inverter and (c) masterslave inverter.

The number of PV panels can help to choose an inverter configuration as inverters are maximum voltage rated, so typically 20 panels giving a 24 volt output would give a 480VDC input into the inverter. As most are rated for approximately 500VDC input, more than 20 panels would require a second inverter and there for eliminate the central inverter configuration. Multiple inverter configurations tend to be more expensive due to more components required, so the best options would tend to be a dual inverter configuration if the power output requires this. Otherwise, a single inverter rated for the output would be most cost effective and would maximize efficiency of the entire system. When choosing an inverter the main considerations are cost, efficiency, warranty, rated power and power factor. A number of meters have been investigated and are summarized in the below. All these inverters may be used with either system and the choice of inverter will depend on the area of panel or tile laid on the roof, which will define the PV system output.

It should be noted that surveys have shown that 63% of all faults with PV arrays are caused by inverters, so from this data, as a general rule, one should if technically possible, minimize the use of multiple inverters where not necessary. In saying that, inverters have improved significantly in last ten years for reliability.

Source1,Source2

BOS packs for the solar tile have been quoted at 2000 euro for the roofers pack, and the electricians pack, including a Fronius or Sunny boy inverter depending on what size of system is ordered. A detailed description of the pack contents is given in appendix G. We can make the assumption that the packs for the on roof panels will be approximately the same but individual quotes were not possible, while we can ignore the cost of laying the solar tiles as normal roof tiles would have to be laid in any case. Solar tiles can be easily laid by qualified roofers.

Total System Losses

The annual output powers generated above are ideal values with no losses incurred, Eideal. To get a more realistic estimation of output, losses incurred due to a multitude of factors must be included such as module soiling, module temperature effects, intermittent shading, mismatching and DC losses, MPP mismatch error, inverter losses and AC losses. Generally, these are estimated at the levels shown below.

This data shows that the power generation capabilities of the system need to be corrected to show Ereal, the actual power generation capability. When we correct for losses, the system output lowers change significantly. A summary is shown below in table 4.3.2 giving values of Ereal for both PV systems. Losses for both systems are expected to be the same due to similar wiring, inverter size and environmental conditions.

Using this real output data we can now calculate the overall efficiency of the entire system. As we can see from table the 4.3.3 below, both systems are close to the 10% efficiency range when we compare total insolation at the location to total power produced per unit area. The Kyocera system is approximately 6% more efficient than the solar tile due to its greater output per unit area.

Below in figure 4.3.4 the real output, Ereal, per meter squared of roof space is graphed to show the base load and power generation levels possible per unit area. From this graph it can be seen that the entire annual load can be satisfied easily from the available roof space. Nine months of the year are easily satisfied with 10% conversion efficiency. January, October and Decembers generation potential fall slightly below the load demand required and therefore, with a grid tied system, these months will be net importers of electrical energy. Excluding BOS losses, all other months could be net contributing to the grid and so could avail of the REFIT scheme.

This data is totaled for the year for both PV arrays to show the accumulated real power generation and consumption in figure 4.3.5 below.

System Cost & ROI

Individually, the different system costs per m2, the BOS efficiency and cost, the ideal and real power generated for the insolation calculated at the dwelling location have been examined. Now all of these should be looked at as an integrated package and a final system chosen for a particular generation strategy. That strategy should depend very much on what the desired goal is. There may be many goals such as

- the production and use of CO2 free energy
- protecting yourself from increasing energy prices
- security of supply
- the possibility of generating a revenue stream from selling power to the grid

In the case of the author it is actually all of the above, and so a detailed analysis of capital costs versus output per year must be made to understand how much of an investment is to be made and so, how much power will be produced on site. A detailed evaluation of both systems for output and cost at the dwelling location using solar radiation data from Valentia Island meteorological station can be downloaded HERE.

From the analysis carried out in table 4.4.1 above the following key point summary can be made
- Offsetting the annual consumption of the dwelling should be carried out with solar tiles due to the lower total capital
costs. Payback time to offset annual consumption is 34 years, instead of 38 years for the on roof solar panels 18

- There is no significant benefit from tiling the entire roof as the payback time reduces to approx 28 year for both, and the capital costs required are high.

