How to recycle solar panels: the cheap and cheerful approach

A recent journal paper suggests a new approach to recycling solar panels [1]. This is very much a cheap and cheerful approach (my words) compared to the gold standard ‘full recovery end of life’ approach. A comparison of the two methods is illuminating. The main author of the paper, Pablo Dias, has since set up a company called Solar Cycle to commercialise his process. It is great to hear of technology progressing from research in a university into the real world. Dias is from the School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, (Sidney, Australia) and some of the contributors to the paper were from other universities in Brazil but Solar Cycle has been set up in Texas, USA. 

The cheap and cheerful approach:

• Involves only mechanical process and electrostatic separation; no high temperatures and no acids
• Produces less pure products – more like metal ‘ore’ than refined metals 
• Is less capital intensive
• Can be economic at small scales

Do people with PV panels consume more electricity?

Calculations of the benefits of renewable energy usually make the assumption that people will continue to use electricity in the same way they did before. However, a lot of studies show this is not the case. Typically electricity use does increase by up up 20% of the renewable energy generated - a rebound effect of 20% However other studies find that on average electricity use is unchanged. A lot depends on financial incentives, and some on attitudes and some on the technology used. This suggests it is possible to 'nudge' this behaviour to gain the most benefit - how is the UK doing in this respect? It may be that we have, by good luck or judgement, avoided the worst outcomes.

Savings on bills and carbon with TOU tariffs

Converting our heating and transport energy to electricity increases demand which puts strain on the grid. However, it is primarily the peak demand that is the problem, so shifting demand away from the peak times helps a lot. When demand is high, wholesale prices and carbon emissions are usually also high, because we need to use less efficient power sources to top up supply. However there are other factors that affect prices and emissions.

It is possible to take advantage of these differences by switching to an electricity tariff that offers higher prices at peak times and lower prices at times of low demand. In this post I compare two: Tide from Green Energy, which has three tariff levels through the day and Agile from Octopus which follows wholesale prices directly (at least for now). I look at both price differences and the carbon savings from shifting your demand away from peak times to the cheapest times. Shifting demand is easiest with a battery. 

The cost of building too many solar farms

Solar panels give us plenty of power in the summer when we don’t need so much and not much in the winter when we do. Building solar is like going to the shops to buy a winter woolly and buying a stack of T-shirts instead. Last time I wrote about this I focussed on our pattern of energy demand and how that can best be matched to wind and solar generation patterns. I concluded that we need some solar now but less in the future. That post was criticised for ignoring costs. So this time I will discuss the extra costs of investing in the wrong sort of renewables.

One year on from the inverter upgrade

We installed our PV panels in 2011 and last year we upgraded the inverter system, installing SolarEdge equipment. We were promised better yields, but are we getting them? After one full year with the new inverter I have a reasonable answer. In this post I show how I have estimated the improvement, correlating yield with the old system with weather data from the MET office and using this to predict what we would have got recently if we had not upgraded. The prediction function I derived was 98% accurate, which I was very pleased with. Using this I have estimated the improvement to be 5.9%.

Does the UK need solar electricity?

I am not against solar PV panels in other countries where the pattern of demand is different, but in the UK our peak heating demand is in the winter time when solar power is low. Wind on the other hand peaks in the winter too so is a natural fit for our demand pattern. But does wind generation really match our demand well, or do we need mix of other types of generation? The answer was not as clear cut as I expected.

Is it worth getting battery storage to go with your solar PV?

Now that the Feed in Tariff rates are reduced and PV is hard to sell, some solar power companies are pushing battery storage instead, to people who already have PV. Unless you are very eco-minded you probably expect the system to at least pay for itself but it is very hard to estimate savings. I have just been visited by salesmen who made some rather misleading statements. Here are some things to ask and some very simple calculations you can use to fact check what the salesman tells you.

Also, always get at least two quotes.

How much electricty does the solar hot water panel pump use?

We have solar panels for heating our hot water. As well as using free energy from the sun, they use some electricity - this powers the pump that circulates heated water through the hot water tank. I have been assured that this pump does not use much electricity - finally I have been able to confirm this by measurement (more or less). In July, I estimate electricity for the pump is about 3.6% of the heat obtained. In winter the pump energy goes up to 6.4%. The reason the yield is not so good in winter is that the water from the panel is not so hot. The pump works just as hard but there is less heat being delivered. However even then, and allowing for the fact that the pump uses electricity whereas our backup water heating is from a gas boiler, we still get 80% savings on carbon emissions.

This is only a sample of one and your system may be different. Also, there are some uncertainties around my measurements. However, I believe these figures are at least plausible. Keep reading to find out how I made my calculations.

How much is reasonable for a PV Feed in Tariff?

The government says that the Feed in Tariffs for renewables including PV panels are too high and must be reduced because the subsidy costs too much [1]. The new strategy is to prioritise energy security and affordability over greenhouse gas emissions [2] but in the same breath they claim that they are committed to meeting climate change targets. Leaked emails show that they know this is unlikely[3]. The question is, how far can the subsidy can be reduced without throttling the PV installations industry altogether? I have done some quick calculations to see what the generator tariff would have to be to get a reasonable return on your investment - though we may have different ideas about what is a reasonable return. To do your own calculations, download the spreadsheet from the Transition Cambridge PV advice page

As of 12th December the government announced the new tariff level for domestic PV will be 4.93p/kWh. This will give you a payback in 15 years if you use more than half of what you generate - as shown in the second table below.

Should you spend some of your pension pot on Solar PV?

Now you have more freedom to do what you like with your pension pot, you might like to spend some of it on solar panels for your home. You may think you won't live long enough to get the benefit but the average life expectancy for women of 65 is another 20 years, and men are not far behind. So, what about the solar panels? There are a number of factors to consider and estimating your benefits is not completely trivial. For a quick estimate, try the Energy Saving Trust calculator. However, if you like spreadsheets, download this from Transition Cambridge because then you can see all the assumptions clearly and adjust them if you want to. I have just brought it up to date. By the way this works equally well if you are less than 55 years old.

The three main variables are:

• Cost - depends partly on the shape of your house.
• Electricity yield - depends on the system capacity, your location, orientation, tilt and shading.
• Self consumption - how much of the power you generate will you use directly rather than exporting it to the grid.

What you could save with a battery to go with your PV panels

The day is coming when batteries are cheap enough that you can get one to go with your solar electricity panels. With this you can use your own energy in the evening as well as during the day. There are several companies developing products, for example Tesla have been working with Solar City to trial solar panel/battery combinations and intend to bring out their own product soon [1]. CCL Components are working with SolarMax [2] and RWE have announced intentions to bring out a home solar storage product. Using a battery (and some clever control devices) you can store the excess energy from your panels during the day and use it through the evening. This saves you more money and is also better for the grid, because it helps to even out electricity demand through the day. I have used data from the HES[4] to see what difference this could make in a typical household.

Solar electricity is like ice cream

In the UK our peak electricity demand is in the winter. Solar PV panels deliver 6 times more power in the summer than in the winter. Solar PV delivers carbon-free electricity with little environmental impact and helps mitigate climate change but it doesn't help 'keep the lights on' in the winter unless we have inter-seasonal energy storage as well. Last year the government gave out £2 million to 16 projects for innovative energy storage solutions - of which £40,000 went towards one project with the potential to deliver inter-seasonal storage [1][2]. This is a paltry sum compared to the many £millions/year paid out in subsidy for PV panels. So why aren't we doing more?

Solar hot water for combi boilers

Making use of solar hot water with a combi boiler is difficult because most combi boilers don't work with preheated water. However, Viridian Solar have a solution for this called the Solar Pod. It relies on the fact that most combi boilers will work with tepid (not hot) water up to about 30C: about 1/3 to 1/2 of the way to the temperature you are aiming for (assuming you want 45C-55C).

How much more does rooftop solar cost?