- The REFIT scheme, while a valuable start on the promotion of micro renewable projects, is not highly enough incentivized in Ireland. The tariff level is too low for PV power generation technology, as compared with other countries such as Germany which offer 42cent/kWh. This low tariff drives the high payback time as the cash generating capabilities of the array are based on the feed in tariff rates available. With a higher REFIT, it may be advantageous to cover the entire roof.

- The 60 year price per kWh looks cheap, but I don’t think these or any other PV collector would last 60 years. Typical warranty periods are 25 years.

- The capital cost of the collector is crucial factor making PV an expensive option for power generation, coming in at approximately 500 euro per m2, noting that the power output per unit area is similar. The current capital costs of solar PV installations do not make it the top choice when looking at a renewable micro generation project. However, in order to take advantage of the introduction of the scheme the author would chose the solar tile system and offset the annual consumption and not choose to maximize the output with the entire roof area.

The payback period is somewhat misrepresenting as it assumes the cost for electricity will not increase over time. If we look at the long term inflationary rate at an average of 4% and apply that to the price of electricity, we see the payback time tumble to under 23 years for this chosen system. It should be noted that domestic electricity prices increased by 33% between 2005 and 2009 (www.sei.ie 3). Figure 4.4.3 below shows this analysis.

The main advantages of having the system installed is that you are protected from radically increasing energy prices as you operate under a net metering scheme and, at any time, you can increase the array size to increase your output in the event of increasing REFIT tariffs. The dwelling will have fixed electricity costs of just under 17cent per kWh over the next 34 years.

PV systems have generally fallen over time due to technological advances and manufacturing improvements (www.renewableenergyworld.com (2008), The German Energy Society, (2008)). Therefore the prudent approach may be to install what is required for present consumption requirements and increase the array size in the event of a significant increase in electricity prices or if the cost per kWp reduces significantly in the coming years. With this array, you should also be able to avoid the soon to be introduced carbon tax in where the user will pay per kWh consumed or per kgCO2. Details of this scheme have not been finalized but it is imagined that micro renewable generators will be credited for each kWh produced or kg CO2 of emissions saved in offsetting conventional fossil fuel based generation.

Is it worth it?

It depends on the reasons for installing it. If the reason is to do with making money, then no, it’s not worth it. There are many other technologies that would be more suitable to Irish climatic conditions. If the reasons are to do with installing a dual purpose technology into your home, generating zero carbon electricity, hedging against large increase in electricity prices or having some security of supply, then, yes the technology is worth it when you look at the life time of the panels and the payback time calculated with increasing energy prices over the coming decades.

When we examine component cost if is found that the cost per kWp of the array is the key factor. As technological improvements are integrated into the design and manufacture of the cell the price will continue to decrease which may help push PV arrays towards a lower payback time. There are currently are no government grants available for the purchase and installation of solar PV in Ireland, unlike other renewable technologies which help offset the capital costs.
Grid Connection vs Stand alone systems

As seen from the comparison with diurnal insolation and daily consumption patterns, stand alone systems are not feasible without a battery pack. This battery pack adds to the cost significantly (up to 8,000 euro). Grid connection systems have multiple advantages that ensure that they are the first choice of system in the majority of cases. Included in these advantages is the REFIT scheme, which reduced the cost significantly. With easy grid connection capabilities available, there is no reason to go stand alone.

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In this, the first of our two part series, we are looking at Solar Panels both thermal and photovoltaic. In particular, looking into the payback times involved when installing a solar panel. Both of the articles are based on papers I have submitted recently for my master in Renewable technology through the University of Ulster and while some of the calculations used in the paper are beyond the scope of this article the results should speak for themselves.

With the recent revision of the building regulations requiring 10kWh/m² of the energy used in a new home come from a renewable source, solar panels are the most obvious choice for most home owners. This along with the retrofit market puts Solar Panels the No 1 choice for renewable energy. There is a vast array of panels on the market and choosing the most efficient and most suitable panels for your location can be a daunting exercise. In this article we will look at two different solar panels, a flate plate and an evacuated tube collector and determine which one is best suited to the Irish Climate and which one will give the best payback time.

Measured Data

For this exercise measured data for a solar HW heating system is used on two different panels. The data used is from the EUROSOL^[1] sheet which gives solar radiation data from 6 locations around Europe. This data can be downloaded here and is interesting to note how the solar radiation data compares from location to location. The two solar panel systems used have an installed area of 4m² with the first panel a flat panel collector made by Gasokol, an Austrian manufacturer, and the second system is an evacuated tube system by Sunda, a Chinese manufacturer of solar panels.

Optimum Angle

If, for example, we move the panels to southern Italy the figures change dramatically with the flat plate collector performing better with an efficiency of 62.9% compared to the evacuated tube system at 56.3%

The orientation and angle of inclination of the panels will of course make an impact on the performance of the system. The obvious orientation is due south and any deviation from this will have an effect on the performance of the system and in turn impact the payback times involved. Less obvious is the angle of inclination which is affected by the location of the dwelling which needs to be taken into account for optimization. For this sample case we are using a fictional dwelling located approx 50 miles from Cork city on the south coast of Ireland.

Using the sunbird jrc online calculator^[2] the optimum angle is calculated at 36 degrees for our location. With a typical rooftop angle of 40 degrees this should be close enough to receive the maximum radiation at this location. If required the angle could be adjusted on the roof to obtain the optimum angle but as we shall see it may be more useful to have the collectors tilted towards a more optimum angle to receive the winter sun as these months have the largest deficit for measured solar radiation.

Since the demand for hot water can usually be met quite easily during the summer months as there is a surplus of energy obtained from the panel to supply the required household hot water needs, hence the requirement for a heat dumps to be installed into the system, but the winter months have the largest solar radiation deficit and it may be more suitable to set up the angle of inclination toward a more optimal winter setting. We will look into this later in the article and see if adjusting the angle has any real impact on the performance of the panels.

Estimating Hot Water Usage

We can calculate the estimated hot water used in a typical house by the number and quantity of water used for each shower, bath and basin of hot water used each week. Although each house uses different volumes of hot water we will say that a typical household uses 400 litres of hot water a week which equates to 17,799 litres of hot water per year. In this case we are assuming that the hot water is heated to between 60 – 70^o C and is used at approximately 40^o C after passing through a mixing valve which would be the common setup used in most Irish houses.

Wasted hot water must also be factored in when we are trying to calculate the payback times for each system. A typical hot water cylinder holds 200 litres of water and we know that for this example there is 342 litres of hot water used every week. If we assume that 50% of this hot water is wasted due to dilution with the cold water and losses to the immediate environment this means that we need to heat 4 X 200 litres to meet the demand of 342 litres of hot water used each week. In this case we are assuming that the dwelling in not a high energy efficient house which would reflect the vast majority of house throughout the country.

Using these figures we can calculate the energy required to meet the annual hot water demand of the house. This give us a figure of 1253.14 kWh/yr for 400 ltires of hot water but when we factor in the waste water we need to double this requirement of energy use to 2506 kWh/yr.

Efficiency

If we now look at our two solar collectors, each with 4 meters squared of installed collector area we can look at the efficiencies calculated using the “radiation data” from the EUROSOL spreadsheet for our location. Comparing the energy extracted from solar insolation and the energy required to heat water over the year gives a distorted view of what portion of the dwellings requirements can be met, as there are months when the insolation is lower than required and, conversely, months when it is higher. It needs to be looked at on a month by month basis.

The efficiency of the flat plate collector comes out at 31.5% while the evacuated tube gives us an efficiency of 45.8% based on our location. What is interesting to note is how the efficiencies change depending on what location the panels are used. If, for example, we move the panels the southern Italy the figures change dramatically with the flat plate collector performing better with an efficiency of 62.9% compared to the evacuated tube system at 56.3%. The superior efficiency of the flat plate collector when located in southern Italy is down largely to the increase in solar radiation and the higher ambient temperature.

Now that we know the efficiency of each collector under similar conditions we can estimate the total output for each system. Again, assuming that the dwelling requires 2506 kWh/yr to meet the demand of the domestic hot water the flat plate collector can supply 58.3% while the evacuated tube 84.7% of the dwellings hot water demand.

Inclination

These figures are based on the annual solar radiation values at our location which give a distorted view as we should be looking at the energy supplied month by month. This is because during the summer months we are going to have a surplus of energy and during the winter months a deficit of energy. When this is taken into account the efficiencies drop to 57.4% for the flat plate collector and 73.7% for the evacuated tube system.

As we mentioned earlier we could adjust the inclination of the panels to capture more of the winter sun when there is a deficit of energy but when we run the calculations we find that there is only a small increase in the annual hot water demand satisfied when the angle is changed from the recommended 36 degrees to a more favourable winter angle of 60 degrees.