The subsidies for solar electricity (PV) panels are currently 5.4p/kWh higher for residential rooftop panels than for ground mounted systems. For large solar farms, the difference is even greater, at 10.4p/kWh. If a quarter of our electricity came from rooftop PV rather than large solar farms then that would cost us £104 on an average household electricity annual bill. This is even worse than the difference between onshore and offshore wind (see How much more does offshore wind cost?). Granted we don't want ugly solar farms cluttering up the countryside - but how ugly are solar farms and how much do we not want them?

How much heat are you getting from your solar panel?

If you have solar panels heating your hot water, do you know how much heat you are getting from them? The reason I ask is that I recently read a report on the performance of hot water panels in the field [1]. The researchers found that most people were very happy with their panels regardless of how much, or how little, solar energy they were getting from them. The proportion of hot water actually supplied by the panels varied from 9% to 98%. I suspect most people don't know what their panels are doing and quite possibly don't have an easy way to find out. I speak from experience here as our hot water system failed back in 2012 and we didn't realise anything was wrong for a couple of months.

How much is too much PV?

The BBC reported today that the owner of a caravan park in Northern Ireland was refused permission to install a 50kWp solar panel array because the local substation could not handle the load - he was only allowed 20 kWp. This comes just a couple of weeks after another item reporting that solar PV panel applications were booming as developers tried to get in before the grid was swamped. The latest figures from DECC show that Solar PV supplied only 2.9% of renewable electricity in 2012 - that is 1,200 GWh from PV compared to 20,000 GWh from wind and wave power, and 41 GWh in total [3]. Renewable sources as a whole contributed only 11.3% in 2012, so PV provided only 0.3% of supply in 2012 [4]. On the other hand, a briefing note from the National Grid to DECC reported the grid could handle 10 GW of PV capacity - in 2012 we had 1.7 GW [5]. So what is the problem?

What will PV panels do to your school's energy bill?

In a previous post I showed you some analysis of gas use data from some schools in Hertfordshire (Potential energy savings in Schools). I also have electricity data from some of the schools from the same source. I am working as a volunteer on a project to raise financing for PV panels for community buildings rooftops, including schools, so I did some analysis to see what impact the panels would have for the sample schools - how much of the power from the panels would be used by the school and how much would be exported to the grid. The schools varied considerably in how much electricity they used at weekends and in the holidays. Also some had a relatively high base load and others presumably are more careful to turn things off at night. Apart from the holidays, their use pattern is probably similar to many other public buildings and offices. First, here are some charts.

What is the value of solar electricity?

In the UK we have Feed in Tariffs (FiTs) which pay us for every unit of electricity we generate from our solar panels whether we use them ourselves or not. This has been a great way to unlock private investment in solar PV installations. However, it also perversely encourages people to use more electricity at home than they would otherwise have done - for example using it to heat their hot water tank even though they would normally do this with gas. There are other ways to incentivise solar PV which are arguably more fair, such as the scheme introduced recently in Minnesota called 'value of solar' [1].

Should I use electricity from my PV panels to heat my hot water tank?

If you have PV panels, you want to make the best use of the free electricity you get from them and I have been asked several times if it is sensible to use it to heat the water in your hot water tank. Unfortunately there is no simple answer to this. You can't just turn the immersion heater on when the sun is shining, as I will explain shortly, so you need special equipment. This has a cost and the payback depends on how much spare energy you have and how much hot water you use. It is hard to get accurate estimates for these but I have explored some scenarios.

Energy storage smooths out the peaks but who will own it?

Solar electricity (PV) panels are still a minor player in the UK electricity market, despite the boom driven by high Feed in Tariffs. PV capacity is now about 980 MW which is less than 5% of the UK absolute minimum base load and in 2011 PV supplied 0.25 TWh through the year out of 34.4 TWh from renewable sources and 370 TWh supplied in total [1]. However, in places where it is a lot sunnier PV can have a major impact on the pattern of electricity generation through the day, and cause supply companies considerable headaches. Energy storage systems could even out the load but depending on whether the storage is managed by the supply companies or their customers this could raise or lower grid overheads. These issues aren't just theoretical any more - Australia is leading the way. The problem is not entirely due to PV but large scale PV makes it worse.