The graph below shows how the surplus summer energy can be reduced by adjusting the angle of inclination, thus allowing the collector to be exposed to a higher level of solar radiation during the winter months, when most additional energy is required for hot water use.

In saying that, the differences are small when the collector’s efficiencies are included. The table below shows the comparison of a 36 degree and 60 degree collector when compared and shows a 2% difference in annual required delivery energy but in opposite directions for the flat plate and evacuated tube systems. This is due to the flat plate systems loosing more in the summer months that it gains in the winter and the annual
deficit rises from 1068kWh to 1121kWh. The evacuated tube system performs better as the energy surplus in the summer is distributed to the winter months which drive the annual deficit from 659 kWh to 616kWh. It would not seem necessary to incorporate the additional costs imposing a 60 degree inclination on a residential installation. Saying that it may be cost effective to optimise the angle of inclination for a large commercial installation.

Cost

If we now look at the capital outlay for each system, including the grants that are available and calculate the saving based on the current price of natural gas we get a payback time of 29.2 years for the flat plate collector and 23.8 years for the evacuated tubes.

These payback times should be viewed as the maximum payback times, particularly when we consider the current government policy in relation to carbon taxes. Also when when we consider the current price of energy is quite low due to the depressed global economic conditions it seems likely that this should increase in the coming years.

If for example the price of natural was to increase to 10c for every kW/h then the payback times for both panels are reduced. This along with proper installation and maintenance of the panels throughout their useful life should hopefully mean that you recoup your money sooner rather that later.

References

1. Developed by Bob Everett & Daryl Grove, © The Open University 2003
2. http://sunbird.jrc.it/pvgis/apps/radmonth.php (accessed Oct 12th 2009)

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Each of the 5 buildings featured uses their own design, heating and building method to produce a final result that is economical in the long term both from a sustainable and financial perspective. These buildings will one day become the standard for all buildings and here are just 5 of these buildings that show how this goal is achievable.

The Green Lighthouse

The Green lighthouse is the first carbon neutral building in Denmark that is used by the University of Copenhagen’s Faculty of Science. The building has been built with natural ventilation and orientated to capture the movement of the sun throughout the day. This coupled with advanced controls on both the light, heating and ventilation has resulted in the zero carbon. The major factor in reducing the carbon output from the building is the buildings circular architectural design of the building.

Ineedra

The Ineedra building is located south of Lyon outside the town of Valence. Built with poroton blocks and a high use of timber the building is heated using a condensing boiler and a heat recovery system. The plan behind the building is to constructive the building with the lifecycle in mind. Each stage of the building has been carefully considered from the construction to the demolition of the building. The design of the building with this in mind gives it a truely sustainable aspect.

Solar Prism

A refurbishment project in the town of Albertslund, Denmark this innovative project takes a poorly insulated 1970′s construction and converts it to a low energy dwelling. This refurbishment has everything thrown at it from a heat pump to heat recovery and both forms of solar panels. What is interesting about this project is the Solar Prism that has been installed on the flat roof of the house to both accommodate the solar panels, let in additional light and if needed in the future is capable of adding further panels.

Tescos – Cambridgeshire

Every big corporate company wants to be seen to be green, eco friendly and sustainable these days and Tescos in no exception but with their news stores are they seem to be putting their money where their mouth is. The retail store in Ramsey, Cambridgeshire is classed as a first zero carbon store the company has constructed. To achieve this milestone a wealth of low energy and low carbon solutions were used from the CHP biofuel heating to LED lighting in the carpark. This along with the extensive use of timber throughout the construction means they’re heading the right way with their green credentials.

House For Life

Another Danish building but this new build residential which has been constructed to produce more energy than it consumes. The house is built in a traditional danish style and with the use of a heat pump, 7m² of solar thermal panels and 50m² of photovoltaics the house will have saved enough carbon to cancel to carbon used in the production of it’s building materials. This along with the aesthetics ensure that this is truly a user and environment friendly house.

Something Missing

While writing this article, it’s always a possibility that we missed some low energy innovative building or other information that would be of interest to our readers. Feel free to share it with us.

Hello and welcome to The Carbon Post. It’s been in development for a while now but as of yesterday we’ve gone live. The driving force behind the site has been from talking to people around the country who are building low energy buildings, developing innovative renewable technology or having new ideas on how we can develop our energy landscape but have no forum to present their ideas or their work.

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